Raw Corn Stover Research Articles

Rapid fractionation of corn stover by microwave-assisted protic ionic liquid [TEA][HSO4] for fermentative acetone–butanol–ethanol production

BackgroundThe use of ionic liquids (ILs) to fractionate lignocelluloses for various bio-based chemicals productions is in the ascendant. On this basis, the protic ILs consisting of triethylammonium hydrogen sulfate ([TEA][HSO4]) possessed great promise due to the low price, low pollution, and high efficiency. In this study, the microwave-assistant [TEA][HSO4] fractionation process was established for corn stover fractionation, so as to facilitate the monomeric sugars production and supported the downstream acetone–butanol–ethanol (ABE) fermentation.ResultsThe assistance of microwave irradiation could obviously shorten the fractionation period of corn stover. Under the optimized condition (190 W for 3 min), high xylan removal (93.17 ± 0.63%) and delignification rate (72.90 ± 0.81%) were realized. The mechanisms for the promotion effect of the microwave to the protic ILs fractionation process were ascribed to the synergistic effect of the IL and microwaves to the depolymerization of lignocellulose through the ionic conduction, which can be clarified by the characterization of the pulps and the isolated lignin specimens. Downstream valorization of the fractionated pulps into ABE productions was also investigated. The [TEA][HSO4] free corn stover hydrolysate was capable of producing 12.58 g L−1 of ABE from overall 38.20 g L−1 of monomeric sugars without detoxification and additional nutrients supplementation.ConclusionsThe assistance of microwave irradiation could significantly promote the corn stover fractionation by [TEA][HSO4]. Mass balance indicated that 8.1 g of ABE and 16.61 g of technical lignin can be generated from 100 g of raw corn stover based on the novel fractionation strategy.

Analysis and enhancement of the energy utilization efficiency of corn stover using strain Lsc-8 in a bioelectrochemical system

The strain Lsc-8 can produce a current density of 33.08 µA cm−2 using carboxymethylcellulose (CMC) as a carbon source in a three-electrode configuration. A co-culture system of strain Lsc-8 and Geobacter sulfurreducens PCA was used to efficiently convert cellulose into electricity to improve the electricity generation capability of microbial fuel cells (MFCs). The maximum current density achieved by the co-culture with CMC was 559 μA cm−2, which was much higher than that of strain Lsc-8 using CMC as the carbon source. The maximum power density reached 492.05 ± 52.63 mW cm−2, which is much higher than that previously reported. Interaction mechanism studies showed that strain Lsc-8 had the ability to secrete riboflavin and convert cellulose into acetic acid, which might be the reason for the high electrical production performance of the co-culture system. In addition, to the best of our knowledge, a co-culture or single bacteria system using agricultural straw as the carbon source to generate electricity has not been reported. In this study, the maximum current density of the three-electrode system inoculated with strain Lsc-8 was 14.56 μA cm−2 with raw corn stover as the sole carbon source. Raw corn stover as a carbon source was also investigated for use in a co-culture system. The maximum current density achieved by the co-culture was 592 μA cm−2. The co-culture system showed a similar electricity generation capability when using raw corn stover and when using CMC. This research shows for the first time that a co-culture or single bacteria system can realize both waste biomass treatment and waste power generation.

Evaluation of fuel and combustion properties of hydrochar derived from Co-hydrothermal carbonization of biomass and plastic

Co-hydrothermal carbonization (Co-HTC) thermochemically transforms multiple solid feedstocks into energy-dense hydrochar. Herein, this study investigated the corn stover-polyurethane mixture at various feedstock ratios (5–15% polyurethane and balance corn stover) on fuel and combustion properties of the hydrochar prepared at various Co-HTC conditions. Results indicate that Co-HTC shows lower mass yield than control HTC with corn stover only, however, it shows significant improvement in energy densification (7.8–34.5%) and fuel ratio (0.22–0.64). The thermogravimetric analysis shows that Co-HTC-derived hydrochars are more thermally stable compared to raw corn stover. The combustion properties evaluated by cone calorimeter indicate that the Co-HTC-derived hydrochars have maximum 1.3 times the peak heat release rate of raw corn stover. The Co-HTC-derived hydrochars along with raw corn stover and control hydrochar persist in smoldering phase (slow combustion) of combustion while raw polyurethane persists in flaming phase (fast combustion). Moreover, Co-HTC-derived hydrochars show relatively lower combustion efficiencies (49.2–75.2%) than raw corn stover (77.2–89.9%) or control hydrochar (75.2–77.9%). In addition, increasing polyurethane percentage in the corn stover-polyurethane mixture could reduce the combustion efficiency of hydrochar.

