Catalytic Pyrolysis of Polypropylene to Benzene, Toluene, and Xylene (BTX) Using a Double-Fluidized-Bed Reactor

The current plastic value chain is highly linear, leading to large amounts of waste plastics that harm the environment and human health. Recycling is required, and among the options, catalytic pyrolysis is particularly suited to convert polyolefin-rich plastic waste into useful chemicals such as benzene, toluene, and xylene (BTX). In this paper, we demonstrate <i>ex situ</i> catalytic pyrolysis of polypropylene in a continuous double-fluidized-bed reactor to produce BTX. The optimal pyrolysis temperature in the first fluidized-bed reactor was 550 °C, giving a BTX yield of 22.3 wt % (based on PP input). Lowering the nitrogen flow rate and the use of smaller catalyst particle sizes favor BTX formation. Our novel reactor concept showed good operational stability at longer times on stream (TOS, 10 h). Catalyst activity was slightly reduced during TOS, as is evident from a small decrease in BTX yields. Detailed catalyst characterization studies showed that coke formation is the main reason for catalyst deactivation. In addition, chemoselectivity was also a function of TOS and the selectivity to benzene and toluene decreased, while higher amounts of xylenes were formed.