The challenge of enzyme cost in the production of lignocellulosic biofuels.

With the aim of understanding the contribution of enzymes to the cost of lignocellulosic biofuels, we constructed a techno-economic model for the production of fungal cellulases. We found that the cost of producing enzymes was much higher than that commonly assumed in the literature. For example, the cost contribution of enzymes to ethanol produced by the conversion of corn stover was found to be $0.68/gal if the sugars in the biomass could be converted at maximum theoretical yields, and $1.47/gal if the yields were based on saccharification and fermentation yields that have been previously reported in the scientific literature. We performed a sensitivity analysis to study the effect of feedstock prices and fermentation times on the cost contribution of enzymes to ethanol price. We conclude that a significant effort is still required to lower the contribution of enzymes to biofuel production costs.

Examining the feasibility of bulk commodity production in Escherichia coli.

Escherichia coli is currently used by many research institutions and companies around the world as a platform organism for the development of bio-based production processes for bulk biochemicals. A given bulk biochemical bioprocess must be economically competitive with current production routes. Ideally the viability of each bioprocess should be evaluated prior to commencing research, both by metabolic network analysis (to determine the maximum theoretical yield of a given biocatalyst) and by techno-economic analysis (TEA; to determine the conditions required to make the bioprocess cost-competitive). However, these steps are rarely performed. Here we examine theoretical yields and review available TEA for bulk biochemical production in E. coli. In addition, we examine fermentation feedstocks and review recent strain engineering approaches to achieve industrially-relevant production, using examples for which TEA has been performed: ethanol, poly-3-hydroxybutyrate, and 1,3-propanediol.

Lignocellulosic ethanol production without enzymes--technoeconomic analysis of ionic liquid pretreatment followed by acidolysis.

Deconstruction of polysaccharides into fermentable sugars remains the key challenge in the production of inexpensive lignocellulosic biofuels. Typically, costly enzymatic saccharification of the pretreated biomass is used to depolymerize its cellulosic content into fermentable monomers. In this work, we examined the production of lignocellulosic recovery, a process that does not require the use of enzymes to produce fermentable sugars. In the base case, the minimum ethanol selling price (MESP) was $8.05/gal, but with improved performance of the hydrolysis, extraction, and sugar recovery, the MESP can be lowered to $4.00/gal. Additionally, two scenarios involving lignin recovery were considered. Although the results based on current assumptions indicate that this process is expensive compared to more established technologies, improvements in the hydrolysis yield, the sugar extraction efficiency, and the sugar recovery were shown to result in more competitive processes.

Biomass deconstruction to sugars.

The production of biofuels from lignocellulosic biomass relies on the depolymerization of its polysaccharide content into fermentable sugars. Accomplishing this requires pretreatment of the biomass to reduce its size, and chemical or physical alteration of the biomass polymers to enhance the susceptibility of their glycosidic linkages to enzymatic or acid catalyzed cleavage. Well-studied approaches include dilute and concentrated acid pretreatment and catalysis, and the dissolution of biomass in organic solvents. These and recently developed approaches, such as solubilization in ionic liquids, are reviewed in terms of the chemical and physical changes occurring in biomass pretreatment. As pretreatment represents one of the major costs in converting biomass to fuels, the factors that contribute to pretreatments costs, and their impact on overall process economics, are described.