Ammonia Fiber Expansion Pretreatment Research Articles

Tuning Structural Characteristics of Corn Stover Through Ammonium and Sodium Sulfite (ASS) Pretreatment for Enhanced Enzymatic Hydrolysis.

The ammonia fiber expansion (AFEX) pretreatment of lignocellulosic biomass offers a significant advantage in terms of obtaining high glucan conversion, with the added benefit of ammonia being fully recyclable. However, despite the high efficiency of AFEX in pretreating lignocellulose, relatively high enzyme loading is still required for effective cellulose conversions. In this study, we have updated the AFEX pretreatment method; ammonia and sodium sulfite (ASS) can be used to produce a more digestible substrate. The results demonstrate that ASS-pretreated corn stover (CS) yields a higher fermentable sugar yield compared with AFEX pretreatment, even at lower enzyme loadings. Specifically, at an enzyme loading of 12 mg protein/g glucan, ASS-CS achieved 88.8% glucose and 80.6% xylose yield. Characterization analysis reveals that lignin underwent sulfonation during ASS pretreatment. This modification results in a more negative zeta potential for ASS-CS, indicating a reduction in nonproductive adsorption between lignin and cellulase through increased electrostatic repulsion.

Water-soluble saponins accumulate in drought-stressed switchgrass and may inhibit yeast growth during bioethanol production

BackgroundDeveloping economically viable pathways to produce renewable energy has become an important research theme in recent years. Lignocellulosic biomass is a promising feedstock that can be converted into second-generation biofuels and bioproducts. Global warming has adversely affected climate change causing many environmental changes that have impacted earth surface temperature and rainfall patterns. Recent research has shown that environmental growth conditions altered the composition of drought-stressed switchgrass and directly influenced the extent of biomass conversion to fuels by completely inhibiting yeast growth during fermentation. Our goal in this project was to find a way to overcome the microbial inhibition and characterize specific compounds that led to this inhibition. Additionally, we also determined if these microbial inhibitors were plant-generated compounds, by-products of the pretreatment process, or a combination of both.ResultsSwitchgrass harvested in drought (2012) and non-drought (2010) years were pretreated using Ammonia Fiber Expansion (AFEX). Untreated and AFEX processed samples were then extracted using solvents (i.e., water, ethanol, and ethyl acetate) to selectively remove potential inhibitory compounds and determine whether pretreatment affects the inhibition. High solids loading enzymatic hydrolysis was performed on all samples, followed by fermentation using engineered Saccharomyces cerevisiae. Fermentation rate, cell growth, sugar consumption, and ethanol production were used to evaluate fermentation performance. We found that water extraction of drought-year switchgrass before AFEX pretreatment reduced the inhibition of yeast fermentation. The extracts were analyzed using liquid chromatography–mass spectrometry (LC–MS) to detect compounds enriched in the extracted fractions. Saponins, a class of plant-generated triterpene or steroidal glycosides, were found to be significantly more abundant in the water extracts from drought-year (inhibitory) switchgrass. The inhibitory nature of the saponins in switchgrass hydrolysate was validated by spiking commercially available saponin standard (protodioscin) in non-inhibitory switchgrass hydrolysate harvested in normal year.ConclusionsAdding a water extraction step prior to AFEX-pretreatment of drought-stressed switchgrass effectively overcame inhibition of yeast growth during bioethanol production. Saponins appear to be generated by the plant as a response to drought as they were significantly more abundant in the drought-stressed switchgrass water extracts and may contribute toward yeast inhibition in drought-stressed switchgrass hydrolysates.

