Notice how the difference between the two alcohols is the additional carbon groups on butanol. Butanol is known to have an octane level comparable to gasoline (lower than ethanol) but has a much higher energy density than ethanol. Tests show that if butanol were to replace gasoline in the engine of currently produced cars, the energy penalty would be around 10%, compared to 27% for ethanol. BP tests also showed the butanol did not have the phase separation problems that ethanol has and so butanol could potentially be pumped in conventional gasoline pipelines. Also, BP preliminary tests show that butanol can be added to a conventional car up to 16%, which is beyond the current 10% allowed for ethanol. (Theoretically a flex-fuel car would run on 85% butanol as well).
Although the most recent announcement from BP and Dupont on 60 new patent applications for their butanol process, the target date for beginning the production of butanol (2010) is still a ways off. Problems with the production of butanol include a very low level of butanol produced by the microorganisms because of several bi-product formations. Also, the butanol is toxic to the organism, much the same as ethanol can be at high levels, and so proper distillation methods need to be developed. Finally, the BP/Dupont partnership has focused on conventional bacteria to produce butanol, at least preliminarily, and so they are not taking advantage of any new cellulosic technologies such as improved microorganisms or gasification technologies. It seems to me that the best method would be to combine both streams into one -- produce butanol using a microorganism shown to grow on multiple feedstocks.
The bottom line is that while ethanol transitions from corn-based to cellulosic, we will also see a gradual transition into fuels that have been termed 'second-generation,' and 'next-generation' biofuels. Second-generation biofuels are those like butanol, which are gasoline substitutes like ethanol but with potentially better qualifications to replace gasoline. Next-generation fuels look to the future where the potential exists to produce synthetic gasoline that could be an exact replacement to imported gasoline made from domestic feedstocks. Next-generation fuels also refer to non-hydrocarbon based fuels such as hydrogen. It will be very interesting to monitor the transitions, struggles, and technological advances that will allow one, some, or all of these fuels to flourish.
For the original article on BP/Dupont research: