Co-liquefaction of high ash coal and electronic waste plastics: Study of liquefaction reaction kinetics and characterization of the co-liquefied oil

Abstract

Thermochemical co-processing of lower rank coals and electronic waste plastics can be a potential way of producing valuable chemical products. This paper is mainly focused on co-processing high ash coal and electronic waste plastics via direct co-liquefaction at 375-425℃ for 8–60 min using N₂ (20 bar initial pressure) to produce high calorific and transportable oil without adding catalyst and solvent. Effects of operating conditions were investigated and the optimum conditions were found to be 425℃ and 30 min for maximizing the oil formation of 30.04 wt%. A kinetic model was developed assuming reaction pathways that assessed 39.51 kJ/mol energy requirement to activate mixed feed to oil formation reaction. Synergistic effect of co-liquefying coal/plastic mixture was observed in the oil quality enhancement in terms of calorific value (from 39.67 to 42.15 MJ/kg), H/C ratio (from 1.21 to 1.29) and dynamic viscosity (from 9.67 to 4.05 mPa-sec) compared to single electronic waste plastic liquefied oil. Major hydrocarbons present in the co-liquefied oil have a carbon chain length C₇-C₂₄, comparable to that of the diesel composition (C₈-C₂₅). A probable reaction mechanism between high ash coal and electronic waste plastic is proposed based on the experimental studies.