Enabling Kinetic Light Hydrocarbon Separation via Crystal Size Engineering of ZIF-8

Abstract

Recent increases in shale gas production provide an excellent opportunity for advancements in the energy-efficient separation of natural gas liquids because these are increasingly used as fuel sources and chemical feedstocks. Current fractionation schemes generally involve cryogenic distillation of C 1 −C 4 hydrocarbons and are extremely energyintensive. Here, we describe the first steps toward a lowerenergy, kinetic pressure-swing-adsorption cycle for the separation of ethane, propane, propylene, and butane using ZIF-8 as a diffusionally selective adsorbent. Crystal engineering techniques were employed to control the diffusive time scale of the separation, allowing for multiple separations using the same adsorbent within reasonable process times. Equimolar separation of ethane/propane mixtures at 293 K exhibited separation factors of 2.7 in the gas phase under nonoptimized conditions, which enhances the concentration of the feed mixture to 75 mol % propane. The separation performance was shown to improve to 3.8 at lower temperatures (81 mol % propane), which is attributed to differences in the activation energy of permeation of the two components. Propane/butane mixtures demonstrated a lower diffusive selectivity and almost negligible enhancement, while propylene/propane showed enhancement beyond ethane/propane due to a strong diffusive selectivity and sorption selectivities closer to unity. Single-component adsorption and diffusion results were incorporated into a computational model of the system and shown to be in relatively good agreement with the experimental values. The model was used to predict the separation system performance and recovery at various temperatures.

ZIF-67 as silver-bullet in adsorptive propane/propylene separation

“…Adsorption based processes, such as Pressure Swing Adsorption (PSA), may present an alternative to dethrone the traditional energy-demanding methods. The tunability of the sorbents should provide a suitable procedure to perform light alkanes/alkenes separation [2,[4][5][6]. Zeolitic Imidazolate Frameworks (ZIFs) are a relatively new class of Metal Organic Frameworks (MOFs), combining the well-defined structures and adjustable pore sizes and the enormous surface area of MOFs with the high hydrothermal/chemical stability of zeolites.…”

Separation of butane isomers using a novel ZIF-8 slurry with extremely high efficiency: from laboratory study to industrial pilot test

“…On the other hand, the higher n-butane uptake on ZIF-8 at lower pressure as shown in Fig. 2(a) and the high n-butane desorption heat ( ~ 20-32 kJ/mol 27 ) indicates that a TSA but not a PSA technique should be adopted when using ZIF-8 as an adsorbent. The heat transfer and heat integration will then be a challenging issue for a fixed-bed as heat conductivity is low for a porous media.…”

Transport Diffusion of Linear Alkanes (C5–C16) through Thin Films of ZIF-8 as Assessed by Quartz Crystal Microgravimetry

“…As described and discussed below, we find that (a) measured uptake capacities are in good agreement with expectations based on fully guest-accessible MOF pores, (b) initial transport dynamics are governed by guest diffusion through MOF crystallites rather than by rates of entry into films at the MOF/vapor permeation, and (c) transport times can be substantially shortened (without changes in diffusivity) by replacing closely packed films of nanocrystallites (dominant 1D intracrystalline diffusion) with loosely packed, electrophoretically deposited films , (dominant 3D intracrystalline diffusion). While not being developed here, the combined results have potentially favorable implications for the development of kinetic separation schemes ,− for closely related and otherwise challenging to separate, linear hydrocarbons.…”