New energy value chain through pyrolysis of hospital plastic waste

Accepted Manuscript New energy value chain through pyrolysis of hospital plastic waste Maria Paraschiv, Radu Kuncser, Mohand Tazerout, Tudor Prisecaru PII:

S1359-4311(15)00424-X

DOI:

10.1016/j.applthermaleng.2015.04.070

Reference:

ATE 6590

To appear in:

Applied Thermal Engineering

Received Date: 17 September 2014 Revised Date:

21 April 2015

Accepted Date: 25 April 2015

Please cite this article as: M. Paraschiv, R. Kuncser, M. Tazerout, T. Prisecaru, New energy value chain through pyrolysis of hospital plastic waste, Applied Thermal Engineering (2015), doi: 10.1016/ j.applthermaleng.2015.04.070. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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NEW ENERGY VALUE CHAIN THROUGH PYROLYSIS OF HOSPITAL PLASTIC WASTE ∗1,2

Maria PARASCHIV, ∗1Radu KUNCSER, 3Mohand TAZEROUT, 4Tudor PRISECARU

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Faculty of Mechanical Engineering and Mechatronics, University Politehnica of Bucharest, 313 Spl. Independentei, 060042, Bucharest, Romania

Highlights - The thermal decompositions of hospital plastic waste

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Research Center for Advanced Materials, Products and Processes (CAMPUS), University Politehnica of Bucharest, 313 Spl. Independentei, 060042 Bucharest, Romania 2 National Institute of R&D for Biological Science, 296 Spl. Independentei, 060031, Bucharest, Romania 3 Ecole des Mines de Nantes, GEPEA UMR 6144, CNRS, 4 Rue Alfred Kastler, 44307, Nantes, France

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- Controlled pyrolysis can be applied to produced valuable molecules or hydrocarbon-based fuels from hospital plastic waste - Maximising of liquid fraction through pyrolysis parameters optimisation

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Abstract In this paper, the evolution in thermochemical behaviours of hospital plastic wastes and changes in chemical composition and characteristics of pyrolysis liquid products have been investigated by using different fixed bed reactor scales. The main objective is to identify the critical technical parameters enabling thermochemical process adaptation in function of raw materials chemical structure, with the aim of maximising the yield of condensable fraction and optimising its energetic properties related to internal combustion engines. It is a step-by-step procedure using three reactor capacity levels, which allows various aspects approach of thermochemical process development from the evaluation of global reaction kinetic parameters to the measurement of physicochemical properties of the final pyrolysis products. In order to reduce the gas and solid fractions with corresponding increasing of condensable products, the transposition of thermal and kinetic information provided by thermogravimetric analysis (TGA) to larger reactors is used to control of process parameters. In this experimental work the mass of samples increases from 0.05g in the thermogravimetric analyser to 600g in the bench scale reactor. Gas-chromatography techniques have been used to identify the chemical composition of gases (GC/TCD) and liquids (GC/FID-MS). It was established that changing the reactor scale does not result in significant differences in pyrolysis product distribution, neither in gas composition. On the other hand, the aspect and the quality of condensable fraction display a high variability. Also, the energy contained in the final valuable pyrolysis product was compared with the energy demand during the thermochemical transformation in order to evaluate the energy efficiency of the process. Keywords: pyrolysis, hospital waste, gas-chromatography/mass spectrometry (GC/TCD, GC/FID-MS) 1.

INTRODUCTION

Due to a massive increase in volume and diversity of plastic waste materials generated by human and industrial activity, statistics show that more than over 260 million tonnes of plastics were produced in the world [10, 35]. Approximately 15 million tonnes of post-consumer plastic waste are generated throughout Europe each year [9, 10], while in the United States 20 million tonnes of waste are produced [35]. Present in many applications mainly because of its ease of implementation, its strength and lightness, the plastic is still one of the least ∗ ∗

corresponding author for chemistry issues, phone/fax: +4021 220 79 09, e-mail: [email protected] corresponding author for energy issues, phone/fax: +4021 220 79 09, e-mail: [email protected]

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recycled materials, with a capitalization rate of approximately 5 %. As the consumption and production of polymers are continuously increasing, the amount of polymer wastes is increasing too, packaging representing the largest single sector. The sector accounts around 40% of world plastics consumption and plastic is the material of choice in nearly half of all packaged goods [10, 11].

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In addition, their potentially harmful effects on the environment and human health have led to an increasing awareness about an urgent need for implementation of an appropriate safe disposal. Due to their raw material (Table 1), there is an obvious need to reduce the generation of plastic wastes and to recycle them. On the other hand, the technologies for energy recovery from wastes have an increasingly role in moderating the problems. In addition, these technologies lead to a substantial reduction in the overall plastic waste volume and the remaining products for final disposal are better managed, meeting the pollution control standards [39].

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Accordingly, modern incinerators are designed to minimize the air pollution, but they are extremely costly to build. There are lots of incinerators currently operating in the world, but only a few are used to produce energy (Fig. 1). Also, local communities are still very opposed to the building of waste incinerators near their homes and anti-pollution measures become more restrictive, with particular concern about dioxin production. As a result, up to 30% by weight of the original waste remains to be land filled and it is often more toxic than the original material [38].

