Conversion of Waste Plastic to Oil: Direct Liquefaction versus Pyrolysis and Hydroprocessing Naresh Shah, Jeff Rockwell, and Gerald P. Huffman* CFFLS, 533 S. Limestone St., University of Kentucky, Lexington, Kentucky 40506-0043 Received November 4, 1998 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 Na 2 CO 3 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 H 2 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 Na 2 CO 3 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. Introduction During recent years, there has been extensive re- search on the liquefaction of waste polymers and the coliquefaction of waste polymers with coal, petroleum resid, and waste oil. Summaries of this research are available in several conference and symposia proceed- ings volumes 1-4 and in a recent review on coprocessing of wastes with coal. 5 A significant amount of research has been conducted on the catalytic liquefaction of plastic. Excellent results have been obtained from liquefaction of individual polymers (polyethylene (PE), polypropylene (PPE), poly- styrene (PS), etc.) and relatively clean mixed plastic using solid acid catalysts and metal-promoted solid acid catalysts. 6-14 For example, Venkatesh et al. 13 and Shabtai et al. 14 have obtained high yields of liquids that consist predominantly of isoalkanes in the gasoline boiling range from HDPE, PPE, and PS at relatively low temperatures (300-375 °C) using Pt-promoted ZrO 2 / SO 4 or ZrO 2 /WO 3 catalysts. However, true post-con- sumer plastic (PCP) contains heteroatoms (principally chlorine, but also nitrogen and some sulfur), paper, dirt, and inorganic matter that can render such catalysts ineffective. In the current paper, the effect of small additions (1- 5%) of a number of solid acid catalysts on the liquefac- tion of true PCP is determined. In addition, a two-step approach is investigated in which PCP is first pyrolyzed and the pyrolysis liquid is then hydrotreated. The later approach is found to be preferable for true PCP. * To whom correspondence should be addressed. (1) Symposium on Coprocessing of Waste Materials and Coal; Anderson, L. L., Meuzelaar, H. L. C., Co-Chairs; Am. Chem. Soc., Div. Fuel Chem. Preprints 1995, 40(1), pp 1-92. (2) Fuel Process. Technol., Special Issue, Coal and Waste; Huffman, G. P., Anderson, L. L., Eds.; 1996, 49, (1-3). (3) Symposium on Liquefaction/Coprocessing; Curtis, C., Stohl, F., Co-Chairs Am. Chem. Soc., Div. Fuel Chem. Preprints 1996, 41(3), 928-1029. (4) Symposium on Feedstock Recycling of Waste Polymers; Eyring, E. M.; Zondlo, J. W., Co-Chairs; Am. Chem. Soc., Div. Fuel Chem. Preprints 1997, 42(4), 968-1086. (5) Davidson, R. M. Coprocessing waste with coal; IEAPER/36, IEA Coal Research: London, U.K., 1997. (6) Taghiei, M. M.; Feng, Z.; Huggins, F. E.; Huffman, G. P. 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