Abstract The increasing production of computers, theprogress in their performance, and the shorter time betweeninnovation and production has led to increasing numbers ofobsolete products. It has thus become necessary to recoversome materials from old computers and to protect the envi-ronment from a new type of pollution. Such recycling is dif-ficult because of the diversity of polymeric materials used,e.g., thermoplastics (polystyrene or acrylonitrile-butadiene-styrene) and thermosets (epoxy resins), and the relativelyhigh levels of flame retardants (halogen- and nitrogen-containing compounds) added during production. Pyrolysisseems to be a suitable way to recover materials and energyfrom such waste without component separation if an effi-cient method for reducing toxic compounds can be applied.In this study, the pyrolysis of plastic and thermoset fractions(keyboards, casings, printed circuit boards, and mixturesthereof) of used computers was studied by thermogravime-try and batch reactor pyrolysis. The degradation productswere separated into three fractions, solid, liquid, andgaseous, each of them being characterized by suitablemethods such as gas chromatography (GC-MSD, gas chromatography-mass spectrometry detection; GC-AED,gas chromatography-atomic emission detection), infrared(FT-IR) and 1H-NMR (nuclear magnetic resonanace) spec-troscopy, and elemental analysis. It has been establishedthat most of the halogens, nitrogen, and sulfur is concen-trated in the residue. However, the elimination of hazardoustoxic compounds, mainly those containing bromine, is nec-essary before being able to safely use the pyrolysis oils asfuels or in refinery or petrochemical industry flows.

Key words Computer scrap · Thermogravimetry · Pyrolysis ·Oils · Toxic products

Introduction

The production of electric and electronic equipment (EEE)is one of the fastest growing economic areas. This develop-ment has resulted in an increase of waste electric and elec-tronic equipment (WEEE). The amount of electronic wastecontinues to increase: the life cycles of some electronicgoods are as short as about 15–20 months and for comput-ers the life cycle has progressively decreased because of thedemand for ever-accelerating speeds in the processing capa-bility of the telecommunication infrastructure.

Recent estimates of the amount of WEEE generated forthe period 1998–2008 suggest that the figure will increase to300000–350000 metric tons per annum.1 The use of plasticsin the E&E (electrical & electronical) sectors shows a clearupward trend, the most important consumption being in IT/telecommunications; in Western Europe in 2005 a total of 1170000 tons of such plastic was used.WEEE is a special cat-egory of waste that has received a great deal of attentionover the past 5 years. WEEE is diverse and complex interms of the material and component makeup as well as interms of the original equipment manufacturing processes.The problem of WEEE is not only one of quantity, but alsothe hazardous impacts associated with its final disposal. Thedisposal of E&E appliances in landfill sites or through incin-eration creates a number of environmental problemsbecause of the presence of additives such as heavy metals(mercury, lead, cadmium, hexavalent chromium) and halo-genated flame retardants (polybrominated), which are haz-ardous to the environment.

Recycling WEEE is an important subject not only from the viewpoint of waste treatment but also in terms ofthe recovery of valuable materials. Mechanical/physical processing provides an alternative means of recoveringvaluable materials but several difficulties exist. The minia-turization of electronic equipment reduces the volume of

J Mater Cycles Waste Manag (2006) 8:99–108 © Springer 2006DOI 10.1007/s10163-006-0151-z

Cornelia Vasile · Mihai Adrian Brebu Tammer Karayildirim · Jale Yanik · Hristea Darie

Feedstock recycling from plastic and thermoset fractions of used computers (I): pyrolysis

SPECIAL FEATURE: ORIGINAL ARTICLE

C. Vasile (*) · M.A. Brebu · H. DarieRomanian Academy, P. Poni Institute of Macromolecular Chemistry,Department of Physical Chemistry of Polymers, 41A Grigore GhicaVoda Alley, Ro. 700487, Iasi, RomaniaTel. +40-232-217454; Fax +40-232-211299e-mail: cvasile@icmpp.ro

T. Karayildirim · J. YanikEge University, Faculty of Science, Department of Chemistry, Izmir,Turkey

Received: October 21, 2005 / Accepted: January 25, 2006

3rd International Symposium on Feedstock Recycling ofPlastics & Other Innovative Plastics Recycling Techniques(ISFR 2005)

waste, but makes collection, repair, and recycling more difficult. Also, the relative costs of repair and buying newelectronic equipment have changed, so that repair is onlyeconomically feasible for large, very expensive electronicgoods. Plastics account for about 15%–22% of the weightof WEEE, of which one-third is suitable for mechanicalrecycling and two-thirds need to be disposed of by othermeans.

