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DOE OSTI2023

Torrefaction of almond shell as a renewable reinforcing agent for plastics: techno-economic analyses and comparison to bioethanol process

Abstract In 2016, the US state of California alone produced nearly 3.5 billion kilograms of almonds, accounting for approximately 84% of the world’s almond production. This generated about 2.58 million metric tons (MTs) of almond residues. Almond shells are currently either burned to generate power or disposed of in landfill. Valorizing almond shells and hulls provides an opportunity to replace petroleum-derived products and divert organic material from landfill. Here we demonstrate a detailed techno-economic analysis (TEA) of an almond shell torrefaction process capable of utilizing the 520 000 MTs of almond shells produced annually in California. Our process also includes preprocessing the torrefied biomass to exploit it as a reinforcing agent for plastics. We further compared the revenue generated from the torrefied biomass and bioethanol derived from the same quantity of almond shells. We considered three different torrefaction facility scales to evaluate trade-offs between economies of scale at the facility and trucking costs to deliver almond shells. A facility that takes in 200 000 MT yr –1 of almond shells results in lower per-unit-output basis capital and operating cost relative to other smaller-scale torrefaction facilities, including 10 000 MT yr –1 and 50 000 MT yr –1 , considered for analysis in this study. The large-sale facility results in a minimum selling price (MSP) of the torrefied biomass of $311.4 MT –1 . An analogous TEA on converting almond residues into bioethanol is also investigated. The MSP of almond shell derived ethanol ($1.71 kg −1 ) is higher than that of corn ($0.48 kg −1 ) or cellulosic biomass ($0.88 kg −1 ) derived ethanol. Compared with the bioethanol route, the torrefied almond shells result in three times more revenue if utilized as a reinforcing agent for plastics.

Liu, Dupeng (ORCID:0000000269514064)↗

NASA NTRS2009

The Crop Evaluation Research for Environmental Strategies (CERES) Remote Sensing 2008 Project Activities

In recent years, the use of Plant Incorporated Protectant (PIP) corn by American producers has been increasing dramatically. PIP corn contains genetically inserted traits that produce toxins in the plant that provide narrowly targeted protection against specific insect pests. The plant producing t oxms can offer significant reductions in the application of broad -spectrum pesticides that have ecological and human health consequences. PIP corn as a percentage of total corn acreage planted in the US is expected to continue to increase as these protective traits are "stacked" with other desirable traits by seed companies, and producers are seeing considerable increases in corn yield as a result. The introduction of corn as a bio-fuel source for ethanol has increased production by over 6 million hectares in 2007. The United States Environmental Protection Agency (USEPA), which is responsible for the registration of PIP crops under the Federal Insecticide, Fungicide and Rodenticide Act, views the use of PIP corn as positive. Broad spectrum pesticide use has declined since the PIP traits have been introduced. As the agricultural landscape sees a higher percentage of corn acres using the PIP technology, the risk of the targeted insect pest populations developing resistance to the toxins, thereby rendering the in will increase as well. This result would negate the effectiveness of the PIP corn traits and could reduce production of a US field corn crop valued at $33 billion dollars in 2006 and place US food and now energy security at risk. Concerns over insect pest resistance development to PIP traits have led the USEPA to team with NASA and the Institute for Technology Development (ITD) to develop geo-spatial technologies designed to proactively monitor the corn production landscape for insect pest infestation and possible resistance development. USEPA resistance management simulation models are combined with NASA remote sensi ng products to monitor the corn landscape for resistance development. The two agencies have entered into an agreement which could potentially lead to the development of next generation NASA sensors that will more specifically address the requirements of the USEPA's resistance development strategy and offer opportunities to study the ever changing ecosystem complexities. The USEPA/NASA/ITD team has developed a broad research project entitled CERES (Crop Evaluation Research for Environmental Strategies). CERES is a research effort leading to decision support system tools that are designed to integrate multi-resolution NASA remote sensing data products and USEPA geo -spatial models to monitor the potential for insect pest resistance development from the regional to the landscape and then to the field level.

