Modeling Chemical Separations in All-Silica Zeolite Crystals and Spiral-Wound Membrane Modules

Abstract

Nanoporous, crystalline materials have the potential to separate chemical mixtures with unprecedented efficiencies in membrane and adsorption-based separations. In order to implement them in industrial processes, modeling and simulation is essential to understand and exploit the underlying complex phenomena. In the first portion of this work, Monte Carlo molecular simulations are used to aid in the understanding of adsorption equilibria of alcohol/water mixtures into all-silica zeolite crystals. In most cases, the simulated equilibria exhibit sufficient agreement with experiment and other molecular-level insights difficult to obtain by experiment alone. The adsorption of pentane-1,5-diol onto MFI-type zeolite exhibits high selectivity for the diol over water due to the diol's ability to form intermolecular hydrogen-bonding networks within the nanopores. This is associated with a slight change in solution concentration inducing a phase change within the nanopores from low adsorbed density to high adsorbed density. Subsequently, the good agreement observed between simulation and experiment is used to develop a combined approach for calculation of adsorption equilibria from experimental measurements. The combined approach yields solvent and solute loadings that are self-consistent with simulation alone, and allow for an assessment of the various assumptions made in the literature. While the assumption made is immaterial to the calculation at low concentrations, a negligent choice of assumption at high concentrations can lead to systematic overestimation or underestimation of calculated solute loading. In the second portion of this work, a mathematical model for a spiral-wound membrane with cross-flow is developed. The model accounts for variation of feed and permeate-side variables in two dimensions, and yields good agreement with experiments performed for the separation of O2/N2 mixtures. The results from the simulations are used to understand the transport phenomena occurring in both dimensions, and the importance of the pressure drop along the permeate channel is realized. As an application of the model, a techno-economic analysis is performed for the propane/propylene separation from a polymerization reactor purge. This analysis identifies a regime in which a profitable investment can be made for a given membrane cost. Taken together, this dissertation contributes toward a better understanding of adsorption equilibria and membrane separation processes, leading to reduced risks in their industrial implementation.