Pilot study on production of aviation fuel from catalytic conversion of corn stover

Aviation fuel is high energy density and is usually produced from refinery in petroleum industry. Production of renewable aviation fuel from biomass eases pressure of carbon emission regulation. The operational processes in this study include steam stripping, hydrolysis of residues, condensation reaction unit, autoclave hydrogenation, fixed-bed hydrodeoxygenation, and oil-upgrading unit. The biomass-derived aviation fuel has a low oxygen content of 0.4 %, while its high heat value is 45.5 MJ/kg. The aviation fuel ranges from C8 ∼ C15, and rich in isoparaffins (50.4 %) while the n-paraffins have a selectivity of 12.2 % and other components are cycloparaffins (19.0 %), aromatic hydrocarbons (11.3 %), and alkenes (5.6 %). The mass yield for aviation fuel from corn stover reaches 10.6 %. This pilot study achieved production of aviation fuel from raw biomass corn stover.

One-pot synthesis of 5-Hydroxymethylfurfural from glucose and corn stover in an aqueous choline chloride/ acetone ternary solvent

Aqueous choline chloride/acetone was developed as a green ternary solvent for catalytic conversion of glucose and raw corn stover into 5-HMF. The results illustrated that acidic ChCl solution played a vital role in promoting the tandem isomerization/dehydration reaction of glucose to 5-HMF, while acetone was identified as an efficient extracting solvent to simultaneously remove 5-HMF from the aqueous phase. The composition of the ternary solvent system was found to have a significant impact on the 5-HMF yield, reaction selectivity, and preventing the further degradation of 5-HMF. A competitive 5-HMF yield of 73.3 mol% was achieved from glucose catalyzed by an ultra-low H2SO4 loading of 2 mmol at 190 °C for 10 min in the ternary ChCl-H2O-acetone solvent with a mass ratio of 1:2:3. This novel solvent system exhibited good stability, high efficiency, and excellent recyclability, employing in catalytic conversion of both glucose and lignocellulose to produce 5-HMF.

Evaluating combustion characteristics and combustion kinetics of corn stover-derived hydrochars by cone calorimeter

This study investigated the combustion properties of corn stover-derived hydrochars using cone calorimeter. Hydrochars were prepared by hydrothermal carbonization (HTC) at 200, 230, and 260 °C for 30 min. Six different heat fluxes (5–50 kW/m2) were applied to hydrochars to determine critical heat flux (CHF), ignition temperature, thermal response, peak heat release rate (pHRR), thermal hazard risk, and combustion efficiency. Results show that increasing the HTC temperature decreased the CHF and ignition temperature but increased the thermal resistivity. Increasing the heat flux decreased the thermal resistivity and ignition time of all the hydrochars. Thermal hazard analysis indicated that the hydrochars posed lower thermal risk than raw corn stover. Finally, combustion kinetics were proposed using two parallel first order reactions for volatile matters and fixed carbon. The reaction rate of volatile matter was significantly higher than the reaction rate of fixed carbon. HTC increased the fixed carbon activation energies to as high as 24.0 MJ/mol. Overall, HTC forms hydrochars which are less flammable, more stable, and a lower thermally risk material for piloted ignition than raw corn stover.