Casas, Joseph C.↗

DOE OSTI2024

Electric Vehicles, Biofuels, and Transitions in Transportation Energy

The decarbonization of power sources for light duty transportation is moving towards the use of renewable energies, biofuels, and electric vehicles. Currently there are three major light transportation fuels: gasoline (US gasoline is 98% E10), biofuels (E85), and electricity. Currently fuel ethanol in biofuels is obtained principally from corn in the US and sugarcane in Brazil with a small amount from cellulose. The transition to alternative fuels has been occurring since 1980, although light transportation still relies on gasoline. The rise of battery electric vehicles (BEV) is now beginning to offset internal combustion engines (ICE), while recent advances in biotechnology and integrated plant design have enhanced the economic feasibility of cellulosic biofuels. This paper explores the potential role of these fuels in reducing the carbon footprint associated with light transportation. We compare three different cases: Gasoline, E85 and full electric based on the Argonne AFLEET tool to calculate generation of greenhouse gases due to manufacturing and operation of BEV and ICE cars, respectively, in the US assuming an average useful automobile life of 200,000 miles or 12 years. We concluded that significant liquid fuel use (both renewable and non-renewable) will continue for the next 50 years. Here, renewable liquid fuels have an important role to play as the transportation sector transitions from petroleum to other energy sources.

09 BIOMASS FUELS↗

DOE OSTI2022

Techno‐economic assessment of single‐stream feedstock logistics supply chain for corn stover and grain

Abstract The state‐of‐technology for corn stover harvest is a multi‐pass system that collects the stover after grain harvest. An alternative is a single‐stream system where the grain and stover are harvested as a bulk material co‐stored and preserved by anerobic fermentation, and finally, co‐transported to a biorefinery. In the present work, four single‐pass whole‐plant bulk systems were compared with a conventional multi‐pass bale system. The single‐stream systems consisted of the harvest of corn grain and a portion of the stover fraction. Four machine configurations were simulated. This work predicted that a multi‐pass bale system would result in a material cost of 111.80 $2021 Mg –1 stover DM delivered to the biorefinery gate. Alternatively, the lowest cost single‐stream system was the self‐propelled forage harvester (SPFH) configured with the whole‐plant header, which delivered feedstock for 74.76 $2021 Mg stover DM –1 . In addition to machine configuration, a sensitivity analysis was performed to understand important drivers of feedstock cost. These analyses revealed that feedstock cost increased with moisture content, fertilizer price, and biorefinery size, and decreased with harvest season length, crop yield, and grower participation. This work demonstrated that single‐stream systems could reduce corn stover feedstock costs in comparison with state‐of‐technology systems. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

09 BIOMASS FUELS↗

DOE OSTI2020

Physico-chemical properties of lignin fractions from acid pretreated corn stover and their effects on enzymatic hydrolysis of microcrystalline cellulose

Lignin has been shown to be a recalcitrance factor in many biomass conversion studies. To better understand the effects of lignin on cellulose conversion, different lignin fractions were extracted from the same dilute acid pretreated corn stover by three sequential isolation methods, namely ethanol extraction, dioxane extraction, and enzyme purification. The physicochemical properties of each lignin fraction including molecular weight distribution, surface area, surface charge, and other structural features varied, depending on the isolation methods. All three lignin fractions had negative surface charges, and ethanol-extracted lignin carried the highest surface charges, followed by dioxane-extracted lignin and cellulase-purified residual lignin. These physicochemical properties of lignin fractions also resulted in different extent of inhibitory effects on enzymatic hydrolysis of microcrystalline cellulose (MCC). Dioxane-extracted lignin exhibited the highest inhibitory effect on glucose release from MCC, followed by the cellulase-purified residual lignin fraction and ethanol-extracted lignin. Furthermore, lignin fractions with higher contents of syringyl (S) substructure and β-O-4 aryl ether interunit linkages showed a stronger negative effect on cellulase hydrolysis of MCC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Integrated Renewable Combined Heat and Power for Ethanol

Conference presentation at 48th International Technical Conference on Clean Energy (Clearwater Clean Energy Conference), Clearwater, Florida, June 16–19, 2024. This project evaluates the technical and economic feasibility of small‑scale combined heat and power (CHP) systems using corn stover to support bioenergy with carbon capture and storage (BECCS) at ethanol facilities. The work includes resource characterization, pilot‑scale gasification and CO 2 capture testing to support techno‑economic analysis, economic evaluation of CHP deployment and potential carbon revenue, and life‑cycle assessment of gasification‑based CHP systems.

