Waste Plastic Liquefaction

My third Ph.D. objective was to evaluate hydrothermal liquefaction(HTL) technology for mixed plastic waste. The HTL treatment of mixed plastic included the liquefaction of polyethylene terephthalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS) plastics by supercritical water with reduced red mud (RM) catalyst under nitrogen environment. The addition of catalyst hindered the synthesis of liquid crude from HDPE, LDPE, PP, PS, and solid from PET feedstock. The RM catalyst also induced low viscosity and acidity to plastic crudes regardless of the reaction condition. The plastic-derived crude oil contained 36-92% gasoline range low boiling products. HDPE produced paraffin compounds and PP and PS decomposed into aromatic or cyclic compounds. The synergistic effect of the plastic mix was found in higher crude oil production. Using waste as a catalyst and feedstock, the outcomes of this HTL study can be applied to develop an efficient HTL process for improved crude products. During my postdoc in Auburn University, I have mentored several undergraduate and graduate students. The next phase of my plastic liquefaction experience came through mentoring students. In one of these mentoring works, we have studied the liquefaction of the polyurethane plastic via both pyrolysis and hydrothermal liquefaction processes. Beside fuel grade compounds, aniline and p-aminotoluene, found predominantly in hydrothermal liquefaction oils. . In another plastic liquefaction study lead by a masters level student , the catalytic co-pyrolysis of polystyrene and pine with red mud (bauxite residue) and ZSM-5 catalysts was investigated as a method for producing aromatic hydrocarbons for use as additives to blend with sustainable aviation fuel . It was found that a positive synergy exists between pine and polystyrene feedstocks during co-pyrolysis that cracks solid and liquid products into gaseous products similarly to that of a catalyst. The co-pyrolysis of pine and polystyrene without a catalyst produced more kerosene-range hydrocarbons than predicted.

Please check the associated publication:

- Depolymerization of household plastic waste via catalytic hydrothermal liquefaction’, Energy & Fuels 2023 37 (17), 13202-13217, DOI: https://10.1021/acs.energyfuels.3c01706

- Upcycling Polyurethane Plastics via Thermochemical Conversion Pathways: A Comparison of Hydrothermal Liquefaction and Pyrolysis Processes’, ACS Sustainable Chemistry & Engineering, October 8, 2024, DOI: https://doi.org/10.1021/acssuschemeng.4c05202

- Production of Aviation Fuel-Range Hydrocarbons Through Catalytic Co-Pyrolysis of Polystyrene and Southern Pine" Catalysts 14, no. 11: 806.DOI: https://doi.org/10.3390/catal14110806