疏水無機薄膜之製備及其於真空薄膜蒸餾與薄膜結晶之應用

Preparation of Hydrophobic Inorganic Membranes for Vacuum Membrane Distillation and Vacuum Membrane Crystallization

柯家傑(Chia-Chieh Ko)

指導教授 ： 童國倫

國立臺灣大學/工學院/化學工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201900283

摘要

伴隨著人類生活品質需求的提高與工業科技的快速發展，純水以及原物料缺乏是已經面臨的問題；同時，在電子科技廠、海水淡化廠或汙水處理廠的廢水排放，也是另一個重要的議題。透過薄膜蒸餾（MD）與薄膜結晶（MCr）程序，可由只含非揮發性物質之水溶液中獲得純水並進一步濃縮達到過飽和狀態以獲得結晶物質，利用此程序對廢水進行再次提濃將有利於達成淨零排放（ZLD）目標。近年來，極端薄膜分離程序之需求越來越高，具備高機械強度、良好熱穩定性及耐化性的無機薄膜（金屬薄膜、陶瓷薄膜等）備受矚目，然而工業化會是個挑戰，相對於平板薄膜，管狀膜及中空纖維薄膜具備量產容易與填充密度高之優點，其中後者更可提供相當高之填充密度（單位設備體積提供之有效面積＞1000 m2/m3）。因此本研究致力於製備疏水陶瓷管狀與中空纖維薄膜、探討製備參數對薄膜結構之影響、證實陶瓷薄膜於MD/MCr程序之適用性、提升陶瓷薄膜本身應用價值。
在本研究中， PMSQ氣凝膠管狀膜與疏水氧化鋁中空纖維膜應用於真空薄膜蒸餾（VMD）與薄膜結晶（VMCr）系統，前者透過溶膠凝膠法將多孔PMSQ氣凝膠成長於氧化鋁管狀膜進行製備，同時進行縮孔與疏水改質；後者透過相轉換與燒結之結合技術進行製備，嘗試製備於VMD中具高效能之疏水陶瓷薄膜。研究過程中，探討合成條件對PMSQ氣凝膠管膜與紡製參數、燒結溫度對疏水氧化鋁中空纖維膜薄膜結構與VMD效能之影響。研究發現：（1）氣凝膠覆蓋情形受溶劑∕前驅物莫耳比值影響，當比值1時，可以避免形成過大的孔洞；（2）改質次數的增加雖然改善了氣凝膠覆蓋情形，卻同時引起平均孔徑與孔隙度的下降；（3）薄膜的多孔結構可透過改變溶膠凝膠法中所使用的鹽酸濃度進行調整，於0.14 wt%鹽酸下所製備的氣凝膠管膜具備較佳的VMD效能；（4）氧化鋁中空纖維薄膜之幾何對稱性易受紡絲間隙影響；（5）中空纖維膜之微結構可透過調整鑄模液流速進行控制；（6）燒結溫度之提升，造成平均孔洞與孔隙度之大幅度下降。
最後於紡絲間隙為20 cm、鑄模液流速為15 ml/min、燒結溫度為1400℃之條件下，製備出具備高水通量（3000 Lm−2h−1bar−1）之氧化鋁中空纖維膜（平均孔洞220 nm），其經過改質劑（FAS）疏水化後，於VMD中呈現出優異效能（通量：60 Lm-2h-1，NaCl擋率＞99.9%，進料：3.5 wt% NaCl水溶液（70℃）），高孔隙（55%）與薄膜較薄之特性使其成為具備最高MD通量之陶瓷膜，甚至可媲美高分子膜。另外，首次成功將陶瓷膜應用於薄膜結晶系統，利用PMSQ氣凝膠管膜與疏水氧化鋁中空纖維薄膜搭配VMCr成功地從高濃度溶液中獲得NaCl或LiCl結晶。

