Boron catalyst turns propane into propene

RESEARCHERS at the University of Wisconsin-Madison have discovered that a boron nitride-based catalyst can convert propane into propene with high selectivity.

Propene, a feedstock for polypropylene, a hugely abundant plastic, is conventionally produced by the steam cracking of naphtha. However refineries are increasingly switching to cheap and abundant shale gas, which produces much more ethene when cracked, so supplies of propene are falling. As a result, the chemical industry is seeking ways to produce more propene. The team at UW-Madison, led by chemical engineering professor Ive Hermans, say that their low-temperature catalyst to make propene has the “potential to be a game-changing technology.”

The catalyst is made from hexagonal boron nitride and boron nitride nanotubes, and catalyses the oxidative dehydrogenation of propane (ODHP). Previously, no catalyst was selective enough for propene, as it is more thermodynamically favourable for over-oxidation to CO₂, and research efforts were switching to non-oxidative dehydration, but Hermans and the team say ODHP could use up to 45% less energy.

“Boron nitride catalysts are nontoxic, they don’t contain precious metals, and they reduce the temperature of the reaction, resulting in energy savings,” said UW–Madison graduate student Joseph Grant.

The team tested the boron nitride catalysts in a quartz tube reactor at 490?C with a gas stream comprising 40% propane, 20% oxygen and 40% inert nitrogen. Around 14% of the propane is converted with 79% selectivity for propene. Instead of producing CO₂ as the main byproduct, the boron nitride catalyst produces ethene, which is in itself a useful olefin. Hermans says that non-oxidative dehydration requires much higher temperatures, of 600–750?C and around 90% propane in the feed gas. While 14% conversion might not sound very high, Hermans explains that many industrial processes are run at low conversion rates to minimise undesired burning.

“The oxidation of cyclohexane to cyclohexanol/cyclohexanone runs at 5% conversion with ~80 % selectivity. Now what makes this boron nitride catalyst so exciting is that it seems to kinetically favour propene (whereas thermodynamically, CO₂ is favoured),” he tells The Chemical Engineer.

Another advantage of the boron nitride catalysts is that they do not need the regeneration step required in other propane dehydrogenation reactions.

Hermans said that as the approach is less resource-intensive, it could be favoured by the chemical industry, although fully scaling-up the process could still be some years away.

Science DOI: 10/bvd9