Conversion of Waste Plastic to Oil:  Direct Liquefaction versus Pyrolysis and Hydroprocessing

Two approaches for the conversion of waste post consumer plastic (PCP) into oil have been investigated: (1) direct liquefaction and (2) pyrolysis followed by hydprocessing of the pyrolysis liquids. The PCPs investigated were a washed PCP provided by the American Plastic Council (APC) and a PCP prepared by dry preparation methods provided by the Duales System Deutschland (DSD). The DSD plastic contained significantly more ash, paper, dirt, and chlorine than the APC plastic and is considered to be more representative of true waste PCP. Direct liquefaction of both plastics was investigated using small additions (1−5 wt %) of a number of different solid acid catalysts. At 445 °C, the catalytic effect on oil yields was negligible for both plastics. Several catalysts had a significant effect on the boiling point distribution for the APC plastic, producing lighter products, but had little or no effect for the DSD plastic. An alternative approach of pyrolysis followed by hydprocessing the pyrolysis liquids was investigated for the DSD plastic. Pyrolysis yields of 75−80% of relatively heavy liquids were achieved at 600 °C. Addition of Na2CO3 to the pyrolysis reactor decreased the chlorine content of the pyrolysis liquids to ∼50 ppm. The boiling point distribution of the pyrolysis liquid was substantially improved (55−65% gasoline fraction) by either thermal or catalytic hydrprocessing (450 °C, 200 psig initial H2 pressure). The effect of adding 1−5% of several catalysts was relatively small, increasing the gasoline fraction over that obtained by thermal hydroprocessing by 5−10%. Addition of Na2CO3 to the hydroprocessing reactor decreases the chlorine content of the final product to a few ppm. These results indicate that pyrolysis followed by hydprocessing of the pyrolysis liquids is a good approach for true PCP that contains a significant amount of chlorine, paper and inorganic material.