Coupling AFEX and steam-exploded sugarcane residue pellets with a room temperature CIIII-activation step lowered enzyme dosage requirements for sugar conversion

In this study, the potential integration of steam explosion (StEx) and ammonia fiber expansion (AFEX) with existing sugar/ethanol mills to form decentralized pre-processing depots was explored. Both StEx and AFEX pretreatment facilitated the production of sugarcane bagasse (SCB) and cane leaf matter (CLM) pellets with significantly higher bulk density, mechanical durability, and hydrophobicity relative to their untreated biomass pellet controls. However, ethanol production from standalone StEx and AFEX-treated SCB and CLM pellets required enzyme dosages greater than 21 mg/g glucan to achieve enzymatic hydrolysis sugar yields of 75% and ethanol titres greater than 40 g.L−1. Coupling AFEX-treated SCB or CLM pellets with a room temperature CIIII-activation step using liquid ammonia lowered enzyme dosage requirements by more than 50% without affecting ethanol titers and production yields (greater than300 L per Mg residual dry matter raw dry biomass (RDM)). In contrast, treating StEx-treated pellets with CIIII-activation using liquid ammonia did not result in similar enzyme dosage reductions, due to pseudo-lignin formation, leading to enzyme deactivation and/or lignin blockage that retarded enzymatic hydrolysis at low enzyme dosages. A gross energy conversion assessment revealed that low enzyme dosage (3-4 mg enzyme/g RDM) ethanol and electricity co-production from AFEX and CIIII-activated SCB and CLM can recover up to 73% of the energy in the untreated biomass, compared to 54% recovered by StEx and CIIII-activation. The results from this work suggest that StEx or AFEX based pre-processing depots can produce dense and mechanically durable biomass pellets. The AFEX-treated pellets can be easily upgraded using a room temperature CIIII-activation step at the biorefinery to significantly reduce bioconversion enzymes.

A New Method to Overcome Carboxyamide Formation During AFEX Pretreatment of Lignocellulosic Biomass.

Lignin-carbohydrate complexes (LCCs) in the plant cell wall are responsible for providing resistance against biomass-degrading enzymes produced by microorganisms. Four major types of lignin-carbohydrate bonds are reported in the literature, namely, benzyl ethers, benzyl esters, phenyl glycosides, and acetyl ester linkages. Ester’s linkages in the plant cell wall are labile to alkaline pretreatments, such as ammonia fiber expansion (AFEX), which uses liquid or gaseous ammonia to cleave those linkages in the plant cell wall and reduce biomass recalcitrance. Two competing reactions, notably hydrolysis and ammonolysis, take place during AFEX pretreatment process, producing different aliphatic and aromatic acids, as well as their amide counterparts. AFEX pretreated grasses and agricultural residues are known to increase conversion of biomass to sugars by four- to five-fold when subjected to commercial enzyme hydrolysis, yielding a sustainable feedstock for producing biofuels, biomaterials, and animal feed. Animal feed trials on dairy cows have demonstrated a 27% increase in milk production when compared to a control feedstock. However, the presence of carboxamides in feedstocks could promote neurotoxicity in animals if consumed beyond a certain concentration. Thus, there is the need to overcome regulatory hurdles associated with commercializing AFEX pretreated biomass as animal feed in the United States. This manuscript demonstrates a modified pretreatment for increasing the digestibility of industrial byproducts such as Brewer’s spent grains (BSG) and high-fiber meal (HFM) produced from BSG and dry distillers grains with soluble (DDGS), while avoiding the production of carboxamides. The three industrial byproducts were first treated with calculated amounts of alkali such as NaOH, Ca(OH)2, or KOH followed by AFEX pretreatment. We found that 4% alkali was able to de-esterify BSG and DDGS more efficiently than using 2% alkali at both 10 and 20% solids loading. AFEX pretreatment of de-esterified BSG, HFM, and DDGS produced twofold higher glucan conversion than respective untreated biomass. This new discovery can help overcome potential regulatory issues associated with the presence of carboxamides in ammonia-pretreated animal feeds and is expected to benefit several farmers around the world.

