Molecular dynamics simulations of binary mixtures of methane and hydrogen in zeolite A and a novel zinc phosphate

Abstract

Molecular dynamics simulations have been used to study binary mixtures of hydrogen and methane in two molecular sieve structures, zeolite NaA and a novel zinc phosphate molecular sieve, Na₃ZnO(PO₄)₃, which has a pore size tuned to light gas separations. Simulations were run at high temperature, T = 500 °C. Equimolar mixtures of methane and hydrogen in both molecular sieve structures were simulated at loadings of 2–16 molecules per unit cell. Self-diffusion coefficients were calculated using the Einstein relationship. Hydrogen was found to have higher self-diffusion Coefficients than methane in both the molecular sieve structures under study. However, in the zinc phosphate molecular sieve the methane remained immobile, allowing for purification and separation of hydrogen, whereas in Zeolite A the methane experienced appreciable cage-to-cage motion.