Researchers across the world are looking into various sources of sustainable feedstock for energy and chemicals production with the hope that these cleaner sources will dramatically reduce our need for petroleum-based feedstock and lower our carbon footprint in the future. One such renewable energy source is biomass derived from naturally-occurring raw materials such as wood and agricultural waste, which can be converted to biofuels and biochemicals.
An intermediate product in the conversion of biomass to biofuels or chemicals is bio-oil. Bio-oil is created by rapidly heating biomass to high temperatures in a process called fast pyrolysis. Just as with raw petroleum, the bio-oil obtained from fast pyrolysis must then be refined further in order to make “green” chemicals or fuel that can be used to power cars, for instance.
But there’s one big hurdle for bio-oil to overcome before it can become a realistic replacement for petroleum: its high oxygen content. Bio-oil is notoriously difficult to work with as a result of its high oxygen levels, which lower its energy content and make the oil extremely viscous, acidic and unstable. In order for bio-oil to be refined into a more stable form of fuel – such as the fuel you put into your car – researchers need to develop safe and efficient methods of removing oxygen from bio-oil.
That’s where Lars Grabow, assistant professor of chemical and biomolecular engineering at the UH Cullen College of Engineering, steps in. Funded by a five-year, $750,000 Early Career Award from the U.S. Department of Energy (DOE), Grabow is currently investigating the use of catalysts – substances which speed up chemical reactions – to effectively remove oxygen from bio-oils in a process called hydrodeoxygenation.
Hydrodeoxygenation of bio-oil involves the use of pressurized hydrogen to remove oxygen in the form of water. Grabow noted that the process of hydrodeoxygenation is very similar to the well-established catalytic process of hydrodesulfurization, which is used by petroleum refineries across the world to remove sulfur from natural gas and other refined petroleum products.
“What we propose is to look at both the chemistries of hydrodesulfurization and hydrodeoxygenization and find similarities at the atomic scale so we hopefully can translate existing knowledge from the hydrodesulfurization field and apply it to hydrodeoxygenation,” explained Grabow. “This will speed up the discovery of catalysts for hydrodeoxygenation and enable widespread use of biomass as feedstock for fuel or chemicals.”
By relating these two processes and translating lessons learned from hydrodesulfurization so they can be applied to hydrodeoxygenation, Grabow hopes they might bypass “a lot of time consuming trial and error testing” and effectively speed up the discovery process for the right catalytic converters for hydrodeoxygenation.
The DOE has a strong interest in advancing this biomass conversion technology, setting the goal that biofuels should be replacing about 30 percent of all fossil-derived fuels by 2025, with biochemicals replacing about 25 percent of all petroleum-derived chemicals by 2025.
Grabow’s chunk of this research project focuses on using computational methods to simulate reactions that take place during the upgrade of bio-oil so his research team can make predictions on which materials might be good catalysts for this type of reaction. Using the computing capabilities available at the University of Houston and at national supercomputing centers, Grabow and his team are analyzing the key properties of known catalysts and identifying novel catalysts through large-scale computational screening studies. This way, time isn’t wasted on synthesizing different materials in order to test them as catalysts – Grabow and his group simply run the computer simulations of the model catalysts, calculate their properties and estimate how useful they will be in the hydrodeoxygenation process. If the computer simulations reveal a certain material to be a bad catalyst, then no time was wasted on synthesizing and testing this material in a lab.
Once Grabow’s team identifies potential catalysts for converting bio-oil to biofuel through these computer simulations, they will then pass the information along to their external collaborators for further testing. Grabow’s collaborators on this project are Steven Crossley, assistant professor of chemical, biological and materials engineering at the University of Oklahoma, and Yuriy Román, assistant professor of chemical engineering at MIT.
In addition to discovering the best catalyst for hydrodeoxygenation, Grabow said there are smaller goals in this research project which would also be quite important successes for his team. For starters, he said, identifying and understanding what kinds of properties make a catalyst good for use in hydrodeoxygenation would be a big step forward.