Production of liquid fuels from waste plastics

Exploratory work was carried out to develop a process for conversion of mixed plastic wastes into liquid transportation fuels or petrochemicals. The concept used is based on thermal depolymerization of the polymers in a suitable solvent followed by catalytic conversion of the resulting polymeric fragments into hydrocarbons with boiling points below 525 degrees C. The process is carried out batch-wise over a zeolite catalyst at temperatures from 350 degrees C to 450 degrees C and at atmospheric pressure. No hydrogen is used and volatile products formed are continuously removed from the reactor. Tests were carried out on polyethylene and polypropylene alone, and on mixtures of the two. Finally, a synthetic mixture of four different plastics was tested. From 90% to 98% of the plastic was converted to gases or distillable hydrocarbons. Of this yield, from 20% to 55% was gas, primarily propylenes and butylenes, and from 32% to 70% was a light hydrocarbon oil. Very little non-distillable coke or residue was formed. The use of mixtures did not affect the high conversions obtained, but the results could only be approximately predicted based on a pro-rating of results for the individual components.