Comparative techno-economic and carbon footprint analysis of 2,3-butanediol production through aerobic and anaerobic bioconversion of carbon dioxide with green hydrogen

Renewable CO₂ and hydrogen have the potential to be the feedstocks of a decarbonized chemical industry, and biochemical conversions offer new alternatives for the industry. There are two options among chemolithotrophic bacteria capable of CO₂ fixation: under aerobic conditions, through the use of the Calvin-Benson-Basham cycle, known to produce large-chain compounds, and under anaerobic conditions, through the Wood-Ljungdahl pathway, known to produce short-chain organic molecules. Here, we report a comparison of both bioconversions, made at a simulated industrial scale, considering techno-economic and environmental variables, and using renewable CO₂ and H₂ as feedstocks. 2,3-butanediol, a mid-range chain compound that can be produced via both routes, was selected for comparison. The comparison was set up in Chile due to expected low-cost renewable hydrogen and renewable CO₂ availability. The assessment showed that the minimum selling price of 2,3-butanediol in the anaerobic case was higher (3.91 (USD kg⁻¹)) than in the aerobic case (3.36 (USD kg⁻¹)), with hydrogen being the largest expense in both processes (50 % and 70 % of total expenses respectively). Further, owing to metabolic restrictions, the anaerobic process required almost five times more CO₂ than the aerobic process to produce the same amount of 2,3-butanediol. A Monte Carlo analysis showed that in most scenarios the aerobic process was more economically favorable. In environmental terms, the aerobic process had a smaller carbon footprint in all the evaluated scenarios. Therefore, the results suggest that the aerobic process is a more suitable alternative to anaerobic bacteria-based processes for producing 2,3-butanediol from renewable CO₂ and hydrogen.