Sugar Platform for Biological Processing of Cellulosic Biomass to Fuels

Simple sugars (mono and disaccharides) are reactive molecules that can be converted biologically or chemically into fuels, chemicals, food, and animal feed.  Significant quantities of simple sugars occur in sugarcane, sugar beets, sweet sorghum, and a few other plants. In nature, these sugars are often polymerized as storage polysaccharides (e.g., starch) in grains like corn, rice, and wheat. Worldwide, grains are the basis of most human food and are either eaten directly or fed to livestock.

There are three different branches of the sugar platform: (1) simple sugars from sugarcane (2) starch from corn via wet or dry milling, and (3) lignocellulose.

To convert simple sugars to ethanol, the key steps include extracting sugar from sugarcane, fermenting the sugar to ethanol, and distilling the resulting ethanol-water mixture to recover ethanol.

To convert starch to ethanol, the corn must be ground and cooked to make the starch available for amylase enzymes to hydrolyze it to sugar. Enzymatically produced sugars are then fermented and the resulting ethanol distilled.

To convert lignocellulose to ethanol, biomass must also be ground and then the plant cell walls disrupted to make the cell walls available for enzymatic conversion to sugars and thence to ethanol.

This article details the complicated process of converting lignocellulose to ethanol. Lignocellulosic ethanol offers important advantages for domestic production of liquid transportation fuels and is now reaching commercial production. Because of the limited need for fossil fuels to convert lignocellulose to ethanol, fossil fuel inputs are highly leveraged and therefore reduce net carbon dioxide emissions.