聚醯胺與聚醯亞胺膜於滲透蒸發與蒸氣揮發之研究

A study of polyamide and polyimide membranes for pervaporation and vapor permeation

范舒晴(Shu-Ching Fan)

指導教授 ： 李魁然 ； 賴君義

中原大學/工學院/化學工程研究所/博士(2004年)

https://doi.org/10.6840/cycu200400277

摘要

中 文 摘 要
本論文探討聚醯胺(polyamide, PA)與聚醯亞胺薄膜(polyimide, PI)結構的變化及成膜方式對薄膜應用在滲透蒸發(pervaporation, PV)與蒸氣滲透(vapor permeation, VP)程序，分離具共沸組成醇類水溶液效能之影響，並深入分析薄膜成膜機制及分離機構。此外，研究也將合成新型有機/無機奈米混成薄膜，藉由無機層材(clay)的添加，提昇聚醯胺或聚醯亞胺之機械性質、化學熱安定性，並進一步評估此改質程序對奈米混成薄膜應用在滲透蒸發與蒸氣滲透程序之可行性。
文中以二胺，例如: 1,4-bis(4-aminophenoxy)2-tert-butylbenzene (BATB)、4-bis(4-amino phenoxy)-2,5-di-tert-butylbenzene(BADTB)、2,2’-dimethyl-4,4’- bis(4-aminophenoxy) biphenyl(DBAPB)、1,4-bis(4-aminophenoxy)benzene(BAPB)、4,4’- Methylenedianiline(MDA)及各種不同結構的二酸例如: 4,4’-hexafluoroisopropylidene dibenzoic acid (6FDAc) 、tertphthalic acid(TPAc)、5-tert-butylisophthalic (TBPAc)或二酸酐例如: 4,4’-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA)、3,3’-4,-4’-Diphenylsulfone tetracarboxylic Dianhydride (DSDA)、4,4’-Biphthalic dianhydride (BPDA)、3,3',4,4'- benzhydrol tetracarboxylic dianhydride(BHTDA)利用 Yamazaki /Higashi method進行直接聚縮合反應，合成一系列不同結構之聚醯胺及聚醯亞胺高分子。而此一系列的聚醯胺與聚醯亞胺均能溶於極性溶劑中，方便於膜材的製備。
由於乾式相轉換法製備之聚醯胺與聚醯亞胺薄膜，應用於PV或VP分離時透過量低是其較大的缺點。利用化學合成導入巨大基團於高分子鏈中可以提昇分離時的透過量，因此研究中藉由導入不同的主鏈基團觀察二胺、二酸或是二酸酐結構的改變對膜材膨潤度與滲透蒸發分離效能的影響。實驗中發現bulky group的導入的確可以提昇透過量，尤其是hexafluoropropyl group，可以有效提昇透過量，不過也由於氟基團的疏水性使得操作在高濃度乙醇進料時，因為膨潤度的上升使得對水的選擇性下降。因此嘗試利用蒸氣滲透分離系統降低薄膜的膨潤度，得以維持選擇性。此外也針對膜材對不同醇類進料於分離效能上的影響作探討，實驗中發現隨著進料醇類疏水性的增加，進料與膜材間的溶解參數差下降，意指進料與膜材間的親合力隨之上升因此吸附選擇性隨之下降。但是由於高碳數的醇類有較大的莫爾體積導致擴散阻力上升，因此當進料為高碳醇水溶液時有最好的選擇比。
由於乾式膜普遍透過量不高，因此本研究嘗試針對聚醯胺的部分利用DMAc為溶劑，水、甲醇、乙醇、丙醇、丁醇為凝聚劑，利用濕式相轉換法成膜方式探討不同的凝聚劑對芳香族聚醯胺薄膜成膜機制的影響。實驗中藉由SEM來觀察薄膜結構的變化，以FTIR microscopy/ATR、染色實驗、滴定霧點實驗等瞭解不同醇類凝聚劑對成膜機制的影響，並且藉由蒸氣滲透實驗分離90wt%乙醇水混合溶液，探討結構與分離效能間的關係。發現當凝聚劑醇類碳數增加時，薄膜的楊氏係數（Young’s modulus）會隨之上升並且薄膜整體的孔隙度（porosity）會隨之下降。利用染色實驗以Fickian’s diffusion law計算出凝聚劑在鑄膜液中的擴散速度則為：水＞甲醇＞乙醇＞正丙醇。最佳的滲透揮發分離效能是以乙醇為凝聚劑所製備之薄膜，在25℃下分離90wt%乙醇水溶液蒸氣[EtOH]vapor=90.8wt%，透過量為657g/m2-h、αwater/EtOH=21。
此外，研究中進一步製備聚醯胺/蒙脫土與聚醯亞胺/蒙脫土奈米混成複合材（polyamide/clay and polyimide/clay hybrid nanocomposite materials）以滲透蒸發分離系統分離醇類水溶液，探討無基層材的添加對聚醯胺與聚醯亞胺薄膜安定性及分離效能上之影響。奈米混成複合材主要是以親油性的蒙脫土先分散於NMP溶劑中，再添加縮合劑以直接縮合的方式所製備而成。奈米混成複合材的層間結構主要是以WXRD與穿透是電子顯微鏡（TEM）做觀察，實驗結果顯示蒙脫土的矽酸鹽層分別以脫層（exfoliated）與插層（intercalated）兩種方式分散於高分子材料中。與未添加蒙脫土的聚醯胺高分子做比較，添加適當的蒙脫土可以有效的增加高分子材的熱穩定性與機械強度。也因為片狀的矽酸鹽層可以抑制高分子主鏈的擾動，因此添加黏土也可以提升玻璃轉移溫度。此外，本研究也針對無機蒙脫土的添加量對滲透蒸發進料的膨潤度與分離效能做探討。實驗發現添加2wt%的蒙脫土於polyamide中具有最佳之滲透蒸發分離效能

