Application of Electrolyte-NRTL Model for Prediction of the Viscosity of Carbon Dioxide Loaded Aqueous Amine Solutions

A method based on the absolute-rate theory has been used and tested for estimation of the dynamic viscosity of CO₂ loaded aqueous solutions of a representative amine: monoethanolamine (MEA). In this approach the electrolyte-NRTL model is applied to estimate the activation free energy of the solution and consequently enable prediction of the dynamic viscosity of the strong electrolyte CO₂:MEA:H₂O system. Three different concentrations of the aqueous MEA solutions with 20, 30, and 43 wt %, in the temperature range from 40 to 70 °C, and CO₂ loadings from 0.1 to 0.5 mol of CO₂/mol of amine were selected for the model investigation. The model displays a reasonable prediction ability from experimental viscosity data in the whole range of system variables. It is shown that the activation free energy for the flow process can be closely estimated through the Gibbs free energy of mixing with a correction on the sign of the energy term in the model equation from positive to negative. The result reveals that, having a reliable thermodynamic model for a selected solution, the absolute-rate-theory approach is applicable for estimation of the viscosities of strong electrolyte systems such as CO₂ loaded alkanolamine solutions at different solution concentrations, temperatures, CO₂ loadings, and operating pressures for various amines and amine blends

The Equilibrium Solubility of Carbon Dioxide in Aqueous Solutions of Morpholine: Experimental Data and Thermodynamic Modeling

Experimental carbon dioxide solubility data in aqueous 34.8 wt % (6.14 m) and 43.5 wt % (8.85 m) morpholine solutions at 40, 60, 100, and 120 °C are presented. The solubility measurements were done in a static vapor liquid equilibrium cell by measuring total pressure. Furthermore, selected data points were confirmed using gas phase GC methodology. The obtained combined solubility data was integrated with speciation data extracted using an established titration method, for thermodynamic modeling of the system. In regression of the model parameters, the liquid phase activity coefficients were determined using the electrolyte-NRTL equations. In addition to binary and pair interaction adjustable parameters included in the electrolyte-NRTL model, the temperature dependent carbamate stability and Henry’s law constants for CO₂ in pure morpholine were also calculated. The determined CO₂ equilibrium properties are in good agreement with most of the experimental data

Facile Method for Determination of Amine Speciation in CO₂ Capture Solutions

A simple and quantitatively reliable method for determination of amine speciation is introduced. The method employs three experimental methods that should be readily accessible. The results for CO₂ loaded aqueous solutions of 30 wt % monoethanolamine (MEA) are used for demonstration of the method and show promising agreement with the more complicated spectroscopic methods reported in the literature. The measurements were done at ambient temperature and atmospheric pressure, since theoretical calculations and experimental data from the open literature revealed no considerable difference in speciation at different temperatures. The procedure is based on acid and base titration of the CO₂ loaded amine solution along with the determination of total CO₂ loading. The quantitative results for the different species concentration in the example MEA solution is in agreement with other available spectroscopic methods, mainly NMR, particularly for the free amine, carbamate, and protonated amine concentrations. Aspen Plus was also used for further assessment of the experimental data

Morpholine Nitrosation To Better Understand Potential Solvent Based CO₂ Capture Process Reactions

The amine assisted CO₂ capture process from coal fired power plants strives for the determination of degradation components and its consequences. Among them, nitrosamine formation and their emissions are of particular concern due to their environmental and health effects. The experiments were conducted using morpholine as a representative secondary amine as a potential CO₂ capture solvent with 100 ppm standard NO₂ gas to better understand the nitrosamine reaction pathways under scrubber and stripper conditions. The role of nitrite in the nitrosation reaction was probed at elevated temperatures. The effects of different concentrations of nitrite on morpholine were evaluated. Formation rate, decomposition rates, activation energy, and the possible reaction pathways are elaborated. Thermal stability tests at 135 °C indicated the decomposition of nitrosamines at the rate of 1 μg/(g h) with activation energy of 131 kJ/mol. The activation energy for the reaction of morpholine with sodium nitrite was found as 101 kJ/mol. Different reaction pathways were noted for lower temperature reactions with NO₂ gas and higher temperature reactions with nitrite