Abstract
Porous, porous/gutter layer and porous/gutter layer/selective layer types of membranes were investigated for their gas transport properties in order to derive an improved description of the transport performance of thin film composite membranes (TFCM). A model describing the individual contributions of the different layers’ mass transfer resistances was developed. The proposed method allows for the prediction of permeation behaviour with standard deviations (SD) up to 10%. The porous support structures were described using the Dusty Gas Model (based on the Maxwell–Stefan multicomponent mass transfer approach) whilst the permeation in the dense gutter and separation layers was described by applicable models such as the Free-Volume model, using parameters derived from single gas time lag measurements. The model also accounts for the thermal expansion of the dense layers at pressure differences below 100 kPa. Using the model, the thickness of a silicone-based gutter layer was calculated from permeation measurements. The resulting value differed by a maximum of 30 nm to the thickness determined by scanning electron microscopy.
Highlights
The development of a membrane production technology is a key element for transferring the potential of novel, high performance membrane materials into technical application
The dense PDMS gutter layer ensuring efficient passage of gases penetrating through the selective layer to the pores of the support is deposited onto porous support so that PDMS does not penetrate into pores, and forms a continuous film of 100 nm to 200 nm thickness
The experimental gas transport data was obtained for gases with different molecular weights: H2, CH4, N2, O2 and CO2
Summary
The development of a membrane production technology is a key element for transferring the potential of novel, high performance membrane materials into technical application. For the design of new high-performance gas separation membranes with transport characteristics dominantly governed by the properties of the selective layer material, the accurate prognosis of the gas transport parameters of the entire multilayer structure of the membrane is necessary. It is apparent that the value of the permeance of a TFCM is smaller than the intrinsic permeance of its selective layer This fact indicates that the resistance of the porous support layer is not negligible. The parameters of the porous support structure such as pore diameter, pore size distribution and tortuosity significantly influence the resulting membrane characteristics, an important fact for the application of modern polymeric membrane materials as polyacetylenes [7], polymers of intrinsic microporosity (PIMs) [8,9], blockcopolymers for CO2 separation [10] or thermally rearranged polymers having extremely good gas transport characteristics [11]. The permeation in the dense gutter layer and in the separation layer was considered, using parameters derived from single gas time-lag measurements
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