Optimization of corn stover biorefinery for coproduction of oligomers and second generation bioethanol using non-isothermal autohydrolysis (original) (raw)
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Social Science Research Network, 2022
To maintain our society's sustainability with respect to people, prosperity, and the planet, we must produce liquid transportation fuels such as bioethanol on the renewable basis at a competitive price to petroleum-based fuels. The major challenges to commercialize cellulosic biofuels are low fermentation efficiency, low ethanol titer, and lack of technology to fully utilize the byproduct from bioconversion process such as lignin which has been underutilized. To overcome these technical barriers, we have proposed a novel design to fully utilize each component of lignocellulosic biomass for biofuels and bio-chemicals production, which involves green technologies such as hydrothermal and organosolv pretreatments to produce a cellulose-rich solid with good recovery of clean lignin after solvent recycling for improvement of plant protein-based adhesives as well as xylose remained in the aqueous phase for furfural upgradation. The focus of this study, as a part of the whole biorefinery concept, is to develop modified simultaneous saccharification and fermentation (mSSF) to enhance ethanol titers and yields, which combines the advantages of both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) via unique decantation process. The mSSF achieved higher ethanol concentration of 58.5 g/L and ethanol yield of 83.5% as compared to the traditional SSF process (49.9 g/L and 71.1%) at the biomass loadings of 20% (w/v). The mSSF also enabled higher ethanol titers of 72.3 g/L at higher loadings of 30% (w/v) with yields of 70.0%. As compared to published high-gravity fermentation, ethanol concentration of 72.3 g/L achieved in this study was the highest one in the lab-scale process, which proved that the proposed mSSF was an effective process to increase ethanol titers without sacrificing ethanol yields. The improved ethanol titers and yields would significantly lower the distillation cost and accelerate the commercialization of cellulosic biofuel production.
Bioethanol production from steam-pretreated corn stover through an isomerase mediated process
New Biotechnology, 2014
Agricultural by-products such as corn stover are considered strategic raw materials for the production of second-generation bioethanol from renewable and non-food sources. This paper describes the conversion of steam-pretreated corn stover to ethanol utilising a multi-step process including enzymatic hydrolysis, isomerisation, and fermentation of mixed hydrolysates with native Saccharomyces cerevisiae. An immobilised isomerase enzyme was used for the xylose isomerisation along with high concentrations of S. cerevisiae. The objective was to assess the extent of simultaneity of the various conversion steps, through a detailed analysis of process time courses, and to test this process scheme for the conversion of lignocellulosic hydrolysates containing several inhibitors of the isomerase enzyme (e.g. metal ions, xylitol and glycerol). The process was tested on two types of hydrolysate after acid-catalysed steam pretreatment: (a) the water soluble fraction (WSF) in which xylose was the largest carbon source and (b) the entire slurry, containing both cellulose and hemicellulose carbohydrates, in which glucose predominated. The results indicated that the ethanol concentration rose when the inoculum concentration was increased in the range 10-75 g/L. However, when xylose was the largest carbon source, the metabolic yields were higher than 0.51 g ethanol /g consumed sugars probably due to the use of yeast internal cellular resources. This phenomenon was not observed in the fermentation of mixed hydrolysates obtained from the entire pretreated product and in which glucose was the largest carbon source. The ethanol yield from biomass suspensions with dry matter (DM) concentrations of 11-12% (w/v) was 70% based on total sugars (glucose, xylose, galactose). The results suggest that xylulose uptake was more effective in mixed hydrolysates containing glucose levels similar to, or higher than, xylose. Analysis of the factors that limit isomerase activity in lignocellulosic hydrolysates excluded any inhibition due to residual calcium ions after the detoxification of the hemicellulose hydrolysates with Ca(OH) 2 . By contrast, most of the enzyme activity ceased during the fermentation of the entire slurry after steam explosion, probably due to synergistic inhibition effects of various fermentation coproducts.
Alkaline pretreatment and enzymatic hydrolysis of corn stover for bioethanol production
Research, Society and Development, 2021
The demand for ethanol in Brazil is growing. However, although the country is one of the largest producers of this fuel, it is still necessary to diversify the production matrix. In that regard, studies with different raw materials are needed, mainly the use of low cost and high available wastes such as lignocellulosic residues from agriculture. Therefore, this study aimed to analyze the bioethanol production from corn stover. An alkaline pretreatment (CaO) was carried out, followed by enzymatic hydrolysis (Cellic Ctec2 and Cellic Htec2) to obtain fermentable sugars. The best experimental condition for the pretreatment and hydrolysis steps resulted in a solution with 0.31 gsugar∙gbiomass-1. Then, the fermentation was performed by the industrial strain of Saccharomyces cerevisiae (PE-2) and by the wild yeast strain Wickerhamomyces sp. (UFFS-CE-3.1.2). The yield obtained was 0.38 gethanol∙gdry biomass-1 was, demonstrating the potential of this process for bioethanol production.
