The Application Of A Slit Pore And Pore Network Model On Gas Separation In Carbon Membranes

The faultiness of the mechanism of gas separation in carbon membranes is one of themain reason, which embarrasses the industrial application of the technology of gas separationin carbon membranes in the present time. In order to solve this problem, two different modelsof membrane pore, a slite pore model and pore network model are used to study themechanism of gas separation in carbon membranes in this essay.First of all, the molecular simulation method ofμVT ensemble NonequilibriumMolecular Dynamics (μVT-NEMD) is conducted to investigate the effects of temperature andpressure on the permeability of pure CH₄ and CO₂, using a slit pore model. Comparing withthe experimental results, the optimal Lennard-Jones interaction parameters are fixed. Andthen, the effects of pore size on the fluxes and wall potential energies of a binary mixture ofCH₄ and CO₂ are studied under the certain values of temperature and pressure of the system.The results show that the process of gas separation in carbon membranes is effected byvarious factors and molecular sieve and selective adsorption is the dominating mechanism ofgas separation.Then, a pore network model is constructed. Using the method of critical path analysis(CPA), a deep insight of the internal structure of membrane pores is attained. Also with abinary mixture of CH₄ and CO₂ as the object investigated and the consideration of theconnectivity effects of membrane pores on gas separation, the different pore size ranges of thespecies which the membrane is intended to transport are fixed basing on the variation ofcomponent flux with pore size stimulated by a slit pore model. Through the same track, thecurve of pore size distribution is stimulated, which fundamentally fit the experimentalconclusion. Thus, it demonstrates that the pore size distribution function could reflect thepractical pore size distribution well and the pore network model constructed in this paper canmainly render the separation process of CH₄ and CO₂ in carbon membranes correctly.At last, the model of pore network is applied to the separation process of coal methane incarbon membranes. Different pore size rages of the three dominating components of coalmethane, which the membrane is intended to transport are fixed. Therefore, the membraneseparation method of two stages is designed. Using the carbon membranes with different poresize range in every stage, the three dominating components of coal methane are separatedfinally. Based on previous work, tail contribution is applied to correct the system error which isbrought by the truncation of molecules' interaction when calculating the chemical potentialenergy and pressure, which is occurred in the simulating process of adopting a slit pore model.A new pore size distribution denoted by a sectional function is presented for the first time inthe calculation process of adopting the pore network mode, which could reflect the practicalpore size distribution well. And the successful application of pore network model toseparating coal methane have proved that this model has a certain contribution to themanufacture of carbon membrane and the application to gas separation.