利用二氧化鈦中間層改善碳分子篩選薄膜黏附特性與增加氣體分離性能之研究

Improving the interfacial adhesion and gas separation performance of CMS membranes by adding titanium dioxide intermediate layers

王敬婷(Ching-Ting Wang)

指導教授 ： 曾惠馨

中山醫學大學/健康管理學院/職業安全衛生學系碩士班/碩士(2014年)

摘要

碳分子篩選薄膜多以非對稱型式存在，並以氧化鋁為基材以提升其整體機械強度。基材表面的物化結構會影響高分子鏈的堆疊狀況、碳膜與基材之間的接合情形，而當兩相接合不完整，就容易產生間隙或裂縫，進而影響薄膜的分離效能。選擇層與基材兩相間的黏附機制主要由機械互鎖、化學鍵結及吸附作用等三個因子所決定。因此，本研究為了提升兩相間的黏附特性，選擇塗佈含有羥基的TiO2做為中間層，以修飾基材的孔洞結構與表面化性，並經由調整TiO2前驅溶液的pH值，以控制TiO2的粒徑大小；此外，本研究亦同時改變基材的粗糙度與鑄膜液的黏滯度，以評估其對黏附強度及氣體分選效能之影響。
實驗結果發現，TiO2的奈米網絡結構可改變基材的孔洞結構，使Al2O3基材的總孔洞體積增加，尤其是中孔及巨孔體積，而有利於兩相間的機械互鎖；此外，TiO2表面的羥基則可與PEI高分子鏈（碳膜的前驅物）產生氫鍵而增強化學鍵結，進而有效地提升兩相間的黏附特性，並使得薄膜的機械強度由187.4 N增強至 215.9 N。
另外，透過調整TiO2 sol-gel溶液 pH值發現，當pH值較低時，會使水解反應較快速而造成塗佈之中間層溶液較易滲入基材孔隙中進行修飾，故可獲得較佳的機械強度，雖損失些微滲透率、但選擇率較佳。而當中間層層數增加，殘留在基材表面的TiO2數量也隨之遞增，而使得化學鍵結強度上升，增強黏附效果，雖然滲透率下降，但可提升選擇率。
當以拋光技術改變中間層粗糙度時，隨著基材表面粗糙度越大，會使中間層滲入較多，讓可提供鍵結的TiO2量降低，使得化學鍵結效應減少，故滲透率會遞增。且高分子鏈也會因為基材表面起伏而排列凌亂導致層間距較大，選擇率會較差。
最後，利用調整薄膜前趨液溫度，改變其黏滯度，當黏滯度較低時，在進行塗佈的旋轉過程中，留在基材表面的鑄膜液較少，且因溶液移動性較高，容易滲入基材的孔洞之中，使得互鎖效應較高，接合程度也增加，使滲透率有逐漸下降的情形。且當鑄膜液的溫度較高時，溶劑揮發速率較快，會使高分子鏈在伸展狀態即固化，因此形成的薄膜較為緻密，碳化後層間距值較小，滲透率會較低。

關鍵字

碳膜 ； 基材 ； 中間層 ； TiO2 ； 粗糙度 ； 黏度

並列摘要

Carbon molecular sieving membrane (CMSM) is generally supported on porous Al2O3 substrate to form asymmetric composite membrane to enhance its mechanical strength and separation performance. However, in our previously studies we have clearly demonstrated that the support layer can have significant effects on polymer segment arrangement and the interfacial adhesion between selective layer and substrate, which will result in defect formation and low separation performance. The adhesion mechanism between them is determined by the mechanical interlocking, chemical bonding and adsorption. Therefore, in this study, the TiO2 nano-network which containing hydroxyl groups was acting as intermediate layer to modify the interfacial adhesion. The particle size of TiO2 was controlled by adjusting the pH of the gel solution. Further, the effect of surface roughness of support and the viscosity of casting dope on the adhesion were also evaluated.
The results indicated that the pore structure of the substrate can be modified by TiO2 nano-network. The surface area and the total pore volume of substrate were increased, which is benefited for mechanical interlocking with polymer chain. Further, PEI chain was bonded by the Hydroxyl groups of the TiO2 to improve the chemical bonding. The mechanical strength of the TiO2-modified Al2O3 support was enhanced from 187.4 N to 215.9 compared to the original one.
The separation performance was observed strongly related with the pH of sol-gel solution, surface roughness and viscosity of dopes. When the pH value was low, the hydrolysis rate was increased to form fine TiO2 particle to penetrate into the voids of the substrate, which can improve the mechanical interlocking and selectivity, but loss some permeability. In addition, using polishing technology to modify the roughness of the intermediate layer, the gas permeability would be increased when the surface roughness was high. The irregular arrangement of polymer chains decrease the ultra-micropore and increase the d-spacing of membrane, so the selectivity will decrease.
At last, we change the polymer solution temperature to adjust the viscosity of dopes. The low viscosity of dopes will penetrate into the substrate to improve the mechanical interlocking, but the permeability will also decreased. When increasing the polymer solution temperature, the polymer chain was rigidified due to the high volatility of solvent. Therefore, the membrane became much dense. The d-spacing was decreased after carbonization and also resulted in low permeability.

並列關鍵字

carbon membrane ； substrate ； intermediate layer ； TiO2 ； roughness ； viscosity

參考文獻

[70] 黃柄橓, 以可見光光觸媒對揮發性有機物之光催化研究, 中興大學環境工程學系所學位論文, (2008) 1-132.

[2] I.E. Agency, Key World Energy Statistics, (2012).

[4] R.A. Hefner Iii, The age of energy gases, International journal of hydrogen energy, 27 (2002) 1-9.

[5] A. Wolsky, E. Daniels, B. Jody, CO2 capture from the flue gas of conventional fossil‐fuel‐fired power plants, Environmental Progress, 13 (1994) 214-219.

[6] W. Salleh, A. Ismail, T. Matsuura, M. Abdullah, Precursor selection and process conditions in the preparation of carbon membrane for gas separation: A review, Separation & Purification Reviews, 40 (2011) 261-311.