Lautech Journal of Engineering and Technology, 2021
In this study, corn stover was converted into ethanol using a locally-fabricated bioreactor and process conditions were optimized. The corn stover biomass used as substrate was milled, screened to 200 μm and hydrolyzed with between 0.1-0.5 M HCl. The hydrolysis experiment was carried out for substrate concentrations of 20, 25, and 30% (w/v) of milled bagasse prepared in a 1000 mL glass jar containing distilled water. For each substrate concentration, the time, temperature, and acid concentration were varied between 10-60 min., 80-97 °C, and 0.1-0.5 M, respectively to find the optimum glucose yield. Glucose concentration in the optimum hydrolysate sample was determined using glucose oxidase method. Fermentation experiment was conducted in the bioreactor using 700 ml of the hydrolysate and Saccharomyces cerevisiae supplemented with minerals to yield ethanol of 21.47 g/L after 48 hours. A linear regression model developed after analysis of variance was able to predict the concentration of glucose produced during the acid hydrolysis, and the optimum ethanol yield of 21.47 g/L compares well with previous reported yield values found in literature.
2012
Background: While simultaneous saccharification and co-fermentation (SSCF) is considered to be a promising process for bioconversion of lignocellulosic materials to ethanol, there are still relatively little demo-plant data and operating experiences reported in the literature. In the current work, we designed a SSCF process and scaled up from lab to demo scale reaching 4% (w/v) ethanol using xylose rich corncobs. Results: Seven different recombinant xylose utilizing Saccharomyces cerevisiae strains were evaluated for their fermentation performance in hydrolysates of steam pretreated corncobs. Two strains, RHD-15 and KE6-12 with highest ethanol yield and lowest xylitol yield, respectively were further screened in SSCF using the whole slurry from pretreatment. Similar ethanol yields were reached with both strains, however, KE6-12 was chosen as the preferred strain since it produced 26% lower xylitol from consumed xylose compared to RHD-15. Model SSCF experiments with glucose or hydrolysate feed in combination with prefermentation resulted in 79% of xylose consumption and more than 75% of the theoretical ethanol yield on available glucose and xylose in lab and PDU scales. The results suggest that for an efficient xylose conversion to ethanol controlled release of glucose from enzymatic hydrolysis and low levels of glucose concentration must be maintained throughout the SSCF. Fed-batch SSCF in PDU with addition of enzymes at three different time points facilitated controlled release of glucose and hence co-consumption of glucose and xylose was observed yielding 76% of the theoretical ethanol yield on available glucose and xylose at 7.9% water insoluble solids (WIS). With a fed-batch SSCF in combination with prefermentation and a feed of substrate and enzymes 47 and 40 g l-1 of ethanol corresponding to 68% and 58% of the theoretical ethanol yield on available glucose and xylose were produced at 10.5% WIS in PDU and demo scale, respectively. The strain KE6-12 was able to completely consume xylose within 76 h during the fermentation of hydrolysate in a 10 m 3 demo scale bioreactor. Conclusions: The potential of SSCF is improved in combination with prefermentation and a feed of substrate and enzymes. It was possible to successfully reproduce the fed-batch SSCF at demo scale producing 4% (w/v) ethanol which is the minimum economical requirement for efficient lignocellulosic bioethanol production process.
Cellulose Chemistry and Technology, 2023
The present study was carried out to optimise the simultaneous saccharification and fermentation process for bioethanol production from corn cobs. Ten (10) different corn genotypes (hybrids) were characterized in terms of chemical composition, including total solid, moisture, cellulose, hemicelluloses, lignin and ash contents. Among different corn genotypes, milled cobs of corn genotype PMH10 were found to have significantly high cellulose (34.05%) and low lignin content (11.87%). With sodium hydroxide pretreatment, the relative proportion of cellulose (56.70%) increased, while that of hemicelluloses, lignin and ash substantially decreased (11.87, 8.61 and 0.6%) in the treated cob residues. The optimization of the simultaneous saccharification and fermentation (SSF) process of pretreated cob residues through response surface methodology showed that maximum ethanol concentration of 3.64 mg/mL could be achieved when SSF was performed at 28.58 FPU/g enzyme dosage, solid loading of 14.95% and yeast inoculum of 9.56%.