In view of the environmental problems involved in themanagement of WEEE, many countries and organizationshave drafted national legislation to improve the reuse, recy-cling, and other forms of recovery of such waste to reducethe amount requiring disposal. However, the recycling ofWEEE is still in its infancy.

WEEE consists of thermoplastics [high-impact poly-styrene (HIPS), acrylonitrile-butadiene-styrene terpolymer(ABS), and ABS-polycarbonate (PC)] for casings and ther-mosets (epoxy resins) as a major component of printedcircuit boards (PCBs). Metal parts can be separated andsent to metal-processing facilities. Most casings can bereprocessed; however, ecological-impact studies in theNetherlands and Germany have demonstrated that there isa limit of 15%–18% to the amount of household thermo-plastic waste that can be mechanically recycled with envi-ronmental benefits. Further mechanical recycling requires arelatively major effort that annuls any environmental gain.2

This means that the majority of the remaining waste mustbe recycled by other techniques. When trying to recover theplastic material from discarded electronic devices, we have to take into consideration the unusually high halogen,nitrogen, and sulfur content resulting from the addition offlame retardants and the fact that thermoset polymerscannot be remolded or reprocessed by remelting.Thermoset composites contain high amounts of inorganicglass reinforcement or mineral filler. In this case, chemicalrecycling could be carried out to obtain some organic products and to recover the reinforcement filler, whichcould be reused. For many years, chlorinated and bromi-nated organic compounds or polymers have been applied asfire retardants by mixing them with the plastic materialsused in computers,TV sets, and other household equipmentto prevent fire damage. Much brominated fire retardant isused in the printed circuit board to increase safety. For thisreason, it is difficult to carry out incineration because thebromine fire retardant generates toxic substances duringcombustion.

Pyrolytic recovery of the organic material content seemsto be a suitable way to utilize electronic waste because themajority of the macromolecular organic substances decom-pose to volatile compounds at elevated temperatures, whilemetals, inorganic fillers, and supports generally remainunchanged. Dehalogenation is a key technology in the feed-stock recycling of mixed halogenated waste plastics (e.g.,electrical/electronic scrap) to render the pyrolysis productscommercially acceptable.

Feedstock recycling of thermosetting resins to formmonomers using hydrogen-donor solvents was proposed bySato et al.3,4 An innovative depolymerization process usingsupercritical CO2 can process heavy metals containing ther-

mosets to recover the monomer.5 The process for metalrecovery tested was the depolymerization of brominatedepoxy resin in a solvent in the presence of an alkali metalcompound.

Watech A/S (Norway) has developed an environmen-tally sustainable method for chemical recycling (feedstockrecycling) of brominated flame-retarded plastic waste.6 Theprocess is based on the pyrolysis of thermally stable flame-retarded polymer mixtures that are rich in bromide (HBr).The specific reactor operating conditions inhibit the forma-tion of dioxins and furans. By adding limestone to thereactor before thermal cracking, the exhaust of hydrogenbromide (HBr) (and other acidic gasses) was limitedbecause the produced hydrogen bromine is neutralized toform calcium bromide. The products from the process werean energy-rich oil condensate, coke, calcium bromide, metalproducts and ceramic products. These products met com-mercial specifications and could be used as raw materials inother applications.