Highly efficient fed-batch modes for enzymatic hydrolysis and microbial lipogenesis from alkaline organosolv pretreated corn stover for biodiesel production

High-density culture for microbial lipid preparation from low-cost lignocellulosic feedstocks is crucial for commercial-scale biodiesel production. Herein, fed-batch saccharification of alkaline organosolv pretreatment (AOP) of corn stover at an extremely high solids content of 47% (w/v) released 299.5 g/L of lignocellulosic sugars including 18.3% of soluble oligosaccharides. Three types of liquid hydrolysates for seed culture, fermentation, and feeding during fed-batch culture were obtained from the hydrolysate slurry using a two-step washing strategy with 99.3% of sugars recovery. Cutaneotrichosporon oleaginosum showed excellent capacity for assimilating both monosaccharides and oligosaccharides for lipid production using the fed-batch culture mode. Lipid concentration, content, and yield gained 42.3 g/L, 64.6%, and 20.4 g/100 g, respectively. Turbid hydrolysate collected with high recovery of high-concentration sugars and simplified process could be directly served as feeding medium. In general, the overall hydrolysis yield and lipid yield using fed-batch mode accounted for 93.2% and 97.6% of those using batch mode, respectively, resulting in a lipid output of 102.8 g/kg raw corn stover. The fatty acid composition and the prediction of biodiesel properties of lipid samples indicated the suitability for high-quality fuel production. This study provided valuable information for designing highly efficient lignocelluloses-to-biodiesel routes.

Sequential Action of Different Fiber-Degrading Enzymes Enhances the Degradation of Corn Stover

Corn stover is one of the most agricultural residue abundances over the world; however, it is extremely prevented from microbial and enzymatic degradation into monomers because of the complex chemical and physical structure. In order to degrade corn stover, a large variety of enzymes with different specificities are required. However, each enzyme has its own reaction condition such as optimal pH and temperature to express its maximum activity. We hypothesize that the best sequence of an enzyme reaction could influence the degradation of corn stover. Therefore, the objective of this study was to investigate the effect of enzyme sequence action on the degradation of corn stover. A complete randomized design was used for this study. Four enzymes were used, cellulase (Cel) (pH 4.8 at 50 °C), hemicellulase (Hem) (pH 5 at 50 °C), pectinase (Pec) (pH 4 at 50 °C) and laccase (Lac) (pH 3 at 30 °C). This was subsequently submitted to enzyme sequence digestion following four steps (6 h incubation for each step) during which a single enzyme in each step was evaluated. The substrate (raw corn stover) was placed in sodium acetate buffer with an enzyme. The supernatant was then collected in each step for further chemical analysis. The results showed that there was a significant difference at p < 0.05 between treatments, suggesting that sequential action of fiber-degrading enzymes affected the chemical composition of corn stover. The best enzyme sequence (in terms of the total reducing sugar in different steps) was Hem-Cel-Pec-Lac (2.2 mg/mL) at p < 0.05; however, the worst enzyme sequence was Lac-Pec-Hem-Cel (0.8 mg/mL) at p < 0.05. Almost all the first steps in the process showed an increasing level of reducing sugar except the step which started with Lac where a lower reducing sugar level was observed. Similarly, xylose showed a higher level in all the processes in the first steps regardless of the enzyme type. It was observed that glucose production was totally dependent on the position of Cel in the enzyme sequence. Therefore, enzyme sequence action may be a useful method for corn stover to improve its degradation as feed stock.

Recent advances in bioelectricity generation through the simultaneous valorization of lignocellulosic biomass and wastewater treatment in microbial fuel cell

The emergence of renewable energy technologies offers a significant advantage in the conversion of organic wastes to bioenergy. Lignocellulosic biomass (LCB) is one of the most widely generated and abundant carbon-based sources and is believed to be a rich source of energy that can be utilized by microbial consortia in a microbial fuel cell (MFC) to generate electricity. Different LCBs like, raw corn stover, rice milling, plant waste, wheat straw, etc. have been utilized in MFCs to produce a substantial amount of electric current. The MFC technology has showcased its ability in the simultaneous treatment of wastewater and converting different organic wastes including LCB into electricity. However, LCBs are known to be very complex in terms of their biodegradability within MFC, therefore, several pre-treatment and extraction techniques have been employed for efficient utilization by microorganisms. The present review article is focused on advancement in bioelectricity generation through MFC by utilizing different lignocellulosic wastes as feedstock, and integrating the treatment of wastewater, thereby creating a hygienic and pollutant-free environment. Moreover, various patents involving lignocellulosic biomass as MFC substrate has been described along with genetic measures for improving the MFC performance has also been illustrated.

