{"id":56907,"date":"2018-10-02T07:32:16","date_gmt":"2018-10-02T05:32:16","guid":{"rendered":"https:\/\/renewable-carbon.eu\/news\/?p=56907"},"modified":"2021-09-09T21:33:18","modified_gmt":"2021-09-09T19:33:18","slug":"chemists-demonstrate-sustainable-approach-to-carbon-dioxide-capture-from-air","status":"publish","type":"post","link":"https:\/\/renewable-carbon.eu\/news\/chemists-demonstrate-sustainable-approach-to-carbon-dioxide-capture-from-air\/","title":{"rendered":"Chemists demonstrate sustainable approach to carbon dioxide capture from air"},"content":{"rendered":"

Chemists at the Department of Energy\u2019s Oak Ridge National Laboratory have demonstrated a practical, energy-efficient method of capturing carbon dioxide (CO2<\/sub>) directly from air. They report their findings<\/a> in Nature Energy<\/em>. If deployed at large scale and coupled to geologic storage, the technique may bolster the portfolio of responses to global climate change.<\/strong><\/p>\n

\"2018-P04585_0\"<\/a>
From left, Radu Custelcean and Neil Williams of Oak Ridge National Laboratory used a solar-powered oven to generate mild temperatures that liberate carbon dioxide trapped in guanidine carbonate crystals in an energy-sustainable way. Credit: Carlos Jones\/Oak Ridge National Laboratory, U.S. Dept. of Energy<\/figcaption><\/figure>\n

\u201cNegative emissions technologies\u2014for net removal of greenhouse gases from the atmosphere\u2014are now considered essential for stabilizing the climate,\u201d said Radu Custelcean of ORNL, who conceived and led the study. This opinion echoes conclusions of a recent report from the National Academy of Sciences. \u201cOur direct-air-capture approach provides the basis for an energy-sustainable negative emissions technology,\u201d he added.<\/p>\n

The accomplishment builds on a proof-of-principle study the chemists conducted last year, which was improved through a two-cycle process that dramatically enhanced the speed and capacity of CO2<\/sub> absorption and that completely recycles both the amino acid sorbent and the guanidine compound.<\/p>\n

It\u2019s cheaper and easier to cut CO2<\/sub> emissions at their source than to recapture emissions from the atmosphere. Regardless, large-scale deployment of technologies such as direct air capture of CO2<\/sub> is now considered necessary to limit the rise in average global temperature to 2 degrees C (~4 degrees Fahrenheit).<\/p>\n

Limiting warming to 2 degrees C would require grabbing billions of tons, or gigatons, of CO2<\/sub> from the atmosphere. In principle, trees could do it. However, to capture CO2<\/sub> at this scale, \u201cyou\u2019d need to plant trees on a surface the size of India,\u201d Custelcean said. Capturing a gigaton of CO2<\/sub> per year with industrial scrubbers would require only approximately 7,000 square kilometers (~2,700 square miles)\u2014an area less than the big island of Hawaii, said co-author Neil Williams.<\/p>\n

For the recent ORNL study, Williams and Flavien Brethom\u00e9 mixed amino acids with water to make an aqueous sorbent to grab CO2<\/sub> from air. Amino acids are safer than caustic sodium or potassium hydroxides or smelly amines, the sorbents used in industrial CO2<\/sub> scrubbers.<\/p>\n

The scientists put their aqueous sorbent in a household humidifier to maximize contact between air and sorbent and thus speed CO2<\/sub> uptake. Once absorbed into the liquid, the CO2<\/sub> formed a bicarbonate salt.<\/p>\n

Colleague Charles Seipp had designed and synthesized an organic compound containing guanidines, chemical groups common in proteins that can bind negatively charged ions. Williams and Brethom\u00e9 added Seipp\u2019s guanidine compound to the loaded amino acid sorbent solution containing bicarbonate, creating an insoluble carbonate salt that precipitated out of solution and regenerating the amino acid sorbent, which could be recycled.<\/p>\n

A critical part of the study was a thorough thermodynamic analysis of the process by Custelcean and Michelle Kidder, who determined how much energy was needed to drive each chemical reaction. The last step\u2014releasing CO2<\/sub> from the carbonate crystals so it can be stored long-term\u2014is especially important for developing an energy-sustainable process. Because the CO2<\/sub> is bound in a guanidine carbonate solid, it can be liberated at much lower temperatures (80\u2013160 degrees C, or 176\u2013320 degrees F) than from the inorganic salts used in current capture technologies, which require temperatures over 800 degrees C (1,472 degrees F) to release the CO2<\/sub>. Nevertheless, the analysis showed the heat needed to release the CO2<\/sub> from the guanidine carbonate crystals is still significant.<\/p>\n

To make the overall process energy-sustainable, Custelcean decided to employ concentrated solar power. He acquired a solar-powered oven, normally used to cook foods using a parabolic mirror to concentrate the sun\u2019s rays. The guanidine carbonate crystals were placed on a tray inside the solar oven, and the CO2<\/sub> was liberated in as little as 2 minutes, in a process regenerating the guanidine compound for recycling.<\/p>\n

\u201cUsing renewable energy is important because as much as possible you want to avoid producing more CO2<\/sub> in the process of trying to capture it,\u201d Custelcean said. This experiment used solar heat, but waste heat\u2014such as from air conditioners and power plants\u2014would work as well, he said.<\/p>\n

Moving forward, the researchers would like to design simpler, more efficient guanidine-based sorbents and gain a better understanding of the structural, thermodynamic and mechanistic aspects of the direct air capture process.<\/p>\n

\u201cAll crystals that we’ve made so far include water that hydrates the carbonate anions,\u201d Custelcean explained. \u201cWhen you try to release the CO2<\/sub>, you have to desorb the water as well, and that takes most of the energy. We are trying to design next-generation guanidine ligands that bind the CO2<\/sub> as \u2018dry\u2019 carbonate.\u201d<\/p>\n

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