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Feedstock recycling from plastics and thermosets fractions of used computers. II. Pyrolysis oil upgrading
Fuel 86 (2007) 477–485 www.fuelfirst.com
Feedstock recycling from plastics and thermosets fractions of used computers. II. Pyrolysis oil upgrading Cornelia Vasile a
a,*
, Mihai Adrian Brebu a, Tamer Karayildirim b, Jale Yanik b, Hristea Darie a
Romanian Academy, ‘‘P.Poni’’ Institute of Macromolecular Chemistry, Department of Physical Chemistry of Polymers, 41A Grigore Ghica Voda Alley, 700487 Iasi, Romania b Ege University, Faculty of Science, Department of Chemistry, 35100 Izmir, Turkey Received 3 May 2006; received in revised form 1 August 2006; accepted 8 August 2006 Available online 11 September 2006
Abstract Liquid products obtained from pyrolysis of plastics and thermosets fractions (keyboard, casings and printed circuits board and their mixture) of used computers were upgraded by thermal and catalytic hydrogenation. The effect of thermal hydrogenation was improved by using catalysts such as commercial hydrogenation DHC-8 catalyst and metal loaded activated carbon. The upgraded degradation products were separated in three fractions (residue, liquids and gases) and characterized by suitable methods such as gas chromatography (GC–MSD, GC–AED), infrared (FT-IR) and 1H-NMR spectroscopy, elemental analysis, etc. Using of catalyst mainly affected the product distribution of upgrading process. Liquids having high amount of aromatics were obtained by upgrading. Most of hazardous toxic compounds in liquids were eliminated after hydrogenation (e.g., halogens were removed mainly by converting them into gaseous hydrogen chloride and bromide). It has been established that the hydrogenation led to elimination of the most of hazardous toxic compounds, mainly those containing bromine. 2006 Elsevier Ltd. All rights reserved. Keywords: Computer scraps; Pyrolysis-hydrogenation; Toxic products
1. Introduction The production of electric and electronic equipment (EEE) is one of the fastest growing areas. This development has resulted in an increase of waste electric and electronic equipment (WEEE). The amount of electronic waste increases, as the life cycles of some electronic goods are short of about 15–20 years and because more accelerated speed is required in the processing capability of the telecommunication infrastructure. The problem of WEEE is not only one of quantity, but also of the hazardous impacts associated with final disposal. The disposal of electronic
*
Corresponding author. Tel.: +40 232 217454; fax: +40 232 211299. E-mail address: [email protected] (C. Vasile).
0016-2361/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2006.08.010
and electrical appliances in landfill sites or their incineration creates a number of environmental problems, because they contain some additives such as heavy metals (mercury, lead, cadmium, hexavalent chromium) and halogenated flame retardants (especially polybrominated ones), which are hazardous for environment. WEEE consist mainly of thermoplastics such as acrylonitrile–butadiene–styrene terpolymer (ABS), high impact polystyrene (HIPS), polycarbonate (PC) that are used for casings and of thermosets (e.g., epoxy resins) as major printed circuits board (PCB) materials. Pyrolysis is one of the best alternatives to treat WEEE because the majority of the macromolecular organic substances is decomposing to volatile compounds at elevated temperatures while metals, inorganic fillers and supports generally remain unchanged and accumulate in the residue.
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However, during thermal pyrolysis the flame retardants in electronic scraps, mainly the halogenated compounds, cause a contamination of all product streams with halogenated organics. Several procedures such as depolymerization using hydrogen donor solvents, [1,2] depolymerization using supercritical CO2, [3], pyrolysis in the presence of limestone, [4] two-stage pyrolysis, [5] staged-gasification comprising pyrolysis (550 C) and high temperature gasification (>1230 C) with bromine recovery by ‘wet’ alkaline scrubbing of the syngas, [6] catalytic debromination using iron oxide– or calcium–carbon composites, [7–10] co-pyrolysis with inorganic solids of basic character (sodium hydroxide, basic zeolites), [11] catalytic processes to recover fibres from polymer based composites, [12] etc. were proposed for feedstock recycling of thermosetting resins. Alkaline hydrothermal treatment and ammonia treatment were proposed as new methods to recover both bromine and bromine-free plastic or oils from brominated HIPS [13,14]. When the alkali carbonates were mixed in the reaction system for the wastes having high Cl or Br amounts, the halogen content in the liquid product decreased to less than 37 ppm [15]. The products from the process were an energy rich oil condensate, coke, calcium bromide, metal product and ceramic product. These products met commercial specifications and could be used as raw materials in other applications. The elimination or substitution of halogen atoms from halogenated aromatic compounds generally requires more energy, not only because of the bonding energy of the Caromatic–X bond that is higher compared to Caliphatic–X bond, but also because of the lack of favourable geometry for a reaction path with lower activation energy. The liquid pyrolysis products often contain significant amounts of asphalthenes, sulphur and nitrogen. They also contain halogens and metals as minor components but their amounts exceed the limits in use of liquids. As a consequence, additional refining and upgrading is required before their use as fuel or chemical feedstock. Denitrification and desulfuration could be achieved by catalytically hydrotreating. It would be obviously the most advantageous solution to carry out pyrolysis and dehalogenation simultaneously or successively. In our previous paper we presented the pyrolysis of plastics and thermosets fractions of used computers aiming at the recovery of some valuable pyrolysis products. [16] The purpose of this work was to upgrade the pyrolysis liquid products by catalytic hydrogenation in order to find applications as fuels or materials. 2. Experimental 2.1. Materials Four pyrolysis oils of WEEE fractions separated from various computer parts such as were considered for this
studied. The WEEE fractions were: (1) casings of monitor, printer, computer and mouse; (2) keyboard; (3) print circuit board (PCB); (4) a mixture prepared by mechanical blending of grinded 1–3 components in the following percentage: 60 wt% casings, 30% printed circuit board (PCB) and 10 wt% keyboard, which is the approximately proportion found in a computer. The pyrolysis procedure, detailed characterization and composition of pyrolysis oils were presented in the previous paper [16]. 2.2. Catalysts The hydrogenation catalysts were powdered commercially available DHC-8 and a metal-loaded activated carbon (M-Ac). M-Ac catalyst was prepared by wet impregnation method using metal salts. Activated carbon used as catalyst support was obtained from pyrolytic carbon black from pyrolysis at 800 C of used scrap truck tires. The demineralized pyrolytic carbon black was activated with carbon dioxide at a flow rate of 350 ml/min for 6 h at 900 C and then loaded with metal by impregnation method. M-Ac has the following characteristics: Mo 2.89 wt%, Ni 4.63 wt%, surface area of 215.13 m2/g. DHC-8 catalyst was a commercial catalyst with specific surface area of 102 m2/g. This catalyst is being used for hydrocracking of vacuum gas oil in Izmir refinery, Turkey. DHC-8 is an amorphous hydrocracking catalyst consisting of non-noble hydrogenation metals on a silica alumina base. It is a bifunctional catalyst incorporating both hydrotreating and hydrocracking functions and was used in sulphide form of powder. The selection of these catalysts was done based on our previous experience because they are resistant to impurities, as that was already tested in feedstock recycling of thermoplastics and waste plastics. 2.3. Hydrogenation Upgrading reactions with or without catalysts were carried out by using a 100 ml shaking type batch autoclave [17]. The autoclave was charged with 15 g of feed and 3 g of catalyst. The autoclave was sealed and purged with nitrogen. Thereafter it was pressurized to 6.5 MPa with hydrogen. Hydrogenation runs were made at 350 C for a reaction time of 120 min. The reaction time, temperature range and the ratio of catalyst to feed were optimized from the data of preliminary studies. At the end of the reaction time the autoclave was cooled down at room temperature by a fun. After ventilation of gas products, liquid and solid products were recovered from the autoclave and centrifuged to separate the liquid and solid portion (residue). Solid products were washed with dichloromethane. After washing, dichloromethane insoluble fraction was dried at the room temperature and weighed. The coke amount was calculated by weight difference of total amount of solid products and catalysts after dichloromethane washing.