09 BIOMASS FUELS↗

DOE OSTI2022

A combination of deep eutectic solvent and ethanol pretreatment for synergistic delignification and enhanced enzymatic hydrolysis for biorefinary process

Here, a novel pretreatment system containing deep eutectic solvents and ethanol (DES-E) for synergistic carbohydrate conversion and delignification was reported in this study. The DES-E pretreatment resulted in an enhanced glucose yield compared to individual DES and ethanol pretreatment for the three tested biomass, including Broussonetia papyrifera, corn stover and pine. To further explore the delignification mechanism, the solubilized lignin and residual lignin from Broussonetia papyrifera was recovered and extracted, then thoroughly characterized. The highest total OH content was found in the DES-E solubilized lignin, which could be used as antioxidant. The presence of ethanol in pretreatment liquor could protect the β-O-4 substructure from breakage and reduce lignin condensation, which favors the subsequent enzymatic hydrolysis. Comparable glucose yield and delignification performance was achieved by recycled DES. DES-E pretreatment offers a promising method for lignin isolation and cellulose digestibility improvement simultaneously.

09 BIOMASS FUELS↗

DOE OSTI2025

Techno-Economic Analysis and Life Cycle Assessment of Alternative Fuels for Locomotives in the U.S. Freight Rail Sector

Freight rail is more energy-efficient than truck transport over long-haul distances, offering a low-energy and emissions-intensive option for transporting freight. This study evaluates techno-economic analysis and life cycle assessment of seven alternative unblended fuels for freight locomotive engines─biodiesel, renewable diesel (RD), bio-oils, methanol, dimethyl ether (DME), ethanol, and ammonia─across 16 fuel pathways utilizing soybean, corn, woody biomass, renewable hydrogen, and waste sources, e.g., sludge, manure, and industrial CO 2 , and compares these to conventional diesel. The minimum fuel selling price (MFSP) ranged from $\$2.05$ to $\$8.27$ per diesel gallon equivalent (2020 US dollars), with biocrude and RDs produced from hydrothermal liquefaction (HTL) of sludge having the lowest MFSPs due to coproduct credits and avoided waste treatment cost. Life cycle GHG emissions ranged from −41 to 53 g of CO 2 e/MJ. RD from waste via HTL achieves negative emissions by diverting sludge/manure from GHG-intensive conventional management. Few pathways such as biocrude, methanol, and DME require additional control for SO X emissions in the refinery, while ethanol, FT-diesel, and bio-oil require additional control for particulate matter emissions. Bio-oil and RD from sludge have lower marginal abatement cost or MAC (–$\$38$/tonne CO 2 lowest) while methanol and ammonia with renewable hydrogen have higher MAC ($\$490$/tonne CO 2 maximum).

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2023

Challenges and Advances in Aqueous Processing of Corn Stover Pellets into High Concentration Slurries

Significant progress has occurred in developing combined enzyme hydrolysis and fermentation technologies for transforming lignocellulosic feedstocks into ethanol and other bioproducts. Various routes described in the literature show that low carbon footprint processes efficiently convert the cellulose and hemicellulose fractions of pretreated corn stover, wood chips, and sugarcane bagasse to sugars and to ethanol.Combinations of different pretreatments at high or low pH or in liquid hot water, followed by enzyme hydrolysis and fermentation or direct conversion of cellulose to ethanol (i.e., by consolidated bioprocessing)have been demonstrated. These successes have brought the need to preparing the feedstock – before it enters the biorefinery – into focus. This paper summarizes recent developments in liquefying corn stover,before pretreatment, so that slurries with yield stresses below 200 Pa are obtained and a “pumpable” corn stover slurry results at initial solids loadings of up to 300 g/L. The manner in which corn stover pellets are combined with water and enzyme in an agitated bioreactor is described, and properties that define slurry behavior are presented. Implications on biorefinery operations are explained in terms of particle properties and the preprocessing of corn stover as well as the team approach used to obtain these results.

