A new chemical catalyst developed at the University of Michigan in Ann Arbor could enable the production of more of the feedstock for the world’s second-most widely used plastic — propylene.
Feedstock propylene is used to make 8 million tons of plastic each year, and it’s in short supply, endangering supply lines for food packaging, automotive components, clothing, medical and lab equipment, and countless other items that rely on plastics.
The new catalyst, which can make propylene from natural gas, is at least 10 times more efficient than current commercial catalysts. And it lasts 10 times longer before needing regeneration. It is made of platinum and tin nanoparticles that are supported by a framework of silica.
“Industry has shifted over the years from petroleum feedstocks to shale gas,” says Suljo Linic, professor of chemical engineering at U-M and senior author of a paper published in Science. “So there has been a push to find a way to efficiently produce propylene from propane, a component of shale gas. This catalyst achieves that objective.”
Propylene has traditionally been produced at oil refineries in massive steam crackers that break down petroleum feedstock into lighter hydrocarbon molecules. But cracking shale gas to produce propylene has been inefficient.
The new catalyst can efficiently produce propylene — a molecule with three carbon atoms and six hydrogens — from propane, which has two additional hydrogens. It uses a process called non-oxidative dehydrogenation. One of the reasons current catalysts are inefficient is that they require adding hydrogen to the process. This approach does not.
The key innovation of the new catalyst is how it uses silica as a support structure for the platinum and tin nanoparticles, rather than the alumina that’s used in current catalysts. Alumina reacts with tin, causing it to separate from the platinum and break the catalyst down. Because the new catalyst holds off this reaction, it has a longer life.
“Silica as support for platinum-tin nanoparticles has been tried before, but conventional synthesis techniques weren’t precise enough to enable close interaction between platinum and tin,” says Ali Hussain Motagamwala, U-M postdoctoral research fellow and first author on the paper.
“We overcame this by first synthesizing a platinum-tin complex with excellent interaction. We then supported this complex onto silica to produce a very well-defined catalyst that is active, selective and stable during nonoxidative propane dehydrogenation.”
A key to commercialization will be finding a way to regenerate the catalyst after it becomes fouled by carbon. Even though current catalysts are short-lived, Linic says, the chemical industry has developed an intricate system that can regenerate the fouled catalyst quickly and efficiently. A similar system will need to be developed for the new catalyst.
While the catalyst is still in the research stage, it holds the possibility of bolstering the world’s propylene supplies, which have been depleted by skyrocketing global demand, COVID-driven production issues, and a series of hurricane-related shutdowns at Gulf Coast oil refineries that produce the chemical.