|(200803_A)||March 19, 2008|
Bioethanol from Paddy Straw and Chaff
Bioethanol is attracting keen interest as a new fuel that could take the place of petroleum and other fossil fuels, and America and Brazil are already producing it for commercial purposes from corn, cane sugar and other raw materials. However, there is growing concern that using food crops to manufacture bioethanol is driving up food prices and exacerbating famine. Consequently the race is on to develop technology for producing energy from nonfood plant materials.
Gekkeikan Research Institute has succeeded in adapting brewing technology to develop a means of producing bioethanol from nonfood plant materials such as paddy straw and chaff. The research was conducted jointly with researchers from Kobe University, Kyoto University and Tohoku University over the space of three years from 2004 as part of an Innovative Technology Development Research Project established by Japan Science and Technology Agency (JST).
The new method involves simple pretreatment of the raw materials with water in a subcritical state marked by high temperature and pressure, followed by ethanol production using “super yeast” that is capable of both converting starch to sugar and fermenting the sugar.
The plant cellulose that is the raw material for bioethanol production is chemically stable and has a very robust structure that is accordingly weakened by pretreatment using subcritical water to make it susceptible to the actions of the super yeast. Subcritical water, which can be created by subjecting water to a high temperature (150-370 °C) and pressure, is highly acidic, but quickly becomes neutral again when temperature and pressure decline.
From the perspectives of environmental impact and safety, the new method is preferable to existing pretreatment methods that use chemical agents such as sulfuric acid since it produces no harmful waste products, and uses simpler equipment than other methods involving pretreatment with supercritical water (above 374 °C and 22.1MPa).
To create the super yeast that produces the bioethanol, koji mold genes that produce cellulolytic enzymes were integrated into sake yeast using cell surface engineering so that the enzymes are densely displayed on the surfaces of the yeast cells. Because super yeast combines the capabilities of koji mold, which converts the cellulose starch (cellooligosaccharide) into sugar (glucose), with that of yeast, which ferments sugar (glucose), it can produce ethanol by itself from cellulose pretreated with subcritical water
The combination of subcritical water treatment with super yeast enables clean and easy pretreatment, and simple and efficient ethanol production, which means that small-scale plants could be built and operated in many different rural locations where the plant materials are produced.
Gekkeikan Research Institute has already demonstrated at the experimental level that the new process can effectively produce ethanol from paddy straw and chaff, and it is now working to refine the process for commercial production through research aimed at boosting alcohol yield and integration with various other technologies.
Gekkeikan hopes that this application of microorganism and enzyme utilization technology and fermentation technology rooted in Japanese sake brewing for the production of bioethanol will contribute to the resolution of environmental issues.
About Gekkeikan Research Institute