CO2 as an alternative carbon source for ethanol production: A simulation-based technical and environmental analysis

Abstract

Three ethanol production scenarios from CO₂ are analyzed: (S1) syngas catalytic conversion; (S2) syngas fermentation; and (S3) bio-conversion of CO₂ with H₂. These three scenarios were simulated in ProSimPlus® software, using flue gas from cement production and biogas as CO₂ sources. Technological performance and environmental impacts evaluated through the Life Cycle Assessment (LCA) method were analyzed. Chemical absorption (CA) and membrane separation (MS) are utilized for carbon capture, while hydrogen is generated by electrolysis. When considering flue gas and CA, scenario S1_CA yielded the lowest ethanol production (0.110 kg/kg-CO₂) but the highest energy consumption: 130 MJ electricity/kg-ethanol and 73 MJ heat/kg ethanol. Contrarily, S3_CA achieved the highest ethanol production (0.345 kg/kg-CO₂) with energy consumption comparable to S2 (86 MJ electricity/kg-ethanol and 20 MJ heat/kg-ethanol). S1 demonstrated the lowest global warming impact (GWP100) with values of –8.60 kg CO₂-eq per kg ethanol for CA (S1_CA) and –10.13 kg CO₂-eq for MS (S1_MS). S1 outperformed both S2 (CA: 0.13 kg CO₂-eq, MS: –0.83 kg CO₂-eq) and S3 (CA: –0.43 kg CO₂-eq, MS: –1.00 kg CO₂-eq). When biogas was used, S3_CA exhibited the lowest impact: 3.00 kg CO₂-eq, compared to S2_CA: 6.36 kg CO₂-eq and S1_CA: 4.10 kg CO₂-eq. S1_MS and S3_MS have close results: 2.34 and 2.44 kg CO₂-eq, respectively, much lower than S2_MS (5.22 kg CO₂-eq). When considering the end-of-life with ethanol combustion, GWP100 results of flue gas-based scenarios become similar (S1) or worse (S2, S3) than current crop/vegetable fermentation production routes, while biogas-based scenarios strongly depend on fugitive emissions control.