Separation of Branched Alkanes Feeds by a Synergistic Action of Zeolite and Metal‐Organic Framework

Abstract

Zeolites and metal‐organic frameworks (MOFs) are considered as “competitors” for new separation processes. The production of high‐quality gasoline is currently achieved through the total isomerization process that separates pentane and hexane isomers while not reaching the ultimate goal of a research octane number (RON) higher than 92. This work demonstrates how a synergistic action of the zeolite 5A and the MIL‐160(Al) MOF leads to a novel adsorptive process for octane upgrading of gasoline through an efficient separation of isomers. This innovative mixed‐bed adsorbent strategy encompasses a thermodynamically driven separation of hexane isomers according to the degree of branching by MIL‐160(Al) coupled to a steric rejection of linear isomers by the molecular sieve zeolite 5A. Their adsorptive separation ability is further evaluated under real conditions by sorption breakthrough and continuous cyclic experiments with a mixed bed of shaped adsorbents. Remarkably, at the industrially relevant temperature of 423 K, an ideal sorption hierarchy of low RON over high RON alkanes is achieved, i.e., n ‐hexane ≫ n ‐pentane ≫ 2‐methylpentane > 3‐methylpentane ⋙ 2,3‐dimethylbutane > isopentane ≈ 2,2‐dimethylbutane, together with a productivity of 1.14 mol dm −3 and a high RON of 92, which is a leap‐forward compared with existing processes.

How Important Is the Internal Hydrophobicity of Metal–Organic Frameworks for the Separation of Water/Alcohol Mixtures?

“…The pore geometry is shown in Figure S1 of the Supporting Information and is best described as being a sequence of rectangular cavities (cuboids) that are rotated 90° to each other. Previous studies on isostructural MIL-160, [Al­(OH)­(furan-2,5-dicarboxylate)], revealed that this pore geometry causes highly efficient entropy-based separations of hexane isomers at room temperature . In contrast to MIL-160, CAU-10 has a larger pore sizewhich is commensurate with the length of short-chain alcoholsand a more pronounced internal hydrophobicityconfirmed by type V water adsorption isotherms with inflection points at relative pressure of 0.08 (MIL-160) or 0.18 (CAU-10) .…”

“…Previous studies on isostructural MIL-160, [Al(OH)(furan-2,5-dicarboxylate)], revealed that this pore geometry causes highly efficient entropy-based separations of hexane isomers at room temperature. 10 In contrast to MIL-160, CAU-10 has a larger pore size�which is commensurate with the length of short-chain alcohols�and a more pronounced internal hydrophobicity�confirmed by type V water adsorption isotherms with inflection points at relative pressure of 0.08 (MIL-160) or 0.18 (CAU-10). 11 CAU-10 is thus a good candidate for studying the liquid phase separation of aqueous alcohol mixtures.…”

Simultaneous Recognition and Separation of Organic Isomers Via Cooperative Control of Pore‐Inside and Pore‐Outside Interactions

“…[ 4 ] Commonly, such mixtures are separated using adsorption methods, which consume low amounts of energy and are environmentally friendly. Numerous adsorbents, including metal–organic frameworks, [ 5 ] covalent organic frameworks, [ 6 ] MFI zeolite membranes, [ 7 ] and organic cages, [ 8 ] have been developed and investigated for the separation of small organic isomers, such as p‐xylene/o‐xylene, [ 9 ] 2‐methylpentane/3‐methylpentane, [ 10 ] 1‐bromopropane/2‐bromopropane, [ 11 ] and 1‐butane/2‐butane. [ 2c ] Despite exhibiting remarkable separation performance, most of these adsorbents lack the ability to recognize the entrapped isomer.…”

From a Metal–Organic Square to a Robust and Regenerable Supramolecular Self‐assembly for Methane Purification

“…[4] As an alternative to energyintensive traditional separation methods such as distillation, extraction, etc., adsorptive separation using porous solid adsorbents such as silica gels, zeolites, activated carbons, and metal-organic frameworks (MOFs) represents a more energy-efficient technology. [5][6][7][8][9][10] The key to address this challenging task is acquiring robust and regenerable adsorbents with optimal separation performance.…”

“…Over the past two decades, the intensive efforts on porous materials have led to the emergence of metalorganic frameworks (MOFs) and covalent-organic frameworks (COFs) which surpass traditional zeolite materials for the separation of some important gaseous mixtures. [5][6][7][8][9][10] Unfortunately, MOFs and COFs, self-assembled through coordination and covalent bonding, respectively, are difficult to be regenerated when their frameworks are destroyed by heating or adsorbing moisture. In contrast, using noncovalent intermolecular interactions allows reversibility during assembly, giving rise to regenerable porous supramolecular self-assemblies (Fresh porous supramolecular materials can be readily recovered by recrystallization of the damaged materials).…”