Researchers at the University of Minnesota are developing a process to remove pollutants from plastic production with selective combustion, according to a press release from the University’s College of Science and Engineering.
The process involves engineering certain materials to only react to one molecule found in a mixture of hydrogen and carbon atoms, called hydrocarbons, and effectively removing toxic pollutants found in different plastics.
Aditya Bhan, a CSE professor, said that when producing plastics, the materials can end up with small impurities that can be harmful to humans and the environment.
The team developed catalysts, a substance that initiates an explosion, that only react to acetylene, a highly flammable, colorless gas found in plastics, leaving the rest of the material untouched, said Matt Jacob, a graduate student working on the project.
“You don’t think of combustion as a selective process. You burn a mixture and everything burns,” Jacob said. “But this is a case where we can take a mixture and only burn one of the molecules.”
When developing polyethylene, a polymer used to make moldable types of plastic used in day-to-day objects like water bottles, shopping bags and containers, scientists start with a single molecule called ethylene, the building block of most plastics, Bhan said.
Scientists then take the single ethylene molecule and combine it with other ethylene molecules. The process involves stitching the molecules together to create long chains of polymers with a catalyst.
If acetylene is not removed, a polymer cannot be stitched together because it is such a highly flammable material, Bhan said.
There is already a process to remove toxins from polymers, called depolymerization, Bhan said, but the process is very expensive and uses a lot of energy.
Jacob said roughly one million metric tons of plastic polymers are made per year, so a new process to remove toxins would make a big impact.
“Maybe it’s only 1% more economically viable, but if you make a 1% impact, it’s going to have a pretty big impact on the energy that you need to use to actually make those molecules or those plastics,” Jacob said.
Bhan said it is necessary to clean up about 20 kilograms of ethylene per person on Earth, since it is an air pollutant and a carcinogen.
The process Bhan and his team are working on could reduce the intensity of the removal process and lessen the carbon footprint of toxin removal.
Jacob said the work they are doing could also streamline the process, especially as they further determine what molecules respond well to the catalyst.
“Say you have a waste stream in that chemical plant that has a composition with one of those trace contaminants that your catalyst has reacted to, then you can target that waste and clean it up,” Jacob said. “We’re trying to generalize it more, but that’s definitely a work in progress.”
The team has worked specifically on removing toxins from plastics, but they are expanding the research to other materials such as medications and fuels, Bhan said.