Thin sulfonated poly(ether ether ketone) films for the dehydration of compressed carbon dioxide

In this thesis, the properties of thin films from highly sulfonated poly(ether ether ketone) (SPEEK) have been investigated within the context of their application as membranes for the dehydration of compressed carbon dioxide. Spectroscopic ellipsometry has been used as the predominant measurement technique. The relationships between the presence of water during film formation and final film properties have been investigated, as well as the water-induced dynamic swelling. Furthermore, the effects on thermal stability of thin SPEEK films when the protons in the sulfonic acid groups are exchanged with sodium ions has been evaluated. Additionally, the feasibility of using composite hollow fibers in the dehydration of compressed carbon dioxide has been assessed with simulations in Aspen Plus®. Thin SPEEK films swell excessively in water, and the extent of water-induced swelling is shown to be correlated with the inherent optical anisotropy of the films. The inherent anisotropy in SPEEK films is indicative for the presence of molecular orientations and internal stresses in the material. Additionally, the hydration state of SPEEK during film formation impacts the final morphology of the films, which can significantly affect the swelling behaviour. Films formed without the presence of water, swell significantly less than their counterparts, prepared in identical way but in a humid atmosphere. Swelling of SPEEK films can be also suppressed by grafting of polyols molecules on sulfonic acid groups, predominantly reducing the affinity for water. Sodium counter-ions strongly enhances thermal stability of SPEEK. No thermally-induced changes have been observed for SPEEK-sodium films when these are heated up to 220 °C for 15 hours. In contrast, SPEEK-proton films that are heated up to only 160 °C for 15 hours exhibit significant decomposition. For dehydration application via membranes, a method is required to remove water from the permeate side such that the high driving force over the membrane is maintained for water permeation. In this study, the usage of a sweep gas in a low pressure, also carbon dioxide, has been discussed.