But cost competitive production technologies have to be put in place and detailed material compatibility studies on the effect on human health have to be done before it can be used as an alternative transportation fuel on a commercial scale.

Butanol is a four carbon alcohol. Recently, butanol produced by fermentation, know as bio-butanol can be mixed in higher ratios with gasoline or diesel without phase separation and for use in existing cars without the need for retrofit as the air-fuel ratio and energy content are closer to that of gasoline as the air-fuel ratio and energy content are closer to that of gasoline. Butanol could gradually replace gasoline as well as diesel due to its high energy content, miscibility, better combustion characteristics, low volatility and other positive qualities, experts say

According to Mritunjay Kumar Shukla of the Dehradun-based Indian Institute of Petroleum kinematic viscosity of butanol is several times higher than that of gasoline and about as viscous as high quality diesel fuel. Latent heat of vapourisation of butanol is less than half of that of ethanol, an engine running on butanol should be easier to start in cold weather than one running on ethanol. Its Stoichometric A/F ratio is 11.2 which allows butanol to function in a standard engine where gasoline is used. The Stoichometric A/F ratio of gasoline is 14.7 while that of ethanol is 9. Butanol's energy content is about 105,000 Btu per US gallon while that of gasoline is about 114,000 Btu per US gallon. In effect butanol has about 92% of the energy of gasoline. Shukla was recently in Delhi on the occasion of the 6th International Bio-fuel Conference organized by Winrock International India (WII).

Additionally as butanol has a very low vapour pressure point (RVP) of o.3 and a high flash point (FP) of 37 degree Celsius it is very safe fuel to use in high temperatures. Consequently butanol is a very versatile fuel and fuel extender in both gasoline and diesel engines.

However, not much studies have been done regarding engine and vehicle testing of butanol. According to Shukla it was demonstrated in June 2006 that n-butanol can be used either 100% in unmodified 4-cycle ignition engine or blended up to 30% with diesel in a compression engine or blended up to 20% with kerosene in a jet turbine engine.

Laboratory experiments were conducted for evaluation of vehicular performance and tailpipe emissions from butanol/gasoline and ethanol/gasoline at AFLAD, Indian Institute of Petroleum, Dehradun on a 4-stroke motorbike (Bajaj Caliber 115) on a chassis dynamometer. Commercially available gasoline fuel was used for taking the baseline data of test vehicle - 99.9% pure ethanol and 99.9% pure butanol were used for preparing blends of 5% and 10% of ethanol with gasoline and butanol with gasoline. All the alcohol blends showed reduction in mass emission of HC, CO and NOx. CO mass emission was found to be lowest with 10% blended butanol. HC mass emission was lowest with 5% blended ethanol. However with all the alcohol blends value of HC mass emission were found to be comparable. Slightly higher NOx mass emission was observed red in case of butanol blends. All the butanol blends offered a smooth engine operation. Better fuel efficiency was observed with butanol blends over ethanol blends.

However, environmental concerns still remain. Human inhalation exposure to butanol-1 (20-50 ppm) is irritating to eyes, nose and throat though no systemic effects occur at this exposure level. There is no report of carcinogenicity with butanol-1 and it is classified under Group-D chemicals by EPA. Release of n-butanol to soil may result in volatilisation from soil surface and biodegradation is expected to be significant. As n-butanol may not bind strongly to the soil and is, therefore, likely to reach the groundwater level. Vapour phase n-butanol in the atmosphere is expected to react with photo chemically generated hydroxyl radicals with a half-life of 1.2 to 2.3 days.

Most common bio-butanol production process is acetone-butanol-ethanol (ABE) fermentation developed by the Russian scientist and later Israeli president C Weitzman at Manchester University by producing a bacteria which later came to be known as C. acetobutylicum. Apart from the ABE route there are EEI's Dual Immobilised reactors with continuous recovery process using two different types of clostridium strains and UK's Green Biological's advance technologies utilizing thermophilic strains. Besides there are emerging technologies for hydrolysis of cellulose using mineral acids, enzymes followed by fermentation of c5/c6 sugars to bio-butanol, Sangi hydroxyapatie (HAP) catalyst for dehydrating bio-ethanol to butanol, gasification of various biological materials to make syngas to produce bio-butanol and CO2 to fuel GTL technologies.#