3.1 Background

Over the past few years, butanol made from biomass, popularly known as biobu­tanol, has gained a lot of attention as a biofuel. Butanol is an alcohol-based fuel that contains four carbons and has chemical properties similar to that of gasoline, thus making it an attractive substitute or additive. Biobutanol can be produced from the fermentation of sugars from biomass or by the gasification of cellulosic biomass. It can be blended in any ratio with gasoline and be used in existing automobiles without any need for engine or fuel line modifications. It is an attractive substitute to gasoline because its BTU content is 110,000 BTU’s per gallon, which is very close to the 115,000 BTU per gallon of gasoline, resulting in little change to fuel economy. The Reid vapor pressure (RVP) of butanol (0.33 psi) is low compared to ethanol (2 psi) or gasoline (4.5 psi), resulting in lower evaporative emissions. The octane values and energy density of butanol are also closer to gasoline than is ethanol. Ethanol is 100% soluble in water whereas the solubility of butanol is 9.1% at 25°C [10]; this results in less water absorbed and rust dissolved into the fuel from tanks and pipelines. An added benefit to the low solubility is reducing the spread into groundwater in case of a spill.

However, biobutanol is not a perfect fuel and has several disadvantages. Butanol is more toxic to humans and animals than lower carbon alcohols. The LD50 oral consumption for a rat for butanol is 790 mg/kg compared to 7,060 mg/kg for ethanol [13]. However, it is well known that gasoline contains chemicals such as benzene, which is toxic and carcinogenic. There have been no definitive tests as to whether butanol will degrade the materials in an automobile over time, but current evidence suggests that this is unlikely [10]. Environmental Energy, Inc. tested a 1992 Buick Park Avenue by driving it 10,000 miles on 100% butanol [33]. No modifications were done to the car and it passed all emission tests performed in 10 states with an average increase in gas mileage of 9%. Compared to gasoline, combustion of butanol reduces the amount of hydrocarbons, carbon monoxide, and smog-creating compounds that are emitted [33].

Butanol is used as an industrial solvent and the market demand is about 350 million gallons a year worldwide, with the United States accounting for 63%. The production of butanol via fermentation is the second oldest fermentation process, next only to ethanol. Since the 1950s however, production of butanol via fermen­tation has not been an economically viable alternative due to the historic low cost of petroleum. A new push for renewable alternative fuel sources has been fueled by the increasing cost of petroleum combined with the generation of more green­house gases. These two reasons and the development of new technologies form the underpinnings of the reemergence of the butanol fermentation process.