It is known that hydrogen halogenide may generally be thermally eliminated from aliphatic halogenated com-pounds by a two-stage pyrolysis process at a lower temper-ature than that used for thermal decomposition of syntheticpolymers, the evolution of HBr taking place. In the case ofplastics containing flame retardants, a two-stage pyrolysisreactor may lead to a halogen-free product, as proposed byBockhorn et al.7 for pyrolytic recycling of polymer mixturescontaining poly vinyl chloride (PVC). However, from halo-genated aromatic compounds, the elimination or the sub-stitution of halogen atoms generally requires more energythan for aliphatic compounds, not only because of thehigher bonding energy of the Caromatic–X bond than that ofthe Caliphatic–X bond, but also because of the lack of favor-able geometry for a reaction path with lower activationenergy. Dehalogenation with bases also has been success-fully applied to halogenated aromatic compounds; however,the question arises of how the products of such a dehalo-genation process would behave under pyrolysis conditionsin the solid or molten phase. Staged gasification, consistingof pyrolysis (550°C) and high-temperature gasification(>1230°C), was proposed by Boerrigter et al.8 In test runswith two plastic WEEE fractions in the ECN Pyromaatinstallation, bromine was recovered by the “wet” alkalinescrubbing of syngas. Sakata and others9,10,11,12 applied a cat-alytic debromination process using a carbon composite ofiron oxide (Fe3O4) catalyst or calcium carbonate–carboncomposite (Ca-C) and completely removed the chlorineand bromine from the liquid pyrolysis products of ABS and other flame-retarded polymers. Blaszo et al. studied the copyrolysis of these plastic materials with inorganicsolids of basic character.13 The volatile thermal decomposi-tion products were analyzed on-line using pyrolysis-gaschromatography/mass spectrometry. The product analysisrevealed that the decomposition reactions of the polymerconstituents are significantly altered in the presence ofstrong inorganic bases. Due to debromination of thedibromo- and tribromophenyl groups of brominated polystyrene, copyrolysis with sodium hydroxide and withbasic zeolites resulted in a considerably reduced yield of

100

dibromo- and tribromostyrenes. From brominated epoxyresins pyrolyzed with sodium hydroxide, enhanced bro-momethane evolution and depressed brominated phenolformation were observed. A diminished production of bromophenols also took place on pyrolysis with sodium-containing silicates. The pyrolysis of the PCBs in TV setsyielded more than 40 compounds, such as phenols, alkyl aro-matics, and furans, as decomposition products. In addition,because the PCBs contained tetrabromophenol A, bromi-nated products were also formed, e.g., HBr (>85%) bro-mophenols (12%), and tetrabromobisphenol A. A catalyticprocess to recover fibers from polymer-based compositeswas applied.14 It was a low-temperature pyrolysis processthat employed a catalyst to maintain the temperature below200°C. The organic materials of the composites were con-verted into low molecular weight hydrocarbons, whichcould be reused as fuel. Bertini and others15 reported on thethermal degradation of end-life polymeric resin-basedmaterials used in electrical and electronic devices and foundthe operating conditions that allowed the recovery of thefiller material with the maximum energy recovery.

ABS is one of the major components of EEE; on pyrol-ysis, it gives important amounts of benzene, toluene, andstyrene. The liquid pyrolysis products often contain signifi-cant amounts of asphalthenes, sulfur, nitrogen, halogens,and metals. As a consequence, additional refining andupgrading is required before these pyrolysis products canbe used as feedstocks for existing conventional refineryprocesses. When alkali carbonate was mixed into the reac-tion system for wastes having high levels of Cl or Br, thehalogen content in the liquid product decreased to less than37ppm.16 Denitrification and desulfuration could beachieved by catalytic hydrotreating. It would be mostadvantageous if pyrolysis and dehalogenation could becarried out simultaneously or successively.

The purpose of this current work was to determine thecomposition of the polymeric material and the amount offiller in different parts of used computers and to study thepossibility of the recovery of some valuable pyrolysis prod-ucts. In a future paper, the upgrading of the pyrolysis oilsby hydrogenation will be presented.

Experimental

Materials

It is always difficult to take a representative sample from aheterogeneous material stream such as WEEE, so a proce-dure to obtain homogenization, size reduction, and goodsampling was applied. WEEE was separated from variouscomputer parts, i.e., (1) monitor, printer, computer, andmouse casings; (2) keyboards; and (3) PCBs, and was shred-ded by cutting and milling to form small, even fragments,generally below 5 or 10mm in diameter.The elemental com-position of these three samples is given in Table 1.

