Selective combustion provides energy-efficient alternative to remove pollutants from industrial processes

This new method could help in the removal of pollutants and improve efficiency for industrial processes ranging from the production of fuels and medications to fertilizers and plastics

The research is published in Science.

By using a bismuth oxide catalyst -- a substance that speeds up a chemical reaction -- the researchers can selectively burn one molecule in a mixture of combustibles. The researchers showed that you can effectively combust even small amounts of acetylene in mixtures with ethylene. Removing acetylene is a crucial process to prevent poisoning of polymerization catalysts, which is vital for the production of polyethylene plastics, a market that exceeds 120 million metric tons annually.

"No one else has shown that you could combust one hydrocarbon present in low concentrations, in mixtures with others," said Aditya Bhan, a Distinguished McKnight University Professor in the Department of Chemical Engineering and Materials Science and lead investigator on the paper.

Conventionally, combustion processes are used to burn all hydrocarbon fuel mixtures at high temperatures to produce heat. The use of a catalyst allowed the researchers to tackle the challenge of burning one molecule but not the others. The bismuth oxide catalyst is unique as it provides its own oxygen during combustion, rather than using oxygen from an outside source, in a process called chemical looping.

"We were able to take oxygen out of the catalyst and put it back in multiple times, where the catalyst changes slightly, but its reactivity is not impacted. Operating in this chemical looping mode avoids flammability concerns," said Matthew Jacob, a University of Minnesota chemical engineering Ph.D. candidate and first author on the paper.

Traditionally, eliminating small concentrations of contaminants is very challenging and energy-intensive, but this new method could provide a more energy-efficient alternative.

"You want to do this process selectively. Removing acetylene and other trace hydrocarbon contaminants in this manner could be more energy efficient," said Matthew Neurock, a professor in Department of Chemical Engineering and Materials Science and senior co-author on the paper. "You just want to be able to go into a gas mixture to remove some molecules without touching the rest of the molecules."

The researchers said the long-term impact could be high because catalysts are used in just about anything we touch in modern society -- from production of fuels and medications to fertilizers and plastics. Understanding how molecules combust -- and don't combust -- on catalyst surfaces is valuable for making fuels and plastics production more efficient.

"If we can understand how a catalyst works, at a molecular atomic level, we can adapt it to any particular reaction," said Simon Bare, a Distinguished Scientist at the SLAC National Accelerator Laboratory at Stanford University, and co-author of the study. "This can help us understand how catalysts, that produce fuels and chemicals needed in modern living, react to their environment."

In addition to Bhan, Jacob, Neurock, and Bare, the University of Minnesota Department of Chemical Engineering and Materials Science team included graduate students Rishi Raj and Huy Nguyen and Professor Andre Mkhoyan, along with Javier Garcia-Barriocanal from the University of Minnesota Characterization Facility. Additional team members included Jiyun Hong, Jorge E. Perez-Aguilar, and Adam S. Hoffman from the SLAC National Accelerator Laboratory at Stanford University.

This work was funded by the U.S. Department of Energy, Office of Basic Energy Sciences. The work was completed in collaboration with the University of Minnesota Characterization Facility and the Minnesota Supercomputing Institute.

Read the entire research paper titled, "Selective chemical looping combustion of acetylene in ethylene-rich streams," visit theScience website.