Carbon Dioxide Appropriation Using Alkanolamine Blends: Vapor-Liquid Equilibrium Modelling Approach

Abstract

Design of sour-gas treating processes with alkanolamine solvents requires knowledge of vapor liquid equilibrium(VLE)of the aqueous acid gas–alkanolamine systems.An approximate thermodynamic model is developed to correlate and predict the vapor-liquid equilibrium(VLE)of CO2 in aqueous N-Ethyl Ethanolamine (EAE) solution in the temperature range (303.1-323.1 K).The values of deprotonation constant(K4)and carbamate reversion constant(K5)are determined by using the model derived from the VLE data of the ternary system(CO2 + EAE+ H2O).The model predictions are in good agreement with the experimental data of CO2 solubility in aqueous EAE solution available in the open literature.Similarly modified Kent Eisenberg model is validated for the quaternary(CO2 + AMP+PZ+ H2O)system.To consider the phase non-ideality in the(CO2+AMP+PZ+H2O)system we assumed the equilibrium constants are a function of temperature,CO2 partial pressure and amine concentration.The adjustable equilibrium constants Ki’ are then estimated.Rigorous thermodynamic model i.e.NRTL model is developed and VLE data of(CO2 + MDEA+ H2O)is correlated to find out the interaction parameters.The model predictions are in good agreement with the experimental data of CO2 solubility in aqueous MDEA solution available in the open literature.Density and viscosity of two novel tertiary alkanolamines including1-(2-hydroxyethyl)piperidine(1-(2-HE)PP)and 2-diethylaminoethanol(DEAE)in their aqueous blends with Piperazine(PZ)have been measured over a temperature range of(303.1, 308.1, 313.1, 318.1, 323.1)K and total amine mass fraction in all the blends was kept constant at 30 %.The mass % ratios of(PZ)/ (1-(2-HE)PP or DEAE)considered for measurements were 3/27, 6/24, 9/21 and 12/18.Density and viscosity of the ternary mixtures were correlated as functions of temperature and amine composition using thermodynamic framework.Modeling and simulation is done in MATLAB platform.