Transient Dynamics In A Membrane Module With A Pulsed Change Of Retentate: Modeling And Experimental Study Of An Unsteady-State Mode Of Membrane Gas Separation Process

The paper brings new insights into the analysis of the dynamics of a novel unsteady-state pulsed retentate membrane process for efficient gas separation and purification applications. Pulsed retentate process involves alternating a closed-mode operation and short-term retentate withdrawals which improves the separation performance of the module. The transient dynamics of the pulsed retentate gas separation is evaluated through a rigorous simulation and experimental study. A new mathematical model is developed to relate the component concentration to the coordinate and time during the process for optimization purposes of the unsteady-state separation. The axial mixing effect on the separation efficiency under unsteady-state conditions, unexplored up to now, is specifically studied by the analysis of the Peclet number behavior. The proposed theoretical model is validated against the experimental data obtained for transient processes under changing retentate flow for a binary model mixture based on He with 1 vol% of n-C4H10 as a high permeable component. The agreement between the simulation and experimental data is shown both for transient and steady-state periods. Customized experimental techniques are used employing periodic gas chromatography samplings and in-situ on-line monitoring of gas mixture composition via mass spectrometry for transients. The complete model of a pulsed retentate operation involving cyclic alternation of non-withdrawal and withdrawal periods is developed and validated both against current experimental data (He/n-C4H10 mixture, PDMS-based membrane) and previously obtained results (N-2/N2O and N-2/CO2 mixtures, poly(arylate-siloxane) membrane). The agreement between the simulation results and the experimental data is shown for short-cycle separation modes, and the discrepancies for longer cycle operation cases are discussed.