Fuel Properties Associated With Catalytic Conversion of Plastics

7 Fuel Properties Associated With Catalytic Conversion of Plastics Sriraam R. Chandrasekaran and Brajendra K. Sharma University of Illinois Urbana Champaign, Champaign, IL, United States

7.1 Introduction Plastics are produced in large quantities due to high demand of their use in agriculture [1], households [2], automobiles [3], packing materials [4], toys [5], electronics [6], and a variety of other applications [7]. The demand for plastics has been increasing by 5% every year since 1990 [8]. The increase in plastics use correspondingly increases the amount of plastic waste being generated. Plastic waste can be classified into at least two categories: municipal and industrial [9]. Industrial plastics are generally more homogeneous and contaminationfree, making them useful for down cycling into lower-grade plastic products. Municipal plastics tend to be more heterogeneous and contain extraneous materials. In general, about 10 wt% of municipal wastes consists of plastics [10,11]. Municipal plastic waste consists primarily of lowdensity polyethylene (LDPE), high-density polyethylene (HDPE), poly(ethylene terephthalate) (PET), polypropylene (PP), polystyrene (PS), and poly(vinyl chloride) (PVC) [8]. Overall, about 50%
70% of total plastic waste is packaging materials derived from polyethylene (PE), PP, PS, and PVC [12]. On average, PE makes up the greatest fraction of all plastic wastes (69%), especially plastic bags [11], and PE comprises 63% of the total packaging waste [12]. PE (low density and high density) and PP are the most widely used plastics [13]. HDPE is recyclable and can be found in plastic bottles, storage boxes, pipes, and cable insulations, among many other uses. LDPE can be utilized for making computer parts, toys, soft bottles, wrappers, back sheets for diapers, and numerous additional applications. In the packaging industry, all three polymers, PP, PS, and PE, are widely used [14,15]. A copolymer of ethylene and propylene is also frequently employed, for example, as rubber and in

computers [14]. PVC is another popular plastic that is associated with a variety of applications, for example, plumbing pipes, electrical cable insulation, tubing’s, automobile seat covers, and rubber replacement in some applications [16]. PET is also a common polymer that has found many applications, for example, films, fibers, food containers, and beverage bottles [17]. Plastic disposal is a major concern in many countries, including the United States [12]. After its initial use, over 60% of the total plastic solid waste (PSW) produced is discarded in landfills throughout the world [8]. Less than 10% of plastic waste is recycled [18]. This is problematic, as plastic waste is a major environmental threat due to its nondegradability [19,20], its potential health risks to aquatic and terrestrial animals [21], and its impact on environmental pollution [22]. The waste plastics that end up in the ocean make a huge plastic soup and garbage patch, like The Great Pacific Garbage Patch, risking the health of aquatic animals. In the last 40 years, the plastic waste in the North Pacific Ocean has increased by 100-fold. The plastic footprint is consider more dangerous than the carbon footprint [23
25]. Some of the proposed solutions for PSW management are incineration or mechanical recycling. However, incineration can contribute to pollution by causing harmful and toxic emissions [26]. Additionally, both of these processes are costly and may or may not be economically viable in different situations [12,27]. Aside from the challenge of plastic waste disposal, another global issue is the energy crisis. Transportation consumes one-third of the world’s energy. The main energy sources for transportation are fossil fuels, coal, oil, and natural gas, all of which are nonrenewable sources of energy. Fossil fuels are also major sources of environmental pollution, greenhouse gases, and ocean

Plastics to Energy. DOI: https://doi.org/10.1016/B978-0-12-813140-4.00007-8 © 2019 Elsevier Inc. All rights reserved.

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PLASTICS

acidification [19,28]. Today, these fuels are being consumed at an unsustainably high rate throughout the world [29]. Even though more than a hundred billion tons of oil and gas have been discovered in the last 40 years [28], the rate at which it is consumed has also increased. The United States alone consumes one-quarter of the global oil supply, while only having 1.6% of the total oil reserve. At the current rate of consumption, the global supply of fossil fuels will be depleted within 40
70 years. Among 195 countries in the world, only 40 can produce fossil fuel, and for some countries, their independent oil reserves still do not satisfy all of their energy needs [19]. Many countries spend a significant portion of their gross national income to purchase oil and gas. A number of studies have been conducted to investigate alternative ways of producing energy. Some of the alternatives for fossil fuel energy are biomass energy [30], wind energy [31,32], hydroelectric energy [33], and nuclear energy [34]. Biobased oils such as palm oil, soybean oil, corn oil, cottonseed oil, and their derivatives are used as lubricants and fuel additives to replace petrochemicals [35
39]. However, even these additional energy sources may not completely solve the problem of increased energy demand. The challenges of plastic waste management and increased energy demand can simultaneously be addressed by the production of fuel from plastics. A number of research groups are currently developing this capacity. The fuels produced from plastics can be clean, and

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have fuel properties similar to fossil fuels [40]. HDPE, LDPE, and PP (plastics identification codes 2, 4, and 5, respectively) are polymers containing only carbon and hydrogen. Unlike biofuels, the absence of oxygen and higher carbon and hydrogen content (Table 7.1) in plastic fuels avoids the need of further upgrading. The absence of water in plastic fuels makes the calorific value very high, and the absence of oxygen content makes the fuel nonacidic and noncorrosive, unlike biofuel [40
43]. Therefore, conversion of these plastic wastes to usable oil is a growing and important field of study that can potentially mitigate the energy crisis. However, the techno-economic evaluation plays an important role in the commercial success of the plastics-to-fuel conversion. The production of fuel from plastics is one of the most demanding research topics throughout the world. Hydrocracking, thermochemical, and catalytic conversion are the most widely used methods for fuel production from plastics [27]. Among them, thermochemical conversion/pyrolysis treatment seems to be the dominant mode used. Thermochemical treatment breaks large polymers into smaller hydrocarbons of various carbon numbers and boiling points in an inert, air-free, or controlled environment at an elevated temperature [9]. The hydrocarbons between the boiling points of 35°C and 185°C can be used as motor gasoline, between 185°C and 290°C as diesel #1, between 290°C and 350°C as diesel #2, between 350°C and 538°C as vacuum gas oil, and 4538°C as residue [40].

Table 7.1 Elemental Composition and Higher Heating Value (HHV)a of Various Plastics Reported by Different Research Groups Investigator

Plastics

C%

H%

O%

HHV (MJ/kg)

Sharma et al. [37]

HDPE

83.9

14.9

0.74

49.4

Sorum et al. [41]

HDPE

86.1

13.0

0.90

46.4

LDPE

85.7

14.2

0.05

46.6

PP

86.1

13.7

0.20

46.4

PS

92.7

7.90

0.00

42.1

PS

90.2

8.50

1.30

PE

85.4

14.4

0.03

PP

85.5

14.4

0.08

PE

80.5

15.5

3.90

Encinar et al. [42]

Zhou et al. [43]

a The HHV (also known gross calorific value) of a fuel is defined as the heat released by a specified quantity of fuel (initially at 25°C) when it is combusted and the products returned to 25°C, and where the latent heat of vaporization of water is taken into account.

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

These fractions can be obtained in different proportions by the appropriate choice of thermal treatment/ degradation temperature, type of plastics, degradation time, and catalyst type [43
45]. The product yields of liquid, gas, and residue vary depending on the type of polymer, degradation temperature, and atmosphere. Some data on product yields obtained for thermal treatments at 400
800°C are presented in Table 7.2. Although the results vary somewhat because they come from different studies, thermochemical treatment seems to be a promising method of producing hydrocarbons from polymers. A subset of the thermal treatment is the gasification process. In this case, the plastic is decomposed to combustible gaseous products at high temperatures, usually with the help of an oxidizing or gasification agent [48,49]. Both of these techniques that convert plastics to fuel do not have negative impacts on the environment. Hydrocracking is the cracking of larger hydrocarbons, such as polymers, into fuel-range hydrocarbons in the presence of hydrogen at elevated temperatures [9,50]. Scott et al. [12] studied PE hydrocracking at 600°C in an activated carbon bed. No char was formed in the process and the major products were gases that had a hydrocarbon range of C5þ. This process produced double the gas fractions of C5þ that were produced from thermal [12]. cracking in an inert atmosphere Hydrocracking is also more effective when performed with a catalyst. The most widely used hydrocracking catalysts are acidic supporting materials (alumina, silica
alumina, and zeolites) loaded with transition metals (Pt, Fe, Ni, and Mo) [9]. For example, Ding et al. [48] used a hybrid catalyst containing a 4:1 weight ratio of SiO2
Al2O3: HZSM-5 loaded with Ni or NiMo. The hydrocracking reaction was carried out at 375°C and 1000 psig for 1 h. The optimal conditions resulted in conversions up to 99%. The product contained mostly hydrocarbons with a range of r C13 [50]. In general, catalytic hydrocracking improves the conversion of polymers into hydrocarbons when compared to noncatalytic hydrocracking. In catalytic conversion, catalysts are added to pyrolysis reactions to improve conversion, improve fuel quality, increase selectivity, and lower the pyrolysis temperature and residence time [9]. The acidic nature of most of the catalysts used enhances conversion by protonating the defective sites of polymers forming on-chain carbonium ions [10]. Selectivity and fuel quality

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vary with the strength of the catalyst’s acidity. Acid catalysts with meso and micropores give higher conversion. Primary cracking takes place in the macroporous surface and, once the polymer is cracked, further cracking is enhanced by micropores [41]. The use of a strong catalyst results in the production of lower hydrocarbons ranging between C3 and C5. A polymer-to-catalyst ratio of 10:1 yields 100% conversion within an hour of contact time [26]. The catalysts used for plastic upgrading are grouped into a few main categories: fluid cracking catalysts (FCC), reforming catalysts, and activated carbon [10]. FCC catalysts include zeolite [10,41,43,70], silica
alumina [9], and clay [9,12]. Reforming catalysts include transition metals loaded in silica
alumina [10]. Activated carbon is also widely used and can be loaded with or without transition metals [12,26]. The life of a catalyst can be increased by using a two-step process that involves thermal cracking followed by catalytic cracking [26]. There are various factors that affect the pyrolysis process, these include feed composition, catalyst type, particle size, catalyst loading, and polymer-tocatalyst ratio. These factors affect both conversion and fuel quality. PE and PP decomposition is faster in the presence of PS because it catalyzes the radical formation reaction. Zeolite-based catalysts are more effective. Ultra-stable zeolites significantly reduce the temperature of cracking. Acidic sites are also very important in cracking, as pore size increases, hydrocarbons further degrade into smaller hydrocarbons such as gas. Fe in charcoal can catalyze the reaction by a radical formation reaction. Reforming catalysts such as Pt/SiO2
Al2O3 have multiple functions for increasing the octane number without increasing the carbon number. The metals in reforming catalysts catalyze hydrogenation and dehydrogenation, whereas acidic sites catalyze isomerization reactions. Particle size also plays an important role in catalytic reactions. Catalysts with smaller particle sizes have larger surface areas for catalytic activities. However, catalysts with larger surface areas may also have a smaller pore size for cracking. Another important factor is catalyst loading. The catalyst can be loaded in two different ways. The first involves liquid phase contact, in which the catalyst is mixed with plastic. However, the catalyst recovery is poor in this method [9]. The second method involves vapor phase contact, in which the catalyst is loaded into a

Table 7.2 Mass Balance of Crude Oil, Residue and Gas Yields on Pyrolysis of PE, PP, and PS Using Various Temperatures

Investigation

Plastics

Reactor

William et al. [18]

PE

Parr mini bench top

PP

Catalyst

500

None

0.00

7.00

95

0.00

5.00

27.0

PET

15

53.0

Alston et al. [6]

Mixed

Sharma et al. [37]

HDPE

Buekens et al. [10]

Proprietary (Natural State Research, Inc.)

Gas (wt %)

93 71

Mixed

2.00 32

370
420

None

90

5.0

5.0

800

None

73

23.5

30.4

440

None

74

17

PP

740

None

48.8

1.60

49.6

PE

760

42.4

1.80

55.8

PS

581

24.6

0.60

PE

400

2 L batch reactor

H-Y-Zeolite

91.0

0.00

9.00

Silica
alumina

93.0

7.00

0.00

600

None

29.0

65.0

14.25 (21.7 H2O)

51.5

Distillation unit

405

Ca(OH)2

Scott et al. [12]

PE

Activated carbon bed

515
795

None

Miskolczi et al. [38]

HDPE

Continuous reactor

520

ZSM-5

Conical spouted bed

500

PP HDPE

9.90

44.0

PETE-1

88
96

None HZSM-5

58
70

HY β zeolite

Uemichi et al. [60]

LDPE

Fixed-bed tubular flow reactor

425

HZSM-5 SiO2
Al2O3

Lin et al. [47]

Mixed

Fluidized bed reactor

330
450

Hybrid fluid catalytic cracking series

15
87

30.0

9

None

Sarker et al. [46]

Elordi et al. [40]

Crude Oil (wt%)

Residue (wt%)

PS Sarker et al. [19]

Beltrame et al. [45]

Pyrolysis Temperature (°C)

20.0

6.00 12.4

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

basket [9,12,51,71]. However, conversion is not very effective due to the lack of direct contact between the plastic and the catalyst.

