A team of engineers from the University of Michigan has devised a new approach for manufacturing an ingredient used in the making of plastics, adhesives, carpet fibers, household cleaners and other products from natural gas.

To accomplish this, the engineers created a new chemical reactor that produces propylene, a chemical used in the making of industrial chemicals, such as ingredients for nitrile rubber used to manufacture automotive hoses and seals and blue protective gloves, for instance.

Source: Sandra Swisher, Department of Chemical Engineering/University of Michigan

While most propylene in use today comes from oil refineries, which collect it as a byproduct of refining crude oil into gasoline, the engineers are eyeing natural gas extracted from shale as a potential alternative to propylene sourced from crude oil. This is because it’s rich in propane, which resembles propylene enough to be considered as a precursor material, the researchers added. Yet, current methods for manufacturing propylene from natural gas are still reportedly too inefficient to bridge the gap in supply and demand.

"It's very hard to economically convert propane into propylene…You need to heat that reaction to drive it, and standard methods require very high temperatures to produce enough propylene. At those temperatures, you don't just get propylene but solid carbon deposits and other undesirable products that impair the catalyst. To regenerate the reactor, we need to burn off the solid carbon deposits often, which makes the process inefficient," the researchers explained.

As such, the engineers developed a new reactor system that produces propylene from shale gas by separating propane into propylene and hydrogen gas. Further, the reactor also removes hydrogen, thereby affecting the balance between the concentration of propane and reaction products in a manner that enables more propylene to be produced. As soon as the propylene and hydrogen gas are separated, the hydrogen can be safely burned away from the propane, subsequently heating the reactor so as to speed up the reactions without producing any undesirable compounds.

The researchers explained that the reactor is able to achieve separation via its nested, hollow-fiber membrane tubing. The innermost tube is composed of materials that split the propane into propylene and hydrogen gas — with the tubing sequestering the majority of the propylene within the innermost chamber, while the hydrogen gas can escape into an outer chamber via pores in a membrane layer of the material. Within that chamber, the hydrogen gas is controllably burned when precise amounts of oxygen are mixed.

An article detailing the new reactor, “Overcoming limitations in propane dehydrogenation by co-designing catalysts/membrane systems,” appears in the journal Science.