One-pot method turns polyethylene into valuable detergent precursor

Though polyethylene (PE) is recyclable, the high-temperature, energy-intensive process yields only low-value products. As a result, industries don’t earn enough money to make recycling PE worth their effort. Now Susannah Scott and coworkers from the University of California, Santa Barbara; the University of Illinois; and Cornell University have developed a catalytic process to upcycle PE into something of higher value: long-chain alkylaromatics (Science 2020, DOI: 10.1126/science.abc5441). Scientists can sulfonate these compounds to make detergents and surfactants. The market for one of the alkylaromatics, linear alkylbenzenes, is about $9 billion per year. To upcycle PE, the researchers seal either high- or low-density PE and an alumina-supported platinum catalyst in a reaction vessel. They then heat the materials to 280 °C for 24 h. The polymer melts and then reacts with the catalyst, releasing H₂. This hydrogenolysizes the PE, and these smaller bits of polymer then aromatize to give the higher-value products in 80% yield. This method “couples a thermodynamically unfavorable reaction, the aromatization, with a thermodynamically favorable reaction, the hydrogenolysis,” Scott says, a key step to getting the temperature below 300 °C.