Catalytic degradation of an LDPE-LLDPE-EVA copolymer mixture with used-HZSM-5 catalyst

The aim of the present work is to study the performance of used-HZSM-5 catalyst in the catalytic cracking of an EVA copolymer + LDPE + LLDPE, with a composition similar to that found in real agricultural film wastes. The crystallinity, number of acid site and surface area of used-HZSM-5 slightly decreased compared to those of fresh HZSM-5, but the catalytic performance of used-HZSM-5 was able to be achieved in the pyrolysis of the polymer mixture. When the polymer mixture was brought into contact with used catalyst (liquid phase contact), a gaseous products yield of 66.5 % was obtained. Used-HZSM-5 gave rise to high selectivity, valuable C₃-C₄ hydrocarbons, most of which were olefins. The selectivity to isobutene over used-HZSM-5 was much higher than that of thermal degradation. When thermally degraded hydrocarbon vapors were brought into contact with used catalyst (vapor phase contact), a gaseous yield of 57.3 % was obtained, with the liquid products mainly distributed over C₅-C₂₅. The product distribution for the second to fourth runs was almost the same as for the first run. The upgrading over Ga/HZSM-5 produced a larger amount of aromatic hydrocarbons compared with that over HZSM-5.