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Butanol (or biobutanol) is a gasoline replacement fuel that is made from biological matter converted into alcohol. It can also be made from petroleum and petrobutanol, but this is becoming less common in fuels.
Butanol vs. Gasoline
Biobutanol compares to gasoline favorably. The energy density of gasoline is about 32 megajoules per liter (32MJ/L) while butanol sports a 29.2MJ/L compared to ethanol's 19.6MJ/L and methanol's 16MJ/L.
This makes butanol close enough to gasoline that it can be a straight across replacement in terms of energy. In theory, a fuel mileage loss of roughly 10% would incur in a straight tradeoff, but this has never been tested.
Most butanol is currently made for industrial uses from petroleum. Butanol as fuel is not common in North America, but is being made mostly from biomass through fermentation processes. The A.B.E. Process uses bacteria to ferment biological mass (usually agricultural waste).
Butanol used to be considered a byproduct of this process, which was primarily used to make acetone. The process also makes a recoverable amount of hydrogen (H2) which can be immediately recycled into energy by burning or through a fuel cell.
New ways of making butanol are being tried, including the creation via algae using solar energy.
Advantages of Butanol
Biomass is readily available for making butanol and the process is simple enough that it can be completely regionalized (from biomass production to fuel). Butanol is much like gasoline, so it can be distributed through the same infrastructure, and it's much easier on the atmosphere and planet than is petroleum-based fuel.
Butanol is very water tolerant, so it can mix easily with gasoline or diesel without the separation issues that water can bring to ethanol mixtures. It can also be burned in most combustion engines made for it without need of water separation (as with diesel) or dehydration (as with ethanol).
Disadvantages of Butanol
Butanol has less energy density than gasoline and a lower octane rating than gasoline, ethanol, or methanol. It has an air-fuel ratio similar to gasoline (11.1 vs. 14.6), but outputs less energy overall.
While the making of butanol is not new, producing it specifically as a fuel is, so no real commercialization has happened yet.
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