Ethanol production and the cost of fermentable sugars from biomass
ABSTRACT The current fermentation alcohol industry in the US is based on utilization of glucose and/or starch derived principally from corn. Biomass materials including wood and agricultural residues, newspaper, and other sources of cellulose could provide a source of fermentable sugars for expanding fuel ethanol production. Prospects for the utilization of biomass for conversion to fermentable hexoses and pentoses are continually improving with advances in enzyme technology, specially engineered microorganisms which can ferment pentoses, and improvement in cellulose pretreatments. Technical and economic factors which affect utilization of sugars from biomass are summarized, and the key steps in wet- and dry-milling of corn are described for purposes of comparison. An approach for estimating fermentable sugar costs is presented to gauge the impact of technical improvements on reducing fermentable sugar costs. An analytical framework resulting from this approach facilitates comparison of effects of feedstock costs, by-product credits, differences in technology, and process costs on the cost of fermentable sugars. A systematic strategy for evaluating differences in cost is presented as a tool for making a first comparison of different technologies and feed stock materials for ethanol production. This analysis suggests that fermentable sugars from enzymatic hydrolysis of cellulose must cost no more than 4–5c lb−1 (8·8–11c kg−1), at current conditions, if they are to be economically competitive with fermentable sugars derived from corn.
- SourceAvailable from: tamu.edu[show abstract] [hide abstract]
ABSTRACT: The economic feasibility of producing ethanol from sweet sorghum juice is projected using Monte Carlo simulation models to estimate the price ethanol plants will likely have to pay for sweet sorghum and the uncertain returns for ethanol plants. Ethanol plants in high yielding regions will likely generate returns on assets of 11%-12% and in low yield areas the returns on assets will be less than 10%.02/2009;
- [show abstract] [hide abstract]
ABSTRACT: Simultaneously achieving economic, environmental and social sustainability is a major challenge for the emerging renewable fuel industry. We approach this problem by demonstrating a cellulosic biorefinery paradigm which produces ethanol and food precursors using lignocellulosic biomass as the exclusive source for carbohydrates and minerals. Enzymatic hydrolysate from Ammonia Fiber Expansion (AFEX)-pretreated corn stover at 18% w/w solids loading was found to be nutrient-rich. This hydrolysate was fermented completely within 48 h in two stages to produce ethanol and native yeast cells. An in-house saccharolytic enzyme production using AFEX-pretreated corn stover as carbohydrate source greatly reduces the dependence on commercial enzymes. The inducer mixture is 2.5–7 times more potent than lactose, a common enzyme inducer. Economic analysis indicates that the proposed paradigm is substantially more cost-effective relative to the 2005 NREL model. This improvement is largely attributed to the native yeast cells co-production and the reduction of enzyme cost through the in-house production. Despite great promise, cellulosic biofuels such as ethanol are struggling to be commercially realized due to high processing costs and low profit margins. Decreasing the costs of low-margin commodities such as fuels requires driving down input costs or increasing revenue by generating valuable co-products. In this paper, we take a holistic approach to lignocellulosic biomass utilization to achieve cost reductions by both routes. The well-known approach to biofuel production via the biochemical route uses as much carbohydrate as possible for ethanol production, the remaining biomass for heat and power generation, and relies on expensive, external sources for hydrolytic enzymes and downstream fermentation nutrients. In contrast, by using Ammonia Fiber Expansion (AFEXÔ) pretreatment, we are able to preserve all nutrients necessary for fermentation, with available excess nutrients used to produce yeast for nutraceuticals, food, and feed related applications (hence, partly offsetting the ''food vs. fuel'' issue of growing dedicated bioenergy crops). In addition, in this novel approach to producing cellulosic biofuels, a small fraction of the pretreated biomass carbohydrates is used to induce and express hydrolytic enzymes at a significantly lower cost. When combined with yeast recycling for improved xylose fermentation, we estimate that these process improvements can decrease the cost of ethanol production by $$0.50 per gallon. The creation of a new multibillion dollar renewable liquid fuel industry demands extensive financial investments, novel technology developments, nationwide policy changes and innovative thinking. The technologies described here are representative of the approaches that can be used to develop this industry. By obtaining additional value via utilization of the entire cellulosic feedstock rather than only the carbohydrate fractions, these and other upcoming process improvements will be necessary to establish a commercially viable bio-based alternative to crude oil derived fuels and chemicals.Energy & Environmental Science 03/2012; 5:7100-7110. · 11.65 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Amino acid production processes with Corynebacterium glutamicum are based on media containing glucose from starch hydrolysis or fructose and sucrose as present in molasses. Simultaneous utilization of various carbon sources, including glucose, fructose and sucrose, in blends is a typical characteristic of this bacterium. The renewable non-food carbon source arabinose, which is present in hemicellulosic hydrolysates, cannot be utilized by most C. glutamicum strains. Heterologous expression of the araBAD operon from Escherichia coli in the wild-type and in an l-lysine producing strain of C. glutamicum was shown to enable production of l-glutamate and l-lysine, respectively, from arabinose as sole carbon source. l-Ornithine and l-arginine producing strains were constructed and shown to produce l-ornithine and l-arginine from arabinose when araBAD from E. coli was expressed. Moreover, the recombinant strains produced l-glutamate, l-lysine, l-ornithine and l-arginine respectively, from arabinose also when glucose-arabinose blends were used as carbon sources.Journal of Biotechnology 07/2011; 154(2-3):191-8. · 3.18 Impact Factor