Abstract:

The primary degradation–reaction products (DRP) identified in Ammonia Fiber Expansion (AFEX)-pretreated corn stover are acetate, lactate, 4-hydroxybenzaldehyde (4HBD) and acetamide. The effects of these products at a broad concentration range were tested on Escherichia coli KO11, a strain engineered for cellulosic ethanol production. Fermentations using glucose or xylose as the sole carbohydrate source and a sugar mixture of glucose and xylose were conducted to determine how these products and sugar selection affected fermentation performance. Co-fermentation of the sugar mixture exhibited the lowest overall ethanol productivity compared to single-sugar fermentations and was more susceptible to inhibition. Metabolic ethanol yield increased with the increasing initial concentration of acetate. Although these degradation–reaction products (with exception of acetamide) are generally perceived to be inhibitory, organic acids and 4-hydroxybenzaldehyde at low levels stimulated fermentation. Adaptation of cells to these products prior to fermentation increased overall fermentation rate.

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Abstract:

Empty palm fruit bunch fiber (EPFBF), a readily available cellulosic biomass from palm processing facilities, is investigated as a potential carbohydrate source for cellulosic ethanol production. This feedstock was pretreated using ammonia fiber expansion (AFEX) and enzymatically hydrolyzed. The best tested AFEX conditions were at 135 °C, 45 min retention time, water to dry biomass loading of 1:1 (weight ratio), and ammonia to dry biomass loading of 1:1 (weight ratio). The particle size of the pretreated biomass was reduced post-AFEX. The optimized enzyme formulation consists of Accellerase (84 μL/g biomass), Multifect Xylanase (31 μL/g biomass), and Multifect Pectinase (24 μL/g biomass). This mixture achieved close to 90% of the total maximum yield within 72 h of enzymatic hydrolysis. Fermentation on the water extract of this biomass affirms that nutrients solely from the pretreated EPFBF can support yeast growth for complete glucose fermentation. These results suggest that AFEXtreated EPFBF can be used for cellulosic biofuels production because biomass recalcitrance has been overcome without reducing the fermentability of the pretreated materials.

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Abstract:

In a dry grind ethanol plant, approximately 0.84 kg of dried distillers’ grains with solubles (DDGS) is produced per liter of ethanol. The distillers’ grains contain the unhydrolyzed and unprocessed cellulosic fraction of corn kernels, which could be further converted to ethanol or other valuable bioproducts by applying cellulose conversion technology. Its compositional variability is one of the factors that could affect the overall process design and economics. In this study, we present compositional variability of distillers’ grains collected from four different dry grind ethanol plants and its effect on enzymatic digestibility and fermentability. We then selected two sources of distillers grains based on their distinctive compositional difference. These were pretreated by either controlled pH liquid hot water (LHW) or ammonia fiber expansion (AFEX) and subjected to enzymatic hydrolysis and fermentation. Fermentation of the pretreated distillers’ grains using either industrial yeast or genetically engineered glucose and xylose co-fermenting yeast, yielded 70–80% of theoretical maximum ethanol concentration, which varied depending on the batch of distillers’ grains used. Results show that cellulose conversion and ethanol fermentation yields are affected by the compositions of distillers’ grains. Distillers’ grains with a high extractives content exhibit a lower enzymatic digestibility but a higher fermentability.

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Abstract:

Distiller’s grains and solubles (DGS) is the major co-product of corn dry mill ethanol production, and is composed of 30% protein and 30–40% polysaccharides. We report a strategy for simultaneous extraction of protein with food-grade biobased solvents (ethyl lactate, D-limonene, and distilled methyl esters) and enzymatic saccharification of glucan in DGS. This approach would produce a high-value animal feed while simultaneously producing additional sugars for ethanol production. Preliminary experiments on protein extraction resulted in recovery of 15–45% of the protein, with hydrophobic biobased solvents obtaining the best results. The integrated hydrolysis and extraction experiments showed that biobased solvent addition did not inhibit hydrolysis of the cellulose. However, only 25–33% of the total protein was extracted from DGS, and the extracted protein largely resided in the aqueous phase, not the solvent phase. We hypothesize that the hydrophobic solvent could not access the proteins surrounded by the aqueous phase inside the fibrous structure of DGS due to poor mass transfer. Further process improvements are needed to overcome this obstacle.