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Table 1. Petrol and energy consumption in plastic making [9, 15, 36, 37] Fig. 1. Average plant capacity of the plants that have supplied data [37]

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So that, plastic waste pyrolysis [3, 22], gasification [24] and liquefaction [27] processes become promising energy recovery techniques for optimal upgrading fuel [21]. Moreover, pyrolysis of plastic mixture [1], based on the decomposition of polymers at different temperatures, allows the treatment of polymers with simultaneous decomposition and separation [2, 18]. Thus, high value chemicals [14, 23, 31] and gasoline [2] or diesel-range fuels [21] can be easily recovered from plastic waste pyrolysis. It is well accepted that plastic behaviour during thermal degradation as well as its kinetics play a vital role in establishing pyrolysis procedures from reactor design point of view and scaling up of industrially viable [13, 16]. Current technologies studied and applied for plastics/polymer thermochemical processing [26, 29, 30, 33], have been investigated and the results are rather contradictory, especially concerning the yields in liquid products and its properties. Also, there are conflicting views related to plastic behaviour in different scale installations with no mentioned large differences from a county to another concerning the polymers main characteristics: molar masse, additives, and copolymers ratio [12, 30]. The enormous range of polymer properties depends on the arrangement and nature of the repeating units and on the types of intra- /intermolecular forces, by the degree of symmetry and uniformity in molecular structure. All these affect the melting and glass-transition temperature, miscibility with other polymers, and consequently the mutual interaction of polymers in their melt [5, 34, 36]. As a result, generalization of the pyrolysis behaviour of plastic wastes is not possible mostly due to the variation in the molecular weight distribution of polymer]. This study has been developed in the frame of 3 years research project funded by the Region of Pays de la Loire (France). The aim was the conception and development of an integrated system for plastic waste valorisation as alternative liquid fuel and the validation of this fuel by experimental analysis into a single cylinder, four-stroke, air cooled, direct injection, constant speed diesel engine developing a power output of 4.5 kW. The study responds to several European directives related to reinforcing the efforts in developing waste-to-energy technologies able to reduce the volume and the toxicity of wastes together with their recycling / energy valorising potential. Knowing that each chemical modification of polymers can induce strong deviation in thermochemical behaviours, the main aim of the first stage of this project was to obtain complete information on plastics waste decomposition during the O2-free thermal processes at different reactor capacity levels. Thus, thermogravimetric analysis and pyrolysis tests in laboratory and bench scale reactors have been performed. The thermogravimetric study was carried out with 0.05 – 0.18g of sample, while in laboratory and bench-scale fixed-bed reactors experiments have been conducted on around 50 (±5%) g and 600 (±5%) g, respectively. In the bench scale reactor, the tests were performed at 550°C. Instead, limited by heating device power, in the laboratory scale reactor the operating temperature was 470°C.

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2. EXPERIMENTAL WORK 2.1. Tested Materials

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The experiments were performed on used polymers (basically hospital plastic wastes, syringe, petri-dishes, bottles, etc...) selected by their large applications and the energy and petroleum consumption required for their production. Their ultimate analysis is presented in Table 2. There are tree plastic classes that concern this study: (1) poly-hydrocarbons – olefin-based polymers (polypropylene - PP, polyethylene - PE) and aromatic-based polymers (polystyrene - PS); (2) oxygenated polymer (polymethyl methacrylate - PMMA); (3) nitrogen containing (latex gloves – Latex). The monomer chemical structures and repeating unit of polymers are shown in Fig. 2 and 3. It can be noticed that the main bond in polymer chains is represented by C – C sigma covalent bond, and, except PE, they have ramification groups, also bounded to the polymer chain by C – C sigma covalent bonds: alkyl (– CH3), phenyl (– C6H5), nitrile (– CN) and methyl-ester (– COOCH3).

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Fig. 2. Chemical structure of monomers involved in studied polymers processing Fig. 3. Repeating chemical structure unit of polymers

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The elemental analysis was performed by using a C, H, N, S – O Analyzer (Flash EA 1112Series). The detection limit of used device is of 0.05 %(wt.), and repeatable results were obtained only for values superior to 0.25 %(wt.). Table 2. Ultimate analysis results for tested materials (%wt.) The wastes were washed, dried and cut in 3mm x 7mm pieces for thermogravimetric analysis and 50mm x 50mm for laboratory and bench scale reactors experiments.

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2.2. Thermogravimetric analysis 2.2.1. Apparatus and procedures

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Pyrolysis was carried out with a thermogravimetric analyser Setaram SETSYS Evolution TGA-DTG/DSC. Small pieces of each sample, 0.05 – 0.18g, were pyrolysed under 20mL/min N2 flow, at different heating rates 5, 10, 20 °C/min, temperature varying from 25 to 700°C. The nitrogen flow rate ensures an inert atmosphere during the run. 2.2.2. Results and discussions

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The weight loss curves (TG) and derivative of weight loss (DTG) registered during the performed pyrolysis are shown in Fig. 4. As expected, due to their uniform structure, polymer degradation appears to be a single–step process (one degradation peak). Only on curve recorded for Latex a pronounced tendency of developing another degradation peak is observed, but corresponding temperatures are too closed, the two peaks not appearing well separated. This behaviour can be due either to the presence of two polymers in the composition of latex gloves, or a different degradation path induced by mineral material presence (about 13 – 14 %wt.). Also, it can be noticed that, despite the similarity in the repeating unit of macromolecular chain (Fig. 3 - mostly simple bond C - C), the presence of ramifications leads to sensible differences both in terms of beginning and ending of thermochemical decomposition, but also in mass loss intensity. Thus, the oxygenated polymer (PMMA) begins to decompose at 320°C and the mass loss advances with a moderate rate, the material being completely decomposed at 430°C. Latex starts the thermochemical decomposition before the temperature reaches 300 °C (Fig. 4), while PP and PE begin to decompose at 380 °C and 400°C, respectively. The presence of nitrile group and carbon-carbon double bond in nitrile rubber (polyacrylonitrile butadiene) may be responsible for the lower stability of Latex. The main information on characteristic temperatures in tested waste thermochemical decomposition are summarised in Table 3. Fig. 4. Registered weight loss during plastics pyrolysis (heating rate 5°C/min)

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Table 3. Thermal information on plastics decomposition

