Selective adsorption and separation of light hydrocarbon gases in VI/IV dipeptide crystals

Abstract

The separation of propane/propylene mixtures remains a subject under intensive research because designing cheaper, greener and sustainable processes is of paramount importance to industry. Dipeptides crystallize into several lattices displaying a variety of porosities that enable the separation of species with approximate size. In this study, we show that microporous crystals of L-Isoleucyl–l-Valine (IV) and L-Valyl-l-Isoleucine (VI) are able to distinguish between methane, propane and propylene. Adsorption equilibrium isotherms were determined and coupled with Molecular Dynamics simulations for computing diffusion and loading of binary mixtures of relevant gases in the dipeptide frameworks to obtain kinetic and equilibrium gas mixtures selectivities. It was found that although the pore diameters in both dipeptide crystals are similar, VI has a higher permselective separation of propane/propylene mixtures displaying a maximum ideal permselectivity of αP(C3H6)/C3/H8) = 1.3.