Pore Network Modeling for Separation of Multicomponent Gas Mixtures by Nanoporous Membranes

Khajvand, Mahdieh | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43508 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Soltanieh, Mohammad; Jamshidi, Saeed
  7. Abstract:
  8. The aim of this research is to model the separation and transport of multi-component gas mixture through a nanoporous membrane by using pore network models (PNM).
    The first part of this project represents the membrane simulating by means of the PNM. A three-dimensional network is used to represent the membrane’s pore space and it consists of two parts; pore and throat. The pores are the main parts of the network and their diameter is characterized according to the pore size distribution of the membrane. Every throat connects two pores and the number of throats which is connected to each pore is named "coordination number". Using a variety size of pores and throats leads to production of an irregular network which is more similar to the real membrane than the regular networks.
    In the second part of this project modeling the separation and transport of gas mixtures through membranes is investigated by using the PNM. The main mechanisms of transport through nanoporous membranes are: hindered diffusion, Knudsen diffusion, viscous flow and surface diffusion. The first three mechanisms indicate the transport of gas within the pore space while surface diffusion is indicative of the transportation of gas on the surface of the pore. The simulations indicate that Knudsen diffusion is the dominant mechanism of transport for pores as small as 7A° - 10A°. In smaller pores, hindered diffusion controls the rate of the molecular transport, and for the pores larger than 3 nm, viscous flow is the dominant mechanism.Within each pore of the simulated membrane mass balance equation is written at steady state condition for each component of the mixture. Thus, for all membrane pores a set of nonlinear equations is obtained. By solving this set of equations the gases pressure inside all pores are determined. Finally the permeance and selectivity of gases are determined by using the gases pressure inside the pores.
    In the present modeling, the effect of different factors including, the temperature, the pressure drop applied externally to the membrane, the membrane’s porosity, the membrane’s thickness, and the mole fraction of component is investigated on the separation factor of membrane. The results of this model are compared with the result of published experimental data concerning transport of hydrogen and nitrogen gases through the silicon carbide membrane, and both are in reasonable agreement. Besides, the results of binary gaseous mixture of hydrogen and nitrogen gases and also ternary gaseous mixture of hydrogen, methane and carbon dioxide gases have been generalized.
  9. Keywords:
  10. Viscous Flow ; Pore Network Model ; Nanoporous Membrane ; Gas Mixtures Separation ; Knudsen Diffusion ; Hindered Diffusion

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