7.2 Pyrolysis Basics 7.2.1 Kinetics The kinetics of pyrolysis can be studied by performing plastic degradation via thermogravimetric analysis (TGA) techniques. Kinetic evaluation involves measuring the amount of mass degraded versus the temperature at regular time intervals [52]. Results of kinetic studies performed by various research groups demonstrate high variability in the rate of the reactions due to variation in pyrolysis parameters, including the measurement system, heating rate, sample mass, and experimental errors [53]. Kinetics studies also show that plastic degradation is a first order reaction consisting of a single-step degradation process, except with PVC [53]. Sorum et al. [41] used a single reaction model for kinetic study, using PS, LDPE, HDPE, and PP, and determined that the activation energy of PS degradation was as low as 311.5 kJ/mol, and HDPE was as high as 445.1 kJ/mol. The difference in activation energy was due to the difference in the number and type of bonds, such as C
C, C
H and C1/4C. The dissociation energy of C
C is 347 kJ/ mol, whereas that of C1/4C is 611 kJ/mol [54]. Dou et al. [71] used refuse plastic fuel for their kinetic study. The rate limiting steps were surface chemical reactions and gas diffusion through the surface. Activation energy was 70.2 and 65.9 kJ/mol, respectively. Yoon et al. [72] performed statistical analyses including pentagonal statistical design and F-test to study the effect of temperature and reaction time on the pyrolysis of waste plastic with waste motor oil. The maximum oil yield from LDPE (95%) and HDPE (92%) was obtained at 450°C with a 30-min residence time, whereas a high PP oil yield (84%) was observed at 426°C with a 12-min residence time. These results showed that PP has a lower activation energy when compared to the activation energies of LDPE and HDPE. The co-processing of waste oil and plastics falls within the pentagonal design boundary. The oil yield values were within 90%
99% confidence limit with runs performed at 460°C and with a residence time of 30 min.

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7.2.2 Thermal Degradation Thermal treatment of plastic wastes usually involves a pyrolysis process conducted in the absence of oxygen at a temperature between 350°C and 900°C [9,57]. Under these conditions, a wide distribution of hydrocarbons is obtained. The weight percent of gases produced increases with temperatures at 650
700°C [26]. Oil containing aromatic hydrocarbons is achieved at 500°C [26]. However, the product distribution depends on the type of the reactor used, and on the heat distribution during pyrolysis. Fluidized bed reactors are utilized for the uniform distribution of heat. The addition of a solvent during cracking is also used for decreasing the viscosity of the products, altering the final product distribution [26]. Sarker et al. [19] chose temperatures between 370°C and 420°C for the degradation of waste plastics into liquid slurry in the presence of oxygen. The liquid slurry was then condensed and converted into five liquid fractions. The yield was 5% gas, 5% char, and 90% liquid. The range of hydrocarbon was between C4H8 and C28H58 [19]. Waste electrical and electronic equipment (WEEE), which includes household appliances, communications equipment, electronic tools, toys, sports equipment, and medical devices constitutes another major source of waste plastic in landfills. WEEE comprises a wide range of polymers, with only some being reusable and recyclable. Alston et al. [6] pyrolyzed WEEE at 800°C. The sample contained a wide range of polymers such as LDPE, PP, PET, PVC, and PS. The gas was 30.4%
45.5% of the final product, with 99.9% of those gases being CH4 to styrene. High reaction temperatures and fast pyrolysis resulted in products with higher gas percentages. Oils and tars were 27.8%
46.7% of the final product, with 93% of the oils/tars being benzene and toluene. The remaining 23.5%
26.7% of the final product was composed of PAHs, alcohols, acids, aldehydes, nitriles, and residues. The total potential fuel was 72%
73.4% of all the product mass. Williams et al. [18] pyrolyzed waste plastic mixtures and individual plastics in the presence of nitrogen and hydrogen at 500°C. Nitrogen was used for pyrolysis, whereas hydrogen was used for liquefaction. Hydrogen gas, tetralin, or acidic catalysts were employed as hydrogen donors in many reactions [46,58,59]. Intermolecular interactions and catalytic activity were promoted by using mixed plastic

178

feedstocks. The compositions of the gas products obtained from plastics mixtures and individual plastics were very similar, whereas higher concentrations of alkanes and aromatics were observed in oil products from mixed plastics [60]. Sharma et al. [37] pyrolyzed HDPE (grocery bags) in a 2 L batch reactor, and analyzed the properties of hydrocarbons produced from the reaction using simulated distillation, a gas chromatography-flame ionization detector (GC-FID), size exclusion chromatography (SEC), nuclear magnetic resonance spectroscopy (NMR), and Fourier transform-infrared spectroscopy (FT-IR). Other fuel properties were studied by wet chemistry techniques. The properties of the blends of pyrolyzed hydrocarbons with ultra-low sulfur diesel (ULSD) and biodiesel were also studied. The oil produced from pyrolysis had paraffinic hydrocarbons as high as 96.8%, a heating value of 46.16 MJ/kg, and an absence of any oxygenated products, making it suitable for diesel fuel and petroleum diesel blends. The simulated distillation result showed the presence of approximately 20% motor gasoline, 41% diesel #1, 23% diesel #2, and 16% vacuum gas oil. For convenience, the ASTM methods used for evaluating the above fuel properties are presented in Table 7.3 [40]. Many patents have been published on the economical and efficient conversion of plastics to fuel and lubricant oil. As an example, US patent 6,822,126 B2 [61] discloses a three-step process for converting plastics to lube oil. The first step is melting the plastic between 150°C and 350°C in an inert environment without depolymerizing. The second step is to pyrolyze the molten plastics in a flow reactor between 500°C and 650°C in an inert condition. This technique reduces the contact time to 15
60 min. The pyrolyzed sample is hydrotreated at 190
340°C. The final step is catalytic dewaxing and recovery of lubricating oil. US patent 7,252,691 B2 [49], discloses a high-value fuel production technique from municipal waste plastics. This process involves removal of recyclable waste, anaerobic digestion, de-watering, and pelletizing of municipal waste (free of recyclable and hazardous material) with high BTU-value waste such as carpet or rubber. These pellets were either used alone or mixed with shredded tires for boiler fuel. The fuel was cleaner than coal or oil. US patent 6,862,568 B1 [62], describes a method in which plastics were decomposed in an oil medium. This method lowers the need for high temperatures that are required for

PLASTICS

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decomposition of plastics to fuel. The mechanism involves free radicals for depolymerization, which were provided from precursors such as PVC, nylon, or initiator compounds containing carbon
nitrogen, carbon
oxygen. The oil medium avoids the recombination of reactive products at a temperature below 375°C.

7.2.3 Catalytic Degradation Sarker et al. [46] used waste polyethylene terephthalate (PETE-1) to produce hydrocarbons via thermal degradation at 405°C, where Ca(OH)2 was used for cracking terephthalic acid. The range of hydrocarbons obtained was from C3 to C27 with very few major components containing oxygenated compounds. Scott et al. [12] pyrolyzed PE in an activated carbon bed at 515
795°C in an inert atmosphere. At 600°C, 50% of the hydrocarbons produced were liquid, with boiling points ranging from 40°C to 240°C. The gas products were at a hydrocarbon range of C5þ. At higher temperatures, mostly char was obtained. When the same reaction was carried out with an activated carbon bed containing Fe, the percentage of aromatic hydrocarbons increased, while the C5þ gas percentage decreased. However, when the reaction was carried out in the presence of hydrogen, char formation was suppressed, the percentage of gas products increased, and the percentage of liquid hydrocarbons increased from 52% to 60%. Product distribution also depends on the type of polymer, and the structure of raw materials and their sources. Miskolczi et al. [38] used two sources of polymers, including HDPE and PP from agricultural and industrial sectors. Plastics from the agricultural sector included elements such as Ca, P, S, and N, and the fuel properties were distorted due to the presence of these contaminants. However, the use of a catalyst has the additional benefit of reducing the concentration of impurities because they attach to the catalyst, and are thus removed from the hydrocarbons. Pyrolysis was carried out in the presence and absence of ZSM-5 catalysts at 520°C. The percentage of gases, lighter hydrocarbons, and gasoline products were higher with the trials performed in the presence of this catalyst. Macro-and micropores play an important role in product formation. The primary cracking takes place in the macroporous surface. The catalyst also promotes the formation of isobutane. Higher volatiles were obtained from

Table 7.3 Central Composite Design, Coded and Actual Experimental Conditions (Variable Screening) Temperature (°C) Run Order Design

Center points

Axial points

Std Order

Coded

Uncoded

Time (min) Coded

Uncoded

Feed Quantity (mg) Coded

Uncoded

N2 Flow Rate (mL/min) Coded

Uncoded

16

1

1

500

1

45

1

16

1

90

11

2

21

400

1

45

21

8

1

90

1

5

21

400

21

15

21

8

21

70

12

6

1

500

1

45

21

8

1

90

13

8

21

400

21

15

1

16

1

90

10

9

1

500

21

15

21

8

1

90

3

10

21

400

1

45

21

8

21

70

2

13

1

500

21

15

21

8

21

70

15

17

21

400

1

45

1

16

1

90

7

19

21

400

1

45

1

16

21

70

5

22

21

400

21

15

1

16

21

70

9

23

21

400

21

15

21

8

1

90

14

28

1

500

21

15

1

16

1

90

4

29

1

500

1

45

21

8

21

70

8

30

1

500

1

45

1

16

21

70

6

31

1

500

21

15

1

16

21

70

27

3

0

450

0

30

0

12

0

80

30

11

0

450

0

30

0

12

0

80

29

14

0

450

0

30

0

12

0

80

26

16

0

450

0

30

0

12

0

80

28

25

0

450

0

30

0

12

0

80

31

26

0

450

0

30

0

12

0

80

25

27

0

450

0

30

0

12

0

80

21

4

0

450

0

30

22

4

0

80

23

7

0

450

0

30

0

12

22

60

17

12

22

350

0

30

0

12

0

80

24

15

0

450

0

30

0

12

2

100

18

18

2

550

0

30

0

12

0

80

19

20

0

450

22

0

0

12

0

80

20

21

0

450

2

60

0

12

0

80

22

24

0

450

0

30

2

20

0

80

180

PP in comparison to HDPE [41]. Elordi et al. [40] used HZSM-5, HY, and β zeolite catalysts at 500°C in a conical spouted bed reactor. The yields were compared with the fluidized bed reactor yields from the literature. The major differences in pyrolysis yields were based on the properties of the catalysts. ZSM-5 has a smaller pore size, resulting in a higher yield of lighter olefins, aromatics, and gases. Nonaromatic compounds and higher hydrocarbons were predominantly produced during pyrolysis runs that utilized a catalyst with larger pores. Catalysts used in combination, such as HZSM-5 and SiO2
Al2O3, seemed to be more beneficial than used individually. The major product of cracking plastics in the presence of HZSM-5 was a gasoline-range lower aromatic compound, whereas the presence of SiO2
Al2O3 produced a lower quality fuel. The usage of dual catalysts resulted in a high yield of gasoline with a high octane rating. Uemichi et al. [60] used a dual catalyst comprised of HZSM-5 and SiO2
Al2O3. The octane rating of the resulting product was improved due to the combination of the two catalysts’ properties of mesoporosity and acidity. Lin et al. [65] investigated the production of fuel by pyrolyzing mixed plastic waste with a preused hybrid fluid catalytic cracking catalyst in a fluidized bed reactor at temperatures ranging from 330°C to 450°C. Lower temperatures increased the length of plastic degradation time. Hybrid catalysts varying in meso- and microporosity enhanced the selectivity of hydrocarbon products. Catalyst deactivation can be prevented by performing the process in two steps: the first step is pyrolysis, and the second step is a catalyst reforming reaction in which gases from the pyrolysis product are treated at higher temperatures for selectivity [44]. Syamsiro et al. [54] used this two-step process for the production of gas from municipal plastic waste. The first step was pyrolysis at 450°C, followed by a catalytic reforming reaction at 450°C. The two catalysts used for this reaction were natural zeolite and Y-zeolite. The nature of plastics and catalysts strongly influenced the quality of liquid, gas, and solid obtained from the reaction. The natural zeolite has a smaller surface area compared to Y-zeolite. Therefore, the liquid yield was higher using natural zeolite, whereas the gas yield was higher using Y-zeolite. The higher surface area means more contact between the catalyst and pyrolysis gas, which cracked to produce gaseous products. The heating value was comparable for

PLASTICS

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pyrolysis using natural zeolite and Y-zeolite. Solids left after the reaction also have HHV and can be used as a blend with coal [44]. Kumar et al. [67] studied the performance of fuel produced from catalytic pyrolysis of waste HDPE as a blend with diesel. Kaolin clay was employed as a catalyst for oil production from HDPE. Performance of the blend was reduced compared to that of diesel fuel. NOx emission increased with an increase in plastic oil percentage. The CO2 emission percentage was lower than that of diesel in all blends. Among the patent literature, US patent 4,851,601 [66] discloses a method in which plastics were softened and melted in a thermal cracking zone between 390°C and 500°C followed by catalytic cracking between 250°C and 340°C. The level of molten plastic was maintained by continuous stirring. The maximum heat transfer was achieved by using inorganic materials called red mud. The acidity of red mud is lower than the zeolites that are used in the catalytic cracking step. Zeolites such as ZSM-5, ZSM-11 are employed for catalytic cracking. The use of zeolites increases the selectivity, reduces the operation temperature, and enhances isomerization. From these studies, we can see that the use of FCC can be very effective in producing lower hydrocarbons, and the choice of catalysts and pyrolysis temperatures can influence solid, liquid, and gas yields. For example, zeolite catalysts produce higher quality fuel than silica
alumina, and can increase the yield of aromatic hydrocarbons. Catalysts lower the activation energy of conversion of plastic to hydrocarbons, and therefore, lower energy requirements for the conversion.