Techno-economic analysis of furfural production with various pretreatment of oil palm empty fruit bunches using SuperPro Designer

Oil palm empty fruit bunches (OPEFB) are solid wastes that can be processed into several chemicals, one of which is furfural. Furfural can be used as a solvent and intermediate compound in many chemical industries. Nowadays, furfural needs in Indonesia are fulfilled through import, especially from China. Therefore, developing a furfural plant in Indonesia is required to fulfill the needs for furfural in Indonesia and surrounding countries. Based on that necessity, this study provides the preliminary study and simulation of furfural production from OPEFB by three kinds of pretreatment methods: soaking in aqueous ammonia (SAA), steam explosion (SE), and ammonia fiber expansion (AFEX). Simulation is conducted using SuperPro Designer Academic License to get the plant’s mass & energy balance and economic parameters. The plant will be built in Kawasan Industri Dumai, Pelintung, Riau. Then, by assuming 7920 hours annual operation time and 2000 kg OPEFB/h input rate, the simulations showed that furfural production with AFEX pretreatment is more economically feasible than with SAA and SE pretreatment. The value of profitability parameters as follows: Internal Rate of Return (IRR) = 49.77%, Net Present Value (NPV) at i = 9.6% = USD 39,210,000, and payback time = 1.75 years.

Ammonia fiber expansion increases in vitro digestibility and fermentability of corn distillers dried grains with solubles with or without carbohydrases

A significant portion of gross energy (GE) in corn distillers dried grains with solubles (DDGS) is indigestible by non-ruminants, and the impact of ammonia fiber expansion (AFEX) on improving GE digestibility is unknown. The objective of this study was to determine the effect of AFEX and enzymes on crystallinity index and neutral detergent fiber (aNDF) degradation in DDGS using a porcine in vitro fermentation system. Two sources of DDGS samples (ICM and POET) were pretreated with liquid ammonia at 100 °C and 2069 kPa for 30 min. The DDGS samples with or without AFEX pretreatment were predigested with pepsin and pancreatin with or without carbohydrases (1500 U/g xylanase, 1100 U/g β-glucanase, 110 U/g mannanase, and 35 U/g galactosidase). Residues were then subjected to in vitro fermentation (directly inoculating DDGS samples with fecal inocula) and accumulated gas production recorded up to 72 h. Concentration of short-chain fatty acids (SCFA) were measured in the fermented solution. On a dry matter (DM) basis, non-protein nitrogen was increased by 20.8 g/kg, and aNDF was decreased by 146 g/kg in corn DDGS after AFEX pretreatment. Pretreatment with AFEX decreased the crystallinity index of fiber in DDGS from about 15 to 0 %, increased (P < 0.01) fermentability of DM and aNDF, and decreased (P < 0.01) unfermented aNDF content after in vitro fermentation for 12 and 72 h. The AFEX pretreated DDGS had greater (P < 0.05) in vitro digestibility of DM and GE, greater production of acetic acid and total SCFA (DM enzymatic hydrolyzed residue basis), greater in vitro digested GE (GE × IVDGE, GE) and digestible energy (GE + energy derived from SCFA) compared with DDGS without pretreatment. Carbohydrase supplementation increased (P < 0.05) in vitro digestibility of GE and DM in AFEX treated POET but not in ICM DDGS. In conclusion, AFEX pretreatment decreased the crystallinity index of fiber and improved the in vitro digestibility and fermentability of corn DDGS.

Evolution of the Lignin Chemical Structure during the Bioethanol Production Process and Its Inhibition to Enzymatic Hydrolysis

To illuminate the lignin evolution after hydrogen peroxide presoaking prior to ammonia fiber expansion pretreatment (H-AFEX) pretreatment and enzymatic hydrolysis, ball-milled wood lignins were sep...

Ammonia Fiber Expansion (AFEX) Pretreatment of Lignocellulosic Biomass.

