Heat effect on mass transfer in N-Methyldiethanolamine aqueous solutions
Advancing the chemical engineering fundamentals
Distillation, Absorption & Extraction (T2-10P)
Keywords: Bubble column; Thermal effect; Methyldiethanolamine; Gas absorption
Many processes in the field of chemical engineering are based on a chemical reaction between a gas and some soluble or insoluble materials present in a liquid. The gas has to be dissolved in the liquid phase such that the chemical reaction can take place. This reaction can occur in isothermal or non-isothermal conditions.
Most theories above gas absorption with chemical reaction have assumed isothermal conditions in order to facilitate the treatment of the experimental data. Shah (1979) reviewed the literature concerning heat effects in systems involving gas-liquid reactions and concluded that, in the majority of these systems, temperature effects are not very important. There exist, however, a large number of important industrial gas-liquid reactions which are accompanied by large heat effects.
Absorption of carbon dioxide with amines has been extensively studied. In spite of the significant amount of experimental and theoretical works on the absorption of CO2 in MDEA solutions (Pacheco and Rochelle, 1998; Shi and Zhong, 2005), there is still a lack of accurate quantitative data on the heat effect on the absorption process. The present work aims to study the temperature change during the CO2 absorption in MDEA aqueous solutions, and the thermal effect on volumetric mass transfer coefficient.
The mass transfer experiments were carried out in a bubble column of rectangular section with 6 cm in each side and 103 cm high. The top plate has a central orifice for outflow of gas and two off-center orifice for inflow of liquid and for a thermometer. The baseplate has one off-center orifice for outflow of liquid and a central orifice for gas inflow through a porous plate of three orifices.
The liquid phases employed were methyldiethanolamine aqueous solutions, in the concentration range from 0.05 to 1M, whereas the gas phase was pure carbon dioxide. The gas flow rate was varied between 10 and 25 L/h. All the experiments were made at ambient pressure and temperature, operating in batches with respect to the liquid phase. The level of liquid in the column was up 100 cm above the sparger.
Finally, the temperature inside the column has been measured using thermocouples placed to different heights, throughout the column. From the results, we deduce that the absorption takes place in a nonisothermal regime. In all the studied gas-liquid systems, for a certain concentration of amine and gas flow-rate, the temperature varies with time and with the column height. This behaviour is more important at high amine concentrations and gas flow-rates.
References:
Shah, Y.T., Gas-Liquid-Solid Reactor Design, McGraw-Hill, New York (1979)
Pacheco, M.A. and Rochelle, G.T., Industrial Engineering & Chemistry Research, 37, 4107-4117 (1998)
Shi, Y. and Zhong, Z., Chemical Engineering Communications, 192, 1180-1193 (2005)
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 13:30 to 15:00, in session Distillation, Absorption & Extraction (T2-10P).
