How Biobutanol Can Be Used as a Motor Fuel

Illustration of a butanol molecule
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Biobutanol is four-carbon alcohol derived from the fermentation of biomass. When it is produced from petroleum-based feedstocks, it's commonly called butanol. Biobutanol is in the same family as other commonly known alcohols, namely single-carbon methanol, and the more-well-known two-carbon alcohol ethanol. The importance of the number of carbon atoms in any given molecule of alcohol is directly related to the energy content of that particular molecule. The more carbon atoms present, especially in a long carbon-to-carbon bond chains, the denser in energy the alcohol is.

Breakthroughs in biobutanol processing methods, namely the discovery and development of genetically modified microorganisms, has set the stage for biobutanol to surpass ethanol as a renewable fuel. Once considered usable only as an industrial solvent and chemical feedstock, biobutanol shows great promise as a motor fuel due to its favorable energy density, and it returns better fuel economy and is considered a superior motor fuel (when compared to ethanol).

Biobutanol Production

Biobutanol is derived mainly from the fermentation of the sugars in organic feedstocks (biomass). Historically, up until about the mid-50s, biobutanol was fermented from simple sugars in a process that produced acetone and ethanol, in addition to the butanol component. The process is known as ABE (Acetone Butanol Ethanol) and has used unsophisticated (and not particularly hearty) microbes such as Clostridium acetobutylicum. The problem with this type of microbe is that it is poisoned by the very butanol it produces once the alcohol concentration rises above approximately 2 percent. This processing problem caused by the inherent weakness of generic-grade microbes, plus inexpensive and abundant (at the time) petroleum gave way to the simpler and cheaper distillation-from-petroleum method of refining butanol.

My, how times change. In recent years, with petroleum prices heading steadily upwards, and worldwide supplies getting tighter and tighter, scientists have revisited the fermentation of sugars for the manufacturing of biobutanol. Great strides have been made by researchers in creating “designer microbes” that can tolerate higher concentrations of butanol without being killed off.

The ability to withstand harsh high concentration alcohol environments, plus the superior metabolism of these genetically enhanced bacteria has fortified them with the endurance necessary to degrade the tough cellulosic fibers of biomass feedstocks such as pulpy woods and switchgrass. The door has been kicked open and the reality of cost competitive, if not cheaper, renewable alcohol motor fuel is upon us.


So, all of this fancy chemistry and intense research notwithstanding, biobutanol has many advantages over here-to-fore easier-to-produce ethanol.

  • Biobutanol has a higher energy content than ethanol, so there is a much lower loss of fuel economy. With an energy content of about 105,000 BTUs/gallon (versus ethanol’s approximate 84,000 BTUs/gallon), biobutanol is much closer to the energy content of gasoline (114,000 BTUs/gallon).
  • Biobutanol can be easily blended with conventional gasoline at higher concentrations than ethanol for use in unmodified engines. Experiments have shown that biobutanol can run in an unmodified conventional engine at 100 percent, but to date, no manufacturers will warrant use of blends higher than 15 percent.
  • Because it is less susceptible to separation in the presence of water (than ethanol), it can be distributed via conventional infrastructure (pipelines, blending facilities and storage tanks). There’s no need for a separate distribution network.
  • It is less corrosive than ethanol. Not only is biobutanol a higher-grade more energy dense fuel, but it is also less explosive than ethanol.
  • EPA test results show that biobutanol reduces emissions, namely hydrocarbons, carbon monoxide (CO) and oxides of nitrogen (NOx). Exact values depend upon the engine state of tune.

But that’s not all. Biobutanol as a motor fuel—with its long chain structure and preponderance of hydrogen atoms—could be used as a stepping-stone in bringing hydrogen fuel cell vehicles to the mainstream. One of the biggest challenges facing hydrogen fuel cell vehicle development is the storage of onboard hydrogen for sustainable range and the lack of hydrogen infrastructure for fueling. The high hydrogen content of butanol would make it an ideal fuel for onboard reforming. Instead of burning the butanol, a reformer would extract the hydrogen to power the fuel cell.


It is not common for one fuel type to have so many obvious advantages without at least one glowing disadvantage; however, with biobutanol versus ethanol argument, that doesn’t appear to be the case.

Currently, the only real disadvantage is there are many more ethanol refining facilities than biobutanol refineries. And while ethanol refining facilities far outnumber those for biobutanol, the possibility of retrofitting ethanol plants to biobutanol is feasible. And as refinements continue with genetically modified microorganisms, the feasibility of converting plants becomes greater and greater.

It’s clear that biobutanol is the superior choice over ethanol as a gasoline additive and perhaps eventual gasoline replacement. For the past 30 years or so ethanol has had most of the technological and political support and has seeded the market for renewable alcohol motor fuel. Biobutanol is now poised to pick up the mantle.