The materials obtained by a systematic disassembly ofWEEE revealed that it is composed of 30% thermoplastic

materials, 15% PCBs and associated components, 23.3%metal, and 31.7% glass.A mixture was prepared by mechan-ical blending of these shredded components in the follow-ing percentages: 60 wt% casings, 30 wt% PCBs, and 10 wt%keyboard materials, which is approximately the proportionfound in a personal computer.

Identification of the polymers in various computer com-ponents was made by successive extraction in methanol,acetone, and benzene followed by IR and 1H-NMR spec-troscopy analyses. The IR spectra of casings and keyboardmaterials are mostly similar and contain bands correspond-ing to ABS or HIPS (2240cm−1 and 770/790cm−1, assignedto the CN and aromatic ring moieties, respectively) withpolycarbonate (PC) bands at 1000–1300cm−1, whereas thespectrum of PCB has peaks in the range 3300–3500cm−1 and1600–1800cm−1, indicating the presence of OH and otheroxygen-containing groups. All computer scrap containshalogenated flame retardants, as evidenced by elementalanalysis and IR spectra (bands at 1000–1200cm−1, 600–750cm−1, and others).

Experiments

Thermogravimetric analysis

The thermogravimetric (TG/DTG, derivative thermogravi-metric) curves were recorded on a Paulik-Paulik-Erdeytype derivatograph (MOM, Budapest, Hungary) under thefollowing operational conditions: heating rate (β) 12°Cmin−

1; temperature range 25°–600°C; film sample mass 50mg, inplatinum crucibles; self-generated atmosphere. Two curveswere recorded for each sample.

Pyrolysis procedure

For the laboratory trials, 200-g batches of ground plastics and thermoset scrap from obsolete computers wereused. The decomposition was performed at about450°–470°C in a batch reactor. The pyrolysis equipment hasbeen described previously.17–19 The volatile decompositionproducts were passed by a cooling/collection system and

101

Table 1. Elemental composition (wt%) of the pyrolyzed samples

Element Casings Keyboards Printed circuit(white + black) boards

(PCBs)

C 63.53 51.24 24.69H 5.11 3.22 1.38N 0.27 1.05 0.85Cl 0.35 2.30 2.05Br 0.8 2.52 4.94S 2.02 4.5 1.97Metals (ash) 3.62 1.82 63.44Volatile 96.38 98.18 36.56

separated into liquids (light fraction), tars (heavy fraction),and gases.

Characterization of pyrolysis products

The gaseous, liquid, and waxy pyrolysis products were characterized by standard methods employed in the petrochemical industry (PIONA, paraffins-isoparaffins-olefins-nephthenes-aromatics analysis), chromatographicmethods adapted for complex mixtures, 1H-NMR, and FT-IR spectroscopy.

The liquid products were analyzed by gas chromatogra-phy with a flame ionization detector (FID) using a Hewlett-Packard model 6890 GC (USA). The column was a HPz-30300 column (length 30m × diameter 0.32mm) coatedwith phenylmethylsiloxane crosslinked at a thickness of 0.50µm. GC-FID was temperature programmed from 40° to280°C at 5°C/min with a final holding time of 30min. Thedata obtained from GC-FID were used to evaluate the sim-ulated distillation curves.20

A quantitative analysis of the liquid products (collectedat the end of the formation of liquid products) was peformed using a gas chromatograph equipped with a flameionization detector (G6800; Yanaco, Japan) to obtain thequantity of hydrocarbons and the carbon number distribu-tion of the liquid products. The temperature program usedfor the analysis of the liquid products was 40°C (hold 15min) and 280°C (rate 5°Cmin−1; hold 37min) and the-column used was 100% methyl silicone (50m × 0.25mm ×0.25µm).

