Strong Bicarbonate Forming Solvents for Absorption of CO2 - Experimental Determination and Modelling of Vapor-Liquid Equilibria Data
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Absorption by amines provides a technology for CO2 capture. New solvents are ofinterest to ameliorate the process, and the two alkanoamines 2-piperidine-ethanol(2-PPE) and 1-(2-hydroxyethyl)-pyrrolidine (1-2HE-PRLD) were investigated inthis work. Ebulliometric vapor-liquid equilibrium (VLE) data of pure 2-PPE and 1-2HEPRLDwere provided by this work. 1-2HE-PRLD was found to be more volatilethan the 2-PPE. VLE data of the binary system 2-PPE/H2O were obtained byebulliometric measurements. Quantification of the vapor and liquid phase concentrationwere done by amine titration and Ion Chromatography. The data wereused to calculate the experimental activity coefficient. Due to the low volatilityof 2-PPE, the uncertainty of the calculated activity coefficient were significant atlow temperatures. At 50C, the uncertainty was about 40%. Such deviations arealso found in other works with amines of similar volatility (50% for MDEA). Therelative uncertainty decreased substantially when the temperature increased, it wasbelow 8% at 100C. The experimental data were used to develop a Non-Random-Two-Liquid (NRTL)model. This was also done for the system 1-2HE-PRLD/H2O, with the experimentaldata taken from literature. Two optimization routines were applied to find themodel parameters. The first routine simultaneously fitted parameters for Antoineequation of pure amine and binary interaction parameters, yielding model predictionsof the amine activity coefficients with AARD less than 14% for both the2-PPE and the 1-2HE-PRLD system. The second routine fitted the two parametersets separately, and gave better fit with respect to the total pressure of the solution(AARD <4%). Furthermore, rigorous electrolyte-NRTL models were developed for the loaded systems2-PPE/H2O/CO2 and 1-2HE-PRLD/H2O/CO2. The model parameters fromthe binary systems were fixed during the optimization. The AARD between theexperimental data and the model predictions were for both systems found to bewithin 12% (PCO2 ) and 9% (Ptotal). These values indicate very good accordancebetween the models and the experimental data. The critical properties of 2-PPE and 1-2HE-PRLD were not found in literature,and thus estimated. They were required for regression of the NRTL and eNRTLmodel parameters, but are however seen to have small influence on the final resultdue to low pressures.