Catalytic cracking of polyethylene over zeolite mordenite with enhanced textural properties

Abstract

Catalytic cracking of low density polyethylene (LDPE) has been investigated using different samples of mordenite zeolite as catalysts. In order to obtain materials with different textural properties, a new synthesis method based on the functionalization of the zeolite seeds with an organosilane was employed. Mordenite samples with BET and external surface areas in the range 385-485 m2/g and 9-57 m2/g respectively, were prepared. LDPE catalytic cracking reactions were performed at 420 ºC for 2h in a batch reactor provided with a screw stirrer under a continuous nitrogen flow. Thermal cracking of LDPE leads to plastic conversion lower than 30%, while values of 40% are reached when traditional mordenite is used as catalyst. In contrast, when mordenite samples with enhanced textural properties were employed, a plastic conversion of 60% is attained, both gas (C1-C5) and gasoline (C6-C12) fractions being obtained as main products. On the contrary, gasoline fraction is not observed and a heavier hydrocarbon fraction in the range C13-C35 is detected when thermal cracking or even catalytic cracking over traditional mordenite samples are carried out. The formation of lighter hydrocarbon products (C6-C12) over mordenite samples with enhanced textural properties is assigned to the higher activity and accessibility of their acid sites, which promotes both end-chain and random scission cracking reactions of the polymer molecules.