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Influence of exchanged cations (Na~+, Cs~+, Sr~(2+) and Ba~(2+)) on xylene permeation through ZSM-5/SS tubular membranes

机译:交换阳离子(Na〜+,Cs〜+,Sr〜(2+)和Ba〜(2+))对ZSM-5 / SS管膜渗透二甲苯的影响

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Na-ZSM-5 membranes were synthesized by secondary growth on the outer surface of stainless steel porous tubes. The membranes were ion-exchanged with Cs~+, Ba~(2+) and Sr~(2+) to investigate their effect upon the separation of p-xylene from m-xylene and o-xylene. The permeation through the membranes was measured between 150 and 400 °C using each xylene isomer separately and a ternary mixture. All the membranes were selective to p-xylene in the temperature range studied. N2 and xylene permeation measurements together with SEM observations were used to determine whether or not cracks and/or pinholes developed after exposure to the xylene isomers at high temperature (400 °C). Neither pore blockage nor extra-zeolitic pores developed after the ion exchange procedure and subsequent calcination. Furthermore, duplicate synthesized membranes of each cation form had similar separation factors and permeances. The duplicate values differ much less than the measurement error. The p-xylene permeation flux decreased in the order: Na-ZSM-5 >Ba-ZSM-5 > Sr-ZSM-5 ≈ Cs-ZSM-5 while the permeation 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 0.54 x 10~(-7) mol s~(-1) m~(-2) Pa~(-1) at 400 °C.
机译:Na-ZSM-5膜是通过在不锈钢多孔管的外表面上二次生长合成的。将膜与Cs〜+,Ba〜(2+)和Sr〜(2+)进行离子交换,研究其对对二甲苯从间二甲苯和邻二甲苯中分离的影响。使用每种二甲苯异构体和三元混合物分别在150至400°C之间测量通过膜的渗透率。在所研究的温度范围内,所有膜均对对二甲苯具有选择性。使用N2和二甲苯渗透测量以及SEM观察来确定在高温(400°C)下暴露于二甲苯异构体后是否出现裂纹和/或针孔。在离子交换程序和随后的煅烧之后,孔堵塞和沸石外孔均未形成。此外,每种阳离子形式的重复合成膜具有相似的分离因子和渗透率。重复值的差异远小于测量误差。对二甲苯的渗透通量依次降低:Na-ZSM-5> Ba-ZSM-5> Sr-ZSM-5≈Cs-ZSM-5,而间二甲苯和邻二甲苯的渗透通量依次降低Na-ZSM-5> Sr-ZSM-5> Ba-ZSM-5> Cs-ZSM-5。表现最佳的膜是Ba-ZSM-5,最大p / o分离系数为8.4,对二甲苯渗透率为0.54 x 10〜(-7)mol s〜(-1)m〜(- 2)在400°C下Pa〜(-1)

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