19 Dec 2017

CAPTURED CARBON COULD BECOME FUEL

Scientists of the Idaho National Laboratory developed an efficient process for turning captured carbon dioxide into syngas, a mixture of H2 and CO that can be used to make fuels and chemicals,.Carbon capture could help coal plants reduce greenhouse gas emissions, yet economic challenges are part of the reason the technology isn't widely used today. That could change if power plants could turn captured carbon into a useable product. Scientists at the U.S. Department of Energy's Idaho National Laboratory have developed an efficient process for turning captured carbon dioxide into syngas, a mixture of H2 and CO that can be used to make fuels and chemicals. The team has published its results in Green Chemistry, a publication of the Royal Society of Chemistry .

Traditional approaches for reusing the carbon from CO2 involve a reduction step that requires high temperatures and pressures. At lower temperatures, the CO2 doesn't stay dissolved in water long enough to be useful. The process developed at INL addresses this challenge by using specialized liquid materials that make the CO2 more soluble and allow the carbon capture medium to be directly introduced into a cell for electrochemical conversion to syngas.

"For the first time it was demonstrated that syngas can be directly produced from captured CO2 -- eliminating the requirement of downstream separations," the researchers wrote in the Green Chemistry paper.

The newly described process uses switchable polarity solvents (SPS), liquid materials that can shift polarity upon being exposed to a chemical agent. This property makes it possible to control what molecules will dissolve in the solvent.

In an electrochemical cell, water oxidation occurs on the anode side, releasing O2 gas and hydrogen ions that then migrate through a membrane to the cathode side. There, the hydrogen ions react with bicarbonate (HCO3-, the form in which CO2 is captured in the SPS), allowing the release of CO2 for electrochemical reduction and formation of syngas. Upon the release of CO2, the SPS switches polarity back to a water-insoluble form, allowing for the recovery and reutilization of the carbon capture media.

When syngas can be produced from captured CO2 at significant current densities, it boosts the process chances for industrial application. Unlike other processes that require high temperatures and high pressures, the SPS-based process showed best results at 25 degrees C and 40 psi.

 



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