Acetone-butanol fermentation revisited.

Furan derivatives, such as 5-hydroxymethylfurfural (HMF), obtained from acid-catalyzed dehydration of carbohydrates, can serve as renewable chemical platforms for the production of fuels and chemical intermediates. Addition of an inorganic salt to concentrated aqueous solutions of fructose (30 wt% fructose on salt free basis) in biphasic systems containing an organic extracting phase improves HMF yields by increasing the partitioning of HMF into the extracting phase, as measured by the partition coefficient, R, equal to the concentration of HMF in the organic phase normalized by the concentration in the aqueous phase. We have studied the impact of solvent choice on HMF yield using primary and secondary alcohols, ketones, and cyclic ethers in the C3–C6 range as extracting solvents in biphasic systems saturated with NaCl. Biphasic systems containing C4 solvents generated the highest HMF yields within each solvent class. Tetrahydrofuran demonstrated the best combination of high HMF selectivity (83%) and high extracting power (R = 7.1) at 423 K. The presence of NaCl provided the additional benefit of creating biphasic systems using solvents that are completely miscible with water in the absence of salt. We have also studied the impact of different salts on HMF yield in systems using 1-butanol as the extracting solvent. Na+ and K+ showed the best combination of extracting power and HMF selectivity of the monovalent and divalent chloride salts tested. Changing the anion of the salt from Cl− to Br− resulted in R-values and HMF selectivity values resembling the non-salt system, while changing to the SO42− divalent species generated a high R-value (8.1), but a low HMF selectivity value (71%).

Solvent Effects on Fructose Dehydration to 5-Hydroxymethylfurfural in Biphasic Systems Saturated with Inorganic Salts

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Transformation of biomass into commodity chemicals using enzymes or cells

Clostridium acetobutylicum naturally produces acetone as well as butanol and ethanol. Since acetone cannot be used as a biofuel, its production needs to be minimized or suppressed by cell or bioreactor engineering. Thus, there have been attempts to disrupt or inactivate the acetone formation pathway. Here we present another approach, namely, converting acetone to isopropanol by metabolic engineering. Since isopropanol can be used as a fuel additive, the mixture of isopropanol, butanol, and ethanol (IBE) produced by engineered C. acetobutylicum can be directly used as a biofuel. IBE production is achieved by the expression of a primary/secondary alcohol dehydrogenase gene from Clostridium beijerinckii NRRL B-593 (i.e., adhB-593) in C. acetobutylicum ATCC 824. To increase the total alcohol titer, a synthetic acetone operon (act operon; adc-ctfA-ctfB) was constructed and expressed to increase the flux toward isopropanol formation. When this engineering strategy was applied to the PJC4BK strain lacking in the buk gene (encoding butyrate kinase), a significantly higher titer and yield of IBE could be achieved. The resulting PJC4BK(pIPA3-Cm2) strain produced 20.4 g/liter of total alcohol. Fermentation could be prolonged by in situ removal of solvents by gas stripping, and 35.6 g/liter of the IBE mixture could be produced in 45 h.

Metabolic Engineering of Clostridium acetobutylicum ATCC 824 for Isopropanol-Butanol-Ethanol Fermentation

Immobilized cells : a review of recent literature

Continuous isopropanol-butanol-ethanol fermentation by immobilized Clostridium beijerinckii cells in a packed bed fermenter

Preliminary experiments were performed to investigate the feasibility of an immobilized cell reactor (with growing cells) for continuous production of n-butanol and isopropanol.

Continuous production of n-butanol and isopropanol by immobilized, growingClostridium butylicum cells

A method has been developed to start a fermentor with immobilized Clostridium butylicum spores aseptically.

W. F. M. van der Laan

Papers

Continuous isopropanol-butanol-ethanol fermentation by immobilized Clostridium beijerinckii cells in a packed bed fermenter

Continuous production of n-butanol and isopropanol by immobilized, growingClostridium butylicum cells

A method for starting a fermentor with immobilized spores of the genus Clostridium aseptically