An NMR spectroscopic method for measuring homogenous liquid phase reaction kinetics in systems that are used in reactive gas absorption processes is presented. In the kinetic experiment, carbon dioxide loaded and unloaded aqueous amine solutions are mixed such that no gas phase is involved. This procedure enables studying liquid phase reaction kinetics without the influence of the kinetics of the physical absorption process. A rapid-mixing NMR flow cell is used for the measurements, which are carried out in stopped-flow mode. 1H NMR spectra are taken at short intervals to monitor the kinetic process. The cell is liquid thermostatted and pressure resistant, such that a wide range of conditions can be studied. The new method was used for studying reaction kinetics in the system monoethanolamine (MEA)–water (H2O)–carbon dioxide (CO2) at temperatures between 293 and 333 K. From the data, information on the kinetics of the reaction of MEA with bicarbonate (HCO3-) to form MEA carbamate was obtained. That reaction was investigated for the first time in the present work without using bicarbonate salts. An Arrhenius model was fitted to the new data. The formation of MEA carbamate from MEA and HCO3- is often neglected in models for describing the reactive absorption of CO2 with aqueous MEA solutions. A process simulation study carried out in the present work reveals that it should be taken into account in predictions of reactive absorption processes that are operated under elevated pressure with a high mole fraction of CO2 in the gaseous phase.
Factors influencing on the liquid phase (reaction) sintering of diamond.
