An Integral Fitting Method for Determining Gas Permeability Constant through Porous Membrane

Although many experiments on membrane reactor use sweep gas for establishing partial pressure, only few works have been dealt with the measurement of permeability constant by using sweep gas. Conventionally, gas permeability constant is determined by the following steps: i) flowing of a single or mixed gas through permeation cell, ii) measuring variables and parameters such as volumetric rate of permeated gas and pressure difference, and iii) solving flux equation using measured variables and parameters to obtain permeability constant. In this study, a method for determining gas permeability constant through porous membrane was developed by fitting experimental and calculated data of binary system. A double cylindrical type of permeation cell with porous membrane as inner tube was used in the experiments, in which two different gases were fed into inlets of the cell (shell and tube sides). Then compositions and volumetric rates of gas exhausting from outlets were measured. Separately, compositions and volumetric rates were also calculated by integrating a set of differential equations derived from species balances in the cell. By using minimization technique, permeability constants were determined when sum of squares of the differences between measured and calculated values reach minimum. This method was tested for determining permeability constants of N₂, CO₂, and H₂ through Vycor glass. At 298 K it was obtained that permeability constants for N₂, CO₂, and H₂ are 2.24 x 10^-11, 2.23 x 10^-11 and 6.82 x 10^-11 mol.s^-1.m^-1.Pa^-1 respectively. Furthermore, experiments and calculations were also conducted for ternary system in which N₂ was fed into shell side while mixture of H₂ /CO₂ was fed into tube side. Calculations of ternary system used the constants determined from binary system. Work on ternary system showed that this method has better results than the conventional one.