Experimental validation of molecular simulation of water transport across zeolite membranes of nanoscale-thickness

Syracuse University, Syracuse NY

Investigators

Abstract

Transport of a fluid in porous media is relevant to extraction of oil from the subsurface, contaminant transport in groundwater, sequestration of carbon dioxide in underground reservoirs, and desalination of seawater through a reverse osmosis membrane to produce drinking water. The porous media offers a resistance to the transport of mass. Differences in resistance between chemical species allow for separation: one component may be unimpeded or even accelerated, while another is impeded. For example, the reverse osmosis membrane is designed to transport water quite efficiently but transport salt quite inefficiently, leading to the production of purified drinking water. To optimize design, engineering transport models of flow through porous media generally treat the system using macroscopic length scales and average resistances, but generally neglect both spatial variations and specific fluid-surface interactions on the molecular scale. Molecular-scale interactions become quite pronounced when a fluid molecule is confined in a pore that is of similar molecular dimension. Models that account for molecular interactions incorporate forcefields, but have not adequately predicted experimental observations. This project will perform an experimental validation of molecular-level transport through a porous material with strong fluid-pore interactions, and for the first time, there will be a one-to-one length scale correspondence between the experimental and theoretical studies which will probe discrepancies. In this project, desalination of seawater through a zeolite membrane is the probe system, due to strong water-zeolite electrostatic interactions that are enhanced upon confinement in sub-nanometer (~0.56 nm) pores. MFI zeolites with varying aluminum composition and thickness (varying from nano- to micro-scale) will be experimentally synthesized and characterized, then transferred onto a support surface to create membranes for transport measurements in a custom-built experimental apparatus. MD simulations will be simultaneously performed for the same zeolites with varying forcefields. The aluminum content will be varied in both techniques to alter the water-zeolite interaction. The experimentally validated molecular models will provide fundamental understanding of water interaction in confined pores, and assist in the development of predictive modeling of thermodynamic properties and transport behavior of water in nano-porous materials. The project includes several outreach components, including undergraduate research projects that target under-represented minorities, a workshop for middle school female students, and a short course in computational methods for undergraduates at Syracuse University.