How to make styrene production greener

Industry analysts estimate that by 2023, chemical makers will produce about 30 million metric tons of styrene—a monomer that’s used to make polystyrene and copolymers. Now, chemical engineers report a way to make styrene that could save energy and significantly reduce CO₂ emissions associated with its production (Nat. Commun. 2021, DOI: 10.1038/s41467-021-21374-2).

The process, developed by North Carolina State University’s Fanxing Li and coworkers, relies on a redox catalyst with a mixed calcium manganese oxide core surrounded by a potassium ferrite shell. In addition to spurring the oxidative dehydrogenation of ethylbenzene to styrene, the material serves a source of oxygen for the reaction, which also produces water. Purging the catalyst with air replenishes its oxygen.

The current industrial route to making styrene from ethylbenzene has a typical single-pass yield of 54%. It requires high temperatures as well as steam, which provides heat and pushes the reaction’s equilibrium toward styrene. The process developed by Li’s team has a 91% yield. And though it does require high temperatures, it doesn’t need any steam, and it generates heat. As a result, the process requires 82% less energy and emits 79% less CO₂ than the industrial route. Li says that while the process—which he has patented—works well in a laboratory, his team still needs to work on scaling it up for large reactors.

“The production of styrene is among the least energy efficient large-scale chemical processes,” says T. Brent Gunnoe, an expert in catalysis at the University of Virginia, in an email. The work from Li’s team, he says, is “an important demonstration of how new approaches to catalyst design can potentially lead to increased energy efficiency.”