Use of Supercritical Water Could Cut Costs for Ethanol

Technology Review
Nov 2, 2011

Super converter: A bag of ground up wood chips feeds a system that converts the wood to sugar using supercritical water at this Renmatix demonstration plant in Kennesaw, Georgia.
Renmatix

Renmatix, a startup based in Kennesaw, Georgia, is using water at high pressure and temperature to transform wood chips into sugar, which can then be fermented to make biofuels and other chemicals. The company says the process can produce sugar for the same price as making it from sugarcane, which has led to profitable biofuels production in Brazil.

Renmatix is addressing the most difficult step in producing ethanol from abundant, cellulosic materials such as wood chips, instead of from corn or sugar crops. Once the sugar is made, the same technology employed in a conventional corn or sugar cane ethanol plant can be used to produce ethanol.

So far, Renmatix has only demonstrated the technology on a small scale, using a facility that can process three tons of wood chips a day. As with all advanced biofuels companies, one of the biggest challenges will be convincing investors to hand over the money needed to build a larger commercial facility to prove the venture is commercially viable. The U.S. Environmental Protection Agency has been forced to waive requirements for cellulosic ethanol because commercial plants for converting cellulosic material to ethanol haven't yet been built. By lowering the cost of producing sugar from cellulosic materials, Renmatix hopes to at last break this logjam.

Researchers and companies have tried many methods of turning cellulose into sugar. Some involve breaking the biomass down using acids or specially tailored enzymes. Others involve using heat and pressure to turn biomass into hydrogen and carbon monoxide, which can be converted to biofuel using inorganic catalysts. Each method has drawbacks: enzymes are expensive; acids are toxic; both processes are slow, and they require expensive equipment. The processes that use high heat and inorganic catalysts also have relatively low yields of the desired fuels.
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