Pyrolysis study of a PVDC and HIPS-Br containing mixed waste

plastic stream: Effect of the poly(ethylene terephthalate)

Thallada Bhaskar, Maki Tanabe, Akinori Muto, Yusaku Sakata *

Department of Applied Chemistry, Faculty of Engineering, Okayama University, 3-1-1 Tsushima Naka, 700-8530 Okayama, Japan

Received 12 July 2005; accepted 21 January 2006

Available online 3 March 2006

Abstract

Pyrolysis of poly(vinylidene chloride) (PVDC), brominated flame retardant containing high impact polystyrene (HIPS-Br), poly(ethylene)

(PE), poly(propylene) (PP), poly(styrene) (PS) mixed were performed in the presence and absence of poly(ethylene terephthalate) (PET) under

atmospheric pressure at 430 8C using a semi-batch operation. We attempted the dehalogenation (Cl, Br) of chlorinated and brominated liquid

hydrocarbons using iron oxide and calcium hydroxide based carbon composites for the production of halogen free liquid hydrocarbons. The

presence of PET in the plastics mixture of PP/PE/PS/PVDC/HIPS-Br affected significantly the formation of pyrolysis products and the pyrolysis

behavior of plastic mixture. We observed the following effects of PET on the pyrolysis of PP/PE/PS/PVCD/HIPS-Br mixed plastic pyrolysis: (i)

The yield of liquid product was decreased and the formation of gaseous products increased during the thermal decomposition, (ii) the waxy residue

was observed in addition to the solid carbon residue and (iii) use of calcium hydroxide carbon composite (CaH–C) removed the major portion of

chlorine and bromine content from the liquid products from PP/PE/PS/PVDC/HIPS-Br pyrolysis, however in the presence of PET, the combination

of calcium hydroxide carbon composite (CaH–C) and iron oxide carbon composites could not dehalogenate the liquid products effectively. X-ray

diffraction analysis reveals the presence of antimony compounds in carbon and wax residues.

# 2006 Elsevier B.V. All rights reserved.

Keywords: PVDC; HIPS-Br; Pyrolysis; PET; Feedstock recycling; Dehalogenation

www.elsevier.com/locate/jaap

J. Anal. Appl. Pyrolysis 77 (2006) 68–74

1. Introduction

The conversion of waste plastics into petrochemical feedstock

represents a sustainable way for the recovery of the organic

content from polymeric waste and also preserves valuable

petroleum resources, in addition to protecting the environment

[1,2]. The worlds limited reserves of coal, crude oil and natural

gas places a great pressure on mankind to reduce, and recycle the

existing non-renewable materials and reduce our reliance on

them. Among the various recycling methods for the waste

plastics, the feedstock recycling has been found to be a promising

method. Pyrolysis of waste plastics is favored because of the high

rates of conversion into oil, which can be used as fuel or feedstock

in refinery. Recycling by pyrolysis has high potential for

heterogeneous waste plastic materials, as the separation is not

economical. There has been plethora of research work on the

pyrolysis of plastics and utilization of pyrolysis products for

* Corresponding author. Tel.: +81 86 251 8081; fax: +81 86 251 8082.

E-mail address: yssakata@cc.okayama-u.ac.jp (Y. Sakata).

0165-2370/$ – see front matter # 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.jaap.2006.01.005

various applications [3–8] including the monographs on the

feedstock recycling of plastics [9]. Municipal waste plastic is a

mixture of non-halogenated and halogenated thermoplastics

such as polyethylene, polypropylene, polystyrene, poly(vinyl

chloride), and PET. It is known that the pyrolysis of mixed

plastics containing PVC or PVDC produces inorganic and

subsequently organic chlorine compounds during the initial

stages of pyrolysis process [10,11].

