We Need Advanced Biofuels: Is Butanol The Best Choice?

by David

More attention is being directed to so-called advanced biofuels lately, as ethanol’s image has become tarnished.

What are the shortcomings that have dimmed ethanol’s luster?  There are quite a few:  First, there are the continuing subsidies. It is interesting to hear the spin from the ethanol producers. On the one hand, they claim that ethanol is the cost-effective biofuel of the future. On the other hand, producers cry foul at any attempt to rein in the subsidies they claim they need to stay in business. Well, are the subsidies really needed or not?

Beyond the economics of production there are other issues. Ethanol has a poor fuel value relative to gasoline, offering only about 60% as much energy per gallon. Ethanol is also inherently incompatible with existing fuel handling infrastructure due its corrosivity and tendency to absorb water from the atmosphere. These two factors alone make ethanol a poor choice as a seamless replacement for gasoline. The fact is, ethanol isn’t.

Finally, there is the blend wall. Various factors limit how much ethanol can be blended with traditional gasoline. Currently, that wall sits at 10%. Even if industry efforts to raise the blend wall to 15% are successful, that limitation still reduces the ability to use ethanol as an interchangeable fuel resource to displace petroleum-derived transportation fuels. To leap over the blend wall higher requires modification of engines, which is why E85 (an 85% ethanol, 15% gasoline blend) is used so little across the country.

What is the answer to this problem? Many industry experts would say it is “advanced biofuels, which is essentially a term operationally defined as a biofuel other than ethanol. What an advanced biofuel really means is a fuel with an energy content approaching that of gasoline that can be interchangeably used in place of gasoline or petroleum-derived diesel. Examples include hydrocarbons such as terpenes (Amyris is a major player working on the production of this type of fuel) and butanol.

Butanol may be the most practical advanced biofuel on the horizon.

What makes butanol such a great biofuel?

Here is the rundown.

1) Butanol has a higher fuel value than ethanol, offering about 85% of the fuel value of gasoline on a gallon-for-gallon basis compared to only about 60% for ethanol. Thus, one gallon of butanol can displace about 1.25 gallons of ethanol. This also means better fuel economy for vehicles running on butanol and butanol blends.

2) Butanol can be blended with gasoline in higher amounts. While ethanol is currently limited to 10% by volume mixed with gasoline, butanol can be blended up to 16% under current US regulations. Higher blends are likely possible without requiring any modifications to engines running on butanol blends. As such, butanol is a much better drop-in fuel and can displace a larger amount of petroleum-derived gasoline or diesel.

3) Butanol can be transported via existing fuel infrastructure and blended directly at existing refineries.

4) Butanol can be produced using the same fermentation plants and same sugar and cellulosic feedstocks as ethanol. It can also be produced from cellulosic feedstocks in the same way that ethanol can.

5) Biobutanol also has a higher theoretical yield from glucose or glucose equivalents compared to an advanced biofuel alternative such as a terpene.

Butamax, a joint venture between DuPont and BP, has announced plans to produce biobutanol by 2012-2013. Butamax does not plan to produce butanol for the world by itself. The company is also planning to offer licenses to other interested producers. Gevo has focused on isobutanol, which has similar properties as a fuel, and has started work in its demonstration plant in St. Joseph, Missouri, with annual output of 1 million gallons announced for later this year unless legal barriers stop them. Other players appear to be further from commercialization, but they all bear watching as advanced biofuels, and butanol in particular, approach the marketplace.

{ 3 comments… read them below or add one }

PatrickG September 1, 2011 at 3:07 pm

What do you think about terpenoid-based biofuels, especially for high-performance needs like rockets and advanced jets?

David September 1, 2011 at 6:05 pm

I think terpenoid-based fuels are excellent products. By manipulating the pathway, terpenes with desired properties–flash point, boiling point, freezing point–can be produced to target different markets. The biggest challenge for these products is cost.

Manisha November 14, 2011 at 6:07 am

How does butanol compare with bio-diesel? Would it be cleaner than bio-diesel in use right now?

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