High-quality NaA zeolite membranes were synthesized using hydrothermal treatment. To obtain high-quality nanoporous inorganic membranes applicable to dehydration of natural gas, LTA zeolite membranes were synthesized and modified in three stages. The morphology and structure of as-synthesized seeds and membranes were characterized via scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and Energy Dispersive X-ray Spectroscopy (EDX). The performance of membranes was evaluated in permeation of water vapor/methane. In the first stage, NaA zeolite membranes were synthesized using secondary growth method via concentrated gel, and showed ideal selectivity of 11 for water vapor/methane. In the second stage, NaA zeolite membranes were synthesized using clear gel, while the effect of synthesis temperature on the membrane structure and performance was also investigated. At synthesis temperature of 80 degrees C, which was chosen as the optimum temperature, the ideal selectivity of 14 was obtained for water vapor/methane. In the last stage, the substrate of LTA zeolite membranes was modified via chlorination, and NaA zeolite membranes were synthesized on chlorinated alumina substrates. Thionyl chloride was used as chlorinating reagent. The membranes synthesized on chlorinated substrates showed ideal selectivity of 26 for water vapor/methane. Moreover, KA zeolite membranes were prepared by ion-exchanging the zeolite layer of the substrate-modified membranes. Ideal selectivity of 37 was observed for water vapor/methane for substrate-chlorinated KA membranes. (C) 2015 Elsevier Ltd. All rights reserved.