Location: Sustainable Biofuels and Co-products Research
2022 Annual Report
Objectives
Objective 1 Develop integrated processes to enable commercial production of value-added products in existing corn ethanol biorefineries.
This includes co-conversion of biomass (corn stover, corn fibers) with corn starch for production of value-added products to enhance biorefinery profitability and stability.
Sub-objective 1-A. Develop technologies that enable the integrated processing of pretreated biomass with grains at existing biofuels production facilities for cellulosic ethanol production.
Sub-objective 1-B. Utilize advanced enzymatic fractionation processes to separate fiber and starch prior to fermentation to generate a fiber rich streams for pretreatment and biomass sugar production studies.
Sub-objective 1-C. Produce and utilize sugars from biomass/grain mixtures for the fermentation of value-added coproducts.
Objective 2 Develop self-sustained biomass pretreatment and conversion processes to enable commercial production of fermentable sugars and lignin-derived products.
This includes but is not limited to the use of Na2CO3, which can be generated by NaOH absorption of CO2, a co-product of aerobic/anaerobic fermentation, for biomass pretreatment. Both lignin fractions obtained prior to pretreatment and after sugar extraction will be investigated as feedstocks for conversion to high-value products or fuels.
Sub-objective 2-A. Develop a process for pretreatment of biomass using the Na2CO3 solutions made by absorption of CO2 from ethanol and 2,3-butanediol (2,3-BDO) fermentations in NaOH.
Sub-objective 2-B. Develop a process using the Na2CO3-pretreated biomass as feedstocks for production of fermentable sugar solutions suitable for use as substrates in industrial fermentations.
Sub-objective 2-C. Develop lignin recovery and conversion processes that generate advanced biofuels, high-value chemicals, or renewable materials.
Objective 3 Develop hybrid biocatalytic/chemical processing technologies to enable the commercial conversion of lignocellulosic sugars to advance biofuels or chemicals.
Fermentable sugars from biomass feedstocks will be utilized to produce a microbial source of 2,3-BDO. The recovered 2,3-BDO will then be investigated by downstream chemical upgrading technologies to produce advance biofuels or high-value chemicals.
Sub-objective 3-A. Develop fermentation processes for the production and recovery of 2,3-butanediol.
Sub-objective 3-B. Develop chemical conversion process to upgrade 2,3-butanediol to an advanced biofuel.
Approach
The first objective will establish technologies that integrate sugars derived from biomass feedstocks that are not directly connected to corn grains (e.g. corn stover and switchgrass) with corn starch-derived sugars for the production of ethanol and/or industrial chemicals. Pretreated biomass will be co-converted with corn or other starch-containing feedstocks for production of cellulosic ethanol within existing biorefineries. The primary focus will investigate additional ethanol production in dry-grind corn facilities. Other investigations will be made into process technologies whereby the fiber isolated from corn kernels prior to ethanol fermentation can be utilized in conjunction with other pretreated biomass to produce additional fermentable sugars. The fermentable sugars will then be utilized in fermentation processes for production of value-added co-products, such as the carotenoid astaxanthin, in existing ethanol biorefineries.
The second objective will develop a self-sustainable pretreatment process for corn stover and switchgrass using sodium carbonate solutions generated by the absorption of carbon dioxide produced from simulated industrial fermentations. This pretreatment process will be optimized in order to maintain at least 85% of the orginal cellulose and at least 70% of the original hemicellulose in corn stover and switchgrass. Following sodium carbonate pretreatment the pretreated biomass will be hydrolyzed to generate fermentable sugars using commercially available enzymes. The enzymatic hydrolysis process will be optimized to maintain at least 50 g/L of total sugars in the hydrolysate and greater than 75% theoretical sugar yields. The residual insoluble solids obtained after pretreatment or enzymatic hydrolysis will also be utilized to develop a process for lignin recovery. The recovered lignin will be utilized as a separate feedstock for the generation of advanced biofuels via biochemical conversion, or in material applications for preparing biobased epoxy resins.
The third objective will investigate fermentation processes for the production of 2,3-butanediol (2,3-BDO) from fermentable sugars of pretreated corn stover or switchgrass. The 2,3-BDO produced by fermentation will be catalytically upgraded to an advanced biofuel. Fermentation processes will be developed and optimized to generate 2,3-BDO at high titers and yields. Additional process development will focus on separation and recovery processes following fermentation in order to obtain a high purity yield of 2,3-BDO for downstream chemical upgrading. The recovered 2,3-BDO will then be upgraded via a multi-step chemical conversion route utilizing dehydration, aldol condensation, and hydrodeoxygenation to generate a hydrocarbon fuel. Both chemical catalyst selection will be identified and process parameters optimized as the upgrading process is investigated.
