Although several separation technologies are technically capable of removing volatile products from fermentation broths, distillation remains the dominant technology. This is especially true for the recovery of biofuels such as ethanol. In this paper, the status of an emerging membrane-based technology, called pervaporation, for this application is reviewed. Several issues and research priorities which will impact the ability of pervaporation to be competitive for biofuel recovery from fermentation systems are identified and discussed. They include: increased energy efficiency; reduction of capital cost for pervaporation systems; longer term trials with actual fermentation broths; optimized integration of pervaporation with fermentor; synergy of performing both alcohol recovery and solvent dehydration by pervaporation with dephlegmation fractional condensation technology; and updated economic analyses of pervaporation at various biofuel production scales. Pervaporation is currently viable for biofuel recovery in a number of situations, but more widespread application will be possible when progress has been made on these issues. Published in 2005 for SCI by John Wiley & Sons, Ltd.

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A review of pervaporation for product recovery from biomass fermentation processes

Multi-column distillation followed by molecular sieve adsorption is currently the standard method for producing fuel-grade ethanol from dilute fermentation broths in modern corn-to-ethanol facilities. As the liquid biofuels industry transitions to lignocellulosic feedstocks, expands the end-product portfolio to include other alcohols, and encounters more dilute alcohol concentrations, alternative separation technologies which are more energy efficient than the conventional approach will be in demand. In this review, alcohol recovery technology options and alcohol dehydration technology options for the production of ethanol and 1-butanol are reviewed and compared, with an emphasis on the energy footprint of each approach. Select hybrid technologies are also described. Published in 2008 by John Wiley & Sons, Ltd

Separation technologies for the recovery and dehydration of alcohols from fermentation broths

Clostridial acetone/butanol fermentation used to rank second only to ethanol fermentation by yeast in its scale of production and thus is one of the largest biotechnological processes known Its decline since about 1950 has been caused by increasing substrate costs and the availability of much cheaper feedstocks for chemical solvent synthesis by the petrochemical industry The so-called oil crisis in 1973 led to renewed interest in novel fermentation and product recovery technologies as well as in the metabolism and genetics of the bacterial species involved As a consequence, almost all of the enzymes leading to solvent formation are known, their genes have been sequenced (in fact, Clostridium acetobutylicum has been recently included in the microbial genome sequencing project), the regulatory mechanisms controlling solventogenesis have begun to emerge and recombinant DNA techniques have been developed for these clostridia to construct specific production strains In parallel, cheap agricultural-waste-based feedstocks have been exploited for their potential as novel substrates, continuous culture methods have been successfully established and new on-line product recovery technologies are now available, such as gas stripping, liquid/liquid extraction, and membrane-based methods In combination with these achievements, a reintroduction of acetone/butanol fermentation on an industrial scale seems to be economically feasible, a view that is supported by a new pilot plant in Austria recently coming into operation

New insights and novel developments in clostridial acetone/butanol/isopropanol fermentation

An overview of advances in acetone-butanol fermentation research is presented with specific reference to the history of acetone-butanol fermentation, genetic manipulation of the butanol-producing Clostridium beijerinckii NCIMB 8052, as well as upstream and downstream processing. Specific reference is made to the development of the hyperamylolytic, hyper-"butanolagenic" C. beijerinckii BA101 strain. Amylolytic enzyme production by C. beijerinckii BA101 was 1.8- and 2.5-fold greater than that of the C. beijerinckii NCIMB 8052 strain grown in starch and glucose, respectively. We confirmed the presence of a phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) associated with cell extracts of C. beijerinckii BA101 by glucose phosphorylation by PEP and ATP-dependent glucose phosphorylation. It was found that C. beijerinckii BA101 was defective in PTS activity and that it compensates for this defect with enhanced glucokinase activity, resulting in an ability to transport and utilize glucose during the solventogenic stage. The principal problem associated with acetone-butanol fermentation by C. beijerinckii or C. acetobutylicum is butanol toxicity/inhibition to the culture. To solve this problem, we have attempted various alternative in situ/online techniques of butanol removal including membrane-based systems such as pervaporation, liquid-liquid extraction, and gas stripping. We found that gas stripping and pervaporation appear to be the most promising of the in situ acetone-butanol fermentation and recovery techniques but, in terms of cost-effective industrial applications, gas stripping appears to be the most promising.

Butanol fermentation research: Upstream and downstream manipulations

This article reviews bioconversion of plant materials such as wheat straw (WS), corn stover (CS), barley straw (BS), and switchgrass (SG) to butanol and process technology that converts these materials into this superior biofuel. Successful fermentation of low‒value WS makes butanol fermentation economically attractive. Simultaneous hydrolysis, fermentation, and product recovery has been successfully performed in a single reactor using WS and C. beijerinckii P260. Research on the production of butanol from other agricultural residues including CS, BS, and SG has steadily progressed. Use of several product‒recovery technologies such as liquid‒liquid extraction, gas stripping, perstraction, and pervaporation has been successfully applied in laboratory‒scale bioreactors. It is expected that these recovery technologies will play a major role in commercialization of this fermentation. By employing in line/in situ product‒recovery systems during fermentation, butanol toxicity to the culture has been drastically reduced. In addition to the use of low‒cost plant materials for the production of this biofuel, process integration is expected to play a major role in the economics of this product. © 2008 Society of Chemical Industry and John Wiley & Sons, Ltd

B. M. Ennis

Papers

The acetone-butanol-ethanol fermentation: a current assessment