The distribution of bromine-, chlorine-, nitrogen-, andoxygen-containing organic compounds was analyzed by agas chromatograph equipped with an atomic emissiondetector (AED; HP G2350A; column, HP-1; cross-linkedmethyl siloxane; 25m × 0.32m × 0.17µm). 1-bromohexaneand 1,2,4-trichlorobenzene were used as internal standardsfor the quantitative determination of bromine and chlorine,and nitrobenzene or nitrogen and oxygen, for, in the GC-AED analysis. The liquid products were also analyzed by agas chromatograph using a mass selective detector (MSD;HP 5973; column, HP-1; cross-linked methyl siloxane;25m × 0.32mm × 0.17µm; temperature program, 40°C (hold10min) and 300°C (rate 5°Cmin−1, hold for 5min)).The composition of the liquid products was characterizedusing a C-NP gram (C stands for hydrocarbon and NP for normal paraffin).22,23 In a similar way, the organicbromine-, chlorine-, nitrogen-, and oxygen-containing com-pounds were characterized using Br-NP, Cl-NP, N-NP, andO-NP grams.

1H-NMR spectra of liquid products were recorded with aBruker GMBH DPX–400 (Germany) using CDCl3 assolvent. On the basis of 1H-NMR spectra, the hydrocarbontypes of the oils were determined.23 FT-IR spectra were recorded on a FT-IR Bomem MB-104 spectrometer(Canada) with a resolution of 4cm−1, a very thin layer of pyrolysis oil being deposited on KBr tablets.Pyrolytic residue was analyzed by FT-IR and elementalanalysis.

Results and discussion

Thermogravimetry

The pathway of decomposition was first elucidated fromTG/DTG curves, see Fig. 1 and Table 2. It was noted thatthe decomposition of all samples occured in two or threesteps: decomposition starts at about 200°C and is almostcomplete at ∼450°C. PCBs behave differently, they decom-pose at lower temperatures leaving a high quantity ofresidue because of the presence of metals.At a temperatureof ∼450°C, 80–90wt% of the polymeric material present in the original feed had been pyrolyzed. According to the literature,22,23 in the step from 370°C, the formation of phenols and alkyl-aromatics is observed along with carbonization. The particular behavior of PCBs duringdecomposition can be explained by the radicals easilyformed from flame retardants, which are present in greateramounts in scrap PCBs. It is known that most flame retar-

102

Fig. 1. Thermogravimetric/derivative thermogravimetric (TG/DTG)curves for various types of computer scrap. PCB, printed circuit board;T, temperature

dants decompose at 300°C, mainly by the removal of hydro-gen bromide. In contrast, the decomposition of epoxy resinis observed at 450°C. Luda and others24 also observed adecrease in the decomposition temperature of epoxy resinin the presence of flame retardants, which implies that theradicals derived from the retardants induced decompositionof epoxy resin.25

Batch pyrolysis

The product distributions on pyrolysis of used computerparts are given in Table 3. On pyrolysis, casings and keyboards give 50–72wt% pyrolysis oil, 12–18wt% tar, and8–15wt% gas and losses. PCBs, because of their high metalcontent, produce 69.78wt% residue, 22.44wt% liquid, and7.8wt% gas and losses. Pyrolysis liquid from PCBs contains∼20wt% water. Mixed feed material exhibits intermediarybehavior. The pyrolysis of the casings gives the highest oilyield.

As was expected, PCBs decompose at a higher rate thanother computer scrap giving a high volume of gas includingwater vapour (see Fig. 2). This was true even when thepyrolysis temperature was decreased to 350°C (lowercurve).

There were no significant differences in the distillationcurves resulting from different types of plastic computerscrap (see Fig. 3). It can easily be seen that pyrolysis oil dis-tillates a high amount at the same temperature of approxi-mately 135°C. This is because approximately 70% of theliquids consist of aromatic derivatives of nC9–nC11 as indi-cated by GC-MSD analysis.A high quantity of light fractionwas obtained from PCBs, in respect with other cuts.

The variation in the refractive index with the boilingtemperature of the cuts (Fig. 4) was also similar for allresulting oils. The values of the refractive index correspondto liquids containing a high quantity of aromatics, as wasalso indicated by the very low aniline points (<−30°C).

