Rigid polymer membranes are recently regarded as state of the art materials for gas separation processes, due to their high permeability and selectivity [1]. Among these, thermally-rearranged polybenzoxazoles (TR-PBOs) have shown outstanding molecular and ionic transport and separation performance, beyond the limits of conventional polymers [?1-4]. Adsorption and diffusion in thermally rearranged polybenzoxazole (TR-PBO) polymer membranes are simulated in single-gas and in CO2/N2 binary mixture focusing at 35 °C and at relative gas concentration corresponding to a fugacity of 5 bar. For this purpose, molecular dynamics simulations are used in a synergistic pairing with Gran Canonical Monte Carlo approach (GCMC) and Ideal Adsorption Solution Theory (IAST). GCMC simulations are compared with IAST simulations to obtain adsorption isotherms in mixtures. The number of molecules present in the polymer matrix is estimated using GCMC. Molecular dynamics simulations are performed, calculating the Maxwell-Stefan diffusion coefficients. As main results, the evaluated diffusion coefficients of CO2 and N2 are in a satisfactory agreement with the values estimated using available permeability experimental data. CO2 diffusivity calculated in mixture conditions is found to be the same as that in single-gas ones, whereas the N2 diffusivity is slightly higher. These differences are explained in terms of the effect of both the mutual gas diffusion and the competing occupancy of the available free space occupied by the CO2 molecules in mixture.
A MOLECULAR INVESTIGATION OF GAS MIXTURE IN THERMALLY-REARRANGED POLYMERIC MEMBRANES
Rizzuto C;Brunetti A;Drioli E;Tocci E
2017
Abstract
Rigid polymer membranes are recently regarded as state of the art materials for gas separation processes, due to their high permeability and selectivity [1]. Among these, thermally-rearranged polybenzoxazoles (TR-PBOs) have shown outstanding molecular and ionic transport and separation performance, beyond the limits of conventional polymers [?1-4]. Adsorption and diffusion in thermally rearranged polybenzoxazole (TR-PBO) polymer membranes are simulated in single-gas and in CO2/N2 binary mixture focusing at 35 °C and at relative gas concentration corresponding to a fugacity of 5 bar. For this purpose, molecular dynamics simulations are used in a synergistic pairing with Gran Canonical Monte Carlo approach (GCMC) and Ideal Adsorption Solution Theory (IAST). GCMC simulations are compared with IAST simulations to obtain adsorption isotherms in mixtures. The number of molecules present in the polymer matrix is estimated using GCMC. Molecular dynamics simulations are performed, calculating the Maxwell-Stefan diffusion coefficients. As main results, the evaluated diffusion coefficients of CO2 and N2 are in a satisfactory agreement with the values estimated using available permeability experimental data. CO2 diffusivity calculated in mixture conditions is found to be the same as that in single-gas ones, whereas the N2 diffusivity is slightly higher. These differences are explained in terms of the effect of both the mutual gas diffusion and the competing occupancy of the available free space occupied by the CO2 molecules in mixture.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
