Sustainable valorization of marine plastic residues via hydrothermal liquefaction for clean energy recovery

Abstract This study evaluates hydrothermal liquefaction (HTL) of real-world marine pollutant residues (MPR) composed of mixed plastics, organic matter, paper, and textiles. Using diatomaceous earth (DE) catalysis and aqueous-phase (AQ) recirculation, the effects on product yield, composition, and energy recovery were examined. Under optimized conditions (380 °C, 80 min, 10 wt% DE, RR = 6 mL g -1 ), a maximum bio crude yield of 51.6% with an HHV of 40.3 MJ kg -1 was achieved. Elemental, molecular, and thermal analyses (CHNS, GC–MS, FTIR, TGA) indicated improved hydrocarbon content and reduced oxygenation in the DE + AQ configuration. Net energy ratio (NER) calculations showed that the process can achieve energy-positive operation under conditions of elevated AQ recirculation temperature, highlighting the importance of heat integration. While these results demonstrate effective conversion of heterogeneous marine residues into energy-dense products, broader sustainability claims require further assessment of emissions, wastewater toxicity, and scale-up feasibility. The study provides experimentally grounded insights into HTL as a potential component of coastal waste valorization strategies.