Engineers at Rice University have developed a new reactor that can convert carbon monoxide (CO) into acetic acid. Using tiny copper cubes as a catalyst, the device is relatively simple and can operate for long periods at a time, allowing the unwanted waste gas to be turned into an industrially useful product.
Carbon monoxide is often generated as a byproduct of industrial processes, and while it’s not directly a greenhouse gas in the atmosphere, it can be an indoor or urban air pollutant that is harmful to human health in higher concentrations.
In the new study, the Rice researchers developed a way to turn this potentially dangerous waste product into something of value. Acetic acid is used in foods such as vinegar, as an antiseptic, a solvent, and in a range of industrial processes and products.
Building on a previous device the team used to convert carbon dioxide into formic acid, the new reactor reduces carbon monoxide into acetic acid.
“We’re upgrading the product from a one-carbon chemical, the formic acid, to two-carbon, which is more challenging,” says Haotian Wang, an author of the study. “People traditionally produce acetic acid in liquid electrolytes, but they still have the issue of low performance as well as separating the product from the electrolyte.”
In this case the electrolyte is solid. It interacts with a catalyst made up of nanoscale copper cubes carefully engineered with corrugated surfaces that help break certain carbon-oxygen bonds to convert the gas into the desired product.
“Sometimes copper will produce chemicals along two different pathways,” says Wang. “It can reduce CO into acetic acid and alcohols. We engineered copper cubes dominated by one facet that can help this carbon-carbon coupling, with edges that direct the carbon-carbon coupling towards acetic acid instead of other products.”
Deionized water is piped through the reactor, where it mixes with the acetic acid to produce a usable solution. The leftover gas is emitted as oxygen.
In lab tests, the device was run continuously for 150 hours, producing a solution that contained up to two percent acetic acid – a weak solution, compared even to vinegar’s four percent acetic acid content, but useful enough. The acid component itself was up to 98 percent pure.
The team says that more work needs to be done to improve the system in order to make it scalable, including making it more stable and more energy efficient.
The research was published in the journal Proceedings of the National Academy of Sciences.
Source: Rice University