Quality assessment of bio-oil and biochar from microwave-assisted pyrolysis of corn stover using different adsorbents

Biofuels in the form of bio-oil and biochar have been produced by microwave heating of corn stover. Different adsorbents such as silicon carbide (SiC) and activated carbon (AC) with different ratios (10%, 20%, and 30%) to corn stover are investigated with the aims of enhancing the absorption of the microwave, maximizing the yields of the desirable products i.e. bio-oil followed by biochar as well as improving their qualities. Use of both the adsorbents improved the heating performance through increase in the maximal temperature and heating rate by 170 °C and 36 °C/min respectively compared to without adsorbent. Use of AC increased the yield of bio-oil up to 45 wt% while SiC increased the gas yields up to a maximum value of 48 wt%. The better physical properties such as 37%, 5.3, 2.9 mPa s, and 1 g/mL for water content, pH, viscosity and density respectively of bio-oil were obtained when using AC as an adsorbent. Also, use of AC helped in producing bio-oils which contained higher carbon and hydrogen contents as well as high calorific value (17 MJ/kg). Similarly, use of AC increased the contents of hydrocarbons and phenols in the bio-oil up to 36% and 28% respectively with low oxygen-containing compounds (2%). Also, use of AC produced the biochar having cleanest pores that were almost free of carbon-like impurities with a higher surface area of the pore (105.2 m2/g). In addition, biochar having low ash content, high carbon content, and calorific value (28 MJ/kg) were achieved. The net energy recovery with respect to raw corn stover was calculated to be of maximum value i.e., 55% when using AC. The AC and SiC were reused for further runs of the experiments (5 times) with few changes in the heating behavior and the yields of the pyrolytic products.

Enantioselective synthesis of D-lactic acid via chemocatalysis using MgO: Experimental and molecular-based rationalization of the triose's reactivity and preliminary insights with raw biomass

The widespread applications of d-lactic acid (D-LaA) significantly prompted the research of its synthesis from renewable biomass via chemo-catalysis. Herein, we developed a robust but simple MgO-d-LaA system without using extra chiral ligand, achieving the highest LaA yield ∼90 % with ∼75 % enantiomeric excess (ee) value to d-LaA from dihydroxyacetone, glyceraldehyde, and pyruvaldehyde. The experimental and quantum chemistry computational results revealed that MgO and d-LaA presented a pronounced synergetic effect, where pre-added d-LaA provided suitable pH to promote [Mg(OH)(H2O)3]+ formation, acting as the active species to facilitate the production of pyruvaldehyde, from dihydroxyacetone and glyceraldehyde. d-LaA interacted with MgII species forming a chiral pocket-like complex, MgII-2(D-Lactate), which combined to pyruvaldehyde giving the transition state with lower strain energy due to the smaller steric repulsion, thus enabling 1, 2-H shift of hydrated-pyruvaldehyde preferentially via si-face attack, leading to d-LaA. The catalytic system could also be applied for the conversion of raw corn stover.

