Mass Transfer Study using a Electrochemical Method
Advancing the chemical engineering fundamentals
Distillation, Absorption & Extraction (T2-10P)
Keywords: Gas absorption, Bubble Column, Electrochemistry; carbon dioxide, Alkanolamines
Many processes in the field of chemical engineering are related to mass transfer operations between different phases, generally gas and liquid phases. One of the most important is the removal of acid gases, such as H2S and CO2 from natural and industrial gases using alkanolamine solutions. The primary amines, such as the monoethanolamine (MEA), are among the industrially important alkanolamines. More stringent regulations governing the emission of toxic gases from industrial sources have evoked an increasing demand for new and efficient abatement techniques. In the last years, the electrochemical method is being used to study the mass transfer and measure the mass transfer coefficient (Kleifges et al., 1997; Oduoza and Wragg, 2000; Vilar and Couret, 1999; Couret, 2001; Verma and Rai, 2003).
Some requirements must be considered in order to analyze the absorption process by electrochemical techniques. On the one hand, the thorough contact between the gas and the absorbent liquid (to transfer the reactant from phase gas to the liquid phase), and on the order hand, the thorough contact between the liquid phase and the solid electrode (to realize an electric current through the system). These requirements can be obtained using a bubble column with embedded electrodes.
In this work, the mass transfer measurements were carried out in a methacrylate 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 one off-center orifice for inflow liquid. The base-plate has one two off-center orifice for outflow liquid and a central orifice for inflow of gas through a porous plate of three orifices. Steel electrodes are located on internal lateral faces. Ten electrodes were used, five in each face, which were collocated ones in front of the others. The distance between each pair of electrodes was 22 cm.
Alkanolamines aqueous solutions were employed as liquid phase, in the concentration range from 0 to 1M, whereas the gas phase was pure carbon dioxide. The gas flow rate was varied between 10 and 25 L/h (2.7-6.8 h-1 normalized flow rate). All the experiments were conducted at ambient pressure and temperature conditions, and in batch regime with respect to the liquid. The level of liquid in the column was up 100 cm above the sparger.
A home-made resistivimeter working at 1kHz was employed to measure the resistance between each pair of electrodes, and the concentration of absorbed gas was calculated from the conductivity, i. e. the inverse of the resistance because the cell constant was 1 (6 cm/6 cm2). Finally, these concentration values allow to obtain the absorption rate.
References:
Couret, F. Journal of Applied Electrochemistry, 31, 193-199, (2001).
Kleifges, K-H. et al. Journal of Applied Electrochemistry, 27, 1012-1020 (1997).
Oduoza, C.F., Wragg, A.A. Journal of Applied Electrochemistry, 30, 1439-1444, (2000).
Verma, A.K., Rai, S. Chemical Engineering Journal, 94, 67-72 (2003).
Vilar, E.O., Couret, F. Canadian Journal of Chemical Engineering, 77, 855-862 (1999)
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 13:30 to 15:00, in session Distillation, Absorption & Extraction (T2-10P).
