US team develops reactor to produce propylene from natural gas

Ann Arbor, Michigan – Researchers at the University of Michigan have developed a new catalyst reactor that can produce propylene from natural gas, as an alternative to crude oil.

The reactor resembles a nested pair of tubes, wherein propane (C3H8) from shale gas flows through the innermost tube, explained the university in a 21 March report.

The reactor splits propane into propylene (C3H6) and hydrogen gas (H2), providing a ‘cleaner’ alternative with reduced manufacturing costs, compared to propylene derived from oil.

According to the University of Michigan, current processes available to source propylene from natural gas are “still too inefficient to bridge the gap in supply and demand”.

“It’s very hard to economically convert propane into propylene,” said Suljo Linic, the Martin Lewis Perl Collegiate professor of chemical engineering.

“You need to heat that reaction to drive it, and standard methods require very high temperatures to produce enough propylene,” added Linic, corresponding author of the study published in Science.

At such high temperatures, he explained, solid carbon deposits and other undesirable products that impair the catalyst are produced in addition to propylene.

And to regenerate the reactor, he added, we need to burn off the solid carbon deposits often, which makes the process inefficient.

According to the University of Michigan, the new reactor system efficiently makes propylene from shale gas by separating propane into propylene and hydrogen gas.

It also gives hydrogen “a way out”, changing the balance between the concentration of propane and reaction products in a way that allows more propylene to be made.

Once separated, the hydrogen can also be safely burned away from the propane, heating the reactor enough to speed up the reactions without making any undesirable compounds.

This separation is achieved through the reactor’s nested, hollow-fibre membrane tubing, according to the report.

The innermost tube is made up of materials that splits the propane into propylene and hydrogen gas.

While the tubing keeps most of the propylene inside the innermost chamber, the hydrogen gas can escape into an outer chamber through pores in a membrane layer of the material.

Inside that chamber, the hydrogen gas is controllably burned by mixing in precise amounts of oxygen.

Because the hydrogen can be burned inside the reactor and can operate under higher propane pressures, the technology could allow plants to produce propylene from natural gas without installing extra heaters.

According to the researchers’ estimate, a plant that produces 500 kilotonnes per annum of propylene could save as much as $23.5 million (€22 million) over other methods starting with shale gas.

The savings are in addition to the operational savings from burning hydrogen produced in reaction, rather than other fuels.

The research was funded by the US department of energy’s office of basic energy sciences, the RAPID manufacturing institute and the National Science Foundation.

The team is pursuing patent protection with the assistance of U-M Innovation Partnerships and is seeking partners to bring the technology to market.