Preparation of a non-hydrothermal NaA zeolite membrane and defect elimination by vacuum-inhalation repair method

- The zeolite membrane is obtained by non-hydrothermal combined dip-coating method.
- The non-crystal geopolymer gel transformed into NaA zeolite after cured at 60 °C.
- The vacuum inhalation repair method improved the separation factor of membrane.
- The repair method is suitable for membranes with mesopore or macropore defects.

This work reports the preparation of a non-hydrothermal NaA zeolite and its stainless steel-supported membrane using geopolymer-gel-thermal-conversion (GGTC) combined with a dip-coating method, which does not require hydrothermal processing. The XRD and high-resolution transmission electron microscopy (HRTEM) analyses indicate that the 1.1Na2O-Al2O3-2SiO2-8H2O geopolymer gels cured at 25 °C nucleate in the geopolymerization stage. After heat-treatment above 60 °C, the crystal nuclei in the geopolymer gels continue to grow and transform into NaA zeolite crystals with good crystallinity. To improve the separation efficiency of the stainless steel-supported NaA zeolite membrane in the pervaporation (PV) process of an ethanol/water mixture, this paper reports a simple vacuum-inhalation repair method for non-zeolitic pores or other defects in the NaA zeolite membrane. After vacuum-inhalation repair of the non-hydrothermal NaA zeolite membrane with sodium alginate solutions and CaCl2 solutions, in that order, the repaired NaA zeolite membrane exhibited a separation factor that was enhanced approximately 7- to 14-fold over that of the unrepaired NaA zeolite membrane.