Bioprocessing for biofuels Blanch, Harvey W
Current opinion in biotechnology,
06/2012, Letnik:
23, Številka:
3
Journal Article
Recenzirano
Highlights ► Cost-effective deconstruction of biomass is key to biofuels production. ► Cellulase costs remain high, reduced enzyme loading is required. ► Metabolic pathway redesign for drop-in fuels ...is required toincrease yields. ► Algal biodiesel challenges include systems for cell harvesting and lysis.
Ionic liquids (ILs) are promising solvents for the pretreatment of biomass as certain ILs are able to completely solubilize lignocellulose. The cellulose can readily be precipitated with an ...anti-solvent for further hydrolysis to glucose, but the anti-solvent must be removed for the IL to be recovered and recycled. We describe the use of aqueous kosmotropic salt solutions to form a three-phase system that precipitates the biomass, forming IL-rich and salt-rich phases. The phase behavior of EmimAc and aqueous phosphate salt systems is presented, together with a process for recycling the EmimAc and enzymatically hydrolyzing the cellulose. This process reduces the amount of water to be evaporated from recycled IL, permitting efficient recycle of the IL. Material balances on the process, with multiple recycles of the EmimAc, quantify the major components from a Miscanthus feedstock through the pretreatment, separation, and enzymatic hydrolysis steps. A more rapid and higher yielding conversion of cellulose to glucose is obtained by use of the three-phase system as compared to the cellulose obtained from biomass pretreated with IL and precipitated with water. The addition of a kosmotropic salt during the precipitation results in partial delignification of the biomass, which makes the substrate more accessible, enhancing the enzymatic hydrolysis. Biotechnol. Bioeng. 2011; 108:511-520.
For the temperature range (80 to 120) °C, viscosity data are reported for imidazolium-based ionic liquids 1-octyl-3-methylimidazolium chloride OmimCl, 1-hexyl-3-methylimidazolium chloride HmimCl, ...1-butyl-3-methylimidazolium chloride BmimCl, 1-ethyl-3-methylimidazolium chloride EmimCl, 1-ethyl-3-methylimidazolium acetate EmimAc, 1-butyl-3-methylimidazolium acetate BmimAc, and 1-butyl-3-methylimidazolium dicyanamide Bmim N(CN)2. Acetate-based ionic liquids have considerably lower viscosities than the corresponding chloride-based ILs. At 25 °C, viscosity data are reported for binary mixtures of BmimAc with diluents water, acetonitrile, dimethylformamide (DMF), and ethylene glycol. Even a small concentration of diluent very much reduces the viscosity of an ionic liquid.
We present a process model for a lignocellulosic ethanol biorefinery that is open to the biofuels academic community. Beyond providing a series of static results, the wiki-based platform provides a ...dynamic and transparent tool for analyzing, exploring, and communicating the impact of process advances and alternatives for biofuels production. The model is available for download (at
http://econ.jbei.org) and will be updated based on feedback from the community of experts in biofuel-related fields. By making the assumptions and performance metrics of this model transparent, we anticipate this tool can provide a consensus on the energy-related, environmental, and economic performance of lignocellulosic ethanol.
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.
Nearly one hundred years ago, the fermentative production of acetone by Clostridium acetobutylicum provided a crucial alternative source of this solvent for manufacture of the explosive cordite. ...Today there is a resurgence of interest in solventogenic Clostridium species to produce n-butanol and ethanol for use as renewable alternative transportation fuels. Acetone, a product of acetone-n-butanol-ethanol (ABE) fermentation, harbours a nucleophilic α-carbon, which is amenable to C-C bond formation with the electrophilic alcohols produced in ABE fermentation. This functionality can be used to form higher-molecular-mass hydrocarbons similar to those found in current jet and diesel fuels. Here we describe the integration of biological and chemocatalytic routes to convert ABE fermentation products efficiently into ketones by a palladium-catalysed alkylation. Tuning of the reaction conditions permits the production of either petrol or jet and diesel precursors. Glyceryl tributyrate was used for the in situ selective extraction of both acetone and alcohols to enable the simple integration of ABE fermentation and chemical catalysis, while reducing the energy demand of the overall process. This process provides a means to selectively produce petrol, jet and diesel blend stocks from lignocellulosic and cane sugars at yields near their theoretical maxima.
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