The chromatograms of the pyrolysis oils are similar forcasings and keyboards but they are very different for PCBs(Fig. 5). GC chromatograms show similar compositions forthe pyrolysis oil of casings and keyboards because they aremade from similar starting materials, but PCB oil shows a

103

Table 2. Thermogravimetric data

Sample Ti (°C) Tm (°C) Tf (°C) Wat700(°C) (wt%) Pyrolyzingmass (wt%)

Casings 169 358 434 16 84Keyboards 161 363 436 6 94PCBs 182 268 348 64.8 35.2Mixture 165 373 422 21.2 78.8

Ti, onset temperature; Tm, temperature corresponding to maximum mass loss rate; Tf, final tem-perature; Wat700(°C), mass loss at 700°C

Table 3. Material balance from the pyrolysis experiments

Pyrolyzed sample Pyrolysis oil Coke and Tar Gasa

(wt%) residue (wt%) (wt%) (wt%)

Casings 71.5 8.5 12.5 7.5Keyboards 51.0 12.5 17.5 19.0PCBs 22.4 69.8 – 7.8Mixture 44.0 30.0 12.5 13.5a Evaluated by difference

0 20 40 60 80 100 1200

4

8

12

16

Vol

ume

(L)

Time (min)

CasingsKeyboardMixturePCB

450oC400 oC

350 oC

Fig. 2. Gas volume versus pyrolysis time for various types of computerscrap

80 120 160 200 240

0

20

40

60

80

wt(

%)

Boiling temperature (oC)

CasingsKeyboardMixturePCB

Fig. 3. Distillation curves of the liquid pyrolysis products of varioustypes of computer scrap

very low aromatic peaks at n-C9–C11, but other peaks arepresent at n-C13 and n-C17; therefore it is expected that ahigh amount of heteroatom-containing compounds will bepresent in oil from PCBs (Fig. 6b–e).

O-NP grams are different for each type of pyrolysis oil (Fig. 6b). Casings gave phenol at n-C11 and phenol de-rivatives at n-C12 [CH3PhOH, (CH3)2PhOH] and n-C13[(CH3)3PhOH] (Fig. 8). Similar O-compounds were alsoproduced by keyboard scrap but in different amounts;diphenyl ether and 2-phenyl 1,3-dioxane were identified at n-C15. PCB oil contained the highest amount of O-compounds, consisting mainly of acetone at n-C5, phenol,and phenol derivatives; large peaks were present at n-C5,n-C10, and n-C13 in the O-NP gram. PCBs gave very highamounts of phenol and isopropylphenol in addition to otherO-compounds. Methylbenzofuran and bisisopropylphenolwere also identified and quantified by GC-MSD. Pyrolysisoil from a mixture of scrap contained similar compounds tothose of the oil from casings, but at higher amounts.

Nitrogen compounds were mainly light aliphatic nitrilesat n-C6–n-C8 but phenylbutironitrile was also present at n-C14. The total amount of nitrogen is higher in keyboard oilcompared to pyrolysis oil from casings. The N-NP gram ofmixed scrap is close to the average of the NP-grams of itscomponents. No nitrogen was found in PCB oil (Fig. 6d).

Casing and keyboard pyrolysis oils contain low amountsof halogen (chlorine and bromine) compounds whose peaksin chromatograms are located at n-C5, n-C13–n-C14, and n-C16 for Cl and at n-C5, n-C12, and n-C15 for Br. Halogens wereidentified both in aliphatic compounds (chloromethane and bromomethane at n-C5) and in aromatic compounds(chlorophenol and bromophenol at n-C11 and n-C12). PCBpyrolysis oil had a higher concentration of halogens and a

104

80 120 160 200 2401.42

1.44

1.46

1.48

1.50

1.52

1.54

CasingsKeyboardMixturePCB

Ref

ract

ive

ind

ex,n

D20

Boiling temperature (°C)

Fig. 4. Refractive indices versus boiling temperatures of the cuts of thepyrolysis liquids resulting from various types of computer scrap

Fig. 5. Chromatograms of the pyrolysis oil resulting from different types of computer scrap

totally different composition. This was expected, consider-ing that epoxy resin is mainly used for PCBs, whereas ABSand HIPS are used for the casings of computer components.The differences between the different fractions of com-puter scrap are better observed from GC-MSD analysis(Figs. 6–8).