7.3 Analytical Quantitative and Qualitative Determination of Pyrolysis 7.3.1 Thermogravimetric Analysis Isothermal TGA runs were conducted on the plastic samples to determine the interaction between the variables based on the CCCD experimental design (Table 7.3). Conversion was determined for all the conducted experiments. Representative contours for the conversion are shown graphically in Fig. 7.1A
C. Fig. 7.1A and B are identical, while Fig. 7.1C is different from the others, indicating that the conversion is mainly

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

(A)

OF

PLASTICS

181

(B)

20

100

0

0

10

0

0

10

20

0 10

80

60

40

20

0 10

95

80

60

40

18

10

10

80

10

0 100

20

80

60

40

20

N2 flow rate (L/min)

80

40

20

8

80

100

100

10

85

100

12

60

14

100

100

20

90

100

75

80

0

10

10

65

0

60

10

0

80

60

10

20

20

6

40

70 40

Feed quantity (mg)

0

0

16

0

0

0

4

60 350

400

450

500

550

350

400

Temperature (ºC)

60

500

550

80

90

(C)

450

Temperature (ºC)

100

20 30

40

90

50

50

90

80

60

70

50

60

0 10

70

40 30

Time (min)

90

100

100

40

80

30

20 20 60

50

10

70

80

90

0

10

40 30

0 350

400

450

500

550

Temperature (ºC)

Figure 7.1 Contour plot representing the percentage yield with respect to temperature and nitrogen flow rate (A), temperature and feed quantity (B), and temperature and time (C).

dependent on temperature and time, with the carrier gas flow rate and the feed quantity having minimal effect. It has been confirmed that temperature and time are the most significant controlling factors influencing yields [43], and our results are in agreement with previous studies. TGA runs were conducted on finely powdered and coarse samples to determine the effect of particle size. It was observed that nitrogen gas flow rate, feed quantity, and particle size had no substantial effect on yield. Thus, these parameters were not considered for further investigation. Nonisothermal TGA experiments were conducted on the catalysts, and thermal stability was assessed by continuously recording the weight loss

at a ramp rate of 10°C/min. The initial temperature of the sample was 40°C. The catalyst was maintained at 100°C for about 15 min (isothermally) to remove moisture, and weight loss was continuously monitored until the final temperature reached 600° C at 10°C/min. All five catalysts showed weight loss around 100°C, indicating moisture loss. Weight loss was more pronounced for magnesium carbonate (Fig. 7.2), and MCM-41 was more thermally stable than other catalysts. It can be seen from the thermograms that, with the exception of MgCO3, catalytic degradation over the temperature range was less pronounced, with an average total weight loss of about 30%.

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110 100

% Weight loss

90 80 70 MCM Y-Zeolites MgCO3 Zr(SO4)2 FCC

60 50 40 0

100

200

300

400

500

600

700

Temperature (ºC)

Figure 7.2 Thermal stability of catalyst using TGA.

The degradation of plastics was studied in the absence of a catalyst, and these results are presented in Fig. 7.5B. The degradation of all the investigated plastics occurred in a temperature range between 400°C and 450°C. As is evident from the figures, the degradation behaviors of PP, landfill liners, and HDPE from the MRF facility are similar, but PUF and PS are different. The difference in degradation temperatures of the three types of polymers (PP, PE from landfill liners, and MRF facility) is not very large, with PP being less resistant to decomposition compared to HDPE. The higher temperature of PE is likely due to the higher activation energy of depolymerization [about 182 kJ/mol for medicine bottle (MB, PP) and 294 for landfill liners and plastic from MRF (PE)] (Table 7.5). These activation energies are in agreement with previously published data of (280
320 kJ/mol) for PE and PP (190
220 kJ/mol) [54]. In an earlier study, linear chain polymers were observed to decompose with more difficulty than branched chain polymers, and the removal of side chain branches accelerated the overall degradation process [67]. The differences in TG curves of different plastic types (PUF, PP, PE, and PS) could be attributed to the different macromolecular structure and depolymerization mechanism of those macromolecular structures. All of the five catalysts were screened for all the polymer types using TGA (Fig. 7.3). The degradation temperature decreased for all polymer types in the presence of catalysts. No significant correlation

between conversion and the catalyst type was observed, although a distinct decrease in degradation temperature can be noticed (Fig. 7.3), indicating that the catalysts are polymer specific. For instance, Y-Zeolites gave better performance for PE and PP, while spent FCC and sulfated zirconia were more effective for PS and polyurethane foams for thermal degradation (Table 7.4). These results are in agreement with previous studies that showed catalytic cracking of PE and PP using zeolites, as reported by Ali et al. [62] and Angyal et al. [77]. Mixed plastics including PS, poly propylene, PE, PET, and PVC were effectively catalyzed by ZSM5 by Lopez et al. [49]. Zeolites are extensively studied owing to their superior acidic properties. De la Puente et al. [78] studied the effect of various catalysts on PS cracking, and indicated that FCC showed a better product distribution in terms of gasoline composition. Spent FCC catalysts were also studied and compared to results of fresh catalysts for PP cracking [48]. Catalysts are generally selected based on the feedstock of interest and the desired end product. All catalysts, except MCM-41, enhanced the degradation of PP. Zeolite-Y was found to be most effective in reducing the Tmax for degradation of PE and PP. The MCM-41 and FCC catalysts had almost no effect on PP degradation, although a small change in temperature profile was noticed for FCC spent catalyst. The number of acid sites on a solid catalyst plays a key role in the catalytic

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Plastics from a recycle unit (polyethylene) 100

80

80 % Conversion

% Conversion

Medicine bottles (polypropylene) 100

60 Virgin Plastic Y zeolites MCM-41 MgCO3 FCC Zr(SO4)2

40

20

60

40

20

0

0 0

100

200

300

400

500

0

600

100

200

300

400

500

600

500

600

Temperature (ºC)

Temperature (ºC) Landfill liners (polyethylene) 100

100

80

80 % Conversion

% Conversion

183

60

40

Packing material (polystyrene)

60

40

20

20

0

0 0

100

200

300

400

500

0

600

100

200

300

400

Temperature (ºC)

Temperature (ºC) Plastics from industry (polyurethene foams) 100

% Conversion

80

60

40

20

0 0

100

200

300

400

500

600

Temperature (ºC)

Figure 7.3 Catalysts screening using TGA.

degradation rate of polyolefins [48,67]. This number increases with increasing aluminum incorporation into the zeolite crystal. Catalyst pore size also influences polyolefin degradation using microporous materials. The number of acid sites that are available for polymer cracking increases with the catalyst amount, thereby enhancing degradation reactions [67]. Thus, more experiments will need to be conducted to optimize the catalyst amount for

maximum conversion at reduced temperatures. Further work will also be needed to determine the catalytic effects on activation energy. The overall conversion for the polyurethane foams was about 60%, in the absence of a catalyst. However, in the presence of a catalyst, the conversion increased by an additional 10%
15%. Sulfated Zirconia provided better conversions at lower temperatures, which was likely due to the

Table 7.4 Kinetic Parameters Comparison With and Without Catalysts MB

Landfill Liners

Polyurethane Waste

Packing Material

PE

Parameters

No catalyst

Catalyst

No catalyst

Catalyst

No catalyst

Catalyst

No catalyst

Catalyst

No catalyst

Catalyst

T10 (K)

663

563

443

384

243

179

376

226

439

336

T50 (K)

695

625

462

425

343

351

400

399

459

392

T90 (K)

709

650

476

431

379

508

416

435

420

470

Activation energy, E (kJ/mol)

182

113

294

169

30

11

182

45

294

87

Significance (R2)

0.90

0.99

0.97

0.87

0.93

0.83

0.96

0.86

0.99

0.98

Note: T10, T50, and T100 are the temperature at which 10%, 50%, and 90% conversion occurred.

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

strong acidic nature of the catalyst. This trend can also be attributed to the acid sites that were available for polymer cracking. While all of the five catalysts supported PS thermal degradation, spent FCC catalysts was the best choice from an economic standpoint. Spent FCC can catalyze the reaction and achieve a similar conversion at a lower temperature than other catalysts. In order to determine optimum conditions, RSM was developed with reaction temperature and time as controlling factors at five different levels. Fourteen experiments were conducted with six center points. These results are summarized in Table 7.5 and Fig. 7.4. Finely powdered PP was mixed with Y-zeolites in a 10:1 ratio and isothermal TGA runs were conducted as per the experimental design from CCD (Table 7.5). The conversion increased as a function of both time and temperature. At a temperature of 450°C, a conversion of about 90% was attained within half an hour of the reaction’s initiation. At higher temperatures (500°C and 550°C), 99% conversion was obtained within 15-min. However, at lower temperatures of 400
450°C, and with sufficient residence time over 45-min, a similar conversion was obtained to that of 450°C at 30-min. RSM plots provided the optimum pyrolysis conditions. Although the other

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four polymers were not subjected to the optimization runs, the process variables such as temperature and time can be reasonably estimated from nonisothermal TGA runs for different catalysts.

7.3.2 Pyrolysis-GC/MS Pyrolysis-GC/MS (Py-GC/MS) is a destructive analytical technique. One of the most frequent use of this technique is the analysis of polymers and copolymers [49,50,63
65,69,70]. The polymer can be identified from comparing the pyrograms and mass spectra with known references. All of the pyrograms were analyzed using Pyrolibrary 2010 to identify the polymer type. The library identified the prescription bottles as PP (#5), the industrial waste as plastic #1, and landfill liners as PE (#2) (Fig. 7.5B,C). The packaging materials were identified to be PS with some coating, and the industrial plastic 2 to be polyurethane (Fig. 7.5D,E). These results were also confirmed from literature and from the information collected from the industrial sources from where the plastics were received. The landfill liners contain a layer of compacted clay overlaid by HDPE. The industrial waste plastic 2 is urethane sealant with carbon black (40%
50%) and calcium carbonate (5%
10%).

Table 7.5 Central Composite Design (RSM) With Catalyst Temperature (°C) Run Order

Standard Order

Time (min)

Conversion

Coded

Uncoded

Coded

Uncoded

%

11

1

21

400

21

15

82.4

1

2

21

400

1

45

82.3

12

3

1

500

21

15

99.9

13

4

1

500

1

45

99.9

10

5

22

350

22

0

4.5

4

6

22

350

0

30

67.1

3

7

2

550

0

30

99.9

2

8

0

450

22

0

3.7

6

9

0

450

2

60

90.5

7

10

0

450

0

30

90.5

5

11

0

450

0

30

90.5

9

12

0

450

0

30

90.5

14

13

0

450

0

30

90.5

8

14

0

450

0

30

90.5

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% Conversion 100

60

10 0

80

50 100 40

20 550

30 20 Time (min)

400 10

0

350

100

60

40

80

40

60

20

20

0 350

400

450

40

500

120

40

10

0 10

Te mp era tur e( ºC )

0

80

60

500 450

50

80

20

80

Time (min)

0 20 40 60 80 100

40

30 100

% Conversion

60

100

80

550

Temperature (ºC)

Figure 7.4 Optimization of temperature and time using RSM.

Figure 7.5 Pictures of plastics studied: (A) MB/polypropylene, (B) landfill liners/PE, (C) packing materials/ Styrofoam, (D) industrial waste plastic1/PE, (E) industrial waste plastic 2/polyurethane.

7.3.2.1 Polypropylene and Polyethylene Thermal degradation of PP or PE under inert atmosphere occurs mainly by dehydrogenation and fragmentation. Alkanes, alkene, and α, ω dienes are commonly formed fragment molecules [49]. For PP pyrolysis, the outstanding peak at six-min was

identified to be pentatriacontene (C35H70) and accounted for about 60% area peak, followed by Tridecene and tetra decene (20%) and Eicosene (10%) (Table 7.6). Many compounds in the pyrogram were identified to be double bonds. As mentioned above, industrial plastics #1 or landfill liners were identified as PE, and their pyrograms

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Table 7.6 Identified Compounds From Py-GCMS of PP With and Without Catalyst Residence Time min

No Catalyst (600°C) Compounds

Area (%)

2.46

5-Tridecene

12.40

2.60

1-Hexene,4-ethyl

6.01

17-Pentatriacontene

12.39

7-Tetradecene

4.45

13.77

4-Tridecene

1.41

13.96

7-Tetradecene

0.31

18.79

17-Pentatriacontene

19.00

3-Eicosene

3.72

19.24

17-Pentatriacontene

9.69

19.94

4-Teradecene

1.33

20.62

7-Octadecyne, 2-methyl

0.87

24.25

17-Pentatriacontene

3.87

25.91

7-Octadecyne, 2-methyl

1.14

29.07

Oxirane, hexadecyl

3.85

29.67

3-Eicosene

3.94

33.39

7-Octadecyne, 2-methyl

1.99

5.17

Retention Time min

33.60

12.25

With Catalyst Compounds

500°C

600°C

2.49

Unidentified (mostly alkanes)

58.41

60.24

3.41

Benzene

6.61

8.80

4.68

Toluene

7.54

11.21

6.76

Benzene, 1,3-dimethyl

8.22

7.98

7.29

O-Xylene

2.39

2.41

9.14

Benzene (tri, tetra) methyl groups

13.96

4.14

15.46

Naphthalene

0.27

0.90

18.56

Naphthalene (di, tri) methyl groups

2.60

1.72

resembled each other. The whole chromatogram of PE pyrolysis was formed from a series of alkene and alkadiene with some alkanes (Fig. 7.5B). Studies indicate the formation of alkene-type compounds during propagation and formation of alkanes, alkenes, and dienes when the reaction is terminated by disproportionation. The results of this study are in agreement with the previous studies [49]. The presence of numerous peaks of about the same intensities in the pyrogram indicates the random scission mechanism of the pyrolysis process and the equal stability of the molecules with

different numbers of carbon atoms. However, there were unidentified smaller peaks for which the library had no information (Fig. 7.6). In the presence of the catalyst at 600°C, larger peaks of lower molecular compounds were formed for both PE and PP (Figs. 7.7, 7.8, Tables 7.6, 7.7). For PP, about 60 area percentage peaks were seen at a shorter residence time, and we believe they were mixtures of lower molecular weight alkanes. A similar trend was obtained for both PE materials. From these results, it can reasonably be assumed that Y-Zeolites are effective catalysts for PP and

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Figure 7.6 Chromatograms of industrial waste 1 and landfill lines both identified as PE.

