Catalytic Cracking of Polyolefins in the Molten PhaseBasic Study for the Process Development of Waste Plastics Liquefaction

Abstract

Abstract:The cracking of polyolefins, especially polyethylene in the molten state was effectively catalyzed by the powdery spent FCC (Fluid Catalytic Cracking) catalyst which was dispersed in it. The activation energy of the catalytic cracking of polyethylene was about 74 kJ/mol. The cracked product was naphtha and middle distillate as the major product and gaseous hydrocarbon (C 1 -C 4 ) as the minor product while little heavy oil was produced. The chemical compositions of the product were: aromatic hydrocarbons, isoparaffins and branched olefins, whereas that of the non-catalyzed products were: n-olefins and n-paraffins with minor amount of dienes with increasing the process time. Additionally, the product pattern shifted from naphtha rich product to kerosene and gas-oil rich product. However, any catalytic product showed low fluid point (< -10 o C), while that of the non-catalyzed product was as high as 40 o C. Catalyst could process, more than 100 times by weight of polyethylene with fairly small amount (~ 30 wt%) of coke deposition. Spent catalyst gave higher hydrocarbons while fresh catalyst gave gaseous product as the major product. Other polyolefins such as polypropylene and polystyrene were tested on same catalyst to show that their reactivity is higher than that of polyethylene and gave the aliphatic products, alkyl benzenes and C 6 -C 9 iso-paraffins as the major product. Product pattern of the cracked product suggested that the reaction proceeded via the primary reactions making paraffins and olefins which were followed by the isomerization, secondary cracking, aromatization and hydrogen transfer which based on the carbenium ion mechanism.