Ag+ anchored on sulfonic functionalized mesoporous silica towards efficient liquid phase Olefin-Paraffin separation

Abstract

Separation of olefin-paraffin gas mixtures has attracted enormous research endeavors as a replacement of the currently used, energy-intensive cryogenic distillation process, while liquid phase olefin-paraffin separation has remained less exploited. The challenge lies in that the difference in physical properties between C6-C8 olefins and paraffins tend to diminish as C = C bond fraction becomes smaller when alkyl chain grows longer. On the other hand, satisfactory adsorption capacity for these bulky molecules requires the use of porous materials beyond microporosity, i.e., mesoporous materials with large pore volume and size, which, nonetheless, lack adsorption selectivity to guarantee satisfactory separation factors. Here, we demonstrate that functionalization of mesoporous silica MCM-41 surface by –COO-, -Ph-SO3- and -SO3- functional groups can be used to immobilize Ag+, which turns the otherwise unselective porous solid into an olefin selective molecular sieving material suitable for liquid phase binary mixture separations. The results underline that ionically anchored Ag+ with intact complexation orbitals outperform coordinatively immobilized Ag+ (on –NH2 or -SH groups), in terms of anti-leaching property, olefin separation factor, as well as recyclability. Small mesopore size can boost olefin adsorption selectivity as accommodated olefins compressed the available space for access of paraffins. Adsorption evaluation for binary C6 to C8 olefin-paraffin mixtures separations discloses that the total adsorption capacity declines, while the separation factor increases, with increasing molecule size.