Influence of the structure of mesoporous adsorbents on transport properties

The transport of caffeine through columns filled with mesoporous silica was studied by liquid chromatography. The mass transfer parameters were measured by modelling the band broadening of the chromatograms. The experimental height equivalent to a theoretical plate (HETP) data were analysed using the general rate model (GRM) in order to determine the effective diffusion coefficient of caffeine in porous particles. Samples are characterized by gas adsorption for pore size determination, whereas the topological tortuosity of the porous particles was determined by electrical measurements. The effective pore diffusion coefficient through porous particles was modelled with a good accuracy by taking into account that both porosity and tortuosity depend on the ratio between the size of the molecule probe and the pore size. This model has been used to estimate the contribution of the surface diffusion coefficients of caffeine which appears to be small for this system.

.Figure optionsDownload as PowerPoint slideResearch highlights
► A new model has been proposed to evaluate the effective pore diffusion though porous media.
► This model takes into account that particle tortuosity depends on the molecule size.
► Better agreement is observed between the new model and data obtained using caffeine in different methanol/water solvents with two mesoporous silicas.