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Project

Development and Application of Polymeric Membranes for CO2 Separation

In this study, two high performance commercial polyimide polymers, Extem and U-Varnish, and an ultra-performance polyamide-imide polymer, Rhodeftal, were selected to be employed as new materials for the preparation of membranes for CO2 separation. The phase separation behaviour of Extem/water/solvent systems for various solvents and Extem/NMP/non-solvent systems for different types of coagulants was investigated. Ternary phase diagrams were constructed based on cloud point data obtained by titration at room temperature. N methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were employed as solvent and water was used as coagulant. The morphology of the membranes prepared from Extem/solvent/water systems (except Extem/DMSO/water) showed a finger-like sub-layer, while a sponge-like structure was observed for the Extem/DMSO/water system, which was unexpected. Water, methanol, and glycerol were employed as coagulants and NMP was selected as solvent. Using methanol as coagulation medium resulted in a thick dense layer over a macroporous sub layer, while a fully sponge-like structure with microporous skin layer was obtained for the Extem/NMP/glycerol system. In order to explore the source of these unexpected observations, several parameters that can have an effect on the membrane morphology such as binary interactions between solvent/non-solvent, heat of mixing, viscosity and diffusion rate, were thoroughly studied. It was found that in the Extem/DMSO/water system, due to the higher viscosity of the casting solution along with the lower diffusion rate, the solvent exchange process occurs at a lower rate compared to other systems, which has led to delay demixing.

The performance of selected polymers in terms of plasticization was analyzed by measuring the permeability of pure CO2 at 35 oC and pressures up to 20 bar. The results showed that Rhodeftal has the highest resistance to plasticization among all tested polymers because of strong intra-molecular interactions between adjacent chain segments. In order to better understand the plasticization phenomenon, the sorption of CO2 in selected polymers was calculated by using a mathematical model based on statistical analysis. In order to improve the gas separation performance of the selected polymers, they were blended with some commercial polymers such as Matrimid and Torlon. The miscibility, inter-molecular interactions, thermal stability and crystallinity (d-spacing) of membrane blends were investigated by different analytical techniques such as DSC, FTIR and XRD. The characterization results indicated that Extem/Torlon and Extem/Matrimid do not form a miscible pair in all studied compositions, while Extem/U-Varnish and Matrimid/Rhodeftal constitute miscible polymer blends. The separation performance of membranes synthesized with these blends was investigated for a gas mixture containing 15% vol. CO2 (balanced with N2). In the case of partially miscible blends, the selectivity significantly increased, while the permeability decreased. In the case of miscible blends, the permeability and selectivity range fall between those of the pure polymers, which was expected.

Finally, the HSP was employed to study the miscibility of two polymers based on polymer-polymer interaction and to find a suitable solvent for both polymers. The results revealed that the calculation of the HSP based on individual solubility parameters can predict the miscibility of two polymers better than the total solubility parameter; it was found that the total solubility parameter is not able to predict the miscibility between polymers successfully. DMF showed the highest affinity with all studied blend polymers, and thus it was used for the preparation of blend solutions.

Date:9 Jul 2014 →  22 Aug 2017
Keywords:Chemical Engineering, Membrane Gas Separation
Disciplines:Catalysis and reacting systems engineering, Chemical product design and formulation, General chemical and biochemical engineering, Process engineering, Separation and membrane technologies, Transport phenomena, Other (bio)chemical engineering
Project type:PhD project