Figure 7.7 Chromatograms of industrial waste 1 and landfill lines from catalytic pyrolysis-GCMS.

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7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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189

Figure 7.8 Chromatograms of MBs identified as PP.

PE pyrolysis. From our previous studies using TGA, it was concluded the catalysts lower the pyrolysis temperature. In order to verify these results, experiments were conducted using catalysts at a reduced temperature of 500°C. For both PP and PE materials, similar compounds were obtained with a small difference between both runs (Tables 7.6 and 7.7). It can be concluded that the catalyst not only increases cracking, but also reduces the energy required for cracking.

7.3.2.2 Polystyrene Pyrolysis of PS with cyclic structure occurred by both end-chain and random-chain scissions. The degradation mechanism is very similar to that of PE. This polymer is broken up from the end groups successively yielding the corresponding monomers, as well as breaking randomly into smaller molecules of one or more benzene-ring structures [51]. This product is monomer recovery with a high fraction, and that the product distribution is strongly dependent on the plastic type [51]. Previous studies reported PS pyrolysis at 500
600°C, yielding monomer, dimer, trimer, styrene, and a small fraction of

toluene and α-methylstyrene. In the present study, styrene was identified to be the major compound (35%) in PS pyrolysis (Table 7.8, Fig. 7.9). Another major compound was identified to be cyclopentapyrene (28%). There were many unidentified peaks for which the library had no information. A spent industrial FCC catalyst was identified to reduce the pyrolysis temperature as well as increase cracking. It can be seen that catalytic cracking at 600°C yielded about 90% area peak, with a residence time of 8-min, indicating a large fraction of low molecular weight compounds, possibly alkanes. However, at a reduced temperature of 500°C, the major peak was about 50% at the same residence time; another larger peak of unidentified compounds was observed at a residence time of 30-min, which may have been dimers/trimmers of PS. The TGA studies also did not indicate any significant change in temperature between the catalytic and noncatalytic, a pattern confirmed in the present study.

7.3.2.3 Polyurethane Polyurethane is an association of two components: a “base resin” (polyols as low molecular

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Table 7.7 Identified Compounds From Py-GCMS of PE With and Without Catalyst Residence Time min

No Catalyst (600°C) Compounds

Area (%)

2.63

2 Decyne

19.02

3.06

1 Octadecyne

4.81

7.08

4,5 Nonadiene

0.99

7.32

Cyclopentane, 1 methyl 3 (2-methyl propyl)

6.97

9.78

E 1,8 Dodecadiene

2.11

10.06

Cyclohexadecane

14.80

12.67

E 1,6 Undecadiene

12.97

Cyclohexadecane

15.56

9 Methylbicyclo [331]nonane

15.84

Cyclohexadecane

18.34

9 Methylbicyclo [331]nonane

18.60

Cyclohexadecane

3.75 14.27 4.45 12.38 4.37 12.08

Industrial Plastic 1 Retention Time min

With Catalyst Compounds

500°C

600°C

2.40

Unidentified (mostly alkanes)

61.38

77.26

3.40

Benzene

5.50

4.66

Toluene

12.17

5.94

7.00

Benzene, 1,3-dimethyl

6.35

6.64

7.30

O-Xylene

3.10

2.54

9.16

Benzene (tri, tetra) methyl groups

5.66

5.21

15.40

Naphthalene

0.76




18.62

Naphthalene (di, tri) methyl groups

2.44

2.00




Landfill Liners Retention Time min

With Catalyst Compounds

500°C

600°C

2.4

Unidentified (mostly alkanes)

55.13

61.94

3.4

Benzene

3.01

4.64

4.66

Toluene

9.76

9.29

Benzene, 1,3-dimethyl

7.07

7.87

7.3

O-Xylene

2.39

7.42

9.16

Benzene (tri, tetra) methyl groups

19.62

7.59

15.4

Naphthalene

0.76

0.51

18.62

Naphthalene (di, tri) methyl groups

0.78

0.63

7

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Table 7.8 Identified Compounds From Py-GCMS of PS With and Without Catalyst Residence Time min 7.72

No Catalyst (600°C) Compounds

Area (%)

Styrene

35.26

28.76

Benzene-1,1 (3-methyl-1-propene-1,3-diyl) bis-

8.01

36.07

Propyl (9Z,12Z)-octadeca-9,12-dienoate

9.68

36.18

Butyl 9-octadeconate

5.80

37.73

Cyclopenta[cd]pyrene

28.75

42.08

Unidentified

10.83

Retention Time min

With Catalyst Compounds

500°C

600°C

3.46

Benzene




0.30

4.8

Toluene




2.76

8.35

Unidentified (mostly alkanes)

52.05

90.34

10

Benzene, 1-ethenyl-4-methyl




3.15

11.61

Benzene, 1-ethenyl-4-methyl




1.22

28.9

Benzene, 1,1-(3methyl-1-propene-1,3 diyl)bis




2.23

30

Unidentified

Figure 7.9 Chromatograms of packaging materials identified as PS.

47




192

PLASTICS

weight esters) and a “catalyst” (polyisocyanates as tolylene diisocyanate, isophorone diisocyanate, diphenylmethane p,p0 -diisocyanate, hexamethylene diisocyanate). The yields of polyurethane pyrolysis are presented in Table 7.9. Formation of diisocynate and small amounts of hydroxylamine were seen for noncatalytic pyrolysis. There was no observable difference in temperature between the catalytic and noncatalytic runs from the TGA study.

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Since they are industrial waste plastics, presence of any extraneous materials, such as filler materials or other additives in polymers, affects the pyrolysis process as well as the catalytic activity. However, in the presence of sulfated zirconia, weight loss was slightly higher. Thus, catalytic fast pyrolysis was conducted using sulfated zirconia. While there is little difference in the formation of alkane compounds between the noncatalytic reactions (52%)

Table 7.9 Identified Compounds From Py-GCMS of Polyurethane With and Without Catalyst Residence Time min

No Catalyst (600 C) Compounds

Area (%)

2.56

Unidentified (mostly alkanes)

52.83

4.75

Toluene

6.79

Benzene,1,3-dimethyl

7.37

o-xylene

2.68

9.18

Mesitylene

4.91

9.36

Benzene,1,2, 4-dimethyl

1.54

10.08

Benzene,2-propenyl

4.81

16.90

Cyclohexene,6-(2-butenyl)-1,5,5-trimethyl

4.81

19.23

Benzene,1-ethyl-2,3-dimethyl-

3.39

20.00

Hexane-1.6-diisocyanato

2.05

20.96

Benzene,1,2,3,5-tetramethyl

1.93

30.40

Docosene

7.04

30.50

Hydroxylamine, O-decyl

0.56

36.10

1-Hexacosene

3.85

45.82

1-Hexacosene

0.75

4.45

Retention Time min

17.89

With Catalyst Compounds

500 C

600 C

2.50

Unidentified (mostly alkanes)

50.42

67.95

9.45

Unidentified (mostly alkanes)

22.28

10.09

9.70

1-Nonylcycloheptane

5.04

1.22

9.90

Tetradecene




1.90

14.30

3-Eicosene

3.70

2.55

16.50

Unidentified

15.93

14.20

0

19.3

Oxirane-2-,2 -spiroindane-11-dicarbonitrile




3.97

19.3

Pthalimic acid oxime

3.28




30.20

Cyclohexadecane

2.63

2.09

30.4

Hydroxylamine, O-decyl

0.12

0.13

35.3

1H-Isoindole-1,3(2H)-dione, 2 phenyl

0.10

0.10

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

and catalytic (72% and 77% for 500°C and 600°C, respectively), there was no significant difference between temperatures for catalytic thermal degradation. About 40%
45% of the residue was found to be in the quartz tube, as we saw in our TGA studies. As described above, these are industrial waste materials from a specific process with filler material (black carbon and calcium carbonate) (Fig. 7.10).

7.4 Pyrolysis Study of Polypropylene and Polyethylene 7.4.1 Polypropylene TGA experiments were validated using a batch scale plastic-to-oil pyrolysis unit. Two runs were conducted at 390°C and 450°C without catalysts, and a third run was conducted at 390°C in the presence of the Y-Zeolite catalyst (optimized from TGA runs). Gases from the pyrolysis reactions were condensed, collected, and referred to as main liquid fractions, while the residual fraction was the fraction that was left in the reactor, and collected

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during the reactor clean-up, including the high boiling fraction and residues. The liquid condensates were collected at various time intervals from 30 min to 2 h, and the conversions were estimated at each time interval. These results are presented in Fig. 7.5. Yield of the total liquid fraction was highest (about 81%) at 450°C when the reaction was complete for the plastics. At 390°C, the yield of the liquid fraction was just 30% in the absence of a catalyst. The results show that 450°C is a slightly more efficient temperature for the PP pyrolysis, while 390°C was too low to reach 30% conversion even after 2 h. In the presence of the catalyst at 390°C, however, the yield of liquid fraction increased to 78%. This conversion increased as a function of time, with the complete reaction occurring within 2 h—validating the TGA results. This yield is comparable to the yield obtained from the uncatalyzed run at 450°C, a full 60°C greater than the catalytic run. Catalytic pyrolysis at lower temperatures would be advantageous, as it enhances cracking with less energy, provides higher collection efficiency, and also allows for narrowing product selectivity. However, the composition and

Figure 7.10 Chromatograms of industrial waste 2 identified as polyurethane.

194

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Main liquid fraction Residual liquid fraction Total liquid fraction

100

% Yield

80

60

40

20

0 390ºC

450ºC Temperature

390ºC (catalyst)

100

% Yield

80

60

40

390ºC (no cat) 450ºC 390ºC (cat)

20

0 0

20

40

60

80

100

120

140

Time (min)

Figure 7.11 Yield of different liquid fractions from batch scale runs (top), yield of main liquid fraction over time (bottom).

quality of the obtained oil would vary depending on the catalysts and reaction conditions. It will also be important to study the economics of using catalysts on an energy consumption basis; we plan to study this in the near future, but an extensive discussion of this topic is outside the scope of this report.

7.4.1.1 Fuel Properties Three major products result from pyrolysis of plastic waste: a liquid product referred to as plastic crude oil (PCO), gaseous products, and solid residue left in the reactor. The complete weight percent of PCO, residue, and gases under various conditions is given in Fig. 7.11. Gaseous products were not analyzed in this study. Literature data suggests that pyrolysis of HDPE and PP produces C2 and C4 in its gaseous product [26]. Solid residues were minimal (0.5%
1.3%) in noncatalyzed pyrolysis at higher temperatures. Catalytic pyrolysis at lower

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temperatures resulted in higher solid residue yield (17%), which is likely due to inorganic content from the catalyst, foreign materials, and unconverted plastic. Noncatalytic pyrolysis gave higher PCO yield in comparison to the catalytic conversion for both MB and Green plastics (GP). PCO yields from pyrolysis of MB at 390°C and 450°C were not significantly different. However, yield increased with increased temperature. PCO obtained from noncatalytic pyrolysis of GP was a waxy liquid which clogged the transfer tube and collection system of the pyrolysis unit during collection, thus preventing sample collection at a regular time interval. The formation of waxy PCO indicated the likely presence of higher-boiling nparaffinic components. The catalysts enhanced cracking even at a lower temperature, therefore, liquid PCO was obtained, unlike noncatalytic pyrolysis. Since the HDPE pyrolysis reactions had higher activation energy (280
320 kJ/mol), the liquid yield increased with temperature (86% at 460°C to 93% at 475°C) [37]. MgCO3 did not show a substantial temperature reduction (only 6°C) using TGA data. However, in the pyrolysis reactor, even at 10°C lower temperature than noncatalyzed pyrolysis, the PCO product was liquid rather than waxy solid in noncatalyzed process. Catalytic pyrolysis of both MB and GP using either Y-Zeolite or MgCO3 resulted in greater gaseous products, as compared to noncatalytic pyrolysis. This was due to the higher amounts of low boiling/molecular weight compounds cracked in the presence of a catalyst. Gas yields depend on the acidity, basity, and pore size of the catalyst. A larger pore size exposed more surface area for the catalytic activity and increased the cracking [24]. The increase in the pyrolysis temperature from 450°C to 500°C in BP also increased the PCO yield. Residue yields decreased with the increase in temperature in all three plastics (Fig. 7.12).

