The 5th ISFR (October 11-14, 2009, Chengdu, China)

EFFECT OF POLYOLEFINS ON THE PYROLYSIS OFBROMINE AND CHLORINE CONTAINING MIXEDWASTE PLASTICS FOR PRODUCTIONOF
HALOGEN FREE LIQUID PRODUCTS
Yusaku Sakata*1, Thallada Bhaskar2, Nona Merry M. Mitan,1 William J. Hall,3
Akinori Muto1, P. T. Williams31

Department of Applied Chemistry, Okayama University, 3-1-1 Tsushima Naka,
Okayama 700-8530, Japan.
E-mail: yssakata@cc.okayama-u.ac.jp
2Process, Reaction Engineering, Corrosion, Biomass Conversion Area,Indian Institute of Petroleum, Dehradun 248 005, India.
E-mail: tbhaskar@iip.res.in
3
Energy and Resources Research Institute, University of Leeds,Leeds, LS2 9JT, United Kingdom.

Abstract: The pyrolysis of non-halogenated polyolefins for the production of chemical
feedstock/fuels is well known process today. However, the pyrolysis of polyolefins mixed
with the halogenated (chlorinated and brominated) plastics produces the various halogenated(organic and inorganic) hydrocarbons in pyrolysis products and removal of such halogen
compounds is possible by use of suitable catalysts/sorbents. The pyrolysis of polyvinyl
chloride and high impact polystyrene with brominated flame retardant mixed plastics werestudied and we showed that the utilization of catalysts/sorbents can be minimized or avoided
by selection of suitable process conditions and parameters.
1. Introduction
Plastics have characteristic properties such as durability, lightness, versatility forenormous number of valuable application in the modern society in domestic, industrialapplications and have become indispensable in our daily lives. The enormous amount ofmixed waste plastics is coming from various sectors including electrical and electronic
appliances. Among the various available treatment methods for the treatment of mixed waste
plastics, feedstock recycling has more advantageous. Feedstock recycling is a decompositionof plastics waste by means of physical-chemical treatment for obtaining the chemical
feedstock. We have shown various catalysts/sorbents and reactions conditions for theproduction of chlorine free hydrocarbons from the PVC mixed waste plastics by- 10 -

PARTⅠ PYROLYSIS
catalytic/sorptive and/or non-catalytic methods. In recent years, much attention has been paid
to the possibility of recycling plastics by pyrolysis and the introduction of the Waste
Electronic and Electrical Equipment (WEEE) Directiv by the European Commission has
inspired an increasing amount of research into using pyrolysis to recycle WEEE plastics.
Unfortunately, WEEE plastics often contain toxic brominated flame retardants, which makes
them particularly problematic to recycle.The waste plastics such as brominated high impact
polystyrene (HIPS-Br) from the electric and electronic appliances along with the otherpolyolefins poses various problems than the chlorinated plastics due to the presence ofinorganic compounds as synergist (Sb2O3 etc.,) and brominated flame retardants. In thepresent investigation, we showed the non-catalytic two step pyrolysis process for theproduction of halogen free/less hydrocarbons as a major liquid product.
2. Experimental
High impact polystyrene (HIPS) with several types of flame retardant and synergist waschosen as it is one of the most commonly used plastics in electrical and electronic equipment.
The polyvinyl chloride (PVC) has been choosen as the chlorinated plastics along with theother polyolefins such as polyethylene (PE), polypropylene (PP), polystyrene (PS) and isusually flame retarded by aryl bromines with antimony trioxide as a synergist. The HIPS
contained either decabromodiphenyl oxide or decabromodiphenyl ethane flame retardant andeither 5% or 0% antimony trioxide. The schematic experimental setup for the pyrolysis of
mixed plastics has been given in fig.1. Decabromo diphenyl ether with antimony trioxideshown as DDO-Sb(5) and Decabromo diphenyl ether without antimony trioxide shown as
DDO-Sb(0). The detailed information on the samples and pyrolysis procedure has been given
elsewhere [1-3].

