(530c) Hydrothermal Liquefaction of Waste Plastics and Lignin

Lignin is the second most abundant biopolymer in nature and is currently underutilized. Plastic waste has increased considerably after the onset of coronavirus pandemic. Therefore, it is desirable to find a sustainable solution for increasing the uses of underutilized lignin and plastic beyond incineration for energy production. In this work, we study the synergetic effects of depolymerizing lignin and plastic (polyolefins) mixture to transportation fuel intermediates using hydrothermal liquefaction. We hypothesize that supercritical water and aromatic mixture produced from lignin depolymerization can cause a high dissolution of molten polyolefin phase, which eventually can promote polymer homolysis and unimolecular reactions like beta-scission and surpass coke formation reactions. Further, the hydrogen radicals produced during the beta-scission reactions of a polyolefin can react with reactive intermediates of lignin depolymerization under supercritical conditions and produce low-molecular-weight aromatic compounds by preventing the coke forming condensation reactions. We further show the effect of lignin chemical structure and branching structure of polyolefins on the quality of produced fuel intermediates under supercritical water conditions. The nuclear magnetic resonance spectroscopy, gel permeation chromatography, and Fourier transform infrared spectroscopy are used to study the chemical characteristics of lignin. Gas chromatography and elemental analysis results will also be presented and will be used to propose a major reaction mechanism of lignin and polyolefin conversion to fuel intermediates under supercritical conditions.