Tertiary recycling of polyethylene to hydrocarbon fuel by catalytic cracking over aluminum pillared clays

The catalytic cracking of polyethylene over an Al pillared saponite, an Al pillared montmorillonite, and their regenerated samples was studied in a semi-batch reactor. Pillared clays were able to convert completely polyethylene in gaseous and liquid hydrocarbons, showing low coking levels. The selectivity and yield to liquid hydrocarbons were high, as the mild acidity of pillared clays avoided excessive cracking to small molecules. Regenerated catalyst samples showed practically identical levels of conversion and selectivity with fresh pillared clay samples. Furthermore, they produced hydrocarbons with practically the same distribution as the fresh samples, confirming that pillared clays can be completely regenerated. Both facts of high yield to liquid products and regenerability make pillared clays potential catalysts for an industrial process of catalytic cracking of plastic waste. The effect of the heating program on the liquid product quality and distribution is also investigated, using two different temperature programs with the same levels of temperature steps, but different duration. The boiling point distribution of the liquid products formed during the second interval of the shorter program was intermediate between this of the lighter liquid produced in the first 10 min of the longer program and the heavier liquid produced between 10 and 20 min. This result clearly shows the importance of the polymer state during each temperature stage.