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.
The environmental benefits and trade‐offs of automotive biofuels are well known, but less is known about aviation biofuels. We modeled the environmental impacts of three pathways for aviation biofuel ...in Australia (from microalgae, pongamia, and sugarcane molasses) using attributional life cycle assessments (LCAs), applying both economic allocation and system expansion. Based on economic allocation, sugarcane molasses has the better fossil energy ratio FER (1.7 MJ out/MJ in) and GHG abatement (73% less than aviation kerosene) of the three, but with trade‐offs of higher water use and eutrophication potential. Microalgae and pongamia have lower FER and GHG abatement (1.0 and 1.1; 53% and 43%), but mostly avoid eutrophication and reduce water use trade‐offs. All have similar and relatively low land use intensities. If produced on land where existing carbon stocks are not compromised, the sugarcane and microalgae pathways would currently meet a 50% GHG abatement requirement. Based on system expansion, microalgae and pongamia had lower impacts than sugarcane for all categories except energy input, highlighting the positive aspects of these next‐generation feedstocks. The low fossil energy conservation potential of these pathways was found to be a drawback, and significant energy efficiencies will be needed before they can affect fossil energy conservation. Energy recovery from processing residues (base case) was preferable over use as animal feed (variant case), and crucial for favorable energy and GHG conservation. However this finding is at odds with the economic preferences identified in a companion technoeconomic study.
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.
Currently, the predominant microbially produced biofuel is starch- or sugar-derived ethanol. However, ethanol is not an ideal fuel molecule, and lignocellulosic feedstocks are considerably more ...abundant than both starch and sugar. Thus, many improvements in both the feedstock and the fuel have been proposed. In this paper, we examine the prospects for bioproduction of four second-generation biofuels (
n-butanol, 2-butanol, terpenoids, or higher lipids) from four feedstocks (sugars and starches, lignocellulosics, syngas, and atmospheric carbon dioxide). The principal obstacle to commercial production of these fuels is that microbial catalysts of robust yields, productivities, and titers have yet to be developed. Suitable microbial hosts for biofuel production must tolerate process stresses such as end-product toxicity and tolerance to fermentation inhibitors in order to achieve high yields and titers. We tested seven fast-growing host organisms for tolerance to production stresses, and discuss several metabolic engineering strategies for the improvement of biofuels production.
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