Enhancing delignification and subsequent enzymatic hydrolysis of corn stover by magnesium oxide-ethanol pretreatment

Sustainable process for fractionation of lignin by the microwave-assisted chemical additive approach: Towards sugarcane leaf biorefinery and characterization

The microwave assisted pretreatment on sugarcane leaf (SCL) biomass for delignification was studied to enhance cellulose digestibility. In this work, microwave assisted with additives were used to delignification SCL for maximize sugar yield recovery. Single factorial and Central composite design (CCD) were employed to optimize the microwave assisted pretreatment conditions for improve delignification efficiency and the sugar yield recovery. The optimized pretreatment conditions were determined to be 4 min pre-treatment time, 500 W microwave power, 1.0 M Na2CO3 and 10 % biomass loading condition produce maximum reducing sugar yield (601 mg g-1) and glucose sugar yield (231 mg g-1) were achieved during saccharification. Pretreated biomass produced reducing sugar and glucose yields that were 4.5 and 4.1 times higher than those of untreated (native) SCL-N biomass, respectively. Additionally, the recyclability study of black liquor, obtained from optimized conditioned treatment of SCL-MSC (Microwave-assisted sodium carbonate pretreated SCL) resulted in considerable saccharification yield up to three pretreatment cycles. The 1H NMR and 13C NMR spectra studies illustrate that aromatic units present in SCL fractionated lignin samples. The variations of structure features and chemical compositions of the raw and pretreated SCL biomass were analyzed by SEM, XRD and XPS analysis. Overall, SCL-MSC pretreatment condition significantly delignification of SCL and led to the maximum sugar production optimized strategies pretreatment conditions was produced maximum amount of sugar, which is great potential for bio-refinery product development.

Enhancing the Enzymatic Saccharification of Grain Stillage by Combining Microwave-Assisted Hydrothermal Irradiation and Fungal Pretreatment

Grain stillage from the liquor industry was pretreated by using microwave-assisted hydrothermal pretreatment, fungal pretreatments, and their combination to enable efficient enzymatic hydrolysis for sugar production. The microwave-assisted hydrothermal (MH) pretreatment was optimized by using a response surface methodology, and the respective maximum reducing sugar yield and saccharification efficiency of 17.59 g/100 g and 33.85%, respectively, were achieved under the pretreatment conditions of microwave power = 120 W, solid-to-liquid ratio = 1:15 (g·mL^-1), and time = 3.5 min. The fungal pretreatment with Phanerochaete chrysosporium digestion (PC) achieved the maximum ligninolytic enzyme activities in 6 days with 10% inoculum size at which the reducing sugar yield and saccharification efficiency reached 19.74 g/100 g and 36.29%, respectively. To further improve the pretreatment efficiency, MH and PC pretreatments were combined, but the sequence of MH and PC mattered on the saccharification efficiency. The MH + PC pretreatment (the MH prior to the PC) was better than PC + MH (the PC prior to the MH) in terms of saccharification efficiency. Overall, the MH + PC pretreatment achieved superior reducing sugar yield and saccharification efficiency (25.51 g/100 g and 66.28%, respectively) over all other studied pretreatment methods. The variations of chemical compositions and structure features of the raw and pretreated grain stillage were characterized by using scanning electron microscopy and Fourier transform infrared spectroscopy. The results reveal that both MH and PC pretreatments mainly functioned on delignification and decreasing cellulose crystallinity, thus enhancing the enzymatic saccharification of the pretreated grain stillage. The combined MH and PC pretreatment could be a promising method to enable cost-efficient grain stillage utilization for downstream applications such as biofuels.

Facilely reducing recalcitrance of lignocellulosic biomass by a newly developed ethylamine-based deep eutectic solvent for biobutanol fermentation

BACKGROUND

Biobutanol is promising and renewable alternative to traditional fossil fuels and could be produced by Clostridium species from lignocellulosic biomass. However, biomass is recalcitrant to be hydrolyzed into fermentable sugars attributed to the densely packed structure by layers of lignin. Development of pretreatment reagents and processes for increasing surface area, removing hemicellulose and lignin, and enhancing the relative content of cellulose is currently an area of great interest. Deep eutectic solvents (DESs), a new class of green solvents, are effective in the pretreatment of lignocellulosic biomass. However, it remains challenging to achieve high titers of total sugars and usually requires combinatorial pretreatment with other reagents. In this study, we aim to develop novel DESs with high application potential in biomass pretreatment and high biocompatibility for biobutanol fermentation.

