Hollow fiber gas separation membranes manufactured from Poly(vinyl chloride) (PVC) have been produced via a dry/wet spinning method for end use in ozone/oxygen gas separations. Ambient temperature production mechanisms were initially targeted. A number of spin runs were undertaken changing aspects of the dope solution and the spinning conditions but produced only very low selectivity membranes. It was concluded that ambient condition spinning was unattainable for the solutions used. In order to explain the low selectivity a rheological study was undertaken which considered flow, oscillatory and creep rheological conditions and modelling of the flow patterns observed across the spinneret annulus. This study showed large differences between the dope at 20°C and 60°C in terms of viscosity and viscoelastic nature. These differences were predicted to make spinning difficult through slippage on the spinneret walls and viscoelastic nature of the solution. Spinning at elevated temperature was undertaken and used to produce membranes under different spinning conditions according to a Taguchi model and which would allow graphical comparisons also in order to assess the validity of the Taguchi analysis in these applications.The membranes produced an array of results all of which indicated solution diffusion through PVC as the controlling transport mechanism under the spinning conditions. Both graphical and Taguchi analysis concluded the same conditions to be optimal; low dope extrusion rate but high convective gas flow rate and residence time producing the best selectivity. The membrane permeation results were used alongside scanning electron microscopy images to model the active layer thickness in the membranes. This concluded that the higher selectivity membranes exhibited lower active layer thicknesses and porosity resulting from the quick formation of a dense surface layer for nodule coalescence preventing further mass transport and hence halting penetration of the active layer. Ozone/oxygen binary gas mixtures showed qualitative evidence of separation. Unfortunately due to equipment limitations it was not possible to provide quantitative data to support this. The membranes have displayed good resistance to oxidative environment and therefore they perhaps offer a viable solution for processes occurring in this type of environment which more common membrane materials may not be suitable for.
|Date of Award||7 May 2015|
- University Of Strathclyde
|Sponsors||EPSRC (Engineering and Physical Sciences Research Council)|
|Supervisor||Simon Shilton (Supervisor) & Peter Hall (Supervisor)|