Xylene Vapor Mixture Separation in Nanocomposite MFI-Alumina Tubular Membranes: Influence of Operating Variables

• Published in: Separation science and technology Vol. 45; no. 1; pp. 21 - 27
• Main Authors: Daramola, M. O., Burger, A. J., Pera-Titus, M., Giroir-Fendler, A., Lorenzen‡, L., Dalmon, J.-A.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.01.2010; Taylor & Francis
• Subjects: Catalysis; Chemical Sciences; Mathematical models; Membranes; MFI; nanocomposite; Nanocomposites; Nanomaterials; Nanostructure; Separation; Xylene; xylenes; zeolite membrane
• ISSN: 0149-6395; 1520-5754
• DOI: 10.1080/01496390903402141

In this study, we present the results of a preliminary investigation on the influence of operating variables (temperature, sweep gas flow rate, and total feed vapor pressure) on xylene vapor mixture separation using tubular nanocomposite MFI-alumina zeolite membrane prepared by the pore-plugging synthesis technique. Within the detection limit of our analytical system, neither m- nor o-xylene was detected in the permeate stream, the membranes displaying therefore "infinite" p-xylene selectivity. The mixture's p-xylene flux displayed a maximum value of ca. 3.5 µmol·m −2 ·s −1 , corresponding to a mixture permeance of 11 nmol·m −2 ·s −1 ·Pa −1 , at 473 K and for a feed composition 0.63 kPa p-xylene/0.27 kPa m-xylene/0.32 kPa o-xylene, being almost unchanged for sweep gas flow rates (N 2 ) higher than 20 mL(STP)/min and increasing with the total xylene vapor pressure at 1 : 1 : 1-3 p/m/o-xylene composition. The experimental p-xylene fluxes can be well predicted by a Maxwell-Stefan model, as expected for a mass transfer process driven by competitive adsorption / surface diffusion. Unlike film-like MFI membranes, the membranes presented here preserved their selectivity to p-xylene for total xylene pressures as high as 150 kPa. This behavior is attributed to the intimate contact between the alumina confining pores and MFI nanoparticles, reducing long-term stresses and thus preventing distortion of the MFI framework during p-xylene adsorption. These results open up potential applications of nanocomposite MFI-alumina for selective p-xylene separations at high loadings, for instance in pervaporation, where the use of film-like MFI membranes is discouraged.