A compact ZSM-5 membrane prepared without structure-directing agent

Compact ZSM-5 zeolite membranes have been prepared on the outer surface of a porous α-alumina tube without structure-directing agents (SDAs) by the seed-assisted crystallization method. An SDA-free gel and an SDA-free clear solution were used for the membrane preparation, respectively. ZSM-5 membranes prepared from the SDA-free gel showed the H₂/i-C₄H ₁₀ ideal selectivity of 13.8 at 200°C, but it decreased to be 2.1 after the pretreatment at 300°C, indicating the limited thermal stability of this kind of ZSM-5 membrane. On the other hand, ZSM-5 membranes prepared from the SDA-free clear solution showed high thermal stability and good separation properties. After the pretreatment at 400°C, the H₂/i-C ₄H₁₀ ideal selectivity was as high as 61 at 270°C. The maximum of the n/i-C₄H₁₀ ideal selectivity was 36 at 300°C and the separation factor was as high as 12.7 at 400°C for a 50/50 n/i-C₄H₁₀ mixture.