Separation of branched alkane feeds by a synergistic action of zeolite and metal-organic framework

Abstract

Zeolites and Metal Organic Frameworks (MOFs) have frequently been considered as “competitors” for the development of new advanced separation processes. The production of high quality gasoline is currently achieved through the energy demanding conventional Total Isomerization Process (TIP) that separates pentane and hexane isomers while not reaching yet the ultimate goal of a Research Octane Number (RON) higher than 92. Herein we demonstrate how an unprecedented synergistic action of two complementary benchmark materials of each family of porous solids, a commercially available zeolite, 5A and the bio-derived Al-dicarboxylate MOF MIL-160(Al), leads to a novel adsorptive process for octane upgrading of gasoline through an efficient separation of pentane and hexane isomer mixtures into fractions of low and high research octane number (RON). 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 pentane and hexane linear isomers by the molecular sieve zeolite 5A. The adsorptive separation ability of this MOF/zeolite duo was further evaluated under industrial operating 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, and an exceptional ideal productivity of 1.14 mol.dm-3 is attained for a final high RON isomers product of 92, which corresponds to a substantial leap-forward when compared with existing processes.

Pore Aperture Control Toward Size‐Exclusion‐Based Hydrocarbon Separations

“…[1,6,7] The industrial production of hexanes results in a mixture of five isomers in which the dibranched isomers 2,2-dimethylbutane (22DMB) and 2,3-dimethylbutane (23DMB) are the most desirable in the production of high-quality gasoline due to their high research octane numbers (RONs) of 94 and 105, respectively. [8] On the other hand, the linear nonbranched n-hexane isomer (nC6) has an RON of 30 which is separated from the mixture and recycled using an isomerization reactor. [9] The remaining mixture contains the monobranched isomers 2-methylpentane (2MP) and 3-methylpentane (3MP) which have RONs of 74 and 75, respectively, along with the di-branched isomers.…”

“…[9] The remaining mixture contains the monobranched isomers 2-methylpentane (2MP) and 3-methylpentane (3MP) which have RONs of 74 and 75, respectively, along with the di-branched isomers. [8,10] Further purification of this mixture to remove the monobranched isomers can be carried out using distillation, thus leaving behind the higher value mixture of dibranched isomers. Zeolite 5 Å is commonly used for separating linear and branched C6 isomers on industrial scale.…”

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

“…Methane purification is of primary importance because it not only produces highly pure methane but also extracts C 2 /C 3 ‐hydrocarbons as important raw materials in petrochemical industry [4] . As an alternative to energy‐intensive 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 [5–10] . 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 metal–organic frameworks (MOFs) and covalent–organic frameworks (COFs) which surpass traditional zeolite materials for the separation of some important gaseous mixtures [5–10] . 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.…”