無機中空纖維膜之結構、孔洞控制與規模化技術開發及其於碳捕捉與滲透蒸發之應用

Abstract

近十幾年來，工業技術的躍進與經濟的蓬勃發展，帶動高規格或極端薄膜分離程序之需求，如超純(無水)溶劑、超純水、重金屬/強酸鹼廢水/溶劑、高溫有害氣體等生產或處理程序。而此需求，間接促進了無機薄膜之研究發展。無機薄膜（如金屬、陶瓷薄膜等）因材料本身具有高化學、機械與熱穩定性，在極端分離環境下，相較於高分子薄膜能展現更好之分離效能與穩定性。目前廣泛應用於化學化工、環工、能源、食品與醫藥等領域之所需分離程序上。 在無機薄膜之基礎研究發展漸趨成熟後，規模化（工業化）製造與系統之技術開發將為下一個發展進程。透過紡製方法所製備之中空纖維型態薄膜，具有量產容易與高填充密度（單位設備體積之有效處理面積 > 1000 m2/m3）之優點，該技術發展水平被視為薄膜技術規模化程度之指標。為此，本研究致力於開發無機中空纖維薄膜之規模化製造技術、探討薄膜結構設計和孔洞控制之方法，並發展可能之應用，為本土無機薄膜製造與應用技術扎根。 第一章節中，首先回顧陶瓷薄膜之發展與傳統製備技術，幫助了解整體研究背景與展望未來。接著介紹陶瓷中空纖維膜之紡製技術，並簡述其成膜機制，為設備建置、結構設計與孔洞控制等研究提供參考資料。最後，介紹陶瓷中空纖維膜於後續應用端（薄膜蒸餾、薄膜接觸器碳捕捉、中空纖維沸石薄膜之氫氣分離與滲透蒸發之應用）之運作原理，以及沸石薄膜之文獻回顧。 第二章中主要探討陶瓷中空纖維膜的紡製參數對其微結構、孔徑之影響，進而對後續薄膜接觸器應用或做為基材使用之中空纖維膜，進行微結構與孔徑設計。透過此研究，成功開發出單一孔徑分佈（~ 0.2 μm）之陶瓷中空纖維膜，為後續使用提供適當之表面孔徑，提升薄膜品質與應用效能。所製備之陶瓷中空纖維膜在疏水化後，於薄膜蒸餾（MD）與薄膜接觸器碳捕捉應用（MC）上，皆展現目前最優異之處理效能（Vacuum MD: 60 L m-2 h-1 for 3.5 wt% salt in water at 70℃; MC: 3.0 mmol m-2 s-1 for 10 vol% CO2 in N2）。本章節最後，提出創新性中孔洞氣凝膠塗佈縮孔改質技術，有效將巨孔的陶瓷膜（> 0.2 μm）縮小孔洞至中孔洞範圍（2~50 nm），並利用氣凝膠的高孔隙度特性（> 90 %）提升薄膜接觸器薄膜表面之接觸面積，大幅提升陶瓷薄膜於薄膜接觸器碳捕捉應用上之效能三倍以上。 第三章中，透過成長MFI型沸石薄膜於陶瓷中空纖維膜上，成功製備成中空纖維沸石薄膜（孔徑~ 5.5Å），進一步將本研究應用廣度推向微孔範圍（< 2 nm）。本章節中將深入探討，陶瓷中空纖維膜之表面曲度對所支撐的沸石薄膜品質之影響。研究發現，所使用的基材之曲度越大（即中空纖維膜外徑越小），可能使得所支撐之沸石薄膜在模板基（template or called “structure directing agents”, SDA）移除過程中，產生更多的晶間缺陷。此外研究發現，所合成之沸石薄膜，其小分子氣體通量（如He、H2）呈現隨溫度上升而上升之正相關趨勢，與理論模型推論不符（遵循Knudsen diffusion mechanism負相關）。透過理論模型與實驗設計，成功解釋此正相關趨勢，乃因中空纖維基材上所乘載之沸石薄膜，在升溫過程中受到基材膨脹之徑向熱應力擠壓，產生晶間缺陷擴大之情形所致。此研究結果說明，發展複合型無機中空纖維薄膜，基材表面曲度效應對薄膜品質之影響應加以考量。 第四章中，研究發現氧化鋁基材之鋁離子在沸石薄膜合成與熱處理過程中，會有擴散至沸石結構，降低其結構Si/Al比導致孔洞疏水性弱化之情形，將不利後續滲透蒸發脫醇（dealcoholization by pervaporation for 5 wt% ethanol in water at 60℃）之應用。本研究提出以沈浸塗佈法（dip-coating）於氧化鋁中空纖維膜上成長多孔釔安定氧化鋯（yttria-stabilized zirconia, YSZ）之薄膜中間層，成功製備釔安定氧化鋯中空纖維薄膜（孔徑~ 80 nm），並證實此YSZ中間層能有效阻擋鋁離子之擴散，幫助製備出純矽MFI型沸石中空纖維膜（silicalite-1 hollow fiber membranes），大幅提升沸石薄膜之孔洞疏水性，改善滲透蒸發脫醇效能。 第五章總結前三章節之研究成果，並根據研究成果與經驗展望未來，以及針對後進可能遭遇之困難給予可能之解決辦法。最後，本研究成功建立的無機中空纖維膜紡製系統與奠定相關研究基礎，將為後續本土無機薄膜研究發展提供一大助力。

Ceramic membranes have attracted considerable attention during the last decade due to their superior mechanical strength, chemical durability and thermal stability. Their great natural properties have made them an alternative to polymeric counterparts in various extreme separation applications, such as the field of environment, energy, chemical, food engineering, pharmaceutical industries, etc. To step into a chapter of industrialization of ceramic membranes, the membrane configurations should be facile to process and scale up. Hence, hollow fiber membrane configurations were born in response, which had a great advantage in achieving attractive membrane packing density (surface-to-volume ratio >1000 m2/m3). First, we focused on the development of the spinning technique for making ceramic hollow fiber membranes. The effects of slurry composition, spinning parameters and sintering temperature on the membrane properties, such as microstructures, pore sizes, porosity and permeability, were investigated. The prepared alumina hollow fiber membranes were demonstrated with competitive performances in membrane contactor applications for both CO2 capture and distillation. Next, for high temperature separation where polymer membranes cannot survive, ceramic membranes have undoubted predominance due to their superior thermal stability. As a result, we developed MFI type zeolite membranes supported by macroporous alumina hollow fiber membranes, attempting to separate H2 from the products (normally H2/CO2) of water-gas-shift (WGS) reaction at 350~550℃. It was found that the alumina hollow fiber supported MFI type zeolite membranes experienced a thermal mismatch between the support and the zeolite layer, which were demonstrated to become serious as the substrate curvature increased. Gas permeation experiments combining with a theoretical model were conducted to study this thermal mismatch problem. Finally, highly permeable alumina supported yttria-stabilized zirconia (YSZ) hollow fiber membrane was successfully prepared by a dip-coating method, which was used to support silicalite-1 membrane for ethanol/water pervaporation (dealcoholization from 5 wt% ethanol in water) for the first time. SED/EDX analysis confirmed the YSZ intermediate layer could be a barrier to restrain the aluminum, its appearance lowering the hydrophobicity of zeolite pores, from diffusion into the zeolite structure during synthesis and calcination. As a result, MFI type zeolite hollow fiber membrane with high Si/Al ratio (∞, silicalite-1) could be obtained when supported by the YSZ coated alumina hollow fiber substrate, exhibiting a promising ethanol/water separation performance in pervaporation.