Researchers at the National Renewable Energy Laboratory (NREL) have found an oxygenate molecule produced from biomass, known as 4-butoxyheptane, which has the potential to be blended with diesel fuel and reduce emissions.
Conventional petroleum-derived diesel fuel is comprised of hydrocarbons. NREL says use of molecules containing oxygen, however, can significantly reduce the intrinsic sooting of fuel upon burning. According to Derek Vardon, a senior research engineer at NREL who worked on the project, biomass is composed of 30% oxygen. If that oxygen can be kept and incorporated into a fuel, more can be gotten from the biomass to improve performance of diesel fuel.
Finding the right molecule
The NREL researchers started by deriving molecules from corn stover. Doing so not only provides several possible options but also uses readily available material from which to derive the molecules. This helps to lower costs of producing it and leads to a circular economy of producing fuel sources.
Predictive models were utilized to determine which molecules would best blend with diesel fuel and help improve its performance. Reserachers prescreened the molecules based on attributes including health, safety and performance.
Vardon says the goal is to develop drop-in biofuels which work with existing infrastructure. Doing so, however, requires the fuel to meet a variety of rules and regulations which eliminates several promising molecules. This is because some molecules may exhibit good qualities in certain required properties but fail in others.
Those molecules which best met the necessary criteria for drop-in fuels quickly became clear to the NREL researchers, of which the 4-butoxyheptane molecule was the most promising.
NREL says the intention is to blend the 4-butoxyheptane molecule into diesel fuel at a mixture of 20-30%. Initial testing has shown this blend level can improve fuel economy and ignition quality, as well as reduce sooting.
However, further research is still necessary. This includes testing the bioblendstock in an actual engine and producing the fuel directly from biomass.
Researchers also conducted an economic and life-cycle analysis which found the oxygenate fuel can be cost-competitive with petroleum diesel. NREL says It can also significantly reduce greenhouse gas (GHG) emissions if the process also yields a high-value co-product such as adipic acid, which is used to manufacture nylon.
NREL worked with Yale University, Argonne National Laboratory and Oak Ridge National Laboratory on the project as part of the Department of Energy's Co-Optimization of Fuels & Engines (Co-Optima) initiative. Research conducted under the Co-Optima initiative aims to find ways of improving fuel economy and vehicle performance, as well as reducing emissions.