M. Clayton Wheeler
Current Research Interests
- Biofuels and Catalysis
- Thermal conversion technologies for converting lignocellulosics to hydrocarbon fuels and chemicals
- Thermal deoxygenation of biomass-derived organic acids
- Hydrodeoxygenation of pyrolysis oils
- Hydrogenation of mixed ketones to mixed alcohols
- Esterification of mixed organic acids
- Hydrogenolysis of mixed esters
- Hydrotreating and fractionation for transportation fuels blend-stocks
- Process simulation and techno-economics
- Catalytic chemical Sensors
- Selective sensor materials and sensing algorithms
- Integrating sensor platforms into microchemical systems using micromachining techniques
- Characterization of sensing mechanisms for selectivity enhancement
Biofuels and Catalysis
There is a pressing need for the development of renewable fuels and energy derived from biomass, wind, geothermal heat and solar radiation in order to meet future economic and environmental requirements. Among these renewable resources, biomass is considered to be the only sustainable and carbon-neutral source for the production of liquid fuels. The US has the potential to sustainably produce biomass which can replace more than one-third of U.S. petroleum consumption. As an alternative feedstock for oil, biomass is also inexpensive at $12 to $24 per barrel of oil equivalent. Compared to agricultural biomass, forest lignocellulosic biomass has particular advantages because it does not need fertile soil, has a 3-4 times higher bulk density, and one order of magnitude lower ash content.
Some strategies which are being pursued to produce liquid fuels from lignocellulosic biomass include
- Hydrolysis of cellulose and xylose to monomeric sugars followed by
- Thermal catalysis to convert sugars to hydrocarbons
- Fermentation of sugars to produce alcohols
- Mixed Culture Robust (MCR) fermentation of sugars to produce organic acids
- Pyrolysis of wood, or its components such as lignin
- Conversion of cellulose to levulinic acid and thermal deoxygenation of the acid to produce Levulene, a hydrocarbon fuel mixture
- Hydrotreating of bio-oils to produce blendstocks for conventional gasoline, diesel, jet fuel and marine fuels.
One focus of my group has been upgrading of organic acids that have been produced by MCR fermentation of pulp mill extracts and algae processing residues. During fermentation, buffers such as calcium carbonate are used to maintain appropriate pH. After drying, the resulting organic acid salts, e.g. calcium acetate and calcium butyrate can be converted to ketones by thermal deoxygenation. We then hydrogenate the mixed ketones to alcohols which can be dehydrated and oligomerized to hydrocarbon fuels. The reaction kinetics are studied using both batch and trickle bed reactor systems.
The major challenge in making hydrocarbon fuels from lignocellulosic biomass is removing the oxygen. If wood is heated to 500°C for a few seconds, it will pyrolyze and form an oil which has large quantities of alcohol, carboxylic acid, and methoxyl functionalities. These oxygenated compounds contribute to high acidity and make the oils unstable. They also significantly reduce the energy density of the oil. We are developing and testing new classes of catalysts for selectively reducing the oxygenated species.
My group has also been working on a new process for converting cellulose-derived levulinic acid to diesel, gasoline and jet fuels. Our process uses no catalysts and no hydrogen to thermally deoxygenate the levulinic acid and produce a crude oil. The product is a mixture of aliphatic and aromatic hydrocarbons which phase separate from water and have neutral pH. Major efforts in this area include understanding the mechanisms and kinetics of the reactions, developing continuous processes based on the bench-scale batch experiment results, and optimizing the integration with the levulinic acid production process. This process is very promising because it is particularly tolerant of impurities in the feed and can use many different feedstocks such as municipal solid wastes, recycled paper, forest residues, and pulp mill wastes.