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Before each hydrogenation experiment the catalyst was regenerated by heating in oxygen atmosphere for 6 h. 2.4. Products characterization The liquid and solid pyrolysis products have been characterized by chromatographic methods adapted for complex mixtures to be analyzed: 1H-NMR and FT-IR spectroscopy and elemental analysis. The liquid products were analyzed by gas chromatography with flame ionization detector using a Hewlett-Packard model 6890 GC. The column was a HP Z-30300 column (30 m length · 0.32 mm diameter) coated with crosslinked phenylmethylsiloxane at a thickness of 0.50 lm. GC–FID was temperature-programmed from 40 to 280 C at 5 C/min with a final holding time of 30 min. The data obtained from GC–FID were used to evaluate the simulated distillation curves. [18] The liquid products were also analyzed by a gas chromatograph using a mass selective detector (GC–MSD; HP 5973; column, HP-1; cross-linked methyl siloxane; 25 m · 0.32 mm · 0.17 lm; temperature program, 40 C (hold 10 min) ! 300 C (rate 5 C min1, hold for 5 min). The distribution of bromine-, chlorine- and nitrogencontaining organic compounds in treated oils was analyzed by a gas chromatograph equipped with atomic emission detector (AED; HP G2350A; column, HP-1; cross-linked methyl siloxane; 25 m · 0.32 m · 0.17 lm). 1-Bromohexane, 1,2,4-trichlorobenzene and nitrobenzene were used as internal standards in the GC-AED analysis for the quantitative determination of bromine, chlorine and nitrogen, respectively. The composition of the liquid products was characterized using C-NP gram (C stands for hydrocarbon and NP from normal paraffin) [19,20]. In a similar way, the organic bromine, chlorine and nitrogen were characterized using Br-, Cl- and N-NP grams (Br, Cl and N stands for bromine, chlorine and nitrogen). 1 H-NMR spectra of liquid products were recorded with a Bruker GMBH DPX – 400 using CDCl3 as solvent. The hydrocarbon types and RON (research octane number) of the oils were calculated according to the correlations developed by Myers et al. [21] on the basis of 1H-NMR spectra. FT-IR spectra have been recorded on a FT-IR Bomem MB-104 spectrometer (Canada) with a resolution of 4 cm1 from a very thin layer of pyrolysis oil being deposited on KBr tablets. The pyrolytic solid residue that is a mixture of catalysts and organic carbonaceous residue resulted from secondary reactions of cyclisation and condensation during hydrogenation was analyzed by FT-IR, atomic absorption spectroscopy and elemental analysis. The thermogravimetric (TG/DTG) curves were recorded on a Paulik–Paulik– Erdey type Derivatograph, MOM, Budapest, under the following operational conditions: heating rate (b) of 12 C min1; temperature range 25–600 C; film sample mass 50 mg, in platinum crucibles; self generated atmosphere. Two curves were recorded for each sample.
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3. Results and discussion The product distribution from hydrogenation process of the pyrolysis oil is given in Table 1. The product distribution from catalytic hydrogenation was changed depending on type of catalyst and of pyrolysis oil. The mass balance for thermal hydrogenation of oils from casings, keyboard and mixture is almost similar with hydrogenation over DHC-8 catalyst namely 60–73 wt% liquid and 27–35 wt% gases and low residue amount of 0–2 wt%. The product distribution from the hydrogenation process of the pyrolysis oil of PCB is different. The liquid is with about ten percentages less (50–55 wt%), the gas amount is almost similar with that obtained from pyrolysis oils of casing and keyboard while the solid residue is in higher amounts of 6–7 wt%. The hydrogenation over metal loaded activated carbon catalyst gave very different results. Higher amount of gases (40–80 wt%) was obtained and more solid residue remained (except for the pyrolysis oil from PCB hydrogenated over DHC-8 that leaves 11 wt% residue). This catalyst seems to have a high activity in promoting cyclisation and condensation reactions, which finally lead to the formation of a greater quantity of carbon on its surface and probably to catalyst deactivation. The catalyst deactivation/activation will be the subject of other study. It was noted that the hydrogenation over metal loaded activated carbon catalyst (M-Ac) gave the highest gas yields and the lowest amount of liquid products. Upgrading of pyrolysis oils obtained from wastes includes a number of reactions such as hydrogenation, dehalogenation, hydrocracking and so on. The used two catalysts have both hydrocracking and hydrotreating effects. But the catalytic reactions involve completely different mechanism. The bond cleavage on acidic sites of DHC-8 proceeds by a carbenium ion mechanism. However, over an active carbon catalyst, cleavages occur via radical mechanism which is similar to thermal cracking. Although commercial DHC8 catalyst has good performance in hydrotreating, the Table 1 Product distribution of hydrogenation processes of pyrolysis oils from different computer scraps Sample
Hydrogenation method
Liquid (wt%)
Solid (wt%)
Gasa(wt%)
Casings
Thermal DHC-8 M-Ac
64.8 60.7 11.4
3.9 2.1 10.0
31.3 37.3 78.6
Keyboard
Thermal DHC-8 M-Ac
62.5 70.5 23.2
0.3 2.0 6.7
37.2 27.5 70.1
PCB
Thermal DHC-8 M-Ac
56.5 50.9 33.2
5.9 11.0 7.7
37.5 38.1 59.1
Mixture
Thermal DHC-8 M-Ac
72.4 65.7 49.1
0.1 0.1 3.3
27.5 34.3 47.6
a
Evaluated by difference.
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impurities such as N-containing compounds are poisons for acidic catalyst while, activated carbon is resistant to impurities. Although the pyrolysis oils were rich in aromatic compounds, high amount of gas formation shows that M-Ac catalyst had excellent cracking activity besides its hydrogenation activity. This result agrees well with the previous studies related to coprocessing of vacuum gas oil with polymers and waste plastics [17,22,23]. These studies have shown the ability of metal loaded activated carbon to act in promoting hydrocracking reactions. The simulated distillation curves do not indicate significant differences between liquid pyrolysis products resulted from various scraps, before and after hydrogenation. For example it can be easily remarked that most of pyrolysis oils from keyboard (55 wt% in the case of hydrogenated products over activated carbon) distillate in a narrow temperature range around 135 C (Fig. 1). This suggest a high content in compounds with boiling points similar to benzene derivatives’’ (e.g., ethylbenzene with b.p. of 136 C).
400 Mixture Mixture thermal Mixture active C Mixture DHC-8
Boiling Temperature (ºC)
350 300 250 200 150 100 50 0 0
20
40 60 Cumulative Volume
80
100
Fig. 1. Simulated distillation curves of the hydrogenated pyrolysis liquids resulted from keyboard.
nD20
1.7
1.6
og en ca at t ov al ed er yt D ica H ll C y -8 h yd ro ge ca na ov ta te er lyt d i ac ca tiv lly at h ed yd ca rog rb en on a te d
Th
er
m
un
al
-h
ly
yd
hy
ro
dr
ge
na te
d
1.5
Fig. 2. Variation of the refractive index of the pyrolysis oils obtained from mixture before and after hydrotreating.
