Simultaneous saccharification of hemicellulose and cellulose of corncob in a one-pot system using catalysis of carbon based solid acid from lignosulfonate

The drive towards sustainable chemistry has inspired the development of active solid acids as catalysts and ionic liquids as solvents for an efficient release of sugars from lignocellulosic biomass for future biorefinery practices. Carbon-based solid acid (SI–C–S–H2O2) prepared from sodium lignosulfonate, a waste of the paper industry, was used with water or ionic liquid to hydrolyze corncob in this study. The effects of various reaction parameters were investigated in different solvent systems. The highest xylose yield of 83.4% and hemicellulose removal rate of 90.6% were obtained in an aqueous system at 130 °C for 14 h. After the pretreatment, cellulase was used for the hydrolysis of residue and the enzymatic digestibility of 92.6% was obtained. Following these two hydrolysis steps in the aqueous systems, the highest yield of total reducing sugar (TRS) was obtained at 88.1%. Further, one-step depolymerization and saccharification of corncob hemicellulose and cellulose to reducing sugars in an IL-water system catalyzed by SI–C–S–H2O2 was conducted at 130 °C for 10 h, with a high TRS yield of 75.1% obtained directly. After recycling five times, the solid acid catalyst still showed a high catalytic activity for sugar yield in different systems, providing a green and effective method for lignocellulose degradation

Preparation of reducing sugars from corncob by solid acid catalytic pretreatment combined with in situ enzymatic hydrolysis

The efficient conversion of hemicellulose and cellulose into reducing sugars remains as one major challenge for biorefinery of lignocellulosic biomass. In this work, saccharification of corncob in the aqueous phase was effectively realized via pretreatment by magnetic carbon-based solid acid (MMCSA) catalyst, combined with the subsequent in situ enzymatic hydrolysis (occurring in the same pretreatment system after separation of MMCSA). Through the combined two-step hydrolysis of corncob, the total sugar (xylose and glucose) yield of 90.03% was obtained, including a xylose yield of 86.99% and an enzymatic digestibility of pretreatment residue of 91.24% (cellulase loading of 20 FPU/g, 24 h). Compared with the traditional enzymatic hydrolysis of pretreated residue, the presented in situ enzymatic hydrolysis system can reach a comparable enzymatic digestibility in one-third reacting time with a half cellulase loading and save about 31% water consumption, which provides a more sustainable and low-cost method for the saccharification of lignocellulose

A study of CO/syngas bioconversion by Clostridium autoethanogenum with a flexible gas-cultivation system

Bioconversion of CO/syngas to produce ethanol is a novel route in bioethanol production, which can be accomplished by some acetogens. Specific culture vessels and techniques are needed to cultivate these microorganisms since they are anaerobic and substrates are gaseous. In this work, gas-sampling bag was applied as a gas-cultivation system to study CO/syngas bioconversion by Clostridium autoethanogenum and was demonstrated to be efficient because of its flexibility and excellent ability to maintain the headspace atmosphere. C autoethanogenum can use CO as the sole carbon and energy source to produce ethanol, acetate as well as CO2. In the experimental range, higher ethanol production was favored by higher yeast extract concentrations, and the maximum ethanol concentration of 3.45 g/L was obtained at 1.0 g/L of yeast extract. Study with various bottled gases showed that C. autoethanogenum preferred to use CO other than CO2 and produced the highest level of ethanol with 100% CO as the substrate. C. autoethanogenum can also utilize biomass-generated syngas (36.2% CO, 23.0% H-2, 15.4% CO2, 11.3% N-2), but the process proceeded slowly and insufficiently due to the presence of O-2 and C2H2. In our study, C. autoethanogenum showed a better performance in the bioconversion of CO to ethanol than Clostridium ljungdahlii, a strain which has been most studied, and for both strains, ethanol production was promoted by supplementing 0.5 g/L of acetate. (C) 2017 Elsevier Inc. All rights reserved