The disposal of halogenated mixed waste plastics is serious

environmental problem [12,13]. Hornung et al. [12] reported

the dehalogenation of brominated organic compounds from the

pyrolysis of brominated flame retardant plastics with the

polypropylene as a reductive agent. The separation of

brominated additives from inert and valuable materials in

electronic scrap can be done by an established pyrolysis

procedure called Haloclean1 [13]. The main characteristics of

this process are good mixing of the electronic scrap by a

rotating conveyor screw, better heat transfer through stainless

steel balls which are added to the feed and low residence time

for gaseous products because of a high nitrogen flow which

leaves several sinter metal plates of the screw. In any case, the

T. Bhaskar et al. / J. Anal. Appl. Pyrolysis 77 (2006) 68–74 69

brominated gases evolving during this two-step pyrolysis need

to be detoxified, in particular as direct scavenging with bases

during the process failed despite showing good potential in

fundamental research [14].

The pyrolysis of brominated flame retardant containing high

impact polystyrene (HIPS-Br) mixed plastics and dehalogena-

tion of liquid products with iron oxide carbon composite (Fe–C)

was reported earlier [15]. Studies on Hydrothermal treatment of

HIPS-Br and recovery of halogen free plastics were reported

[16]. The studies on the pyrolysis of HIPS-Br/PVDC and mixed

with other common polyolefins (PE, PP, and PS) have not been

found in the literature. The effects of PET on pyrolysis of PP/

PE/PS/PVC/HIPS-Br and dehalogenation of liquid products by

calcium carbonate carbon composite (Ca–C) were reported in

our earlier publication [17]. The calcium hydroxide carbon

composite (CaH–C) in the present investigation is economic-

ally cheaper (low cost) than Ca–C. The highly expensive and

conventional noble metal hydrodehalogenation catalysts are not

advisable for the dehalogenation of halogenated waste plastics

pyrolysis. In the present investigation, we report the pyrolysis

of PP/PE/PS/PVDC/HIPS-Br and PP/PE/PS/PVDC/HIPS-Br/

PET under atmospheric pressure at 430 8C. The distribution of

chlorine and bromine content in the degradation products,

effect of PET in pyrolysis mixture, dehalogenation of liquid

products by calcium hydroxide (CaH–C), and iron oxide (Fe–

C) carbon composites were investigated.

2. Experimental

2.1. Materials

The high-density polyethylene (PE) was obtained from

Mitsui Chemical Co. Ltd., Japan; polypropylene (PP) from Ube

Fig. 1. Schematic experimental se

Chemical Industries Co. Ltd., Japan; polystyrene (PS) from

Asahi Kasei Industries Co., Ltd., Japan; poly(vinylidene

chloride) (PVDC) from Geon Chemical Co. Ltd. (Cl content

in PVDC: 73.2 wt.%). Commercially available high impact

polystyrene (HIPS) containing brominated (Br: 10.8 wt.%)

flame retardant was used in the present investigation. The

synergist Sb2O3 was 5 wt.%, the flame retardant was

decabromodiphenyl oxide (DDO). Poly(ethylene terephthalate)

(PET) was obtained from Eastman Kodak Co., Ltd. The grain

sizes of PP, PE, PS and PVC were about 3 mm � 2 mm. The

mixture of PP, PE, and PS was abbreviated as 3P (PE (3 g)/PP

(3 g)/PS (2 g) and used in the manuscript.

2.2. Preparation of Fe–C and CaH–C

About 90 wt.% of a-FeOOH was mixed with 10 wt.%

phenol resin (commercial name: Bell pearl S890, average

molecular weight: 10,000, monomer: less than 50 ppm) by

mechanical kneading. The obtained catalyst Fe3O4–C had a

surface area (BET) of 83 m2 g�1 and pore volume of

0.44 ml g�1. It is designated as Fe–C (iron oxide carbon

composite) and contained about 95 wt.% of Fe3O4 and 5 wt.%

carbon. Powder X-ray diffraction analysis confirmed the

presence of Fe3O4 phase in Fe3O4–C. In a similar way

CaH–C was prepared with ca. 65 wt.% of Ca (OH)2 and the

remaining was carbon. The Fe–C and CaH–C was coopera-

tively developed with Toda Kogyo Co., Ltd., Japan.

2.3. Pyrolysis and analysis procedure

Pyrolysis of 3P (PE (3 g)/PP (3 g)/PS (2 g))/PVDC (1 g)/

HIPS-Br (1 g) and 3P (PE (2 g)/PP (3 g)/PS (2 g))/PVDC (1 g)/

HIPS-Br (1 g)/PET (1 g) was performed in a glass reactor

t-up for the pyrolysis studies.