7.4.1.2 Gasoline and Diesel Products From Distillation of Medicine Bottles— Polypropylene Distillation was conducted to separate MG, D1, D2, and vacuum gas oil (VGO) fractions. Distillation of PCOs from all three runs showed that 35
50 wt% of the product consisted of MG, 25
40 wt% D1, and less than 15% of D2, VGO, and fractions below 35°C (Fig. 7.13). PCO from

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Pyrolysis product yield

Gas yield %

Residue yield %

Crude-oil yield % 0

20 BP 500 GP 430 w/Y-zeolite MB 390 w/Y-zeolite

40

60

BP 450 GP 475 MB390

80

100

GP450 w/MgCO3 GP 460 MB 450

Figure 7.12 Product yields from pyrolysis of MBs, green plastic (storage box) and black plastic (corrugated plastic).

Figure 7.13 Distillation fractions of PCO from MBs mass percent of motor gasoline (35
185°C), diesel #1 (185
290°C), diesel #2 (290
350°C), vacuum gas oil plastic crude ( . 350°C), and a fraction below 35°C.

catalytic conversion had a higher content of MG, indicating that the catalyst supports cracking. PCO from 390°C contained a higher percent of both MG and D1, as compared with conversion at 450°C. However, the total recovery of PCO from the run at 390°C was less than that recovered at 450°C.

7.4.1.3 Size Exclusion Chromatography Analysis SEC analysis on triplicates was employed to determine the molecular weight distribution of constituents MG, D1, D2, and VGO fractions. The weight-average molecular weight (Mw), polydispersity index (PDI), and molecular weight at peak end were determined from retention time, calibration curves, and signal intensities from SEC data. The

fuels fractions have a very narrow range of PDI, between 1.2 and 1.4, indicating the presence of a narrow molecular weight distribution (Table 7.10). This result was expected, as these fuel fractions have a narrow range of hydrocarbon boiling points. The lower temperature fractions (MG) had a lower MW compared to higher temperature fractions (VGO). Such results indicated that, on average, the molecular weight distribution in lower temperature fractions was lower than that of higher temperature fractions. The MG and D1 obtained from pyrolysis at 390°C had higher molecular weight compared to that of MG and D1 from pyrolysis at 450°C and from catalytic conversion. The D2 and VGO of MB at 390°C had higher molecular weight distribution than MB at 450°C. This result illustrated that the higher temperature enhanced cracking of the larger

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Table 7.10 Molecular Weight Distribution of the Distillate Fraction Obtained From MBs With/Without Catalyst Fuel Fractions

Sample

Motor gasoline 35
185

1. MB 450

68.6

84.3

1.23

2. MB 390

70.6

90.3

1.28

3. MB 390 with Y-zeolite

60.0

85.5

1.38

Diesel #1 185
290

Diesel #2 290
350

Vacuum gas oil 350 1

Mn

Mw

PDI

4. MB 450

140

175

1.25

5. MB 390

147

208

1.27

6. MB 390 with Y-zeolite

113

166

1.47

4. MB 450

313

452

1.43

5. MB 390

279

337.5

1.21

6. MB 390 with Y-zeolite (290
300)

176

239

1.36

4. MB 450

793

1155

1.45

5. MB 390

618

890.5

1.44

6. MB 390 with Y-zeolite (300 1 )

388.5

580.5

1.5

Figure 7.14 Boiling point distribution of the fractions (35
185°C, 185
350°C, and 350°C 1 ) obtained from distillation of PCO from MBs except for MB 390 with Y-zeolite. Due to unavailability of enough samples having higher boiling point fraction, the cut fractions were changed for MB 390w/Y-zeolite.

polymer, when compared to that of the lower temperature. The molecular weight from the catalytic conversion fraction was lowest compared to other thermochemical degradation, indicating the catalyst promotes cracking.

distillation. The MG fraction obtained from distillation contained more than 83% gasoline and less than 10% diesel, whereas D1 from distillation contained more than 80% D1, ,5% D2, and approximately 10% MG. No vacuum gas oil was detected in any of the MG and D1fractions.

7.4.1.4 Simulated Distillation by GC-FID Simulated distillations were performed on fuel fractions to obtain the boiling point distribution. The product yields are represented in Fig. 7.14. The results agree with the fraction obtained from

7.4.1.5 Chemical Characterization of Plastic Oil Fractions Elemental analysis of MB fuel fractions, D1, D2, and VGO revealed approximately 86% carbon,

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

14% hydrogen, and 0% nitrogen and oxygen content (Table 7.11). This result was consistent with the properties of MBs prior to pyrolysis, including PCO. The MB is PE (CH2), therefore, crude oil and fuel fractions were composed of C and H. The HHV of CO (B49 MJ/kg) was due to higher C and H contents. 7.4.1.5.1 NMR and IR Analysis 1

H spectra provided further information regarding the presence of hydrocarbons in MG and D1 fractions. MG displayed high aliphatic functionality (1H NMR 0.5
2.7 ppm), with B90% of the spectral area located in these regions (Table 7.12). With the use of the catalyst for pyrolysis, the proton percentage increased to .90% in the region between 0.5 and 2.7 ppm. Plastic oil fractions obtained from noncatalytic pyrolysis had a higher percent of

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alkenes when compared to catalytic runs. The alkenes percent was lower in D1 than MG, indicating the relative stability of the product. No aromatic species was detected. 1H NMR clearly shows the absence of oxygenated species such as carboxylic acids, aldehydes, ketones, ethers, or alcohols. Fig. 7.15 shows the FT-IR spectral analysis of MG and diesel #1 fractions obtained from the pyrolysis of MB, with and without catalysts. The FT-IR data agrees with 1H NMR data. The FT-IR spectrum of the catalyzed MG and D1 fraction is dominated by alkane peaks. The peaks at the 2800
3000 cm21 wavelengths represent C
H stretching vibrations of the chemical functional groups
CH3,
CH2, and
CH, respectively. The presence of C 5 C stretching vibrations between the wavelengths of approximately 1640
1650 cm21 suggest the presence of alkenes. The peaks at

Table 7.11 Elemental Content and Heating Value of a Motor Gasoline and Diesel #1 Obtained From PCO From MBs (PP) Pyrolyzed at 450°C, 390°C and in the presence of a catalyst Sample Motor gasoline 35
185°C

Diesel #1 185
290°C

Diesel #2 290
350°C

Vacuum gas oil .350°C

C%

H%

N%

O%

HHV (MJ/kg)

MB 450

85.7

14.3

0

0

49.3

MB 390

85.6

14.4

0

0

49.4

MB 390 with Y-zeolite

85.5

14.5

0

0

49.5

MB 450

85.6

14.4

0

0

49.4

MB 390

85.7

14.3

0

0

49.3

MB 390 with Y-zeolite

85.8

14.2

0

0

49.2

MB 450

85.5

14.4

0.1

0

49.4

MB 390

85.7

14.3

0.03

0

49.3

MB 390 with Y-zeolite

85.8

14.2

0.03

0

49.2

MB 450

85.6

14.3

0.1

0

49.3

MB 390

85.7

14.2

0.1

0

49.2

MB 390 with Y-zeolite

85.6

14.3

0.02

0

49.3

Table 7.12 Relative Percentages of Alkanes and Alkenes Protons MB Motor Gasoline and Diesel #1 Fraction as Determined by 1 H NMR Spectroscopy

Motor gasoline 35
185

Diesel #1 185
290

Alkanes (%)

Alkenes (%)

1. MB 450

89.8

10.2

2. MB 390

90.7

9.3

3. MB 390 w/ Y-Zeolite

94

6

1. MB 450

92.8

7.2

2. MB 390

93.5

6.4

3. MB 390 w/ Y-Zeolite

96.6

3.4

198

PLASTICS

0.20

MB 450 35–185ºC

MB 450 185–290ºC

0.20

0.15

0.15

0.10

0.10

0.05

0.05 0.00

0.00 0.25 0

Absorbance

ENERGY

0.25

0.25

500

1000

1500

2000

2500

3000

3500

4000

4500

MB 390 35–185ºC

0.20

0.25 0

500

1000

1500

2000

2500

3000

0.20

3500

4000

4500

MB 390 185–290ºC

0.15

0.15

0.10

0.10

0.05

0.05

0.00

0.00 0.25

TO

0

500

1000

1500

0.20

2000

2500

3000

3500

4000

4500

0.25

0

500

1000

1500

2000

0.15

0.15

0.10

0.10

0.05

0.05

3000

3500

4000

4500

MB 390 w/Y-Zeolite 185–290ºC

0.20

MB 390 w/Y-Zeolite 35–185ºC

2500

0.00

0.00 0

500

1000

1500

2000

2500

3000

3500

4000

4500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Wave number Figure 7.15 FT-IR showing the presence of alkanes and alkenes in motor gasoline and diesel #1 fractions obtained from the pyrolysis of MBs with/without catalyst.

2800
3000 and 1320
1480 cm21 show the presence of higher concentration of alkanes. The absence of any other peaks indicates the absence of additional functional groups (Fig. 7.13). For example, if aromatics were present, we would expect a peak between 3000 and 3100 cm21. 7.4.1.5.2 Properties of Gasoline and Diesel Fractions

The cloud point was higher in both MG and D1 fractions obtained from catalytic runs. The higher pyrolysis temperature also increased the cloud point of D1. However, such an increase was not observed in MG. The pour point was similar in all MG and D1 samples and was not detected for MG obtained from catalytic runs and noncatalytic runs at 390°C. CFPP in MG was not different in any of the three runs. Only D1 obtained from noncatalytic runs at 450°C met the minimum oxidative stability specified by EN 590 (IP, 110°C) of 20 h. However, ASTM D975 didn’t specify any limits. IP was not detected for any MG sample. IP for the D1 sample from catalytic runs and the runs at 390°C did not meet the minimum requirement. The KV result indicated the viscosity was very similar in all MG samples. The D1’s KV is within the range of 1.9
4.1 cSt, as specified by ASTM D975 for petrodiesel, with the exception of the D1 obtained from

catalytic runs [37]. The DCN is slightly below 40, the minimum limitation given by ASTM D975 for diesel [37]. The flash point satisfied the minimum requirement of 52°C set by ASTM D975. However, the D1 obtained from pyrolysis at 450°C had a lower flash point, possibly due to the higher content of shorter-chain and lower molecular weight constituents promoted by higher temperatures. Maximum wear scars of 620 μm are specified as the upper limit for lubricity (60°C) in ASTM D975. The wear scar was well below the petrodiesel standard. The shorter wear scar was due to longer-chain constituents in the run without catalysts. The acid value was negligible in all MG and D1. The complete results are illustrated in Table 7.13. The heating value was higher than that of ULSD (45.15 MJ/kg) [37]. The HHV calculated by elemental content differed only up to 3 MJ/kg in HHV obtained using ASTM method (bomb calorimetry method). 7.4.1.5.3 Hydroprocessing

The D2 was analyzed for the presence of alkenes using 1H NMR, which indicated 5.1% alkenes and 94.8% alkanes. Diesel stability can be increased by saturating the olefins with hydrogen. Therefore, the D2 obtained at 450°C was hydrotreated in the presence of a hydrotreating catalyst: Sulfide CoMo-

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Table 7.13 Fuel Properties of Motor Gasoline and Diesel Obtained From MB Pyrolysis Motor Gasoline

Diesel

MB 450

MB 390

MB w/ Yzeolite

MB 450

MB 390

MB w/ Yzeolite

CP

263.8

, 2 73.0

, 2 74.0

271.3

256.2

272.0

PP

, 2 74.0

n/a

n/a

, 2 74.0

, 2 74.0

, 2 74.0

CFPP

, 2 50.0

, 2 50.0

, 2 50.0

, 2 50.0

, 2 50.0

, 2 50.0

Low temperature

°C

IP, 110°C

h

n/a

n/a

n/a

20.8 (3.1)

6.6 (0.1)

4.8 (0.1)

KV, 40°C

cSt

0.6

0.6

0.6

2.0

2.0

1.7

n/a

n/a

n/a

34.8

36.3

34.1

n/a

n/a

n/a

69.0

74.0

77.0

n/a

n/a

n/a

169.0

304.0

423.8

0.7

0.8

0.7

0.8

0.8

0.8

0.7

0.7

0.7

0.8

0.8

0.8

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.4

0.1

0.0

45.8(0.3)

46 (0.5)

46.1 (0.4)

46.2(0.3)

45.8 (0.18)

46.1 (0.1)

Surface tension at 25°C

20.4 (0.1)

20.3 (0.1)

20.4 (0.1)

24.4 (0.2)

24.4

20.4 (0.1)

Surface tension at 40°C

19.1 (0.1)

19.0 (0.2)

19.0 (0.1)

22.6 (0.1)

23.0 (0.1)

19.0 (0.1)

DCN Flash point

°C

Wear scar, 60°C SG, 15°C Density, 15° C

kg/m

Moisture

ppm

3

AV HHV

MJ/kg

Table 7.14 Relative Percentages of Alkenes and Alkenes Protons in MB Diesel #2 Fraction as Determined by 1H NMR Spectroscopy Hydrogen % ratio in MB Diesel #2 fraction

Alkanes (%)

Alkenes (%)

Before hydroprocessing

94.8

5.1

After hydroprocessing

98.2

1.8

Alumina. The hydrotreated product yield was approximately 95 wt% in each run. The product was analyzed using 1H NMR. Hydrotreating decreased the alkenes down to 1.8% from 5.1%, improving the oxidative properties of the D2 fraction. The results are given in Table 7.14 and Fig. 7.16.