After hydrogenation the refractive indices of the pyrolysis oil from mixture decreases mainly after catalytic hydrogenation over metal-loaded activated carbon, because of the hydrogenation of some aromatic compounds with high refractive indices (Fig. 2). The 1H-NMR spectra of the upgraded pyrolysis liquids from mixture are almost similar to casings and keyboard components. The signals corresponding to the unsaturated structures (3–5.5 ppm range) disappeared showing the efficiency of the hydrogenation treatments (Fig. 3). Table 2 shows the content of hydrocarbon types in pyrolysis oils upgraded by thermal and catalytic hydrogenation. For comparison purpose, hydrocarbon types of unhydrogenated pyrolysis oils are also given. The distribution of hydrocarbon types in unhydrogenated oils (except the oils from PCB) is almost similar, consisting of aromatics (60– 65%) and olefins (33–37%). The use of catalysts slightly increased the content of aromatic hydrocarbons with 2– 9%. This shows that catalytic upgrading could not provide hydrogenation of aromatics, it only led to cracking of aromatics into gas compounds. As expected, the paraffin content increased due to the hydrogenation of olefins. The low isoparafin index shows that there is no isomerization during upgrading. The oils have considerable high RON because of their high aromatic content. FT-IR analysis is sensitive to the composition change of the pyrolysis products. Similar to 1H-NMR analysis, no significant differences could be observed by FT-IR between pyrolysis liquids from casing, keyboard and mixture but the spectra were changed after hydrogenation treatment, especially in the ‘fingerprint’ region – Fig. 4. The shift of the bands after hydrogenation, e.g. both aromatic ring stretching at 1472 and 1553 cm1 and aromatic wagging (866 and 778 cm1), the –CH3 stretching (2986 cm1) and –OH stretching (3477 cm1) indicates a strong modification of the aromatic environment. New absorption bands appeared at 1279–1188 cm1, whereas those at 1172– 1159 cm1 (phenolic –OH) disappeared. It can be remarked that the composed band from 1140–1350 cm1 is particular for each upgraded oils. These bands can be assigned to the substituted aromatic compounds that probably differ by the position of substituents. Changes in oil composition after hydrogenation are also evidenced by the apparition of the bands at 3370 and 740 cm1 while the bands at 3410, 2240, 770, 810 and 830 cm1 disappear and the ratio between the bands at 2920 and 2950 cm1 is modified. It is clear that –CN groups (2240 cm1) and also –OH groups involved in Hbonds (3410 cm1) are eliminated by hydrogenation. It can be also supposed that the alkylation degree of some compounds decreased. The differences between sample composition before and after hydrogenation can be easily remarked from the GC– MSD chromatograms (Fig. 5) that have particular pattern for each hydrogenation procedure used. Some of the light compounds and most of heavy compounds were removed by hydrogenation.
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481
Fig. 3. 1H-NMR spectra of the pyrolysis liquid resulted from mixture of computer scraps before and after hydrotreating.
Table 2 Hydrocarbons content of the pyrolysis oil before and after hydrogenation, vol% Sample
Hydrogenation method
Aromatics
Parafins
Olefins
H/C
Isoparafin index
RON
Casing
No treatment Thermal DHC-8 M-Ac
66.54 67.62 69.46 68.81
0.00 32.38 30.54 31.19
33.46 0.00 0.00 0.00
0.97 1.25 1.19 1.20
0.02 0.05 0.03 0.04
87.46 87.87 87.92 87.89
Keyboard
No treatment Thermal DHC-8 M-Ac
63.81 59.11 65.03 67.13
0.00 40.89 34.97 32.87
36.19 0.00 0.00 0.00
1.08 1.36 1.27 1.23
0.01 0.06 0.05 0.05
87.10 87.05 87.57 87.86
PCB
No treatment Thermal DHC-8 M-Ac
80.40 84.56 88.05 89.33
15.95 15.44 11.95 10.67
3.65 0.00 0.00 0.00
1.02 1.04 0.93 0.92
0.03 0.17 0.14 0.10
89.05 90.75 90.89 90.61
Mixture
No treatment Thermal DHC-8 M-Ac
62.75 72.43 66.70 65.51
0.00 27.57 33.30 34.49
37.25 0.00 0.00 0.00
0.99 1.21 1.21 1.25
0.01 0.05 0.04 0.04
87.02 88.39 87.73 87.56
GC–MSD analysis proves the high content of benzene derivatives in pyrolysis oil from casing, keyboard and mixture (Fig. 6a) predicted by the distillation curves. Styrene, ethylbenzene and a-methylstyrene were the main benzene derivatives in untreated pyrolysis oils. Styrene and a-methylstyrene were converted to ethylbenzene and cumene, respectively after hydrogenation. Also the amount of toluene and benzene is increased and propylbenzene is formed, (this was not identified before hydrotreatment). Contrary
to casing and keyboard the pyrolysis oil from PCB contains small amount of benzene derivatives (about 6%) that is increased to 14–17% by hydrogenation (Fig. 6b). Styrene was removed during upgrading. The C-NP grams showing the global composition of pyrolysis oils (Fig. 7a) are almost similar for casings, keyboard and mixture. After hydrogenation a high amount of light aromatic compounds at n-C8 and n-C10 is formed while the amount of heavier compounds is decreased (no
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0.8
Mixture Thermal DHC-8 Active carbon
0.6 0.4 0.2 0.0 2000
Mixture Thermal DHC-8 Active carbon
1.0 Absorbance, a.u.
Absorbance, a.u.
1.0
0.8 0.6 0.4 0.2 0.0
2500 3000 Wavenumber, cm-1
Absorbance, a.u.
1.0 0.8
3500
1000
1200
1400
1600
1800
Wavenumber, cm-1 Mixture Thermal DHC-8 Active carbon
0.6 0.4 0.2 0.0 400
600 800 Wavenumber, cm-1
Fig. 4. FT-IR spectra in different wavenumber ranges for the unhydrogenated and hydrogenated liquid pyrolysis products resulted from mixture of computer scraps.
Fig. 5. GC–MS chromatograms of the liquid products resulted from mixture of the computer scraps before (Mix) and after hydrogenation thermal (Th), over DHC-8 and activated carbon (Act-C).
PCB Mixture
PCB DHC8 Mixture active C
40 30
PCB M-AC
Mixture DHC8
20 10
ene ene ene ene ene ene ene ene enz Styr Tolu Cum benzBenz Xyl tyr ylb thS yl e p M Eth o Pr haalp
M
0
GC-MSD area ,%
50
PCB thermal
Mixture thermal
8 C C e H D tiv al c m re tu re a her ix t tu M ix ure t M ix ure t ix M
GC-MSD area ,%
60
8 6
PCB D HC8 PCB M -AC PCB th ermal PCB
4 2 0 lbe
y Eth
ne
nze
e
ren
Sty
e
uen
Tol
e ne zen me ben pyl Pro
Cu
Fig. 6. The proportion of the main aromatics found in pyrolysis oil from mixture of computer scraps (a) and PCB (b) before and after hydrotreating.
peak at carbon number higher than n-C15 in catalytic hydrogenation). The distribution of the compounds in respect with carbon number is narrower than that existed
before hydrogenation. No significant difference is observed for different procedures of thermal or catalytic hydrotreating.
C. Vasile et al. / Fuel 86 (2007) 477–485 70
4000
60 Mixture Mixture thermal
Mixture - 5496 ng/ml
O amount, ng/ml
Mixture thermal - 2627 ng/ml
Mixture active C
Area,%
PhO H
3500
50 40
Mixture DHC8
30 20
3000
Mixture active C - 1750 ng/ml
2500
Mixture DHC8 - 3427 ng/ml
2000
CH3PhOH, (CH3)2PhOH
1500
(CH3)3PhOH
1000
10
500 `
0 8
6000
10
12 14 Carbon number
R-CN
16
0 10
18
5000 4000
12
13 14 Carbon number
Cl-NP
Py-CH3
3000 2000
11
15
16
17
50
Mixture - 7909 ng/ml Mixture thermal - 168366 ng/ml Mixture active C - 1798 ng/ml Mixture DHC8 - 3514 ng/ml
Cl amount, ng/ml
6
N amount, ng/ml
483
PhC3H6CN
Mixture - 119.5 ng/ml
40 Mixture DHC8 - 17.3 ng/ml
30 20 10
1000
0
0 5
6
7
8
9 10 11 12 Carbon number
13
14
15
16
5
10
15 Carbon number
20
25
Fig. 7. NP grams of pyrolysis oil from mixture of computer scraps before and after hydrogenation: (a) C-NP grams, (b) O-NP grams, (c) N-NP grams, (d) Cl-NP grams.
