J Porous Mater (2007) 14:273–278 DOI 10.1007/s10934-006-9062-6
Cu/SBA-15 as adsorbent for propane/propylene separation E. I. Basaldella Æ J.C. Tara Æ G. Aguilar Armenta Æ M. E. Patin˜o Iglesias
Published online: 26 January 2007 Springer Science+Business Media, LLC 2007
Abstract Samples of mesoporous silica SBA-15 were prepared under hydrothermal conditions where Cu cations were incorporated to the structure by impregnation in order to compare the adsorption behavior in the presence and absence of this element. The adsorption/desorption equilibrium isotherms of propylene, propane, and N2 were measured to evaluate their usefulness in the propane/propylene separation. All the adsorption isotherms of SBA-15 measured in the absence of Cu cations were described by the Freundlich equation, while the adsorption isotherms of propane on Cu/SBA-15 were better represented by the Henry equation and those of propylene were satisfactorily described by the Langmuir model in the range P < 100 Torr. The adsorption uptake of propylene increased and that of propane decreased in Cu/SBA-15 as compared to the amounts observed in the SBA-15 sample. The presence of Cu atoms in the adsorbent lattice increased the selectivity towards propylene. Under some working conditions the adsorbed amount of propylene in Cu/SBA-15 sample was totally reversible and the propane uptake, negligible.
1 Introduction Propane/propylene separation represents an important and costly process in the chemical industry, where cryogenic distillation has been used for many years. Separation by adsorption has been investigated as an alternative to the mentioned distillation, being the most promising technique the separation via p-complexation using Cu+ or Ag+ [1–6]. Besides, the novel material SBA-15 is an ordered, hydrotermally stable silica framework that has been tested for a wide range of applications in the fields of adsorption, catalysis, heavy metal remediation and controlled drug delivery [7–11]. Moreover, the potential of mesoporous silica SBA-15 as an adsorbent for hydrocarbon separation has been recently reported [12, 13]. In the present work, Cu cations were incorporated in a SBA-15 mesoporous silica and its adsorption properties were investigated to evaluate its usefulness in the propane/ propylene separation.
2 Experimental Keywords SBA-15
Adsorption Mesoporous materials
E. I. Basaldella (&) J. C. Tara Centro de Investigacio´n y Desarrollo en Ciencias Aplicadas Dr Jorge J. Ronco, CINDECA (CONICET-CIC-UNLP), 47 No. 257 La Plata, Argentina e-mail:
[email protected] G. A. Armenta M. E. Patin˜o Iglesias Centro de Investigacio´n, Facultad de Ciencias Quı´micas, Beneme´rita Universidad Auto´noma de Puebla, Puebla, Me´xico
SBA-15 was prepared according to [14], using tetraethyl orthosilicate TEOS (Aldrich) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly (ethylene glycol), H(–OCH2CH2)x[–OCHCH3CH2–]y (–OCH2CH2–)zOH (average Mw = 5800, Aldrich) as the organic structure—directing agent. A gel having the corresponding composition was stirred overnight at 35C and submitted to hydrothermal conditions at 80C for 16 h. The resulting solid phase was filtered, washed, dried at 110C, and calcined at 590C in air for 6 h. The sample containing Cu cation (Cu/SBA-15)
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3 Results and discussion 3.1 Characterization of samples The XRD patterns (range 1.5 < 2h < 60) of starting SBA-15 and Cu/SBA-15 samples (Fig. 1) showed two weak reflections at about 1.6 and 1.7. These results are in agreement with patterns previously reported for this
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was obtained by impregnating the SBA-15 with a CuCl solution, followed by drying and calcination at 350C in nitrogen flow for 2 h. The starting SBA-15 and the corresponding Cu/SBA-15 samples were characterized by DRX and TPR. XRD patterns were recorded with a Philips APD 1700 diffractometer, using CuKa radiation, at 40 Kv, 30 mA, 0.02 step size and 1s step time. Size and morphology of solid particles were observed by scanning electron microscopy (SEM) using a Philips 505 microscope. The samples were coated by a thin Au film. Semi quantitative chemical analysis was carried out by X-ray dispersion (EDAX), using a DXPRIME 10 fitted to the scanning electron microscope. The adsorption equilibrium isotherms of propylene, propane, and N2 were determined in a conventional high-vacuum volumetric device, totally made of Pyrex glass and equipped with grease-free valves. The high vacuum (