RESULTS

Several DESs with betaine chloride and ethylamine chloride (EaCl) as hydrogen bond acceptors were synthesized. Among them, EaCl:LAC with lactic acid as hydrogen bond donor displayed the best performance in the pretreatment of corncob. Only by single pretreatment with EaCl:LAC, total sugars as high as 53.5 g L^-1 could be reached. Consecutive batches for pretreatment of corncob were performed using gradiently decreased cellulase by 5 FPU g^-1. At the end of the sixth batch, the concentration and specific yield of total sugars were 58.8 g L^-1 and 706 g kg^-1 pretreated corncob, saving a total of 50% cellulase. Utilizing hydrolysate as carbon source, butanol titer of 10.4 g L^-1 was achieved with butanol yield of 137 g kg^-1 pretreated corncob by Clostridium saccharobutylicum DSM13864.

CONCLUSIONS

Ethylamine and lactic acid-based deep eutectic solvent is promising in pretreatment of corncob with high total sugar concentrations and compatible for biobutanol fermentation. This study provides an efficient pretreatment reagent for facilely reducing recalcitrance of lignocellulosic materials and a promising process for biobutanol fermentation from renewable biomass.

Co-fermentation of magnesium oxide-treated corn stover and corn stover liquor for cellulosic ethanol production and techno-economic analysis

MgO is an effective catalyst to reduce the recalcitrant structure of corn stover and reduce sugar degradation during pretreatment. To evaluate the economic feasibility of MgO pretreatment, techno-economic analysis was performed at a commercial scale of 700,000 MT stover per year based on the collected experimental data. Compared to LHW pretreatment, MgO pretreatment reduced total capital investment due to elimination of solids washing and increased ethanol yield by 78.4 L/MT stover due to higher xylose yield (53.4 vs 10.9%), thus resulted in a lower minimum ethanol selling price (MESP) of $0.72/liter. Although washing of MgO-pretreated solids improved glucose (73.0 vs 69.5%) and xylose (66.0 vs 53.4%) yields, MESP did not decrease but increase by $0.08/liter due to the high capital cost of solid-liquid separation unit. Tween 80 also improved glucose (73.1 vs 69.5%) and xylose (62.6 vs 53.5%) yields. However, its high cost limited its economic feasibility in ethanol production.

Boosting fermentable sugars by integrating magnesium oxide-treated corn stover and corn stover liquor without washing and detoxification

Integration of MgO-treated corn stover and corn stover liquor for enzymatic hydrolysis was studied to improve sugar yield and concentration as well as to simplify the bioconversion process. Results showed that under the same enzymatic hydrolysis conditions (2 mL enzyme/g biomass and 10% substrate loading), MgO-treated corn stover plus corn stover liquor had a similar glucose yield (70.4 vs. 68.8%) and concentration (40.4 vs. 41.5 g/L) but a higher xylose yield (56.6 vs. 25.3%) and concentration (16.7 vs. 10.6 g/L) compared with using MgO-treated corn stover only. Corn stover slurry from MgO pretreatment was near-neutral and free of 5-hydroxymethylfurfural and furfural, eliminating the need for washing and detoxification and lightening the burden for wastewater treatment. In addition, Tween 80 significantly reduced the irreversible binding of lignin to enzyme, increasing xylose and glucose yields by 14.7 and 6.2% and sugar concentration by 7.4 g/L, respectively.

High-solids hydrolysis of corn stover to achieve high sugar yield and concentration through high xylan recovery from magnesium oxide-ethanol pretreatment

MgO-ethanol pretreatment was studied to boost sugar conversions and concentrations during enzymatic hydrolysis. Although corn stover pretreated by MgO and 50% ethanol had the highest glucan and xylan recoveries (89 and 71%), excessive xylan/glucan ratio (54.8%) hinders the access of enzyme to internal cellulose and hemicellulose and only 57% glucan and 46% xylan conversions and 43 g/L sugars were obtained after hydrolysis (10%-solids loading and 2 mL enzyme/g treated biomass). Corn stover pretreated by MgO and 30% ethanol had a moderate xylan/glucan ratio (39.1%), achieving higher glucan and xylan conversions (58 and 48%) and sugar concentrations (70 g/L) after hydrolysis (16%-solids loading and 1 mL enzyme/g treated biomass). A 16%-solids loading largely avoids the poor mixing issue caused by excessive high-solids loading. The addition of Tween 80 effectively eased the binding of lignin with enzyme, boosting glucan and xylan conversions to 67 and 68% and sugar concentrations to 89 g/L.