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標題: | 製備高分子萃取膜回收金屬離子並評估其操作穩定性 Recovery of Metal Ions by Polymer Inclusion Membranes and Evaluation on the Process Stability |
作者: | Yueh-Hsien Li 李岳憲 |
指導教授: | 王大銘(Da-Ming Wang) |
關鍵字: | 高分子萃取膜,穩定性,水解反應,具分散反萃取相支撐式液膜,質傳阻力, Polymer inclusion membranes (PIM),Supported liquid membranes with strip dispersion (SLMSD),Polymer inclusion membranes with strip dispersion (PIMSD),Indium recovery,Boron recovery,Stability,Hydrolysis, |
出版年 : | 2018 |
學位: | 博士 |
摘要: | 本研究主要致力於開發具有萃取能力之高分子萃取膜(Polymer Inclusion Membranes, PIM),應用於離子回收程序上,並且針對它的材料穩定性進行探討。高分子萃取膜,為近年來廣為發展的膜分離技術,藉由將對目標物有反應性之萃取劑於製膜過程中添加入製程中,製備出具有萃取性的薄膜,且因為固態薄膜,使得萃取劑不會因為與進料相的接觸而流失,造成透過效率下降,甚至是汙染水相溶液,被視為是未來能夠作為離子回收程序的選擇之一。
研究中以商業化Di-(2-ethylhexyl) phosphate acid (D2EHPA)作為萃取劑,製備具有銦萃取性之高分子膜,以鹽酸作為反萃取溶液,檢視高分子萃取膜於強酸接觸之下,銦的透過效率以及材料穩定性。研究結果顯示,隨著操作的進行,透過係數呈現下降的趨勢;經由傅立葉轉換紅外線光譜儀的鑑定,發現在經過強酸反萃取相溶液的接觸之後,薄膜中乙醯基團之特徵吸收峰減弱,同時羥基之特徵吸收峰增強,顯示三醋酸纖維素高分子因強酸的接觸造成水解反應(Hydrolysis)的發生,並且在掃描式電子顯微鏡觀察結果中也發現,經過酸液接觸的膜表面呈現較為不平整。進一步地利用X射線光電子能譜儀分析薄膜中含磷成份,發現接觸酸液前後,膜內磷的含量由6.1 wt%降至2.0 wt%,顯示萃取劑與塑化劑等含磷有機相成份的流失。 本研究提出結合具分散反萃取相之操作程序(Polymer Inclusion Membranes with Strip Dispersion, PIMSD),利用含有萃取劑之有機相,將強酸反萃取溶液分散其中,希望藉此達到保護膜材免於直接長時間接觸酸液。當置入0.6 M D2EHPA作為有機相,於操作20小時內皆無觀察到透過係數隨時間改變之現象,且進料相pH值並未觀察到顯著的變化;但當進行更長時間的試驗,進料相pH值則仍會下降,顯示氫離子仍會因水解而透過至進料相,形成材料穩定性問題。 在嘗試結合具分散反萃取相的方式之後,本研究進一步地結合疏水性聚丙烯多孔膜的程序,改善穩定性的問題。由於聚丙烯 (Polypropylene, PP) 具有絕佳的抗化性,使得擁有良好的材料穩定性。於具分散反萃相高分子萃取膜程序中,置入聚丙烯薄膜於高分子萃取膜與具分散反萃取液之間,因本身疏水性使得水相的強酸液滴不會接觸到高分子萃取膜,經過連續5天的操作,進料相pH值並未觀察到明顯的改變,銦透過係數為1.9x10^-4 m/min,成功地達到改善材料穩定性的目的。 本研究中藉由結合具分散反萃取相以及聚丙烯薄膜方式達到改善穩定性的目的,因此,對於透過係數與質傳阻力之間的關係進行討論。利用膜分離程序中所得的銦透過係數,進行質傳阻力的探討。從結果中發現,高分子萃取膜於成膜過程當中,將會相分離成油相組成含量較多(Polymer-poor phase或Gel phase)以及高分子含量較多(Polymer-rich phase)的區域;經由分析高分子萃取膜與支撐式液膜兩系統之間的質傳阻力,其關係為Rgel=2.3Rliq' ,這也說明高分子萃取膜其透過係數並未因為是固態膜而降低至一個數量級。 另外,本研究利用具分散反萃取相支撐式液膜(Supported Liquid Membranes with Strip Dispersion, SLMSD)的技術,進行硼回收的長時間穩定性操作試驗,由於目前商業化硼萃取劑中,以2,2,4-Trimethyl-1,3-pentanediol (TMPD)萃取效果最佳,但由於為二醇類小分子,存在水溶性的疑慮,因此藉由較長時間的試驗,測試操作穩定性。於較大規模(膜面積為8.1 m2)支撐式液膜系統長時間試驗中,結果顯示,在操作12天之後,透過係數降為原先的1/6,其原因為TMPD本身水溶性所造成,使得有機相中萃取劑含量隨操作而減少。本研究嘗試將TMPD萃取劑於製膜程序中,添加進入鑄膜液中,製備出具硼萃取性之高分子萃取膜。由於TMPD萃取劑藉由膜內TBEP塑化劑使其溶解於膜內,成為固態膜,因此理論上較不會溶出進入進料側。當經過較長時間試驗時,發現反萃取相之氫氧根離子會透過至進料相,使進料相pH值上升,顯示高分子萃取膜於接觸強鹼反萃取液的情況下,發生水解反應造成材料穩定性的問題。進一步地利用結合聚丙烯膜的程序改善回收硼的系統,經過連續15天的操作,進料相pH值並未觀察到明顯的改變,皆維持於2.65左右。 