Scientists have published findings of their new study in Green Chemistry wherein they have highlighted a new technique that could increase the value of captured carbon.
Carbon capture is seen as a means to reduce greenhouse gas emissions and hence have a positive impact on the planet, but there are economic challenges that need to be met so as to ensure that the value of the captured carbon increases and it can be used in or made part of 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. If we look at traditional approaches for reusing the carbon from CO2, it involves 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.
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.
As promising as the idea was, in the first experiments, too much hydrogen and not enough syngas was being produced. The results improved when the team introduced a supporting electrolyte to increase the ionic conductivity. Adding potassium sulfate increased electrolyte conductivity by 47 percent, which allowed the efficient production of syngas.
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.