Last month’s column discussed replacing petroleum-based military fuels with nonpetroleum alternatives. Options included coal and gas-to-liquid technologies.
At least one U.S. Department of Defense entity, the Defense Advanced Research Projects Agency, is pursuing another angle—renewable JP-8 from biomass in the form of 1) triacylglyceride, the primary component of vegetable oils, animal fats and algae oils or 2) lignocellulose, the primary component of wood, grass and other nonfood fibrous materials. Because triacylglyceride chemistry is reasonably similar to petroleum chemistry, processing triacylglycerides to JP-8 can utilize, with some tailoring, many of the same technologies developed for refining petroleum. Because lignocellulose chemistry is significantly different from petroleum chemistry, converting lignocellulose to JP-8 will likely require significant technology development rather than simple tailoring of existing refinery processes.
Unlike traditional biodiesel processing in which the oxygen content of triacylglyceride feedstock is carried through production and incorporated into the finished methyl or ethyl ester fuel, triacylglyceride conversion to JP-8 requires oxygen removal to yield a hydrocarbon-only fuel with the same mass-based energy content of petroleum JP-8. While the major technical challenges of producing JP-8 from triacylglyceride have been overcome, a major question remains: where can we get enough triacylglyceride to replace 5 billion gallons of oil? If you are aware of the food-versus-fuel debate, you know it is a debate that fuel advocates probably cannot win. To address these concerns, DARPA recently initiated a program to develop new triacylglyceride sources, an important one of which is algae.
Key advantages of algae versus traditional crop oil triacylglyceride sources are 1) algae are theoretically capable of producing up to 1,000 times more triacylglyceride per acre than the highest-yielding crop sources, 2) algae do not require premium agricultural land for cultivation, 3) many triacylglyceride-producing algae do not require freshwater but thrive on salty, briny water, much of which is located under deserts, and 4) most people do not eat algae.
A future algae-to-fuel industry could work like the following. First, algae cultivation centers could be set up in sunny deserts with access to large underground briny water supplies.
Coal-fired power plants would be equipped to capture carbon dioxide, and a carbon dioxide pipeline network would be built. Then, carbon dioxide could be captured at power plants and piped to algae cultivation centers, where algae could be grown with the combination of carbon dioxide, briny water and sunlight. The algae could then be harvested, converted to jet (and diesel) fuel and piped into the fuel market.
Of the biomass-to-fuel concepts currently being developed, few, if any, appear to offer greater potential for more petroleum replacement than an algae pathway. Strong leadership and high oil prices will help make that happen.
Ted Aulich is a senior research manager at the EERC in Grand Forks, N.D. He can be reached at firstname.lastname@example.org or (701) 777-2982.