Wassgren, Carl↗

DOE OSTI2021

Hydrolysis of lignocellulose by anaerobic fungi produces free sugars and organic acids for two–stage fine chemical production with Kluyveromyces marxianus

Development of the bioeconomy is driven by our ability to access the energy-rich carbon trapped in recalcitrant plant materials. Current strategies to release this carbon rely on expensive enzyme cocktails and physicochemical pretreatment, producing inhibitory compounds that hinder subsequent microbial bioproduction. Anaerobic fungi are an appealing solution as they hydrolyze crude, untreated biomass at ambient conditions into sugars that can be converted into value-added products by partner organisms. However, some carbon is lost to anaerobic fungal fermentation products. To improve efficiency and recapture this lost carbon, we built a two-stage bioprocessing system pairing the anaerobic fungus Piromyces indianae with the yeast Kluyveromyces marxianus, which grows on a wide range of sugars and fermentation products. In doing so we produce fine and commodity chemicals directly from untreated lignocellulose. P. indianae efficiently hydrolyzed substrates such as corn stover and poplar to generate sugars, fermentation acids, and ethanol, which K. marxianus consumed while producing 2.4 g/L ethyl acetate. An engineered strain of K. marxianus was also able to produce 550 mg/L 2-phenylethanol and 150 mg/L isoamyl alcohol from P. indianae hydrolyzed lignocellulosic biomass. Despite the use of crude untreated plant material, production yields were comparable to optimized rich yeast media due to the use of all available carbon including organic acids, which formed up to 97% of free carbon in the fungal hydrolysate. Furthermore, this work demonstrates that anaerobic fungal pretreatment of lignocellulose can sustain the production of fine chemicals at high efficiency by partnering organisms with broad substrate versatility.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2021

Controlling Bacterial Contamination During Fuel Ethanol Fermentation Using Thermochemically Depolymerized Lignin Bio-Oils

Lactic acid bacteria (LAB) contamination during fuel ethanol fermentation can lead to significant economic loses. To circumvent this, fuel ethanol plants add antibiotics prophylactically, but their overuse has resulted in the emergence of antibiotic-resistant LAB strains. Lignin is a sustainable biopolymer that can be found as a waste product from lignocellulosic biorefineries. Technical lignins and their smaller phenolic subunits have been shown to exhibit broad-spectrum antimicrobial properties, but there is a lack of demonstrations of lignin derivatives with highly selective properties in the literature. Here, corn stover lignin from a biorefinery was oxidatively depolymerized using an environmentally benign organic oxidant, peracetic acid, into a bio-oil that has selective antimicrobial properties against LAB and not yeasts. The resulting bio-oil demonstrated up to 90% inhibition of commercially sampled LAB (including antibiotic-resistant strains) at 4 mg ml-1 with no inhibition against an industrial yeast strain. These antimicrobial properties of the bio-oil are attributed to larger unidentified lignin oligomers, compared to monolignols, that have a membrane damaging mode of action. Using the bio-oil (4 mg ml-1) during simultaneous saccharification and fermentation (SSF) of raw corn starch showed no inhibition of enzymatic activity, and in LAB contaminated fermentations the bio-oil treatments showed an 8% increase in ethanol yields at higher bacterial contamination ratios (l : 100 yeast to LAB, CFU per ml). This study illustrates the efficacy of using lignin bio-oil as an antibiotic replacement during fuel ethanol fermentation and demonstrates the highly selective antimicrobial properties of lignin oligomers, which creates a viable lignin valorization strategy for biorefineries.

bio-oil↗

DOE OSTI2022

Using Incremental Changes to Convert Lignocellulosic Feedstocks to Cellulosic Ethanol

One billion tons of biomass feedstocks have been identified for the production of renewable biofuels and biochemicals. This is one of the key carbon feedstocks to supply energy to the transportation sector for light duty, heavy duty and aviation fuels. Utilization of lignocellulosic feedstocks supports an improved energy security by reducing demand of petroleum imports, agricultural development, job creation, and reducing greenhouse gas emissions. To date, however, operational challenges have stymied the industrial production of large volumes of lignocellulosic-based fuels and chemicals. As a result, significant research investment has been led by the United States Department of Energy to understand and improve operational reliability at pioneer cellulosic biorefineries. In this perspective article lignocellulosic conversion technologies are described that have been adopted from the starch ethanol process. The developed process culminated in successful demonstration of 1,000-h integrated runs using several feedstocks, including switchgrass, energy sorghum, and two types of corn kernel fiber. This report highlights process development that solved several of the issues that plagued—and continue to plague—many in the cellulosic sugars space such as biomass feeding into equipment, high ash content, diversified co-product value, and others.

