Surface silylation of silicalite membranes and their pervaporation performance for the separation of ethanol from ethanol-water mixtures

Abstract

The silicalite membrane, which is a type of zeolite membrane, has the highest hydrophobicity. An improvement in membrane selectivity would enhance the energy efficiency of the separation process. An enhancement in the hydrophobicity of silicalite membranes is possible by surface modification. Tubular silicalite membranes were hydrophobized by silylation, and their pervaporation (PV) performance for the separation of ethanol from a dilute ethanol-water mixture was investigated. The tubular silicate membranes were prepared by the secondary growth method, which consists of seeding by electrophoretic deposition and hydrothermal synthesis. Trimethylchlorosilane (TMCS), methyltrichlorosilane, propyltrichlorosilane, and 3,3,3-trifluoropropyltrichlorosilane were examined as the silylation reagents. The desired improvement in hydrophobicity and membrane performance were achieved only in case of TMCS. The contact angle increased from 20 to 130° and the PV performance improved after the silylation. A permeate EtOH concentration of 85.9 vol % with a total flux of 0.31 kg/m²·h from a 5 vol % EtOH aqueous solution at 30°C was obtained.