Evaluating the possibility of high-pressure desorption of CO2 via volatile co-solvent injection

Abstract

This work evaluates the possibility of employing a volatile co-solvent injection for recovering CO2 from loaded monoethanolamine at 120 °C under pressures above those achievable through regular desorption processes. This co-solvent would be fed directly into the reboiler, percolating the column and delivering higher operational pressures without significatively affecting the chemical equilibrium between CO2 and the amine. Removal of this co-solvent would be required before the lean amine is recirculated to the absorber. A shortcut methodology for screening possible co-solvent candidates is presented, and MESH calculations of hypothetical stripping processes employing the high-pressure desorption approach are performed to illustrate the expected behavior of these systems. Pressures above 500 kPa are theoretically obtainable through the use of co-solvents which are less volatile than CO2 but that are still gases at 25 °C and 101.325 kPa, such as isobutane and dimethyl ether. These co-solvents will leave the desorber fractioned between the distillate and the bottom product, thus requiring two additional separation process for recovery. Less volatile solvents will concentrate at the bottom stages of the desorber, while more volatile solvents will flow straight through the column all the way up to the distillate without effectively delivering pressures as high as desired. In other words, this methodology results in a delicate optimization problem of finding ideal volatilities and operational conditions. Though no detailed energy analysis is performed in this preliminary assessment, we have identified a promising opportunity for CO2 production at higher pressures and enumerated the issues one should be concerned with when looking further into high-pressure desorption.