Effects of Pore Connectivity on the Sorption of Fluids in Nanoporous Material: Ethane and CO2 Sorption in Silicalite

Siddharth Gautam,David R Cole

doi:10.3390/chemengineering5030055

Abstract

Adsorption of fluids in nanoporous materials is important for several applications including gas storage and catalysis. The pore network in natural, as well as engineered, materials can exhibit different degrees of connectivity between pores. While this might have important implications for the sorption of fluids, the effects of pore connectivity are seldom addressed in the studies of fluid sorption. We have carried out Monte Carlo simulations of the sorption of ethane and CO2 in silicalite, a nanoporous material characterized by sub-nanometer pores of different geometries (straight and zigzag channel like pores), with varied degrees of pore connectivity. The variation in pore connectivity is achieved by selectively blocking some pores by loading them with methane molecules that are treated as a part of the rigid nanoporous matrix in the simulations. Normalized to the pore space available for adsorption, the magnitude of sorption increases with a decrease in pore connectivity. The increased adsorption in the systems where pore connections are removed by blocking them is because of additional, albeit weaker, adsorption sites provided by the blocker molecules. By selectively blocking all straight or zigzag channels, we find differences in the absorption behavior of guest molecules in these channels.

Highlights

Sorption of fluids in porous media is an essential aspect to understand the fluidsubstrate interaction [1]
We have addressed the deviations caused by the inter-crystalline space that can be found in real samples of silicalite [7] and Mg-MOF-74 [8]
To address the effects that different degrees of pore connectivity might have on the sorption capabilities of silicalite, we report grand canonical Monte Carlo (GCMC)

Summary

Introduction

Sorption of fluids in porous media is an essential aspect to understand the fluidsubstrate interaction [1]. Deviation from model pore structure can result from several factors. We have addressed the deviations caused by the inter-crystalline space that can be found in real samples of silicalite [7] and Mg-MOF-74 [8]. The models of silicalite and Mg-MOF-74 used in these computations had artificially inserted inter-crystalline space to represent a real powder sample used in the experiments. Silicalite is an all-silica analogue of ZSM-5 zeolite, and it is a model nanoporous material often used to study fluid-substrate interactions and confined fluid behavior [9,10,11,12,13,14]. With its network of ~0.55 nm diameter elliptical channels running along the crystallographic axis b and interconnected by channels of similar size running in a sinusoidal or zigzag fashion in the plane a–c, ZSM-5 provides a good opportunity to understand severe confinement with different pore geometries [12,13,14]

Methods

Results

Discussion

Conclusion