09 BIOMASS FUELS↗

DOE OSTI2022

Yield stress and flow behavior of enzyme liquefied slurries from corn cobs and corn stover pellets

With the increase in population, the world will depend on renewable sources to meet the increasing energy needs. The use of lignocellulosic biomass as a renewable source has been proven efficient for conversion to cellulosic ethanol and capable of contributing to thresholds for energy demand while reducing greenhouse gases by 90% when compared with fossil fuels. However, limitations in feeding and flow within biorefineries is encountered when system plugging occurs due to biomass compaction and a high yield stress for slurries formed during its processing, thereby preventing transport of biomass materials between plant unit operations. In some cases, this leads to unexpected plant shutdowns increasing industrial operational costs. As an alternative, enzyme-assisted liquefaction for slurry creation from corn stover at solids loadings up to 30% is reported in this work. Two different kinds of biomass (pelleted corn stover and cobs) were liquefied in a fed-batch process using commercial enzymes Celluclast 1.5L or Ctec-2 at 1FPU or 3 FPU per gram of dry solids in 10 mM sodium citrate buffer solution (pH 4.8). Pellets were fed into a 1 L stirred bioreactor according to a pre-defined fed-batch protocol over the first 5 hours until reaching 30% of solids loading. After 6, 24 and 96 hours, samples were taken and characterized with respect to their sugar composition, rheology and water absorption. Successful slurry creation with dramatically reduced yield stress was achieved for corn stover for both assessed enzymes. Yield stresses of 178±7 Pa (3 FPU, Celluclast 1.5L) and 79±6 Pa (3 FPU, Ctec-2) were measured for corn stover at 24 hours, compared to 6,000 Pa for samples without enzyme. Yield stress was 155± 29 Pa (3FPU, Ctec-2) and 257 ± 72 Pa (1 FPU,Celluclast 1.5L) for corn cobs at 24 hours. Yield stress decreased when residence time increased with an enhanced fluidity noted for higher enzyme concentrations. A profile for 6, 24 and 96h of yield stress measurements is presented.

Guitierrez, Diana↗

DOE OSTI2023

Enzyme-assisted liquefaction for different fractions of corn stover pellets

With an increase in population, the world will depend on renewable sources to meet the increasing energy needs. The use of lignocellulosic biomass as a renewable source has been proven efficient for conversion to cellulosic ethanol and capable of contributing to thresholds for energy demand while reducing greenhouse gases by 90% when compared with fossil fuels. However, limitations in feeding and flow within biorefineries are encountered when system plugging occurs due to biomass compaction and a high yield stress for slurries formed during its processing. Furthermore, differences in the biomass source present a challenge to the continuity of operations and reliability in the process. This work explores enzyme-assisted liquefaction for solid loadings up to 30% as an alternative for the creation of slurry from two different types of biomass (pelleted corn stover and cobs) that were liquefied in a fed-batch process using commercial enzymes Celluclast 1.5L or Ctec-2 at 1FPU/g or 3 FPU/g of dry solids in a 10 mM sodium citrate buffer solution (pH 4.8). Pellets were fed into a 1 L stirred bioreactor according to a predefined fed-batch protocol during the first 5 hours until 30% solid loading was reached. After 6, 24 and 96 hours, samples were taken and characterized with respect to their composition, rheology, and water absorption. Successful slurry creation with dramatically reduced yield stress was achieved for corn stover for both enzymes assessed. Yield stresses of 178±7 Pa (3 FPU, Celluclast 1.5L) and 79±6 Pa (3 FPU, Ctec-2) were measured for corn stover at 24 hours, compared to 6,000 Pa for samples without enzyme. Yield stress was 155± 29 Pa (3FPU, Ctec-2) and 257 ± 72 Pa (1 FPU, Celluclast 1.5L) for corn cobs at 24 hours. A profile for 6, 24 and 96h of yield stress measurements and sugar conversion is presented.