Oxygen containing compounds consisted mainly of phenol and its derivatives and they were reduced after hydrogenation (Fig. 7b and Fig. 8a). This is mainly due to the decrease of phenol amount; however new compounds such as methylphenol were observed after hydrogenation. The most efficient catalyst in this reduction was activated carbon that totally removed the oxygen from pyrolysis oil of casings and reduced to more than a half the oxygen amount from keyboard and mixture pyrolysis oil. It was interesting to found that thermal process shown better deoxygenation effect compared to catalytic process over DHC-8. In the case of mixture oil, although heavy O-compounds were not observed after hydrogenation, phenol, methyl phenol and dimethylphenol still remained in the oil (Fig. 8a). In the case of PCB oil, isopropylphenol was
decreased by hydrotreating, whereas the others increased slightly (Fig. 8b). All aliphatic and aromatic nitriles were removed from oil by thermal and catalytic hydrotreating (Fig. 7c). However new nitrogen-containing heterocyclic compounds (e.g., methylpyridine at n-C11) were formed after hydrogenation although they were not identified in untreated oils. Chlorine containing compounds are importantly diminished over DHC-8 and removed by the other two hydrogenation procedures – Fig. 7d. Bromine containing compounds were not found in upgraded (hydrogenated) pyrolysis oils. The hydrogenation over all catalysts used allows eliminating almost totally the hazardous toxic compounds, mainly those containing chlorine and bromine.
Mixture Mixture thermal
PCB
Mixture M-Ac
2
PCB thermal
1.5 1
Mix
ture
Mix
0.5
Mix
ture
0 nol nol nol ol Phen ethylphe ethylphe ropylphe 2M Dim Isop
Mix
ture
ture
ther
M-A
mal
c
DHC
8
GC-MSD area , %
GC-MSD area , %
Mixture DHC 8
40 35 30 25 20 15 10 5 0 enol enol enol eter enol enol nol Phe ethylph ethylph thylph opylph opylph iphenyl E D Pr Isopr 2M Dim
PCB M-AC PCB DHC8
PC BD B M HC8 -AC Bt her ma l
PC
PC B
PC
Fig. 8. The proportion of the phenol and main phenol derivatives found in pyrolysis oil from a mixture of various computer scraps (a) and PCB (b) before and after hydrotreating.
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Fig. 9. TG/DTG curves of the pyrolysis residue from mixture ( ), ) and hydrogenation residue of the pyrolysis oil from mixture PCB ( ( ).
An important amount of heteroatoms in pyrolysis oils were concentrated in solid residue after hydrotreating (approximate values: Br: 5–15 wt%, C: 2–6 wt%, N: 2–4 wt%, S: 0.2–1 wt%). This might be a result of condensation of heavy fractions in pyrolysis oils or of adsorption/ reaction with/or catalyst components. The fact that the amount of hetereoatoms in residue from thermal upgrading is higher than that in residue from catalytic upgrading shows that used catalysts promote removing of a part of hetereoatoms in gas form, such as HCl, NH3, HBr and H2O. Bands corresponding to both inorganic (400–450 cm1) and organic (690–750 cm1) halogen were found in FT-IR spectra of hydrogenation residue, showing that pyrolysis oils contained volatile halogens. The TG characterisation of pyrolysis and hydrogenation residues gives information on the possibilities of their recovery. As it can be seen from TG/DTG curves in Fig. 9 the thermal behaviour of the residue of pyrolysis from mixture and PCB are stable up to 320 C then a very slow process of mass loss takes place in a wide temperature range up to 700 C. Residue of hydrogenation process of the pyrolysis oil from mixture has a mass loss of 6 wt% at low temperature, and a very large region of mass loss between 320 and 970 C. Finally it is totally decomposed and 78.7 wt% would be transformed into volatile products after additional heating. Because the hydrogenation residue contained large molecular weight hydrocarbons, the left (21.3 wt%) consisted of thermally stable hydrocarbons (coke). The other two residues leave a higher quantity of solid material after heating, because of their metal content. 4. Conclusions In this study, the upgrading of pyrolysis oils from different parts of waste computer scrap was investigated. The
obtained pyrolysis oils consisted of mainly aromatic hydrocarbons and contained halogen-compounds coming from the flame retardant in scraps. In upgrading process, a combination of hydrogenation and hydrocracking occurred. By considering the impurities in pyrolysis oil cause the deactivation of conventional acidic catalyst (DHC-8), the activated carbon, a neutral catalyst, was also used. The metal loaded activated carbon catalyst was found the most efficient both mainly as hydrocracking catalyst and also in removal of hazardous compounds from pyrolysis oils resulted from flame retarded computer scraps. The most part of the oxygen containing compounds are converted in aromatic hydrocarbons after hydrogenation while the hazardous compounds containing oxygen, nitrogen, halogens and sulphur have been eliminated. Upgrading process assured a good stability of the pyrolysis oils because of the elimination of olefins. However, upgraded oils contained high amount of aromatics (60–89 wt%). For this reason, it is concluded that they can be considered as feedstock for the production of basic aromatics in petrochemical industry. Acknowledgements This work was done in the framework of an interacademic exchange between Romanian and Turkish Academies of Sciences. We are grateful for their support and also to Prof. Sakata Yusaku at Okayama University for his help in performing GC–MSD experiments. References [1] Sato Y, Kodera Y, Kamo T. Analysis of chlorine distribution in the pyrolysis products of PVDC mixed with PE, PP and PS. Energy Fuel 1999;13:364–8. [2] Kawai N, Tsujita K, Kamo T, Sato Y. Chemical recovery of bisphenol-a from polycarbonate resin and waste. In: Proceedings of ISFR’2002 the 2nd international symposium on feedstock recycling of plastics & other innovative recycling techniques, September 8–11 2002, Ostend, Belgium, CD-A48; 2002. [3] van Schindel PPAJ, van Kasteres JMN. Design and optimisation of a separation, purification and upgrading process for polymers from electronic and electric equipment. In: Proceedings of ISFR’2002 the 2nd International symposium on feedstock recycling of plastics & other innovative recycling techniques, September 8–11 2002, Ostend, Belgium, CD-A33; 2002. [4] Agnes F. The Watech process for treatment of plastic waste with brominated flame-retardants. In: Proceedings of ISFR’2002 the 2nd international symposium on feedstock recycling of plastics & other innovative recycling techniques, September 8–11 2002, Ostend, Belgium, A86; 2002. [5] Bockhorn H, Hornung A, Hornung U, Jakobstroer P, Kraus M. Dehydrochlorination of plastic mixtures. J Anal Appl Pyrol 1999;49:97–106. [6] Boerrigter H, Andre´ B, Oudhuis J, Tange L. Bromine recovery from the plastics fraction of waste of electrical and electronic equipment (WEEE) with staged gasification, Paper R’02 WEE in Pyromaat, Netherland; 2002. [7] Bhaskar T, Kaneko J, Muto A, Sakata Y, Jakab E, Matsui T, et al. Effect of poly(ethylene terephthalate) on the pyrolysis of brominated
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flame retardant containing high impact polystyrene and catalytic debromination of the liquid products. J Anal Appl Pyrol 2004;71:765–77. Bhaskar T, Kaneko J, Muto A, Sakata Y, Jakab E, Matsui T, et al. Pyrolysis studies of PP/PE/PS/PVC/HIPS-Br plastics mixed with PET and dehalogenation (Br, Cl) of the liquid products. J Anal Appl Pyrol 2004;72:27–33. Sakata Y, Bhaskar T, Uddin MDA, Muto A, Matsui T. Development of a catalytic dehalogenation (Cl, Br) process for municipal waste plastic-derived oil. J Mater Cycles Waste Manage 2003;5:113–24. Bhaskar T, Murata K, Matsui T, Brebu MA, Uddin MDA, Muto A, et al. Studies on thermal degradation of acrylonitrile_/butadiene_/ styrene copolymer (ABS-Br) containing brominated flame retardant. J Anal Appl Pyrol 2003;70:369–81. Blazso M, Czegeny Zs, Csoma Cs. Pyrolysis and debromination of flame retarded polymers of electronic scrap studied by analytical pyrolysis. J Anal Appl Pyrol 2002;64:249–61. Allred RE. Recycling process for scrap composites and prepregs. Sampe J 1996;32:46–50. Brebu M, Bhaskar T, Muto A, Sakata Y. Alkaline hydrothermal treatment of brominated high impact polystyrene (HIPS-Br) for bromine and bromine-free plastic recovery. Chemosphere 2006; 64:1021–5. Brebu M, Sakata Y. Novel debromination method for flameretardant high impact polystyrene (HIPS-Br) by ammonia treatment. Green Chem, in press. Sato Y, Ito S, Gonzalez R, Kawai N, Tsujita K, Tomii K, et al. Halogen fixation and chemical recycling of wastes from electrical
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appliances and automobile shredder dust by liquid-phase cracking. In: Proceedings of ISFR’2002 the 2nd international symposium on feedstock recycling of plastics & other innovative recycling techniques, September 8–11 2002, Ostend, Belgium, A20; 2002. Vasile C, Brebu MA, Karayildirim T, Yanik J, Darie H. Feedstock recycling from plastics and thermosets fractions of used computers. I. Pyrolysis. J Mater Cycle Waste Manage, in press. Karagoz S, Yanik J, Ucar S, Song C. Catalytic coprocessing of lowdensity polyethylene with VGO using metal supported on activated carbon. Energy Fuel 2002;16:1301–6. Test method for boiling range distribution of petroleum fractions by gas chromatography ASTM D 2887; 1994. Murata K, Hirano Y, Sakata Y, Uddin MDA. Basic study on a continuous flow reactor for thermal degradation of polymers. J Anal Appl Pyrol 2002;65:71–90. Shiraga Y, Uddin MdA, Muto A, Narazaki M, Sakata Y, Murata K. Proceedings of international symposium on advanced energy technology, Sapporo, 185. Myers ME, Stollsteimeir JR, Wins AM. Determination of hydrocarbon type distribution and hydrogen/carbon ratio of gasolines by nuclear resonance spectrometry. Anal Chem 1975;47:2010–5. Karago¨z S, Yanık J, Uc¸ar S, Sag˘lam M, Song C. Catalytic and thermal degradation of high-density polyethylene in vacumm gas oil over non-acidic and acidic catalysts. Appl Catal A: Gen 2003; 242:51–62. Karago¨z S, Karayildirim T, Uc¸ar S, Yuksel M, Yanık J. Liquefaction of municipal waste plastics in VGO over acidic and non-acidic catalysts. Fuel 2003;82:415–23.
