Introduction In this work sorption and permeation of gases (carbon dioxide, methane, butane, oxygen, nitrogen), vapours (hydrocarbons, alcohols, water) and their binary mixtures in the high free volume polymer membranes (polymers based on polymer of intrinsic microporosity PIM-1 and high free volume glassy perfluoropolymers Teflon AF 2400) is reported. The gravimetric sorption method together with the integral (time-lag) and the differential flow permeation were used in order to elucidate the effect of the internal microporous-like polymer structure on gas/vapour mass transport. Determination of the appropriate permeability P, diffusion D and solubility S coefficients was based on the solution of the Fick's laws under corresponding initial and boundary conditions. The employment of the solution-diffusion model, where P= D*S, gives advantage to compare both used methods directly. All experiments were carried out at temperature of 25°C and at selected gas/vapour pressures. The experimental arrangement also allows suggesting of the new diffusion models [1]. Gas/vapour penetration through a flat circular membrane with thickness of tens of micrometers can be assumed as diffusion in very thin cylinder and further solved in cylindrical coordinates under the assumptions of a circular symmetry of diffusion coefficient of penetrant and the independency of demanded function on angle. The model function describing the distribution of concentration in the membrane depends on the diameter of membrane r, the coordinate of diffusion direction z and time t only. The main aims are solutions of this diffusion equation for model functions D(t), D(r) and D(r,t). It is obvious that D(r,t) functions are the most desirable because they can bring new point of view in the theory of swelling for polymeric membranes. Experimental The permeation experiments were carried out using the "classical" fixed volume pressure increase apparatus (time-lag) and the differential flow permeameter (H2 as a carrier gas) connected with set of gas chromatograph with mass spectrometer (Perkin Elmer) [2] with experimental setting which enables to measure the transient as well as the steady-state permeate fluxes. The gravimetric sorption apparatus with a calibrated McBain quartz spiral balance and with an automatic charge-coupled device (CCD) camera system detection of sample-target-point position [2] was used for study of transient and equilibrium sorption and determined isotherms were quantitatively parameterized with the Guggenheim, Anderson and De Boer (GAB) layered-adsorption model [3]. Figure 1. Transient sorption of methanol (equilibrium vapor activity a = 0.51), ethanol (equilibrium vapor activity a = 0.41) and butan-1-ol (equilibrium vapor activity a = 0.59) in the PIM-1 membrane of thickness 41.9 µm. Symbols represent measured values, curves represent the convective-diffusive mode of transport [4]. Conclusions Anomalous nature of mass transport in high free volume polymers is demonstrated by distinct trends for gases, alkanes and alcohol vapors in the correlations of diffusion coefficients on penetrant molecular volume and solubility coefficients with square of critical temperature. The results obtained in this work for polymers with intrinsic microporosity indicate the occurrence of transport mode that has a different nature than the classically employed solution-diffusion model [4]. The ongoing work on gas/vapour mass transport in and through AF 2400 revealed the anomalous trends recently [5]. Acknowledgement The work leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° NMP3-SL-2009-228631, project DoubleNanoMem. The authors are also thankful for financial support of the Grant Agency of Czech Republic (Grant No. 106/10/1194). References [1]M. Zga?ar, M. ?ípek, K. Friess, The new models of diffusion coefficient for permeation of organic vapours in polymeric membranes, Proceedings of ICOM 2011, Amsterdam. [2]K. Friess, J.C. Jansen, O. Vopi?ka, A. Randová, V. Hynek, M. ?ípek, L. Bartovská, P. Izák, M. Dingemans, J. Dewulf, H. Van Langenhove, E. Drioli, J. Membr. Sci. 338 (2009) 161-179. [3]S. Basu, U.S. Shivhare, A.S. Mujumdar, Models for Sorption Isotherms for Foods: A Review, Drying Technol. 24 (2006) 917-930. [4]O. Vopi?ka, K. Friess, V. Hynek, P. Sysel, M. Zga?ar, M. ?ípek, K. Pilná?ek, J.C. Jansen, P.M. Budd, Equilibrium and transient sorption of vapors and gases in he polymer of intrinsic microporisity PIM-1, in preparation. [5]J.C. Jansen, K. Friess, E. Drioli, Organic vapour transport in glassy perfluoropolymer membranes. A simple semi-quantitative approach to analyze clustering phenomena by time lag measurements, J. Membr. Sci. 367 (2011) 141-151.
