Butanol has sufficiently similar characteristics to gasoline to be used directly in any gasoline engine without modification and substitution. Butanol is superior to ethanol as a fuel additive in many regards: higher energy content, lower volatility, less hydroscopic (thus does not pick up water), and less corrosive. Also, branched chain 4-carbon alcohols including isobutanol, 2-methyl-1-butanol and 3-methyl-1-butanol have higher octane numbers compared with n-butanol, and thus are good candidates as fuel additives.
Butanol can be produced by clostridia fermentation. Clostridia naturally possess pathways that allow the conversion of sugar into solvents, known as acetone–butanol–ethnol (ABE) fermentation. Clostridium acetobutylicum is the species that is most often used for the industrial production of butanol. But that species has product inhibition, so we didn’t get high concentration. Therefore, we use some catalyst to convert butyric acid to butanol. Then we can use mixed culture system and we didn’t care about product inhibition.