Rethink Carbon Capture

Two much-less energy intensive processes target carbon dioxide emissions.

By Seán Ottewell, Editor at Large

Initially, the scientists weren’t considering carbon dioxide removal at all.

Two new processes, one lab-based and the other operating commercially, are forcing engineers and scientists to rethink their strategies for dealing with carbon dioxide (CO2) emissions.

The first, developed by a team of scientists at the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL), Oak Ridge, Tenn., is described as a simple, reliable process to capture the gas directly from ambient air.

Initially, the scientists weren’t considering CO2 removal at all; rather, they were looking for methods to remove contaminants such as sulfates, chromates and phosphates from water. To achieve this, they synthesized a version of the strong base guanidine. This, in turn, bound strongly with the negatively-charged contaminants to form insoluble crystals that are easily separated from water.

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“When we left an aqueous solution of the guanidine open to air, beautiful prism-like crystals started to form,” says Radu Custelcean of ORNL’s chemical sciences division. He adds, “After analyzing their structure by X-ray diffraction we were surprised to find the crystals contained carbonate, which forms when carbon dioxide from air reacts with water.”

In most current capture technologies, once the CO2 is released from a binding compound, it is transported through a pipeline to underground storage. However, the capture materials must be heated to 900°C to release the gas in the first place and this, in turn, can emit yet more CO2.

The ORNL process is much less energy intensive. Custelcean explains: “We were able to release the bound carbon dioxide by heating the crystals at 80–120°C, which is relatively mild when compared with current methods.” After heating, the crystals reverted to the original guanidine material. The recovered compound was then recycled through three consecutive carbon capture and release cycles.

Custelcean believes such air capture methods are gaining traction, but the ONRL process needs further development followed by aggressive implementation to be effective against global warming. Also, he says a better understanding is needed of the guanidine material and how it could benefit both existing and future carbon capture and storage applications.

To understand the guanidine material’s crystalline structure and properties, the scientists are making use of the ORNL’s spallation neutron source (SNS) to analyze carbonate binding in the crystals. Getting a better understanding of the molecular mechanism behind carbon capture and release will, they say, help in the design of the next generation of sorbents.

The scientists also plan to evaluate the use of solar energy as a sustainable heat source to release the bound CO2 from the crystals.

More on their work can be found in the journal Angewandte Chemie International Edition.

Meanwhile Carboclean, formed in India but now operating from London, U.K., has made what it describes as a breakthrough in treating CO2 with its new carbon capture and utilization (CCU) technology.

At its heart is a new — unnamed — CO2-stripping chemical that’s slightly more efficient than the amine used in current carbon capture and storage (CCS) technologies. However, Carboclean maintains that CCU technology needs less energy, is less corrosive and requires much less investment in new plant than the CCS alternative.

The new process has been installed on the coal-fired boiler at Tuticorin Alkali Chemicals, Bengal, India. That firm now is using the CO2 from its own boiler to make baking soda — a base chemical with a wide range of uses including glass manufacture, sweeteners, detergents and paper products.

In an interview with BBC Radio 4, Tuticorin managing director Ramachandran Gopalan said, “I am a businessman. I never thought about saving the planet. I needed a reliable stream of carbon dioxide, and this was the best way of getting it.” He added that the plant now has virtually zero emissions to air or water.

Crucially, says Carboclean CEO Aniruddha Sharma, the technology is running without subsidy and therefore is a major advance for carbon capture technology which as a whole has languished for decades under high costs and lukewarm government support.

He adds: “So far the ideas for carbon capture have mostly looked at big projects and the risk is so high they are very expensive to finance. We want to set up small-scale plants that de-risk the technology by making it a completely normal commercial option.”


Ottewell2Seán Ottewell is Chemical Processing's Editor at Large. You can email him at sottewell@putman.net.

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