CANBERRA: Gases pouring from a factory chimney may look like waste, but researchers are exploring whether some of that pollution could eventually become raw material for fuels and useful chemicals.
A team from Australia, France and China has developed a system that converts carbon dioxide in industrial exhaust into carbon monoxide without first separating and purifying the CO2.
Carbon monoxide is not a finished fuel but, when combined with hydrogen, it can be used to produce synthetic fuels and chemicals through established industrial processes.
The study, published in Nature Communications, could help overcome one of the main obstacles facing carbon-capture technologies: real factory emissions are far messier than the purified carbon dioxide commonly used in laboratory experiments.
Why factory exhaust is difficult to use
Industrial flue gas usually contains only a modest amount of carbon dioxide, mixed with far larger quantities of nitrogen, oxygen and other impurities.
With less CO2 available, conversion becomes less efficient, while oxygen can trigger competing reactions and waste much of the electricity being supplied.
Many existing approaches therefore begin by extracting and purifying the carbon dioxide. This adds equipment, consumes energy, and raises costs before conversion can even begin.
The new method instead uses a specially designed mixture of organic solvents to control the environment in which the reaction takes place.
By weakening hydrogen bonding within the liquid, the researchers were able to suppress unwanted reactions and favour the conversion of carbon dioxide into carbon monoxide.
In simpler terms, they adjusted the liquid surrounding the reaction so the CO2 had a better chance of becoming the intended product despite the other gases present.
Encouraging results, with caveats
During tests, the system was fed a simulated exhaust mixture containing 15% carbon dioxide and 8% oxygen, with nitrogen making up the remainder.
It converted the CO2 into carbon monoxide with near-total selectivity, meaning very little of the electrical current went towards unwanted products. The system also operated for more than 100 hours without a major drop in performance.
When connected to a high-efficiency solar cell, it achieved a solar-to-fuel efficiency of about 5.5%, similar to some systems supplied with purified CO2.
The researchers also showed that the approach could function with carbon dioxide concentrations as low as 1%.
These findings are promising, but the system has not yet been tested over long periods using exhaust taken directly from a working steel mill, cement plant or power station.
Notably, real emissions may contain sulphur compounds, nitrogen oxides, dust and other contaminants that could damage catalysts or reduce performance. Further work will also be needed to determine whether the process can be scaled up economically.
A possible use for unavoidable emissions
The technology is not a licence for factories to continue releasing unlimited carbon dioxide. Reducing fossil-fuel use and improving energy efficiency remain essential, while capturing and reusing carbon does not necessarily prevent it from eventually returning to the atmosphere.
However, some industries, including cement, steel and chemicals, produce emissions that are especially difficult to eliminate completely.
For these sectors, turning part of an exhaust stream into a useful feedstock could reduce reliance on newly extracted fossil carbon while avoiding some of the cost and energy involved in purifying CO2 first.
While the study is an early step rather than a finished solution, it suggests factory emissions may one day be seen not only as pollution to contain, but also as a source of carbon that can be recovered and put back to work.
