Ternary Diffusion Coefficients of Aqueous Alkanolamine Solutions: Diethanolamine + N-methyldiethanolamine + Water
Advancing the chemical engineering fundamentals
Distillation, Absorption & Extraction (T2-10P)
Keywords: ternary diffusion coefficient, Taylor dispersion technique, mutual diffusion coefficient, gas absorption, carbon dioxide
Aqueous alkanolamine solutions are the industrially important solvents used in the natural gas, petroleum chemical plants, and ammonia industries for the removal of CO2 and H2S from gas streams. Utilizing the advantages of absorption characteristics of various amines, the aqueous blended amines were recently proposed as potential absorbents for acid gases removal in the absorption processes. Thermophysical properties such as diffusion coefficients are needed in evaluation of mass transport properties. The mutual diffusion coefficients of aqueous alkanolamine solutions were reported in the literature, and the ternary diffusion coefficients of monoethanolamine (MEA) + N-methyldiethanolamine (MDEA) +water were also studied. However, the ternary diffusion coefficients for other aqueous blended alkanolamines have not yet been reported. Therefore, the objective of this study was to measure the ternary diffusion coefficients of aqueous blended alkanolamine systems diethanolamine (DEA) + MDEA + water using the Taylor dispersion technique for temperatures 30 to 50 oC. The ternary diffusion coefficients were studied for solutions containing the total amine concentrations, 2, 3, and 4 kmolm-3 for vasrious molar amine ratios of 0.25, 0.5, and 0.75. The corresponding mutual diffusion coefficients of aqueous DEA and aqueous MDEA solutions were also measured. In a Taylor experiment, a delta function of solution is injected into a laminar carrier stream of reference fluid which flows in a long capillary tube. The concentration profiles of dispersed solutes are determined by a differential refractometer. The working equations for the ternary diffusion coefficients were adopted from the expressions presented by Leaist and coauthors. A regression procedure is used to calculate the ternary diffusion coefficients from the refractive index profiles. The main diffusion coefficients (D11 and D22) and the cross coefficients (D12 and D21) were reported as function of temperature and concentration of alkanolamines. The measured ternary diffusion coefficients were compared with the predicted values which calculated from the Onsager phenomenological coefficients, the activity, and partial molar volume of components. It was found out that the predicted values for ternary diffision coefficients generally followed the trend of the experimental values.
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Presented Tuesday 18, 13:30 to 15:00, in session Distillation, Absorption & Extraction (T2-10P).
