Modeling And Simulations Of Zeolite Film Based Processes For Separation Of Hydrocarbon Mixtures

With a particular focus on the separation of hydrocarbon mixtures with zeolite film based processes,this thesis adopted the Maxwell-Stefan (MS)formulation to describe the surface diffusion,activated gaseous diffusion,bulk diffusion and Knudsen diffusion taking place within a membrane module consisting of the zeolite film and support;then a mass transfer model and the related numerical methodology were developed to yield the simulation results for studying the roles of coupling of adsorption and diffusion and their effects on the performance of the module,including the concentration distributions of guest molecules and the flux and selectivity.It is hoped that the present work would be useful for materials and process design,development and optimization of such processes.First,for studying the separation processes that are recpectively carried out in a single unsupported membrane(M),a single supported membrane with the feed on the membrane side(membrane+support,MS), and a double-sided membranes on both sides of support (membrane+support+membrane,MSM),an one dimensional steady/ unsteady model was established by applying the MS formulation.Finite volume method and Fortran language were used to solve the model equations.Compared with the experimental or simulation results reported in the literature,the model was proved to reasonably predict the following properties:multicomponent diffusion and adsorption in a zeolite membrane module.Secondly,simulation results of permeation fluxes of single gas and binary mixture of methane and ethane for the module consisting of a single MFI zeolite membrane and a single support layer show that:·The support resistance leads to significantly decreased permeation fluxes of both the single gas and binary mixture,and is related to structures of the support layer such as the pore diameter and voidage.Particularly for heavier diffusive molecules or at a relatively low separation temperature, the effect of the Knudsen diffusion should be accounted for.·The activation energies of surface diffusion of methane and ethane are estimated to be 7.8±0.1和9.0±0.5 kJ·mol^-1.The activated gaseous fluxes of methane and ethane increase with an increase in temperature,and exceed the corresponding surface diffusion fluxes at elevated temperatures.Thirdly,studying the permeation character of isomerous alkanes (n-butane and i-butane)when they diffuse in the module consisting of a single MFI zeolite membrane and a single support shows that:·The activation energies of surface diffusion of n-butane and i-butane are estimated to be 12.7±0.1and 20.8±0.4 kJ·mol^-1,respectively.·The i-butane is weakly confined molecule,when it diffusion in MFI zeolite membrane,the activated gaseous fluxes exceed the corresponding surface diffusion fluxes.The activated gaseous fluxes of n-butane and i-butane increase with an increase in temperature.The support resistance is found to decrease the permeation fluxes,and is related to structures of the support layer such as the pore diameter and voidage.The selectivity between n-butane and i-butane is high under 400K,because the activated gaseous fluxes of i-butane is small and the effect of the competitive adsorption is remarkable;above 400K,the selectivity decreases with an increase in activated gaseous fluxes of i-butane.·Under normal pressures,the adsorption selectivity of i-butane/n-butane/propylene is in the order of n-butane＞propylene＞i-butane for an 1:1:1 mixture;during 2.5-7s,the selectivity of propylene is high;high pressure is in favor of separation of propylene.Finally,discussing single gas and binary mixture of methane,ethane, propane and n-butane through zeolite membrane module that was on both sides of the porous support,it is demonstrated that:·Because without reverse transferring of sweep gases in support,the press difference of support is decreased,whereas the membrane's press difference is increased,which is in favor of enhancing permeation fluxes and increasing selectivity.·For the binary permeation of methane and ethane through the MSM modular,the selectivity of ethane is increased.