Splitting Mono- and Dibranched Alkane Isomers by a Robust Aluminum-Based Metal–Organic Framework Material with Optimal Pore Dimensions

Abstract

The separation of alkanes with different degrees of branching, particularly mono- and dibranched isomers, represents a challenging yet important industrial process for the production of premium gasoline blending components with high octane number. We report here the separation of linear/monobranched and dibranched alkanes through complete molecular sieving by a robust aluminum-based MOF material, Al-bttotb (H3bttotb = 4,4′,4″-(benzene-1,3,5-triyltris­(oxy))­tribenzoicacid). Single- and multicomponent adsorption experiments reveal that the material adsorbs linear and monobranched alkanes, but fully excludes their dibranched isomers. Adsorption sites of alkanes within the MOF channels have been identified by single-crystal X-ray diffraction studies, and the adsorption mechanism was explored through computational calculations and modeling. The highly selective adsorption of the MOF should be attributed to its optimal pore dimensions.

Designer Metal–Organic Frameworks for Size‐Exclusion‐Based Hydrocarbon Separations: Progress and Challenges

“…More recently, Yu et al reported the total separation of dibranched alkanes from their linear and monobranched isomers at ambient temperature and pressure by a rigid MOF, Al(bttotb) (H 3 bttotb = 4,4′,4″‐(benzene‐1,3,5‐triyltris(oxy))tribenzoicacid). [ 109 ] It has 1D channels with a diameter of ≈5.6 Å, comparable to the kinetic diameter of monobranched alkanes. The MOF adsorbs linear and monobranched hexanes with relatively fast kinetics at room temperature, but fully excludes dibranched 22DMB.…”

Two-Effects-in-One: Kinetic Quantum and Molecular Sieving Effect in a Robust-Flexible [Th6Co2] Cage for both Isotope and Isomer Separation

“…Accordingly, we then measured C 6 vapour adsorption at 30 °C and the results were shown in Figure 3e. Ultrahigh n-HEX adsorption capacity up to 209 mg/g was observed, exceeding most top level materials for this task [45][46][47][48][49][50][51][52][53] such as Al-bttotb (151 mg/g), 49 Ca-tcpb (150 mg/g), 48 MIL-53(Fe)-(CF 3 ) 2 (32 mg/g), 47 and Fe 2 (BDP) 3 (113 mg/g) 46 . By contrast, no adsorption and very low adsorption of 10.7 mg/g was observed for the dibranched isomers of 22DMB and 23DMB, owing to MS effect, since the kinetic diameter of dibranched isomers is far larger than the window of [Th 6 Co 2 ] cage.…”

“…In the literature, all reports are focused on the separation of C 6 vapour via multicomponent column breakthrough measurements. [45][46][47][48][49][50][51][52][53] From the viewpoint of saving energy, the direct separation of C 6 isomer from liquid mixture is more desirable, as these C 6 isomers are essentially liquid at room temperature with boiling point more than 58°. In each case, the activated Th-Co-Cage-1 samples were rst immersed in commercially binary mixture.…”

Upgrading Octane Number of Naphtha by a Robust and Easily Attainable Metal‐Organic Framework through Selective Molecular Sieving of Alkane Isomers

“…However, none of these materials are capable of separating monobranched alkanes and their dibranched isomers with high efficiency. We recently reported two MOF‐based splitters, Ca(H 2 tcpb) [14] and Al‐bttotb, [15] that separate monobranched and dibranched alkanes through selective molecular sieving. Nevertheless, they are both built on relatively complicated linkers, making their scale‐up synthesis difficult/expensive.…”