The C-NP grams are mostly similar for the pyrolysis oilsof casings, keyboards, and the mixture. Casings and key-boards give mainly aromatic derivatives, especially styreneand ethylbenzene and then toluene, cumene, and α-methyl-styrene (Fig. 7), corresponding to peaks in the n-C9–n-C11

range in the C-NP gram (Fig. 6a) and other small peaks atn-C14, n-C18–n-C19, and n-C22. In the same region, PCBs give

105

0

5

10

15

20

25

30

35

40

5 10 15 20 25Carbon number

C,a

rea

%

Casing

Keyboard

PCB

Mixture

C-NP

(a)

0

1000

2000

3000

4000

5000

5 10 15 20 25Carbon number

Oam

ou

nt

,ng

/ml

Casing - 1416 ng/ml

Keyboard - 2876 ng/ml

PCB - 52112 ng/ml

Mixture - 5496 ng/ml

O-NP

17150 22128

(b)

0

10

20

30

40

50

60

5 10 15 20 25Carbon number

Cla

mo

unt,

ng/

ml

Casing - 39.6 ng/ml

Keyboard - 44.3 ng/ml

PCB - 212.5 ng/ml

Mixture - 119.5 ng/ml

Cl-NP

(c)

0

2000

4000

6000

8000

10000

12000

5 6 7 8 9 10 11 12 13 14 15 16Carbon number

Nam

ount

,ng

/ml

Casing - 4979 ng/ml

Keyboard - 15819 ng/ml

Mixture - 7909 ng/ml

N-NP

(d)

0

200

400

600

800

1000

5 10 15 20 25Carbon number

Br

amo

un

t,n

g/m

l

Casing - 106.8 ng/ml

Keyboard - 199.6 ng/ml

PCB - 3338.1 ng/ml

Mixture - 346.6 ng/ml

Br-NP

(e)

Fig. 6. Normal paraffin (NP) grams of the pyrolysis oil from various types of computer scrap: a C-NP gram, b O-NP gram, c N-NP gram, d Cl-NP gram, and e Br-NP gram

different distribution, indicated by many peaks in Cl-NPand Br-NP grams (Fig. 6c,e). No sulfur-containing com-pounds were identified in the pyrolysis oils. The nitrogen-containing heterocyclic compounds (methylpyridine atn-C11) formed were not identified.

The 1H-NMR spectra (Fig. 9) are mostly similar for the pyrolysis oils from casings, keyboards, and the mixture;however, the signals corresponding to unsaturated structures (3–5.5ppm) are much stronger for pyrolysis oilfrom keyboards than the signals in the spectrum of oil

from casings, whereas those of oil from the mixture hadsignals of intermediate strength. The distribution of hydrocarbon types in pyrolysis oils are mostly similar, con-sisting of aromatics (60–65vol%) and olefins (33–37vol%)(Table 4).

FT-IR spectra are sensitive to composition differences inthe pyrolysis products. The FT-IR spectra of the pyrolysisoils resulting from various types of computer scrap are dif-ferent in the “fingerprint” region (Fig. 10). In the IR spec-trum of PCBs (Fig. 10a), the contributions of aromatic

106

0

5

10

15

20

25

30

35

GC

-MS

D a

rea,

%

E t h y l b e n z e n e

S t y r e n e

T o l u e n e

C u m e n e

P r o p y l b e n z e n e

B e n z e n e X y l e n e

alpha-Methylstyrene

Casi ng Ke yb oa rd

Mi xt ur e PC B

Ca si ng

Ke yb oa rd

Mi xt ur e

PC B

Fig. 7. The proportion of themain aromatics found in various types of computer scrapGC-MSD, gas chromatography-mass spectroscopy detection

0

0. 5

1

1. 5

2

2. 5

3

GC

-M S

D a

r ea

,%

P h e n o l

B r o m o p h e n o l

2 M e t h y l p h e n o l

M e t h y l b e n z o f u r a n

D i m e t h y l p h e n o l

E t h y l p h e n o l

P r o p y l p h e n o l

I s o p r o p y l p h e n o l

Diphenylether

Dibenzofuran

B i s i s o p r o p y l p h e n o l

Ca si ng Ke yb oa rd

Mi xt ur e PC B

Ca si ng

Ke yb oa rd

Mi xt ur e

PC B

36 .0 9 1 6. 99 Fig. 8. The proportion of the phenoland main phenol derivatives foundin pyrolysis oil of various types ofcomputer scrap