Lignocellulosic materials are plant-derived feedstocks, such as crop residues (e.g., corn stover, rice straw, and sugar cane bagasse) and purpose-grown energy crops (e.g., miscanthus, and switchgrass) that are available in large quantities to produce biofuels, biochemicals, and animal feed. Plant polysaccharides (i.e., cellulose, hemicellulose, and pectin) embedded within cell walls are highly recalcitrant towards conversion into useful products. Ammonia fiber expansion (AFEX) is a thermochemical pretreatment that increases accessibility of polysaccharides to enzymes for hydrolysis into fermentable sugars. These released sugars can be converted into fuels and chemicals in a biorefinery. Here, we describe a laboratory-scale batch AFEX process to produce pretreated biomass on the gram-scale without any ammonia recycling. The laboratory-scale process can be used to identify optimal pretreatment conditions (e.g., ammonia loading, water loading, biomass loading, temperature, pressure, residence time, etc.) and generates sufficient quantities of pretreated samples for detailed physicochemical characterization and enzymatic/microbial analysis. The yield of fermentable sugars from enzymatic hydrolysis of corn stover pretreated using the laboratory-scale AFEX process is comparable to pilot-scale AFEX process under similar pretreatment conditions. This paper is intended to provide a detailed standard operating procedure for the safe and consistent operation of laboratory-scale reactors for performing AFEX pretreatment of lignocellulosic biomass.

Synergistic effect of hydrogen peroxide and ammonia on lignin

To reveal the synergistic effect of hydrogen peroxide and ammonia on lignin, four kinds of ball-milled wood lignins, named as UN-L, HP-L, AFEX-L and H-AFEX-L respectively, were isolated from corn stover of untreated, hydrogen peroxide pretreatment alone, ammonia fiber expansion pretreatment alone and combined hydrogen peroxide and ammonia fiber expansion pretreatment. Modern analytical techniques including elemental analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy and two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance (2D-HSQC NMR) spectroscopy were applied to analyze the characteristics of the obtained lignins. The results showed that oxidation, ammonolysis were main chemical reaction during H-AFEX pretreatment. The action site of oxidation was S unit, while that of ammonolysis were ferulate and p-coumarate ester bonds. The synergistic effect of hydrogen peroxide and ammonia strengthened ammonolysis effect whereas weakened oxidation effect. Ammonia selectively degraded the ester bond, while hydrogen peroxide selectively degraded the resinol structure. The synergistic effect of hydrogen peroxide and ammonia could not only effectively degrade lignin, but also greatly reduce its PI to obtain homogeneous lignin fragments.

Comparison and intrinsic correlation analysis based on composition, microstructure and enzymatic hydrolysis of corn stover after different types of pretreatments

Pretreatment is a key step in the energy utilization of lignocellulosic biomass. Different types of pretreatments (ultrafine grinding pretreatment, alkaline hydroxide peroxide pretreatment, dilute acid pretreatment, and ammonia fiber expansion pretreatment) were conducted on corn stover. The lignocellulosic composition, microstructural parameters, and glucose yield of differently pretreated corn stover were characterized and compared. Then qualitative and quantitative correlation analyses of the parameters were carried out to explore the correlations among the composition, microstructure properties, and enzymatic hydrolysis efficacy of corn stover after different types of pretreatments and identify the main properties affecting enzymatic hydrolysis. Qualitative correlation analysis found that cellulose content, specific surface area, pore volume, enzyme-accessible pore volume, and surface area of cellulose had significant positive correlations with glucose yield. The results of quantitative correlation analysis were GY = 15.01 × cellulose content-339.05, GY = 13.06 × SSA + 172.35, GY = 7226.27 × PV + 129.14, GY = 8628.61 × EAPV + 125.61, and GY = 1.18 × SAC-287.21.

Isolation of lignin from Ammonia Fiber Expansion (AFEX) pretreated biorefinery waste

In this study, we investigate the isolation of lignin from the unhydrolyzed solids (UHS) by-product stream of 2nd-generation biofuel production. Under reflux conditions, aqueous solutions of acetone, ethanol (EtOH), acetic acid (AcOH), and γ-valerolactone (GVL) displayed approximately 53, 51, 53, and 65% yields of extractable solids, respectively, from corn stover UHS after Ammonia Fiber Expansion pretreatment and then enzymatic hydrolysis. Detailed chemical characterization was done including nuclear magnetic resonance, gel permeation chromatography, and thermogravimetric analysis. This characterization showed that material extracted from UHS using EtOH:H2O and acetone:H2O contained a lignin fraction that most resembled native lignin; although, the material extracted using acetone:H2O contained a significant carbohydrate component. Results suggest that solvent polarity, rather than other solvent properties (e.g., reflux temperature), are dominating factors determining the mass yields of extractable solids from UHS.

