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The catalytic degradation of high-density polyethylene to hydrocarbons was studied over different zeolites. The product range was typically between C-3 and C-15 hydrocarbons. Distinctive patterns of product distribution were found with different zeolitic structures. Over large-pore ultrastable Y, Y, and beta zeolites, alkanes were the main products with less alkenes and aromatics and only very small amounts of cycloalkanes and cycloalkenes. Medium-pore mordenite and ZSM-5 gave significantly more olefins. In the medium-pore zeolites secondary bimolecular reactions were sterically hindered, resulting in higher amounts of alkenes as primary products. The hydrocarbons formed with medium-pore zeolites were lighter than those formed with large-pore zeolites. The following order was found regarding the carbon number distribution: (lighter products) ZSM-5 < mordenite < beta < Y < US-Y (heavier products). A similar order was found regarding the bond saturation: (more alkenes) ZSM-5 i mordenite < beta < Y < US-Y (more alkanes). Dependent upon the chosen zeolite, a variety of products was obtained with high values as fuel, confirming catalytic degradation of polymers as a promising method of waste plastic recycling.
Manos et al. (Sat,) studied this question.