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Results show closed values for temperature corresponding to maximum rate of PP and PE thermal degradation (Tmax). Furthermore, despite the delay registered on the beginning, the process appears to evolve faster in the case of PE. As concerning the weight loss, overlapping TG curves recorded for PE and PP, sensible differences are identified at the beginning. Then, they have similar trends that indicate close thermochemical behaviours. This tendency, can be explained by the presence of the same chemical bonds in their molecular structures (Fig.3), while the larger gap registered in the onset of pyrolysis reactions is most likely due to the presence of methyl group ramifications in PP structure, exhibiting a slightly lower thermal stability then PE. The conversion rate of pyrolysis is 100% for PP, PE, PS and PMMA, and 75% for Latex, the last one containing different powder additives in its composition. Used latex gloves represent a challenge due to their chemical composition: a complex mixture of organic and mineral compounds. Considering that after oxygen-free thermal processing the mineral part will be completely recuperated, the pyrolysis may become an interesting alternative as an economical way either for chemicals or energy recovery of organic matters. 2.2.3. Kinetic model

(1)

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dx E   n = A ⋅ exp − ( 1 − x) dt R ⋅ T  

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Using data from TGA, the kinetic parameters of plastic pyrolysis were determined applying the Coats–Redfern [4] method. This integration method is based on the general rate equation of reaction conversion, Eq. 1, and it is usually applied to study the thermochemical degradation kinetics of polymers [25, 34, 38], coal [17] or plastic/coal co-pyrolysis [7], biomass [19, 28], electric and electronic equipment wastes [18], municipal wastes [2, 16]. It is consider as first step in thermochemical behaviours of raw materials involved in biofuel and/or alternative fuels development [20, 25, 37]. The TGA is used thus to identify the very first parameters for pyrolysis and gasification [19] of new petrochemical feedstock such as polymer wastes [1, 15]. Also, the combustion of possible new solid fuel are firstly studied be TGA/DTA [17].

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w0 − wt w0 − w f

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where A - pre-exponential factor, E - activation energy [kJ/mol], R - the universal gas constant [J/(mol·K)], T temperature [K], t - time [s], x - conversion and n - reaction order. Many authors assume that plastic pyrolysis is a first order reaction. The weight loss fraction, x, or pyrolysis conversion can be calculated with Eq. 2.

(2)

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where w0 is the original mass of sample; wt is the mass at time t and wf is the mass at the end of pyrolysis. For a constant heating rate H during pyrolysis, H = dT/dt, rearranging and integrating Eq. 1 give:

 A ⋅ R  2R ⋅ T  E  ln( 1 − x)  ln − = ln 1 − −     2  E  R ⋅ T T  H ⋅E 

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Since for most values of E in the temperature range of pyrolysis, the expression ln[AR/HE(1−2RT/E)] is essentially constant, if the left side of Eq. 3 is plotted versus 1/T, a straight line may be obtained if the process can be assumed as a first order reaction. Then, by using the equation of the line in intercept – slope form, the activation energy and pre-exponential factor can be determined. Table 4 summarises the determined values for kinetic parameters and some related results from literature. The activation energy values of tested plastic samples are distributed between 107kJ/mol and 305kJ/mol, being in the same range to those obtained by other authors. Comparing the temperature range of decomposition obtained at different heating rates, sensible differences are identified. For all studied materials more heating rate increases, a higher maximum peak is registered (see in Fig.

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5 the graph representation for PP). This evolution can be explained by the fact that at higher heat transfer rate, temperature differences and temperature gradients increase combined with a serious effect of thermal lag, between test point and specimen, outer layer and inside the particle. A lower heating rate helps to moderate the phenomena [15].

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Table 4. Kinetic parameters obtained for pyrolysis of plastics

Fig. 5. Weight loss at different heating rates (example for PP)

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From the thermogravimetric study of plastic wastes we concluded that tested materials decompose in the thermal range of 300 – 500°C, with a maximum reaction rate varying from 380°C (PMMA and Latex) to 460°C (PE). A good agreement between the calculated and experimental curves was observed, which support the initial hypothesis of one stage 1st order reaction mechanism with corresponding kinetic parameters for a constant heating rate. 2.3. Laboratory and Bench scale pyrolysis

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2.3.1 Apparatus and procedures

The schematic diagram of the pyrolysis unit is the same for both installations, just different sizes (Fig. 6). Laboratory installation includes a stainless steel reactor with a volume of 0.8L, equipped with a thermocouple and heated by an electrical heater (0.28kW). Using glass condensing system the pyrolysis vapours are separated into condensable (liquids/waxes) and non-condensable (gases) phases.

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The bench-scale installation used in this work consists of a cylindrical steel reactor (2) placed into an electrically heated enclosure (1) with a maximum installed power of 5kW. The pyrolysis vapours were condensed by passing through a glass-condenser cooled with water (3). The liquid fraction was collected into a 1000ml flask cooled with ice (4), while the gaseous fraction was collected in Tedlar bags for gas sampling, and then analysed. The device has a double opening system for gas sampling in certain temperature ranges (5).

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This reactor has multiple thermocouples (6) placed at different level that allowed the thermal transfer study in the fixed bed and the temperature evolution inside the reactor. These thermocouples are connected with an acquisition system (7) and the values are registered all along the process. Fig. 6. Schematic diagram of the pyrolysis unit

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In both experimental devices, the yield of solid and condensable pyrolysis products was determined by weighting the liquid collected in the glass condensing system and the residual coke remaining in the reactor after the experiment, while the gas yield was calculated by difference. The mass sample was limited by waste density. Thus, the laboratory reactor couldn’t be filled with more than 50(±5)g and the bench-scale reactor with 600(±5%)g of sample. Another limit is related to the condensation system, especially during the maximum range of degassing. As seen in the ATG / DTG curves, once reached the decomposition temperature, the process is carried out quickly, so the corresponding amount of pyrolysis vapours should be effectively cooled to assess the real amount of condensable and gaseous products. Thus, using the information offered by thermogravimetric studies (thermal range of degradation and the temperature corresponding to maximum intensity of the mass loss at different heating rate) the cooler system has been adapted with one or two connected condensers that allowed the complete condensation of pyrolysis vapours. For each individual sample 3 experiments have been performed. In laboratory reactor, the maximum temperature was 470°C and three residence times at final temperature have been tested (0min, 10min and 20min). The electrical heating operated at full charge gave for the used reactor geometry and sample mass a heating rate of 5 – 7 °C/min.

