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A review of cellulosic biofuel commercial‐scale projects in the United States

In contrast to a few years ago, when cellulosic ethanol via enzymatic hydrolysis was the only widely recognized technology for commercially producing cellulosic biofuels, a diversity of approaches are currently under commercial development. While no commercial‐scale (≥20 million gallons per year) cellulosic biofuel facilities are operating at present, at least ten biorefinery projects employing six different pathways are expected to begin operations by 2014. These biorefineries will employ the following pathways: (i) catalytic pyrolysis and hydrotreating to hydrocarbons; (ii) gasification and Fischer‐Tropsch synthesis to hydrocarbons; (iii) gasification and methanol‐to‐gasoline synthesis; (iv) dilute acid hydrolysis, fermentation to acetic acid, and chemical synthesis to ethanol; (v) enzymatic hydrolysis to ethanol; and (vi) consolidated bioprocessing (single‐step enzyme production, hydrolysis, and fermentation) to ethanol. This review provides an overview of the six pathway technologies, comprehensive descriptions of each of the ten biorefinery projects, and a discussion of the current direction of cellulosic biofuel commercialization efforts and its implications for the revised Renewable Fuel Standard. © 2013 Society of Chemical Industry and John Wiley & Sons Ltd