Integration of Air Classification and Hydrothermal Carbonization to Enhance Energy Recovery of Corn Stover

Air classification (AC) is a cost-effective technology that separates the energy-dense light ash fraction (LAF) from the inorganic-rich high ash fraction (HAF) of corn stover. HAF could be upgraded into energy-dense solid fuel by hydrothermal carbonization (HTC). However, HTC is a high-temperature, high-pressure process, which requires additional energy to operate. In this study, three different scenarios (i.e., AC only, HTC only, and integrated AC–HTC) were investigated for the energy recovery of corn stover. AC was performed on corn stover at an 8 Hz fan speed, which yielded 84.4 wt. % LAF, 12.8 wt. % HAF, and 2.8 wt. % below screen particles. About 27 wt. % ash was reduced from LAF by the AC process. Furthermore, HTC was performed on raw corn stover and the HAF of corn stover at 200, 230, and 260 °C for 30 min. To evaluate energy recovery, solid products were characterized in terms of mass yield, ash yield, ultimate analysis, proximate analyses, and higher heating value (HHV). The results showed that the energy density was increased with the increase in HTC temperature, meanwhile the mass yield and ash yield were decreased with the increase in HTC temperature. Proximate analysis showed that fixed carbon increased 18 wt. % for original char and 27 wt. % for HAF char at 260 °C, compared to their respective feedstocks. Finally, the hydrochar resulting from HAF was mixed with LAF and pelletized at 180 bar and 90 °C to densify the energy content. An energy balance of the integrated AC–HTC process was performed, and the results shows that integrated AC with HTC performed at 230 °C resulted in an additional 800 MJ/ton of energy recovery compared to the AC-only scenario.

Enhanced glucose production from cellulose and corn stover hydrolysis by molten salt hydrates pretreatment

Molten salt hydrates (MSHs) are remarkable in breaking through the recalcitrant structure of microcrystalline cellulose and raw biomass. After being pretreated in 60 wt% LiBr at 130 °C for 2 h, cellulose crystallinity as well as degree of polymerization (DP) decreased. It was found that 91.3% yield of pretreated cellulose was removed from MSHs by filteration followed by being hydrolyzed into glucose with a high yield of 75.3% by dilute acid under mild reaction conditions. The pretreatment process also works on raw corn stover hydrolysis. After being pretreated at 100 °C for 5 h, 88.4% yield of cellulose in biomass was recovered and can be hydrolyzed into 54.9% yield of glucose with dilute acid. It was found that the cellulose in corn stover can be easier degraded compared with microcrystalline cellulose during MSHs pretreatment, which dues to the formation of acetic acid from hemicellulose hydrolysis. The proposed pretreatment technique presents a promising potential for glucose production from biomass in a commercial way.

An understanding for improved biomass pyrolysis: Toward a systematic comparison of different acid pretreatments

Naturally occurring AAEMs in biomass exhibit detrimental effects to biomass pyrolysis as producing less oil with lower quality. Acid pretreatments are cheap and effective methods for mitigating AAEMs effect, thus improving the pyrolysis performance. In the current study, a combination of different experiment techniques and theoretical kinetic analysis was conducted to systematically compare the effects of both acid infusion and washing pretreatments. By utilizing Py-GC/MS system, the product distribution from pyrolysis of raw and acid pretreated corn stovers was obtained. Compared to that of raw corn stover, significant reduction of char and improvement of sugars, especially levoglucosan (55% yield based on cellulose), from pyrolysis of acid washed corn stover were achieved because of the thorough removal of AAEMs in corn stover. As for acid infused corn stover, maintaining reaction in acid buffer condition (3~5 wt% acid infusion) kept the sugar yield at relatively high level. Further increase of acid infusion over 5 wt% resulted in strong dehydration reaction of sugars and sharp decrease of phenolic compounds. The DTG pattern and the key kinetic parameters of corn stover dramatically changed with acid pretreatment. Strong condensation reaction between cellulose and lignin in acid infused corn stover were also suggested by kinetic analysis. Besides, the evolution of major phenolic monomers from lignin component versus temperature was revealed by TG/PI-TOF-MS system. As for acid pretreated corn stover, the agglomeration associated with the increase of char production were further ascribed to the enhanced polymerization of vinyl-phenols and other simple phenols. Overall, the study provides insights into the fast pyrolysis behavior of acid pretreated biomass for producing high-quality bio-oil and value-added chemicals.

