The compact ZSM-5 membranes was synthesized on porous alumina substrates by pre-coating nanosized ZSM-5 seeds and then employing the twice hydrotheiTnal synthesis with adding the promoter NaCI. Effect of Na~+ concentration on the formation of membrane was investigated in this work, indicating that adding a certain mount of NaCI can boost the growth of zeolite crystals on the substrates, thus forming the compact membrane consisted of highly intergrown crystals. The separating performance of zeolite membranes indicated that using a mixture with a composition of A1_2O_3: 84SiO_2: 10Na_2O : 100NaCl: 15TPABr: 3500H_2O as synthesis gel, the ideal selectivity of H2/C3H8 could reach a maximum value of 23.7 at room temperature and pressure difference of 0.1 MPa, and the permselectivity decreased to 9.4 at testing temperature of 200 ℃ , which is still higher than the corresponding Knudsen diffusion value (4.69), suggesting that the membrane synthesized by this method was defect-free.

Key words: MOLECULAR SIEVE, NANOPHASE MATERIALS, ZSM-5, GAS SEPARATION, ADSORPTION, ALUMINIUM OXIDE, SODIUM CHLORIDE, HYDRO-THERMAL REACTION