Biomass-derived syngas fermentation into biofuels: opportunities and challenges.

Selection and optimization of microbial hosts for biofuels production.

In this paper, five most emerging renewable energy sources are analyzed. These emerging renewables are either special or advanced forms of the mainstream energy sources (solar, wind, geothermal, biofuels, biomass, and hydro) or brand new technologies. The five emerging renewable technologies discussed in this paper include marine energy, concentrated solar photovoltaics (CSP), enhanced geothermal energy (EGE), cellulosic ethanol, and artificial photosynthesis. Marine energy is divided into wave energy, tidal energy, tidal/ocean currents, salinity gradient, and ocean thermal energy conversion. CSP technologies are divided into parabolic troughs, linear Fresnel reflectors, parabolic dishes, and solar towers. The process for developing EGE reservoirs is also explained in detail. Cellulosic ethanol energy extraction is explained for both cellulolysis and gasification. Artificial photosynthesis is explained by considering semiconductor particles, electrolyzers, artificial leaves, and dye-synthesized solar cells. Each emerging renewable source's explanation is followed by its market share, challenges, implications for increased adoption, future prospects, and drawbacks.

Emerging renewable and sustainable energy technologies: State of the art

The production of biofuels from renewable sources is a major challenge in research. Methanol, ethanol, dimethyl ether (DME), synthetic natural gas (SNG), and hydrogen can be produced from syngas which is the result of the gasification of biomasses. Syngas composition varies according to the gasification technology used (such as fixed bed reactors, fluidized bed reactors, entrained flow reactors), the feedstock characteristics, and the operating parameters. This paper presents a review of the predominant biomass gasification technologies and biofuels obtained from syngas by biomass gasification.

https://www.mdpi.com/1996-1073/11/4/811/pdf

Biofuels production by biomass gasification: A review

The development of low-cost, sustainable, and renewable energy sources has been a major focus since the 1970s. Fuel-grade ethanol is one energy source that has great potential for being generated from biomass. The demonstration of the fermentation of biomass-generated producer gas to ethanol is the major focus of this article in addition to assessing the effects of producer gas on the fermentation process. In this work, producer gas (primarily CO, CO(2), CH(4), H(2), and N(2)) was generated from switchgrass via gasification. The fluidized-bed gasifier generated gas with a composition of 56.8% N(2), 14.7% CO, 16.5% CO(2), 4.4% H(2), and 4.2% CH(4). The producer gas was utilized in a 4-L bioreactor to generate ethanol and other products via fermentation using a novel clostridial bacterium. The effects of biomass-generated producer gas on cell concentration, hydrogen uptake, and acid/alcohol production are shown in comparison with "clean" bottled gases of similar compositions for CO, CO(2), and H(2). The successful implementation of generating producer gas from biomass and then fermenting the producer gas to ethanol was demonstrated. Several key findings following the introduction of producer gas included: (1) the cells stopped growing but were still viable, (2) ethanol was primarily produced once the cells stopped growing (ethanol is nongrowth associated), (3) H(2) utilization stopped, and (4) cells began growing again if "clean" bottled gases were introduced following exposure to the producer gas.

Fermentation of biomass-generated producer gas to ethanol.

A recently discovered clostridial bacteria converts components of synthesis gas (CO, CO 2 , H 2 ) into liquid products such as ethanol, butanol and acetic acid Isolated from an agricultural lagoon, the stability and productivity characteristics of the bacteria were studied in a continuous 45 l bubble column bioreactor at 37°C using artificial blends of CO, CO 2 , and N 2  Preliminary results on the rates of cell growth, substrate utilization, product formation, and yields of products and cells from CO are discussed At steady state, apparent yields (mole C in products per mole CO consumed) of ethanol, butanol, and acetic acid were 015, 0075 and 0025, respectively, and the cell yield was 025 g / mol CO The theoretical yield of ethanol is 033 if CO is only utilized for the production of ethanol The experimental yield of CO 2 from CO was approximately 60% compared to the theoretical yield of 67% with ethanol as the sole product As a comparison with another ethanol-producing bacteria, the results of a similar fermentation study using batch-grown Clostridium ljungdahlii showed yields of 0062 for ethanol and 0094 for acetic acid and a cell yield of 1378 g / mol 

