Production of aromatic hydrocarbons by catalytic degradation of polyolefins over H-gallosilicate

Low-and high-density polyethylene and polypropylene have been degraded in a fixed-bed now reactor system with and without H-gallosilicate catalyst at 375-550 degreesC to investigate the product distribution and the catalyst s tability. The thermal degradation of the polyolefins mainly produced waxy h ydrocarbons, with the yield largely depending on the polymer type. On the o ther hand, the catalytic degradation over the gallosilicate yielded lighter hydrocarbon mixtures that were rich in valuable aromatic components, mostl y benzene, toluene, and xylenes. The product distribution was influenced li ttle by the structure of the polymers to be degraded. This can be explained by a mechanism involving frequent skeletal isomerization of the decomposed fragments. The unsaturated fragments, which were the most abundant and the reby the most important reaction intermediates, rapidly isomerized on the a cidic gallosilicate, and the resulting isomers were distributed in thermody namically equilibrated concentrations. The catalytic degradation of polyole fins thus proceeds through similar intermediates regardless of the structur e of the degrading polymers, leading to almost the same product distributio ns. The gallosilicate exhibited a stable catalytic activity for the degrada tion of polyolefins when reused, because of a very low yield of coke deposi ted on the catalyst surface.