W. J. Groot

Technologies for butanol recovery integrated with fermentations

Abstract In-situ product recovery can improve the performance of a butanol fermentation. Five technologies for in-situ product recovery have been compared on the basis of design parameters and energy efficiency. These five technologies are: stripping, adsorption, liquid—liquid extraction, pervaporation and membrane solvent extraction. From these, pervaporation and liquid—liquid extraction are considered to have the greatest potentials.

Pervaporation for simultaneous product recovery in the butanol/isopropanol batch fermentation

SummaryIn the butanol/isopropanol batch fermentation the substrate conversion can be raised by simultaneous product recovery using pervaporation with silicon tubing as a membrane.

Butanol recovery from fermentations by liquid-liquid extraction and membrane solvent extraction

Extraction can successfully be used for in-situ alcohol recovery in butanol fermentations to increase the substrate conversion. An advantage of extraction over other recovery methods may be the high capacity of the solvent and the high selectivity of the alcohol/water separation. Extraction, however, is a comprehensive operation, and the design of an extraction apparatus can be complex. The aim of this study is to assess the practical applicability of liquid-liquid extraction and membrane solvent extraction in butanol fermentations. In this view various aspects of extraction processes were investigated.Thirty-six chemicals were tested for the distribution coefficient for butanol, the selectivity of alcohol/water separation and the toxicity towards Clostridia. Convenient extractants were found in the group of esters with high molar mass.Liquid-liquid extraction was carried out in a stirred fermenter and a spray column. The formation of emulsions and the fouling of the solvent in a fermentation broth causes problems with the operation of this type of equipment. With membrane solvent extraction, in which the solvent is separated from the broth by a membrane, a dispersion-free extraction is possible, leading to an easy operation of the equipment. In this case the mass transfer in the membrane becomes important.With membrane solvent extraction the development of a process is emphasized in which the extraction characteristics of the solvent are combined with the property of silicone rubber membranes to separate butanol from water. In the case of apolar solvents with a high molar mass, the characteristics of the membrane process are determined completely by the solvent. In the case of polar solvents (e.g. ethylene glycol), the permselectivity of the membrane can profitably be used. This concept leads to a novel type of extraction process in which alcohol is extracted with a water-soluble solvent via a hydrophobic semipermeable membrane. This extraction process has been investigated for the recovery of butanol and ethanol from water. A major drawback in all processes with membrane solvent extraction was the permeation of part of the solvent to the aqueous phase.The extraction processes were coupled to batch, fed batch and continuous butanol fermentations to affirm the applicability of the recovery techniques in the actual process. In the batch and fed batch fermentations a three-fold increase in the substrate consumption could be achieved, in the continuous fermentation about 30% increase.

Increase of substrate conversion by pervaporation in the continuous butanol fermentation

SummaryIn a continuous fermentation of glucose to butanol and isopropanol by immobilized Clostridium beyerinckii cells the products were removed continuously by pervaporation. Both the glucose conversion and the reactor productivity were 65–70% higher than in a continuous fermentation without product removal.

Batch and continuous butanol fermentations with free cells: integration with product recovery by gas-stripping

SummaryIn a butanol batch fermentation the substrate consumption was increased threefold using in-situ product recovery by gas-stripping, in comparison with a control fermentation without product recovery. In a continuous fermentation in-situ recovery led to an increase in the biomass concentration, resulting in a threefold increase in productivity. The substrate consumption was increased by 10%. An external stripper was used as apparatus for the butanol recovery.

Continuous production of butanol from a glucose/xylose mixture with an immobilized cell system coupled to pervaporation

SummaryGlucose and xylose can be converted continuously and simultaneously to butanol using immobilized cells. Xylose is only converted when glucose is completely consumed and the biocatalyst is not fully inhibited by butanol. With pervaporation for in-situ butanol recovery the complete conversion of a feed containing 60 kg/m3 of mixed sugars is achieved.

Ethanol production in an integrated process of fermentation and ethanol recovery by pervaporation

In ethanol fermentations inhibition of the microorganism by ethanol limits the amount of substrate in the feed that can be converted. In a process high feed concentrations are desirable to minimize the flows. Such high feed concentrations can be realized in integrated processes in which ethanol is recovered from the fermentation broth as it is formed. In this study ethanol recovery by pervaporation was coupled to glucose fermentations by bakers yeast. Pervaporation was carried out with commercial silicone based hollow-fibre membrane modules with relatively high fluxes. Three different types of process configurations with pervaporation were investigated. Two of these configurations also included cell retention by microfiltration, in order to optimize the productivity. In the systems with pervaporation a feed containing 360 kg/m3 glucose could be converted almost completely. This feed concentration is a factor three higher than in a process without ethanol recovery. The productivity was 14 kg/m3 h in a system with pervaporation only, and could be increased to 43 kg/m3 h in the system with all recycle by microfiltration. The kinetic data suggest that accumulation of inhibitory compounds occurs in the integrated system. The integrated process was relatively easy in operation.

Integration of pervaporation and continuous butanol fermentation with immobilized cells I: Experimental results

Abstract In alcoholic fermentations substrate conversion is limited by product inhibition, but it can be increased by in situ product recovery. In this stud Experiments with a commercially available pilot plant plate-and-frame pervaporation module are described for the separation of alcohols from aqueous mi

Kinetics of ethanol production by baker's yeast in an integrated process of fermentation and microfiltration

The productivity of a fermentation is proportional to the biomass concentration. The productivity can therefore be increased by retention of the cells in the fermentor. In this study microfiltration was used for cell retention in a fermentation of glucose to ethanol by bakers yeast. Compared to a system without cell retention the productivity could be increased 12-fold to 55 kg/m3 h at a biomass concentration of 135 kg/m3. Maximal ethanol concentrations of 76 kg/m3 were obtained at conditions of growth. At zero growth conditions in the integrated system the ethanol concentration could be increased to about 115 kg/m3, and could be produced for at least 10 hours. The fermentation results in the integrated system could be described reasonably well with a mathematical model based on a different linear inhibition kinetics for growth and substrate consumption.

Ethanol production in an integrated fermentation/membrane system. Process simulations and economics

Four systems comprising of an ethanol fermentation integrated with microfiltration and/or pervaporation, and a conventional continuous culture, were compared with respect to the performance of the fermentation and economics. The processes are compared on the basis of the same kinetic model. It is found that cell retention by microfiltration leads to lower production costs, compared to a conventional continuous culture. Pervaporation becomes profitable at a high selectivity of ethanol/water separation and low membrane prices.