Separating xylene isomers by commensurate stacking of p-xylene within channels of MAF-X8.

The development of energy-efficient processes for selective separation of p-xylene from mixtures with its isomers is of vital importance in the petrochemical industries. Current industrial practice uses BaX zeolite that has high adsorption selectivity for p-xylene. Finding para-selective structures is challenging. With state-of-the-art simulation methodologies we systematically screened a wide variety of zeolites and metal-organic frameworks (MOFs). Our investigations highlight the crucial importance of the channel dimension on the separation. MAF-X8 is particularly noteworthy because the channel dimensions and geometry allow "commensurate stacking" which we exploit as a separation mechanism at saturation conditions. Due to a significantly improved capacity compared to BaX, the cycle times for p-xylene with MAF-X8 are found to be about a factor of 4.5 longer. This is expected to result in significant process improvements.