T. Bhaskar et al. / J. Anal. Appl. Pyrolysis 77 (2006) 68–7470

Table 1

Yields and properties of liquid products from pyrolysis of 3P/PVDC/HIPS-Br and mixed with PET at 430 8C

Sample Mode Yield of degradation products (wt.%) Liquid products

Liquid (L) Gas (G)a Residue [R] Cnpb Density (g/cm3)

Carbon Wax

3P/PVDC/HIPS-Br Thermal 65 24 11 0 12.3 0.82

CaH–C 2 g 62 27 11 0 11.0 0.80

3P/PVDC/HIPS-Br/PET Thermal 52 29 10 9 11.1 0.83

CaH–C 2 g 52 29 9 10 10.6 0.80

CaH–C 1 g + FeC 1 g 51 30 11 8 10.8 0.81

a G = 100 � (L + R).b Average carbon number of liquid product.

Fig. 2. Cumulative volume of liquid products obtained from pyrolysis of 3P/

PVDC/HIPS-Br and 3P/PVDC/HIPS-Br/PET by batch operation at 430 8C.

(length: 350 mm; id 30 mm) under atmospheric pressure by

batch operation with identical experimental conditions (Fig. 1).

Briefly, 10 g of mixed plastics was loaded into the reactor for

thermal degradation, in another reactor quartz grains (thermal)

were charged and kept at 350 8C. The quartz grains were used

to maintain the similar space velocities in the absence of CaH–

C or Fe–C. In a typical run, the reactor was purged with

nitrogen gas (purity 99.99%) at a flow rate of 30 ml min�1 and

kept the flow till the end of the experiment. The reactor

temperature was increased to the degradation temperature

(430 8C) at a heating rate of 15 8C min�1. A schematic

experimental set-up (Fig. 1) for the pyrolysis of mixed plastics

and the other detailed analysis procedure can be found in

elsewhere [7,18,24]. The amount of Cl and Br content

(condensable gaseous products such as HCl, HBr) in water

trap was analyzed using an ion chromatograph (DIONEX, DX-

120 Ion Chromatograph) and designated as gas (HBr) in

Tables 2 and 3. The halogenated hydrocarbons in the (non-

condensable) gaseous products were not analyzed. The

quantitative determination of chlorine and bromine in residue

was measured using combustion flask and then subjected to ion

chromatograph.

The composition of the liquid products was characterized

using C–NP grams (C stands for carbon and NP from normal

paraffin), Cl–NP gram (Cl stands for chlorine) and Br–NP gram

(Br stands for bromine). The curves were obtained by plotting

the weight percent of Cl, which was in the liquid products

against the carbon number of the normal paraffin determined by

comparing the retention times from GC analysis using a non-

polar column. In briefly, the NP gram is a carbon number

distribution of hydrocarbons derived from the gas chromato-

gram based on boiling points of a series of normal paraffin’s.

Further details on the NP gram can be found elsewhere [19].

Powder X-ray diffraction analysis of carbon and wax residue

products was carried out by X-ray diffractometer (RINT2500/

RIGAKU).

3. Results and discussion

The pyrolysis of 3P/PVDC/HIPS-Br and 3P/PVDC/HIPS-

Br/PET was performed at 430 8C under atmospheric pressure.