7.4.2 Polyethylene 7.4.2.1 Gasoline and Diesel Products From Distillation of Green Plastics— High-Density Polyethylene Distillation was conducted to separate MG, D1, D2, and VGO fractions. Distillation of PCOs from

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Figure 7.16 Diesel #2 obtained from MB pyrolysis without catalyst at 450°C showing alkanes and alkenes as determined by 1H NMR spectroscopy.

Figure 7.17 Distillation fractions that are obtained from GP pyrolysis with Y-zeolite, MgCO3 and without catalyst.

all three runs showed a wide range of product distribution. Catalytic runs using Y-zeolite had selectivity towards MG; MgCO3 had selectivity towards diesel; and noncatalytic runs had selectively toward vacuum gas oil, as shown in Fig. 7.17. PCO from catalytic conversion had a higher MG content, indicating that the catalyst supported cracking. Therefore, choice of catalyst can increase or change the selectivity of the product (Fig. 7.17).

7.4.2.2 Size Exclusion Chromatography Analysis SEC analysis was employed to determine the molecular weight distribution of the MG, D1, D2, and VGO fractions. The fuel fractions with lower boiling points had lower molecular weight when compared to the higher boiling point fractions. The runs with catalysts had higher PDI, indicating catalysts favor the formation of larger varieties of

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Table 7.15 Molecular Weight Distribution of Distillate Fraction Obtained From Green Plastic With/Without Catalyst Fuel Fractions

Sample

Motor gasoline 35
185

1. GP 460

47.6

65.3

1.37

2. GP 430 w/Y-zeolite

43.3

76.3

1.91

3. GP 450 w/MgCO3

51.3

Diesel #1 185
290

Mn

VGO 350 1

PDI

116

2.26

162

179

1.10

5. GP 430 w/Y-zeolite

83

141

1.70

6. GP 450 w/MgCO3

109

169

1.54

7. GP 460

281

301

1.06

8. GP 430 w/Y-zeolite

275

295

1.09

9. GP 450 w/MgCO3

293

321

1.09

10. GP 460

670

809

1.19

11. GP 430 w/Y-zeolite

477

527

1.11

12. GP 450 w/MgCO3

472

509

1.08

4. GP 460

Diesel #2 290
350

Mw

Table 7.16 Elemental Composition and HHV of Distillate Fractions Obtained by Noncatalytic and Catalytic Pyrolysis of GP Sample Motor gasoline 35
185°C

Diesel #1 185
290°C

Diesel #2 290
350°C

Vacuum gas oil .350°C

C%

H%

N%

O%

HHV (MJ/kg)

GP 460

85.5

14.4

0

0.07

49.4

GP with Y-zeolite

85.3

14.5

0.2

0

49.5

GP with MgCO3

85.4

14.4

0.2

0

49.4

GP 460

85.6

14.4

0.02

0

49.4

GP with Y-zeolite

85.8

14

0.2

0

48.9

GP with MgCO3

85.5

14.3

0.2

0

49.3

GP 460

85.5

14.5

0.02

0

49.5

GP with Y-zeolite

86.0

14

0

0

49.0

GP with MgCO3

85.0

15

0

0

50.1

GP 460

85.5

14.5

0.01

0

49.6

86

14

0

0

49.0

GP with Y-zeolite GP with MgCO3

The numbers shown are the average of two measurements, while oxygen is determined by subtracting total percentage of C, H, and N from 100%.

hydrocarbons. The runs in the absence of catalysts had a very narrow range of PDI (between 1.1 and 1.5), indicating narrow molecular weight distribution (Table 7.15). These fuel fractions also had a narrow range of boiling point hydrocarbons. Such results indicated that, on average, the molecular weight distribution in lower temperature fractions was lower than that of higher temperature fractions.

7.4.2.3 Elemental Analysis The elemental composition of distillate fractions MG, D1, D2, and VGO showed approximately 85% carbon, 15% hydrogen, and a negligible amount of nitrogen and oxygen. This result is similar to that of the raw plastic and the PCO. A higher content of carbon and hydrogen increased the HHV of the distillates to approximately 50 MJ/kg (Table 7.16). The HHV is similar to that found in petroleum fuels.

202

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Figure 7.18 Boiling point distribution of the fractions (35
185°C, 185
350°C and .350°C) obtained from distillation of PCO from green plastic except green plastic with Y-zeolite.

Table 7.17 Relative Percentages of Alkanes and Alkenes Protons in Green Plastic Diesel #2 Fraction as Determined by 1H NMR Spectroscopy

Motor gasoline 35
185

Diesel #1 185
290

Alkanes (%)

Alkenes (%)

1. GP 460

89.2

10.8

2. GP 430 w/Y-zeolite

94.1

5.9

3. GP 450 w/MgCO3

89.8

10.2

4. GP 460

93.1

6.9

5. GP 430 w/Y-zeolite

96.7

3.3

6. GP 450 w/MgCO3

94

6

7.4.2.4 Simulated Distillation

7.4.2.5 Fuel Analysis

Simulated distillations were performed on PCO and fuel fractions to verify the purity in terms of boiling point distribution. The data obtained from SimDist were processed in MATLAB into four fractions based on boiling point distribution: ,185; 185
290; 290
350; and .350°C equivalent of MG (,185°C), D1 (185
290°C), D2 (290
350°C), and VGO ( . 350°C). The results are in agreement with the fractions obtained from distillation (Fig. 7.18). The MG fraction obtained from distillation contained more than 83% gasoline, with the remainder being diesel. The D1 fraction from distillation contained more than 80% D1, 1%
8% D2, and approximately 10% MG. No VGO was detected in any of the MG and D1 fractions.

7.4.2.5.1 NMR and FT-IR Analysis

From 1H NMR measurements, we determined the olefin character of MG and D1, which is related to the stability of these products. Table 7.17 illustrates the 1H NMR spectra of MG and D1 obtained from GP pyrolysis with and without catalysts. The peaks between 0.5 and 2.7 indicate protons attached to alkanes. The alkanes’ proton percentage is higher in runs without a catalyst. The percent of alkanes obtained from the catalytic runs using MgCO3 was similar to runs without a catalyst. The MG and D1 obtained from runs using Y-zeolite produced a higher percentage of alkanes compared to that of noncatalyzed pyrolysis and pyrolysis with MgCO3. No aromatic groups were detected in any of these fractions.

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

Percentages determined using integration values obtained from 1H NMR spectra of signals corresponding to chemical shifts indicative of the functionalities indicated (alkenes: 4.5
6.5 ppm; alkanes: 0.5
2.7 ppm). Results obtained from the FT-IR spectral analysis confirmed the NMR data. The FT-IR data is dominated by alkane peaks. The peaks at the 2800
3000 cm21 wavelengths represent C
H stretching vibrations of the chemical functional groups,
CH3,
CH2, and
CH, respectively. The presence of C 5 C stretching vibrations between the wavelengths of approximately 1640
1650 cm21 suggest the presence of alkenes. The peaks at 2800
3000 and 1320
1480 cm21 show the presence of higher concentration of alkanes. The absence of any other peaks indicates the absence of additional functional groups (Fig. 7.19). For example, if aromatics were present, we would expect a peak between 3000 and 3100 cm21.

With regard to cold flow properties, the cloud point was higher in both MG and D1 fractions obtained from catalytic runs, and was significantly higher with Y-zeolite. Similar results were obtained for the pour point. However, PP was not detected for MG obtained from the run with Y-zeolite.

203

0.30

GP 35–185ºC

0.25

0.25

0.20

0.20

0.15

0.15

0.10

0.10

0.05

0.05

0.00

GP 185–290ºC

0.00 0

500

1000

1500

2000

2500

3000

3500

4000

4500

0.30

Absorbance

PLASTICS

CFPP in MG was not different in any of the three runs. As expected, CFPP was higher in D1 from the run with Y-zeolite, as shown in Table 7.18. The oxidative stability was not up to the standard specified by EN 590, which indicates a minimum oxidative stability (IP, 110°C) of 20 h. However, ASTM D975 does not specify any limits. The KV result indicates the viscosity is very similar in all MG and D1 samples, with a slightly lower viscosity in MG and D1 obtained from runs with Y-zeolite. The DCN was above 40, the minimum limitation given by ASTM D975 for diesel [37]. The flash point satisfied the minimum requirement of 52°C, set by ASTM D975. However, the D1 obtained from the Y-zeolite run had a flash point below the minimum limits specified in the petrodiesel standard, this might be due to the higher content of shorter-chain and lower molecular weight constituents. Maximum wear scars of 620 μm are specified as the upper limit for lubricity (60°C) in ASTM D975. The wear scar was well below the petrodiesel standard. The shorter wear scar was due to the longer-chain constituents in runs without catalysts. The acid value was negligible in all the MG and D1 products. The heating value was higher than that of the ULSD (45.15 MJ/kg) [37]. D1 has a higher energy content than MG because of the larger hydrocarbon chain in D1. The HHV calculated by elemental content

7.4.2.5.2 Properties of Gasoline and Diesel Fractions

0.30

OF

0

500

1000

1500

2000

2500

3000

GP w/MgCO3 35–185ºC

0.25

3500

4000

4500

GP w/MgCO3 185–290ºC

0.30 0.25

0.20

0.20

0.15

0.15

0.10

0.10

0.05

0.05

0.00

0.00 0

500

1000

1500

2000

2500

0.30

3000

3500

4000

4500

GP w/Y-Zeo 35–180ºC

0.25

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0.30

GP w/Y-Zeo 180–290ºC

0.25

0.20

0.20

0.15

0.15

0.10

0.10

0.05

0.05 0.00

0.00 0

500

1000

1500

2000

2500

3000

3500

4000

4500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Wave Number

Figure 7.19 FT-IR showing the presence of alkanes and alkenes in motor gasoline and diesel #1 fractions obtained from the pyrolysis of GP with/without catalyst.

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Table 7.18 Fuel Properties of Motor Gasoline and Diesel Obtained From GP Pyrolysis Motor Gasoline

Diesel

GP 460

GP 430 w/ Y-zeolite

GP 450 w/ MgCO3

GP 460

GP 430 w/ Y-zeolite

GP 450 w/ MgCO3

CP

228.2

,2 73.0

234.0

218.8

239.9

222.9

PP

,2 73.0

n/a

,2 73.0

228.0

250.0

227.3

CFPP

,2 50.0

,2 50.0

,2 50.0

227.3

241.7

227.3

Properties

Units

Low temperature

°C

Oxidative stability IP, 110°C

h

n/a

n/a

n/a

1.4 (0.6)

0.8 (0.2)

1.3 (0.1)

KV, 40°C

cSt

0.7

0.6

0.7

1.6

1.6

1.7

n/a

n/a

n/a

62.2

47.7

63.7

n/a

n/a

n/a

74.0

24.0

77.0

n/a

n/a

n/a

234.3

500.5

433.3

0.7

0.7

0.7

0.8

0.8

0.8

0.7

0.7

0.7

0.8

0.8

0.8

0.0

0.0

0.0

0.0

393.0

0.0

0.0

0.0

0.0

0.1

0.1 (0.03)

0.0

45.4 (0.2)

45.6 (0.3)

45.8 (0.1)

46 (0.2)

46 (0.3)

46.5 (0.1)

Surface tension at 25°C

21.5 (0.1)

20.4 (0.1)

21.3 (0.1)

25.4

25.3

25.7

Surface tension at 40°C

20.0 (0.1)

18.8 (0.1)

19.6 (0.1)

23.8 (0.1)

23.7 (0.1)

24.0 (0.1)

DCN Flash point

°C

Wear scar, 60°C SG, 15°C Density, 15° C

kg/m

Moisture

ppm

3

AV HHV

MJ/kg

The value in parentheses represents standard deviation from the reported means (n 5 3).

Table 7.19 Relative Percentages of Alkanes and Alkenes Protons in Green Plastic Diesel #2 Fraction as Determined by 1 H NMR Spectroscopy Hydrogen % Ratio in GP Diesel #2 fraction

Alkanes (%)

Alkenes (%)

Before hydroprocessing

96.1

3.9

After hydroprocessing

99.8

0.2

differed only up to 3 MJ/kg in HHV obtained using ASTM methods (bomb calorimetry method). 7.4.2.5.3 Hydroprocessing

The D2 was analyzed for the presence of alkenes by 1H NMR. The results indicated the presence of 3.9% alkenes and 96.1% alkanes (Table 7.19). The

stability of diesel can be increased by saturating the olefins with hydrogen. Therefore, D2 obtained from pyrolysis GP at 460°C was hydrotreated in the presence of a hydrotreating catalyst. Sulfide CoMoAlumina was used for the hydrotreatment. The yield was approximately 95 wt% in each run. The product was analyzed using 1H NMR. Hydrotreating

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Figure 7.20 Diesel #2 obtained from GP pyrolysis without catalyst at 460°C.

decreased the alkenes down to 0.2% from 3.9%, improving the oxidative properties of D2 fraction. The results are given in Table 7.9 and Fig. 7.15. Percentages determined using integration values obtained from 1 H NMR spectra of signals corresponding to chemical shifts indicative of the functionalities indicated (alkenes: 4.5
6.5 ppm; alkanes: 0.5
2.7 ppm) (Fig. 7.20).

