Catalytic pyrolysis of polystyrene in different reactors: Effects of operating conditions on distribution and composition of products

Abstract

The effects of temperature and pressure on product distribution were investigated by catalytic slow pyrolysis of polystyrene in a fixed bed. Simultaneously, the catalytic fast pyrolysis of polystyrene was carried out in a fixed-fluidized bed to study the effects of temperature and reaction time on the product distribution. The slow and fast pyrolysis experiments of polystyrene were conducted using γ- Al2O3 (basic) as catalyst and silica sand as control group. The compositions of oil and gas products were analyzed by GC-FID, GC-MS and GC to investigate the catalytic activity of basic catalyst. The results showed that catalytic slow pyrolysis and catalytic fast pyrolysis achieved maximum oil yields of 94.6 wt% and 92.19 wt%, respectively. In slow pyrolysis, toluene, ethylbenzene, and styrene were the main products, and the introduction of catalyst led to reduced yields of toluene, ethylbenzene, cumene, and α-methyl styrene. However, the main product of fast pyrolysis was only styrene, with a recycling rate nearly 80% under catalytic conditions. The presence of the catalyst increased the yield of styrene, with slow pyrolysis rising from 27.15% to 32.58%, and fast pyrolysis increasing from 82.28% to 86.56%. Longer residence time strengthened secondary reactions to generate more aromatics such as toluene and ethylbenzene. Both catalytic slow and fast pyrolysis yielded higher styrene contents than thermal pyrolysis because the basic catalyst reduced the occurrence of secondary reactions.