Feedstock recycling from plastics and thermosets fractions of used computers. II. Pyrolysis oil upgrading Cornelia Vasile a
a,*
, Mihai Adrian Brebu a, Tamer Karayildirim b, Jale Yanik b, Hristea Darie a
Romanian Academy, ‘‘P.Poni’’ Institute of Macromolecular Chemistry, Department of Physical Chemistry of Polymers, 41A Grigore Ghica Voda Alley, 700487 Iasi, Romania b Ege University, Faculty of Science, Department of Chemistry, 35100 Izmir, Turkey Received 3 May 2006; received in revised form 1 August 2006; accepted 8 August 2006 Available online 11 September 2006
Abstract Liquid products obtained from pyrolysis of plastics and thermosets fractions (keyboard, casings and printed circuits board and their mixture) of used computers were upgraded by thermal and catalytic hydrogenation. The effect of thermal hydrogenation was improved by using catalysts such as commercial hydrogenation DHC-8 catalyst and metal loaded activated carbon. The upgraded degradation products were separated in three fractions (residue, liquids and gases) and characterized by suitable methods such as gas chromatography (GC–MSD, GC–AED), infrared (FT-IR) and 1H-NMR spectroscopy, elemental analysis, etc. Using of catalyst mainly affected the product distribution of upgrading process. Liquids having high amount of aromatics were obtained by upgrading. Most of hazardous toxic compounds in liquids were eliminated after hydrogenation (e.g., halogens were removed mainly by converting them into gaseous hydrogen chloride and bromide). It has been established that the hydrogenation led to elimination of the most of hazardous toxic compounds, mainly those containing bromine. 2006 Elsevier Ltd. All rights reserved. Keywords: Computer scraps; Pyrolysis-hydrogenation; Toxic products
1. Introduction The production of electric and electronic equipment (EEE) is one of the fastest growing areas. This development has resulted in an increase of waste electric and electronic equipment (WEEE). The amount of electronic waste increases, as the life cycles of some electronic goods are short of about 15–20 years and because more accelerated speed is required in the processing capability of the telecommunication infrastructure. The problem of WEEE is not only one of quantity, but also of the hazardous impacts associated with final disposal. The disposal of electronic
*
Corresponding author. Tel.: +40 232 217454; fax: +40 232 211299. E-mail address: [email protected] (C. Vasile).
0016-2361/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2006.08.010
and electrical appliances in landfill sites or their incineration creates a number of environmental problems, because they contain some additives such as heavy metals (mercury, lead, cadmium, hexavalent chromium) and halogenated flame retardants (especially polybrominated ones), which are hazardous for environment. WEEE consist mainly of thermoplastics such as acrylonitrile–butadiene–styrene terpolymer (ABS), high impact polystyrene (HIPS), polycarbonate (PC) that are used for casings and of thermosets (e.g., epoxy resins) as major printed circuits board (PCB) materials. Pyrolysis is one of the best alternatives to treat WEEE because the majority of the macromolecular organic substances is decomposing to volatile compounds at elevated temperatures while metals, inorganic fillers and supports generally remain unchanged and accumulate in the residue.
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However, during thermal pyrolysis the flame retardants in electronic scraps, mainly the halogenated compounds, cause a contamination of all product streams with halogenated organics. Several procedures such as depolymerization using hydrogen donor solvents, [1,2] depolymerization using supercritical CO2, [3], pyrolysis in the presence of limestone, [4] two-stage pyrolysis, [5] staged-gasification comprising pyrolysis (550 C) and high temperature gasification (>1230 C) with bromine recovery by ‘wet’ alkaline scrubbing of the syngas, [6] catalytic debromination using iron oxide– or calcium–carbon composites, [7–10] co-pyrolysis with inorganic solids of basic character (sodium hydroxide, basic zeolites), [11] catalytic processes to recover fibres from polymer based composites, [12] etc. were proposed for feedstock recycling of thermosetting resins. Alkaline hydrothermal treatment and ammonia treatment were proposed as new methods to recover both bromine and bromine-free plastic or oils from brominated HIPS [13,14]. When the alkali carbonates were mixed in the reaction system for the wastes having high Cl or Br amounts, the halogen content in the liquid product decreased to less than 37 ppm [15]. The products from the process were an energy rich oil condensate, coke, calcium bromide, metal product and ceramic product. These products met commercial specifications and could be used as raw materials in other applications. The elimination or substitution of halogen atoms from halogenated aromatic compounds generally requires more energy, not only because of the bonding energy of the Caromatic–X bond that is higher compared to Caliphatic–X bond, but also because of the lack of favourable geometry for a reaction path with lower activation energy. The liquid pyrolysis products often contain significant amounts of asphalthenes, sulphur and nitrogen. They also contain halogens and metals as minor components but their amounts exceed the limits in use of liquids. As a consequence, additional refining and upgrading is required before their use as fuel or chemical feedstock. Denitrification and desulfuration could be achieved by catalytically hydrotreating. It would be obviously the most advantageous solution to carry out pyrolysis and dehalogenation simultaneously or successively. In our previous paper we presented the pyrolysis of plastics and thermosets fractions of used computers aiming at the recovery of some valuable pyrolysis products. [16] The purpose of this work was to upgrade the pyrolysis liquid products by catalytic hydrogenation in order to find applications as fuels or materials. 2. Experimental 2.1. Materials Four pyrolysis oils of WEEE fractions separated from various computer parts such as were considered for this
studied. The WEEE fractions were: (1) casings of monitor, printer, computer and mouse; (2) keyboard; (3) print circuit board (PCB); (4) a mixture prepared by mechanical blending of grinded 1–3 components in the following percentage: 60 wt% casings, 30% printed circuit board (PCB) and 10 wt% keyboard, which is the approximately proportion found in a computer. The pyrolysis procedure, detailed characterization and composition of pyrolysis oils were presented in the previous paper [16]. 2.2. Catalysts The hydrogenation catalysts were powdered commercially available DHC-8 and a metal-loaded activated carbon (M-Ac). M-Ac catalyst was prepared by wet impregnation method using metal salts. Activated carbon used as catalyst support was obtained from pyrolytic carbon black from pyrolysis at 800 C of used scrap truck tires. The demineralized pyrolytic carbon black was activated with carbon dioxide at a flow rate of 350 ml/min for 6 h at 900 C and then loaded with metal by impregnation method. M-Ac has the following characteristics: Mo 2.89 wt%, Ni 4.63 wt%, surface area of 215.13 m2/g. DHC-8 catalyst was a commercial catalyst with specific surface area of 102 m2/g. This catalyst is being used for hydrocracking of vacuum gas oil in Izmir refinery, Turkey. DHC-8 is an amorphous hydrocracking catalyst consisting of non-noble hydrogenation metals on a silica alumina base. It is a bifunctional catalyst incorporating both hydrotreating and hydrocracking functions and was used in sulphide form of powder. The selection of these catalysts was done based on our previous experience because they are resistant to impurities, as that was already tested in feedstock recycling of thermoplastics and waste plastics. 2.3. Hydrogenation Upgrading reactions with or without catalysts were carried out by using a 100 ml shaking type batch autoclave [17]. The autoclave was charged with 15 g of feed and 3 g of catalyst. The autoclave was sealed and purged with nitrogen. Thereafter it was pressurized to 6.5 MPa with hydrogen. Hydrogenation runs were made at 350 C for a reaction time of 120 min. The reaction time, temperature range and the ratio of catalyst to feed were optimized from the data of preliminary studies. At the end of the reaction time the autoclave was cooled down at room temperature by a fun. After ventilation of gas products, liquid and solid products were recovered from the autoclave and centrifuged to separate the liquid and solid portion (residue). Solid products were washed with dichloromethane. After washing, dichloromethane insoluble fraction was dried at the room temperature and weighed. The coke amount was calculated by weight difference of total amount of solid products and catalysts after dichloromethane washing.
