6239 r2010 American Chemical Society pubs.acs.org/EF Energy Fuels 2010, 24, 6239–6247 : DOI:10.1021/ef101010n Published on Web 11/16/2010 Study of the Pyrolysis Kinetics of a Mixture of Polyethylene, Polypropylene, and Polystyrene Paula Costa,* ,† F. Pinto, † A. M. Ramos, ‡ I. Gulyurtlu, † I. Cabrita, † and M. S. Bernardo § † LNEG-UEZ, Estrada do Pac -o do Lumiar 22, 1649-038 Lisboa, Portugal, ‡ REQUIMTE, Departamento de Quı´mica, and § UBiA, FCT-Universidade Nova de Lisboa, 2829-516 Caparica, Portugal Received August 3, 2010. Revised Manuscript Received October 15, 2010 The principal aim of this study was the identification of possible routes for the reaction mechanism of a plastic waste mixture pyrolysis. Kinetic studies of a mixture of equal percentages of polyethylene (PE), polypropylene (PP), and polystyrene (PS) were performed in order to analyze if the direct conversion of plastic wastes into gaseous, liquid, and solid products was favored, or if parallel reactions and/or reversible elementary steps should be considered. The experiments were carried out in a six microautoclave system. On the basis of the experimental results obtained at different temperatures and reaction times, a reaction pathway was proposed. The fitting of a kinetic model to the experimental data was performed. The models reasonably fit the results and gave a satisfactory explanation of several experimental data of thermal degradation of the plastic waste mixture tested. The kinetic parameters were estimated, and a dependence of the activation energy and of the pre-exponential factor on temperature was observed, so it was verified that the rate constant of some reactions exhibited nonlinear temperature dependence on the logarithmic form. This fact probably indicates that temperature affects the reaction mechanism. The product composition was also analyzed, and on the basis of the data obtained, reaction mechanisms were proposed. Introduction Present societies are over dependent on petroleum for fuels and for raw materials, essentials for many industries. In the world, this fuel is the most consumed to produce energy. Hence, efforts have to be undertaken to implement better management solutions of the petroleum resources, both for optimization of the energy efficiency technologies and for finding alternative routes for obtaining fuels. This aim may be achieved by recycling processes and reutilization of the re- sources from petroleum, which reduces its increasing utiliza- tion. Furthermore, the fraction of plastic in municipal solid wastes (MSW) is continuously rising, being therefore one of the main concerns of the developed societies. The need of finding urgent solutions for the mentioned problems led to the idea of applying pyrolysis technology to plastic waste, to allow its energy recovery whenever mechan- ical or physical recycling cannot be applied. In the pyrolysis process, not only can industrial plastic waste mixtures be used, that cannot be incorporated in the industrial process, but also the plastic mixtures present in municipal solid wastes can be used. Pyrolysis is a thermochemical process, which has the inherent advantage of high flexibility with respect to feedstock characteristics, so it can be applied to plastic mixtures with contaminants. This is the main advantage of this process. It is fundamental to study the kinetic of the pyrolysis of plastic waste mixtures in order to verify if the reaction path- ways proposed for the individual pyrolysis of each kind of plastics can be applied to the pyrolysis of plastic waste mixtures. The present study is very important to test the possibility of foreseeing the product distribution and its composition based on plastic waste composition of the mix- tures used and on pyrolysis conditions. The studies found in the literature showed that the informa- tion on this subject is limited and sometimes contradictory; enough experimental results do not exist to enable an objective and accurate analysis of the pyrolysis of plastic waste mix- tures. This process has been reported by some research groups; however, different technologies and experimental parameters have been used. Nevertheless, only a few studies with the aim of finding the possible presence of interactions and synergetic effects during the degradation of mixed plastic wastes were found. In some cases, the results reported are contradictory. For instance, Wu et al. 1 did not observe interactions between the different components during the pyrolysis of a mixture of HDPE (high density polyethylene), LDPE (low density polyethylene), PP (polypropylene), PS (polystyrene), ABS (acrylonitrile butadiene styrene), and PVC (polyvinylchloride). Also Westerhout et al. 2,3 tested mixtures of PE and PP with different compositions and did not observe significant interactions when they were processed together. However, other authors obtained significantly different re- sults during the thermal degradation of plastic waste mixtures compared with the individual pyrolysis of the same plastics. Some authors observed that the interaction between the compounds produced during the plastic waste pyrolysis was highly dependent on the kind of plastic used. For example, the presence of PS in the waste mixture seemed to affect *To whom correspondence should be addressed. Fax: 351.21.7166569. E-mail: paula.costa@ineti.pt. (1) Wu, C.-H.; Chang, C.-Y.; Hor, J.-L.; Shih, S.-M.; Chen, L.-W.; Chang, F.-W. Waste Manage. 1993, 13, 221–235. (2) Westerhout, R. W. J.; Waanders, J.; Kuipers, J. A. M.; van Swaaij, W. P. M. Ind. Eng. Chem. Res. 1998, 37, 2316–2322. (3) Westerhout, R. W. J.; Waanders, J.; Kuipers, J. A. M.; van Swaaij, W. P. M. Ind. Eng. Chem. Res. 1998, 37, 2293–2300. (4) Williams, E. A.; Williams, P. T. J. Chem. Technol. Biotechnol. 1997, 70,9–20.