Technologies
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There are currently many ways to produce ethanol. This outline describes the three referred most often. The first one, the most common one, is the fermentation of crops containing sugars and/or starch. The second one, currently at the demonstration stage, is often called cellulosic ethanol; it uses enzymes to produce ethanol out of cellulose-based materials such as wood waste, straw and other organic biomass feedstock . The third one, also at the demonstration stage, is a thermochemical process; it involves the gasification of the biomass into synthesis gas before the production of ethanol.
Fermentation of crops containing sugars and/or starch
Ethanol can be produced from crops containing sugars and / or starch. For example, Brazil produces very large quantities of ethanol from sugar cane, while in the United States the main feedstock has been corn. With sugar crops such as cane, beets etc, the ethanol production process involves fermentation of the sugars, followed by distillation to recover the alcohol and a dewatering process to purify the product to fuel alcohol standards. Starch containing crops, such as corn, potatoes, etc, are also suitable if available at reasonable costs. In these cases, the crops are milled and the starch is hydrolysed to sugars, followed by fermentation, distillation and dewatering as above. A more common variant of the process using grains involves recovery of oils, proteins and other non-sugar components, contained in the feedstock, thus optimizing product yield and economics. The production technologies are feedstock dependent, but once the sugars are available the subsequent steps are the same. The most common crops considered for ethanol production in North America, are corn and grains. In the longer term, it is possible to genetically improve new crops with high starch or sugar content that would better serve as feedstocks.
Cellulosic ethanol
Newer technologies point to the possibility of producing ethanol form cellulose, a polysaccharide that can be hydrolysed into sugars. There has been considerable research in Canada over the last 25 years on improving the production economics of ethanol from materials containing cellulose such as wood, straws, corn stalks and other organic wastes. Processes using cellulose-based materials are currently at the demonstration stage and appear promising in the medium to long term. These processes have more complex front-end elements. One venue involves hydrolysing the cellulose with enzymes or acids into sugars followed by the traditional fermentation, distillation steps. By using non-food feedstock, they could improve economics and sustainability.
Thermochemical process
Another route involves gasification of biomass and organic wastes into synthesis gas (CO2 and H2) followed by catalytic synthesis into methanol, ethanol, butanol or other product. The syn gas could also be obtained through the steam reforming/partial oxidation of biogas of landfill gas. These thermochemical processes, are currently at the demonstration stage, and entail additional production steps involving complex processes and substantially higher capital investments up-front. Operating procedures and ongoing requirements for inputs also require technical expertise. By using non-food feedstock, this process could also improve economics and sustainability. (http://www.syntecbiofuel.com/technology.html)
Modified: 03-31-2008
