'Super-dry' reaction converts CO2 into less harmful, more useful chemicals
Image credit: Tony Webster
Belgian researchers have developed a new technique to turn carbon dioxide from exhaust fumes into useable chemicals.
The chemical process, described in the latest issue of the journal Science, involves what the researchers call as a ‘super-dry’ reaction, meaning it doesn’t require the use of water.
In the process, two types of greenhouse gas - methane and carbon dioxide - react, assisted by a nickel-based catalyst. Calcium oxide is used in the reaction to absorb carbon dioxide and iron oxide serves as a solid oxygen carrier.
“With this process, we intensify the conversion of CO2 by making maximal use of CH4 as reducing gas,” said the study’s lead author, Lukas Buelens of the Ghent University. “The generated CO can be used directly or combined with a green H2 source for the production of chemicals or fuels.”
Previously, the so-called ‘dry reforming’ of methane has been used to break the greenhouse gas into CO and H2. In this reaction carbon monoxide reacts with water to re-form carbon dioxide. Eliminating water from these reactions has proved to be an active area of research.
In the current study, the team used calcium oxide as a CO2 sorbent in which calcium carbonate is formed. This has several benefits that has allowed a higher carbon monoxide yield and an opportunity to remove water that is formed from the oxidation of methane.
First, from an economic and practical standpoint, because CO2 is removed in situ, the feed gas can be of lower stock quality.
Secondly, the formation of calcium carbonate can be coupled with methane reformation and iron oxide reduction resulting in a more energetically favourable process.
Then, when calcium carbonate decomposes into CO2 and CaO, the carbon dioxide is reduced to CO over the iron oxide oxygen carrier. According to the authors, it is at this point that the feed is switched to inert gas to regenerate the system.
They obtained a 45 per cent higher CO yield, but this yield could be even higher by optimising conditions.
Importantly, their two-flow reaction set-up seems to have some versatility that prior dry-reforming reactions lacked, either by changing the gas feedstock ratios or by changing to a multi-reactor configuration.
Additionally, their initial flow system uses a less expensive nickel catalyst because carbon deposition has been eliminated. Their system is more efficient for CO2 utilisation than prior dry-reforming reactions and may serve as a model for optimised CO2 conversion.