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Abstract:

Ammonia fiber expansion (AFEX) pretreatment is an ammonia-based process for improving the susceptibility of lignocellulosic biomass to enzymatic attack. Four parameters – ammonia loading, water loading, reaction temperature, and residence time – can be varied in order to optimize AFEX pretreatment. The effect of these parameters on process economics of ethanol production was studied using a leading biorefinery model. Ammonia loading and residence time had the greatest impact on the economics of ethanol production, primarily due to processing costs for the chilled water condenser and the capital cost of the AFEX reactor. Water loading and reaction temperature had only modest impact on process economics. In addition, the impact of pretreatment conditions on makeup ammonia requirements was explored experimentally, which ranged from 15 to 25 g ammonia/kg biomass. Overall, pretreatment conditions can change the costs of ethanol production by up to 35 cents per gallon ethanol in an 850 ton/day refinery. By linking the results obtained from this Aspen model to experimental results for ethanol production and makeup ammonia recovery, this study can be used to create an economic optimum for AFEX pretreatment in contrast with simply maximizing fermentable sugar production.

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Abstract:

Background: Pretreatment chemistry is of central importance due to its impacts on cellulosic biomass processing and biofuels conversion. Ammonia fiber expansion (AFEX) and dilute acid are two promising pretreatments using alkaline and acidic pH that have distinctive differences in pretreatment chemistries.

Results: Comparative evaluation on these two pretreatments reveal that (i) AFEX-pretreated corn stover is significantly more fermentable with respect to cell growth and sugar consumption, (ii) both pretreatments can achieve more than 80% of total sugar yield in the enzymatic hydrolysis of washed pretreated solids, and (iii) while AFEX completely preserves plant carbohydrates, dilute acid pretreatment at 5% solids loading degrades 13% of xylose to byproducts.

Conclusion: The selection of pretreatment will determine the biomass-processing configuration, requirements for hydrolysate conditioning (if any) and fermentation strategy. Through dilute acid pretreatment, the need for hemicellulase in biomass processing is negligible. AFEX-centered cellulosic technology can alleviate fermentation costs through reducing inoculum size and practically eliminating nutrient costs during bioconversion. However, AFEX requires supplemental xylanases as well as cellulase activity. As for long-term sustainability, AFEX has greater potential to diversify products from a cellulosic biorefinery due to lower levels of inhibitor generation and lignin loss.

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Abstract:

Cellulosic biofuel systems have the potential to significantly reduce the environmental impact of the world’s transportation energy requirements. However, realizing this potential will require systems level thinking and scale integration. Until now, we have lacked modeling tools for studying the behavior of integrated cellulosic biofuel systems. In this paper, we describe a new research tool, the Biorefinery and Farm Integration Tool (BFIT) in which the production of fuel ethanol from cellulosic biomass is integrated with crop and animal (agricultural) production models. Uniting these three subsystems in a single combined model has allowed, for the first time, basic environmental and economic analysis of biomass production, possible secondary products, fertilizer production, and bioenergy production across various regions of the United States. Using BFIT, we simulate cellulosic ethanol production embedded in realistic agricultural landscapes in nine locations under a collection of farm management scenarios. This combined modeling approach permits analysis of economic profitability and highlights key areas for environmental improvement. These results show the advantages of introducing integrated biorefinery systems within agricultural landscapes. This is particularly true in the Midwest, which our results suggest is a good setting for the cellulosic ethanol industry. Specifically, results show that inclusion of cellulosic biofuel systems into existing agriculture enhances farm economics and reduces total landscape emissions. Model results also indicate a limited ethanol price effect from increased biomass transportation distance. Sensitivity analysis using BFITrevealed those variables having the strongest effects on the overall system performance, namely: biorefinery size, switchgrass yield, and biomass farm gate price.

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Dr. Bruce Dale presented "Why Energy is (Really) Important: Biofuels Are Not Optional" at the MABA Winter meeting in Lansing, Michigan on January 11, 2012.

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Dr. Bruce Dale presented "Designing Sustainable Bioenergy Systems II" at the AIChE Annual Conference in Minneapolis, MN on October 19, 2011.

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Dr. Bruce Dale presented "Inventing the Biofuel Future: We Can Have Biofuel for Fuel and Eat It Too" at the ACS Midland Section in Midland, MI on October 6, 2011.

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