7.5 Comparison of Pyrolysis Oil Fuel Blends With Commercial Fuel 7.5.1 Properties of Pyrolyzed Polypropylene Samples and Comparison to Ultra-Low Sulfur Diesel Shown in Tables 7.20
7.22 are the fuel properties of various pyrolyzed PP samples along with a comparison to the petrodiesel standards ASTM D975 and EN 590. Fuel properties of interest included cold flow (CP, PP, and CFPP), oxidative stability (IP), AV, DCN, density, energy content, KV, lubricity, specific gravity, and surface tension (Tables 7.20
7.27). Nearly all of the samples yielded very low CP, PP, and CFPP values, thereby indicating excellent

low temperature performance. In particular, MB390, MB450, and MB390/450 provided CP ,
55oC, PP ,
74oC, and CFPP ,
50oC. In addition, PP 450, PP500, and PP500 PS yielded PP ,
74oC and CFPP ,
50°C. Such values represented significant enhancement over ULSD, which provided CP, CFPP, and PP values of
17.5°C,
16.0°C, and
20.3°C, respectively. EN 590 prescribes a minimum IP (110°C) of 20 h, whereas ASTM D975 does not contain an oxidative stability specification. The only samples that were above the minimum specification were MB450 (20.8 h), PP500 (22.7 h), and PP500 PS ( . 24 h). The remainder of the samples provided values that ranged from 0.8 (GP430) to 17.1 h (PP450). In contrast, the IP of ULSD was .24 h. The presence of unsaturated constituents may explain the reduced stabilities of most of the samples relative to ULSD. Presumably, MB450, PP500, and PP500, and PS contained fewer oxidatively susceptible double bonds than the remainder of the samples. Both the American and European petrodiesel standards specify limits for KV at 40°C with ranges specified of 1.9
4.1 mm2/s (ASTM D975) and 2.0
4.5 mm2/s (EN 590). Several samples provided KVs below the minimum limits specified in the standards, including MB390/450 (1.73 mm2/s), GP430 (1.57 mm 2 /s), GP450 (1.73 mm 2 /s),

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Table 7.20 Fuel Properties of Pyrolyzed PP Bottles and ULSD Along With a Comparison to Petrodiesel Fuel Standardsa Units

ASTM D975b

EN 590

ULSD

MB 390

MB 390/450

MB 450

CP

°C




c




c

218

256 (1)

272 (1)

271 (1)

PP

°C




c




c

220 (1)

, 2 74

, 2 74

, 2 74

CFPP

°C




c




c

216

, 2 50

, 2 50

, 2 50

IP, 110°C

h




c

20 min

.24

6.6 (0.1)

4.8 (0.1)

20.8 (3.1)

AV

mg KOH/g


c


c

N/Dd

0.15 (0.01)

N/D

0.38 (0.02)

KV, 40°C

mm2/s

1.9
4.1

2.0
4.5

2.28 (0.01)

1.96

1.73

1.96

40 min

51 min

47.4 (0.9)

36.3

34.1

34.8

520 max

460 max

581 (5)

304 (5)

424 (20)

169 (2)


c


c

0.841

0.793

0.735

0.791




820
845

849 (1)

0.792

0.734

0.790

DCN Wear scar, 60°C

μm

SG, 15°C 3

c

Density, 15°C

kg/m

ST, 40°C

mN/m


c


c

25.1 (0.2)

23.0 (0.1)

22.9 (0.1)

22.6 (0.1)

HHV

MJ/kg


c


c

45.15 (0.19)

45.78 (0.19)

46.07 (0.39)

46.16 (0.26)

a Values in parentheses represent standard deviations from the reported means (n 5 3). Where no value is indicated, standard deviation was zero. b For No. 2 grade S15 (15 ppm S) ULSD. c Not specified. d Not detected.

GP/HDPE (1.65 mm2/s), 1:1 MB450/GP450 (1.77 mm2/s), and 1:3 PPB450/GP450 (1.87 mm2/s). In addition, MB390 (1.96 mm2/s) and MB450 (1.96 mm2/s) were below the minimum limit listed in EN 590, but within the range specified in ASTM D975. All other samples were within the ranges specified in both standards and were similar to that of ULSD (2.28 mm2/s). A potential explanation for the reduced KV of several samples relative to ULSD may be a lower content of branched aromatics and longer-chain hydrocarbons in the samples with lower KV. It has been previously reported that KV increases with chain length, aromatization, and/or branching [71]. Lubricity specifications are included in ASTM D975 and EN 590, with maximum wear scars (60° C) of 520 and 460 μm, respectively, prescribed

using the high-frequency reciprocating rig lubricity test. With the exception of GP430 (500 μm), all of the samples yielded wear scars below the maximum limits prescribed in the petrodiesel standards and below that obtained for ULSD (581 μm). The samples that provided the shortest wear scars (MB450, PP500, and PP500 PS) also yielded the highest AVs. It is known from previous studies that carboxylic acids significantly improve lubricity [72]. AV is, of course, a measure of carboxylic acid content in a sample. Neither ASTM D975 nor EN 590 specifies limits for AV. The minimum limits specified for cetane number (CN) in ASTM D975 and EN 590 are 40 and 51, respectively. Reported herein is DCN. The ASTM D6890 method (DCN), which requires a much smaller sample size, is approved as an alternative

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Table 7.21 Fuel Properties of Pyrolyzed PP Bottles and ULSD Along With a Comparison to Petrodiesel Fuel Standardsa Units

GP 430

GP 450

PP 450

PP 500

PP 500 PS

GP/HDPE

CP

°C

240 (0)

223 (1)

225 (1)

233 (2)

237 (1)

219 (1)

PP

°C

250 (1)

227 (1)

,2 74

,2 74

,2 74 (1)

228 (1)

CFPP

°C

242 (1)

227 (1)

,2 50

,2 50

,2 50 (1)

227 (1)

IP, 110°C

H

0.8 (0.2)

1.3 (0.1)

17.1 (1.7)

22.7 (1.0)

.24

1.4 (0.6)

AV

mg KOH/g

N/D

N/D

0.30 (0.03)

0.37 (0.01)

0.96 (0.04)

N/Db,c

KV, 40°C

mm2/s

1.57

1.73

2.42 (0.01)

2.49 (0.01)

2.48

1.65

47.7

63.7

38.2

38.6

35.5

62.2

500 (17)

433 (22)

229 (15)

202 (6)

194 (8)

235 (6)

0.799

0.791

0.797

0.798

0.800

0.787

0.798

0.790

0.797

0.797

0.800

0.787

DCN Wear scar, 60°C

μm

SG, 15°C 3

Density, 15°C

kg/m

ST, 40°C

mN/m

23.7 (0.1)

24.0 (0.1)

23.1 (0.1)

23.4 (0.1)

23.3 (0.1)

23.8 (0.1)

HHV

MJ/kg

46.01 (0.31)

46.46 (0.08)

46.11 (0.11)

46.20 (0.18)

46.14 (0.19)

45.95 (0.16)

a Values in parentheses represent standard deviations from the reported means (n 5 3). Where no value is indicated, standard deviation was zero. b None detected. c Not determined due to insufficient sample size.

to the more traditional CN method (ASTM D613) specified in ASTM D975 [73]. The only samples that provided DCNs above the minimum limits were GP450 (63.7) and GP/HDPE (62.2). The remainder of the samples yielded DCNs lower than that of ULSD (47.4). Structural factors that negatively influence DCN include increased branching, unsaturation and aromatics content, as well as shorter hydrocarbon chain lengths [74]. It is therefore likely that the samples that failed the DCN specifications contained greater amounts of branched, aromatic, and/or shorter-chain hydrocarbons. The inferred presence of such structural features causing the low DCNs may also be responsible for the excellent cold flow properties discussed previously, as it is well-known that increased branching and reduced chain lengths tend to lower the melting point. It is interesting to note that GP450 and GP/HDPE yielded the highest CP, CFPP, and PP values as well as the highest DCNs

( . 62), thereby suggesting that these samples contained the highest concentrations of linear and longer-chain hydrocarbons. Furthermore, without exception, samples that yielded PP ,
74°C and CFPP ,
50°C also provided DCNs ,40. ASTM D975 does not contain a density specification, but EN 590 prescribes a range of 820
845 kg/m3 at 15°C. None of the synthetic samples provided densities within the range specified in EN 590. In contrast, ULSD conformed to EN 590 with a density of 849 kg/m3. The lower densities of the samples relative to ULSD may be due to a greater percentage of aromatics in ULSD. Aromatics exhibit higher densities than linear, branched, and cyclic hydrocarbons that are more likely to comprise the synthetic samples [52]. Also measured was SG, which is not specified in the petrodiesel standards. As was the case with density, the SGs of the samples were lower than that of ULSD (0.841). Even though ST influences fuel

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Table 7.22 Fuel Properties of Pyrolyzed PP Bottlesa 1:1 MB450/ GP450

1:1 PPB450/ GP450

1:3 PPB450/ GP450

3:1 PPB450/ GP450

CP

232

229

226 (1)

234

PP

238

235 (1)

227 (1)

239 (1)

CFPP













2.2 (0.4)

8.6 (0.9)

N/D

N/D

Units

IP, 110°C

h

b

5.9 (0.9)

4.2 (0.1) c

AV

mg KOH/g

0.21 (0.4)

N/D

KV, 40°C

mm2/s

1.77

2.01

1.87

2.18













202 (8)

353 (2)

365 (2)

310 (5)

























DCN μm

Wear scar, 60°C SG, 15°C

3

Density, 15° C

kg/m

ST, 40°C

mN/m

23.1 (0.1)

23.4

23.6 (0.1)

23.3

HHV

MJ/kg

46.18 (0.12)

46.23 (0.04)

46.09 (0.09)

46.09 (0.07)

a Values in parentheses represent standard deviations from the reported means (n 5 3). Where no value is indicated, standard deviation was zero. b Not determined due to insufficient sample size. c None detected.

Table 7.23 Fuel Properties of Pyrolyzed PP Bottles Blended With ULSDa

Units

5% MB450

20% MB450

5% GP450

20% GP450

5% 1:1 MB450/ GP450

20% 1:1 MB450/ GP450

CP

°C

215

216

215

216

215

229 (1)

PP

°C

229 (1)

233 (1)

229 (1)

230 (1)

226

231 (1)

IP, 110° C

h

.24

.24

.24

21.5 (1.5)

.24

.24

AV

mg KOH/g

N/Db

N/D

N/D

N/D

N/D

N/D

KV, 40° C

mm2/s

2.21

2.15

2.19

2.13

2.19

2.10

Wear scar, 60°C

μm

417 (8)

306 (9)

524 (3)

267 (11)

447 (6)

310 (5)

Density, 15°C

kg/m3

845

837

845

837

845

837

ST, 40° C

mN/m

24.8 (0.1)

24.4

24.8 (0.1)

24.6 (0.1)

24.8 (0.1)

24.6 (0.1)

HHV

MJ/kg

45.24 (0.20)

45.41 (0.25)

45.42 (0.28)

45.58 (0.18)

45.24 (0.13)

45.19 (0.14)

Values in parentheses represent standard deviations from the reported means (n 5 3). Where no value is indicated, standard deviation was zero. b None detected. a

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Table 7.24 Ratio Factors for Estimating the Capital Investments Based on Purchased Equipment Costs Percent of Delivered Equipment Cost Solid Processing Plant

Solid
Fluid Processing Plant

Fluid Processing Plant

Purchased equipment

100

100

100

Purchased equipment installation

45

39

47

Instrumentation and controls

18

26

36

Piping

16

31

68

Electrical systems

10

10

11

Buildings

25

29

18

Yard improvements

15

12

10

Service facilities

40

55

70

Total direct plant cost

269

302

360

Engineering supervision

33

32

33

Construction expenses

39

34

41

Legal expenses

4

4

4

Contractors fees

17

19

22

Contingency

35

37

44

Total indirect plant cost

128

126

144

Working capital (15% total capital investment)

70

75

89

Total capital investment

467

503

593

Direct Costs

Indirect costs

atomization, it is not specified in either ASTM D975 or EN 590 [53]. The STs of the synthetic samples (,23.9 mN/m) at 40°C were below ULSD (25.1 mN/m). The HHVs of the synthetic samples ( . 45.7 MJ/ kg) were higher than ULSD (45.15 MJ/kg). The higher HHVs of the samples relative to ULSD were attributed to the higher content of aromatics in ULSD, as aromatics contain less energy than saturated constituents likely to comprise the synthetic samples. Therefore, the proposed lower aromatics content within the synthetic samples, versus ULSD causing lower density and SG, may also be partially responsible for higher energy content. In addition, the synthetic sample yielding the highest energy content (GP450; 46.46 MJ/kg) also provided the lowest DCN and highest cold flow properties. Longer-chain hydrocarbons not only increase DCN and melting point, but also contain greater energy

content due to the presence of a larger number of energetic carbon
hydrogen bonds. Energy content is not specified in the petrodiesel standards.