C. Vasile et al. / Fuel 86 (2007) 477–485
Before each hydrogenation experiment the catalyst was regenerated by heating in oxygen atmosphere for 6 h. 2.4. Products characterization The liquid and solid pyrolysis products have been characterized by chromatographic methods adapted for complex mixtures to be analyzed: 1H-NMR and FT-IR spectroscopy and elemental analysis. The liquid products were analyzed by gas chromatography with flame ionization detector using a Hewlett-Packard model 6890 GC. The column was a HP Z-30300 column (30 m length · 0.32 mm diameter) coated with crosslinked phenylmethylsiloxane at a thickness of 0.50 lm. GC–FID was temperature-programmed from 40 to 280 C at 5 C/min with a final holding time of 30 min. The data obtained from GC–FID were used to evaluate the simulated distillation curves. [18] The liquid products were also analyzed by a gas chromatograph using a mass selective detector (GC–MSD; HP 5973; column, HP-1; cross-linked methyl siloxane; 25 m · 0.32 mm · 0.17 lm; temperature program, 40 C (hold 10 min) ! 300 C (rate 5 C min1, hold for 5 min). The distribution of bromine-, chlorine- and nitrogencontaining organic compounds in treated oils was analyzed by a gas chromatograph equipped with atomic emission detector (AED; HP G2350A; column, HP-1; cross-linked methyl siloxane; 25 m · 0.32 m · 0.17 lm). 1-Bromohexane, 1,2,4-trichlorobenzene and nitrobenzene were used as internal standards in the GC-AED analysis for the quantitative determination of bromine, chlorine and nitrogen, respectively. The composition of the liquid products was characterized using C-NP gram (C stands for hydrocarbon and NP from normal paraffin) [19,20]. In a similar way, the organic bromine, chlorine and nitrogen were characterized using Br-, Cl- and N-NP grams (Br, Cl and N stands for bromine, chlorine and nitrogen). 1 H-NMR spectra of liquid products were recorded with a Bruker GMBH DPX – 400 using CDCl3 as solvent. The hydrocarbon types and RON (research octane number) of the oils were calculated according to the correlations developed by Myers et al. [21] on the basis of 1H-NMR spectra. FT-IR spectra have been recorded on a FT-IR Bomem MB-104 spectrometer (Canada) with a resolution of 4 cm1 from a very thin layer of pyrolysis oil being deposited on KBr tablets. The pyrolytic solid residue that is a mixture of catalysts and organic carbonaceous residue resulted from secondary reactions of cyclisation and condensation during hydrogenation was analyzed by FT-IR, atomic absorption spectroscopy and elemental analysis. The thermogravimetric (TG/DTG) curves were recorded on a Paulik–Paulik– Erdey type Derivatograph, MOM, Budapest, under the following operational conditions: heating rate (b) of 12 C min1; temperature range 25–600 C; film sample mass 50 mg, in platinum crucibles; self generated atmosphere. Two curves were recorded for each sample.
479
3. Results and discussion The product distribution from hydrogenation process of the pyrolysis oil is given in Table 1. The product distribution from catalytic hydrogenation was changed depending on type of catalyst and of pyrolysis oil. The mass balance for thermal hydrogenation of oils from casings, keyboard and mixture is almost similar with hydrogenation over DHC-8 catalyst namely 60–73 wt% liquid and 27–35 wt% gases and low residue amount of 0–2 wt%. The product distribution from the hydrogenation process of the pyrolysis oil of PCB is different. The liquid is with about ten percentages less (50–55 wt%), the gas amount is almost similar with that obtained from pyrolysis oils of casing and keyboard while the solid residue is in higher amounts of 6–7 wt%. The hydrogenation over metal loaded activated carbon catalyst gave very different results. Higher amount of gases (40–80 wt%) was obtained and more solid residue remained (except for the pyrolysis oil from PCB hydrogenated over DHC-8 that leaves 11 wt% residue). This catalyst seems to have a high activity in promoting cyclisation and condensation reactions, which finally lead to the formation of a greater quantity of carbon on its surface and probably to catalyst deactivation. The catalyst deactivation/activation will be the subject of other study. It was noted that the hydrogenation over metal loaded activated carbon catalyst (M-Ac) gave the highest gas yields and the lowest amount of liquid products. Upgrading of pyrolysis oils obtained from wastes includes a number of reactions such as hydrogenation, dehalogenation, hydrocracking and so on. The used two catalysts have both hydrocracking and hydrotreating effects. But the catalytic reactions involve completely different mechanism. The bond cleavage on acidic sites of DHC-8 proceeds by a carbenium ion mechanism. However, over an active carbon catalyst, cleavages occur via radical mechanism which is similar to thermal cracking. Although commercial DHC8 catalyst has good performance in hydrotreating, the Table 1 Product distribution of hydrogenation processes of pyrolysis oils from different computer scraps Sample
Hydrogenation method
Liquid (wt%)
Solid (wt%)
Gasa(wt%)
Casings
Thermal DHC-8 M-Ac
64.8 60.7 11.4
3.9 2.1 10.0
31.3 37.3 78.6
Keyboard
Thermal DHC-8 M-Ac
62.5 70.5 23.2
0.3 2.0 6.7
37.2 27.5 70.1
PCB
Thermal DHC-8 M-Ac
56.5 50.9 33.2
5.9 11.0 7.7
37.5 38.1 59.1
Mixture
Thermal DHC-8 M-Ac
72.4 65.7 49.1
0.1 0.1 3.3
27.5 34.3 47.6
a
Evaluated by difference.
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impurities such as N-containing compounds are poisons for acidic catalyst while, activated carbon is resistant to impurities. Although the pyrolysis oils were rich in aromatic compounds, high amount of gas formation shows that M-Ac catalyst had excellent cracking activity besides its hydrogenation activity. This result agrees well with the previous studies related to coprocessing of vacuum gas oil with polymers and waste plastics [17,22,23]. These studies have shown the ability of metal loaded activated carbon to act in promoting hydrocracking reactions. The simulated distillation curves do not indicate significant differences between liquid pyrolysis products resulted from various scraps, before and after hydrogenation. For example it can be easily remarked that most of pyrolysis oils from keyboard (55 wt% in the case of hydrogenated products over activated carbon) distillate in a narrow temperature range around 135 C (Fig. 1). This suggest a high content in compounds with boiling points similar to benzene derivatives’’ (e.g., ethylbenzene with b.p. of 136 C).
