Advanced Biofuels, a Transformative Industry
At the recent U.S. DOE-sponsored Biomass Conference 2012: Confronting Challenges, Creating Opportunities, much of the focus was on liquid fuels from biomass. Several presenters, including U.S. Secretary of Energy Steven Chu, mentioned butanol as a highly-regarded advanced biofuel.
As part of the ongoing research at the Energy & Environmental Research Center, we have been developing a catalytic pathway to convert ethanol or mixtures of methanol and ethanol to higher alcohols, including butanol, through Guerbet condensation reactions. Simply stated, cellulosic biomass such as wood chips can be converted into a mixture of gases in a gasifier, and the resulting syngas can be passed over a catalyst and converted to alcohols like ethanol. The goal of EERC’s research is to alleviate one of the major challenges and costs involved with cellulosic ethanol production, which is the coproduction of undesired quantities of methanol with the ethanol product. Current biorefinery processing technology and associated commercial catalysts render the production of unwanted concentrations of methanol unavoidable. Methanol production is undesirable, as it is not an ideal gasoline additive because of its water affinity, corrosive nature, volatility-raising impact when blended with gasoline, and low volumetric energy content versus gasoline. Two potential solutions to the methanol problem are to limit its production, and/or separate it from ethanol. Both of these potential solutions present economic challenges.
Rather than fight methanol production during the syngas conversion process, the EERC is developing technology to capitalize on it. Utilizing an easily-produced, mixed-alcohol product from a biomass-derived syngas—about 60 percent methanol, 30 percent ethanol, 10 percent higher alcohols—as feedstock to a condensation reaction yields a mixture of branched alcohols, or isoalcohols, comprising at least 65 percent isobutanol and significant quantities of higher isoalcohols including isohexanols and isooctanols.
According to the Argonne National Laboratory, use of cellulosic ethanol to displace gasoline reduces greenhouse gases (GHGs) by 85 percent. By extension, the use of cellulosic isobutanol and higher isoalcohols to replace gasoline should reduce GHGs by a similar amount. Because isobutanol offers gasoline compatibility advantages versus ethanol, gasoline–isobutanol blends may be transportable via pipeline, which would further reduce GHG emissions.
The EERC technology will maximize the yield of mixed alcohols and subsequent isobutanol from biomass while also generating replacements for high-value, normal alcohol- and isoalcohol-based chemical intermediates and solvents currently derived from fossil fuels.
The flexibility to produce fuel and higher-value normal alcohol and/or isoalcohol chemical intermediates represents a commercial advantage that should serve as an offset to the financial risk of building a cellulosic fuel plant. Propanol, butanol, isobutanol and isohexanol have broad markets, carry a higher price, and are renewable in derivation, making them eligible for various credits and incentives worldwide. Of course there is the added branding of lower-carbon-footprint fuel and chemicals that can displace appreciable volumes of their petroleum-derived counterparts.
Additionally, this technology could take ethanol produced in current grain-based plants and react it with higher alcohols, commanding a greater return when compared to fuel-grade ethanol, enhancing profitability at these plants.
David Danielson, U.S. DOE assistant secretary for energy efficiency and renewable energy, believes that building a substantial and clean renewable energy industry in the U.S. will be transformative, and once again prove that the country is capable of anything. The EERC plans to be part of that transformative industry.
Author: Bruce C. Folkedahl
Senior Research Manager