Activity Coefficients in the Adsorbed Phase

In the processing industries, distillation is the most common technology for separation of mixtures containing water and alcohols Due to the formation of water/alcohol azeotropes, the production of pure alcohols requires the addition of entrainers, such as cyclohexane, that alter the vapor/liquid equilibrium. The recovery of the entrainer requires an additional distillation processing step, placing additional energy demands because of vapor/liquid phase transformations in condensers, reboilers and solvent recovery sections. For background refer to my papers Krishna, R. Highlighting Diffusional Coupling Effects in Ternary Liquid Extraction and Comparisons with Distillation. Ind. Eng. Chem. Res. 2016, 55, 1053-1063. https://doi.org/10.1021/acs.iecr.5b04236. Krishna, R. Highlighting Multiplicity in the Gilliland Solution to the Maxwell-Stefan Equations Describing Diffusion Distillation. Chem. Eng. Sci. 2017, 164, 63-70. https://doi.org/10.1016/j.ces.2017.01.060. The use of membrane permeation devices in hybrid distillation-membrane processing schemes offers energy-efficient alternatives to azeotropic and extractive distillation operations in production of purified alcohols. The membranes may be constructed as thin films of zeolites (e.g. CHA 1-3, DDR, LTA, MFI, FAU or zeolitic imidazolate frameworks (ZIFs). There are strong non-idealities in mixture adsorption due to hydrogen bonding and molecular clustering. I discuss the RAST modelling of mixture adsorption. Consult our paper Krishna, R.; van Baten, J. M. Fundamental Insights into the Variety of Factors that Influence Water/Alcohol Membrane Permeation Selectivity J. Membr. Sci. 2024, 698, 122635. https://doi.org/10.1016/j.memsci.2024.122635. Krishna, R.; van Baten, J. M. How Reliable is the Real Adsorbed Solution Theory (RAST) for Estimating Ternary Mixture Equilibrium in Microporous Host Materials? Fluid Phase Equilib. 2024, 114260. https://doi.org/10.1016/j.fluid.2024.114260. Krishna, R. Elucidation and Characterization of Entropy Effects in Mixture Separations with Micro-porous Crystalline Adsorbents. Sep. Purif. Technol. 2019, 215, 227-241. https://doi.org/10.1016/j.seppur.2019.01.014.