Designing 3D Membrane Modules for Gas Separation Based on Hollow Fibers from Poly(4-methyl-1-pentene)

Designing hollow fiber (HF) membrane modules occupies one of the key positions in the development of efficient membrane processes for various purposes. In developing HF membrane modules, it is very important to have a uniform HF distribution and flow mixing in the shell side to significantly improve mass transfer and efficiency. This work suggests the application of different textile 3D HF structures (braided hoses and woven tape fabrics). The 3D structures consist of melt-spun, dense HFs based on poly(4-methyl-1-pentene) (PMP). Since the textile processing of HFs can damage the wall of the fiber or close the fiber bore, the membrane properties of the obtained structures are tested with a CO2/CH4 mixture in the temperature range of 0 to 40 °C. It is shown that HFs within the textile structure keep the same transport and separation characteristics compared to initial HFs. The mechanical properties of the PMP-based HFs allow their use in typical textile processes for the production of various membrane structures, even at a larger scale. PMP-based membranes can find application in separation processes, where other polymeric membranes are not stable. For example, they can be used for the separation of hydrocarbons or gas mixtures with volatile organic compounds

Advanced methods for analysis of mixed gas diffusion in polymeric membranes

The rapid advancement of membrane gas separation processes has spurred the development of new and more efficient membrane materials, including polymers of intrinsic microporosity. The full exploitation of such materials requires thorough understanding of their transport properties, which in turn necessitates the use of powerful and reliable characterization methods. Most methods focus on the permeability, diffusivity and solubility of single gases or only the permeability of mixed gases, while studies reporting the diffusion and solubility of gas mixtures are extremely rare. In this paper we report the use of a mass-spectrometric residual gas analyser to follow the transient phase of mixed gas transport through a benzotriptycene-based ultrapermeable polymer of intrinsic microporosity (PIM-DTFM-BTrip) and a polydimethylsiloxane (PDMS) membrane for comparison, via the continuous online analysis of the permeate. Computational analysis of the entire permeation curve allows the calculation of the mixed gas diffusion coefficients for all individual gases present in the mixture and the identification of non-Fickian diffusion or other anomalous behaviour. The mixed gas transport parameters were analysed by three different approaches (integral, differential and pulse signal), and compared with the results of the ‘classical’ time lag method for single gases. PDMS shows very similar results in all cases, while the transport in the PIM gives different results depending on the specific method and instrument used. This comparative study provides deep insight into the strengths and limitations of the different instruments and data elaboration methods to characterize the transport in rubbery and high free volume glassy membranes with fundamentally different properties and will be of help in the development of novel membrane materials