Features correlated to improved enzymatic digestibility of corn stover subjected to alkaline hydrogen peroxide pretreatment

As one of the leading pretreatment approaches, alkaline hydrogen peroxide (AHP) pretreatment can enhance the enzymatic digestibility of lignocellulose significantly. In this study, the glucan conversion of AHP pretreated corn stover (CS) without and with water-wash were 28.4% and 50.0% higher than that of raw material, respectively. In order to systematically understand its mechanism, analyses of the features of AHP pretreated and raw CS, such as specific surface area, crystallinity, zeta potential, water holding capacity and swelling capacity and others were performed. The weight-average molecular weight (Mw) of the sugars in the hydrolysate and the particle size distribution of the hydrolysis residue were also analyzed. These results explained why AHP-CS was more conducive to enzymatic hydrolysis. The deeper reason was that the removal of lignin and the destruction of hydrogen bonds within cellulose and hemicellulose increased the accessibility of cellulose and reduced the non-productive adsorption of cellulase, which significantly improved the enzymatic digestibility.

Production of levulinic acid and biocarbon electrode material from corn stover through an integrated biorefinery process

To overcome the inefficient biomass conversion, waste generation, and lack of co-production in biorefineries, an integrated process was proposed for the conversion of corn stover into levulinic acid and biocarbon electrode material. Corn stover was pretreated through hydrothermal process using 0.45 wt% K2CO3 which removed 76 wt% lignin and 85 wt% xylan while preserving 83 wt% glucan. This was followed by acid hydrolysis to produce levulinic acid at varying H2SO4 concentrations and reaction time in a batch reactor at 190 °C. At a reaction time of 5 min in 2 wt% H2SO4, 35.8 wt% and 30 wt% glucan in raw and pretreated corn stover was converted to levulinic acid, respectively. The residue from acid hydrolysis was converted into biocarbon for supercapacitor electrodes via a two-step thermal activation process which showed a specific capacitance of 120 F g−1. The proposed integrated biorefinery concept provides multiple value-added products for a greater financial and environmental sustainability.

Corn Stover as Substrate for Biogas Generation and Precursor for Biosilica Production via Anaerobic Digestion

Production of fuels and chemicals from renewable biomass is crucial to sustainability of bio-based economy. In this study, anaerobic digestion of corn stover (CS) was carried out to produce biogas under mesophilic conditions. The study also investigated the potential of corn stover digestate ash as a potential source for biosilica production. A cumulative volume of 930 mL of biogas was produced with methane content of 85.87%. Higher and lower calorific values of biogas were calculated to be 36.30 MJ/m3 and 32.70 MJ/m3, respectively. Calcination of raw CS (RCS) and the digestate (CSD) was carried out at 600 °C for 3 hours. The samples generated, raw corn stover ash (RCSA) and corn stover digestate ash (CSDA) were characterized using X‐ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), and X‐ray diffractometer (XRD). The XRF results revealed that CSDA biosilica content was 60.49%, which was 34.84% higher than RCSA. There was reduction in most of the metallic impurities in CSDA compared to RCSA. Potassium oxide was drastically reduced from 12.34% to 1.60%, while Al2O3 was reduced from 7.17% to 6.95%. SEM images showed the changes in the surface morphology of RCSA and CSDA, while FTIR spectra identified the changes in the key functional groups present in the samples. The study showed that CS and its digestate could serve as profitable renewable feedstocks for bioenergy production and bio-based chemicals like silica.
 Keywords: Anaerobic Digestion; Biogas; Biosilica; Corn Stover; Digestate; Calorific Value

Bio-oil and biochar from microwave-assisted catalytic pyrolysis of corn stover using sodium carbonate catalyst