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In bench scale reactor the pyrolysis tests were carried out at 550°C, the residence time at this temperature was 10min and the variable parameter was the heating rate. In this purpose, the experiments run with 3 different power range: 25% (corresponding to a measured heating rate of 5 – 7°C/min), 50% (measured heating rate of 14 – 16°C/min), and 100% (measured heating rate of 22 – 25°C/min) of maximum power.

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2.3.2. Investigation Methods

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The liquid fractions were analysed by gas chromatography with flame-ionised detector (FID) using a PERKIN ELMER Autosampler XL Gas Chromatograph. The column was VARIAN WCOT Fused Silica type (30 m length x 0.39 mm interior diameter, film thickness being 0.25 µm). The injector temperature was 250°C. The chromatograph programme was comprised of 1 min at 45°C followed by a ramp to 300°C at a rate of 7°C·min−1. The final temperature was held for 10 min. The equipment design allowed the split of the carrier gas flow to perform analyses using FID and MS detectors simultaneously. The mass spectrometer was operated at electron impact ionisation energy of 70 eV. The scan range was 30 – 450 m/z and the individual compounds were identified from the GC/MS chromatograms using Library MS NIST. The gas fraction was analysed by gas chromatography with thermal conductivity detector (TCD) using a PERKIN ELMER Clarus 500 Gas Chromatograph. The column was CARBOXEN – 1006 PLOT type (30 m length x 0.53 mm interior diameter), used for permanent gases identification (CO, CO2, CH4, C2H2, C2H4, C2H6, methyl-acetylene, propylene, C3H8 and n-C4H10). The calibration curves were determined for each individual compound and the obtained data were used for heat value calculation. The higher heating value and viscosity of liquid fractions were measured with a PARR 6200 CALORIMETER and a Vibro-Viscometer SV10, and for the flash point a NPM 440 model PENSKY MARTENS apparatus was used, ISO-normalised for petroleum products. As for the density, measurements have been done at room temperature by using a series of hydrometers ISOM50T calibrated in [g/L] (from 700 g/L to 900 g/L). 2.3.3. Results and discussions

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The first step in this study was to observe the thermal range of waste conversion according to the reactor capacity, establishing the influence of material mass on the heat transfer inside the reactor and the corresponding changes in pyrolysis product distribution.

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The obtained product yields in this study and other published works are presented in Table 5 - 6. For comparison, only few examples have been selected, just to show gross differences registered mostly due not only to the polymer quality and characteristics, but also to technical parameters and reactor geometry. Table 5. Product yields obtained during pyrolysis at different residence time (laboratory scale installation, 470°C)

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Table 6. Chemical composition (% vol) and low heating value (LHV, MJ/Nm3) of pyrolysis gaseous fractions Gases analyses show that poly-hydrocarbon polymers realise gases reached in hydrocarbons like methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8) and propylene (C3H6). On the other hand, oxygenated compounds of polymers appear to eliminate the oxygen as gaseous products, such as carbon mono- and dioxide (CO, CO2) during pyrolysis processes. Due to small amounts of gases realised in PMMA pyrolysis, the analysis could not be performed. The same problem of gas quantity generates some dysfunction in performed quantitative analyses for PS and Latex, too. A typical chromatogram obtained after gas chromatographic analysis is shown in Fig. 7: Fig. 7. Compounds identified in gas fraction resulted during PP pyrolysis Liquids analysis, showed that liquid fraction obtained by PP pyrolysis is composed of alkanes, alkenes and naphthenes with a molecular chain of C9 – C28, and that from PE contain only alkanes and alkenes in a larger molecular range, respectively C8 – C43. PS pyrolysis gave a liquid fraction with four major compounds, all of them having at least one aromatic ring (Fig. 8): styrene (C8H8), α-methylstyrene (C9H10), 1,3-diphenylpropane (C15H16) and 1,3-diphenyl-2-butene

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(C16H16). Pyrolysis liquid resulted from PMMA processing contain a single major compound (Fig. 9), while that from Latex has three (Fig. 10): Limonene (C10H16), 1,7-heptadien-3-yne (C7H8) and 1,3-dimethylbenzene (C8H10). Fig. 8. Major compounds identified in liquid fraction resulted after PS pyrolysis

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Fig. 9. Major compound identified in liquid fraction resulted after PMMA pyrolysis Fig. 10. Major compounds identified in liquid fraction resulted after Latex pyrolysis

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Putting together the results obtained from these complementary analyses allowed the evaluation of best valorisation way, energetic one or material recovery. Moreover, following the aim of this work, cumulative analysis results lead to the choice for next larger scale reactor experiments. Thus, we exclude the PS mainly for its high aromatic contents, knowing that despite their high energetic potential such compounds are responsible for soot and particulate emissions during engine combustion. PMMA liquid, containing practically the dimmer of methyl methacrylate, is more suitable for material recovery and reuse in polymerisation process. Nevertheless, it is easily inflammable and its clear aspect and oxygen content (32.0% wt) suggest the possible use in gasoline blend in the same way that currently bio-ethanol (with 34.8%wt in oxygen) is used in gas stations. As concluded, for bench-scale installation PE, PP, PMMA and Latex were tested at different oven power range, corresponding to specific heating rates. The pyrolysis product distribution is presented in Table 7 and the energetic properties of liquid fraction are presented in Table 8. Table 7. Pyrolysis product yields at 550°C, for different power range (bench scale installation) Table 8. Physical – chemical characteristics of pyrolysis condensable fractions

