製備多孔疏水性二氧化矽薄膜及其於二氧化碳捕捉之應用

Synthesis of hydrophobic silica membranes for membrane contactors used for carbon dioxide capture

陳建樺(Jian-Hua Chen)

指導教授 ： 童國倫

中原大學/工學院/化學工程研究所/碩士(2011年)

https://doi.org/10.6840/cycu201100892

摘要

本研究旨在將具有耐化性、耐熱性與高機械強度的無機陶瓷材料製備成薄膜接觸器，並應用於Post-combustion的二氧化碳捕捉，文中將探討薄膜表面疏水程度與薄膜孔洞對二氧化碳回收效能之影響。
研究中先以FAS溶劑對氧化鋁陶瓷薄膜表面進行疏水改質，其結果發現，改質時間從2 hr增加至10 hr，接觸角從123°提升至142°，而當改質時間超過10小時後則再無明顯地變化，接觸角幾乎維持一定值，這結果表示薄膜表面能接枝疏水官能基的活性點已趨飽和。然而，在長時間連續操作的吸收實驗中，由結果可得知，導致薄膜被濕潤的因素不僅與膜材表面之疏水程度有關外，孔洞大小亦是影響的主因之一。
因此，本研究也將針對陶瓷薄膜孔洞進行縮孔改質，以提升薄膜之抗濕性與耐久性。為達到縮孔之目的，在實驗中，成功以溶膠凝膠法將具有中孔洞的二氧化矽氣凝膠成長於陶瓷薄膜孔洞與表面上，再對此複合型薄膜進行表面疏水化改質（定義為Al2O3/SiO2-FAS），而改質後的複合型薄膜之液滴接觸角仍具有高疏水性質，因此能同時具有縮孔及疏水之特性。此外，由吸收實驗中發現，二氧化碳之初始吸收通量於薄膜縮孔前後並無明顯差異，顯示出二氧化矽氣凝膠確實具有相當高之孔隙度(90%以上)以利氣體透過並維持一高通量值。隨後，再以長時間連續操作的吸收實驗測試此薄膜之耐久性後發現，氣凝膠縮孔技術確實能有效地減緩液體滲入薄膜，使其吸收通量可維持非常好地穩定性。
最後，本研究中利用FAS的自我接枝特性，試圖於薄膜表面與孔洞中成長出網狀的疏水結構，使疏水程度增高，減低薄膜潤濕以提升二氧化碳之吸收通量。從實驗結過顯示，隨著接枝次數的增加；表面接觸角亦有些微地增加，在四次的接枝改質後，其液滴接觸角能提升至149°左右，幾乎已達超疏水標準，而二氧化碳吸收通量亦由0.00085 mol/m2s提升至0.0011 mol/m2s左右，並於四天的連續式吸收實驗下展現出良好之穩定性，證明了藉由多次的接枝改質步驟能有效地提升薄膜之抗濕性與耐久性，並成功地將無機薄膜應用於薄膜接觸器之二氧化碳捕捉技術上，且能獲得良好的穩定吸收效能。

關鍵字

全氟辛基三乙氧基矽烷 ； 薄膜接觸器 ； 二氧化碳捕捉 ； 陶瓷薄膜

並列摘要

The purpose of this study is using ceramic materials with chemical resistance, thermal stability and high mechanical strength to prepare a membrane as a membrane contactor for the capture of carbon dioxide in the post-combustion process. In this paper, we will explore the effect of the carbon dioxide removal efficient with degree of hydrophobic of membrane surface and membrane pore size.
First of all, we used the fluoroalkylsilanes(FAS) to modify the surface of alumina membrane in order to raise the degree of hydrophobic. As results, the surface contact angles of the membranes were 123° and 142° when the FAS grafting times were 2 and 10 hours, respectively. After 10 hours had elapsed, an increase in FAS grafting time did not increase the surface contact angle, indicating that saturation of FAS grafted onto the membranes had been reached. However, in the test of durability, the result was unsatisfactory because the modified membrane was wetted nevertheless. We found there are a number of reasons for the phenomenon of wetting. One is the degree of hydrophobic of membrane surface, and another reason is membrane pore size.
Therefore, we decided to shrink the membrane pore size for enhancing the membrane durability. As results, mesoporous SiO2 aerogels were successfully coated on macroporous Al2O3 membranes (denoted by Al2O3/SiO2 membranes) via a sol-gel process to shrink the pore sizes of the Al2O3 membranes for the study of CO2 absorption. The as-coated SiO2 aerogel membranes revealed the hydrophobic characteristics by surface modification of FAS reagents. The initial CO2 absorption flux of the Al2O3/SiO2-FAS membranes was almost the same as this of the Al2O3-FAS membranes, respectively, indicating the coated layer of mesoporous silica aerogels on macroporous Al2O3 membrane will not affect the CO2 absorption flux. Mesoporous SiO2 aerogels are exceeding 90% porosities, resulting in the unchanged CO2 absorption fluxes after the coating of SiO2 aerogels on the Al2O3 membranes. And then, the membrane durability really was increase after the shrinkage process.
After all, the hydrophobicity of Al2O3/SiO2 membranes resulting from FAS modifications is the most important issue affecting CO2 capture, Al2O3/SiO2-FAS membranes with different amounts of FAS modification were also prepared, and their CO2 absorption was tested. The surface contact angles of the Al2O3/SiO2-FAS membranes with four FAS modifications were raised to 149°. The increase in the surface contact angles of the modified membranes resulted from the increase in the number of FAS modifications, i.e., as a result of self-grafting of the FAS molecules onto the original FAS molecules grafted onto the membrane. The superhydrophobic Al2O3/SiO2-FAS membranes can be successfully prepared via four FAS modifications. The CO2 absorption flux of the Al2O3/SiO2-FAS membranes increased from 0.00085 to 0.0011 mole/m2s when the number of FAS modifications increased from one to four, indicating that conducting four FAS modifications can effectively prevent membrane pore wetting in AMP solutions and facilitate higher CO2 absorption flux.
The results indicate the as-prepared Al2O3/SiO2-FAS membranes can be operated CO2 absorption continuously for long term periods. This work suggests FAS-modified SiO2 aerogel membrane is the potential membrane in membrane contactor for CO2 capture.

並列關鍵字

ceramic membrane ； Fluoroalkylsilanes(FAS) ； membrane contactor ； carbon dioxide ； Silica aerogel

參考文獻

張昊崴，平板式氟碳薄膜親疏水性對二氧化碳回收效能影響之研究，私立中原大學化學工程學系碩士論文，中壢（2008）。

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