A Mini-Review on Syngas Fermentation to Bio-Alcohols: Current Status and Challenges

Abstract

Biomass gasification produces syngas, mainly comprised of CO and H2 along with H2S, CO2, N2, and tar compounds. Inorganic carbon present in syngas as CO and CO2 can be utilized for the production of several value-added chemicals including ethanol, higher alcohols, fuels, and hydrogen. However, chemical sequestration operates at a high temperature of 300–500 °C and pressure of 3–5 MPa in the presence of heavy metal catalysts. Catalyst regeneration and the maintenance of high temperature and pressure increased the cost of operation. Microorganisms like algae and bacteria including Acetobacterium and Clostridium also have the potential to sequester carbon from the gas phase. Research has emphasized the production of microbial metabolites with a high market value from syngas. However, scale-up and commercialization of technology have some obstacles like inefficient mass transfer, microbial contamination, inconsistency in syngas composition, and requirement for a clean-up process. The current review summarizes the recent advances in syngas production and utilization with special consideration of alcohol and energy-related products along with challenges for scale-up.

Syngas Fermentation: Cleaning of Syngas as a Critical Stage in Fermentation Performance

“…The pathway contains two branches, the methyl and carbonyl branch. In the methyl branch, the methyl group obtained from the reduction of CO/CO 2 is transformed into formate by formate dehydrogenase and by a sequence of multiple steps forms methyl radicles that are further assimilated along with CO, forming acetyl-CoA [37]. CO can also be oxidized by biological water gas shift reaction into CO 2 , and the reducing equivalents derived from the reaction are conserved as reduced ferredoxin [150,151].…”

“…Anaerobic microorganisms can use C1 substrates as carbon sources, producing short-chain acids, alcohols, or methane. However, the use of syngas requires special cleaning procedures since this gas carries ash particles, nitrogen/sulfur gaseous compounds (H 2 S, SO 2 , COS, NH 3 , HCN, NOx), oxygen, condensable organics, and tar, which can inhibit the activity of microorganisms [35][36][37]. Since the fermentation needs to be coupled to a syngas-producing process, the integration of biomass gasification and subsequent biological syngas conversion seems the logical sequence.…”

Syngas conversion to biofuels and biochemicals: a review of process engineering and mechanisms

“…4 Since the demand for energy worldwide is predicted to increase by 47% over the next 30 years and the consumption of liquid fuel is predicted to climb by 64% relative to 2020, hence, in order to reduce the demand for carbon-based fuels, increasing the production of biofuels might be a more sustainable approach. 5,6 The market for biofuels will reach USD 201.21 billion by 2030, expanding at a compound annual growth rate (CAGR) of 8.3% between 2021 and 2030. Utilizing cutting-edge techniques to achieve better titers, rates, and yields is essential for the environmentally responsible, cost-effective, and sustainable production of biofuels.…”

“…Since the demand for energy worldwide is predicted to increase by 47% over the next 30 years and the consumption of liquid fuel is predicted to climb by 64% relative to 2020, hence, in order to reduce the demand for carbon-based fuels, increasing the production of biofuels might be a more sustainable approach. 5,6…”

Research on Real-Time Prediction of Hydrogen Sulfide Leakage Diffusion Concentration of New Energy Based on Machine Learning

“…Later, after decades of development and improvement, researchers established mathematical models applicable to the study of heavy gas diffusion simulations. In the 1970s, Blackmore and Wheatly [14,15] conducted a review and analysis of most of the heavy gas [16][17][18][19] diffusion models established at that time. The ones that are the most applied currently include the BM model [20], box model [21], shallow model [22], and hydrodynamic approach [23], but there are great limitations in the use of these models.…”