Comparison of Five Acetogens for Production of C2 – C6 Alcohols and Acids from CO2
- Type: Conference Presentation
- Conference Type: AIChE Annual Meeting
- Presentation Date: November 11, 2021
- Duration: 15 minutes
- Skill Level: Intermediate
- PDHs: 0.50
The use of fossil fuels, which results in huge CO2 emissions causing negative environmental impacts, is unsustainable. In addition, there are over 15 billion gallons of corn ethanol produced per year in the United States generating over 43 million tons per year of high purity biogenic CO2. This biogenic CO2 can potentially be converted to additional ethanol using autotrophic microorganisms. The conversion of waste carbon streams to valuable products is an emerging research field that addresses the need to reduce greenhouse (GHG) emissions, improve carbon conversion efficiency and generate additional revenues towards a circular carbon economy. Thermochemical and electrocatalysis methods have been developed to convert CO2 to formic acid, CO, H2 and CH4. However, these methods suffer from a low carbon conversion efficiency and catalyst poisoning. Biological CO2 conversion is a novel process in which the cells directly convert CO2 at near ambient temperatures and pressures into biofuels and biobased products. This can generate additional revenue from CO2-containing waste streams for biorefineries and other industries. The objective of this study is to compare five different acetogens (Clostridium ragsdalei strain P11, C. carboxidivorans strain P7A and three new clostridial strains A, B and C) for their ability to convert CO2 to C2 â C6 alcohols and acids via the acetyl-CoA pathway. In addition, the effects of inoculum preparation on cell activity and product profiles were examined. Experiments were performed with inocula prepared with syngas (CO:CO2:H2) and CO2:H2. Inoculum preparations and fermentations were performed in 250 mL bottle assays with 50 mL working volume at 37Â°C and 125 â 150 rpm. After inoculum preparation, fermentations were performed with a gas mix containing CO2:H2:N2 (20:60:20) that was fed daily for 360 h. Results showed that all strains converted CO2 into various amounts of C2 â C6 alcohols and fatty acids depending on the inoculum preparation technique. All five strains prepared with syngas inocula produced alcohol. However, acetic acid was mostly produced by all strains with CO2:H2 inocula. Strain P11 was the best CO2 and H2 consumer regardless of the inoculum preparation technique, producing 2 g/L ethanol and 6 g/L acetic acid from syngas inoculum. All strains with CO2:H2 inocula produced mostly acetic acid (~ 12 g/L) from CO2, with the highest from strains P11, P7A and strain A. Notably, strain C produced ethanol, butanol, hexanol and acetic, butyric and hexanoic acids with either syngas or CO2:H2 inocula. Additional results from enzyme activities of the five strains from syngas and CO2:H2 inocula will be presented to explain the variations in C2 â C6 alcohols and fatty acids profiles during CO2 conversion. This research is expected to advance our understanding of biological CO2 conversion into valuable products with increased carbon utilization towards realizing the circular carbon economy.
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