Influence of exchanged cations (Na+, Cs+, Sr2+, Ba2+) on xylene permeation through ZSM-5/SS tubular membranes

¨ A. M. TARDITI, E. A. LOMBARDO

SEPARATION AND PURIFICATION TECHNOLOGY

Elsevier

Año: 2008 vol. 61 p. 136 - 147

1383-5866

Na-ZSM-5 membranes were synthesized by secondary growth on the outersurface of stainless steel porous tubes. The membranes were ion-exchanged with Cs+,Ba2+ and Sr2+ to investigate their effect upon the separation of p-xylene from m-xyleneand o-xylene. The permeation through the membranes was measured between 150 and400 ºC using each xylene isomer separately and a ternary mixture. All the membraneswere selective to p-xylene in the temperature range studied. N2 and xylene permeationmeasurements together with SEM observations were used to determine whether or notcracks and/or pinholes developed after exposure to the xylene isomers at hightemperature (400 ºC). Neither pore blockage nor extra-zeolitic pores developed after theion exchange procedure and subsequent calcination. Furthermore, duplicate synthesizedmembranes of each cation form had similar separation factors and permeances. Theduplicate values differ much less than the measurement error. The p-xylene permeationflux decreased in the order: Na-ZSM-5 > Ba-ZSM-5 > Sr-ZSM-5  Cs-ZSM-5 while thepermeation flux of the m- and o-xylene decreased in the order Na-ZSM-5 > Sr-ZSM-5 >Ba-ZSM-5 > Cs-ZSM-5. The membrane that exhibited the best performance was Ba-ZSM-5, with a maximum p/o separation factor of 8.4 and a p-xylene permeance of 0.54x 10-7 mol s-1m-2 Pa-1 at 400°C