Isobutanol: A New Product from Revamped Ethanol Plants

by Jess Hewitt and KSL (Lee Enterprises Consulting/Biofuels Digest) ... Now, there is also competition for production between renewable fuels. Ethanol plants can produce fuel ethanol but they can also be retrofitted or become the host facility to produce butanol. Butanol differs from ethanol in composition, physical characteristics and economics. We present the case for renewable butanol production.

Made from petrochemicals, Isobutanol has a variety of uses as a solvent and chemical building block. In the past few years more technologies have been used to create Isobutanol from renewable resources. Financially, creating Isobutanol from renewable feedstocks yields a product that cannot compete with the existing Isobutanol production techniques. Therefore the production of renewable Isobutanol has been severely limited to small-scale production.

However, sometimes a renewable product can prove to be an extremely effective fuel^[i]. In the United States, Renewable Isobutanol qualifies as an Advanced Biofuel and has an approved pathway for production from many feedstocks. The Environmental Protection Agency (EPA) rewards Isobutanol with renewable energy credits through its Renewable Energy Standard. In fact, the EPA assigns renewable credits (RINS^[ii]) on the basis of energy content, and Isobutanol has higher energy content (1.3 RINS per gallon) than ethanol (1.0 RINS per gallon).

Of course, Isobutanol production comes at a cost. The cost offset of RINS has not been above 35% of Isobutanol’s intrinsic value. Even with the RIN value considered, the product is still more than twice the price of ethanol, on average^[iii]. Consequently, Isobutanol has not generally been used as a substitute for ethanol in most applications. However, recently gasoline makers have begun to use Isobutanol to serve a growing market for alternatives to fuels containing ethanol. But do the positives outweigh the negatives?

To summarize, Isobutanol costs more than ethanol (negative) but has more power and can be used in less costly gasoline (positive). Unfortunately, the positives do not yet outweigh the negatives, so an Isobutanol-blended gasoline cannot be cost competitive with ethanol-blended gasoline. This is why almost all refiners dropped consideration of an Isobutanol-blended gasoline.

One oil company took an alternative view. Gulf Racing Fuels is responsible for the off-road fuels of Gulf Oil. They specialize in boutique fuels to meet the needs for high performance and specialty engines. Most importantly, Gulf does not use ethanol. Gulf knew that there was an entire class of consumers who only wanted an ethanol-free fuel. They also knew this market segment had very high price elasticity. Stated more simply, they would pay more for an ethanol-free fuel.

The big question is: will there be enough volume of renewable Isobutanol? The answer is no. In the short term, oil companies will source additional Isobutanol from petrochemical manufacturers. In the long term, there will be a significant need for more renewable Isobutanol production. Where will the new supplies of Isobutanol be made? To get to that answer we need to know how renewable Isobutanol can be made.

Starting from petroleum sources, butanol is typically produced either by the Oxo-process utilizing propylene with hydrogen and carbon monoxide (usually in the form of synthesis gas) [(i) and (ii)] over an expensive rhodium catalyst, or the Aldol-process starting from acetaldehyde.

The second, green-pathway is the ABE-fermentation process (Acetone, Butanol, Ethanol) that was pioneered by Chaim Weizmann during World War I. During 1950s the ABE fermentation process was not competitive with natural petroleum sources and hence ignored in the US and European industry. However, some production processes continued in China, Russia and South Africa until the early 1980s. This has changed dramatically in recent years. For example, China has lead efforts to re-commercialize the ABE fermentation process. With investments over $200 million towards installing 0.21 million tons per annum of solvent capacity with plans to expand it to 1 million tons per annum.

A number of biotechnology ventures with proprietary approaches to microbial strain selection and engineering, feedstock handling, bioreactor management, and product separation have emerged as a new generation of butanol producers since early 2000. Depending on the niche one may produce either n/iso butanol. Most of these operational plants operate in a semi-continuous mode to minimize downtime, and the lag phase wherein one fermentation cycle can take almost 21 days. In addition, the plants are located either immediately next to the ethanol plants or retrofitted to reduce utility and operating costs.

Co-located operations tend to share effluent treatment facilities based on anaerobic digestion (AD). Biogas, produced from the AD process, can be used to generate power and heat.

With an improved strain tolerance for higher butanol concentrations and an increase in volumetric productivity by about 50%, the production costs for bio-butanol would be similar to the production costs for petroleum derived butanol.