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

Summary We examined the effect of gas-stripping on the in situ removal of acetone, butanol, and ethanol (ABE) from batch reactor fermentation broth. The mutant strain (Clostridium beijerinckii BA101) was not affected adversely by gas stripping. The presence of cells in the fermentation broth affected the selectivities of ABE. A considerable improvement in the productivity and yield was recorded in this work in comparison with the non-integrated process. In an integrated process of ABE fermentation-recovery using C. beijerinckii BA101, ABE productivities and yield were improved up to 200 and 118%, respectively, as compared to control batch fermentation data. In a batch reactor C. beijerinckii BA101 utilized 45.4 g glucose l )1 and produced 17.7 g total ABE l )1 , while in the integrated process it utilized 161.7 g glucose l )1 and produced total ABE of 75.9 g l )1 . In the integrated process, acids were completely converted to solvents when compared to the non-integrated process (batch fermentation) which contained residual acids at the end of fermentation. In situ removal of ABE by gas stripping has been reported to be one of the most important techniques of solvent removal. During these studies we were able to maintain the ABE concentration in the fermentation broth below toxic levels.

Production of acetone, butanol and ethanol by Clostridium beijerinckii BA101 and in situ recovery by gas stripping

This article describes the use of biofilm reactors for the production of various chemicals by fermentation and wastewater treatment. Biofilm formation is a natural process where microbial cells attach to the support (adsorbent) or form flocs/aggregates (also called granules) without use of chemicals and form thick layers of cells known as "biofilms." As a result of biofilm formation, cell densities in the reactor increase and cell concentrations as high as 74 gL-1 can be achieved. The reactor configurations can be as simple as a batch reactor, continuous stirred tank reactor (CSTR), packed bed reactor (PBR), fluidized bed reactor (FBR), airlift reactor (ALR), upflow anaerobic sludge blanket (UASB) reactor, or any other suitable configuration. In UASB granular biofilm particles are used. This article demonstrates that reactor productivities in these reactors have been superior to any other reactor types. This article describes production of ethanol, butanol, lactic acid, acetic acid/vinegar, succinic acid, and fumaric acid in addition to wastewater treatment in the biofilm reactors. As the title suggests, biofilm reactors have high potential to be employed in biotechnology/bioconversion industry for viable economic reasons. In this article, various reactor types have been compared for the above bioconversion processes.

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Biofilm reactors for industrial bioconversion processes: employing potential of enhanced reaction rates

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

Butanol, ‘a superior biofuel’ production from agricultural residues (renewable biomass): recent progress in technology†

An investigation was performed into the operation of an integrated system for continuous production and product recovery of solvents (acetone-butanol-ethanol) from the ABE fermentation process. Cells of Clostridium acetobutylicum were immobilized by adsorption onto bonechar, and used in a fluidized bed reactor for continuous solvent production from whey permeate. The reactor effluent was stripped of the solvents using nitrogen gas, and was recycled to the reactor. This relieved product inhibition and allowed further sugar utilization. At a dilution rate of 1.37 h−1 a reactor productivity of 5.1 kg/(m3 · h) was achieved. The solvents in the stripping gas were condensed to give a solution of 53.7 kg/m3. This system has the advantages of relieving product inhibition, and providing a more concentrated solution for recovery by distillation. Residual sugar and non-volatile reaction intermediates are not removed by gas stripping and this contributes to high solvent yields.

Integration of continuous production and recovery of solvents from whey permeate: use of immobilized cells of Clostridium acetobutylicum in a flutilized bed reactor coupled with gas stripping

Cells of Clostridium acetobutylicum were immobilized by adsorption onto bonechar and used for the production of solvents (ABE fermentation) from whey permeate When the process was performed in packed bed reactors operated in a vertical or inclined mode, solvent productivities approximating 6 kg/(m3h) were obtained However, the systems suffered from blockage due to excess biomass production and gas hold-up These problems were less apparent when a partially-packed bed reactor was operated in the horizontal mode A fluidized bed reactor proved to be the most stable of the systems investigated, and a productivity of 48 kg/(m3h) was maintained over a period of 2000 h of operation The results demonstrate that this type of reactor may have a useful future role in the ABE fermentation

Reactor design for the ABE fermentation using cells of Clostridium acetobutylicum immobilized by adsorption onto bonechar

A continuous bioreactor where cells were recycled using a cross-flow microfiltration (CFM) membrane plant was investigated for the production of solvents (ABE fermentation) from whey permeate using Clostridium acetobutylicum P262. A tubular CFM membrane plant capable of being backflushed was used. The continuous fermentations were characterized by cyclic solventogenic and acidogenic behaviour, and ultimately degenerated to an acidogenic state. Steady-state solvent production was obtained for only short periods. This degeneration is attributed to the complex morphological behaviour of this strain of organism on this substrate. It is postulated that to achieve steady-state solvent production over extended periods of time, it is necessary to maintain a balance among the various morphological cell forms, i.e. acid-producing vegetative cells, solvent-producing clostridial cells, and inert forms, e.g. spores.

Production of solvents (ABE fermentation) from whey permeate by continuous fermentation in a membrane bioreactor

A published process for the fermentative production and recovery of acetone-butanol-ethanol (ABE) has been modelled and analysed. Postulation of a Variable Yield Function has led to an unexpected Value Function. Given a desired ABE production range of 1.6×106 kg per year to 32×106 kg per year, and a typical fixed (or variable) cost term, γ, of $0.4 per kg ABE, the process has been shown to be unprofitable in the range 2×106 kg per year to 18 × 106 kg per year. Profitability is achieved at low production values (less than 2×106 kg per year), and at high production values (greater than 18×106 kg per year). Conversely, profitability is achieved for the comparable fixed yield case, forγ=$0.4 per kg ABE, for all production values, with the profitability increasing linearly with production.

I. S. Maddox

Papers

Integration of continuous production and recovery of solvents from whey permeate: use of immobilized cells of Clostridium acetobutylicum in a flutilized bed reactor coupled with gas stripping

Reactor design for the ABE fermentation using cells of Clostridium acetobutylicum immobilized by adsorption onto bonechar

Production of solvents (ABE fermentation) from whey permeate by continuous fermentation in a membrane bioreactor

The effect of a variable yield function on the profitability of an integrated ABE fermentation product recovery system