FSC hollow fibre membranes - Optimization of coating and drying procedures

Abstract

Composite hollow fibre membranes were prepared by coating PVAm and PDMS, on a PSf support. Bundles consisting of 100 fibres were placed in PVC tubes with diameter 0.6cm, which gave a packing density of 30,3%. The bundles were then coated with PVAm and PDMS. The drying during the coating procedure was controlled and done under four different relative humidity, 74%, 87%, and 96%. To investigate the difference in morphology, mechanical strength and quality of the sample, SEM, DMA and FTIR were used. Coating of fibre bundles dried under 74%, 87% and 96% relative humidity gave all soft fibres and selective layers with thickness between 0.6-1,5m where observed on the hollow fibres. On all the fibres areas without any selective coating layer was observed.

Two modules were coated and dried with air of relative humidity of 74% for different times. Gas permeation results for module 1 gave a CO2/N2 selectivity of 2 and a permeance of 0.201m3(STP)/m2barh while the gas permeation results for module 2 gave a CO2/N2 selectivity of 58 and a permeance of 0.799 m3(STP)/m2barh. The low selectivity for module 1 was blamed upon bad coating in the upper part of the module due to low shaking under the coating procedure. For the modules, it was observed congestion of the PVAm between fibres which caused the fibres to harden and stick together. This PVAm layer between the fibres was observed to be between 12-23m, this congestion caused a decrease in the permeance for the membrane. The fibres did not stick more together or harden more with drying under lower relative humidity, but did hardener and did stick more together with increasing layer of selective PVAm coating layer.