(754d) Sorption of CO2/CH4 Mixtures in a Polymer of Intrinsic Microporosity (PIM) : Effect of Temperature, Presence of a Tetrazole Unit (TZ PIM) and Thermal Treatment

Authors: 
De Angelis, M. G., University of Bologna
Gemeda, A. E., University of Bologna
Guiver, M. D., Hanyang University
Sarti, G., University of Bologna

The aim of this work is the study of solubility selectivity with respect to CO2/CH4 mixture of a polymer of intrinsic microporosity (PIM-1) and a modified PIM containing tetrazole unit (TZ-PIM). Sorption experiments were carried out at  25°C, 35°C and 50°C up to a pressure of 35 atm at three molar fractions of CO2 (10.9, 31.3, 50.9%).  Pressure decay equipped with gas chromatograph was used for the experiments.

The solubility coefficient of CO2 is lower for mixed gas experiment than for pure gas experiment, as well as the solubility coefficient of CH4, however the decrease of solubility coefficient of CH4 is higher than that of CO2. This behaviour gives rise to mixed gas solubility selectivity values higher than corresponding pure gas solubility selectivity. Sorption enthalpies were calculated at different gas mixture compositions.

The same mixed gas sorption experiments were also performed in TZ-PIM (PIM containing tetrazole unit) [3] at 25°C, 35°C and 50°C and molar fraction of CO2, 11.3% CO2, 30.7% CO2 and 50.3% CO2 up to a pressure of 35 atm. Solubility selectivity of TZ-PIM for CO2/CH4 mixture is higher than solubility selectivity of PIM-1. This is due to the tetrazole group which improves the solubility of CO2 while leaving unaffected the solubility of CH4. Solubility coefficient for both gases decreases with increasing temperature.

Finally, in order to study the physical ageing, we performed a series of tests in which the ageing of films of PIM-1 and TZ-PIM is accelerated with high temperature treatments under vacuum at 120, 140 and 160°C. The effect of thermal treatment is more evident on the diffusivity than on the solubility coefficient, in both types of membranes. In particular the diffusivity of both gases decreases with increasing heat treatment temperature. Trends of diffusivity with concentration are also thoroughly inspected.

[1]O. Vopicka, M. G. De Angelis, N. Du, N. Li, M. D. Guiver, G. C. Sarti, Mixed gas sorption in glassy polymeric membranes: II. CO2/CH4 mixtures in a polymer of intrinsic microporosity (PIM-1), J. Membrane Sci.   2014, 459, pp. 264 - 276

[2] O. Vopicka, M. G. De Angelis, G. C. Sarti, Mixed gas sorption in glassy polymeric membranes: I. CO2/CH4 and n-C4/CH4 mixtures sorption in poly(1-trimethylsilyl-1-propyne) (PTMSP), J. Membrane Sci.  2014, 449, pp. 97 - 108

[3] N. Du, G. P. Robertson, M. M. Dal-Cin, L. Scoles, M. D. Guiver Polymers of intrinsic microporosity (PIMs) substituted with methyl tetrazol, Polymer 53 (2012) 4367-4372