Researchers have developed a laboratory process that turns carbon dioxide from a simulated factory exhaust stream into a useful industrial material without first separating the carbon dioxide into a highly purified gas.
The approach could help remove one of the costly and energy-intensive steps involved in recycling industrial carbon emissions. However, it has so far been tested only under controlled laboratory conditions, not at an operating factory.
The research was led by scientists at Université de Montpellier and Adelaide University. Their findings were published in Nature Communications.
Why factory exhaust is difficult to reuse
Factory exhaust is not made up of pure carbon dioxide. It contains a mixture of gases, including nitrogen and oxygen, as well as other substances that can vary from one industrial site to another.
That creates a problem for technologies designed to turn carbon dioxide into fuels or chemicals. Many of these systems work best when they receive a concentrated or purified stream of carbon dioxide.
Separating the carbon dioxide from the rest of the exhaust requires additional equipment and energy. This can make carbon-recycling projects more complicated and expensive before the conversion process has even begun.
The new study explored whether the conversion equipment itself could be made more tolerant of a mixed gas stream.
A system designed to work with other gases present
The researchers used electricity and a specially chosen organic liquid to convert carbon dioxide into carbon monoxide. The liquid helped prevent oxygen from interfering with the main reaction.
Carbon monoxide is not the finished fuel. It is an industrial building block that can be used to make products including methanol, fuels, plastics and other chemicals, according to the U.S. Department of Energy’s National Energy Technology Laboratory.
For the main test, the team used a simulated exhaust mixture containing 15% carbon dioxide, 8% oxygen and 77% nitrogen. The system continued operating for more than 100 hours while maintaining high selectivity for carbon monoxide.
In simple terms, nearly all the electrical charge used at the carbon-conversion side of the device went toward making the intended product rather than unwanted byproducts.
That does not mean nearly all the carbon dioxide entering the system was converted. The study reported that 8.4% of the incoming carbon dioxide was converted during a single pass through the device. A larger industrial system might need to recycle the remaining gas or improve the amount converted on each pass.
The device also produced a second useful chemical
The process produced another chemical at the opposite side of the device. It converted an added substance called dimethyl sulfide into dimethyl sulfoxide, commonly known as DMSO.
DMSO is used as a solvent for substances including dyes, resins and polymers, according to the U.S. Environmental Protection Agency.
Producing a useful chemical at both sides of the device could eventually make the process more commercially attractive. However, the DMSO was not made from the factory emissions. It required a separate chemical input, and the study did not show that the combined process would be profitable at industrial scale.
Why avoiding full purification could matter
The main business advantage is the possibility of simplifying the equipment needed before carbon conversion begins.
If a future system could work directly with partially treated exhaust, manufacturers might need less equipment to separate and purify the carbon dioxide. That could reduce energy use, lower operating complexity and make carbon-utilization projects easier to install.
The researchers believe the approach could eventually be relevant to industries such as steel, cement, chemicals, alumina refining and energy production.
Adelaide University said the process could make carbon utilization more practical and potentially more economical. The university also emphasized that the system was designed to tolerate oxygen, which has been a major obstacle when trying to convert carbon dioxide directly from mixed exhaust gases.
The researchers also connected the system to a high-efficiency solar cell. Under laboratory conditions, about 5.5% of the incoming solar energy was stored in the carbon monoxide produced.
The technology is still at an early stage
Several important questions remain before the process could be used by industry.
The researchers used a manufactured gas mixture rather than exhaust taken from an operating factory. The main mixture contained carbon dioxide, oxygen and nitrogen, while real industrial exhaust can contain additional contaminants that may affect performance.
The gas was also pressurized to 20 bar, and the test lasted a little over four days. Industrial equipment would need to operate reliably for much longer and handle far larger volumes of gas.
The study did not provide a full commercial cost assessment. Any future assessment would need to consider the cost of electricity, pressure equipment, chemicals, catalysts, maintenance, product separation and recycling the carbon dioxide that is not converted on the first pass.
The process should also be viewed as carbon utilization rather than permanent carbon removal. If the carbon monoxide is later turned into fuel and burned, some or all of the carbon could eventually return to the atmosphere.
Even with those limitations, the study presents a useful change in direction. Instead of treating mixed factory exhaust only as something that must be extensively cleaned before use, researchers are trying to design conversion equipment that can work with a less purified gas stream.
If that approach can be proven with real industrial emissions and scaled economically, it could reduce a major barrier that currently makes factory carbon recycling more difficult and expensive.