關鍵字

零排放 ； 薄膜蒸餾 ； 薄膜結晶 ； 疏水 ； 無機陶瓷薄膜 ； 中空纖維薄膜 ； 氣凝膠

並列摘要

Lack in pure water and raw material is an urgent problem accompanying with the rise in life quality requirement and the rapid development in industrial technology. Furthermore, the treatment of the discharge from technology plants, seawater desalination plants and wastewater treatment plants is another issue. Membrane distillation (MD) and membrane crystallization (MCr) are relatively emerging membrane separation processes with potential to recover pure water and minerals from non-volatile concentrated aqueous solution that offers exciting opportunities to achieve the target, “Zero Liquid Discharge, (ZLD).” In recent years, inorganic membranes including metal, ceramic membranes have attracted great of interest due to its high mechanical strength, good thermal stability and chemical durability that can be used in extreme membrane separation process for various application such as ultra-pure water or organic solvent production and heavy-metal wastewater treatment, however industrialization might be a challenge. Tubular and hollow fiber membrane are more attractive because of their large-scale production and high packing density, especially hollow fiber which provides packing density greater than 1000 m2/m3, as respect to flat sheet membrane. This study is dedicated to preparation of hydrophobic tubular and hollow fiber membranes, investigation of fabricated parameter effect on membrane structures, applicability confirmation of ceramic membranes for MD/MCr process.
In this study, PMSQ tubular aerogel membrane and hydrophobic alumina hollow fiber membrane were applied to VMD and VMCr processes. The former was prepared by coating PMSQ aerogel on alumina tubular support via sol-gel method, and the latter was fabricated by combined phase-inversion and sintering method and hydrophobilization. To optimization, we explored the influence of preparation parameters on the structures of both membranes and VMD performance. Our findings led us to give following conclusions: (1) Growth quality of PMSQ aerogel on alumina tubular support was depended on solvent/precursor molar ratio. (2) Even though the raise in modified frequencies improved the growth quality, it caused the decay in average pore size and porosity. (3) Pore size of PMSQ tubular aerogel membrane can be tuned by changing the HCl concentration used in sol-gel method. (4) Air gap was important for making alumina hollow fiber with symmetric cross-sectional geometry. (5) Suspension flow rate affected the microstructures in alumina hollow fiber. (6) Raise in sintering temperature, 1400 to 1500℃, caused significant drop in average pore size and porosity of alumina hollow fiber.
Finally, the alumina hollow fiber membrane which prepared with the parameters of 20 cm, 15 ml/min and 1400℃ in air gap, suspension flow rate and sintering temperature, exhibited 220 nm in average pore size and high pure water flux as 3000 Lm−2h−1bar−1. After hydrophobilizaiton, the hydrophobic alumina hollow fiber membrane showed 60 Lm-2h-1 in permeate flux and over 99.9% in rejection in VMD using 3.5 wt% NaCl aqueous solution at 70℃ at 3 kPa. The high porosity of 55% and thin thickness of hollow fiber made the permeate flux exceeded that of PMSQ tubular aerogel membrane that also overtook the literature data. Furthermore, well-VMD-performance ceramic membranes were applied to VMCr and eventually produced NaCl and LiCl crystals from highly concentrated aqueous solution. It is the first time applying ceramic membrane to MCr process.

並列關鍵字

Zero liquid discharge (ZLD) ； Membrane distillation (MD) ； Membrane crystallization (MCr) ； Hydrophobic ； Inorganic membrane ； Hollow fiber ； Aerogel

參考文獻

[1] M.M. Shirazi, A. Kargari, M.J. Shirazi, Direct contact membrane distillation for seawater desalination, Desalin. Water Treat. 49 (2012) 368–372.

[2] I. Shiklomanov, World fresh water resources. In Water in Crisis: A Guide to the World's Fresh Water Resources, P.H. Gleick Editor, Oxford University Press, Inc.: New York, NY, USA (1993).

[3] E. Drioli, A. Ali, F. Macedonio, Membrane distillation: Recent developments and perspectives, Desalination 356 (2015) 56–84.

[4] E. Drioli, A. Criscuoli, E. Curcio, Membrane Contactors: Fundamentals, Applications and Potentialities, Elsevier Science: Amsterdam, The Netherlands, (2006).

[5] A. Alkhudhiri, N. Darwish, N. Hilal, Membrane distillation: A comprehensive review, Desalination 287 (2012) 2–18.