Structural modelling of silicon carbide-derived microporous carbon and its application in CO2 capture and separation of volatile gases from moist streams

Abstract

The adsorption of volatile gases in microporous materials has wide applications in gas separation, including CO 2 capture and natural gas dehydration. It has also attracted a large amount of attention for energy storage applications such as electrochemical energy storage in supercapacitors and adsorptive methane/hydrogen storage. Nevertheless, the development of efficient gas storage/separation technologies requires fundamental knowledge of fluid transport in narrow pore spaces, since the behavior of fluids under tight confinement differs markedly from that in the bulk.Along with the rapid development of a broad range of new microporous materials such as carbide derived carbons (CDCs), carbon nanotubes and metal-organic frameworks, there has been wide growth in their potential applications, especially in emerging nanotechnologies, thus the development of this understanding has become even more crucial.This study contributes to such understanding by investigating adsorption and transport of industrially important gases in the microporous structure of silicon carbide-derived carbon (SiC-DC). Initially, a realistic model of silicon carbide-derived carbon is developed using the hybrid reverse Monte Carlo (HRMC) method, which reliably represents the atomistic structure of the actual carbon sample and successfully predicts its gas adsorption and fluid transport properties.Following this part, structural characteristics of the constructed model are investigated using different computational methods to reveal the underlying correlations between such characteristics and the behavior of fluid transport in the highly disordered structure of SiC-DC. This study also explores adsorption and self-diffusion of fluid molecules in the amorphous SiC-CD model, providing more insight into the internal resistances and energy barriers to gas diffusion. The strong influence of structural heterogeneity arising from the disordered nature of the microporous carbon on molecular diffusion is also examined here using a range of computational techniques. The computational methods employed include molecular dynamics (MD) simulation, nudged elastic band (NEB) method and analysis of the free energy map of the system. It is shown that disordered structure of SiC-DC has larger energy barriers to diffusion of carbon dioxide, rather than methane despite smaller molecular size of CO 2 . It is also demonstrated that activation energy barriers for methane obtained from MD simulation are in remarkable agreement with that of macroscopic kinetic uptake at low loading, which is an indication of accuracy of the HRMC constructed model in capturing internal resistances and constrictions of the actual sample. However, quasi elastic neutron scattering (QENS) measurements suggests a smaller activation energy barrier for methane compared to the results obtained from MD simulations and macroscopic kinetic uptake experiments, which is due to the much smaller length scale in QENS compared to the macroscopic length scale. IIIDue to the significance of water a...