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Bioethanol
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
A recent approach for obtaining ethanol from biomass is the syngas platform (Figure 9.1). In syngas fermentation, non-food-based feedstocks such as second and third-generation feedstocks are first converted to syngas using gasification technology and this gas is further fermented to ethanol using acetogenic bacteria (Devarapalli and Atiyeh 2015). Syngas is mainly a mixture of CO, CO2,and H2. However, depending upon the type of feedstock from which it is produced, it can contain trace amounts of CH4, NH3, H2S, NO, and some other hydrocarbons (Munasinghe and Khanal 2010). In addition to syngas, the industrial flue gases which are comprised of similar gas composition as syngas also can be converted to ethanol by acetogenic bacteria (Devarapalli and Atiyeh 2015). The syngas-fermenting organisms mainly include Clostridium autoethanogenum, Clostridium ljungdahlii, Acetobacterium woodii, Butyribacterium methylotrophicum, and Clostridium carboxidivorans (Henstra et al. 2007). These organisms metabolize syngas using the Wood-Ljungdahl pathway and convert it to organic acids and alcohols (Daniell et al. 2012). The overall biochemical reactions to convert syngas to ethanol and acetic acid can be represented by following equations: () 6CO+3H2O→C2H5OH+4CO2 (
Bioethanol production
Published in Ozcan Konur, Bioenergy and Biofuels, 2017
Carlos Ariel Cardona Alzate, Carlos Andrés García, Sebastián Serna Loaiza
Different microorganisms (e.g., Clostridium ljungdahlii, C. autoethanogenum, Acetobacterium woodii, C. carboxidivorans, and Peptostreptococcus productus) have been used to produce liquid fuels from synthesis gas (Munasinghe and Khanal, 2011). The main limitations of syngas fermentation is the low productivity and poor solubility of gaseous substrates in the liquid phase.
Ethanol production by syngas fermentation in a continuous stirred tank bioreactor using Clostridium ljungdahlii
Published in Biofuels, 2019
Bimal Acharya, Animesh Dutta, Prabir Basu
Syngas, a mixture of carbon monoxide, hydrogen and carbon dioxide, is used in the biochemical conversion process in the presence of a biocatalyst or microorganism to produce biofuel. Syngas fermentation is defined as the process to convert syngas into various chemical products like ethanol, alcohol, and organic acid. Commonly used biological catalysts or microorganisms in syngas fermentation are Clostridium ljungdahlii, Clostridium ragsdalei, Clostridium carboxidivorans, Clostridium autoethanogenum, and Alkalibaculum bacchi [7–10]. These biocatalysts play an important role to metabolize syngas into bioethanol and acetic acid through the wood–ljungdahl pathway [11]. There are number of challenges to economically operate continuous fermentation by using biomass extracted syngas in a bioreactor because it needs complex distillation due to low ethanol concentration, advanced cleaning of toxic contaminants in biomass extracted syngas, and cheaper growth medium or media ingredients [12–15].
Towards practical application of gasification: a critical review from syngas and biochar perspectives
Published in Critical Reviews in Environmental Science and Technology, 2018
Siming You, Yong Sik Ok, Daniel C. W. Tsang, Eilhann E. Kwon, Chi-Hwa Wang
Anaerobic microorganisms (carboxydotrophic homoacetogens) can ferment syngas to produce biofuels and chemicals via the reductive acetyl-CoA pathway, where syngas is converted into acetyl-CoA that can be incorporated into biomass, and indirectly (via acetate) and directly reduced to acetaldehyde and then ethanol (Martin, Richter, Saha, & Angenent, 2016). The major challenges of syngas fermentation include the slow mass transfer of syngas components in fermentation medium and relatively low volumetric productivity (Drzyzga et al., 2015; Yang & Ge, 2016b). Stirred tank reactors and biotrickling filters (packed-bed reactor) have been developed to promote the mass transfer by increasing the specific surface area between syngas compositions and fermentation medium (Munasinghe & Khanal, 2010; Shen, Brown, & Wen, 2017). Membrane biofilm reactors (MBfR) where a biofilm is directly attached to the membrane through which the gases diffuse have been applied for syngas fermentation (Henstra, Sipma, Rinzema, & Stams, 2007). Typical advantages of MBfR include high gas utilization efficiencies, low energy consumption, and small reactor footprints. However, more research is warranted regarding biofilm management, and the design of scalable reactor and cost-effective membranes (Martin & Nerenberg, 2012), which are still challenging in large-scale applications.
Production of chemicals in thermophilic mixed culture fermentation: mechanism and strategy
Published in Critical Reviews in Environmental Science and Technology, 2020
Kun Dai, Wei Zhang, Raymond Jianxiong Zeng, Fang Zhang
An alternative pathway that converts the recalcitrant organic wastes (such as lignocellulose and sludge) into syngas and then the syngas is utilized for syngas fermentation, was proposed in the last few decades (Liew et al., 2016). The major components of syngas are carbon monoxide (CO) and H2, and the minor components are CO2, CH4, H2S, and NOX. Until now, syngas fermentation has mainly focused on mesophilic conditions and the metabolites conversion into carboxylic acids, ethanol, and MCFA via the enriched mixed microbes of Clostridium carboxidivorans, Clostridium ljungdahlii and Clostridium kluyveri (Martin, Richter, Saha, & Angenent, 2016; Molitor et al., 2016; Ramió-Pujol, Ganigué, Bañeras, & Colprim, 2015). Wang, Zhang, et al. (2018) found that caproate production from H2 and CO2 at 25 °C (5.7 g/L) was higher than that of 35 °C (1.0 g/L). Roghair, Hoogstad, et al. (2018) demonstrated that high CO2 loading could promote caproate production (10.8 g/(L·d)) due to excessive ethanol oxidation (up to 29%). However, Roghair, Liu, et al. (2018) also reported that ethanol oxidation was proportionally inhibited by caproate and the chain elongation was completely inhibited at 20 g/L n-caproate. Thus, the caproate separation is also necessary in syngas fermentation. Luo, Jing, Lin, Zhang, and An (2018) proposed to convert syngas to CH4 by mesophilic MCF and found that the intermediate of acetate also had obvious inhibition on syngas conversion when the acetate concentration was higher than 2 g/L.