The calcium hydroxide carbon composite (CaH–C) and iron

oxide carbon composite (Fe–C) were used for the dehalogena-

tion (Cl, Br) of halogenated liquid hydrocarbons by vapor phase

contact. The pyrolysis products were classified into three

groups: gas, liquid, and solid residue. The solid residue in the

bottom of the reactor (at the end of reaction) was designated as

carbon residue and the residue at the top of the reactor (coated

on the walls of the reactor) designated as waxy residue. Table 1

shows the yield of degradation products and average carbon

number (Cnp), density of liquid products. The pyrolysis of 3P/

PVDC/HIPS-Br yielded the liquid products ca. 65 wt.%, the

presence of PET decreased the yield of liquid products to

52 wt.%. There are no significant differences in the density of

liquid products obtained in all the runs (Table 1). The average

carbon number (Cnp) of liquid products were found to decrease

with the addition of PET, and the decrease of Cnp in the catalytic

runs is expected due to the cracking of high molecular weight

hydrocarbons. The presence of PET with 3P/PVDC/HIPS-Br

produced the waxy compounds ca 10 wt.%. The gaseous

products were comparatively lower from 3P/PVDC/HIPS-Br

than 3P/PVDC/HIPS-Br/PET mixed plastics. The cumulative

volume of liquid products obtained during the 3P/PVDC/HIPS-

Br than 3P/PVDC/HIPS-Br/PET was shown in Fig. 2. The

presence of PET in the mixture decreased the total yield

(Table 1) and also the rate of formation of liquid products from

the reactor (Fig. 2). The collection of liquid products (rate of

T. Bhaskar et al. / J. Anal. Appl. Pyrolysis 77 (2006) 68–74 71

Table 2

Distribution of chlorine content in the pyrolysis products of 3P/PVDC/HIPS-Br and mixed with PET at 430 8C

Sample Mode Cl conc. (ppm) Cl amount (mg)

Oil Gas (HCl) Oil Gas (HCl) Residue [R]

Carbon Wax

3P/PVDC/HIPS-Br Thermal 3540 6440 23 515 42 –

CaH–C 2 g 44 5 0 0.4 35 –

3P/PVDC/HIPS-Br/PET Thermal 3820 7700 20 616 23 6

CaH–C 2 g 450 6 2 0.4 29 5

CaH–C 1 g + Fe–C 1 g 280 36 1 3 36 4

formation) was earlier from 3P/PVDC/HIPS-Br than 3P/

PVDC/HIPS-Br/PET.

The distributions of chlorine and bromine in various

pyrolysis products from 3P/PVDC/HIPS-Br and 3P/PVDC/

HIPS-Br/PET are summarized in Tables 2 and 3, respectively.

The dehalogenation (Cl, Br) was performed by using CaH–C

with 3P/PVDC/HIPS-Br and 3P/PVDC/HIPS-Br/PET pyr-

olysis. In addition, the mixture of CaH–C and Fe–C was also

used for the dehalogenation (Cl, Br) of liquid products from

3P/PVDC/HIPS-Br/PET. The chlorine and bromine concen-

tration in the pyrolysis of 3P/PVDC/HIPS-Br liquid products

(thermal) was 3540 and 730 ppm, respectively, and the use of

CaH–C completely removed the bromine and more than 98%

of chlorine removed (3540 to 40 ppm) from the liquid

products. The addition of PET to 3P/PVDC/HIPS-Br

produced (thermal) the liquids with 3820 ppm of chlorine

and 1410 ppm of bromine. The bromine concentration was

doubled and also small increase in chlorine concentration was

observed in liquid products with the addition of PET to 3P/

PVDC/HIPS-Br. The CaH–C (2 g) in 3P/PVDC/PET/HIPS-

Br pyrolysis decreased the chlorine to 450 ppm and bromine

concentration to 490 ppm. It is known from our earlier reports

that the silica supported and carbon composites of iron oxides

effectively worked as a dehalogenation catalysts and calcium

based carbon composites worked as sorbents [20,21]. In the

3P/PVDC/HIPS-Br /PET pyrolysis, CaH–C (1 g) and Fe–C

(1 g) used for the dehalogenation (Cl, Br) of liquid products.

Tables 1 and 2 show that use of CaH–C + Fe–C could

decrease the chlorine and bromine than the use of CaH–C

alone; but still contains the chlorine and bromine around

200 ppm.

Table 3

Distribution of bromine content in the pyrolysis products of 3P/PVDC/HIPS-Br an

Sample Mode Br conc. (ppm)

Oil G

3P/PVDC/HIPS-Br Thermal 730 32

Ca–C 2 g n.d.