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It was established that, only in the cases of PE the polymer conversion into condensable products slightly increases with thermal rate increasing. Along with this, however, a larger waxes fraction is obtained, which cannot be used in Diesel-engines. It is interesting to note that liquid and waxes are produced during the entire degradation process, and after 5 – 12 hours of storage at room temperature, waxes include the liquid and form a gel completely solidified at 10 - 15°C. The colour of the condensable fractions varies from light-yellow (PP, PE) to dark-brown (Latex) with viscosities at 20°C varying between 0.85mPa·s for PMMA to 6.20mPa·s for PP. 2.4. Energy balance and economic considerations

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The registered data concerning the energy consumption during the pyrolysis tests (electricity consumption for pyrolysis of 500g plastic) and the heat of combustion of recovered liquids fraction enabled to make an energy balance of the process. Thus, Fig. 11 shows the tendency of energy balance in function of oven power range.

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Fig 11. Energy balance in PP, Latex and PMMA pyrolysis

As it can be seen, even if only the use of obtained liquid fraction in the simplest way is considered (conversion in heat), in all studied cases a positive energy balance has been obtained, and the best ratio is obtained for the higher heating rate, which correspond to the lowest reaction time. Conversely, the higher heating value of obtained liquid fuels decreases when the heating rate increases. Considering that we are facing here to a waste it can be considered that the price for raw material is zero. In fact, every laboratory (clinical, hospital, chemistry, biochemistry etc.) using such plastic products pays to deposit these types of waste. Nevertheless, waste collection and selection still are expensive steps in waste valorisation. Thus, to improve the economic balance a more efficient technological route for waste processing or pyrolysis oils use should be considered. One more economical way is too use this oil into a CHP engine that produces electricity and heat. Electric and thermal efficiencies are expected to be 35% and 50%, respectively meaning that by combusting the pyrolysis oil, 35% of its lower heating value (LHV) is converted into electricity and 50% of its LHV is converted into heat [26, 32]. Taking into account that the sales price of electricity is usually higher than the price of heat, and the needed temperature for plastic pyrolysis (450 – 470°C), an appropriate economic strategy is to use the heat for pyrolysis process and to sale the electricity.

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3. Conclusions

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This work is dedicated to identify changes in polymers thermochemical behaviours during the pyrolysis run at different reactor scale, and influence parameters that allow adapting the process at larger scale in order to optimise liquid fraction. It was established that the total conversion obtained during pyrolysis in laboratory scale reactor was in close agreement with TGA results, the temperature related to maximum weight loss being in the thermal range of maximum period of vapours condensing. It was found that, even for the same polymers class (e.g. polyhydrocarbon), the yield of pyrolysis products depends firstly on chemical structure of raw materials. The presence of ramification group on macromolecular chain leads to a decrease in thermal stability; accordingly, the decomposition of PMMA and Latex starts at lower temperatures (300 – 320 °C). The second influence factor appears to be the thermal rate used during the process. Moreover, energetic characteristics of pyrolysis products are strongly depending on the plastics types. During pyrolysis, plastics generate three products, all of them having the potential to be reused. Thus, as claimed above, this process has further advantages: the product gas has a high calorific value and can be used to provide the energy requirements of the process plant; the oil may be combusted into an internal combustion engine or a boiler fuel. The solid residue obtained only in Latex pyrolysis may be a calcined and reused in latex gloves manufacture or other applications. Depending on plastics type or interests, the process could be lead with or without cooling step of pyrolysis vapours in the condenser. When the liquid fraction shows good similarity to regular diesel fuel, the process can be optimised to obtain a maximum quantity of this fraction. Considering its higher heating value, the entire energy potential of plastics might be recuperated. Furthermore, pyrolysis became not only a technique to obtain alternative fuels, but also an efficient way to reduce a bulky, high polluting industrial waste while producing cleaner energy. The PP pyrolysis liquid products are mainly 1-alkenes, n-alkanes, ranging from C 8 to C43, with excellent energetic characteristics, while PP pyrolysis produces a solidified gel. Despite its high calorific value, it cannot be use in diesel engine without further processing to improve its viscosity. Related to this point, a catalytic cracking of pyrolysis vapours will be considering for the next step of this study. The process should be able to converts heavy hydrocarbons into gas and lighter liquid product by secondary cracking reaction. Compared with PE and PP, the pyrolysis liquid of PS has only 4 major aromatic compounds, styrene being the most abounded, and the incondensable products contain 7.52% (vol.) hydrogen. Pyrolysis liquid of Latex has a very good energetic potential, but the high volatility makes it unsuitable for diesel engine. Direct combustion of pyrolysis vapours will be more recommended considering the fact that the energy potential of gaseous fraction can be also used in the same time. As concerning the liquid recovered from PMMA pyrolysis, it has indeed the energetic properties similar to those of ethanol, so it cannot be burned directly in diesel engines. Combustion in blend with gasoline would be more advisable. Nevertheless, experimental analyses in spark-ignition engine are necessary in order to establish its performances as liquid fuel for internal combustion engines. Compared to results reported in other published works, the applied thermal profile lead to higher conversion rates into liquid product. Nevertheless, the experimental work needs adjustment in order to reduce the waxes content in PE condensable fractions. Further tests are to be performed either in catalytic systems or pyrolysis process applied on polymer mixture. References:

