Tom Granström

Continuous two stage acetone-butanol-ethanol fermentation with integrated solvent removal using Clostridium acetobutylicum B 5313.

The objective of this study was to optimize continuous acetone-butanol-ethanol (ABE) fermentation using a two stage chemostat system integrated with liquid-liquid extraction of solvents produced in the first stage. This minimized end product inhibition by butanol and subsequently enhanced glucose utilization and solvent production in continuous cultures of Clostridium acetobutylicum B 5313. During continuous two-stage ABE fermentation, sugarcane bagasse was used as the cell holding material for the both stages and liquid-liquid extraction was performed using an oleyl alcohol and decanol mixture. An overall solvent production of 25.32g/L (acetone 5.93g/L, butanol 16.90g/L and ethanol 2.48g/L) was observed as compared to 15.98g/L in the single stage chemostat with highest solvent productivity and solvent yield of 2.5g/Lh and of 0.35g/g, respectively. Maximum glucose utilization (83.21%) at a dilution rate of 0.051/h was observed as compared to 54.38% in the single stage chemostat.

Butanol production from lignocellulosics

Clostridium spp. produce n-butanol in the acetone/butanol/ethanol process. For sustainable industrial scale butanol production, a number of obstacles need to be addressed including choice of feedstock, the low product yield, toxicity to production strain, multiple-end products and downstream processing of alcohol mixtures. This review describes the use of lignocellulosic feedstocks, bioprocess and metabolic engineering, downstream processing and catalytic refining of n-butanol.

Biobutanol: the outlook of an academic and industrialist

The gradual shift of transportation fuels from oil based fuels to alternative fuel resources and worldwide demand for energy has been the impetus for research to produce alcohol biofuels from renewable resources. Currently bioethanol and biodiesel can, however, not cover an increasing demand for biofuels. Hence, there is an extensive need for advanced biofuels with superior fuel properties. The present review is focused on the development of biobutanol, which is regarded to be superior to bioethanol in terms of energy density and hygroscopicity. Although acetone–butanol–ethanol (ABE) fermentation is one of the oldest large-scale fermentation processes, butanol yield by anaerobic fermentation remains sub-optimal. For sustainable industrial scale butanol production, a number of obstacles need to be addressed including choice of feedstock, low product yield, product toxicity to production strain, multiple end-products and downstream processing of alcohol mixtures. Metabolic engineering provides a means for fermentation improvements. Different strategies are employed in the metabolic engineering of Clostridia that aim to enhance the solvent production, improve selectivity for butanol production, and increase the tolerance of Clostridia to solvents. The introduction and expression of a non-clostridial butanol producing pathway in E. coli is a most promising strategy for butanol biosynthesis. Several rigorous kinetic and physiological models for fermentation have been formulated, which form a useful tool for optimization of the process. Due to the lower butanol titers in the fermentation broth, simultaneous fermentation and product removal techniques have been developed to improve production economics. With the use of new strains, inexpensive substrates, and superior reactor designs, economic ABE fermentation may further attract the attention of researchers all over the world. The present review is attempting to provide an overall outlook on discoveries and strategies that are being developed for commercial n-butanol production.

Continuous acetone-butanol-ethanol fermentation using SO2-ethanol-water spent liquor from spruce

SO2-ethanol-water (SEW) spent liquor from spruce chips was successfully used for batch and continuous production of acetone, butanol and ethanol (ABE). Initially, batch experiments were performed using spent liquor to check the suitability for production of ABE. Maximum concentration of total ABE was found to be 8.79 g/l using 4-fold diluted SEW liquor supplemented with 35 g/l of glucose. The effect of dilution rate on solvent production, productivity and yield was studied in column reactor consisting of immobilized Clostridium acetobutylicum DSM 792 on wood pulp. Total solvent concentration of 12 g/l was obtained at a dilution rate of 0.21 h(-1). The maximum solvent productivity (4.86 g/l h) with yield of 0.27 g/g was obtained at dilution rate of 0.64 h(-1). Further, to increase the solvent yield, the unutilized sugars were subjected to batch fermentation.

The two stage immobilized column reactor with an integrated solvent recovery module for enhanced ABE production.

The production of acetone, butanol, and ethanol (ABE) by fermentation is a process that had been used by industries for decades. Two stage immobilized column reactor system integrated with liquid-liquid extraction was used with immobilized Clostridium acetobutylicum DSM 792, to enhance the ABE productivity and yield. The sugar mixture (glucose, mannose, galactose, arabinose, and xylose) representative to the lignocellulose hydrolysates was used as a substrate for continuous ABE production. Maximum total ABE solvent concentration of 20.30 g L(-1) was achieved at a dilution rate (D) of 0.2h(-1), with the sugar mixture as a substrate. The maximum solvent productivity (10.85 g L(-1)h(-1)) and the solvent yield (0.38 g g(-1)) were obtained at a dilution rate of 1.0 h(-1). The maximum sugar mixture utilization rate was achieved with the present set up which is difficult to reach in a single stage chemostat. The system was operated for 48 days without any technical problems.

