Thermal or Catalytic Degradation of Polypropylene

Abstract

Thermal degradation of polypropylene over glass beads at 476-551°C or catalytic degradation over silica-alumina and CaX zeolite at 428-499°C was carried out under an atmospheric pressure and in terms of a fixed bed flow reactor system. The presence of these catalysts remarkably accelerated the degradation of polypropylene. At the initial stage of the reaction, at 499°C, and under the following feed rate of polypropylene: 0.098 g/min, the yields of gaseous products were 76 and 68 wt% over silica-alumina and CaX, respectively, while it was 10 wt% in thermal degradation case. These catalytic degradations gave a completely different product distribution from that of thermal one and produced less amount of olefins than that of the latter. The amount of olefins in C₂-C₅ gaseous products in silica-alumina case was more than 60 mol%, which was about twice as large as that in CaX case. For liquid products formed over both catalysts at an initial stage of the reaction, difference in average molecular weight, iodine number, or infrared spectrum was not detected.
The distribution of gaseous products in CaX case was more influenced by a contact time or temperature of the reaction than that in silica-alumina case, but the rate of formation of gaseous products was less dependent on the above factors in the former. These results were considered to be due to the difficulty of diffusion of reactant or product into CaX with smaller pores than those of the latter.