氧氣化學吸附對碳分子篩薄膜 氣體分離效能與化學老化行為之影響

Effect of oxygen doping on gas separation performance and chemical aging behavior of carbon molecular sieve membranes

陳顯修(Shian-Shiou Chen)

指導教授 ： 李魁然 ； 胡蒨傑

中原大學/工學院/化學工程研究所/碩士(2014年)

https://doi.org/10.6840/cycu201400711

摘要

本研究使用商業化聚醯亞胺薄膜(Kapton)作為製備碳分子篩薄膜之前驅物，在碳化程序中，通入含有不同氧氣濃度之氧氣/氬氣混合氣體至高溫爐體，爐體氣氛中之氧氣會預先與碳結構的不穩定位置產生化學吸附，以達到預先穩定化之目的，期許可以減緩碳分子篩薄膜之化學老化現象，並探討預先吸附氧氣對孔洞結構、氣體分離效能與化學老化現象之影響。
研究中先使用TGA(thermalgravimetric analysis)鑑定前驅物薄膜之熱穩定性及裂解溫度，藉此決定碳化溫度。使用ATR-FTIR(attenuated total reflectance-fourier transform infrared spectroscopy)、XRD(x-ray diffraction)與XPS(x-ray photoelectron spectroscopy)分析薄膜碳化前後以及預先吸附氧氣前後的化學組成、化學結構與殘碳率。使用PALS(positron annihilation lifetime spectroscopy)鑑定碳分子篩薄膜的孔洞分佈，且觀察化學老化現象所造成孔洞分佈之變化。在35℃下進行N2、O2及CO2的氣體透過測試，並週期性的觀察化學老化現象對氣體分離行為之影響。
ATR-FTIR與XRD的鑑定結果顯示，前驅物薄膜碳化前後之化學組成與結構型態有明顯的差異，且當碳化溫度從600℃上升至800℃，有機鏈段的熱裂解會使有機官能基逐漸消失，而熱排列運動會使分子鏈排列更緊密，使得分子層間距變小。經過預先吸附氧氣之反應後，氣體透過量與氣體選擇性分別呈現下降與上升的趨勢。在5%的氧氣氣氛下，可製備最適化的預先吸附氧氣反應之碳分子篩薄膜，從XPS鑑定結果顯示，此碳分子篩薄膜有最高的氧元素組成比例，且可有效減緩氧氣化學吸附所造成之氣體透過量下降與氣體選擇性上升的程度。從PALS鑑定結果顯示，與未預先吸附氧氣之製程相較，進行預先吸附氧氣程序可以減少碳分子篩薄膜孔洞往小尺寸偏移的程度，因此，本研究結果可用於製備具有高氣體分離效能及穩定性之碳分子篩薄膜。

關鍵字

氣體分離 ； 聚醯亞胺 ； 碳分子篩薄膜 ； 老化

並列摘要

In this study, Kapton was choosed as a precursor to fabricate CMSM. In order to reduce the chemical aging of the CMSM, we introduced the mix gas which contained different amount of oxygen into the furnace during pyrolysis procedure. The oxygen doped the unstable site and stabilized the micropore of CMSMs. In addition, we investigated the effect of oxygen doping on pore size, gas separation performance and chemical aging behavior.
Thermalgravimetric analysis (TGA) was used to survey the thermal stability and to determine the pyrolysis temperature of Kapton precursor. Besides, The chemical composition, d-spacing, degree of residual carbon of the precursor, undoped and doped carbon molecular sieve membrane were characterized by attenuated total reflectance - fourier transform infrared spectroscopy (ATR-FTIR), x-ray diffraction (XRD) and x-ray photoelectron spectroscope (XPS) respectively. In order to understand the effect of chemical aging, the positron annihilation lifetime spectroscopy (PALS) was used to characterize the pore size distribution. Also, N2, O2 and CO2 permeation was tested periodically.
The results of FTIR-ATR and XRD indicated that the chemical composition and chemical structure changed after carbonization. The organic functional groups disappear during carbonization process. When the pyrolysis temperature was increasing from 600℃ to 800℃, it led carbon atoms rearrangment and form amorphous carbon molecular sieve. The result of gas permeation measurement indicated that the gas permeability decrease and gas selectivity increase after oxygen doping. Optimum oxygen doped CMSM can be obtained under the circumstance of 5% oxygen pyrolysis atmosphere. From the result of XPS, it showed that the 5% oxygen doped CMSM has maximum oxygen content. Oxygen doping can effectively reduce the decreasing in permeability and increasing in selectivity caused by chemical aging. Form the result of PALS, it showed that 5% oxygen doped CMSM can reduce the pore size shrinkage. One can fabricate CMSMs with high gas separation performance and stability by using the results developed in this work.

並列關鍵字

carbon molecular sieve membranes(CMSMs) ； kapton ； gas separation ； aging

參考文獻

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

4. M.H. Klopffer, B. Flaconneche, “Transport properties of gases in polymers: bibliographic review”, Oil Gas Sci. Technol. 56 (2001) 223-244.

5. D.R. Paul, Y.P. Yampol'skii, Polymeric Gas Separation Membranes, CRC Press, Inc., Canada (1994).

6. L.M. Robeson, Correlation of separation factor versus permeability for polymeric membranes, J. Membr. Sci. 62 (1991) 165-185.

7. L.M. Robeson, The upper bound revisited, J. Membr. Sci. 320 (2008) 390-400.