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Studies were performed on the effect of CaCO3 and CaCl2 supplementation to fermentation medium for ethanol production from xylose, glucose, or their mixtures using Scheffersomyces (Pichia) stipitis. Both of these chemicals were found to improve maximum ethanol concentration and ethanol productivity. Use of xylose alone resulted in the production of 20.68 ± 0.44 g L(-1) ethanol with a productivity of 0.17 ± 0.00 g L(-1) h(-1), while xylose plus 3 g L(-1) CaCO3 resulted in the production of 24.68 ± 0.75 g L(-1) ethanol with a productivity of 0.21 ± 0.01 g L(-1) h(-1). Use of xylose plus glucose in combination with 3 g L(-1) CaCO3 resulted in the production of 47.37 ± 0.55 g L(-1) ethanol (aerobic culture), thus resulting in an ethanol productivity of 0.39 ± 0.00 g L(-1) h(-1). These values are 229 % of that achieved in xylose medium. Supplementation of xylose and glucose medium with 0.40 g L(-1) CaCl2 resulted in the production of 44.84 ± 0.28 g L(-1) ethanol with a productivity of 0.37 ± 0.02 g L(-1) h(-1). Use of glucose plus 3 g L(-1) CaCO3 resulted in the production of 57.39 ± 1.41 g L(-1) ethanol under micro-aerophilic conditions. These results indicate that supplementation of cellulosic sugars in the fermentation medium with CaCO3 and CaCl2 would improve economics of ethanol production from agricultural residues.

Four different processes for butanol production from corn, namely, batch fermentation and distillative recovery (BFDR), batch fermentation and pervaporative recovery (BFPR), fed-batch fermentation and pervaporative recovery (FBFPR), and immobilized cell continuous fermentation and pervaporative recovery (ICCFPR) were evaluated. Pervaporative recovery significantly reduces the cost of butanol production. Depending upon the byproduct credit, which is approximately 3.7 times that of the amount of butanol produced, BFDR, BFPR, FBFPR, and ICCFPR result in a butanol price of $0.55, $0.14–0.39, $0.12–0.37, and $0.11–0.36×kg–1, respectively. The price of butanol was recently reported at $1.21×kg–1 by Chemical Marketing Reporter. It should be noted that all three components (acetone, butanol, and ethanol: ABE) diffuse through the pervaporation membrane. Further separation and purification of the solvents would require distillation, which has been considered in this exercise. This article also details the impact of byproduct credit, rate of return, and tax on butanol price.

Acetone butanol ethanol (ABE) was produced in an integrated continuous one-stage fermentation and gas stripping product recovery system using Clostridium beijerinckii BA101 and fermentation gases (CO(2) and H(2)). In this system, the bioreactor was fed with a concentrated sugar solution (250-500 g L(-1) glucose). The bioreactor was bled semi-continuously to avoid accumulation of inhibitory chemicals and products. The continuous system was operated for 504 h (21 days) after which the fermentation was intentionally terminated. The bioreactor produced 461.3 g ABE from 1,125.0 g total sugar in 1 L culture volume as compared to a control batch process in which 18.4 g ABE was produced from 47.3 g sugar. These results demonstrate that ABE fermentation can be operated in an integrated continuous one-stage fermentation and product recovery system for a long period of time, if butanol and other microbial metabolites in the bioreactor are kept below threshold of toxicity.

In these studies, butanol (acetone butanol ethanol or ABE) was produced from wheat straw hydrolysate (WSH) in batch cultures using Clostridium beijerinckii P260. In control fermentation 48.9 g L(-1) glucose (initial sugar 62.0 g L(-1)) was used to produce 20.1 g L(-1) ABE with a productivity and yield of 0.28 g L(-1 )h(-1) and 0.41, respectively. In a similar experiment where WSH (60.2 g L(-1) total sugars obtained from hydrolysis of 86 g L(-1) wheat straw) was used, the culture produced 25.0 g L(-1) ABE with a productivity and yield of 0.60 g L(-1 )h(-1) and 0.42, respectively. These results are superior to the control experiment and productivity was improved by 214%. When WSH was supplemented with 35 g L(-1) glucose, a reactor productivity was improved to 0.63 g L(-1 )h(-1) with a yield of 0.42. In this case, ABE concentration in the broth was 28.2 g L(-1). When WSH was supplemented with 60 g L(-1) glucose, the resultant medium containing 128.3 g L(-1) sugars was successfully fermented (due to product removal) to produce 47.6 g L(-1) ABE, and the culture utilized all the sugars (glucose, xylose, arabinose, galactose, and mannose). These results demonstrate that C. beijerinckii P260 has excellent capacity to convert biomass derived sugars to solvents and can produce over 28 g L(-1) (in one case 41.7 g L(-1) from glucose) ABE from WSH. Medium containing 250 g L(-1) glucose resulted in no growth and no ABE production. Mixtures containing WSH + 140 g L(-1) glucose (total sugar approximately 200 g L(-1)) showed poor growth and poor ABE production.

This article discusses the separation of butanol from aqueous solutions and/or fermentation broth by adsorption. Butanol fermentation is also known as acetone butanol ethanol (ABE) or solvent fermentation. Adsorbents such as silicalite, resins (XAD-2, XAD-4, XAD-7, XAD-8, XAD-16), bone charcoal, activated charcoal, bonopore, and polyvinylpyridine have been studied. Use of silicalite appears to be the more attractive as it can be used to concentrate butanol from dilute solutions (5 to 790-810 g L(-1)) and results in complete desorption of butanol (or ABE). In addition, silicalite can be regenerated by heat treatment. The energy requirement for butanol recovery by adsorption-desorption processes has been calculated to be 1,948 kcal kg(-1) butanol as compared to 5,789 kcal kg(-1) butanol by steam stripping distillation. Other techniques such as gas stripping and pervaporation require 5,220 and 3,295 kcal kg(-1) butanol, respectively.

The effect of factors such as gas recycle rate, bubble size, presence of acetone, and ethanol in the solution/broth were investigated in order to remove butanol from model solution or fermentation broth (also called acetone butanol ethanol or ABE or solvents). Butanol (8 g L(-1), model solution, Fig. 2) stripping rate was found to be proportional to the gas recycle rate. In the bubble size range attempted (0.5 and 0.5-5.0 mm), the bubble size did not have any effect on butanol removal rate (Fig. 3, model solution). In Clostridium beijerinckii fermentation, ABE productivity was reduced from 0.47 g L(-1) h(-1) to 0.25 g L(-1) h(-1) when smaller (0.5 mm) bubble size was used to remove ABE (Fig. 4, results reported as butanol/ABE concentration). The productivity was reduced as a result of addition of an excessive amount of antifoam used to inhibit the production of foam caused by the smaller bubbles. This suggested that the fermentation was negatively affected by antifoam.