This study demonstrates the successful implications of hydrothermal and secondary growth techniques for synthesis of high property Silicalite-1 and ZSM-5 zeolites. To prepare ZSM-5 a membrane, the nanosized Silicalite-1 powder was first synthesized as a seed from a clear solution. The effects of variations in the synthesis time, aluminum content and the number of seeding on the characteristics of ZSM-5 zeolite were studied. It was found that three subsequent seeding steps enhance significantly quality of membranes surface morphology which led to regular growth of ZSM-5 crystals. The zeolite membranes produced were characterized using SEM, TEM, TGA, DSC and N2 adsorption techniques. At room temperature, permeance of CO2 was higher than those of N2 and CH4 and the ideal selectivities for CO2/N2 and CO2/CH4 were 9.6 and 6.5 at mean pressure of 0.5 bar, respectively. Improved zeolite membrane was fabricated by dip-coating of membrane in PDMS solution. Ideal selectivity of produced composite membrane for CO2/N2 and CO2/CH4 was obtained as 21 and 14.2, respectively. Ideal selectivity of CO2/N2 and CO2/CH4 and CO2 permeance decreased with mean pressure in the ZSM-5 zeolite membranes whereas, for composite membrane the selectivities and CO2 permeance increased by mean pressure due to adsorption effect in the range of 0.5–1.5 bar and then remained constant by increasing of mean pressure.

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