Gutierrez, Diana↗

DOE OSTI2020

Effects of blending C3-C4 alcohols on motor gasoline properties and performance of spark ignition engines: A review

Supplementing petroleum fuels with sustainable and renewable alternatives is a good option for increasing the sustainability of transportation fuels. Alcohols are particularly attractive blendstocks for spark ignition engines, mainly due to their desirable fuel properties including high octane, evaporative cooling, and reduced sooting propensity. Although the use of SI engines is widespread around the world, predominately for light duty vehicles, concerns about CO2 emissions and other sustainability issues necessitate increased engine efficiencies, reduced tailpipe pollutants, and lower lifecycle carbon emissions. The intelligent blending of C2-C4 alcohols into motor gasoline is a viable method for achieving these goals. There are a multitude of ways to produce renewable alcohols such as through fermentation from first-generation feedstocks (sugar and corn) and second-generation feedstocks (lignocellulosic biomass), or by gasification and mixed alcohol fuel synthesis routes from lignocellulosic biomass. Currently ethanol is extensively used in motor gasoline fuels worldwide and although many have proposed the use of C3 and C4 alcohols in motor gasoline as an improvement over ethanol, the higher cost of production and lack of clear definition as to their benefit over ethanol when blended into motor gasoline have led to slow acceptance into the market. In this review, special emphasis is placed on the effects of blending C3 and C4 alcohols into motor gasoline in terms of physicochemical properties, volatility behavior, and engine performance when compared to ethanol blends. Furthermore, the impact of blending C3 and C4 alcohols with gasoline on emission (particulate matter, nitrogen oxides, carbon monoxide, hydrocarbons, and unregulated oxygenates) and combustion (volumetric efficiency, thermal efficiency, fuel consumption, and cold performance) characteristics is discussed. Although there are some disagreements in the literature over the effect of alcohols predominately around the type of SI engine, i.e., port fuel injected versus direct fuel injected and engine operating mode, generally it is stated that alcohols can potentially reduce soot, unburned hydrocarbons and CO emissions while increasing thermal efficiency when proper engine configuration/calibration is used. Lastly, research that must be conducted to find the optimum combination of alcohol blends and engine configurations is highlighted and discussed.

09 BIOMASS FUELS↗

DOE OSTI2024

Potential for Combined Heat and Power with Carbon Capture and Storage at U.S. Ethanol Facilities

Conference paper presented at 17th International Conference on Greenhouse Gas Control Technologies (GHGT-17), Calgary, Alberta, Canada, October 20–24, 2024. Economic conditions in the United States have positioned ethanol producers as early adopters of industrial CO 2 capture and storage (CCS) from fermentation processes, creating an opportunity to further reduce emissions. Replacing fossil fired energy with biogenic combined heat and power (CHP) coupled with CCS could enable ethanol production to achieve net negative CO 2 emissions, with gasification based CHP better matching ethanol facilities’ heat and power needs than combustion based systems. Pilot scale testing showed that while 100% biomass gasification increased tar formation, cofeeding corn stover with coal and optimizing gasifier configurations offered promising pathways to reduce tar and improve operational performance.

09 BIOMASS FUELS↗

DOE OSTI2022

High Solids Loading Aqueous Slurry Formation of Corn Stover Before Pretreatment in a Fed-batch Bioreactor

