Zeolite/polysulfone混成薄膜之 氣體分離效能研究

Study on gas separation performance of zeolite/polysulfone hybrid membranes

石健忠(Chien-Chung Shih)

中原大學/工學院/化學工程研究所/碩士(2011年)

https://doi.org/10.6840/cycu201100657

摘要

本研究利用一個全新的方法製備高分子和zeolite 4A混摻之多孔性混成薄膜應用在氣體分離上，混成薄膜ㄧ般由連續相(高分子)及非連續相(分子篩)所組成，而從文獻上發現，製備混成薄膜的時候，高分子相為緻密的型態，並沒有孔洞的存在，因此透過阻力相當高。即便分子篩有良好的透過效能，也會因為高分子相的阻力大，使得其透過量提升有限。
本研究嘗試以polysulfone作為連續相，藉由成膜機制的改變，使用不同的凝聚劑控制成膜的速率，製備出封閉的孔洞(尺寸約在4~5 μm)結構的高透過量薄膜，同時將zeolite 4A嵌在孔洞和孔洞之間，形成氣體可以經過的橋樑，提供良好的選擇比，期望可以得到一高氣體透過量的混成薄膜。
實驗結果發現，薄膜的分離性能隨著zeolite添加量的提升，而有透過量上升，選擇比下降的趨勢。這是由於介面間的孔隙隨著zeolite添加量的上升而增多，因此會有高的透過量，但過低的選擇比。為了抑制介面孔隙的生成，本實驗選用熱處理改質的方法以提高選擇比。
研究中探討不同熱處理溫度對薄膜結構型態及氣體分離效能的影響，實驗結果發現其薄膜型態與熱處理溫度有密切關係，250℃熱處理，會使得原本多孔的結構完全消失，如此雖可以提升選擇比，但透過量會大幅降低。最後得到200℃是最適當的熱處理溫度。
混成薄膜經由改善薄膜結構及介面相容性之後，的確可以大幅的提升透過量，相對於PSf緻密膜(透過量1.5 Barrer，選擇比5.6)，可以在維持4以上的選擇比，將透過量提升至20 Barrer以上。本研究同時也利用正子湮滅壽命光譜儀的技術，探討熱處理對於介面相容性的改善；數據顯示薄膜的孔洞尺寸會呈現雙分佈，這兩種孔洞分別是高分子的自由體積，及高分子和分子篩之間的介面孔隙，熱處理之後兩種尺寸的孔洞皆有縮小的趨勢，因此推斷熱處理不單讓高分子相變緻密，同時也改善了介面之間的相容性。

關鍵字

氣體分離 ； 混成薄膜 ； 沸石 ； 聚砜

並列摘要

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.

並列關鍵字

hybrid membranes ； gas separation membranes ； polysulfone ； zeolite 4A

參考文獻

63. 范舒晴, 聚醯胺與聚醯亞胺膜於滲透蒸發與蒸氣揮發之研究, 私立中原大學 化學工程學系, 博士學位論文, (2004).

2. T. Matsuura, Synthetic Membranes and Membrane Separation Processes , CRC Press, Inc., Canada, (1994).

3. M.H.V. Mulder, Basic Principles of Membrane Technology, Kluwer Academic Publishers,The Netherlands, (1996).

4. M. Kurata, Thermodynamics of Polymer Solutions, Harwood Academic, London, (1982).

5. P. Vandeweerdt, H. Berghmans, Temperature-concentration behavior of solution polydisperse, atactic poly ( methyl methacrylate ) and its influence on the formation of amorphous,microporous membranes, Macromolecules, 24 (1991) 3547-3552.