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Zhu J.,Nanjing Forestry University | Zhu J.,Jiangsu Key Laboratory of Biomass based Green Fuel and Chemicals | Yang J.,Nanjing Forestry University | Zhu Y.,Nanjing Forestry University | And 6 more authors.
Bioprocess and Biosystems Engineering | Year: 2014

The prehydrolyzate obtained from acid-catalyzed steam-exploded corn stover (ASC) mainly contains xylose and a number of inhibitory compounds that inhibit ethanol fermentation by Pichia stipitis. In this study, the effects of the ASC prehydrolyzate, specifically those of the carbohydrate-degradation products, lignin-degradation products (which were extracted from ASC prehydrolyzate using ethyl acetate), and six major phenolic compounds (added to pure-sugar media individually or in combination), on ethanol fermentation were investigated. Results indicate that the effects of the carbohydrate-degradation products were negligible (10 h delayed) compared with those of pure-sugar fermentation, whereas the effects of the lignin-degradation products were significant (52 h delayed). Meanwhile, the inhibitory effects of the major phenolic compounds were not caused by certain types of inhibitors, but were due to the synergistic effects of various inhibitors. © 2014 Springer-Verlag. Source


Zhu J.,Nanjing Forestry University | Zhu J.,Jiangsu Key Laboratory of Biomass based Green Fuel and Chemicals | Shi L.,Nanjing Forestry University | Zhang L.,Nanjing Forestry University | And 5 more authors.
Bioprocess and Biosystems Engineering | Year: 2016

The difference in the enzymatic hydrolysis yield of acid-catalyzed steam-exploded corn stover (ASC) before and after washing with water reached approximately 15 % under the same conditions. The reasons for the difference in the yield between ASC and washed ASC (wASC) were determined through the analysis of the composition of ASC prehydrolyzate and sugar concentration of enzymatic hydrolyzate. Salts produced by neutralization (CaSO4, Na2SO4, K2SO4, and (NH4)2SO4), sugars (polysaccharides, oligosaccharides, and monosaccharides), sugar-degradation products (weak acids and furans), and lignin-degradation products (ethyl acetate extracts and nine main lignin-degradation products) were back-added to wASC. Results showed that these products, except furans, exerted negative effect on enzymatic hydrolysis. According to the characteristics of acid-catalyzed steam explosion pretreatment, the five sugar-degradation products’ mixture and salts [Na2SO4, (NH4)2SO4] showed minimal negative inhibition effect on enzymatic hydrolysis. By contrast, furans demonstrated a promotion effect. Moreover, soluble sugars, such as 13 g/L xylose (decreased by 6.38 %), 5 g/L cellobiose (5.36 %), 10 g/L glucose (3.67 %), as well as lignin-degradation products, and ethyl acetate extracts (4.87 %), exhibited evident inhibition effect on enzymatic hydrolysis. Therefore, removal of soluble sugars and lignin-degradation products could effectively promote the enzymatic hydrolysis performance. © 2016 Springer-Verlag Berlin Heidelberg Source


Yang J.,Nanjing Forestry University | Rong Y.,Nanjing Forestry University | Gao L.,Nanjing Forestry University | Zhu J.,Nanjing Forestry University | And 7 more authors.
Huagong Xuebao/CIESC Journal | Year: 2016

Aiming at the effect of inhibitors on yeast ethanol fermentation during the fuel ethanol biorefinery process, a new green detoxification technology-ionic liquid extraction was developed for detoxification of the prehydrolyzate obtained from washed acid-catalyzed steam-exploded corn stover (ASC). The extractive performances of two kinds of imidazolium-based ionic liquids (alkylimidazolium hexafluorophosphate [Cnmim][PF6] (n=4,6,8) and alkylimidazolium tetrafluoroborate [Cnmim][BF4] (n=6,8)) for the ASC prehydrolyzate were investigated and compared. The results indicated that the extraction efficiency of the inhibitors decreased with the increase of alkyl chain length on the cation of ionic liquids. Ionic liquid with BF4 - anion had much higher extraction efficiency for the inhibitors than those with PF6 - anion because of the stronger effective charge in BF4 -. Compared to the extraction efficiency of sugars and inhibitors, [C8mim][BF4] was selected as the extractant for detoxification of the ASC prehydrolyzate. Its detoxification results indicated that 85.13% of 5-hydroxymethylfurfural, 53.22% of formic acid, 47.53% of acetic acid and 65.05% of total phenols could be removed, while the loss of sugars was less than 6%. © All Right Reserved. Source


Zhu J.,Nanjing Forestry University | Zhu J.,Jiangsu Key Laboratory of Biomass based Green Fuel and Chemicals | Zhu Y.,Nanjing Forestry University | Zhang L.,Nanjing Forestry University | And 6 more authors.
Separation and Purification Technology | Year: 2014

Trialkylamine was an effective extractant for the removal of inhibitors from corn stover prehydrolyzate. Ethanol fermentability of the extracted prehydrolyzate was improved significantly. An approach for regeneration and valuable solutes (mainly acetic acid) recovery from such extractant was to back-extract the extractant containing inhibitors with sodium hydroxide. The influences of NaOH concentration, aqueous-organic phase ratio (A/O) on the extractant regeneration were investigated. The results indicated that 17.5 g/l NaOH could remove 100% acetic acid at A/O of 1:1. 175 g/l NaOH at A/O of 1:10 could also reach the same effect. Likewise, the results of 175 g/l NaOH at A/O of 1:1 repeatedly back-extracted the extractant for ten cycles were the same as before. The performance of regenerated extractant on extraction the corn stover prehydrolyzate showed almost no change after reused ten cycles. So NaOH was very suitable to regenerate the extractant containing inhibitors in bioethanol industry. © 2014 Elsevier B.V. All rights reserved. Source


Zhu J.,Nanjing Forestry University | Zhu J.,Jiangsu Key Laboratory of Biomass based Green Fuel and Chemicals | Rong Y.,Nanjing Forestry University | Yang J.,Nanjing Forestry University | And 8 more authors.
Applied Biochemistry and Biotechnology | Year: 2015

High-efficiency xylose utilization is one of the restrictive factors of bioethanol industrialization. However, xylonic acid (XA) as a new bio-based platform chemical can be produced by oxidation of xylose with microbial. So, an applicable technology of XA bioconversion was integrated into the process of bioethanol production. After corn stover was pretreated with acid-catalyzed steam-explosion, solid and liquid fractions were obtained. The liquid fraction, also named as acid-catalyzed steam-exploded corn stover (ASC) prehydrolyzate (mainly containing xylose), was catalyzed with Gluconobacter oxydans NL71 to prepare XA. After 72 h of bioconversion of concentrated ASC prehydrolyzate (containing 55.0 g/L of xylose), the XA concentration reached a peak value of 54.97 g/L, the sugar utilization ratio and XA yield were 94.08 and 95.45 %, respectively. The solid fraction was hydrolyzed to produce glucose with cellulase and then fermented with Saccharomyces cerevisiae NL22 to produce ethanol. After 18 h of fermentation of concentrated enzymatic hydrolyzate (containing 86.22 g/L of glucose), the ethanol concentration reached its highest value of 41.48 g/L, the sugar utilization ratio and ethanol yield were 98.72 and 95.25 %, respectively. The mass balance showed that 1 t ethanol and 1.3 t XA were produced from 7.8 t oven dry corn stover. © 2015, Springer Science+Business Media New York. Source

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