3P/PVDC/HIPS-Br/PET Thermal 1410 24

Ca–C 2 g 490

Ca–C1g + Fe–C1g 190 1

n.d.: not detected

The effect of PET on the 3P/PVC [18] and 3P/PVC/HIPS-Br

[22], and 3P/PVDC [23] showed that the formation the

halogenated hydrocarbons are higher than in the absence of

PET. The thermal degradation of 3P/PVDC [24] produced the

liquid products with chlorinated hydrocarbons ca. 250 ppm and

the presence of presence of HIPS-Br with 3P/PVDC produced

the liquid products with ca. 3540 ppm of chlorine compounds

(Table 2). The formation of chlorinated hydrocarbons in liquid

products is higher from 3P/PVDC/HIPS-Br (10 wt.% PVDC)

than from 3P/PVDC (10 wt.% PVDC) even though the PVDC

content is same. The formation of SbBr3 was observed with 3P/

PVC/HIPS-Br and there is no SbBr3 with 3P/PVC/PET/HIPS-

Br [17]. However, the formation of SbBr3 in 3P/PVDC/HIPS-

Br liquid products was trace and could not find any SbBr3 in 3P/

PVDC/HIPS-Br/PET liquid products. The quantitative analysis

of halogenated hydrocarbons in liquid products was performed

by GC–AED. The qualitative analyses of the liquid products for

halogenated hydrocarbons (Cl, Br) were performed by GC–

MSD and the compounds are similar to the 3P/PVC/PET/HIPS-

Br [17].

The liquid products were analyzed by gas chromatography

with flame ionization detector (GC–FID) for the volatility

(boiling point) distribution of hydrocarbons in the liquid

products and the results are presented in the form of Normal

Paraffin gram (C–NP gram) proposed by Murata et al [19].

Fig. 3 illustrates the C–NP gram of the liquid products

obtained by analyzing their gas chromatogram. The carbon

numbers in the abscissa of the NP-gram are equivalent to

retention values (boiling point) of the corresponding normal

paraffin and the ordinate shows the weight percent of the

corresponding hydrocarbons [g(Cn)/g(Oil) � 100 wt.%]. The

d mixed with PET at 430 8C

Br amount (mg)

as (HBr) Oil Gas (HBr) Residue [R]

Carbon Wax

0 5 25 13 –

2 0 0.2 12 –

0 7 19 12 2

2 3 0.2 10 3

4 1 1 14 9

T. Bhaskar et al. / J. Anal. Appl. Pyrolysis 77 (2006) 68–7472

Fig. 5. Br–NP gram of liquid products obtained from pyrolysis of 3P/PVDC/

HIPS-Br and 3P/PVDC/HIPS-Br/PET by batch operation at 430 8C.

Fig. 3. C–NP gram of liquid products obtained from pyrolysis of 3P/PVDC/

HIPS-Br and 3P/PVDC/HIPS-Br/PET by batch operation at 430 8C.

wide range of hydrocarbons (low to high boiling point)

composed of linear olefins and paraffins are present in all the

runs and there is no significant differences in the boiling point

distribution of liquid products in all the runs (with and without

CaH–C and Fa–C). The hydrocarbons such as styrene

monomer, styrene dimmer, styrene trimer, a-methyl styrene,

toluene from PS; propylene dimer, propylene trimer etc. from

PP could found in the C–NP gram.

Similar to the C–NP gram, the carbon number distribution of

chlorinated or brominated hydrocarbons [weight percent of

chlorine or bromine = g(Cl or Br)/g(Oil) � 100 wt.%] in the

liquid product was prepared from the GC–AED chromatogram

and designated as Cl–NP gram shown in Fig. 4 and Br–NP gram

shown in Fig. 5. Fig. 4 shows that the major portion of

chlorinated hydrocarbons in 3P/PVDC/HIPS-Br and 3P/PVDC/

PET/HIPS-Br are same and formation of new Cl-compounds in

the presence of PET. The main chlorine containing hydro-

carbons are in the boiling point range of n-C6, n-C8, n-C10 and

n-C19 and chlorinated hydrocarbons exists in the carbon

number less than n-C20 of normal paraffin boiling point. Fig. 5

shows the effect of PET on the high concentration of

brominated hydrocarbons in the liquid products. The drastic

Fig. 4. Cl–NP gram of liquid products obtained from pyrolysis of 3P/PVDC/

HIPS-Br and 3P/PVDC/HIPS-Br/PET by batch operation at 430 8C.

increase of brominated hydrocarbons at n-C9 and n-C19 are

significant with the addition of PET. The brominated

hydrocarbons observed till C21. The main bromine containing

hydrocarbons are in the boiling point range of n-C6, n-C9, n-

C11, n-C16, and n-C19.

