Downscaling Industrial-Scale Syngas Fermentation to Simulate Frequent and Irregular Dissolved Gas Concentration Shocks

Abstract

In large-scale syngas fermentation, strong gradients in dissolved gas (CO, H2) concentrations are very likely to occur due to locally varying mass transfer and convection rates. Using Euler-Lagrangian CFD simulations, we analyzed these gradients in an industrial-scale external-loop gas-lift reactor (EL-GLR) for a wide range of biomass concentrations, considering CO inhibition for both CO and H2 uptake. Lifeline analyses showed that micro-organisms are likely to experience frequent (5 to 30 s) oscillations in dissolved gas concentrations with one order of magnitude. From the lifeline analyses, we developed a conceptual scale-down simulator (stirred-tank reactor with varying stirrer speed) to replicate industrial-scale environmental fluctuations at bench scale. The configuration of the scale-down simulator can be adjusted to match a broad range of environmental fluctuations. Our results suggest a preference for industrial operation at high biomass concentrations, as this would strongly reduce inhibitory effects, provide operational flexibility and enhance the product yield. The peaks in dissolved gas concentration were hypothesized to increase the syngas-to-ethanol yield due to the fast uptake mechanisms in C. autoethanogenum. The proposed scale-down simulator can be used to validate such results and to obtain data for parametrizing lumped kinetic metabolic models that describe such short-term responses.

Experimental Insights into the Fermentation of Pyro-Syngas to Ethanol in a Semi-Batch and Continuous Stirred Bioreactor with Mathematical Modelling and Optimization

“…Similar observations have been reported by other researchers [15]. The yield coefficients, Y X CO , Y X H2 , and YCO E of the present study are 0.67 g/mol, 0.18 g/mol, and 6 mol/mol, respectively whereas the reported ranges are 0.24-2.6 g/mol, 0.20-0.37 g/mol, and 2-10.5 mol/mol, respectively [15][16][17][18][19][20][29][30][31][32]. Therefore, the model parameters are very much comparable with the literature data.…”

“…Henry's constant, correlating the gas and liquid phase concentration of a component under equilibrium, varies with temperature for all gases and hence is the same for all studies. The values of K L a for CO, CO 2 , and H 2 have varied from 23.5-100.7 h −1 , 27-116.7 h −1 , and 20-87.4 h −1 , whereas in reported studies their values have varied from 4.69-22.7 h −1 , 2.54-26.2 h −1 , and 6.67-19.4 h −1 , respectively [15][16][17][18][19][20]. The value of K L a for CO has also been reported to be 198 h −1 in one study [20].…”

“…Very recently, Puiman et al developed a scale-down model using a Euler-Lagrangean simulation to assess the fluctuations of gaseous components, CO, H 2 , etc. during the industrial-scale operation of syngas fermentation [18]. Elisa M. de Medeiros et al developed a dynamic model using growth kinetics on CO and H 2 and also dealt with optimization of the operation of a continuous stirred tank bioreactor [19].…”

A novel experimental method to determine substrate uptake kinetics of gaseous substrates applied to the carbon monoxide‐fermenting Clostridium autoethanogenum

“…Still, phenotype-altering mutations might accumulate in the genome during long-term exposure to fluctuating conditions (Ingelman et al, 2023). It can, however, be argued that strains with such mutations resemble industrial workhorses since microorganisms continuously experience fluctuating conditions in industrial-scale systems (Puiman et al, 2023).…”

Toward Net-Zero Greenhouse Gas Emission: Techno–Economic and Life Cycle Analyses of Routes for Triacetic Acid Lactone (TAL) Bioproduction

“…20 Moreover, acetic acid and ethanol hold promise from the standpoint of sustainability because of their potential production from various agro-industrial wastes via processes like syngas fermentation, methanol carbonylation, 21 and anaerobic digestion with acetogens that employ the Wood−Ljungdahl pathway. 22 The utilization of acetic acid and ethanol benefits the carbon footprint of TAL production when used as a feedstock for YL production platforms. 18 One added benefit of ethanol when compared with acetic acid is its reducing power; ethanol consumption generates two molar equivalents of NADH which can be used to fuel biosynthetic pathways.…”