With the increase on population the world will depend on renewable sources to meet the increasingly energy needs. Use of lignocellulosic biomass as a renewable source has been proven efficient for conversion to cellulosic ethanol and capable of contributing to achieve the threshold on energy demand while reducing greenhouse gases in 90% when compared with fossil fuels (Wang et al., 2007, 2012). However, the processing of biomass encounters limitations in feeding and flow within biorefineries due to the system plugging by compaction and slurry high yield stress, preventing transport of biomass materials and in some cases unexpected plant shutdowns that results in high operational costs (dos Santos et al., 2021; Ximenes et al., 2021). Different solutions for biomass handling and slurry formation from densified materials like pellets have been studied. Cellulosic biomass residues are typically processed in pretreatment reactors to which acid or base is added (Humbird et al., 2002). Other pretreatments such as liquid hot water (LHW) and steam explosion that act without the addition of chemicals use pressures above the saturation vapor of water, to disrupt biomass structure (Ruiz et al., 2021). Although these methods are widely known, the use of pretreatments like acid digestion and LHW present challenges like waste disposal and could be energy inefficient (Mosier et al., 2005). Alternatively other approaches like enzymatic liquefaction have been applied for biomass transformation into slurries with promising results and without the use of pretreatments (dos Santos et al., 2021). Nevertheless, enzymatic liquefaction implementation faces difficulties due to the recalcitrant properties of biomass, its variability, and the release of enzyme inhibitors. While it has been proven that chemical composition properties in biomass have effects on enzyme inhibition (Huang et al., 2022; Kim et al., 2011; Zhai et al., 2018), hindering the efficiency of the liquefaction, not ample research has been conducted in understanding the physical properties as particle size, porosity, water adsorption retention and their effect in the ability to form a slurry at high solids concentration (Yan et al., 2020). In order to improve lignocellulosic biomass handling and formation of biomass slurries, enzyme assisted liquefaction for slurry creation from corn stover at solids loadings up to 30% is reported in this work. Two different kinds of biomass (pelleted corn stover and cobs) were liquefied in a fed-batch process using commercial enzymes Celluclast 1.5L or Ctec-2 at 1FPU or 3 FPU per gram of dry solids in 10 mM sodium citrate buffer solution (pH 4.8). Pellets were fed into a 1 L stirred bioreactor according to a predefined fed-batch protocol over the first 5 hours until reaching 30% of solids loading. After 6, 24 and 96 hours, samples were taken and characterized with respect to their sugar composition, rheology and water absorption. Successful slurry creation with dramatically reduced yield stress was achieved for corn stover for both assessed enzymes. Yield stresses of 178±7 Pa (3 FPU, Celluclast 1.5L) and 79±6 Pa (3 FPU, Ctec-2) were measured for corn stover at 24 hours, compared to 6,000 Pa for samples without enzyme. Yield stress was 155± 29 Pa (3FPU, Ctec-2) and 257 ± 72 Pa (1 FPU, Celluclast 1.5L) for corn cobs at 24 hours. Yield stress decreased when residence time increased with an enhanced fluidity noted for higher enzyme concentrations. A profile for 6, 24 and 96h of yield stress measurements is presented.

Gutierrez, Diana↗

DOE OSTI2023

Co-Harvest and Anaerobic Co-Storage of Corn Grain and Stover as Biomass Feedstocks

This research investigated the utility of co-harvesting and anaerobic co-storage of corn grain and stover to positively influence their physical and chemical characteristics as a biomass feedstock. Corn grain and stover were harvested in 2019 and 2020 with a self-propelled forage harvester. Stover yield, moisture content, and composition were altered by the harvest date, stubble height, and header configuration. Harvest date had the utility of varying the stover moisture content (p < 0.001) from 42.3% to 53.5% (w.b.) and 43.1% to 53.9% (w.b.) for the 2019 and 2020 harvest years, respectively. Stubble height was also utilized to vary stover moisture content. A negative linear relationship was established between stubble height and stover moisture content for the early (R2 = 0.76) and late harvest (R2 = 0.91) dates for both years. Stover yield also showed a negative linear relationship (R2 = 0.76) with stubble height over both years. Regardless of the stubble height, the row-crop header collected more stover (p < 0.001) than the ear-snapper header. In 2020, harvested stover ranged from 5.0 to 10.5 Mg ha-1, with ha-1 representing 41% to 85% of the total available stover. In both years, stover ash content was less than 64 g kg-1. Material stored in pilot-scale silos (19 L) was well conserved during anaerobic storage, with average DM losses of 4.8% and 3.4% in 2019 and 2020, respectively. Grain moisture content averaged 23.6% (w.b.) at harvest, and 31.0% (w.b.) after storage as moisture migrated from the moist stover to the drier grain. Harvesting whole-plant corn with a forage harvester had the unwanted effect of reducing the particle size of the grain fraction, which would complicate downstream utilization. However, reducing the harvester cutterhead speed increased the fraction of intact kernels from 47% to 85% by mass. The studied system was a viable alternative to conventional corn grain and stover systems for producing feedstocks for biochemical conversion.

09 BIOMASS FUELS↗