Acetone-butanol production, extractive systems

Acetone-butanol production, extractive fermentation in aqueous two-phase systems, 80... 

Production of bulk chemicals. The production of solvents is normally characterized by a general inhibition phenomenon which has been mainly attributed to the changes in membrane permeability, or to the toxic effects on the metabolic pathway. Aqueous two-phase systems have been shown to be effective as media for the extractive fermentation of a number of solvents which include ethanol, acetone-butanol and acetic acid (3). Improved productivity has been achieved in most of the cases as compared to the conventional fermentations, which is significantly due to the elimination of product inhibition. However, there is an indication that changes in the microenvironment of the microbial cells due to the presence of non-metabolizable polymers could also contribute, in the initial phases, to the increased production. The addition of PEG and dextran to a growth medium, for instance, was shown to give increased initial ethanol yields, as a result of decrease in the chemical potential of water (8). 

The interest in w-butanol as a biofuel has increased in recent years owing to its superior fuel qualities compared to ethanol. These include a higher octane number, lower heat of vaporization, higher energy density (energy/volume), and lower vapor pressure. However, in the traditional ABE (acetone-butanol-ethanol) fermentation process, the concentration of n-butanol coming from the fermenter is lower than that achieved in ethanol fermentation. In addition, acetone and ethanol are also produced. Recent studies to improve yield and increase w-butanol concentration have explored fed-batch systems with stripping, adsorption, liquid-liquid extraction, distillation, and/or pervaporation to recover products. 

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