Large-Scale Computational Screening of Zeolites for Ethane/Ethene Separation

Abstract

Large-scale computational screening of thirty thousand zeolite structures was conducted to find optimal structures for separation of ethane/ethene mixtures. Efficient grand canonical Monte Carlo (GCMC) simulations were performed with graphics processing units (GPUs) to obtain pure component adsorption isotherms for both ethane and ethene. We have utilized the ideal adsorbed solution theory (IAST) to obtain the mixture isotherms, which were used to evaluate the performance of each zeolite structure based on its working capacity and selectivity. In our analysis, we have determined that specific arrangements of zeolite framework atoms create sites for the preferential adsorption of ethane over ethene. The majority of optimum separation materials can be identified by utilizing this knowledge and screening structures for the presence of this feature will enable the efficient selection of promising candidate materials for ethane/ethene separation prior to performing molecular simulations. ■ INTRODUCTIONEthene is one of the largest production chemical products today due in large part to the demand for polyethylene. Global annual production capacity exceeds 152 million tonnes and is projected to grow by 20% over the next 5 years. 1 Large-scale production of ethene involves separating it from other light hydrocarbons, including methane, ethane, and propane. To achieve acceptable purity, these compounds are typically separated using a series of low-temperature distillations at high pressure. 2 The low relative volatility of the ethane-ethene mixture makes the separation energy and capital intensive. Several other approaches for separating light olefins and paraffins have been proposed in the literature. These include physical and chemical absorption processes, extractive distillation, membranes, and adsorption onto porous materials. 2−8 The similarity of molecular sizes in these mixtures contributes to the difficulty of the separation. Adsorbent materials can potentially provide better separation of these components. By interacting more strongly with one component of the mixture, an adsorbent may provide an adsorbed mixture richer in one component or limit the diffusion of one component for a kinetic separation. 3 Previous efforts with porous materials have looked into both physically adsorbing materials, such as zeolites, 7 and chemically adsorbing materials, such as metal−organic frameworks (MOFs) with open metal sites. 5,6 In addition, zeolitic imidazolate frameworks and specifically ZIF-8 has been investigated as a potential candidate for performing kinetic separation via the enhanced diffusivity of ethene compared to ethane within the material. 4 For this work, we focus on zeolite structures as a possible candidate for adsorption-based separation and focus on ethane/ethene separation.Zeolites are porous aluminosilicates with pore diameters on the order of 0.5 to 5 nm. While roughly 200 zeolite topologies have been identified in experiments, only a handful of these materials are used on an industrial scale...

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