Powder X-ray diffraction (XRD) analysis of carbon

residue from 3P/PVDC/HIPS-Br and carbon residue and

wax residue from 3P/PVDC/HIPS-Br/PET pyrolysis (ther-

mal) were performed (Fig. 6(a)–(c)). The XRD analysis of

carbon residue 6(a) from 3P/PVDC/HIPS-Br showed the

presence of a small and single peak due to Sb2O3 but the

carbon residue from 3P/PVDC/HIPS-Br/PET 6(b) showed the

presence of various antimony oxides and also peak due to

antimony bromine oxide. The wax residue of 3P/PVDC/

HIPS-Br/PET run 6(c) showed the crystalline nature and

presence of SbBr3. The XRD information revealed that the

presence of bromine in the carbon residue was found in the

absence and presence of PET in the mixed plastics. However,

the phase of oxides was difference in each case and the

quantity of bromine content was relatively less with 3P/

PVDC/HIPS-Br carbon residue than 3P/PVDC/HIPS-Br/PET

carbon residue. In addition, bromine was concentrated in the

wax residue with the presence of PET and there are no waxy

products in the absence of PET. There is no indication of the

presence of chlorine in waxy or carbon residue from the XRD

peaks.

The yield of liquid products were higher and gaseous

products were lower from 3P/PVC/HIPS-Br and/with PET than

3P/PVDC/HIPS-Br and/with PET. The quantity of PVC and

PVDC were same (1 g) but the chlorine concentration in the 3P/

PVC/HIPS-Br and/with PET liquid products were lower than

3P/PVDC/HIPS-Br and/with PET liquid products. The HIPS-

Br was 0.5 g with 3P/PVC/HIPS-Br and/with PET and HIPS-Br

was 1 g with 3P/PVDC/HIPS-Br and/with PET, but the bromine

concentration was very high with 3P/PVC/HIPS-Br and/with

PET liquid products than 3P/PVDC/HIPS-Br and/with PET

liquid products. The discussions on other 3P/PVC/HIPS-Br

and/with PET pyrolysis products can be found in elsewhere

[17]. The detailed mechanistic investigations and synergistic

T. Bhaskar et al. / J. Anal. Appl. Pyrolysis 77 (2006) 68–74 73

Fig. 6. (a) X-ray diffraction analysis of carbon residue from 3P/PVDC/HIPS-Br pyrolysis at 430 8C; (b) X-ray diffraction analysis of carbon residue from 3P/PVDC/

HIPS-Br/PET pyrolysis at 430 8C; (c) X-ray diffraction analysis of wax residue from 3P/PVDC/HIPS-Br/PET pyrolysis at 430 8C.

formations for the high chlorine and lower brominated

hydrocarbons in liquid products are in progress.

4. Conclusions

The pyrolysis of 3P/PVDC/HIPS-Br and 3P/PVDC/HIPS-

Br/PET was performed at 430 8C at the atmospheric pressure

and analysed the distribution of halogen (chlorine and

bromine) content in degradation products. Calcium hydroxide

carbon composite (CaH–C) and iron oxide carbon composite

was applied for the dehalogenation of liquid products. The

yield of liquid products was decreased and yield of gaseous

products was increased with the addition of PET. The

concentration of halogenated hydrocarbons (Cl, Br) was

increased in the presence of PET and formation of waxy

compounds was observed. The dehalogenation of hydro-

carbons was not complete with the CaH–C (1 or 2 g) alone or

with the combination of Fe–C (1 g) in the presence of PET

with 3P/PVDC/HIPS-Br. The traces of SbBr3 were found in

the liquid products of 3P/PVDC/PET/HIPS-Br and could not

find with the presence of PET. It can be concluded that the

presence of small quantities of PET can produce the higher

concentration of halogenated hydrocarbons in the liquid

products.

Acknowledgements

The authors thank Ministry of Education, Culture, Sports,

Science and Technology, Japan and Centre of Excellence

Program for the 21st Century—Strategic Solid Waste Manage-

ment for Sustainable Society at Okayama University for

financial support to carryout the research work.

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