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۱Asymptotic Analysis of Binary Gas Mixture Separation by Nanometric Tubular Ceramic Membranes: Cocurrent and Countercurrent Flow Patterns (انگلیسی)
نویسنده(ها): ، ،
اطلاعات انتشار: فصلنامه مهندسي شيمي ايران، سوم،شماره۳، Summer ۲۰۰۶، سال
تعداد صفحات: ۱۴
Analytical gas–permeation models for predicting the separation process across membranes (exit compositions and area requirement) constitutes an important and necessary step in understanding the overall performance of membrane modules. But, the exact (numerical) solution methods suffer from the complexity of the solution. Therefore, solutions of nonlinear ordinary differential equations that govern the performance of the membrane modules for gas separations by approximate and asymptotic methods are useful in the design and comparison of processes. In this work, the asymptotic methods were applied for predicting the performance of nanometric tubular ceramic membranes in the separation of binary gas mixtures with cocurrent and countercurrent flow patterns. Also, the exact (numerical) solutions of the governing equations using the fourth order Rung–Kutta technique were proposed. The comparison of the results showed a good agreement between the exact solution and asymptotic analysis methods over the whole range of selectivities ( ). Because, the asymptotic curves into the former ( ) and latter ( ) boundaries had a suitable overlap with each other to cover the whole range of selectivities. The accuracy of this method was verified by a comparison of the predicted results with different literature experimental data and mathematical models. This result suggests the use of the asymptotic analysis method to provide excellent shortcut, preliminary design information.

۲Synthesis and Seeding Time Effect on the Performance of Nanostructure Sodalite Membranes (انگلیسی)
نویسنده(ها): ، ،
اطلاعات انتشار: فصلنامه مهندسي شيمي ايران، چهارم،شماره۱، winter ۲۰۰۷، سال
تعداد صفحات: ۱۷
Secondary growth technique was successfully applied for the synthesis of nanostructure sodalite membranes with vacuum seeding on tubular α–Al2O3 supports. In the seeding process, a thin, uniform and continuous seeding layer was closely attached to the support external surface by the pressure difference between the two sides of the support wall. The final nanostructure sodalite top–layers were synthesized on the seeded support into a stainless steel autoclave with a Teflon holder. The effect of seeding time on the microstructure of the synthesized sodalite top–layers was investigated at four different levels 60, 120, 180 and 240 s. The synthesized membranes were characterized by XRD, SEM and mercury porosimetry. The obtained results showed that sodalite zeolite was synthesized on the membranes top–layers with uniform surfaces. But, the top–layers thickness increases by increasing the seeding time and tends to reach a plateau. Further increasing the seeding time causes dense top–layers to form. Also, the performance of the manufactured sodalite membranes was evaluated by permeations of single gases (H2 and N2) under different pressure differences at a temperature of 283K. It is found that the membrane permeance shows a maximum value at seeding time 180 s with a constant permselectivity (H2\N2) of about 2.5. The permeation results were confirmed by SEM micrographs which showed a thick and low–dense top–layer in the membranes manufactured with the seeding time of 180 s.
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