Hydroprocessing of waste plastics to produce diesel under low processing temperatures using ionic liquid catalyst

Abstract

Plastics play an indispensable role in daily life due to their durability, light weight, cost-effectiveness, and versatility, making the development of efficient waste management solutions vital for addressing the challenges posed by synthetic plastic disposal at the end of their lifecycle. Plastics, mostly sourced from petroleum-based feedstocks, can be reprocessed into petroleum products by catalytic and hydrothermal techniques. Pyrolysis oil, which predominantly consists of unsaturated hydrocarbons, requires upgrading to saturated aromatic compounds through hydroprocessing for use in vehicle fuel applications. This work introduces an innovative method employing ionic liquid-supported solid catalysts for the hydroprocessing of waste plastics into fuel at low processing temperatures. Specifically, 1-ethyl-3-methylimidazolium triflate (EMIM-OTf) immobilized on mesoporous Ni/SBA-15 was used as a hydroprocessing catalyst. Unlike previous studies requiring high reaction temperatures (300-400 degrees C) with heterogeneous catalysts, our process converted plastic pyrolysis oil to diesel-equivalent fuel at 190 degrees C under 70 bar H2 pressure. GC-MS analysis confirmed olefin conversion into paraffins and the aromatization of reactants, yielding benzene and naphthalene derivatives. The resulting n-paraffins and isoparaffins matched commercial diesel by 95 % and 90 %, respectively, with a 3.65 % increase in aromatics. The physicochemical properties of the hydroprocessed pyrolysis oil (HMP-PO) complied with EN 590 European diesel standards. This study highlights a low-temperature strategy, contributing to energy efficiency and plastic waste mitigation.