1. Preparation of Supported MFI Zeolite Membranes
by Cross-Flow Filtration
L. Donato1, A. Garofalo1, E. Drioli1, O. Alharbi2, C. Algieri1
1 National Research Council ‑ Institute for Membrane Technology (ITM–CNR), c/o The University of Calabria, cubo 17C, Via Pietro BUCCI, Rende CS, Italy
2 King Abdulaziz City for Science and Technology (KACST), Saudi Arabia
I N T R O D U C T I O N
In recent years, zeolite membranes have attracted increasing interest in many separation processes owing to their crystalline structure and to their pore diameters close to molecular size of different species.
For their high thermal and chemical stability (high resistance to chlorine, oxidants and solvents), they can be used where the polymeric membranes fail.
MFI Membranes Preparation Procedure
The best operating seeding conditions were used to prepare MFI membranes
Seeding procedure
Hydrothermal treatment [6]
Seeds
Synthesized Silicalite crystals (≈ 500 nm)
Zeolite concentration
0.032 wt. %
pH suspension
7,0
Tilting 0°
Rotation
0,05 rpm
Feed flow rate
8 ml min-1
Temperature
23°C
Time
36 minutes
Pore size
(α-A2O3 support)
70 nm
Molar ratio
4 SiO2: 0.9 NaOH : 0,9 TPAOH : 1000 H2O
Solution aging
12 hours
Temperature
175°C
Time
70 hours
However, the industrial application of zeolite membranes is limited by the costs and low reproducibility in the synthesis process [1]. Up to date, their use are only represented by LTA zeolite membranes for organic solvent dehydration by means of pervaporation and vapour permeation processes [2].
MFI Membranes Calcination
Membranes synthesis was carried out in presence of the organic template, therefore calcination of the membranes was required for removing the TPAOH [7].
The most used methods for their preparation are the in situ and the secondary growth. The latter decoupling the nucleation from crystal growth gives the possibility to optimize the conditions of each step, separately. It presents two steps: the seeding of zeolite crystals on the support and the crystals growth by hydrothermal treatment.
Permeation Test
Membranes characterization was performed by permeation tests with a bubble soap flowmeter, measuring a single gases (N2 and CO2) transport through the membranes.
In this work for the first time was demonstrated the possibility to prepare tubular MFI zeolite membranes by secondary growth method using the new cross-flow seeding procedure [3-4]
MFI zeolite topology
α-Al2O3 tubular supports
(IKTS, Germany)
dpore [nm]
I.D. [mm]
O.D. [mm]
Leff[cm] 70
100
200 7 10
P E R M E A T I O N R E S U L T S
DEFECT-FREE MEMBRANES
Gas-tight membranes !!!
BEFORE CALCINATION
Presence of
intercrystalline defects
AFTER CALCINATION
N2 Permeance
(µmol s-1 m-2 Pa-1)
CO2 Permeance
Ideal Separation Factor
CO2/N2
2.1
3.8
1.8
cross-flow filtration of a water suspension of zeolite seeds through a porous support;
support rotation along its longitudinal axis;
support tilting with respect to the horizontal plane.
Influence of the crystals size
Crystals of two different size were synthesized [8].
The tilting allowed air bubbles, eventually formed inside the support during filtration and responsible for local defects, to go up. The rotation was required to achieve the deposition over the whole membrane area. These three different aspects guaranteed a uniform and sufficient coverage of the support with zeolite seeds.
XRD Analysis
SEM Analysis
Crystals size
≈ 500 nm
≈ 200 nm
E X P E R I M E N T A L W O R K
First was investigated the influence of different seeding parameters (support pore size, zeolite slurry concentration and crystals size) on the membrane quality.
Influence of the support pore size
The use of supports with pore size of 70 nm favoured the formation of more compact and uniform zeolite layer consisting in smaller zeolite crystals also better organized.
For instance, Ramsay et al. [5] prepared MFI membranes on supports with dpore = nm and obtained more homogeneous zeolite layers for the smaller dpore support (80 nm).
Results
Three different supports pore size were considered: 70 nm, 100 nm and 200 nm
F U T U R E W O R K
Membrane preparation using nanocrystals of about 200 nm.
Membrane post treatments to seal the intercrystalline defects.
Membrane applications in water treatment.
Influence of the zeolite concentration
References
[1] J. Caro, M. Noack, P. Kolsch, Adsorpt. 11 (2005) 215.
[2] M. Kondo, H. Kita, J. Membr. Sci. 361 (2010) 223.
[3] C. Algieri, P. Bernardo, G. Barbieri, E. Drioli, Micropor. Mesopor. Mat. 119 (2009) 129.
[4] C. Algieri, P. Bernardo, G. Barbieri, E. Drioli, “Procedimento per la produzione di membrane zeolitiche su supporti porosi tubolari”, RM 2008 A
[5] J. D. F. Ramsay et al., FOAA6, May 1998 © Elsevier.
[6] G. Xomeritakis, A. Gouzinis, S. Nair, T. Okubo, M. He, R. N. Overney, M. Tsapatsis, Chem. Eng. Sci. 54 (1999) 3521.
[7] E. R. Geus and H. van Bekkum, Zeolites 15 (1995) 333.
[8] A. E. Persson, B. J. Schoeman, J. Sterte, and J. E. Otterstedt, Zeolites 14 (1994) 557.
Zeolite slurry concentration of wt.%, due to the higher degree of the crystals dispersion in the aqueous suspension, allowed a more homogeneous and uniform distribution of them on the support surface.
Results
Three different zeolite slurry concentrations were considered: wt.%, 0.07 wt.%and 0.1 wt.%