Fig. 1 Schematic experimental setup for the pyrolysis of mixed plastics- 11 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
3. Results and Discussion
3.1 Pyrolysis of PVC/PVDC mixed plastics
100o

Heating rate 5 C/min

Weight loss , wt%

8060

PVCPS PP

PE

500

550

40

200
250

300

350

400

450

600

o

Temperature , C

Fig.2 TGA Profiles of PVC, PP, PE, and PS
TGA studies showed (Fig. 2) the decomposition temperature of PVC and they are much
lower than for PE, PP, and PS which are main components in municipal waste plastics. The
first decompositionstep is the loss of HCl from either PVC or PVDC. The formation ofchlorinated hydrocarbons during PVC, PVDC mixed plastics pyrolysis can be followed fromScheme 1. The HCl evolved from the PVC or PVDC reacts with the olefinic hydrocarbons
produced from the commingled plastics such as PE, PP and PS. Based on the decomposition
behavior of PVC and PVDC samples, the temperature profiles were modified from mode 1(single step) to controlled pyrolysis (two step) toremove the HCl evolved from the PVC orPVDC from the Pyrolysis of plastic wastes. For the pyrolysis of 3P/PVC (mode 1), the reactor
temperature was increased from room temperature to the final temperature of 4300C and kept
till the end of pyrolysis experiment (nitrogen 30 ml/min). For the pyrolysis of 3P/PVC (mode2), the reactor temperature was increased from room temperature to 330 0C (nitrogen flow 55ml/min) and kept for 2 h at 3300C (nitrogen flow 55 ml /min) and then subsequently increased
to a final temperature of 4300C and kept till the end of the pyrolysis experiment [3].

Fig.3 Plausible steps for the formation of chlorinated hydrocarbons during
pyrolysis of PVC, PVDC mixed plastics.
- 12 -

PARTⅠ PYROLYSIS

3.2 Pyrolysis of BFR (Brominated Flame Retardant) containing mixed plastics
The waste plastics from electric and electronic equipment contains brominated flame
retardants and also contain antimony trioxide, which is added to the polymers as a synergist toincrease the flame retardant properties of the brominated additives. Antimony trioxide is used
as a synergist in combination with polybromodiphenyl oxides (commonly referred to as
polybrominated diphenyl ethers or PBDEs) and decabromodiphenyl ethane, both of which areused as fire retardants in polystyrene based polymers and co-polymers. Antimony trioxide
acts as a synergist by promoting the release of bromine radicals during combustion via theformation of volatile antimony bromides, the bromine radicals then quench the combustion
process by aggressively scavenging other radicals which are required for the propagation of aflame. Water is a secondary product of the conversion of antimony trioxide to antimony
bromide and it is thought that the hydrogen necessary for this reaction is obtained from thepolymer chains. Therefore, antimony trioxide is thought to have a significant impact on thepyrolysis of flame retarded polymers. Several investigations have been carried out into theeffect that antimony trioxide has on both the pyrolysis products and the fate of the bromine
content of plastics during pyrolysis. Similar to PVC/PVDC mixed plastics, the pyrolysis
mixed plastics containing BFRs produce the bromine compounds in the pyrolysis products
and needs suitable catalyst/sorbent for the removal of bromine compounds from the pyrolysis
liquid products, in order to use them as fuel or chemical feedstock. Based on thethermogravimetric profiles (Fig. 3), we have showed the controlled pyrolysis method (Fig. 4)
with the two steps to produce the bromine less pyrolysis liquids from the HIPS-Br plastic
mixed with polyolefins.

Fig.4 Thermogravimetric profiles of Brominated flame retardantcontaining various polystyrene samples- 13 -

The 5th ISFR (October 11-14, 2009, Chengdu, China)

Fig.5 Temperature profile for the pyrolysis of Brominated flame retardant containing
polystyrene with various polyolefins (HIPS-Br with PE/PP/PS)
4. Conclusions
We present the pyrolysis of PVC/PVDC or HIPS-Br containing mixed polyolefins liquid
products with the very low halogen compounds without the use of any catalyst or sorbents.
The optimization of process parameters is more effective in controlling the quantity andquality of pyrolysis products.
References[1] T. Bhaskar, R. Negoro, A. Muto, Y. Sakata, Green. Chem. 2008, 6, 697.
[2] T. Bhaskar, W. J. Hall, N. M. M. Mitan, A. Muto, P. T. Williams, Y. Sakata, Polym.
Degrad. Stabil, 2007, 92, 211.
[3] W. J. Hall, N. M. M. Mitan, T. Bhaskar, A. Muto, P. T. Williams, Y. Sakata,
J. Anal.Appl.Pyrolysis, 2007, 80, 406.

- 14 -