Using steam explosion or AFEX™ to produce animal feeds and biofuel feedstocks in a biorefinery based on sugarcane residues

AbstractSustainable integration of biofuel (primarily bioethanol) and highly digestible livestock feed in production systems is a potential way to increase the economic returns to agriculture and simultaneously promote energy security, particularly in developing countries. In this work we evaluated the efficacy of steam explosion (StEx) and ammonia fiber expansion (AFEX™) as potential processes for improving the in vitro rumen digestibility, metabolizable energy, and ethanol yields from sugarcane crop residues (bagasse and cane leaf matter, CLM). Ammonia fiber expansion pretreatment enhanced the in vitro true digestibility and metabolizable energy content of sugarcane crop residues by 69% and 26%, respectively compared to untreated controls. On the other hand, StEx increased the true digestibility and metabolizable energy content of the sugarcane residues by 54% and 7%, respectively. Ammonia fiber expansion also increased the total nitrogen content of both sugarcane bagasse and CLM to more than 20.2 g kg−1 dry forage, a more than 230% improvement relative to untreated controls. High solid‐loading enzymatic hydrolysis and fermentation of StEx‐ and AFEX™‐pretreated sugarcane crop residues generated yields of up to 3368 and 4360 L of ethanol per hectare of sugarcane cultivated, respectively, at a biomass‐degrading enzyme dosage of 20 mg protein per gram glucan. This research strongly suggests that the use of suitably pretreated sugarcane crop residues in integrated sugarcane biofuel‐livestock production systems can increase the total per hectare agricultural output without increasing the area of sugarcane cultivated. In effect, this integrated approach promotes more sustainable biofuel production and increased food production while avoiding the potential for indirect land use change. © 2018 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Structural Characterization of Corn Stover Lignin after Hydrogen Peroxide Presoaking Prior to Ammonia Fiber Expansion Pretreatment

The hydrogen peroxide presoaking prior to ammonia fiber expansion (H-AFEX) pretreatment is an effective and promising method for agricultural residues to decrease biomass recalcitrance and enhance ...

Conversion of lignocellulosic agave residues into liquid biofuels using an AFEX\u2122-based biorefinery

BackgroundAgave-based alcoholic beverage companies generate thousands of tons of solid residues per year in Mexico. These agave residues might be used for biofuel production due to their abundance and favorable sustainability characteristics. In this work, agave leaf and bagasse residues from species Agave tequilana and Agave salmiana were subjected to pretreatment using the ammonia fiber expansion (AFEX) process. The pretreatment conditions were optimized using a response surface design methodology. We also identified commercial enzyme mixtures that maximize sugar yields for AFEX-pretreated agave bagasse and leaf matter, at ~ 6% glucan (w/w) loading enzymatic hydrolysis. Finally, the pretreated agave hydrolysates (at a total solids loading of ~ 20%) were used for ethanol fermentation using the glucose- and xylose-consuming strain Saccharomyces cerevisiae 424A (LNH-ST), to determine ethanol yields at industrially relevant conditions.ResultsLow-severity AFEX pretreatment conditions are required (100–120 °C) to enable efficient enzymatic deconstruction of the agave cell wall. These studies showed that AFEX-pretreated A. tequilana bagasse, A. tequilana leaf fiber, and A. salmiana bagasse gave ~ 85% sugar conversion during enzyme hydrolysis and over 90% metabolic yields of ethanol during fermentation without any washing step or nutrient supplementation. On the other hand, although lignocellulosic A. salmiana leaf gave high sugar conversions, the hydrolysate could not be fermented at high solids loadings, apparently due to the presence of natural inhibitory compounds.ConclusionsThese results show that AFEX-pretreated agave residues can be effectively hydrolyzed at high solids loading using an optimized commercial enzyme cocktail (at 25 mg protein/g glucan) producing > 85% sugar conversions and over 40 g/L bioethanol titers. These results show that AFEX technology has considerable potential to convert lignocellulosic agave residues to bio-based fuels and chemicals in a biorefinery.