High solid simultaneous saccharification and fermentation of wet oxidized corn stover to ethanol
2004
In this study ethanol was produced from corn stover pretreated by alkaline and acidic wet oxidation (WO) (195jC, 15 min, 12 bar oxygen) followed by nonisothermal simultaneous saccharification and fermentation (SSF). In the first step of the SSF, small amounts of cellulases were added at 50jC, the optimal temperature of enzymes, in order to obtain better mixing condition due to some liquefaction. In the second step more cellulases were added in combination with dried baker's yeast (Saccharomyces cerevisiae) at 30jC. The phenols (0.4-0.5 g/L) and carboxylic acids (4.6-5.9 g/L) were present in the hemicellulose rich hydrolyzate at subinhibitory levels, thus no detoxification was needed prior to SSF of the whole slurry. Based on the cellulose available in the WO corn stover 83% of the theoretical ethanol yield was obtained under optimized SSF conditions. This was achieved with a substrate concentration of 12% dry matter (DM) acidic WO corn stover at 30 FPU/g DM (43.5 FPU/g cellulose) enzyme loading. Even with 20 and 15 FPU/g DM (corresponding to 29 and 22 FPU/g cellulose) enzyme loading, ethanol yields of 76 and 73%, respectively, were obtained. After 120 h of SSF the highest ethanol concentration of 52 g/L (6 vol.%) was achieved, which exceeds the technical and economical limit of the industrial-scale alcohol distillation. The SSF results showed that the cellulose in pretreated corn stover can be efficiently fermented to ethanol with up to 15% DM concentration. A further increase of substrate concentration reduced the ethanol yield significant as a result of insufficient mass transfer. It was also shown that the fermentation could be followed with an easy monitoring system based on the weight loss of the produced CO 2. B 2004 Wiley Periodicals, Inc.
Polymers
Bio-based treatment technologies are gaining great interest worldwide, and significant efforts are being afforded to develop technology for the use of lignocellulosic biomass. The potential of corn stover (CS) as a feedstock for bioethanol production was investigated by creating an optimal pretreatment condition to maximize glucose production. The current study undertook the impact of novel physico-chemical pretreatment methods of CS, i.e., autoclave-assisted oxalate (CSOA) and ultrasound-assisted oxalate (CSOU), on the chemical composition of CS and subsequent saccharification and fermentation for bioethanol production. The delignification was monitored by physicochemical characterizations such as SEM, XRD, FTIR, CHNs, and TGA. The results evidenced that delignification and enzymatic saccharification of the CS pretreated by CSOA was higher than CSOU. The optimum enzymatic saccharification operating conditions were 1:30 g solid substrate/mL sodium acetate buffer at 50 °C, shaking sp...
Transformation of lignocellulose from corn stove for bioethanol production
Maejo International Journal of Energy and Environmental Communication, 2021
The use of fossil fuels, as well as the environmental issues associated with their burning, has pushed for the development of clean, renewable energy sources. Biofuels made from lignocellulosic biomass are considered a carbon-neutral and sustainable method. As the demand for non-petroleum fuels grows, more attention will be placed on developing a cost-competitive liquid transportation biofuel like ethanol. This study was conducted to produce bioethanol utilizing the SHF (separate hydrolysis and fermentation) technique from corn stove lignocellulose. Pretreatment with sodium hydroxide at various concentrations was also studied. The influence of enzymatic saccharification, fermentation time, and substrate concentration on sugar yield and, eventually, ethanol production was investigated. Fermentation was carried out by using the enzymatically saccharified hydrolysate and monoculture of Saccharomyces cerevisiae. The results reveal that pretreatment with 2% NaOH followed by 48 hours of h...
Chapter 16 Production of Bioethanol from Biomass : An Overview
2013
This chapter analyzes the main research trends on production of fuel ethanol from lignocellulosic materials. The main features of different pretreatment and detoxification methods are presented. The importance of process integration to simplify the overall process and improve the conversion of biomass into ethanol is discussed. Strategies for microbial strain development are disclosed in the framework of such integrated processes like simultaneous saccharification and co-fermentation and consolidated bioprocessing. The main challenges to fully develop the biomass-to-ethanol process are highlighted. Finally, the need of integrating the research efforts on molecular techniques and process integration is recognized. 16.1 Lignocellulosic Biomass as Feedstock The biomass is organic matter made by living organisms that contain energy stored from the sun. The radiant energy from sunlight is absorbed by plants. This energy is converted into chemical energy in the form of glucose, starch or ...