BackgroundFor economical bioethanol production from lignocellulosic materials, the major technical challenges to lower the production cost are as follows: (1) The microorganism should use efficiently all glucose and xylose in the lignocellulose hydrolysate. (2) The microorganism should have high tolerance to the inhibitors present in the lignocellulose hydrolysate. The aim of the present work was to combine inhibitor degradation, xylitol fermentation, and ethanol production using a single yeast strain.ResultsA new process of integrated aerobic xylitol production and anaerobic ethanol fermentation using non-detoxified acid pretreated corncob by Candida tropicalis W103 was proposed. C. tropicalis W103 is able to degrade acetate, furfural, and 5-hydromethylfurfural and metabolite xylose to xylitol under aerobic conditions, and the aerobic fermentation residue was used as the substrate for ethanol production by anaerobic simultaneous saccharification and fermentation. With 20% substrate loading, furfural and 5-hydroxymethylfurfural were degraded totally after 60 h aerobic incubation. A maximal xylitol concentration of 17.1 g l-1 was obtained with a yield of 0.32 g g-1 xylose. Then under anaerobic conditions with the addition of cellulase, 25.3 g l-1 ethanol was produced after 72 h anaerobic fermentation, corresponding to 82% of the theoretical yield.ConclusionsXylitol and ethanol were produced in Candida tropicalis W103 using dual-phase fermentations, which comprise a changing from aerobic conditions (inhibitor degradation and xylitol production) to anaerobic simultaneous saccharification and ethanol fermentation. This is the first report of integrated xylitol and ethanol production from non-detoxified acid pretreated corncob using a single microorganism.

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BACKGROUND 2,3‐Butanediol and succinic acid are staple chemicals that are widely used in the chemical industry. In this study, a new strategy for the simultaneous fermentation of 2,3‐butanediol and succinic acid by Enterobacter cloacae using xylose was developed. The mechanism by which the succinic acid pathway was enhanced during 2,3‐butanediol fermentation in E. cloacae was studied. In addition, the sodium bicarbonate feeding mode and time, pH, and aeration rate were optimized. Fed‐batch fermentation was performed under the optimal conditions using industrial xylose as a raw material. RESULTS The succinic acid pathway was enhanced by the addition of sodium bicarbonate during 2,3‐butanediol fermentation. Interestingly, a simple increase of the initial pH had no effect on the production of succinic acid. The sodium bicarbonate feeding mode and time, pH and aeration rate were optimized. Under the optimum conditions, including a sodium bicarbonate feeding mode of 2 and time of 12 h, a pH of 6.5 and an aeration rate of 0.4 vvm, a maximum of 40.67 g L‐1 of 2,3‐butanediol and 21.79 g L‐1 of succinic acid were obtained after a 72 h fed‐batch fermentation when xylose was used as raw material, with a total 2,3‐butanediol + succinic acid yield of 0.69 mol mol‐1 xylose. CONCLUSION 2,3‐Butanediol and succinic acid were produced in a single fermentation step using E. cloacae. The production of 2,3‐butanediol and succinic acid was enhanced by controlling the sodium bicarbonate feeding mode and time, pH, and aeration rate. This type of fermentation provides a promising means of lowering the cost of production of these chemicals by reducing the fermentation operating time and fermentation equipment maintenance. © 2017 Society of Chemical Industry

It is important to develop full-performance bio-jet fuel based on alternative feedstocks. The compound 1-butanol can be transformed into jet fuel through dehydration, oligomerization, and hydrogenation. In this study, a new catalyst consisting of Zn-Mn-Co modified γ-Al2O3 was used for the dehydration of high-concentration 1-butanol to butenes. The interactive effects of reaction temperature and butanol weight-hourly space velocity (WHSV) on butene yield were investigated with response surface methodology (RSM). Butene yield was enhanced when the temperature increased from 350 °C to 450 °C but it was reduced as WHSV increased from 1 h−1 to 4 h−1. Under the optimized conditions of 1.67 h−1 WHSV and 375 °C reaction temperature, the selectivity of butenes achieved 90%, and the conversion rate of 1-butanol reached 100%, which were 10% and 6% higher, respectively, than when using unmodified γ-Al2O3. The Zn-Mn-Co modified γ-Al2O3 exhibited high stability and a long lifetime of 180 h, while the unmodified γ-Al2O3 began to deactivate after 60 h. Characterization with X-ray diffraction (XRD), nitrogen adsorption-desorption, pyridine temperature-programmed desorption (Py-TPD), pyridine adsorption IR spectra, and inductively coupled plasma atomic emission spectrometry (ICP-AES), showed that the crystallinity and acid content of γ-Al2O3 were obviously enhanced by the modification with Zn-Mn-Co, and the loading amounts of zinc, manganese, and cobalt were 0.54%, 0.44%, and 0.23%, respectively. This study provides a new catalyst, and the results will be helpful for the further optimization of bio-jet fuel production with a high concentration of 1-butanol.