Multi-step process for conversion of waste plastics to hydrocarbon liquids

Abstract

A method for thermally converting plastics and biomass, and especially non-recyclable waste plastic and or biomass, to primarily liquid phase hydrocarbons is a three step process comprised of hydrothermal treatment, steam cracking and coking. Plastic or plastic and biomass feedstocks are reduced in particle size to inch minus or smaller and suspended in a liquid slurry. The slurry is pumped to high pressure and heated to a temperature high enough to initiate de-polymerization. The resulting partially de-polymerized slurry is sent to a multi-phase separation system via a pressure reduction valve and thereafter subjected to steam cracking to further reduce the average molecular weight of the hydrocarbon components. The resulting gas phase hydrocarbon mixture is quenched, and naphtha, middle distillate, and heavy oils are condensed out. The residual heavy oil phase is further reduced in pressure and sent to a coker from which additional liquid hydrocarbon product is recovered.