Oxidative dehydrogenation has long been considered a more-energy-efficient way to make propylene from propane, but the method produces small yields. Now, a new approach from researchers at Northwestern University, Evanston, Ill., results in higher yields while also using less energy. The findings could support more-energy-efficient production processes for many plastics, and could benefit smaller chemical plants where energy consumption is very important and current engineering strategies may not be feasible, say the researchers.
“Instead of searching for the right catalyst, we deconstructed the oxidative dehydrogenation reaction down into two components — dehydrogenation and selective hydrogen combustion — and then designed a tandem material that does both reactions, in a particular order. This produced the highest yields of propylene ever reported,” says Justin Notestein, professor of chemical and biological engineering at Northwestern and co-corresponding author on the research.
Tests produced 30% yield from a single pass through the reactor at 450°C, compared to 800°C for traditional propylene production; more than 75% of the carbon atoms in the propane converted to propylene. By comparison, heating propane in the absence of oxygen doesn’t produce yields greater than 24%, and the catalysts often are unstable, the researchers note.
The approach uses a platinum-based catalyst that selectively removes hydrogen from propane to make propylene, and an indium oxide-based catalyst that selectively burns the hydrogen, but not the propane or propylene. An article in the journal Science contains more detail.
“We found that the nanostructure really matters,” Notestein explains. “…This nanostructure is able to separate and sequence the reactions, even though both catalysts can do both reactions.”
Optimization of process conditions and independent tuning could yield further improvements, believe the researchers, but they will need the help of partners. The team is open to collaborating and discussing licensing or sponsored projects.
“Our reactors are not large enough to carry out experiments relevant for scaleup,” says Notestein. “This reaction is a tightly coupled pairing of an exothermic and endothermic reaction, and heat management will be an issue at larger scales. There are significant composition gradients down the reactor bed. These could be controlled and exploited through staged O2 addition, for example. With respect to composition, many platinum alloys are excellent for dehydrogenation,” he adds.
