Multistep-catalyzed organosilica membranes with engineered microstructure for pervaporation separation of organic solvents

The industrial synthesis of Methyl tert-butyl ether (MTBE) typically requires the addition of excess methanol (MeOH) for catalytic reaction. However, the efficient separation of pure MTBE from MeOH/MTBE azeotropic mixtures has remained a research focus in this field. Membrane based separation technology has shown high promise in the purification of organic solvents. Herein, 1,2-bis(triethoxysilyl)ethane (BTESE) derived organosilica membranes with different sub-nanopore structures were fabricated by modulating the acidic/alkaline environment during the sol-preparation process. The sol sizes and the resultant membrane structure were precisely tailored by adjusting the acidic and alkaline environment within the organosilica sols. The resulting materials synthesized via sole acid catalysis, acid-base two-step catalysis, and acid-base-acid three-step catalysis were designated as BTESE-A, BTESE-AB, and BTESE-ABA, respectively. A series of characterization were adopted for probing the networks from the perspectives of sol particle size, functional group and segment cross-linking structure. The separation performance of these membranes for MeOH/MTBE mixtures was systematically investigated. BTESE membranes fabricated under different sols exhibit distinct separation performance. Investigation revealed that altering the catalytic conditions during sol preparation effectively modulates the sol size, thereby influencing the separation performance of the resulting pervaporation membranes. The permeation flux of BTESE-A, BTESE-AB, and BTESE-ABA membranes were 1048.8, 1543.8, and 1482.1 g·m −2 ·h −1 , and the MeOH concentration in permeated side was 99.95%, 96.43% and 99.58%, respectively, for MeOH/MTBE mixtures (15/85) at 40 °C. Notably, compared with the BTESE-A and BTESE-AB membranes, the BTESE-ABA membrane exhibits superior permeation flux and separation factor, making it the optimal choice for MeOH/MTBE separation. More importantly, BTESE-ABA membrane also shows high promise in MeOH/other organic solvents separations. This study provides theoretical guidance for the regulation of sol sizes and offers a more effective separation strategy for the efficient separation of organic solvents mixtures.