CO2 absorption in alkaline solution
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- Master i teknologi 
Density and viscosity for monoethanolamine (MEA) solution are important for estimation of mass transfer in CO2 removal by absorption. A literature search on density, viscosity, surface tension and contact angle was performed. Density and viscosity data for unloaded MEA solution are presented in several articles. Density and viscosity for loaded MEA solution was found in Weiland et al. (1998). This article presents data for 10, 20, 30 and 40 weight percent loaded MEA solution at 25 °C. No data for loaded solution above 25 °C was found. The object of the experimental work was to perform density and viscosity measurements above 25 °C. CO2 loaded MEA solution was prepared by bubbling CO2 through the MEA solution. To analyse the amount of CO2 absorbed in the loaded MEA solution, a procedure from StatoilHydro and one from SINTEF were tested. After several tests, the method from StatoilHydro was replaced with the method from SINTEF. This method gave the most reliable results and was easier to execute. Samples with varying loading and fixed concentration were prepared by mixing loaded and unloaded solution with the same concentration together. 20, 30, 40, 50, 70, 90 and 100 wt % unloaded MEA solution were prepared and measured for density and viscosity at 25, 40, 50, 70 and 80 °C. For loaded MEA solution, 20, 30 and 40 wt % MEA with 0.1, 0.2, 0.3, 0.4 and 0.5 moles of CO2/moles of MEA were prepared and measured for density and viscosity at the same temperature range as for unloaded MEA solution. The experimental work was executed in co-operation with StatoilHydro. Density and viscosity measurements were then compared with literature data and values calculated form Aspen HYSYS. The viscosity measurements were in excellent accordance with literature values at 25 °C, with less then 4 % deviation. The measurements at higher temperatures were compared to correlations on viscosity and density from Weiland et al. (1998). The maximum deviation for the viscosity was 12 %, and 1.5 % for the density. Density and viscosity for MEA solutions show a significant dependence on the MEA concentration and CO2 loading, and decreases with increasing temperature. Mass transfer correlations from Shetty & Cerro, Billet & Schultes, and Onda et al. with Bravo & Fair were studied in order to observe change of mass transfer due to change in viscosity and density. A change in viscosity of 12 % (maximum deviation) gave a difference of about 2 % in mass transfer coefficient for Shetty & Cerro and Billet & Schultes, and less then 9 % for Onda et al. with Bravo & Fair. This shows that accurate viscosity data is not that important in calculation of mass transfer coefficients due to other uncertain parameters. The correlations form Weiland et al. (1998) can therefore be used for calculations of density and viscosity.