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A. Angyal, N. Miskolczi, L. Bartha. Petrochemical feedstock by thermal cracking of plastic waste. J. Anal. Appl. Pyrolysis 2007; 79 (1 – 2): 409 – 414. A. Demirbas. Pyrolysis of municipal plastic wastes for recovery of gasoline-range hydrocarbons. J. Anal. Appl. Pyrolysis 2004; 72: 97–102. A.K. Panda, R.K. Singh, D.K. Mishra. Thermolysis of waste plastics to liquid fuel. A suitable method for plastic waste management and manufacture of value added products - A world prospective. Renewable and Sustainable Energy Reviews 2010; 14: 233–248 A.W. Coats, J.P. Redfern. Kinetic parameters from thermogravimetric data. II. Journal of Polymer Science Part B: Polymer Letters, DOI: 10.1002/pol.1965.110031106. Nature 1964; 201: 68 – 69. B.K. Sharma, B.R. Moser, K.E. Vermillion, K.M. Doll, N. Rajagopalan. Production, characterisation, and fuel properties of alternative fuel from pyrolysis of waste plastic grocery bags. Fuel Processing Technology 2014; 122: 79-90.

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[14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]

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[13]

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[10] [11] [12]

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B.S. Kang, S.G. Kim, J.S. Kim. Thermal degradation of poly(methyl methacrylate) polymer: Kinetics and recovery of monomers using a fluidized bed reactor. Journal of Analytical and Applied Pyrolysis 2008; 81 (1): 7-13. C. Qian, M. Zhou, J. Wei, P. Ye, X. Yang. Pyrolysis and co-pyrolysis of lignite and plastic. International Journal of Mining Science and Technology 2014; 24(1): 137-141. D.S. Achilias C. Roupakias, P. Megalokonomos, A.A. Lappas, E.V. Antonakou. Chemical recycling of plastic wastes made from polyethylene (LDPE and HDPE) and polypropylene (PP). Journal of Hazardous Materials 2007; 149: 536 – 542. European plastics associations (http://www.plasticsrecyclers.eu/ ; http://www.plasticsconverters.eu/ ; http://www.plasticseurope.co.uk/) European Union statistics - Statistics Explained - Recycling – secondary material price indicator, 2011 French Environment and Energy Management Agency (ADEME) J. Blumm, A. Lindemann. Characterization of the thermophysical properties of molten polymers and liquids using the flash technique. High Temperatures-High Pressures 2003/2007; 35/36 (6): 627-632. J.F. Mastral, C. Berrueco, J. Ceamanos. Modelling of the pyrolysis of high density polyethylene: Product distribution in a fluidized bed reactor. J. Anal. Appl. Pyrolysis 2007; 79 (1 - 2): 313 – 322. J.M. Arandes, J. Erena, M.J. Azkoiti, M. Olazar, J. Bilbao. Thermal recycling of polystyrene and polystyrene-butadiene dissolved in a light cycle oil. J. Anal. Appl. Pyrolysis 2003; 70 (2): 747 – 760. J.M. Encinar, J.F. González, Pyrolysis of synthetic polymers and plastic wastes. Kinetic study, Fuel Process. Technol. 2008; 89(7): 678 - 686. K.-H. Lee. Pyrolysis of municipal plastic wastes separated by difference of specific gravity. J. Anal. Appl. Pyrolysis 2007; 79 (1 - 2) 362 – 367. K. Jayaraman, I. Gokalp. Gasification characteristics of petcoke and coal blended petcoke using termogravimetry and mass spectrometry analysis. Applied Thermal Engineering 2015; 80: 10-19. L. Cafiero, E. Castoldi, R. Tuffi, S.V. Ciprioti. Identification and characterization of plastics from small appliences and kinetic analysis of their thermally activated purolysis. Polymer Degradation and Stability 2014; 109: 307-318. L. Prasad, P.M.V. Subbarao, J.P. Subrahmanyam. Pyrolysis and gasification characteristics of Pongamia residue (de-oiled cake) using thermogravimetry and downdraft gasifier. Applied Thermal Engineering 2014; 63: 379-386. L. Zhou, Y. Wang, Q. Huang, J. Cai. Thermogravimetric characteristics and kinetic of plastic and biomass blends co-pyrolysis. Fuel Processing Technology 2006; 87 (11): 963–969. M. Mani, C. Subash, G. Nagarajan. Performance, emission and combustion characteristics od a DI diesel engine using waste plastic oil. Applied Thermal Engineering 2009; 29: 2738-2744. M. Newborough, D. Highgate, P. Vaughan. Thermal depolymerisation of scrap polymers. Applied Thermal Engineering 2002; 22(17):1875-1883. M. Sarker, M. M. Rashid, M. S. Rahman, M. Molla. A New Kind of Renewable Energy: Production of Aromatic Hydrocarbons Naphtha Chemical by Thermal Degradation of Polystyrene (PS) Waste Plastic. American Journal of Climate Change 2012; 1(3): 145 – 153. N. Couto, V. Silva, E. Monteiro, S. Teixeira, R. Chacartegui, K. Bouziane, P.S.D. Brito, A. Rouboa. Numerical and experimental analysis of municipal solid waste gasification process. Applied Thermal Engineering 2015; 78: 185-195.

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NEW ENERGY VALUE CHAIN THROUGH PYROLYSIS OF HOSPITAL PLASTIC WASTE ∗1,2

Maria PARASCHIV, ∗1Radu KUNCSER, 3Mohand TAZEROUT, 4Tudor PRISECARU

1

University Politehnica of Bucharest, Faculty of Mechanical Engineering and Mechatronics, 313 Spl. Independentei, 060042, Bucharest, Romania

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4

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Research Center for Advanced Materials, Products and Processes (CAMPUS), University Politehnica of Bucharest, 313 Spl. Independentei, 060042 Bucharest, Romania 2 National Institute of R&D for Biological Science, 296 Spl. Independentei, 060031, Bucharest, Romania 3 Ecole des Mines de Nantes, GEPEA UMR 6144, CNRS- 4, rue Alfred Kastler, 44307, Nantes, France

Table 1. Petrol and energy consumption in plastic making [9, 15, 36, 37] Energy Consumption [MJ/ kg]

M AN U

Petrol Consumption [L/kg] No.

min

max

Melting Point [°C]

Material

Total

Oil

Others

PVC

0.75

1.65

100 – 260

53

24

29

2

PE

0.57

0.72

105 – 130

70

55

15

3

PP

0.54

0.68

130 – 170

73

58

15

4

PS

0.50

0.72

240

80

55

25

5

PET

0.47

1.28

250 - 260

84

31

53

6

PC

0.37

1.10

155

107

36

71

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1

No.

