Sustainable CO2 Utilisation Routes from Green Hydrogen and Methane Production via Dark Fermentation-Anaerobic Digestion of Biomass Wastes

Abstract

This research project presents a comprehensive analysis of a sustainable process integrating several processes to achieved a sustainable rout for utilizaing CO2 from the two-stage digestion of water hyacinth biomass. Reverse water gas shfit, solid oxide electrolysis cells, oxygen- gasification of digestate, and Fischer-Tropsch synthesis, are integrated to convert CO2 into valube liquid fuel, which is methanol. The process is designed to enhance resource efficiency, reduce CO2 emissions, and utilize waste products effectively. The anaerobic digestion of water hyacinth biomass yields biogas rich in CO2 and CH4. This biogas helps in managing invasive plant species and provides a significant amount of CO2 that feeds into the Reverse Water-Gas Shift, while the CH4 contributes to hydrogen production through dark fermentation. The residual digestate from anaerobic digestion is further processed in the oxygen-gasification stage. The SOEC system operates at 750°C with a thermodynamic efficiency of 91.9%, producing hydrogen from water with a production rate around 700 t/day. The oxygen generated is used in the gasification process. The oxy-gasification of digestate converts it into valuable syngas, manily CO and H2, with a reasonablly highe fuel efficiency. The syngas, after cleaning and processing, is used for enhanced methanol production. The methanol synthesis process operates at 200°C and 50 bar, yielding methanol with a CO conversion rate of 19.04% and a methanol selectivity of 62%. The process shows a total heat release of 160 MJ/hr, with a reactor temperature rise from 200°C to 319.18°C, managed through effective heat removal and thermal management.