Formation of ethanol from carbon monoxide via a new microbial catalyst

This study reports an industrially applicable non-sterile xylitol fermentation process to produce xylitol from a low-cost feedstock like corn cob hydrolysate as pentose source without any detoxification. Different immobilization matrices/mediums (alginate, polyvinyl alcohol, agarose gel, polyacrylamide, gelatin, and κ-carrageenan) were studied to immobilize Candida tropicalis NCIM 3123 cells for xylitol production. Amongst this calcium alginate, immobilized cells produced maximum amount of xylitol with titer of 11.1 g/L and yield of 0.34 g/g. Hence, the process for immobilization using calcium alginate beads was optimized using a statistical method with sodium alginate (20, 30 and 40 g/L), calcium chloride (10, 20 and 30 g/L) and number of freezing–thawing cycles (2, 3 and 4) as the parameters. Using optimized conditions (calcium chloride 10 g/L, sodium alginate 20 g/L and 4 number of freezing–thawing cycles) for immobilization, xylitol production increased significantly to 41.0 g/L (4 times the initial production) with corn cob hydrolysate as sole carbon source and urea as minimal nutrient source. Reuse of immobilized biomass showed sustained xylitol production even after five cycles.

/pdf/enhanced-xylitol-production-using-immobilized-candida-3rnuy5uup9.pdf

Enhanced xylitol production using immobilized Candida tropicalis with non-detoxified corn cob hemicellulosic hydrolysate.

Different classes of solvents were explored for liquid–liquid extraction (solvent extraction) of 2,3-butanediol (BDO) from aqueous solutions. Initially, the activity coefficients (γ∞) of BDO in various solvents were predicted using thermodynamic models, namely conductor-like-screening model-real solvents (COSMO-RS) and universal functional group activity coefficient model (UNIFAC-LL). These models were validated by comparing the distribution coefficients (Kd) predicted from modeling with experimental data for the solvents. Lower chain alcohols and derivatives of phenol showed highest Kd. 1-butanol, 2-sec-butylphenol (SBP) and cyclohexanol showed experimental Kd of 1.6, 1.2 and 0.9, respectively in aqueous fermented BDO broth. The UNIFAC-LL and COSMO-RS based predictions provided qualitative trend for the ranking of solvents, in reasonable agreement with the experimental data. In terms of numerical ability, UNIFAC-LL model performance is better compared to COSMO-RS. However, this work shows that the incorp...

Rapid Solvent Screening Using Thermodynamic Models for Recovery of 2,3-Butanediol from Fermentation by Liquid–Liquid Extraction

Continuous countercurrent liquid–liquid extraction method for the separation of 2,3-butanediol from fermentation broth using n-butanol and phosphate salt

BACKGROUND

Solvent extraction of 2,3-butanediol from dilute fermented systems is a challenging downstream unit operation. Addition of certain kosmotropic salts to the aqueous fermentation broth during the solvent extraction process can have considerable influence on the distribution of 2,3-butanediol. This work evaluates the usefulness of solvent extraction and the salting-out effect on the extraction characteristic of 2,3-butanediol in aqueous synthetic and fermented solutions.



RESULTS

Addition of 10 wt% dipotassium phosphate (K2HPO4) to the fermented 2,3-butanediol broth during solvent extraction results in 1.5–3-fold increase in distribution coefficient (Kd) and 7–14-fold increase in separation factor (α) for 2,3-butanediol using 2-sec butyl phenol and 1-butanol as extractants. Of various solvent–salt combinations studied; 2-sec butyl phenol + 10 wt% K2HPO4 provided Kd and α of 3.04 and 59.17 whereas 1-butanol + 10 wt% K2HPO4 provided Kd and α of 2.41 and 15.68, respectively, in fermented 2,3-butanediol broth solution.



CONCLUSION

This study demonstrated the prospects of repulsive salts addition to the fermented broth during the solvent extraction process. The results showed that this study may be used as a model to choose an appropriate combination of water-immiscible (hydrophobic) organic solvent and inorganic salt type and concentration for the economical recovery of 2,3-butanediol from fermentation broth. © 2014 Society of Chemical Industry

Srinivasan Rajagopalan

Papers

Formation of ethanol from carbon monoxide via a new microbial catalyst

Enhanced xylitol production using immobilized Candida tropicalis with non-detoxified corn cob hemicellulosic hydrolysate.

Rapid Solvent Screening Using Thermodynamic Models for Recovery of 2,3-Butanediol from Fermentation by Liquid–Liquid Extraction

Continuous countercurrent liquid–liquid extraction method for the separation of 2,3-butanediol from fermentation broth using n-butanol and phosphate salt

Repulsive effect of salt on solvent extraction of 2,3-butanediol from aqueous fermentation solution