Optimization of fed-batch enzymatic hydrolysis from alkali-pretreated sugarcane bagasse for high-concentration sugar production

Fed-batch enzymatic hydrolysis process from alkali-pretreated sugarcane bagasse was investigated to increase solids loading, produce high-concentration fermentable sugar and finally to reduce the cost of the production process. The optimal initial solids loading, feeding time and quantities were examined. The hydrolysis system was initiated with 12% (w/v) solids loading in flasks, where 7% fresh solids were fed consecutively at 6 h, 12 h, 24 h to get a final solids loading of 33%. All the requested cellulase loading (10 FPU/g substrate) was added completely at the beginning of hydrolysis reaction. After 120 h of hydrolysis, the maximal concentrations of cellobiose, glucose and xylose obtained were 9.376 g/L, 129.50 g/L, 56.03 g/L, respectively. The final total glucan conversion rate attained to 60% from this fed-batch process. (C) 2014 Published by Elsevier Ltd

Ethanol Production from High Solids Loading of Alkali-Pretreated Sugarcane Bagasse with an SSF Process

A fed-batch process and high-temperature simultaneous saccharification and fermentation (SSF) process were investigated to obtain high sugar yield and ethanol concentration. Different amounts of alkali-pretreated sugarcane bagasse were added during the first 24 h. For the highest final dry matter (DM) content of 25% (w/v), a maximal glucose and total sugar concentration of 79.53 g/L and 135.39 g/L, respectively, were achieved with 8.3 FPU/g substrate after 120 h of hydrolysis. Based on the hydrolysis experiment, two processes for ethanol production from sugarcane bagasse, simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF), were also compared using S. cerevisiae. The results indicated that ethanol concentration and yield in the SHF were higher, while ethanol productivity (gram per unit volume and over time) was lower. For 25% substrate loading, the ethanol productivity and ethanol concentration could reach 0.38 g.L-1.h(-1) and 36.25 g/L SSF in 96 h, respectively, while that of SHF could reach 0.32 g.L-1.h(-1), with an ethanol concentration of 47.95 g/L in 152 h for SHF. When high-temperature simultaneous saccharification and fermentation (SSF) process was performed by using Kluyveromyces marxianus NCYC 587 at 42 degrees C, 42.21 g/L ethanol (with an ethanol productivity of 0.44 g.L-1.h(-1)) was produced with 25% dry matter content and 8.3 FPU cellulase/g substrate, which meant 16.4% more ethanol when compared with SSF of S. cerevisiae

Saccharification of sugarcane bagasse by magnetic carbon-based solid acid pretreatment and enzymatic hydrolysis

Saccharification of sugarcane bagasse is one of the most important process for its conversion to high value biofuels and chemicals. In the present work, a sustainable hydrolysis method combined with catalytic pretreatment by magnetic carbon-based solid acid and subsequent enzymatic hydrolysis were applied for the enhanced reducing sugar (xylose and glucose) production from sugarcane bagasse. The pretreatment condition was optimized via response surface methodology with Box-Behnken design. Under optimized conditions (the ratio of sugarcane bagasse, catalyst and water is 1:1:25 (g:g:mL), 170 degrees C for 10 min), the highest xylose yield of 91.62 % was achieved for 10 min. The enzymatic digestibility of the pretreated sugarcane bagasse under the optimum condition was reached up to 94.26 % at 72 h under the enzyme loading of 20 FPU/g, which is much higher than that of natural sugarcane bagasse. Meanwhile, FTIR, XRD and SEM were used to characterize the effects of the pretreatment process. Overall, this study provides a greener and high-efficiency method for saccharifying sugarcane bagasse to produce reducing sugars

Synergistic Enhancement Effect of Compound Additive of Organic Alcohols and Biosurfactant on Enzymatic Hydrolysis of Lignocellulose

