A new process for making a key ingredient in plastics, adhesives, carpet fibers, household cleaners and more from natural gas could cut manufacturing costs in a post-oil economy by millions of dollars – thanks to a new chemical reactor developed by University of Michigan engineers was developed.
The reactor produces propylene, a working chemical that is also used to make a long list of industrial chemicals, including components of nitrile rubber, used in car hoses and gaskets and in blue protective gloves. Most propylene used today comes from oil refineries, which produce it as a byproduct of refining crude oil into gasoline.
As oil and gasoline fall out of fashion in favor of natural gas, solar and wind energy, production of propylene and other petroleum-derived products could fall short of current needs unless new ways to produce them are found.
Natural gas extracted from shale rock is a possible alternative to propylene, which is produced from petroleum. It is rich in propane, which is so similar to propylene that it represents a promising precursor. However, current processes for producing propylene from natural gas are still too inefficient to close the gap between supply and demand.
“It is very difficult to convert propane into propylene economically,” says Suljo Linic, Martin Lewis Perl Collegiate Professor of Chemical Engineering and corresponding author of the study published in Science.
“You have to heat the reaction to drive it, and the standard methods require very high temperatures to produce enough propylene. At these temperatures you get not only propylene, but also solid carbon deposits and other undesirable products that degrade the catalyst. To the “To regenerate the reactor, we often have to burn off the solid carbon deposits, which makes the process inefficient.”
The researchers’ new reactor system efficiently produces propylene from shale gas by splitting propane into propylene and hydrogen gas. It also allows the hydrogen to escape by changing the balance between the concentration of propane and reaction products so that more propylene can be produced. Once the hydrogen is separated, it can be safely burned away from the propane, heating the reactor enough to speed up the reactions without producing unwanted compounds.
This separation is achieved by the reactor’s nested hollow fiber membrane tubes. The innermost tube is made of materials that break down the propane into propylene and hydrogen gas. While the tubes keep most of the propylene in the innermost chamber, the hydrogen gas can escape into an outer chamber through pores in a membrane layer of the material. In this chamber, the hydrogen gas is burned in a controlled manner by adding precise amounts of oxygen.
Because the hydrogen can be burned inside the reactor and operated under higher propane pressure, the technology could allow plants to produce propylene from natural gas without installing additional heaters. A plant that produces 500,000 tons of propylene annually could save up to $23.5 million compared to other methods that start with shale gas, researchers estimate. These savings are in addition to the operational savings resulting from burning the hydrogen produced in the reaction instead of other fuels.