Study on gas separation performance ofzeolite/polysulfone hybrid membranes

• Main Authors: Chien-Chung Shih, 石健忠
• Other Authors: Chien-Chieh Hu
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/82669709930658984863

碩士 === 中原大學 === 化學工程研究所 === 99 === In this study, we introduced a new methodology to fabricate hybrid membrane―zeolite 4A/polysulfone―and to apply them to membrane gas separation. Hybrid membrane contains two phases, continuous (polymer) and discontinuous (molecular sieve) phase. From previous studies, the morphology of the polymer phase is always dense. Despite the high performance of the molecular sieve, the permeability cannot become high because of the high resistance of the polymer phase. In this research, we chose the polysulfone to be the continuous phase, and we used different coagulants (non-solvent) to control the membrane formation rate to prepare a porous membrane consisting of closed pores (4~5μm size). Compared to a dense structure matrix, this membrane had a high gas permeability but a low selectivity due to its closed pores. To connect these pores to form a path for gases, we therefore used zeolite 4A. A porous matrix can offer a high permeability, and zeolite particles, which can offer sufficient O2/N2 selectivity, should lock on the pore walls. By means of this method, we expected that we could get high performance. From the experimental results, we could find that the permeability of the hybrid membrane increased and selectivity decreased with zeolite loading increasing. This is as a result of adding the zeolite, which led to an interface between the polymer and the zeolite. More zeolite loading increased the number of interface, that is why we obtained a high permeability but a low selectivity with zeolite loading increasing. To improve interfacial adhesion, we applied heat treatment to the hybrid membrane. We analyzed the heat treatment effect on the membrane morphology and the gas performance. We found that this treatment did have an effect based from SEM images and gas permeability data. Heat treatment at 250℃ caused the porous structure to disappear completely. Such is not what we wanted to do in this study, because although this high temperature resulted in increasing the selectivity, the permeability was sacrificed to a great extent. And we found that the optimum heat treatment temperature was 200℃ from the SEM and gas permeability data. The results showed that hybrid membrane could increase the permeability substantially after improving the membrane morphology and the interfacial compatibility. Compared to a membrane with a conventional dense structure, such a porous membrane really helped to increase the permeability. We could obtain a gas permeability of 20 Barrer and sustained a selectivity between 4.1 and 4.5. We also used positron annihilation lifetime spectroscopy (PALS) to study the improvement in the interfacial compatibility after the heat treatment. It was observed that the membrane pore size had two types of distribution. The first one referred to the free volume in the polymer phase, and second described that in the interface between the polymer and the zeolite. Both the free volume and the interfacial gap became smaller after the heat treatment. Hence, we can conclude that the heat treatment not only caused the polymer phase to become denser but also improved the interfacial compatibility.