While pondering what happened to advanced biofuels I found myself wondering what happened to another widely touted biofuel option - bio-butanol.
The key way [butanol is better than ethanol] is higher energy density. Whereas ethanol is around about two-thirds the energy density [of gasoline], with butanol we’re in the high eighties [in terms of percent].
It’s less volatile [than ethanol]. It isn’t as corrosive, so we don’t have issues with it at higher concentrations beginning to eat at aluminum or polymer components in fuel systems and dispensing systems. And it’s not as hydroscopic–it doesn’t pick up water, which is what ethanol can do if you put it in relatively low concentrations. So we can put it through pipelines.
A range of companies are still pursuing the bio-butanol dream, with one (Optinol) recently declaring it had achieved "energy cost parity" with ethanol for its for (sugar derived) bio-butanol. Another company (Cobalt) is now producing reasonably large volumes of fuel at a pilot plant. BP and Dupont also have a joint venture that they hope will produce butanol at a price competitive with petrol.