Conditioning of SO2-ethanol-water spent liquor from spruce for the production of chemicals by ABE fermentation.

Abstract The objective of this study is to develop a process for conditioning spent liquor produced by SO2-ethanol-water (SEW) fractionation of spruce wood chips for fermentation to butanol, ethanol and acetone/isopropanol, i.e., by means of the so called acetone-butanol-ethanol (ABE) process using Clostridia bacteria. This study serves as part of an overall project aiming at the development of economic processes for producing chemicals and biofuels from mixed forest biomass via SEW fractionation and ABE fermentation technologies.

Oil palm empty fruit bunch to biofuels and chemicals via SO2–ethanol–water fractionation and ABE fermentation

A process has been developed for conversion of spent liquor produced by SO2-ethanol-water (SEW) fractionation of oil palm empty fruit bunch (OPEFB) fibers to biofuels by ABE fermentation. The fermentation process utilizes Clostridia bacteria that produce butanol, ethanol and acetone solvents at a total yield of 0.26 g/g sugars. A conditioning scheme is developed, which demonstrates that it is possible to utilize the hemicellulose sugars from this agricultural waste stream by traditional ABE fermentation. Fractionation as well as sugar hydrolysis in the spent liquor is hindered by the high cation content of OPEFB, which can be partly removed by acidic leaching suggesting that a better deashing method is necessary. Furthermore, it is inferred that better and more selective lignin removal is needed during conditioning to improve liquor fermentability.

Wheat flour based propionic acid fermentation: an economic approach.

A process for the fermentative production of propionic acid from whole wheat flour using starch and gluten as nutrients is presented. Hydrolysis of wheat flour starch using amylases was optimized. A batch fermentation of hydrolysate supplemented with various nitrogen sources using Propionibacterium acidipropionici NRRL B 3569 was performed. The maximum production of 48.61, 9.40, and 11.06 g of propionic acid, acetic acid and succinic acid, respectively, was found with wheat flour hydrolysate equivalent to 90 g/l glucose and supplemented with 15 g/l yeast extract. Further, replacement of yeast extract with wheat gluten hydrolysate showed utilization of gluten hydrolysate without compromising the yields and also improving the economics of the process. The process so developed could be useful for production of animal feed from whole wheat with in situ production of preservatives, and also suggest utilization of sprouted or germinated wheat for the production of organic acids.

Biobutanol from Lignocellulosic Wastes

The perceived inability to economically provide conventional petroleum to meet the growing energy demands is facing a diverse and broad set of challenges. The major technical and commercial drawbacks of the existing biofuels (bioethanol or biodiesel) have prompted the continuing development of more advanced biofuels such as biobutanol. Acetone–butanol–ethanol (ABE) fermentation is an old process which recently attracted new interests for the production of butanol as an advanced biofuel. Efficient use of low cost lignocellulosic wastes as a carbon source for ABE fermentation can be a proper approach for the economical production of biobutanol. This chapter focuses on the utilization of lignocellulosic materials in ABE fermentation process. It explains the ABE fermentation process especially the processes that were economically used in the Soviet Union, China, and South Africa in the twentieth century. It also summarizes different technologies that have been suggested for the utilization of lignocelluloses for biobutanol production.

A green process for the production of butanol from butyraldehyde using alcohol dehydrogenase: process details

Depletion of energy sources has drawn attention towards production of bio-butanol by fermentation. However, the process is constrained by product inhibition which results in low product yield. Hence, a new strategy wherein butanol was produced from butyraldehyde using alcohol dehydrogenase and NADH as a cofactor was developed. Butyraldehyde can be synthesized chemically or through fermentation. The problem of cofactor regeneration during the reaction for butanol production was solved using substrate coupled and enzyme coupled reactions. The conventional reaction produced 35% of butanol without regeneration of cofactor using 300 μM NADH. The process of substrate coupled reaction was optimized to get maximum conversion. NADH (30 μM) and 100 μg per ml of alcohol dehydrogenase (320 U mg−1) could convert 17.39 mM of butyraldehyde to butanol using ethanol (ratio of butyraldehye to ethanol 1 : 4) giving a maximum conversion of 75%. The enzyme coupled reaction under the same conditions showed only 24% conversion of butyraldehyde to butanol using the glutamate dehydrogenase-L-glutamate enzyme system for the regeneration of cofactor. Hence, substrate coupled reaction is suggested as a better method over the enzyme coupled reaction for the cost effective production of butanol.