(298d) Co-Depolymerization of Lignin and Plastic Waste Using Hydrothermal Liquefaction Technology

Depolymerization of plastics is one of the most challenging tasks in the chemical upcycling of plastic-based waste because the disassociation of the stable carbon-carbon bonds is only possible at a very high reaction temperature. Lignin is the second most abundant biopolymer in nature, which is currently underutilized. Therefore, it is desirable to find a sustainable solution for increasing the use of underutilized lignin and plastic beyond incineration for energy. Processes like pyrolysis and combustion are associated with energy disadvantages as there is a need to dry the feedstock before processing. However, this shortcoming can be overcome with Hydrothermal liquefaction technology (HTL) due to its ability to upgrade wet materials to value-added products like high-quality fuel. In this research, the effects of HTL process conditions (temperature between 300 ÌŠC to 400 ÌŠC, pressure, and residence time) on the quality and quantity of co-depolymerization of plastics and lignin products are delineated. The dichloromethane solvent is used to extract the organics from the HTL product mixture. We further determine the effect of the lignin chemical structure and branching structure of polyolefins on the quality of produced fuel intermediates under supercritical water conditions. Gas chromatography, Nuclear Magnetic Resonance (NMR) spectroscopy, and elemental analysis results are used to propose a major reaction mechanism of lignin and polyolefin conversion to fuel intermediates under sub and supercritical conditions. The initial results show that the feedstock conversion is found to increase as the temperature increases. However, for lignin and polyethylene mixture, the oil phase yield is seen to be maximum around 370 ÌŠC and a decline in the oil yield is seen as the temperature increases beyond 370 ÌŠC.