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Coupling between mass transfer and chemical reactions during the absorption of CO2 in a NaHCO3-Na2CO3 brine : experimental and theoretical study

par Wylock, Christophe ;Colinet, Pierre ;Cartage, Thierry ;Haut, Benoît
Référence Chemical Reaction Engineering XI : Green Chemical Reactor Engineering (CRE XI)(26-31 août 2007: Bilbao (Espagne)), Chemical Reaction Engineering XI : Green Chemical Reactor Engineering (CRE XI)
Publication Publié, 2007-08-26

Abstract de conférence

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Résumé :

A key step of the refined sodium bicarbonate (BIR) production by the Solvay process consists in the gas-liquid mass transfer of CO2 from a gaseous mixture of CO2 and air to a NaHCO3-Na2CO3 brine. This transfer takes place in 20-m high and 2.5-m wide bubbles columns (the BIR columns). The gas phase leaving the columns still contains an important quantity of CO2 (molar fraction close to 0.2). It causes a huge CO2 emission to the atmosphere (the equivalent of 150 Smarts driving at 100 km/h, for a single column). Several chemical reactions take place during the CO2 absorption in the liquid. These reactions modify (accelerate) the gas-liquid mass transfer rate. This work aims to reach a fundamental understanding of the coupling between the gas-liquid transfer of CO2 and the resulting chemical reactions in the liquid phase. A mathematical modelling of this coupling is first developed. The equations of the model are solved numerically, using Femlab. This model is validated against experimental results. Two different approaches are followed. First, a stirred tank reactor is filled with a NaHCO3-Na2CO3 brine and pure CO2 bubbles are dispersed through the liquid. The dissolved CO2 concentration and pH are measured against time. The diffusion-reaction model is incorporated into a model of the stirred tank reactor, developed with Matlab. Experimental results are compared to the simulations of this model. On the other hand, an original experimental device is set up. A NaHCO3-Na2CO3 brine is put in contact with gaseous CO2 in a Hele-Shaw cell (small gap between two transparent plates). The time evolution of the CO2 concentration profile in the liquid phase near the gas-liquid interface is followed using a Mach-Zehnder interferometer. The developed and validated diffusion-reaction model will be used in a close future in order to optimize the CO2 transfer in the BIR columns. As a direct consequence of this optimization, the CO2 emission of the BIR production will hopefully be reduced.