400 Mixture Mixture thermal Mixture active C Mixture DHC-8
Boiling Temperature (ºC)
350 300 250 200 150 100 50 0 0
20
40 60 Cumulative Volume
80
100
Fig. 1. Simulated distillation curves of the hydrogenated pyrolysis liquids resulted from keyboard.
nD20
1.7
1.6
og en ca at t ov al ed er yt D ica H ll C y -8 h yd ro ge ca na ov ta te er lyt d i ac ca tiv lly at h ed yd ca rog rb en on a te d
Th
er
m
un
al
-h
ly
yd
hy
ro
dr
ge
na te
d
1.5
Fig. 2. Variation of the refractive index of the pyrolysis oils obtained from mixture before and after hydrotreating.
After hydrogenation the refractive indices of the pyrolysis oil from mixture decreases mainly after catalytic hydrogenation over metal-loaded activated carbon, because of the hydrogenation of some aromatic compounds with high refractive indices (Fig. 2). The 1H-NMR spectra of the upgraded pyrolysis liquids from mixture are almost similar to casings and keyboard components. The signals corresponding to the unsaturated structures (3–5.5 ppm range) disappeared showing the efficiency of the hydrogenation treatments (Fig. 3). Table 2 shows the content of hydrocarbon types in pyrolysis oils upgraded by thermal and catalytic hydrogenation. For comparison purpose, hydrocarbon types of unhydrogenated pyrolysis oils are also given. The distribution of hydrocarbon types in unhydrogenated oils (except the oils from PCB) is almost similar, consisting of aromatics (60– 65%) and olefins (33–37%). The use of catalysts slightly increased the content of aromatic hydrocarbons with 2– 9%. This shows that catalytic upgrading could not provide hydrogenation of aromatics, it only led to cracking of aromatics into gas compounds. As expected, the paraffin content increased due to the hydrogenation of olefins. The low isoparafin index shows that there is no isomerization during upgrading. The oils have considerable high RON because of their high aromatic content. FT-IR analysis is sensitive to the composition change of the pyrolysis products. Similar to 1H-NMR analysis, no significant differences could be observed by FT-IR between pyrolysis liquids from casing, keyboard and mixture but the spectra were changed after hydrogenation treatment, especially in the ‘fingerprint’ region – Fig. 4. The shift of the bands after hydrogenation, e.g. both aromatic ring stretching at 1472 and 1553 cm1 and aromatic wagging (866 and 778 cm1), the –CH3 stretching (2986 cm1) and –OH stretching (3477 cm1) indicates a strong modification of the aromatic environment. New absorption bands appeared at 1279–1188 cm1, whereas those at 1172– 1159 cm1 (phenolic –OH) disappeared. It can be remarked that the composed band from 1140–1350 cm1 is particular for each upgraded oils. These bands can be assigned to the substituted aromatic compounds that probably differ by the position of substituents. Changes in oil composition after hydrogenation are also evidenced by the apparition of the bands at 3370 and 740 cm1 while the bands at 3410, 2240, 770, 810 and 830 cm1 disappear and the ratio between the bands at 2920 and 2950 cm1 is modified. It is clear that –CN groups (2240 cm1) and also –OH groups involved in Hbonds (3410 cm1) are eliminated by hydrogenation. It can be also supposed that the alkylation degree of some compounds decreased. The differences between sample composition before and after hydrogenation can be easily remarked from the GC– MSD chromatograms (Fig. 5) that have particular pattern for each hydrogenation procedure used. Some of the light compounds and most of heavy compounds were removed by hydrogenation.
C. Vasile et al. / Fuel 86 (2007) 477–485
481
Fig. 3. 1H-NMR spectra of the pyrolysis liquid resulted from mixture of computer scraps before and after hydrotreating.
Table 2 Hydrocarbons content of the pyrolysis oil before and after hydrogenation, vol% Sample
Hydrogenation method
Aromatics
Parafins
Olefins
H/C
Isoparafin index
RON
Casing
No treatment Thermal DHC-8 M-Ac
66.54 67.62 69.46 68.81
0.00 32.38 30.54 31.19
33.46 0.00 0.00 0.00
0.97 1.25 1.19 1.20
0.02 0.05 0.03 0.04
87.46 87.87 87.92 87.89
Keyboard
No treatment Thermal DHC-8 M-Ac
63.81 59.11 65.03 67.13
0.00 40.89 34.97 32.87
36.19 0.00 0.00 0.00
1.08 1.36 1.27 1.23
0.01 0.06 0.05 0.05
87.10 87.05 87.57 87.86
PCB
No treatment Thermal DHC-8 M-Ac
80.40 84.56 88.05 89.33
15.95 15.44 11.95 10.67
3.65 0.00 0.00 0.00
1.02 1.04 0.93 0.92
0.03 0.17 0.14 0.10
89.05 90.75 90.89 90.61
Mixture
No treatment Thermal DHC-8 M-Ac
62.75 72.43 66.70 65.51
0.00 27.57 33.30 34.49
37.25 0.00 0.00 0.00
0.99 1.21 1.21 1.25
0.01 0.05 0.04 0.04
87.02 88.39 87.73 87.56
GC–MSD analysis proves the high content of benzene derivatives in pyrolysis oil from casing, keyboard and mixture (Fig. 6a) predicted by the distillation curves. Styrene, ethylbenzene and a-methylstyrene were the main benzene derivatives in untreated pyrolysis oils. Styrene and a-methylstyrene were converted to ethylbenzene and cumene, respectively after hydrogenation. Also the amount of toluene and benzene is increased and propylbenzene is formed, (this was not identified before hydrotreatment). Contrary
to casing and keyboard the pyrolysis oil from PCB contains small amount of benzene derivatives (about 6%) that is increased to 14–17% by hydrogenation (Fig. 6b). Styrene was removed during upgrading. The C-NP grams showing the global composition of pyrolysis oils (Fig. 7a) are almost similar for casings, keyboard and mixture. After hydrogenation a high amount of light aromatic compounds at n-C8 and n-C10 is formed while the amount of heavier compounds is decreased (no
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0.8
Mixture Thermal DHC-8 Active carbon
0.6 0.4 0.2 0.0 2000
Mixture Thermal DHC-8 Active carbon
1.0 Absorbance, a.u.
Absorbance, a.u.
1.0
0.8 0.6 0.4 0.2 0.0
2500 3000 Wavenumber, cm-1
Absorbance, a.u.
1.0 0.8
3500
1000
1200
1400
1600
1800
Wavenumber, cm-1 Mixture Thermal DHC-8 Active carbon
0.6 0.4 0.2 0.0 400
600 800 Wavenumber, cm-1
Fig. 4. FT-IR spectra in different wavenumber ranges for the unhydrogenated and hydrogenated liquid pyrolysis products resulted from mixture of computer scraps.
Fig. 5. GC–MS chromatograms of the liquid products resulted from mixture of the computer scraps before (Mix) and after hydrogenation thermal (Th), over DHC-8 and activated carbon (Act-C).
PCB Mixture
PCB DHC8 Mixture active C
40 30
PCB M-AC
Mixture DHC8
20 10
ene ene ene ene ene ene ene ene enz Styr Tolu Cum benzBenz Xyl tyr ylb thS yl e p M Eth o Pr haalp
M
0
GC-MSD area ,%
50
PCB thermal
Mixture thermal
8 C C e H D tiv al c m re tu re a her ix t tu M ix ure t M ix ure t ix M
GC-MSD area ,%
60
8 6
PCB D HC8 PCB M -AC PCB th ermal PCB
4 2 0 lbe
y Eth
ne
nze
e
ren
Sty
e
uen
Tol
e ne zen me ben pyl Pro
Cu
Fig. 6. The proportion of the main aromatics found in pyrolysis oil from mixture of computer scraps (a) and PCB (b) before and after hydrotreating.
peak at carbon number higher than n-C15 in catalytic hydrogenation). The distribution of the compounds in respect with carbon number is narrower than that existed
before hydrogenation. No significant difference is observed for different procedures of thermal or catalytic hydrotreating.
