Alternative thermochemical routes for green ethanol production from steel residue gas: Technical feasibility, economic viability and environmental sustainability assessment

This study aims to develop and evaluate a novel thermochemical route for ethanol production from steelwork residue gas, with a particular focus on enhancing environmental sustainability through carbon utilization. Herein, four different residue gas to ethanol (R2E) processes with different compositions of coke oven gas (COG) and Linz–Donawitz gas (LDG) as hydrogen and carbon-rich feeds, respectively, are proposed. A techno-economic analysis was conducted, supported by the development of a heat exchange network, to assess the economic feasibility and energy efficiency of the processes. As a result, the process with the combined COG–LDG feed showed the highest economic viability (a minimum selling price, $0.74/kg). Life-cycle assessments were conducted to compare the environmental impacts of the proposed R2E processes with that of the conventional bioethanol route. The LDG-based process that uses COG as a supplementary hydrogen supply showed a negative carbon footprint (−35 g CO_2-eq./MJ ethanol), outperforming other ethanol production routes. A global sensitivity analysis was conducted on major cost drivers (e.g., feed gas prices and carbon tax rate), to evaluate both the economic feasibility and CO₂ reduction potential of the proposed R2E processes across various countries, thereby enabling a comprehensive comparison of their sustainability against biomass-based ethanol production.