Vapor–Liquid Equilibrium Measurements for Aqueous Mixtures of NH₃+ MDEA + CO₂and KOH + MDEA

Abstract

Isothermal vapor−liquid equilibrium measurements were performed for aqueous solutions containing N-methyl diethanolamine (MDEA), MDEA + ammonia (NH 3 ), MDEA + potassium hydroxide (KOH), MDEA + carbon dioxide (CO 2 ), NH 3 + CO 2 , and MDEA + NH 3 + CO 2 . The experiments were carried out between 310 and 390 K and 0.07 and 34 bar using a static synthetic apparatus. Overall, 202 data points are reported in terms of total volume, total number of moles, temperature, and pressure. The experimental results for MDEA(aq), NH 3 (aq) + CO 2 (aq), and MDEA(aq) + CO 2 (aq) are in good agreement with the calculations done using the Extended UNIQUAC model within the studied range. The data presented in this work are also comparable to previously published measurements. This work reports for the first time VLE measurements for aqueous mixtures of MDEA + NH 3 and MDEA + KOH. These data suggest that the interactions between MDEA(aq) and NH 3 (aq) or K + (aq) ions have a minor effect on the equilibrium pressures. Consequently, other physical properties are needed to describe the thermodynamic state of these systems, such as heat capacity, heat of dilution, and other phase equilibrium measurements. The isothermal VLE measurements for solutions containing NH 3 (aq) showed a pressure minimum that was confirmed by model estimates and by other works done in similar conditions. As a consequence, it is not possible to estimate the partial pressure of CO 2 based on the difference between the pressure at equilibrium conditions and the partial pressure of the lean solvent. This paper demonstrates that this common approach to determining the partial pressure of gases may introduce a bias in these values. The dissolution of CO 2 into MDEA(aq) + NH 3 (aq) mixtures changes the speciation of the system, leading to an increase in the concentration of their protonated species (MDEAH + (aq) and NH 4 + (aq), respectively). For this reason, the interaction between these charged species must be determined in order to perform reliable phase equilibrium calculations. Ultimately, the measurements reported in this work can be used for thermodynamic modeling of CO 2 capture solvents to ensure accurate results in process simulation.

Aqueous 2-Ethyl-4-methylimidazole Solution for Efficient CO2 Separation and Purification

“…CO 2 capture is the most economical and feasible method to restrain carbon emissions from industrial point sources [13]. According to the current technical progress, amine chemisorbents, such as ethanolamine (MEA) [14,15], N-methyldiethanolamine (MDEA) [16], and piperazine (PZ) [17], have fast absorption rate, high absorption capacity, and mild operating conditions, and are often used to capture CO 2 , which is also one of the most mature CO 2 separation technologies at present [18][19][20]. Especially, aqueous solutions of MEA have been extensively studied in post-combustion CO 2 capture systems, and it is regarded as the benchmark for all CCS processes [14,15,21].…”