C. Vasile et al. / Fuel 86 (2007) 477–485 70
4000
60 Mixture Mixture thermal
Mixture - 5496 ng/ml
O amount, ng/ml
Mixture thermal - 2627 ng/ml
Mixture active C
Area,%
PhO H
3500
50 40
Mixture DHC8
30 20
3000
Mixture active C - 1750 ng/ml
2500
Mixture DHC8 - 3427 ng/ml
2000
CH3PhOH, (CH3)2PhOH
1500
(CH3)3PhOH
1000
10
500 `
0 8
6000
10
12 14 Carbon number
R-CN
16
0 10
18
5000 4000
12
13 14 Carbon number
Cl-NP
Py-CH3
3000 2000
11
15
16
17
50
Mixture - 7909 ng/ml Mixture thermal - 168366 ng/ml Mixture active C - 1798 ng/ml Mixture DHC8 - 3514 ng/ml
Cl amount, ng/ml
6
N amount, ng/ml
483
PhC3H6CN
Mixture - 119.5 ng/ml
40 Mixture DHC8 - 17.3 ng/ml
30 20 10
1000
0
0 5
6
7
8
9 10 11 12 Carbon number
13
14
15
16
5
10
15 Carbon number
20
25
Fig. 7. NP grams of pyrolysis oil from mixture of computer scraps before and after hydrogenation: (a) C-NP grams, (b) O-NP grams, (c) N-NP grams, (d) Cl-NP grams.
Oxygen containing compounds consisted mainly of phenol and its derivatives and they were reduced after hydrogenation (Fig. 7b and Fig. 8a). This is mainly due to the decrease of phenol amount; however new compounds such as methylphenol were observed after hydrogenation. The most efficient catalyst in this reduction was activated carbon that totally removed the oxygen from pyrolysis oil of casings and reduced to more than a half the oxygen amount from keyboard and mixture pyrolysis oil. It was interesting to found that thermal process shown better deoxygenation effect compared to catalytic process over DHC-8. In the case of mixture oil, although heavy O-compounds were not observed after hydrogenation, phenol, methyl phenol and dimethylphenol still remained in the oil (Fig. 8a). In the case of PCB oil, isopropylphenol was
decreased by hydrotreating, whereas the others increased slightly (Fig. 8b). All aliphatic and aromatic nitriles were removed from oil by thermal and catalytic hydrotreating (Fig. 7c). However new nitrogen-containing heterocyclic compounds (e.g., methylpyridine at n-C11) were formed after hydrogenation although they were not identified in untreated oils. Chlorine containing compounds are importantly diminished over DHC-8 and removed by the other two hydrogenation procedures – Fig. 7d. Bromine containing compounds were not found in upgraded (hydrogenated) pyrolysis oils. The hydrogenation over all catalysts used allows eliminating almost totally the hazardous toxic compounds, mainly those containing chlorine and bromine.
Mixture Mixture thermal
PCB
Mixture M-Ac
2
PCB thermal
1.5 1
Mix
ture
Mix
0.5
Mix
ture
0 nol nol nol ol Phen ethylphe ethylphe ropylphe 2M Dim Isop
Mix
ture
ture
ther
M-A
mal
c
DHC
8
GC-MSD area , %
GC-MSD area , %
Mixture DHC 8
40 35 30 25 20 15 10 5 0 enol enol enol eter enol enol nol Phe ethylph ethylph thylph opylph opylph iphenyl E D Pr Isopr 2M Dim
PCB M-AC PCB DHC8
PC BD B M HC8 -AC Bt her ma l
PC
PC B
PC
Fig. 8. The proportion of the phenol and main phenol derivatives found in pyrolysis oil from a mixture of various computer scraps (a) and PCB (b) before and after hydrotreating.
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Fig. 9. TG/DTG curves of the pyrolysis residue from mixture ( ), ) and hydrogenation residue of the pyrolysis oil from mixture PCB ( ( ).
An important amount of heteroatoms in pyrolysis oils were concentrated in solid residue after hydrotreating (approximate values: Br: 5–15 wt%, C: 2–6 wt%, N: 2–4 wt%, S: 0.2–1 wt%). This might be a result of condensation of heavy fractions in pyrolysis oils or of adsorption/ reaction with/or catalyst components. The fact that the amount of hetereoatoms in residue from thermal upgrading is higher than that in residue from catalytic upgrading shows that used catalysts promote removing of a part of hetereoatoms in gas form, such as HCl, NH3, HBr and H2O. Bands corresponding to both inorganic (400–450 cm1) and organic (690–750 cm1) halogen were found in FT-IR spectra of hydrogenation residue, showing that pyrolysis oils contained volatile halogens. The TG characterisation of pyrolysis and hydrogenation residues gives information on the possibilities of their recovery. As it can be seen from TG/DTG curves in Fig. 9 the thermal behaviour of the residue of pyrolysis from mixture and PCB are stable up to 320 C then a very slow process of mass loss takes place in a wide temperature range up to 700 C. Residue of hydrogenation process of the pyrolysis oil from mixture has a mass loss of 6 wt% at low temperature, and a very large region of mass loss between 320 and 970 C. Finally it is totally decomposed and 78.7 wt% would be transformed into volatile products after additional heating. Because the hydrogenation residue contained large molecular weight hydrocarbons, the left (21.3 wt%) consisted of thermally stable hydrocarbons (coke). The other two residues leave a higher quantity of solid material after heating, because of their metal content. 4. Conclusions In this study, the upgrading of pyrolysis oils from different parts of waste computer scrap was investigated. The
obtained pyrolysis oils consisted of mainly aromatic hydrocarbons and contained halogen-compounds coming from the flame retardant in scraps. In upgrading process, a combination of hydrogenation and hydrocracking occurred. By considering the impurities in pyrolysis oil cause the deactivation of conventional acidic catalyst (DHC-8), the activated carbon, a neutral catalyst, was also used. The metal loaded activated carbon catalyst was found the most efficient both mainly as hydrocracking catalyst and also in removal of hazardous compounds from pyrolysis oils resulted from flame retarded computer scraps. The most part of the oxygen containing compounds are converted in aromatic hydrocarbons after hydrogenation while the hazardous compounds containing oxygen, nitrogen, halogens and sulphur have been eliminated. Upgrading process assured a good stability of the pyrolysis oils because of the elimination of olefins. However, upgraded oils contained high amount of aromatics (60–89 wt%). For this reason, it is concluded that they can be considered as feedstock for the production of basic aromatics in petrochemical industry. Acknowledgements This work was done in the framework of an interacademic exchange between Romanian and Turkish Academies of Sciences. We are grateful for their support and also to Prof. Sakata Yusaku at Okayama University for his help in performing GC–MSD experiments. References [1] Sato Y, Kodera Y, Kamo T. Analysis of chlorine distribution in the pyrolysis products of PVDC mixed with PE, PP and PS. Energy Fuel 1999;13:364–8. [2] Kawai N, Tsujita K, Kamo T, Sato Y. Chemical recovery of bisphenol-a from polycarbonate resin and waste. In: Proceedings of ISFR’2002 the 2nd international symposium on feedstock recycling of plastics & other innovative recycling techniques, September 8–11 2002, Ostend, Belgium, CD-A48; 2002. [3] van Schindel PPAJ, van Kasteres JMN. Design and optimisation of a separation, purification and upgrading process for polymers from electronic and electric equipment. In: Proceedings of ISFR’2002 the 2nd International symposium on feedstock recycling of plastics & other innovative recycling techniques, September 8–11 2002, Ostend, Belgium, CD-A33; 2002. [4] Agnes F. The Watech process for treatment of plastic waste with brominated flame-retardants. In: Proceedings of ISFR’2002 the 2nd international symposium on feedstock recycling of plastics & other innovative recycling techniques, September 8–11 2002, Ostend, Belgium, A86; 2002. [5] Bockhorn H, Hornung A, Hornung U, Jakobstroer P, Kraus M. Dehydrochlorination of plastic mixtures. J Anal Appl Pyrol 1999;49:97–106. [6] Boerrigter H, Andre´ B, Oudhuis J, Tange L. Bromine recovery from the plastics fraction of waste of electrical and electronic equipment (WEEE) with staged gasification, Paper R’02 WEE in Pyromaat, Netherland; 2002. [7] Bhaskar T, Kaneko J, Muto A, Sakata Y, Jakab E, Matsui T, et al. Effect of poly(ethylene terephthalate) on the pyrolysis of brominated
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