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Process-Based Model of Mixed-Matrix Membrane
Čapek, P. ; Hejtmánek, Vladimír ; Veselý, M. ; Sysel, P. ; Kočiřík, Milan ; Brabec, Libor ; Zikánová, Arlette ; Bernauer, B. ; Fíla, V.
The focus of this contribution was on the formulation and verification of a process-based model of the mixed-matrix membrane that consisted of the polyimide matrix synthesized from the monomers 4,4’-(hexafluoroisopropylidene)diphtalic anhydride and 4,4’-oxydianiline, and silicalite-1. When a solution of a polyimide precursor in N,N-dimethylformamide was ready, silicalite-1 particles were dispersed in the solution and the dispersion was subsequently cast on a Teflon support plate. An initial mass ratio of silicalite-1 and polyimide was about 1:1. After solvent removal, the films were heated in subsequent steps up to 230°C for two hour. From a process-based model point of view, a key operation of the entire synthesis was slow sedimentation of silicalite particles in the viscous solution. Preliminary observation of 2D cuts through the solid membrane in a scanning electron microscope revealed that there were a lot of contacts among the silicalite particles. Therefore, a sequential (ballistic) deposition algorithm, well representing sedimentation in a low-energy environment, was used to create an off-lattice model of spatial distribution of the silicalite particles in the polyimide matrix.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22012102413461 - PDF
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Reconstructed 3D Microstructure and Effective Diffusivity of a Zeolite-Polyimide Mixed Matrix Membrane
Čapek, P. ; Hejtmánek, Vladimír ; Fryčová, M. ; Sysel, P. ; Kočiřík, Milan ; Brabec, Libor ; Zikánová, Arlette ; Bernauer, B. ; Fíla, V.
In our work we focused on a two-phase system consisting of the polyimide matrix synthesized from the monomers 4,4’-(hexafluoroisopropylidene)diphtalic anhydride (6FDA) and 4,4’-oxydianiline (ODA), and silicalite-1 [3, 4]. Its microstructure on the scale capturing the morphology of silicalite particles was reproduced by means of stochastic reconstruction. Then, effective diffusivity of an arbitrary fluid in the reconstructed composite material was determined by exploiting random walk simulation. Resulting values were compared with the corresponding values obtained using two traditional correlations for conductivity of composite materials. Image processing and analysis as the first step of stochastic reconstruction was a bit inexact in terms of an estimation of the volume fractions of both phases.
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Propustnost podél hranic zrn v dobře definovaných polykrystalických vrstvách silikalitu-1 a v samostatných krystalech
Brabec, Libor ; Zikánová, Arlette ; Kočiřík, Milan
Self-supporting silicalite-1 layers were grown on mercury surface from clear solutions at temperatures 140-180 oC. Large silicalite-1 crystals were synthesized using TPABr as template. Layer morphology and thickness were characterized by SEM. Phase purity of silicalite-1 and orientation of crystals were determined by XRD. Layers with the thickness > 40 .mu.m were found to be highly compact. Wet HF etching of as-synthesized polycrystalline silicalite-1 layers caused formation of deep sharp slits at grain boundaries and thus it visualized them. Contrary to this result etching of calcined layers led to a kind of a negative image represented by preserved thin shells at crystal boundaries which were found to be impregnated by carbon residues formed during template removal. Results of etching experiments give a strong indication of the existence of a thin amorphous silica interface between neighbouring crystals. The etching patterns were somewhat different for large silicalite-1 crystals.
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