Co-liquefaction of triacetyl cellulose (TAC) from waste LCDs and high-sulfur low-rank coal (HSLC) by sub/supercritical water: Synergistic effect, desulfuration, and resource recovery.

To address the challenges of treatment of triacetyl cellulose (TAC) from waste liquid crystal displays (LCDs) and the upgrading demand for high-sulfur low-rank coal (HSLC), a novel synergistic co-liquefaction process was developed using a sub/supercritical water (Sub/SCW) system in this study, aiming to simultaneously achieve waste recovery and energy upgrading. The Sub/SCW co-liquefaction demonstrated efficient degradation of TAC (nearly 100 %) and synchronous conversion of HSLC (maximum conversion ratio of 76.69 %), exhibiting remarkable synergistic effects. By the Sub/SCW co-treatment, the sulfur contained in the co-liquefied oil could decrease from 1.95 % to 0.03 %. Optimized process parameters were 375 °C, 60 min, and an appropriate coal/TAC ratio. GC-MS analysis showed that the co-liquefied oil was rich in ketones (30.13 %), phenols (21.53 %), and aromatic hydrocarbons (21.44 %). The Sub/SCW co-liquefaction process followed a free radical reaction pathway. Acetic acid derived from the hydrolysis of TAC and HO· radicals generated in the Sub/SCW system played a crucial role in the formation of strong electrophilic OH+ and the removal of organic sulfur and inorganic sulfur from the HSLC. HSLC sustained dehydration, decarboxylation, and hydroxylation reactions, resulting in the breakage of bridge bonds, side chains, and various functional groups in its macromolecular structure into reactive fragments including aromatic compounds, alkyl groups, carboxyl groups, and aryl groups. The cellulose structure of depolymerized TAC resulting from cleavage and hydrolysis, reactions produced abundant radical fragments and small molecules. These intermediates ultimately form new molecules through rearrangement, polymerization, and other pathways. Life cycle assessment (LCA) results indicated that the Sub/SCW co-liquefaction process exhibited lower carbon dioxide emissions. The proposed process offers both environmental and economic benefits, providing an innovative solution for the resource recovery and pollutants removal of electronic waste and HSLC.