Bioconversion of low-carbon syngas to ethanol and the process development
As an effort to achieve carbon neutrality,utilization of biomass gasification-based syngas(mainly consisting of CO,CO2,and H2)has been extensively studied.Conversion of syngas to fuel ethanol has the dual effects of carbon emission reduction and energy production.Since syngas can not be completely converted in chemical catalytic process,the tail gas produced,known as low-carbon syngas,is considered to be further utilized by biological process.In this study,fermentation of Clostridium autoethanogenum for ethanol production was investigated from the aspects of gaseous substrate and fermentation technology.Results showed that Clostridium autoethanogenum preferentially consumed CO other than CO2 and H2 in syngas fermentation,the ratio of CO consumption to H2 consumption was 0.99±0.12,and the molar ratio of ethanol and acetic acid achieved was 0.78±0.10;when 100％CO was used as substrate,the ratio of CO consumption to CO2 production was 1.72±0.21,and the molar ratio of ethanol and acetic acid was 1.00±0.11.During the process of xylose-syngas co-fermentation,xylose was consumed slowly,and compared to syngas fermentation,the cell density increased,but ethanol concentration was lower.Cell activities were not affected when 4g/L of sodium acetate was added in the medium,while significant inhibition on cell growth was observed under higher concentrations(≥12g/L).Fermentation results in the 3L stirred-tank reactor showed that the ethanol yield was low once"acid crash"happened,while lowering temperature at the late logarithmic phase of cell growth could prevent"acid crash".Consequently,the maximum ethanol concentration obtained was 3.46g/L,maximum ethanol and acetic acid molar ratio was 2.01,and the highest ethanol yield was 0.35g/(L·d).This study provided references for the process optimization of ethanol production from low-carbon syngas via Clostridium autoethanogenum fermentation.
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