Material

EP

Table 2. Ultimate analysis results for tested materials (%wt.)

S

O

83.97 ± 1.03

14.21 ± 0.36

nd

nd

1.20 ± 0.06

PE

nd

85.20 ± 0.92

14.63 ± 0.12

nd

nd

< 0.1

PS

nd

89.93 ± 0.14

8.13 ± 0.82

nd

nd

< 0.1

4

PMMA

nd

60.12 ± 1.12

8.27 ± 0.43

nd

30.21 ± 2.13

0

5

Latex

0.52 ± 0.22

69.55 ± 0.22

7.66 ± 0.38

nd

8.31 ± 1.57

13.69 ± 0.13

3

∗

H

nd(*)

2

∗

Ash C

PP

1

(*)

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N

Elemental Analysis

nd – non-detected

corresponding author for chemistry issues, phone/fax: +4021 220 79 09, e-mail: [email protected] corresponding author for energy issues, phone/fax: +4021 220 79 09, e-mail: [email protected]

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Table 3. Thermal information on plastics decomposition Material

Ti, [°C]

Tmax, [°C]

Tf, [°C]

1 2 3 4

PP PE PS PMMA

380 ± 0.92 400 ± 0.27 375 ± 0.88 320 ± 0.31

475 ± 0.09 500 ± 0.63 460 ± 0.92 430 ± 0.98

5

Latex

300 ± 0.91

455 ± 0.12 460 ± 0.41 420 ± 0.87 380 ± 0.33 380 ± 0.26 410 ± 0.92

Reaction time, [min] 16.7 ± 0.89 15.0 ± 0.62 17.5 ± 0.84 20.0 ± 0.12

460 ± 1.44

33.3 ± 1.52

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No.

Table 4. Kinetic parameters obtained for pyrolysis of plastics

M AN U

Kinetic parameters

No.

Material

E (kJ/mol) PE

PS Latex PMMA

TE D

PP

305 ± 1.66 6.15 (± 2.06) ⋅ e20 270.0 [20] 3.65 ⋅ e18 [20] 254.2 [15] 5.53 ⋅ e15 [15] 301 ± 1.38 3.71 (± 2.06) ⋅ e20 270.0 [20] 3.65⋅e18 [20] 265.8 [15] 1.33⋅e17 [15] 256 ± 2.67 5.50± 2.06⋅e18 286.5 [15] 4.31⋅ e19 [15] 107 ± 2.06 6.72 (± 2.06) ⋅ e7 148.8 [25] 1.74 ⋅ e11 [25] 206 ± 0.72 8.20 (± 2.06) ⋅ e15 (*) 2 R – correlation coefficient

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EP

1 2 3 4 5 6 7 8 9 10 11

A (min-1)

R2 (*) 0.999 ± 0.06 0.997 [20] 0.980 [15] 0.999 ± 0.10 0.997 [20] 0.990 [15] 0.999 ± 0.09 0.990 [15] 0.990 ± 1.11 0.993 [25] 0.999 ± 0.12

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Table 5. Product yields obtained during pyrolysis at different residence time (laboratory scale installation, 470°C) Residence time (min)

5-7

0

Residue 13.20 ± 1.50

10

11.80 ± 0.70

20

10.50 ± 0.20

2 PE 3 4 5 6 7 8 9 10

PP

11 12 13

-

-

5-7

0 10 20 -

5-7

0 10 20

5-7

0 10 20

PS

15 16

Latex

17 PMMA

5-7 -

3.50 ± 0.30 3.00 ± 0.20 0.00 1.60 [2] 0.11 [15] 20.00 [8] 1.12 [2]

81.50 ± 0.20 (liquid) 80.50 ± 0.80 (liquid) 82.00 ± 1.30 (liquid) 48.80 [2] 83.34 [15] 64.70 [8] 95.99 [2]

15.00 ± 0.50 16.50 ± 0.60 18.00 ± 1.30 49.60 [2] 16.55 [15] 15.30 [8] 2.89 [2]

3.80 ± 1.30 2.30 ± 0.50 0.00

87.00 ± 0.30 (liquid) 86.00 ± 0.80 (liquid) 89.00 ± 0.60 (liquid)

9.20 ± 1.10 11.70 ± 1.00 11.00 ± 0.60

28.00 ± 0.30 25.80 ± 0.20 25.20 ± 0.10

65.00 ± 1.50 (liquid) 65.90 ± 2.30 (liquid) 63.20 ± 2.40 (liquid)

7.00 ± 1.30 8.30 ± 2.00 11.60 ± 2.20

0

98.00 ± 1.70 (liquid) 99.30 [6]

2.00 ± 1.70 0.50 [6]

0.00 0.20 [6]

18.00 ± 0.80 21.00 ± 0.60 3.30 [8]

EP

18 19

Gas 17.00 ± 1.20

52.50 [8]

Condensable 69.80 ± 0.10 (of which 65% waxes) 70.20 ± 0.30 (of which 72% waxes) 68.50 ± 0.80 (of which 78% waxes) 44.20 [8]

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14

Pyrolysis products (%wt)

RI PT

1

Heating range (°C·min-1)

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Material

M AN U

No.

