Convective dissolution in porous media is pivotal in natural and industrial processes, including the subsurface storage of carbon dioxide ( \({{CO}_{2}}\) ). Convective dissolution can arise when a denser layer forms at the interface between two fluids and strongly enhances the mass transfer rate with respect to diffusion only. Despite its significance, the interplay between diffusion, convection, and dissolution under realistic thermodynamic conditions remains largely unexplored. In a recent study (Imuetinyan et al. in Transp Porous Media 151:1687–1708, 2024), we investigated the convective dissolution of two miscible liquids in saturated transparent porous media. Here, we extend this approach to study the convective dissolution of a layer of gaseous \({{CO}_{2}}\) injected on top of a porous medium saturated with a liquid mixture of cyclohexanol and toluene within a high-pressure cell at different temperatures. In such configuration, convective dissolution is induced by the density difference between the saturating fluid and a \({{CO}_{2}}\) -rich boundary layer generated at the interface by diffusion. Different Rayleigh numbers (Ra) from \(10^{4}\, \hbox {to}\,10^5\) are investigated by modifying the \({{CO}_{2}}\) injection pressure. The system is investigated by shadowgraphy, an optical tool extremely sensitive to density variations. Then, by image variance analysis, we study the temporal evolution of the convective dissolution process, highlighting the diffusion, dissolution and convection phases, and we quantify the onset time of convection and the convective front speed. We find that the dimensionless plume velocity scales as \(\sim \sqrt{\textrm{Ra}}\) , indicating that flow regimes critically impact the convective mixing in porous media.