Study of transport of gases and vapours in high free volume polymers
Johannes C Jansen
2012
Abstract
Introduction In this work sorption and permeation of gases (carbon dioxide, methane, butane, oxygen, nitrogen), vapours (hydrocarbons, alcohols, water) and their binary mixtures in the high free volume polymer membranes (polymers based on polymer of intrinsic microporosity PIM-1 and high free volume glassy perfluoropolymers Teflon AF 2400) is reported. The gravimetric sorption method together with the integral (time-lag) and the differential flow permeation were used in order to elucidate the effect of the internal microporous-like polymer structure on gas/vapour mass transport. Determination of the appropriate permeability P, diffusion D and solubility S coefficients was based on the solution of the Fick's laws under corresponding initial and boundary conditions. The employment of the solution-diffusion model, where P= D*S, gives advantage to compare both used methods directly. All experiments were carried out at temperature of 25°C and at selected gas/vapour pressures. The experimental arrangement also allows suggesting of the new diffusion models [1]. Gas/vapour penetration through a flat circular membrane with thickness of tens of micrometers can be assumed as diffusion in very thin cylinder and further solved in cylindrical coordinates under the assumptions of a circular symmetry of diffusion coefficient of penetrant and the independency of demanded function on angle. The model function describing the distribution of concentration in the membrane depends on the diameter of membrane r, the coordinate of diffusion direction z and time t only. The main aims are solutions of this diffusion equation for model functions D(t), D(r) and D(r,t). It is obvious that D(r,t) functions are the most desirable because they can bring new point of view in the theory of swelling for polymeric membranes. Experimental The permeation experiments were carried out using the "classical" fixed volume pressure increase apparatus (time-lag) and the differential flow permeameter (H2 as a carrier gas) connected with set of gas chromatograph with mass spectrometer (Perkin Elmer) [2] with experimental setting which enables to measure the transient as well as the steady-state permeate fluxes. The gravimetric sorption apparatus with a calibrated McBain quartz spiral balance and with an automatic charge-coupled device (CCD) camera system detection of sample-target-point position [2] was used for study of transient and equilibrium sorption and determined isotherms were quantitatively parameterized with the Guggenheim, Anderson and De Boer (GAB) layered-adsorption model [3]. Figure 1. Transient sorption of methanol (equilibrium vapor activity a = 0.51), ethanol (equilibrium vapor activity a = 0.41) and butan-1-ol (equilibrium vapor activity a = 0.59) in the PIM-1 membrane of thickness 41.9 µm. Symbols represent measured values, curves represent the convective-diffusive mode of transport [4]. Conclusions Anomalous nature of mass transport in high free volume polymers is demonstrated by distinct trends for gases, alkanes and alcohol vapors in the correlations of diffusion coefficients on penetrant molecular volume and solubility coefficients with square of critical temperature. The results obtained in this work for polymers with intrinsic microporosity indicate the occurrence of transport mode that has a different nature than the classically employed solution-diffusion model [4]. The ongoing work on gas/vapour mass transport in and through AF 2400 revealed the anomalous trends recently [5]. Acknowledgement The work leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° NMP3-SL-2009-228631, project DoubleNanoMem. The authors are also thankful for financial support of the Grant Agency of Czech Republic (Grant No. 106/10/1194). References [1]M. Zga?ar, M. ?ípek, K. Friess, The new models of diffusion coefficient for permeation of organic vapours in polymeric membranes, Proceedings of ICOM 2011, Amsterdam. [2]K. Friess, J.C. Jansen, O. Vopi?ka, A. Randová, V. Hynek, M. ?ípek, L. Bartovská, P. Izák, M. Dingemans, J. Dewulf, H. Van Langenhove, E. Drioli, J. Membr. Sci. 338 (2009) 161-179. [3]S. Basu, U.S. Shivhare, A.S. Mujumdar, Models for Sorption Isotherms for Foods: A Review, Drying Technol. 24 (2006) 917-930. [4]O. Vopi?ka, K. Friess, V. Hynek, P. Sysel, M. Zga?ar, M. ?ípek, K. Pilná?ek, J.C. Jansen, P.M. Budd, Equilibrium and transient sorption of vapors and gases in he polymer of intrinsic microporisity PIM-1, in preparation. [5]J.C. Jansen, K. Friess, E. Drioli, Organic vapour transport in glassy perfluoropolymer membranes. A simple semi-quantitative approach to analyze clustering phenomena by time lag measurements, J. Membr. Sci. 367 (2011) 141-151.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
