科研之友
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摘要
A theoretical foundation for a new characterization method for dual-mode sorption membranes is presented. The method relies on simultaneous monitoring of pressure decay and pressure rise and continuous evaluation of the respective instantaneous upstream and downstream time lags as well as their ratio. Assuming the simplest gas transport model in dual-mode sorption membranes, i.e. complete immobilization and instantaneous equilibrium between Henry's and Langmuir's sites, the expression for the upstream time lag and the ratio of the upstream and downstream time lags for dual-mode sorption membranes has been derived using Frisch's asymptotic solution. The analytically derived ratio between the upstream and downstream time lags is used as an extra equation that reduces the number of permeation experiments required to fully recover the kinetic and sorption parameters of the membrane. The proposed characterization method, developed for the ideal boundary conditions, is extended to the real boundary conditions, in which gas concentrations at the upstream and downstream interfaces of the membrane vary with time, by recognizing a set of unique relationships between the maximum downstream time lag and the time at which the ratio of the upstream and downstream time lags is equal to the unique value that would exist under the ideal boundary conditions. Finite difference numerical modeling was utilized to examine the proposed method under the real boundary conditions using some case studies from the literature. The accuracy of the recovered kinetic and sorption parameters is promising and allows the elimination of challenging sorption measurement involving dense membranes.
- 出版日期2017-11-15
