As the ethanol industry evolves, more plants are seeking ways to increase their product slate and margin. One option is manufacture of isobutanol and its derivatives including octane, jet fuel blendstock and other drop-in hydrocarbons. Commercial production of bio-based isobutanol, alongside ethanol, has taken place since 2014 at Gevo’s Luverne, Minn., facility (Figure 1). The side-by-side operation there shares various streams between the two production trains to minimize capital and operating cost. The facility currently is being upgraded to enable production of 1.5 million gal/y of isobutanol and 15 million gal/y of ethanol. We have restarted isobutanol production with an expected output of 750,000 to 1 million gallons of isobutanol in 2016. Once the process is fully optimized at this scale, isobutanol should yield EBITDA profit margins of approximately $0.50 to $1.00 per gallon, providing a compelling return on capital to the producer.
Isobutanol is a colorless sweet-smelling liquid found naturally in fruits as well as in commercial ethanol fermentations and distilled spirits like whiskey. In contrast to ethanol, isobutanol has low water solubility and properties more like a hydrocarbon due to its chemical structure.
Isobutanol is commercially attractive both in traditional markets, such as solvents, coatings and chemical intermediates, and emerging ones such as fuel blends. Bio-based isobutanol has unique fuel properties and qualifies under the U.S. Renewable Fuel Standard for a Renewable Identification Number (RIN) — and thus should enjoy burgeoning demand in the fuels market. For example, due to isobutanol’s low water solubility, high octane and low vapor pressure, the marine market has strongly embraced isobutanol/gasoline blends. Indeed, the National Marine Manufacturers Association officially has endorsed Gevo’s bio-based isobutanol as a drop-in fuel for marine and recreational boat engines.
Isobutanol also can be chemically converted, using conventional unit operations, into isobutylene, which is a building block for isooctane, jet fuel, plastics, rubber, lubricants and other hydrocarbons. Switching to such products made from renewable raw materials is becoming increasingly important to companies looking to reduce their dependence on petroleum and improve the sustainability of the chemical business system. Moreover, as true drop-in replacements, the materials avoid the need for changes in assets and business models to adapt to a new molecule.
At South Hampton Resources, a company with a site in Silsbee, Texas, Gevo converts isobutanol to isobutylene, which then is used to make isooctane, isooctene and jet fuel (isoparaffinic kerosene) at the plant (Figure 2). Gevo has been producing and selling alcohol-to-jet fuel (ATJ) derived from isobutanol since 2011 when the fuel was used in certification trials, including test flights with the U.S. Air Force, Army and Navy. Gevo is working toward commercializing this ATJ production process. Isooctane made at this site has been sold into specialty fuels applications, including supplying Total with isooctane used in its Formula One racing fuels.
Gevo’s process for making isobutanol from renewable feedstocks (Figure 3) relies on two proprietary developments: the yeast that produces isobutanol and a product recovery technology that continuously removes the isobutanol as it’s formed. Our yeast, which has been in development and optimization for over five years using the latest biotechnology tools, achieves commercially attractive yields and rates. Moreover, it is safe for use in animal feed, which is a key byproduct and source of revenue.