Table 4. Type of hydrocarbonated content (vol%) of the pyrolysis oils evaluated from 1H-NMRspectra

Sample Aromatics Paraffins Olefins H/C Isoparaffin RONindex

Casings 66.54 0 33.46 0.97 0.02 87.46Keyboards 63.81 0 36.19 1.08 0.01 87.10PCBs 61.5 0 38.5 0.98 0.01Mixture 62.75 0 37.25 0.99 0.01 87.02

H/C, hydrogen/carbon; RON, research octane number

structures (1563, 1472, and 868–778cm−1), of phenolic struc-tures (3477 and 1172–1159cm−1), and of geminal –CH3

(1390–1362cm−1) are evident. The presence of brominemainly in PCBs is demonstrated by the shift of the aromaticring stretching toward the lowest frequencies of theirrespective allowed range.24 It is noteworthy that the bandfrom 1140 to 1350cm−1 is different for each pyrolysis oil.These bands can be assigned to the substituted arenes,which probably differ in terms of the substituents’ positions.The IR spectrum of the oil resulting from mixed scrap fea-

tured bands of all the components, but the maxima of thebands are shifted to large wave numbers; therefore somecomponents interact.

Residue

The oxygen, nitrogen, halogens, and sulfur were concen-trated in the solid residues, as established by their FT-IRspectra and elemental analysis (Table 5). These results are

similar to those obtained by other authors. Agnes Friese6 inthe Watech A/S process found that halogenated flame retar-dants are cracked during pyrolysis and most of the halogensremain in the coke. From the FT-IR spectra, it was estab-lished that the C-X bonds are prevalently aromatic(1000–1200cm−1) in the residue from PCBs and mixed scrapand aliphatic (600–700cm−1) in the residue from casings andkeyboards. The charring of the residue was indicated by theincreased level of aromatization (1500–1600cm−1).

Conclusions

Pyrolysis experiments were carried out to recover valuableproducts, energy, or both from thermoplastic and thermosetfractions of computer waste. A temperature range of430°–460°C was found to be optimal for the pyrolysis exper-iments. This temperature range yielded a mixture of lighthydrocarbons. The liquid phase, consisting mainly of aro-

107

Fig. 9. 1H-NMR (nuclear magnetic resonance) spectroscopy spectra ofthe liquid pyrolysis products resulting from various types of computerscrap

2400 2000 1600 1200

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Fig. 10a–c. FT-IR (infrared spectroscopy) spectra of the liquid pyrol-ysis products resulting from various types of computer scrap. a–c Showdifferent parts of the spectrum

Table 5. Elemental analysis of the pyrolysis residue of the varioustypes of computer scrap

Element Casings Keyboards PCBs Mixture(wt%) (wt%) (wt%) (wt%)

C 74.43 78.57 61.09 64.7H 4.4 3.05 2.01 2.35N 6.24 4.08 0.61 2.55Cl 2.15 1.84 3.64 2.14Br 4.86 4.15 8.41 4.27S 2.51 4.52 0.29 3.64

matics and phenol derivatives, varied from 20 to 60wt%,depending on the computer component undergoing pyro-lysis. Various halogen-containing compounds originating inthe flame retardant employed in these electronic deviceswere also found. Their concentration in pyrolysis oil was inthe range 40–210ng/ml for chlorine and 100–3300ng/ml forbromine. PCBs yielded considerably higher amounts ofhalogens compared to casings and keyboards.Therefore, theelimination of hazardous toxic compounds, mainly thosecontaining bromine, is necessary before safely using thepyrolysis oils as fuels or in refinery or petrochemical indus-try flows. This will be the subject of another article.

Acknowledgments This work was carried out in the framework of aninteracademic exchange between the Romanian and Turkish Acade-mies of Sciences. We are grateful for their support and also to profes-sor Sakata at Okayama University for his help in performing theGC-MSD experiments.

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