非对称复合膜的结构参数及涂复层性能对气体渗透选择性的影响

Effects of Structure Parameters and Coating Permeability of Asymmetric Composite Membrane on Its Permselectivity to Gases

根据气体渗透的阻力迭加概念,导得致密层中微孔未完全堵实(完全堵实仅是其特例)时一维稳态渗透速率表达式。以H_2和N_2通过表皮层涂复硅橡胶的聚矾非对称复合膜渗透为例,计算和分析了致密层中微孔完全堵实时膜结构参数1_1,1_2和ε对JH_2和αH_2/N_2的影响,及由于部分微孔未堵上产生的对JH_2和αH_2/N_2的影响。并考察了涂层材料的本征选择渗透性对了JH_2和αH_2/N_2的影响。

The success of asymmetric composite membrane system is a greatbreakthrough in membrane gas separation technology.The performanceof this kind of membrane permeator depends not only on its instinctpermeability,but also on membrane structure.Because the magnitude order of the size of pores in dense layer of the membrane can varyfrom 10~2 to 10~4 Angstroms,it is difficult to completely fill all thepores,small and larger with only one solution of coating material.On the basis of series/parallel resistance combination of gaspermeation through composite membrane,this paper presents a fluxexpression of one-dimensional steady-state permeation with aconsideration of incomplete filling of the pores (defectfree coatingis only a particular case)J=K_1K_2/k_1l_2+K_2l_1+(K_0-K_1)θ+K_1+l_1+l_2·ε (1)where l_1 and l_2 is the thickness of coating layer and dense layerrespectively,K_1 and K_2 is the instinct permeability of coatingmaterial and substrate respectively,ε is surface porosity of denselayer in substrate,θ is the fraction of unfilled pores and K_0 is theeffective permeability of an unfilled pore.If all the pores in dense layer are filled completely,θ=0,theneqn.(1)changs intoJ=K_1K_2/K_1l_2+K_2l_2+K_1ε/l_1+l_2 (2)Computation results show that eqn. (2) an RM model establishedby Henis and Tripodi are identical in predicting permeation fluxthough they are somewhat different in formula.With a reference to the membrane structure parameters and thecharacteristics of our I-type membrane separator,taking thepermeation of H_2 and N,through silicone rubber coated polysulfoneasymmetric composite membrane as an example,this paper has madecalculations and analyses of the effects of strucure parameters,such as l_1,l_2 and ε,and incomplete pore filling on J_(H2) and α_(H2/N2)·The effects of instinct permeability and selectivity of coatingmaterials on J_(H2) and α(H_2/N_2) of the composite membrane have alsobeen studied.Calculation results have shown that the thinner the coatinglayer,the more advantageous it will be to separation.The thickerthe dense layer of substrate,the larger the separation factor α,but the smaller the J,and the thickness of dense layer is much moreimportant than that of coatiog layer.Surface porosity of dense layerε has a critical value,ε_0=0.01(l_1+l_2)/l_1+l_2(K/K_2)_(?)where subscript s representsslow gas.If surface porosity ε is larger than ε.,performance of selective permeation will become worsen.Contrary if ε is smallerthan ε.,it is useless reducing the surface porosity to increaseseparation effectiveness.When the size of pores in dense layer isvery small,the performance of the membrane will not be affactednotably,even if there is a small amount of unfilled pores.But,if the unfilled pores are a bit larger,the performance will bereduced greatly.For a given asymmetric substrate,the instinctpermeability of a coating material is more important than its instinctselectivity,and the characteristics of a composite membrane arepredominantly determinded by its substrate.