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Table 6. Chemical composition (%vol) and low heating value (LHV, MJ/Nm3) of pyrolysis gaseous fractions UnNo. Material H2 CO CO2 CH4 C 2H 4 C 3H 6 C 2H 6 C 3H 8 LHV known 20.16 6.24 31.15 21.47 18.36 2.60 69.22 1 < 0.5 nd < 0.5 PP ± 1.06 ± 0.83 ± 0.41 ± 0.66 ± 0.33 ± 1.06 ± 2.13 33.15 19.37 23.00 8.27 7.00 64.30 14.23 2 < 0.5 nd < 0.5 PE ± 0.96 ± 0.47 ± 0.23 ± 0.39 ± 0.42 ± 1.45 ± 2.00 7.52 24.18 21.22 8.80 15.78 1.33 21.20 48.46 3 nd < 0.5 PS ± 1.01 ± 0.18 ± 0.35 ± 0.96 ± 0.06 ± 0.87 ± 1.24 ± 1.02 5.66 15.96 28.95 18.25 3.97 8.90 8.58 10.70 39.16 4 < 0.5 Latex ± 1.16 ± 1.46 ± 1.43 ± 1.02 ± 1.28 ± 0.51 ± 0.36 ± 2.01 ± 2.54

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Table7. Pyrolysis product yields at 550°C, for different power range (bench scale installation)

2

PE

3 4 5 6 7 8 9 10 11 12

PP

Latex

PMMA

Residue

25%

0

50%

0

100%

0

25% 50% 100% 25% 50% 100% 25% 50% 100%

0 0 0 21 ± 0.0 22 ± 0.3 23 ± 1.0 0 0 0

Condensable 83 ± 1.2 (of which 78% waxes) 84 ± 0.6 (of which 85% waxes) 88 ± 0.1 (of which > 90% waxes) 89 ± 1.5 (liquid) 91 ± 1.3 (liquid) 92 ± 0.2 (liquid) 72 ± 1.1 (liquid) 72 ± 0.3 (liquid) 73 ± 0.3 (liquid) 98 ± 0.5 (liquid) 98 ± 0.3 (liquid) 98 ± 0.1 (liquid)

Gas 17 ± 1.2 16 ± 0.6

RI PT

1

Pyrolysis products (%wt)

Oven power range

SC

Material

M AN U

No.

12 ± 0.1

11 ± 1.5 9 ± 1.3 8 ± 0.2 7 ± 1.5 6 ± 0.3 4 ± 1.1 2 ± 0.5 2 ± 0.3 2 ± 0.1

Table 8. Physical – chemical characteristics of pyrolysis condensable fractions Measured Characteristic

1 2 3 4 5 6 7 8 9 10 11 12

Diesel PE (gel) PP

/ / 25% 50% 100% 25% 50% 100% 25% 50% 100% /

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Latex

PMMA

Ethanol

Density [g/L]

Viscosity [mPa·s]

HHV [MJ/kg]

Flash Point [°C]

850 ± 1.30 740 ± 1.00 740 ± 1.12 740 ± 1.14 860 ± 1.38 860 ± 1.31 860 ± 1.22 900 ± 2.35 900 ± 2.51 900 ± 2.00 795 ± 1.30

3.10 ± 0.01 5.70 ± 0.03 6.20 ± 0.04 5.50 ± 0.03 2.57 ± 0.02 3.00 ± 0.03 2.18 ± 0.04 0.91 ± 0.03 0.85 ± 0.01 0.86 ± 0.01 1.10 ± 0.03

43.00 ± 0.30 45.70 ± 1.10

58.00 ± 1.00 - 3.00 ± 1.00

TE D

Material

EP

No.

Oven power range

46.80 ± 0.50 < - 10.00 46.40 ± 0.30 < - 10.00 27.17 ± 1.03 29.80 ± 0.30

17.00 ± 0.00

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NEW ENERGY VALUE CHAIN THROUGH PYROLYSIS OF HOSPITAL PLASTIC WASTE ∗1,2

Maria PARASCHIV, ∗1Radu KUNCSER, 3Mohand TAZEROUT, 4Tudor PRISECARU

1

University Politehnica of Bucharest, Faculty of Mechanical Engineering and Mechatronics, 313 Spl. Independentei, 060042, Bucharest, Romania

EP

TE D

M AN U

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Research Center for Advanced Materials, Products and Processes (CAMPUS), University Politehnica of Bucharest, 313 Spl. Independentei, 060042 Bucharest, Romania 2 National Institute of R&D for Biological Science, 296 Spl. Independentei, 060031, Bucharest, Romania 3 Ecole des Mines de Nantes, GEPEA UMR 6144, CNRS- 4, rue Alfred Kastler, 44307, Nantes, France

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Fig 1. Average plant capacity of the plants that have supplied data [37]

Fig. 2. Chemical structure of monomers involved in studied polymers processing

∗ ∗

corresponding author for chemistry issues, phone/fax: +4021 220 79 09, e-mail: [email protected] corresponding author for energy issues, phone/fax: +4021 220 79 09, e-mail: [email protected]

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Fig. 3. Repeating chemical structure unit of polymers

Fig. 4. Registered weight loss during plastics pyrolysis (heating rate 5°C/min)

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Fig 5. Weight loss at different heating rates (example for PP)

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Fig 6. Schematic diagram of the pyrolysis unit

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Fig.7. Compounds identified in gas fraction resulted during PP pyrolysis

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Fig.8. Major compounds identified in liquid fraction resulted after PS pyrolysis

Fig.9. Major compound identified in liquid fraction resulted after PMMA pyrolysis

Fig.10. Major compounds identified in liquid fraction resulted after Latex pyrolysis

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Fig 11. Energy balance in PP, Latex and PMMA pyrolysis