Rapid synthesis of faujasite/polyethersulfone composite membrane and application for CO2/N2 separation

Abstract

Rapid growth of faujasitic membranes on polyethersulfone support was investigated. The membrane growth occurred in a novel zeolite reactor, where the extent of supersaturation of the synthesis gel 8.5 Na2O: 1 Al2O3: 10.9 SiO2: 487H2O was controlled by removal of water from the reaction system. The gel remaining after removal of half the water from the reaction was isolated and used as a coating on the polymer support. Along with this reactive gel, coating of a uniform film of nanozeolite seed deposition on the porous polymer support was also investigated. Eight variations of the gel-seed combinations were examined for membrane growth. The optimal membrane synthesis condition was defined as coating of the PES support by a nanozeolite seed layer of 250–300 nm thickness, and then introduction into the reactor after water is removed, and continuing the reflux process with reintroduction of the water for another hour. Further characterization included X-ray diffraction, optical microscopy and detailed scanning electron microscopy. Leak test of a dye through the membrane and the mechanical stability of the membrane via a tape test were performed. The transport properties of these membranes for CO2/N2 separation were evaluated. There were three ways the membrane samples were prepared and handled for transport measurements. Prior to transport measurements, all samples were covered with PDMS. Initial attempts placed the seeded PES support into the growth reactor. These samples all exhibited poor transport properties with CO2/N2 selectivities less than 10. For the second group, the seeded PES supports were placed in a holder that ensured flatness during the zeolite growth process. There was significant improvement in the transport properties, with half of the membranes exhibiting CO2/N2 selectivity greater than 20. With the third group of membranes also grown in the flat geometry, care was taken to keep them flat through all the subsequent steps including washing, drying and putting on the PDMS layer. Transport properties improved further. The twelve membranes in this group exhibited CO2/N2 separation factor in the range of 16–110 with CO2 permeance in the range of 180–2000 GPU (1 GPU = 3.3 × 10−10 mol/m2·Pa).