The major aim of the present work is to develop the polymer inclusion membranes (PIM), and evaluate their process stability. PIM is formed by casting a solution containing an extractant, a plasticizer and a base polymer. Stability has been the main advantage attributed to PIM in comparison with other liquid membranes. We used di-(2-ethylhexyl) phosphate acid (D2EHPA) as extractant and prepared CTA-PIM membranes to recover indium, which hydrochloric acid solution as stripping phase, and then to evaluate the stability. When 5 M HCl as stripping phase, the indium permeability was 2.3×10^-4 m/min, but it decreased with time, by observation and analysis of Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM), the membrane surface was hydrolyzed by acidic stripping solution, and the content of phosphorous atoms within membrane decreased. Combination with strip dispersion, called polymer inclusion membranes with strip dispersion (PIMSD), there was no significant variation in feed pH and indium permeability maintained 2.5×10^-4 m/min during 20 hours operation. For long-term operation, the feed pH also declined from 1.00 to 0.67, it means that the acid-catalyzed hydrolysis still occurs. We proposed an operation scheme which combined PIMSD and hydrophobic microporous polypropylene (PP) membrane, by using PP membrane to protect CTA-PIM membrane. As a result, this scheme could maintain the feed pH and indium permeability during 5 days. In addition, the boron long-term stability was examed by supported liquid membranes with strip dispersion (SLMSD) technique, which 2,2,4-trimethyl-1,3-pentanediol (TMPD) as boron extractant. TMPD is a good commercial extractant for boron extraction, but it is slightly soluble in water, hence the long-term operation stability in SLMSD would be evaluated. For long-term operation, the permeability decreased from 3.1×10^-5 m/min to 4.9×10^-6 m/min after 12 days operation, and then we re-added 0.1 M TMPD extractant to the original organic solution, the boron permeability increased from 4.9×10^-6 m/min to 1.5×10^-5 m/min, it mean that the TMPD extractant was loss out of the organic phase. In the next, we proposed a PIM separation process to recover boron. It was observed that, the feed pH value would increase sharply after about 2 hours, we thought it caused by hydrolysis of CTA polymer, this behavior revealed the material stability of PIM membrane, hence, we proposed an operation scheme which combined PIMSD with PP membrane to improve the stability. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/70069 |
DOI: | 10.6342/NTU201800371 |
全文授權: | 有償授權 |
顯示於系所單位: | 化學工程學系 |
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