Progress Report
Objective 1: Recovery of corn kernel fiber after the production of ethanol has been completed and the recovered fiber has been pretreated using sodium carbonate. Two different fiber recovery processes were utilized to generate the fiber for pretreatment. The first method incorporated our newly patented process modified grinding protocol in conjunction with an enzymatic treatment to recover germ prior to fermentation. The germ contains approximately 80% of the kernel oil and can potentially be recovered as a value-added coproduct. The second method recovered the fiber from the entire corn kernel without separate recovery of the germ. Fermentation experiments are being done using each of the pretreated fiber samples and will be evaluated for ethanol production in mixtures with corn. Enzymatic conversion efficiencies will also be evaluated for comparison with other pretreated fiber and pretreatment methods.
Objective 2: A corn stover pretreatment process has been developed using the recovered sodium carbonate solution formed from the reaction of carbon dioxide (fermentation by-product) and sodium hydroxide solution. A 5% (weight by volume) solid loading of milled corn stover and the recycled solution were mixed and chemically pretreated to 150 degrees C for 90 minutes in a sealed stainless-steel reactor. The pretreated biomass is subjected to enzymatic hydrolysis studies to maximize fermentable sugars available for downstream fermentation. Research is continuing to complete sugar and biomass composition analysis. In addition, the absorption column reaction was improved by controlling temperature to reduce precipitation formation and by evaluating the effect of different random packing materials on carbon dioxide effervescence. Additional work is in the planning stages for pretreating switchgrass biomass and performing enzymatic hydrolysis studies to compare the release of fermentable sugars with other feedstocks.
Objective 3: The product of Paenibacillus (P.) polymyxa fermentation (2,3-butanediol) was separated and recovered using a non-energy intensive process. Due to the high boiling point of 2,3-butanediol (177 degrees C) a solubility-based separation process was investigated instead of distillation. An aqueous solution containing 2,3-butanediol was prepared and subjected to a solubility-based separation. Salts of different composition were mixed in a known volume of the 2,3-butanediol solution at the saturation level followed by the addition of an organic solvent. The combination of the salt with the organic solvent serves to create a phase separation between the aqueous and organic layers. A combination of different salts and organic solvents (both miscible and immiscible with water) have been evaluated. As expected the organic solvents immiscible with water provide a more defined phase separation layer with the aqueous solution. Greater mass recovery of 2,3-butanediol could be achieved from the aqueous layer by increasing the volume of organic solvent. At the current conditions evaluated up to 44% of the initial 2,3-butanediol could be separated from an aqueous solution into an organic solvent. Continued experiments are underway to understand the behavior for this separation process by calculating partition coefficients for the recovered product, and to determine organic solvent and salt loadings that can provide the greatest amount of 2,3-butanediol separation and recovery. Further investigations will also be made with P. polymyxa fermentation broth.
Accomplishments
Review Publications
Garcia-Negron, V., Chmely, S., Ilavsky, J., Keffer, D.J., Harper, D.P. 2022. Development of nanocrystalline graphite from lignin sources. ACS Sustainable Chemistry & Engineering. 10(5):1786-1794. https://doi.org/10.1021/acssuschemeng.1c05969.
Kizzire, D.G., Garcia-Negron, V., Harper, D.P., Keffer, D.J. 2022. Local structure analysis and modeling of lignin-based carbon composites through the hierarchical decomposition of the radial distribution function. ChemistryOpen. https://doi.org/10.1002/open.202100220.
Johnston, D., Nghiem, N.P. 2021. Mixed fermentation of corn and pretreated corn stover for fuel ethanol production. Cereal Chemistry. 98:926-934. https://doi.org/10.1002/cche.10434.
Bhatia, G., Juneja, A., Johnston, D., Rausch, K., Tumbleson, M.E., Singh, V. 2021. Characterization of amylose lipid complexes and their effect on the dry grind ethanol process. Starch/Starke. https://doi.org/10.1002/star.202100069.
Strahan, G.D., Mullen, C.A., Stoklosa, R.J. 2022. Application of diffusion ordered NMR spectroscopy to the characterization of sweet sorghum bagasse lignin isolated after low moisture anhydrous ammonia (LMAA) pretreatment. BioEnergy Research. https://doi.org/10.1007/s12155-021-10385-y.
