Polymer waste is a cause of increasing environmental concern in the developed world [1]. While incineration can be used to recover the waste as energy, the loss of a potential chemical source and the negative public acceptance has limited the extend to which this solution has been applied. It is also undesirable to dispose of waste plastics by landfill due to high costs and poor biodegradability [2]. If one accepts that landfill storage is not the most rational solution and can only be considered as provisional, then one is left with the most desired primary and secondary waste recycling processes. These are limited to present technical limitations for the treatment of mixed plastic wastes, together with the limited size of the market for recycled products, difficulties in maintaining product quality, and fluctuations in the price. Owing to these limitations, tertiary, chemical or feedstock recycling is growing in importance [3].
Several methods for the recycling of waste polymers have been proposal, of which pyrolysis is a promising approach with potential applications. Pyrolysis, i.e. thermal cracking of the polymers to give low molecular weight materials, is attractive, but unfortunately gives a very broad range of products. It also requires high temperatures typically more than 500 8C and even up to 900 8C [4-6]. Catalytic pyrolysis is being investigated as a means to address these problems [7][8][9]. Catalysts can promote the degradation reaction to occur at lower temperatures, with implies lower energy consumptions. In addition, the shape selectivity exhibited by certain catalysts allows the formation of a narrower distribution of products, which may be directed towards fuels, chemicals and valuable hydrocarbons with higher market values. Lots of studies have been conducted describing the cracking of pure polymers over various cracking catalysts with the textural properties, such as surface area, particle size and pore size distribution, and the differences in the catalytic activities as they control the accessibility of bulky plastic molecules to internal catalytically active sites [10][11][12][13][14][15][16][17][18][19][20]. In this way polymer wastes are converted into monomers, chemicals or various hydrocarbons. Unfortunately it can only be applied to pure polymers and mixed polymer wastes are not recommended. It also seems that in the process of polymer pyrolysis, a particular kind of catalyst is effective for a particular kind of polymer. Therefore, understanding the behaviour of catalysts on post-consumer polymer waste is essential to evaluate their potential application in commercial feedstock recycling processes.