Remarkable performance of a few water lean solvents

https://doi.org/10.1016/j.seppur.2020.118193

“Obtaining and treating vapor–liquid equilibrium data, kinetic rate data and mass transfer rate data can be incredibly time-consuming. For a quick evaluation of a large number of new solvents, fast methods such as checking their CO₂ absorption capacities and absorption rates in a bubbling cell can be very practical.

Surely, this type of data is hierarchically less meaningful than VLE or kinetics. We are not making an unfair distinction in stating so. The CO₂ capacity of a solvent is nothing more than one single vapor–liquid equilibrium point, taken at one single CO₂ partial pressure and one single temperature. Similarly, its rate of absorption is confined by the very specific, hardly scalable experiment of bubbling CO₂ into one flask of solvent. In other words, one can obtain capacity and rate information from VLE and kinetic data, but not the opposite.

And yet, some reports on rate and capacity are the most interesting one can find regarding water-lean solvents. Woertz [33] screened more than 20 different solvents at about 540 kPa of CO₂ partial pressure and 25 °C, and many of the combinations that outperformed their aqueous counterparts (e.g.: aqueous MEA mixed DEGDME or NMP) are still being studied and re-invented to this day. Woertz [33] was also the first to note down the shifting in absorption rates in water-lean solvents, simply by writing down ‘fast’ or ‘slow’ on a list with diverse formulations, thus registering that absorption in TEG-MEA-water mixtures is particularly morose.