Catalytic thermal cracking of post-consumer waste plastics to fuels: Part 1 - Kinetics and optimization

Authors: CHANDRASEKARAN, SRIRAAM - University Of Illinois; KUNWAR, BIDHYA - University Of Illinois; Moser, Bryan; RAJAGOPALAN, NANDAKISHORE - University Of Illinois; SHARMA, BRAJENDRA - University Of Illinois

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2015
Publication Date: 8/24/2015
Publication URL: http://handle.nal.usda.gov/10113/62307
Citation: Chandrasekaran, S.R., Kunwar, B., Moser, B.R., Rajagopalan, N., Sharma, B.K. 2015. Catalytic thermal cracking of post-consumer waste plastics to fuels. 1. Kinetics and optimization. Energy and Fuels. 29(9):6068-6077.

Interpretive Summary: This research revealed that post-consumer waste plastics are suitable as pyrolysis feedstocks for production of alternative fuels. Pyrolysis is defined as decomposition of material at elevated temperatures (above 570 deg F) in the absence of oxygen. The principal benefit of pyrolysis is conversion of low energy density substrates into higher density liquid and solid fractions. In the case of waste plastics, the liquid fraction was suitable as diesel fuel, as determined by comparing its fuel properties to those of conventional petroleum diesel as well as internationally accepted diesel fuel standards. Waste plastics were studied as feedstocks because of their proliferation in the environment and accumulation in municipal landfills. The objective of the current study was to explore their utility as a feedstock for production of liquid transportation fuels, thus reducing their impact on the environment while simultaneously reducing American dependence on foreign sources of petroleum oil. These results will be important to the alternative fuels industry, municipalities with landfills and litter issues, petroleum companies, plastics manufacturers, environmental organizations, and consumers. This research may ultimately improve market penetration, availability, and public perception of domestically produced alternative diesel fuels, thus affording greater independence from imported petroleum-based fuels while simultaneously enhancing economic opportunities across America.

Technical Abstract: Thermogravimetric analysis (TGA) was used to investigate thermal and catalytic pyrolysis of waste plastics such as prescription bottles (polypropylene/PP), high density polyethylene, landfill liners (polyethylene/PE), packing materials (polystyrene/PS), and foams (polyurethane/PU) into crude plastic oils. In the first phase of this investigation, a statistical design experiments approach identified reaction temperature and time as the most important factors influencing product oil yield. Kinetic parameters including activation energy determined for both catalytic and non-catalytic processes showed a reduction in activation energy for the catalytic reactions. In the second phase, the interactions of reaction temperature and time with a number of catalysts were investigated to determine the effect on the yield of crude plastic oil. It was found that Y-Zeolites increased conversion at reduced temperature for PP and PE while spent fluid catalytic cracking and sulfated zirconia catalysts supported pyrolytic decomposition of PS and PU foams. Response surface methodology (RSM) was utilized to optimize TGA conditions for pyrolytic decomposition of PP. The results were then validated through batch scale experiments and the resulting crude oils were characterized and distilled into motor gasoline, diesel #1, diesel #2, and vacuum gas oil fractions. Catalysts enhanced cracking at lower temperatures and narrowed the molecular weight (hydrocarbon) distribution in the crude oils. Chemical characterization of the crude oils indicated an increased gasoline-range fraction in oils obtained in the presence of catalyst while the distillate fractions were more evenly distributed among gasoline-range and diesel-range hydrocarbons in the absence of catalyst. The distillates obtained were characterized for fuel properties, elemental composition, boiling point, and molecular weight distribution. The fuel properties of the diesel-range distillate (diesel fraction) were comparable to those of ultra-low-sulfur diesel (ULSD).