Separation of C₆ Paraffins Using Zeolitic Imidazolate Frameworks: Comparison with Zeolite 5A

Abstract

The separation of paraffin isomers is a very important topic in the petrochemical industry. Zeolite 5A is industrially used to sieve alkane isomers, but its pore size does not allow the separation of monobranched and dibranched alkanes by a kinetic mechanism. In this publication, we compare three ZIF materials in the separation of C6-paraffin isomers: ZIF-8, ZIF-76, and a new material called IM-22. The performance of the materials is evaluated by a breakthrough curve of binary mixtures of n-hexane, 3-methylpentane, and 2,2-dimethylbutane. We show that ZIF-8 is a very attractive alternative to zeolite 5A because it exhibits a high (kinetic) selectivity for the adsorption of linear alkanes and at the same time a high adsorption capacity. The new material IM-22, a ZIF with CHA topology, seems to be particularly suited for the separation of mono-and dibranched paraffin isomers.

Polymer Transport Properties

“…Pure ZIF-8 membranes (209-212) fabricated on ceramic or polymer supports as well as ZIF-8-enabled mixed-matrix membranes (196,213,214); both show attractive productivity and selectivity for separating propylene/propane mixtures. While ZIF-8 demonstrates excellent diffusion selectivities for C 4 and heavier hydrocarbon mixtures, its diffusivity is usually unattractive for practical separation applications unless performed at elevated temperatures (199,200). IR microscopy was employed to study diffusion of CO 2 , CH 4 , C 2 H 4 , and C 2 H 6 in ZIF-8 by Caro and co-workers (204,205), and the results are in good consistency with the macroscopic method at low surface concentrations.…”

Investigating the influence of diffusional coupling on mixture permeation across porous membranes

“…7a) from crystallographic data is 3.26Å, but the lattice framework flexibility is such that molecules as large as 2,2 dimethylbutane can be transported for one cage (approximately 1170Å 3 in size) to an adjacent cage [23,31,32]. By contrast, lattice flexibility has little influence on the inter-cage hopping across narrow 8-ring windows of CHA, LTA, ITQ-29, SAPO-34, and DDR zeolites [33,34].…”

Synthesis of ZIF-8 from recycled mother liquors

“…ZIF-8 with its thermal stability up to 400°C and BET surface area of 1300-1600 m 2 /g with a pore size of 0.34 nm [2] has also potential in separation processes by membrane [3][4][5][6] or adsorption processes [7].…”