In the present study, bio-oil and biochar have been produced from microwave-assisted catalytic pyrolysis of corn stover (CS). The effects of microwave power (MWP) and mixing of sodium carbonate as a catalyst at different ratios have been examined. Both MWP and the catalyst improved the heating and increased the maximum temperatures of pyrolysis process. Rise in MWP increased the gas yield but decreased the biochar yield, while the bio-oil yield was not significantly affected. The use of catalyst increased the bio-oil yield and enhanced its properties. Increase in the ratios of catalyst from 10% to 30%, did not contribute a significant effect either on the yield or on the properties of the products. The water content in bio-oil was found to be in the range of 53.09–73.79%, while the minimum viscosity was observed to be 3.31 mPa s. The maximum higher heating value (HHV) of bio-oil and biochar were 13.17 MJ/kg and 29.77 MJ/kg respectively. The bio-oil samples were characterized chemically by a gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR). Most of the chemical group compounds in the bio-oil were identified to be alcohol, phenols, alkynes, acids, and aromatic. The net energy recovery from the raw CS was in the range of 28.29–42.97%.

Oxidative submerged lime pretreatment and high-solids saccharification of corn stover

Economic commercial-scale production of biofuels from lignocellulose depends, in part, on the development of a suitable pretreatment. In pursuit of that goal, this study assesses the repeatability and effectiveness of submerged lime pretreatment (SLP) of two batches of corn stover designated “Field” and “Module.” SLP was performed with 0.15 g Ca(OH)2 g−1 biomass and 10 g H2O g−1 biomass at 50 °C for 4 weeks while purging with air. SLP was repeated 14 times and the results of the mass balances, closures, and compositions of raw and SLP corn stover are presented. The glucan content of corn stover prior to pretreatment was determined to be 36.1 ± 0.7% (Module washed), 37.5 ± 0.4% (Field washed), and 32.6 ± 1.4% (Field unwashed). For washed corn stover (Module and Field), the standard deviation and coefficient of variation were <1%, demonstrating that the measurements were repeatable. For unwashed Field corn stover, because of its higher content of water-soluble components, the variability was slightly higher. The mass closures were above 96% with less than 2% standard deviation. The glucan content of SLP corn stover was 44.3 ± 0.8% (Module washed), 41.5 ± 0.5% (Field washed), and 42.9 ± 2.2% (Field unwashed). This study also presents a reliable analytical method for assessing the enzymatic digestibility of high-solids (15%) lignocellulose. Inositol is used as an internal standard to determine the final reactant volume, which is difficult in high-solids saccharification. After SLP, the overall glucan digestibility was ~80% (standard deviation < 4%, coefficient of variation < 5%), supporting the potential of SLP as a reproducible, cost-effective, and scalable pretreatment.

Butanol production coupled with acidogenesis and CO2 conversion for improved carbon utilization

Butanol production from lignocellulosic biomass has a low overall yield due to carbon loss in the form of xylose during the biomass pretreatment and CO2 during the fermentation processes. This research presents a cascading process for producing butanol coupling three bioprocesses. First, an indigenous microbial community performed the direct acidogenesis of raw corn stover producing an H2-CO2 gas stream and volatile fatty acids (VFA) using the most biodegradable fraction. The acidogenesis process had maximum hydrogen productivity of 87 mL/L day and VFA production of 8.5 g/L of acetic acid, 3.7 g/L of butyric acid, and 2.2 g/L of propionic acid. The acidogenesis process experienced a species succession with early colonizing bacteria dominated by Lactobacillus being replaced with more succeeding microbial groups dominated by Enterococcous, Prevotella, and Megasphaera. Second, the spent solids of corn stover were used for producing acetone-butanol-ethanol (ABE) using a mixed culture bioaugmented with Clostridium saccharobutylicum. A simplex centroid mixture design served to elucidate the effects of adding different mixtures of acetic, butyric, and propionic acids on butanol production. Pure butyric acid improved three times the butanol titer compared to the control treatment with no acid addition (610 mg/L versus 230 mg/L of butanol, respectively). Opposite, acetic and propionic acids inhibited the butanol production. Finally, additional butanol was produced using an H2-CO2 gas stream, where the type of inoculum and culture medium affected the process. An inoculum enriched with Spirochaetales, Pseudomonas, Enterobacter, and Proteiniphilum grown on a culture medium with trace metals reached the highest butanol titer of 889 mg/L. This cascading process improved the carbon utilization by producing butanol from VFA and CO2, and not only from cellulose.