Junjun Zhu

Detoxification of corn stover prehydrolyzate by trialkylamine extraction to improve the ethanol production with Pichia stipitis CBS 5776

In order to realize the separated ethanol fermentation of glucose and xylose, prehydrolysis of corn stover with sulfuric acid at moderate temperature was applied, while inhibitors were produced inevitably. A complex extraction was adopted to detoxify the prehydrolyzate before fermentation to ethanol with Pichia stipitis CBS 5776. The best proportion of mixed extractant was 30% trialkylamine-50% n-octanol -20% kerosene. Detoxification results indicated that 73.3% of acetic acid, 45.7% of 5-hydroxymethylfurfural and 100% of furfural could be removed. Compared with the undetoxified prehydrolyzate, the fermentability of the detoxified prehydrolyzate was significantly improved. After 48 h fermentation of the detoxified prehydrolyzate containing 7.80 g/l of glucose and 52.8 g/l of xylose, the sugar utilization ratio was 93.2%; the ethanol concentration reached its peak value of 21.8 g/l, which was corresponding to 82.3% of the theoretical value.

An integrated process to produce ethanol, vanillin, and xylooligosaccharides from Camellia oleifera shell

This study aims to present an integrated process that can be used to produce ethanol, vanillin, and xylooligosaccharides from Camellia oleifera shell. After the shell was pretreated with NaOH, two fractions were obtained: solid and liquid fractions. The solid fraction was hydrolyzed with cellulase and then fermented with Pichia stipitis to produce ethanol. The liquid fraction was subjected to oxidation to prepare vanillin or hydrolysis with xylanase to prepare xylooligosaccharides. The optimal pretreatment conditions of an orthogonal test were as follows: 12% NaOH concentration; 120°C; 150 min; and liquid-solid ratio of 10.0. After pretreatment, the solid fraction containing cellulose and a small part of xylan at 10% substance concentration via enzymatic hydrolysis and glucose-xylose cofermentation could obtain 17.35 g/L of ethanol, 80.90% of the theoretical yield. The liquid fraction was initially hydrolyzed with xylanase to produce 1758.63 mg/L of xylooligosaccharides (DP2-6) and then oxidized to produce 322.07 mg/L of vanillin.

A new magnesium bisulfite pretreatment (MBSP) development for bio-ethanol production from corn stover.

This study established a new more neutral magnesium bisulfate pretreatment (MBSP) using magnesium bisulfate as sulfonating agent for improving the enzymatic hydrolysis efficiency of corn stover. Using the MBSP with 5.21% magnesium bisulfate, 170°C and pH 5.2 for 60 min, about 90% of lignin and 80% of hemicellulose were removed from biomass and more than 90% cellulose conversion of substrate was achieved after 48 h hydrolysis. About 6.19 kg raw corn stover could produce 1 kg ethanol by Saccharomyces cerevisiae. Meanwhile, MBSP also could protect sugars from excessive degradation, prevent fermentation inhibition formation and directly convert the hemicelluloses into xylooligosaccharides as higher-value products. These results suggested that the MBSP method offers an alternative approach to the efficient conversion of nonwoody lignocellulosic biomass to ethanol and had broad space for development.

Comparative Detoxification of Vacuum Evaporation/Steam Stripping Combined with Overliming on Corn Stover Prehydrolyzate

Tow kinds of physical methods, vacuum evaporation and steam stripping, combined with overliming (calcium hydroxide) were applied to remove inhibitors which were produced simultaneously during the pretreatment of lignocellulosic biomass. Corn stover was steam exploded; the filtrate was hydrolyzed with dilute sulfuric acid. The acid hydrolyzate was then detoxified and fermented by yeast. Physical methods could remove volatile compounds from the acid hydrolyzate. When the acid hydrolyzate was condensed 11.13 times by vacuum, it could remove 59.89 % formic acid and 77.72 % acetic acid. At a steam stripping time of 120 min, 58.79 % formic acid and 80.83 % acetic acid were removed. While furfural was stripped off completely by the two methods. Overliming could reduce the contents of furans, however, sugars, especially pentoses, were also removed partially. The results of fermentation of the detoxified and undetoxified acid hydrolyzates by Pichia stipitis CBS 5776 showed that “steam stripping(120 min) + overliming(pH11, 60 ¿, 90 min)” could improve its fermentability significantly. In 24 h, the ethanol reached its peak of 15.92 g/l, 80.34 % of theoretical.

Bioethanol production: an integrated process of low substrate loading hydrolysis-high sugars liquid fermentation and solid state fermentation of enzymatic hydrolysis residue.

An integrated process of enzymatic hydrolysis and fermentation was investigated for high ethanol production. The combination of enzymatic hydrolysis at low substrate loading, liquid fermentation of high sugars concentration and solid state fermentation of enzymatic hydrolysis residue was beneficial for conversion of steam explosion pretreated corn stover to ethanol. The results suggested that low substrate loading hydrolysis caused a high enzymatic hydrolysis yield; the liquid fermentation of about 200g/L glucose by Saccharomyces cerevisiae provided a high ethanol concentration which could significantly decrease cost of the subsequent ethanol distillation. A solid state fermentation of enzymatic hydrolysis residue was combined, which was available to enhance ethanol production and cellulose-to-ethanol conversion. The results of solid state fermentation demonstrated that the solid state fermentation process accompanied by simultaneous saccharification and fermentation.

Degradation profiles of non-lignin constituents of corn stover from dilute sulfuric acid pretreatment.

Corn stover was separated into four derived streams: ethanol extractives (EE), hot water extractives (HWE), extracted cellulose, and extracted hemicelluloses. They were separately treated with 0.75% dilute sulfuric acid at 180°C for 40 minutes. Over 100 degradation products were separated and identified using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography (LC). These products contained compounds from several chemical classes, including sugars, aromatics, carboxylic acids, furans, alcohols, aldehydes, and cyclenes. Itaconic acid, succinic acid, fumaric acid, azelaic acid, DL-isoborneol, and 3-methyl-2-furoic acid were detected in the dilute sulfuric acid pretreated corn stover for the first time. Potential microbial fermentation inhibitors and valuable chemical building blocks were evaluated. In an effort to identify and develop inhibitors which are useful for controlling and improving the lignocellulosic biorefinery process, how they originated from the corn stover constituents was examined.

Quantitative proteomic analysis of xylose fermentation strain Pichia stipitis CBS 5776 to lignocellulosic inhibitors acetic acid, vanillin, and 5-hydroxymethylfurfural

&NA; To obtain a global insight into the dynamic protein expression pattern in Pichia stipitis during xylose fermentation in the presence of three representative inhibitors (acetic acid, vanillin and 5‐hydroxymethylfurfural), proteins were extracted for quantitative proteomic analysis using 8‐plex isobaric tag for relative and absolute quantitation (iTRAQ) on a liquid chromatography‐mass/mass spectrometry instrument. Interestingly, aconitase (Aco1p) and NAD‐isocitrate dehydrogenase (Idh1p) were upregulated during the middle exponential phase in the presence of the three inhibitors during tricarboxylic acid cycle. We speculated that yeast cells adaptively increased the expression of the tricarboxylic acid cycle proteins to compensate for low NADH derived from glycolysis in the presence of the three inhibitors. Proteins related to amino acid metabolism, aminoacyl tRNA synthesis and stress response were also significantly affected in the presence of the three inhibitors. Taken together, quantitative proteomic analysis is capable of monitoring P. stipitis xylose fermentation under inhibitor conditions and identifying physiological changes, such as stress response.