Synthesis of ZSM-5 zeolite membranes without organic templates using a varying-concentration technique

摘要

Template-free nanosized ZSM-5 seeds with an average size of 15 nm were prepared from a synthesis solution with the composition 12Na_2O:100SiO_2:2Al_2O_3:2500H_2O. By the use of these seeds, thin ZSM-5 zeolite membranes were prepared on the outer surface of a porous α-alumina tube with a pore size of 2 μm in a gel system by varying-concentration synthesis with organic-free template. The first composition synthesis sol-gel was the same as seeds of molar composition and the second one was 12Na_2O : 100SiO_2 : 2Al_2O_3 : 5000H_2O at 180 °C for 10 h, respectively. XRD shows that the film consists of well-crystallized ZSM-5 zeolite . SEM investigation indicats that the zeolite films on the supports are defect free and the film thickness is approximately 8 μm. The permeances for H_2, N_2, CH_4 and CO_2 are 8.94 × 10~(-7), 3.27 × 10~(-7), 3.9 × 10~(-7), 3.14 × 10~(-7) and 0.874 × 10~(-7) mol·m~2·s~(-1) ·Pa~(-1), respectively. The ideal selectivity of membrane at room temperature for H_2/CO_2, H_2/N_2, H_2/CH_4 are 2.84, 2.73 and 2.29, respectively.