The insufficient of lignocellulose degradation enzymes, such as cellulase and hemicellulase, is the major obstacle that hinders the bioconversion of lignocellulosic biomass to monosaccharides, especially during the woody biomass hydrolysis process. The addition of additives has received significant attention due to their enhancement of the enzymatic degradation efficiency of lignocellulose. In the present study, a combination of organic alcohols and a biosurfactant could synergistically enhance the saccharification of the cellulose substrate of Avicel, as well as that of pretreated poplar. Results showed that compound additives can greatly improve the conversion rate of enzymatic hydrolysis. The combination of 0.1% (v/v) n-decanol and 1% (v/v) sophorolipid dramatically increased the poplar enzymatic conversion rate from 17.9% to 85%, improving it by 67.1%. Enzyme-rich Hypocrea sp. W63 was fermented to obtain beta-glucosidase (BGL) and xylanase (XYL), which were used as auxiliary enzymes during enzymatic hydrolysis. It was found that the effects of such a combination of additives improved the filter paper activity, stability, and longevity, helping in the recovery of the cellulase cocktail. The compound additives associated with the commercial cellulase and Hypocrea sp. W63 enzyme solution formed an excellent formula for improving the stability of BGL and XYL. The results provide insight into compound additives and the use of a cellulase and auxiliary enzyme cocktail to improve enzymatic hydrolysis for lignocellulose conversion into biofuels

Impact of Alkaline Pretreatment Condition on Enzymatic Hydrolysis of Sugarcane Bagasse and Pretreatment Cost

A combined severity factor (R-CSF) which is usually used to evaluate the effectiveness of hydrothermal pretreatment at above 100 degrees C had been developed to assess the influence of temperature, time, and alkali loading on pretreatment and enzymatic hydrolysis of lignocellulose. It is not suitable for evaluating alkaline pretreatment effectiveness at lower than 100 degrees C. According to the reported deducing process, this study modified the expression of R-CSF = log[C-OH-(n) x t x e((Tr-Tb))/14.75] as R-CSF = log [COH- x t x e([-13700/Tr+273)) + 36.2]} which is easier and more reasonable to assess the effectiveness of alkaline pretreatment. It showed that R-CSF exhibited linear trend with lignin removal, and quadratic curve relation with enzymatic hydrolysis efficiency (EHE) at the same temperature. The EHE of alkali-treated SCB could attain the maximum value at lower R-CSF, which indicated that it was not necessary to continuously enhance strength of alkaline pretreatment for improving EHE. Within a certain temperature range, the alkali loading was more important than temperature and time to influence pretreatment effectiveness and EHE. Furthermore, the contribution of temperature, time, and alkali loading to pretreatment cost which was seldom concerned was investigated in this work. The alkali loading contributed more than 70% to the pretreatment cost. This study laid the foundation of further optimizing alkaline pretreatment to reduce cost for its practical application

Improved Ethanol Production Based on High Solids Fed-Batch Simultaneous Saccharification and Fermentation with Alkali-Pretreated Sugarcane Bagasse

Alkali-pretreated sugarcane bagasse fiber was subjected to fed-batch simultaneous saccharification and fermentation (SSF) with a pre-hydrolysis process to increase the solids loading and produce a high concentration of ethanol. The hydrolysis medium and yeast feeding modes were investigated to determine suitable conditions for high sugar yield and ethanol production. Batch addition resulted in a cumulative substrate concentration of up to 36% (w/v) and enhanced ethanol concentrations, while ethanol conversion efficiency gradually declined. Enzymatic pre-hydrolysis and fermentation with fed-batch mode contributed to the SSF process. The highest ethanol concentration was 66.915 g/L with the conversion efficiency of 72.89%, which was achieved at 30% (w/v) solids content after 96 h of fermentation. Hydrolyzed medium and yeast were added in batch mode at 24 h of enzymatic hydrolysis and fermentation, respectively. Thus, combining the fed-batch mode with pre-hydrolysis SSF produced a high yield of ethanol