The Need for Renewable Fuels
In the 1970s, the world suffered its first energy crisis. As a result, governments worldwide, particularly the US Government, strongly encouraged and supported the development of alternative fuels for transportation, particularly a renewable liquid fuel that could be produced from domestically available renewable resources. Ethanol has been proven to be a desirable renewable liquid fuel for transportation. In particular, ethanol can be produced from cellulosic biomass (corn stover, rice straw, wood, grasses, waste papers, etc.), which is abundantly available throughout the world – especially in our country. These feedstocks are also inexpensive and some of them exist as agricultural, municipal or industrial wastes. Converting such wastes to ethanol also helps to solve waste disposal problems.
In response to this urgent need, Purdue University established its Laboratory of Renewable Resources Engineering to focus on the development of ethanol fuel from cellulosic biomass. It was known that more than 70% of these resources could be converted to sugars. Presumably these sugars would be fermented to ethanol by microorganisms, particularly by the Saccharomyces yeast. The Saccharomyces yeast, also known as baker’s yeast, is the most effective microorganism for the fermentation of glucose and related hexose (six carbon) sugars to ethanol. It is the only microorganism that has been used for large-scale ethanol production.
However, it was found that the Saccharomyces yeast was unable to ferment the sugar known as “xylose” (a five carbon pentose sugar), the second major sugar (next only to glucose) present in most types of cellulosic biomass. Unfortunately, there were also no other known naturally occurring microorganisms that could effectively convert both glucose and xylose to ethanol.