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

Abstract

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.