Water sorption in pretreated grasses as a predictor of enzymatic hydrolysis yields

This work investigated the impact of two alkaline pretreatments, ammonia fiber expansion (AFEX) and alkaline hydrogen peroxide (AHP) delignification performed over a range of conditions on the properties of corn stover and switchgrass. Changes in feedstock properties resulting from pretreatment were subsequently compared to enzymatic hydrolysis yields to examine the relationship between enzymatic hydrolysis and cell wall properties. The pretreatments function to increase enzymatic hydrolysis yields through different mechanisms; AFEX pretreatment through lignin relocalization and some xylan solubilization and AHP primarily through lignin solubilization. An important outcome of this work demonstrated that while changes in lignin content in AHP-delignified biomass could be clearly correlated to improved response to hydrolysis, compositional changes alone in AFEX-pretreated biomass could not explain differences in hydrolysis yields. We determined the water retention value, which characterizes the association of water with the cell wall of the pretreated biomass, can be used to predict hydrolysis yields for all pretreated biomass within this study.

Application of hydrogen peroxide presoaking prior to ammonia fiber expansion pretreatment of energy crops

This work presents the application of ammonia fiber expansion (AFEX) pretreatment both with (H-AFEX) and without hydrogen peroxide presoaking of energy crops moso bamboo, giant reed, and Miscanthus. The influences of AFEX and H-AFEX pretreatments on chemical composition and enzymatic hydrolysis were assessed. The results address the solid recovery, delignification, hydrolysis sugar yields, and micro-structural morphology of varying H-AFEX pretreatment conditions of energy crops. A strong negative correlation between solid recovery and H2O2 loading was found for all pretreated samples with H2O2 loading <2.0. In comparison with AFEX process, the addition of hydrogen peroxide in H-AFEX pretreatment could result in increases in glucose yields at the expense of xylose. The maximum sugar yields of moso bamboo, giant reed, and Miscanthus were 269.0, 424.6, and 485.0g per kg dry biomass respectively, which were obtained under their optimal pretreatment conditions following enzymatic hydrolysis. The micrograph of H-AFEX-treated giant reed demonstrated that the modified porous structure resulted in increased enzyme accessible surface area, and facilitated the subsequent enzymatic hydrolysis.

Biorefining of Lignocellulosic Feedstock by a Modified Ammonia Fiber Expansion Pretreatment and Enzymatic Hydrolysis for Production of Fermentable Sugars.

Wheat straw was pretreated and afterwards enzymatically hydrolyzed using a modified ammonia fiber expansion (AFEX) process under different reaction conditions to produce fermentable sugars. Instead of liquid ammonia, aqueous ammonia (25 % w/v) was used to test its influence on the sugar concentration and yield of the sugars. It is shown that a protein extraction after the pretreatment can distinctly improve the result obtained for the enzymatic hydrolysis. This modified AFEX process using aqueous ammonia represents a simpler and less expensive variant of the AFEX process usually described in literature. Thus, the described process can be used for the primary refining of lignocellulosic feedstocks in the sense of a roadmap for biorefinery.

