Basic study on a continuous flow reactor for thermal degradation of polymers

A continuous flow reactor for thermal degradation of polymer such as polyethylene (PE), polypropylene (PP) and polystyrene (PS) was operated at the feed rate of 0-1.5 kg h^-1 in order to investigate the characteristics of the continuous flow operation and the thermal degradation behavior of polymers. Rate studies on thermal degradation of polymers were made at various temperatures and under a steady state. The activation energies, calculated on the basis of the rate of volatilization, were 221, 216 and 208 kJ mol^-1 for thermal degradation of PE, PP and PS, respectively. These activation energies indicate that a chemical reaction takes a role of rate controlling step in this reactor system. By continuous flow operation, polymers were converted to the liquid product with high yield of 93.6-96.2, 96.1-99.1 and 99.9 wt.% for PE, PP and PS. The liquid products consisted of a wide spectrum of hydrocarbons distributed C₄-C₃₀. Thermal degradation by continuous flow operation is a suitable technique for converting plastic polymers into liquid hydrocarbons which could be used as feed stock materials. Based on the observed information, a macroscopic mechanism was proposed. The thermal degradation of polymers consists of two distinct reactions which simultaneously occur in the reactor. One is a random scission of links which causes a molecular weight reduction of the raw polymer, and the other is a chain-end scission of C-C bonds, which causes the generation of the volatile product. The chain-end scission takes a place at the gas-liquid interface in the working reactor.