Concentrating Carbon Dioxide – What Do We Know from Power Plant Capture Research?

Abstract:

Geologic materials, basically calcium or magnesium-rich rocks, can provide much of the thermodynamic driving force for distributed carbon capture from air – if we can work out appropriate processes. One apparent challenge is that the rate of reaction is slower than we would like it to be. This rate is a combination of the mineralization rate (forming calcite from solution) and, since the reactions are much faster in water, the rate at which carbon dioxide can be added to solution, providing a more concentrated source of CO₂(aq) for reaction. This latter problem of mass transfer across the gas-liquid interface is addressed in power plant capture schemes through increasing the chemical driving force, catalytic formation of dissolved CO₂ via carbonic anhydrase and its analogues, and simple increases of surface area. An important learning from that body of research is that surface area is critically important – no amount of catalysis or chemical driving force can make up for simple transfer area. This talk will relate those learnings in power plant capture studies to the issue of accumulating CO₂ to react with rocks for permanent sequestration. Not only is it important to create surface area for the reactive rocks, such as by grinding or fracturing, but it is equally valuable to increase the concentration of CO₂(aq) by rapid transfer across the gas-water interface. Successful future carbon dioxide management schemes will have to take advantage of every kinetic advantage possible, in order to make good use of the thermodynamic advantage that geologic materials present for controlling atmospheric carbon levels.