Assessment of the Lignin-Derived Inhibition of Enzymatic Hydrolysis by Adding Untreated and Ammonia-Fiber-Expansion-Treated Lignin Isolated from Switchgrass

Lignin, which is considered one of the most recalcitrant components, limits the enzymatic hydrolysis of cellulose. When ball-milled lignin from switchgrass ranging from 21.4 to 64.3 mg/mL was added to a cellulose substrate (Avicel), the glucose release decreased from 17.4 to 22.4% compared to the hydrolysis rate of zero lignin addition. However, the cellulose decreasing conversion was reduced to 8.5% with 21.4 mg/mL ammonia fiber expansion (AFEX)-treated lignin addition, as a result of the structural modification by AFEX pretreatment. The inhibitory effect of lignin was stronger on cellulose hydrolysis than on hemicellulose hydrolysis. The results showed that the free lignin released from biomass reduced the impact of the added lignin and that the AFEX pretreatment intensity was the key factor in increasing the enzymatic efficiency. The lignin structural modifications by AFEX pretreatment, such as slight increases in the molecular weight, degree of polymerization, and syringyl/guaiacyl ratio, reduced the ...

Impact of ammonia fiber expansion (AFEX) pretreatment on energy consumption during drying, grinding, and pelletization of corn stover

ABSTRACTPretreatment and densification of biomass can increase the viability of bioenergy production by providing a feedstock that is readily hydrolyzed and able to be transported over greater distances. Ammonia fiber expansion (AFEX™) is one such method targeted for use at distributed depots to create a value-added and densified feedstock for bioenergy use. However, the pretreatment process results in a high-moisture material that must be dried, further size reduced, and pelletized, all of which are energy-intensive processes. This work quantifies the energy consumption required to dry, grind, and densify AFEX-pretreated corn stover compared to non-pretreated stover and explores the potential of reduced drying as a means to conserve energy. The purpose of this work is to understand whether material property changes resulting from AFEX pretreatment influence the material performance in downstream formatting operations. Material properties, heat balance equations, and a rotary drum dryer model were used to model a commercial-scale rotary drum dryer for AFEX-pretreated corn stover, showing the potential to reduce dryer energy consumption by up to 36% compared to non-pretreated corn stover. Laboratory-measured grinding and pelleting energies were both very sensitive to material moisture content. Overall, the total energy required for drying, grinding, and pelleting amounts to a savings of up to 23 kWh/dry Mg for the AFEX-pretreated material when dried to a low moisture content, equating to up to 0.61 $/Mg savings for gas and electricity. Grinding and pelleting of high-moisture AFEX-pretreated stover was shown to be more costlier than the savings collected through reduced drying. Although the energy and cost savings shown here are modest, the results help to highlight operational challenges and opportunities for continued improvement.

Physical and chemical characterizations of corn stalk resulting from hydrogen peroxide presoaking prior to ammonia fiber expansion pretreatment

To effectively improve enzymatic digestibility of carbohydrate in lignocellulosic biomass, hydrogen peroxide presoaking prior to ammonia fiber expansion (H-AFEX) was applied as pretreatment to corn stalk. Enzymatic hydrolysis using cocktail enzymes including cellulase, β-glucosidase and xylanase at 72h after pretreatment under optimal conditions, the glucan and xylan conversions of 88.9% and 86.3% were achieved, respectively. It was about 3.31-fold in sugar yield for H-AFEX-treated corn stalk compared with untreated material. The results of composition analysis and enzymatic hydrolysis showed that H-AFEX pretreatment was effective to remove lignin and improve glucan digestibility. The characteristics of biomass surface and cell wall, biomass crystallinity, and chemical structure changes of H-AFEX-treated corn stalk were determined by digital microscope system, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR), respectively. The results demonstrated that H-AFEX pretreatment induced some morphology changes including partial damages in vascular bundle and deconstruction of cell wall, and the modified biomass structure could increase surface area accessibility and create favorable conditions for enzymatic hydrolysis obviously. Due to removal amorphous substances, the crystallinity index of H-AFEX-treated corn stalk increased comparing with that of raw material. FTIR data showed that H-AFEX process induced changes in chemical structure and cross linking such as removal/dissolution of lignin and hemicelluloses, cleavage of bonds linkage, and decrystallization of cellulose. As a result, H-AFEX pretreatment effectively reduced recalcitrance of corn stalk, and promoted subsequent enzymatic hydrolysis.