Location: Sustainable Biofuels and Co-products Research
2016 Annual Report
Objectives
1: Develop technologies that enable the integrated processing of sorghum grains and sweet sorghum juice at existing biofuels production facilities and that enable the commercial production of new co-products at sorghum-based biorefineries.
1A: Develop technologies that enable the integrated processing of sorghum grains at existing biofuels production facilities.
1B: Develop technologies that enable the integrated processing of sweet sorghum juice at existing biofuels production facilities.
1C: Develop technologies that enable the commercial production of new co-products at sorghum-based biorefineries.
2: Develop technologies that enable the commercial production of marketable C5-rich and C6-rich sugar streams from sorghum lignocellulosic components.
2A: Develop technologies that enable the commercial production of marketable C5-rich sugar streams from sorghum lignocellulosic components.
2B: Develop technologies that enable the commercial production of marketable C6-rich sugar streams from sorghum lignocellulosic components.
3: Develop technologies that enable the commercial conversion of sorghum lignocellulosic components into fuels and industrial chemicals.
3A: Develop technologies that enable the commercial production of industrial chemicals from the C5-rich sugar stream obtained from the enzymatic hydrolysis of pretreated sorghum cellulosic components.
3B: Develop technologies that enable the commercial production of additional ethanol and industrial chemicals from the C6-rich sugar stream obtained from the enzymatic hydrolysis of the cellulose-enriched residue.
3C: Develop technologies that enable the use of byproducts and wastes generated in ethanol and other fermentation processes in the sorghum biorefinery for production of energy and chemicals.
Approach
In conjunction with collaborators, develop technologies that enable commercially-preferred bio/chemical processes for converting all components of sorghum plants, including grains, juice, and bagasse, into fuels, industrial chemicals and consumer products. Develop commercially viable processes for incorporation of sorghum grains into existing commercial corn-based ethanol plants and evaluate the effects of this process modification on overall water balances in the existing plants. Develop commercially viable technologies for using sweet sorghum juice and sorghum biomass, including both carbohydrates and lignin, for the production of important platform chemicals, i.e. chemicals that can be used as precursors for production of a wide range of industrial chemicals and consumer products. Develop technologies for capturing the carbon dioxide gas generated in ethanol fermentation for use in other fermentation processes that requires CO2 as a secondary feedstock in addition to fermentable sugars. Develop technologies for conversion of the wastes generated in cellulosic ethanol and industrial fermentation processes into methane for internal use as an energy source. Develop an integrated process combining the aforementioned process components for a sorghum-based biorefinery.
Progress Report
Objective 1: Fermentation studies utilizing grain sorghum and sweet sorghum juice have been ongoing. Evaluation of enzyme addition during fermentation has demonstrated several important differences relative to corn that will be beneficial in determining the best practices for sorghum integration at existing ethanol facilities. Sweet sorghum juice studies have shown that the juice alone is deficient in nutrients needed by the yeast for rapid fermentation and requires nutrient supplementation. When the juice is mixed with corn, the nutrient levels routinely added for corn are sufficient for fermentation. Microbial contamination in the incoming sweet sorghum juice is a significant concern. Contamination control must be adequately addressed to prevent widespread contamination if the juice is to be effectively used at existing ethanol facilities.
Fractionation studies utilizing grain sorghum are also ongoing. Recovery of a protein rich fraction that is low in fiber has been accomplished. Further analysis and yield determinations are currently being conducted. Alternative fractionation methods are also being evaluated. The protein rich fraction has potential uses in animal diets where high fiber content is undesirable.
Objective 2: Sweet sorghum bagasse was washed with water to recover the residual sugars (sucrose, glucose, fructose) that remained in the solids after juice extraction. The optimum conditions such as solid/water ratio, washing time and washing temperature were determined for maximizing sugar recovery. The washed solids were subjected to low moisture anhydrous ammonia (LMAA) pretreatment to increase the efficiency of the subsequent enzymatic hydrolysis. The pretreated solids were hydrolyzed with a commercial hemicellulase enzyme product to produce a xylose-rich solution, which could be used in fermentation processes for production of various chemicals using suitable xylose-metabolizing microorganisms.
Another objective was to produce a solution of multiple fermentable sugars, which included both six-carbon sugars such as glucose and sucrose and five-carbon sugars such as xylose. To achieve this objective, both washed and unwashed sweet sorghum bagasse were pretreated with the LMAA process and subsequently subjected to enzymatic hydrolysis. The results indicated that LMAA pretreatment did not degrade the residual sugars in the unwashed bagasse to a significant extent and hence washing was not necessary for total sugar production by enzymatic hydrolysis. The optimal conditions of the LMAA pretreatment process such as reaction time and reaction temperature were determined for maximizing total sugar production from the pretreated bagasse in the subsequent enzymatic hydrolysis step.
Objective 3: Ethanol fermentation was performed and the carbon dioxide co-product was absorbed in a sodium hydroxide solution in a glass absorption column to form a sodium carbonate solution. Six stainless-steel reactors were constructed for study of the use of the sodium carbonate solution for pretreatment of sweet sorghum bagasse to enhance the subsequent enzymatic hydrolysis for fermentable sugar production. Preliminary pretreatment experiments were performed. Statistics software was used to design the experiments to be performed on the optimization of the pretreatment process using sodium carbonate as the pretreatment chemical. These experiments are in progress and will be completed in the next fiscal year.
Accomplishments
None.
Review Publications
Nghiem, N.P., Montanti, J.M., Johnston, D. 2016. Sorghum as a renewable feedstock for production of fuels and industrial chemicals. AIMS Bioengineering. 3(1):75-91.
