UMaine researchers develop new thermal deoxygenation process to convert biomass to hydrocarbon fuels; no catalysts or hydrogen required
A University of Maine chemical engineer and his research team have developed a new process—thermal deoxygenation (TDO)—to transform biomass, including forest residues, municipal solid waste, grasses, and construction wastes, into a hydrocarbon fuel oil. The process requires no catalysts or hydrogen, and is “a spin on chemistry used to make acetone back in the 1800s”, said M. Clayton Wheeler, a UMaine associate professor of chemical and biological engineering.
Based on a mixed-carboxylate platform, the new fuel developed by Wheeler and undergraduate students in his lab has boiling points that encompass those of jet fuel, diesel, and gasoline. Further refining to meet emissions standards would be needed in order to use the UMaine oil in vehicles that drive on public ways, but Wheeler believes the oil can be refined as simply as any other current oil at a standard refinery.
The TDO process starts with the conversion of cellulose to organic acids. The acids are then combined with calcium hydroxide to form a calcium salt. That salt is heated to 450 °C (842 °F) in a reactor, which constantly stirs the salt. This produces a reaction resulting in a dark amber-colored oil.
The reaction removes nearly all of the oxygen from the oil as both carbon dioxide and water, and without the need for any outside source of hydrogen to remove the oxygen. Therefore, most of the energy in the original cellulose source is contained in the new oil.
Biomass has a lot of oxygen in it. All of that oxygen is dead weight and doesn’t provide any energy when you go to use that as a fuel. If you’re going to make a hydrocarbon fuel, one of the things you have to do is remove oxygen from biomass. You can do it by using hydrogen, which is expensive and also decreases the energy efficiency of your process. So if there’s a way to remove the oxygen from the biomass chemically, then you’ve densified it significantly. Our oil has less than 1 percent oxygenates. No one else has done anything like this.—Clay Wheeler
The TDO process does not require an uncontaminated cellulose source; researchers in Wheeler’s lab at UMaine recently used unpurified, mixed carboxylates which were produced from grocery store waste such as banana peels, cardboard boxes and shelving to successfully make a batch of the fuel.
T. J. Schwartz, A. R. P. van Heiningen and M. C. Wheeler (2010) Energy Densification of Levulinic Acid by Thermal Deoxygenation, Green Chemistry 12, 1353–1356 DOI: 10.1039/C005067A