Nonmonotonic Rayleigh-Taylor Instabilities Driven by Gas–Liquid CO₂ Chemisorption

Abstract

Density variations induced by gas absorption in reactive aqueous solutions often trigger buoyancy-induced motions, generally in the form of plumes monotonically sinking into the bulk liquid and enhancing the absorption rate. Here, we contrast two types of CO 2 -absorbing alkaline solutions, studying their dynamics inside a vertical Hele-Shaw cell by interferometry. While the first one indeed behaves as expected, the second one leads to a quite unusual oscillatory (phase-slipping) dynamics of convective plumes, which moreover does not lead to a significant transfer enhancement. Thanks to a simplified model of momentum and species transport, we show that this particular dynamics is related to a non-monotonic density stratification, resulting in a stagnant layer close to the interface. Conditions for this to occur are highlighted in terms of the ratios of species' diffusivities and their contribution to density, a classification deemed to be useful for optimizing chemisorption (e.g. for CO 2 capture or sequestration) processes.

Chemical control of dissolution-driven convection in partially miscible systems: theoretical classification

“…Even if the density stratification is initially buoyantly stable, a hydrodynamic instability can develop in the gravity field if the dissolution modifies the density of the host phase. This situation can happen in solutions separated by a semi-permeable membrane 1,2 or in biphasic systems, with the dissolving phase being for instance liquid 3,4 , solid 5 , or gaseous [6][7][8][9][10][11][12][13] . Dissolution-driven convection has recently gained much interest in the context of carbon dioxide (CO 2 ) capture or sequestration [14][15][16] .…”

Experimental and numerical analysis of buoyancy-induced instability during CO2 absorption in NaHCO3–Na2CO3 aqueous solutions

“…It should be noted that a similar criterion, restricted to the case ν B = ν C = 1, has been presented in Wylock et al (2014). Although the criterion presented in this paper can be rigorously applied only in the case of an instantaneous reaction taking place at the interface, it is worth to mention that it is verified in all the cases considered in this paper (this can be verified thanks to values presented in Table 1).…”

“…This absorption, initially driven by the coupling between diffusion and chemical reactions, eventually leads to the apparition of a peculiar gravitational instability with nonmonotonic dynamics, and liquid plumes generated at some distance from the gas-liquid interface (Wylock et al, 2014). Considering that this instability is triggered by a Rayleigh-Taylor like mechanism, a two-dimensional model, coupling diffusion, chemical reaction and convection, is proposed to simulate the onset and the dynamics of such an instability.…”

“…Recently, the carbon dioxide (CO 2 ) absorption in aqueous alkaline solutions inside a Hele-Shaw cell became more and more studied in the framework of the CO 2 sequestration in deep saline aquifers (Loodts et al, 2014a,b;Javaheri et al, 2010;Kim and Choi, 2012;Kim, 2015;Riaz et al, 2006;Rongy et al, 2012;Wylock et al, 2008Wylock et al, , 2011Wylock et al, , 2013Wylock et al, , 2014. Using these HeleShaw cells, many of these studies have indeed highlighted the occurrence of a Rayleigh-Taylor (RT) instability when CO 2 is absorbed in alkaline solutions, resulting from an unstable liquid density stratification during the absorption.…”

“…-to develop a mathematical model of the transport phenomena taking place in a Hele Shaw cell during the absorption of CO 2 in an initially quiescent liquid, considering a generic chemical reaction CO 2 + ν B B → ν C C in the liquid phase, without any particular assumption on its reaction rate (contrary to what we have done for instance in Wylock et al (2014));…”