7.5.2 Properties of Blends With Ultra-Low Sulfur Diesel Depicted in Table 7.23 are fuel properties of blends of selected pyrolyzed PP samples with ULSD. Samples selected for blending with ULSD included MB450, GP450, and 1:1 MB450/GP450, as these were determined to have the best combination of fuel properties relative to the other samples. For each sample, blends of 5 and 20 vol% in ULSD were investigated. Fuel properties determined were cold flow (CP and PP), density, oxidative stability (IP), AV, energy content, KV, lubricity, and surface tension. Other properties such

210

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Table 7.25 Estimation of Fixed Capital Investment for Different Units Units Parameters

Capital Costs

kg/day

% of Equipment Cost

12,000



Capital cost (reactor from vendor)

$

3,295,227



Capital cost (refiner, if needed, from vendor)

$

310,293

Purchased equipment (E, from vendor)

$

3,605,520



$

103,232

Direct Costs Equipment installation cost (from vendor)

Piping

$

31

1,117,711

Electricals

$

10

360,552

Buildings

$

29

1,045,601

Yard improvements

$

12

432,662

Service facilities

$

55

1,983,036

Land

$

6

216,331

Total direct cost

8,864,645

Indirect Costs Engineering and supervision

$

32

1,153,766

Construction expense

$

34

1,225,877

4

144,221

Legal expense Total indirect cost

2,523,864

Total direct and indirect costs

$

11,388,509

Contractors fee

$

19

685,049

Contingency

$

37

1,334,042

Fixed capital investment

$

13,407,600

Note: -  Calculated as a scaled up cost using a factor of 0.6 for stainless steel reactor.

as CFPP, DCN, and specific gravity were not measured due to insufficient sample size. As the percentage of synthetic samples increased in blends with ULSD, values for PP became progressively lower due to the superior low temperature performance of the samples relative to ULSD. However, CP values of the blends were higher than that of ULSD despite the fact that the CPs of the unblended samples were significantly lower than ULSD. A potential explanation for such a phenomenon may be that the samples become less soluble in ULSD at subambient temperatures, thus facilitating crystallization. CFPP was not measured due to insufficient sample volume. Oxidative stability was not negatively affected, as the percentage of sample increased in blends with ULSD, as nearly all 5% and 20% samples yielded IPs .24 h. The lone exception was that of

the 20% blend of GP450 in ULSD, which provided an IP of 21.5 h. This result was not surprising, as GP450 yielded a very low IP of 1.3 h. Comparison to the IP specification listed in EN 590 revealed that all of the blends were above the minimum limit of 20 h. Lower KVs were noted as the concentration of synthetic samples increased in blends with ULSD. In addition, all blends provided KVs lower than that of unblended ULSD. However, comparison to the petrodiesel standards revealed that all blends were within the limits prescribed in the petrodiesel standards. Progressively shorter wear scars were observed as the blend ratio increased due to the enhanced lubricities of the synthetic samples relative to ULSD. The effect was more pronounced in the case of PPEH-H, as it exhibited better lubricity than

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

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Table 7.26 Estimation of Operational Costs for 1 Unit of 12,000 kg/day Capacity Over Three Shifts Category

Costs

Raw material

Units

12,000

Raw material cost

5

Days of operation

350

Shift hours

8

kg/24 h cents/kg days h/day

Labors cost

100,800

$/annum (3 shift operation)

Plant manager

184,800

$/annum

Utilities

1

kWh/[email protected]/kWh

Operation/maintenance

3

% of total capital

Federal, state, local taxes Insurance Product Density of crude oil Product

35

% of FC

1

% of FC

8400 850 2,610

Selling price (fractions)

PPEH-L. With the exception of the 5% GP450 blend, all blends yielded lubricities that were below the maximum limits specified in ASTM D975 and EN 590. It was not surprising that the GP450 blends exhibited the longest wear scars, as unblended GP450 provided the longest wear scar of the synthetic samples blended with ULSD. Density decreased as the percentage of sample increased in blends with ULSD. All blends provided densities that fell within the range specified in EN 590. In addition, none of the blends contained a detectable amount of acids, as determined via AV. Such a result was expected, as the unblended synthetic samples also had low AVs, as discussed previously mention the section of discussion. Lastly, energy content of the blends increased slightly with concentration of ULSD. This was expected, as the synthetic samples provided higher HHVs than ULSD. The highest increases were noted for GP450 blends, which was because GP450 contained the greatest energy content of the synthetic samples studied herein.

7.6 Techno-Economic Analysis An economic analysis of a plastics-to-fuel facility is presented below to assess whether the technology has potential to be carried out at a

4

kg/24 h kg/m3 gallon/24 h $/gallon

commercial scale. The analysis provides estimated investment costs and a net present value for a 12 tons/day plant. The 12 tons/day plant is assumed to be comprised of a single reactor operating on a mixture of PE and PP waste that does not have a ready secondary market. The investment costs are furthermore estimated as a green field project even though it is both preferable and likely that such a plant be collocated at an existing waste collection and processing facility. The capacity of 12 tons/day represents less than 10% of PE and PP plastic waste generated in Illinois. Investment costs include direct and indirect plant costs. The direct plant costs include expenditures related to purchase of equipment and installation and associated costs for instrumentation, piping and insulation, electrical, building and yard improvements, service facilities, and acquirement of land. The indirect plant costs include contractor’s fees and contingency. There are various methods to estimate investment costs. The percentage of delivered equipment cost method is used for preliminary and study estimates. This method requires determination of the major delivered equipment cost. The other items included in the total direct plant cost are then estimated as percentages of the delivered equipment cost. The additional components of capital investment are based on percentages of the total direct plant cost, total direct and indirect plant

Table 7.27 Economic Profitability Analysis for 1 Unit of 12,000 kg/day Time (Years) Cost

1

2

3

4

6

7

8

9

3,653,901

3,653,901

3,653,901

3,653,901

3,653,901

3653901

3,653,901

3,653,901

3,653,901

3,653,901

13,407,600

0

0

0

0

0

0

0

0

0

Raw materials

210,000

210,000

210,000

210,000

210,000

210,000

210,000

210,000

210,000

210,000

Utilities

491,400

491,400

Labor

285,600

285,600

491,400

491,400

491,400

491,400

491,400

491,400

491,400

491,400

285,600

285,600

285,600

285,600

285,600

285,600

285,600

285,600

Operation

402,228

402,228

402,228

402,228

402,228

402,228

402,228

402,228

402,228

402,228

Insurance

134,076

134,076

134,076

134,076

134,076

134,076

134,076

134,076

134,076

134,076

1,340,760

1,340,760

1,340,760

1,340,760

1,340,760

1,340,760

1,340,760

1,340,760

1,340,760

1,340,760

13,407,600

2,130,597

2,130,597

2,130,597

2,130,597

2,130,597

2,130,597

2,130,597

2,130,597

2,130,597

BTDepreciation

789,837

789,837

789,837

789,837

789,837

789,837

789,837

789,837

789,837

Tax @35%

276,443

276,443

276,443

276,443

276,443

276,443

276,443

276,443

276,443

1,854,154

1,854,154

1,854,154

1,854,154

1,854,154

1,854,154

1,854,154

1,854,154

1,854,154

Product

Units $

Capital

Depreciation Cash flow BT

0

Cash flow AT 1 depreciation Rate

%

1

NPV

$

2,450,611

5

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

costs, or total capital cost investment. Eq. (7.1) summarizes the method Cn 5 ½ΣE 1 Σðf1 E 1 f2 E 1 F3 E 1 . . .ÞðfI Þ

(7.1)

where Cn is the total capital investment, E is the equipment cost, and f1 and f2 are multiplying factors for piping, electrical, instrumentation, etc. fI is the indirect cost factor greater than 1.

7.6.1 Estimation of Capital Investment Typical ratio factors for estimating capital investments based on purchased equipment costs are presented in Table 7.24 [57] for various types of plants. These values are based on fixed capital investments ranging from under $1 million to over $100 million. The plastics-to-fuel facility is assumed to have characteristics similar to a solid
fluid processing plant for estimation purposes.

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PLASTICS

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7.6.4 Variable Production Cost 7.6.4.1 Materials Cost Since the plastic considered for conversion in this study is a waste material with no secondary markets, it was assumed to be available at 5 cents/kg.

7.6.4.2 Utilities The reactor is assumed to be heated using electricity. From the energy balances, and based on guidance from the manufacturer (BLEST, Inc.), the energy to convert 1 kg of plastics-to-fuel
type material is estimated to be 1 kWh. Electricity is estimated to be available at 11.7 cents/kWh. Alternative forms of energy such as natural gas, if used, would result in lower utility costs than estimated here.

7.6.4.3 Operation/Maintenance Cost The cost of operating, maintaining, and repairing supplies is assumed to be 3% of the overall equipment costs/annum.

7.6.2 Major Equipment

7.6.4.4 Labor Costs

The major equipment in the plastics-to-fuel facility is the reactor, associated solids conveying systems, condensers, and other items such as transfer pumps. One manufacturer, Blest, was contacted to obtain estimates for the major equipment at various scales—220, 1000, and 4000 kg/day systems. Costs were estimated for larger system (12,000 kg/day) using the following formula:

Labor requirements for a fluid plant range between 0.33 and two employee-hours per 1000 kg of a product. For a solid fluids plant such as shale oil, the labor requirements would be intermediate, in the range of two to four employees for 1000 kg product. Plant managers and operators were chosen based on four employee-hours/1000 kg product. For the overtime or night shifts about 16% was added to the base salary. This assumption is also quite conservative, as it is likely that the plant will be collocated with a waste collection and recycling facility (Fig. 7.21)

EC 5 EB X 0:6

(7.2)

where EC is the cost of equipment of required capacity, EB is the cost of the equipment of known capacity, and X is the ratio of the required capacity to the known capacity.

Manufacturing cost distribution 18.75

7.6.3 Manufacturing Costs The operating and production cost for the 12,000 kg/day plant is summarized in Table 7.26. The majority of the costs (about 32%) are derived from utility costs, followed by maintenance costs (26.4%) (Fig. 7.21): The raw materials and the labor add about 32% of the total manufacturing cost.

26.40 35.21

32.26

8.80

13.79

Raw materials

Utilities

Labor

Maintenance

Insurance

Figure 7.21 Manufacturing cost distribution.

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7.6.4.5 Fixed Charges These expenses are independent of production rate. They include expenditures for depreciation, insurance, financing, and rents. Depreciation rate (10%) in this study was calculated by the straight line method assuming a plant life of 10 years with no salvage value.

7.6.4.6 Cash Flow An investment in a manufacturing process must earn more than the cost of capital in order for it to be worthwhile. The larger the additional earnings, the more profitable the venture, and the greater the justification for putting the capital at risk. Cash flow is the net annual cash flow calculated after tax. The annual cash income, ACI, is the difference between the revenue, AS, from the annual sales of a product and the total annual cost, ATE, required to produce and sell the product: ACI 5 AS 2 ATE

(7.3)

Net annual cash income, ANCI, is the annual cash income minus the annual amount of tax, AIT. ANCI 5 ACI 2 AIT

(7.4)

Annual amount of tax, AIT, is calculated from the following equation AIT 5 ðACI 2 AD 2 AA Þt

(7.5)

where AD is the annual depreciation charge, AA is the annual amount of other allowances, and t is the fractional tax rate. The cash flow calculations for a single unit of 12,000 kg/day are presented in Table 6.27 for a discount rate of 1%. The IRR for this capacity is 4.6%. These estimates will be affected by the fluctuating fuel (product) prices, feedstock prices, and proximity of the plant to raw material.

7.7 Conclusions and Future prospects Fuel production from plastics is attractive because it simultaneously addresses the issues of waste management and alternative energy

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generation. The optimization of conversion parameters such as the choice of catalysts, reactor design, pyrolysis temperature, and plastic-tocatalyst ratio play a very important role in the efficient processing of gasoline and diesel grade fuel. The use of a catalyst for thermal conversion lowers the energy required for conversion, and catalyst choice is important for efficient fuel production. A catalyst with higher acidic properties and a higher porosity can enhance conversion. For example, FCC catalysts catalyze the production of aromatic and gaseous hydrocarbons, whereas dual catalysts like zeolite and metal-loaded catalysts can be used for producing hydrocarbons and isomerized products, which increase the octane rating of fuels. Uniform distribution of heat and mass is another important factor in conversion. A fluidized bed reactor is an excellent choice to ensure uniform distribution of heat, resulting in better conversion. Despite the recent advancements in plastic conversion technology, several issues remain. A major challenge with the production of fuel from PSW is the presence of PVC, which produces HCl gas during pyrolysis. However, researchers have been able to remove chlorine to some extent by using HCl adsorbents to pretreat the plastics. Catalysts will also need improvement. For example, it will be useful to use dual catalysts with a combination of high acidic properties, porosity, and hydrogenation properties, identify accessible and cheaper catalysts to use on large scales, and prevent deactivation and increase catalyst reuse. In fact, the use of metal-loaded biochar may partly mitigate the high cost of catalysts. It is very important to devise efficient methods to produce fuel from mixed plastics, or to exclude or remove PET and PVC from mixed plastics before pyrolysis. The product yield and quality can be improved by finding alternative heating modes such as IR and microwave heating to reach the final temperature quickly. A thorough study of the effect of heating rates on product yields and distribution will be very important to produce fuel-range hydrocarbons. There are many other factors that affect the economics of fuel production in terms of raw material handling, such as collection, classification, washing and shredding, transportation, electric energy, heating gas, and cooling water. The cost of each step varies from US $65 to $400/ton [41]. The landfill costs in the United States may vary from $25 to $150/ton depending on the region of the country

7: FUEL PROPERTIES ASSOCIATED WITH CATALYTIC CONVERSION

[75]. It was reported that a well-run curbside recycling program can cost, under general circumstances, between $50 and $150/ton [76]. Therefore, the cost of recycling plastic is relatively inexpensive compared to the production of fuel from plastic, and the cost of fossil fuel is currently cheaper than the production of fuel from plastics [41]. However, the demand of fossil fuel, the issue of disposing of plastic waste, and environmental effect make the production of fuel from plastic economically attractive in the long term. Certainly, continued research and development is needed in this field.

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