第七章 Gas Membrane Separation (part 2-1).ppt

Gas Membrane Separation 1. History 2. Mechanism 3. Membrane Preparation 4. Membrane Characterization 5. Membrane module 6. Mathematic model for gas membrane separation 7. Applications 6. Important parameters 7 Permeation mechanism of gas in composite membrane For composite membrane: Acceptable permeability and high permselectivity can be got . Consists of a porous asymmetric support membrane and a coating layer. The support membrane is a porous substrate with a dense layer. The coating layer is selective with a thickness of 0.1-1.0μm,which is much thinner than homogeneous membrane. 8 Mathematical model of membrane gas separator 8.1 Complete Mixing Flow According to material balance of the gas mixture and the fast gas, we obtain: 8.2 Slug Flow Pressure gradient equation of compressible fluid flowing in permeable Assumptions of hollow fiber membrane gas separator: The gas pressure drop on the shell side is negligible. The axial diffusion of gases is negligible. The gas flow can be treated as an ideal plug flow. Non-ideal gas behavior and concentration polarization are believed to take place. The permeation competition of different components is negligible. 8.4 Application Examples ofMathematical Model Experimental data: Comparation of experimental data with calculated results 14.9 15.1 2.0 2 32.8 32.0 3.4 1 Experimental data Calculated result Serial number Mathematical model of plate-frame membrane gas separator （7-60） （7-61） From the permeation equation of the slow gas: （7-62） （7-63） - Permeability of the fast gas m3（STP）/（m2·s·Pa） -Separation factor Take cocurrent flow for example: （7-64） （7-65） （7-66） （7-67） Boundary condition: When purge gas exists,shown in fig.7-12(c), Boundary condition becomes: 8.3 Mathematical model of hollow-fiber membrane gas separator Fig.7-14 Countercurrent slug flow model Fig.7-13 Schematic representation of fluid in hollow fiber membrane The description of continuous equat