關鍵字

聚醯胺 ； 薄膜 ； 蒸氣揮發 ； 滲透蒸發 ； 聚醯亞胺

並列摘要

Abstract
In this article, the effects of membrane structure and membrane formation processes of polyimide and polyamide membranes on the pervaporation and vapor permeation performance of dehydrating an aqueous alcohol solution was investigated. The membrane formation mechanism and separation mechanism were also discussed. Furthermore, novel organic/inorganic hybride nanocomposite (polyamide/clay and polyimide/clay) membranes were synthesized to improve mechanical properties and thermal stability. The pervaporation and vapor permeation performance of these novel organic/inorganic hybride nanocomposite membranes for dehydrating aqueous alcohol solution was evaluated.
The aromatic polyamides and polyimides were prepared by using Yamazaki /Higashi method to direct polycondensation of various diamines such as 1,4-bis(4-aminophenoxy)2-tert-butylbenzene (BATB)、4-bis(4-amino phenoxy)-2,5-di-tert-butylbenzene(BADTB)、2,2’-dimethyl-4,4’- bis(4-aminophenoxy) biphenyl(DBAPB)、1,4-bis(4-aminophenoxy)benzene(BAPB)、4,4’- Methylenedianiline(MDA) with diacids 4,4’-hexafluoroisopropylidene dibenzoic acid (6FDAc) 、tertphthalic acid(TPAc)、5-tert-butylisophthalic (TBPAc) or dianhydrides 4,4’-(Hexafluoroisopropylidene)diphthalic anhydride (6FDA)、3,3’-4,-4’-Diphenylsulfone tetracarboxylic Dianhydride (DSDA)、4,4’-Biphthalic dianhydride (BPDA)、3,3',4,4'- benzhydrol tetracarboxylic dianhydride(BHTDA). All of polyamides and polyimides were soluble in polar solvents and facilitate to membranes fabrication.
In general, the disadvantage of using dense homogeneous polyamide and polyimide membranes prepared via a dry phase inversion for pervaporation and vapor permeation is the low permeation rate. It was known that a bulky segment or larger pendent groups were introduced into the backbone of the polyamide or polyimide, resulting in the permeation rate increases. Thus, to improve the permeation rate of the dense membranes, bulky segment was introduced into the main chain of the polyamide or polyimide polymers. Effects of substituted groups on the swelling degree and pervaporation performance were observed. It was found that introducing bulky substituted groups, such as hexafiuoropropane group the permeation rate could be enhanced. However, the swelling degree of the fluorine-containing membranes increases with increasing the alcohol concentration in the feed, resulting in the lower separation factor. Hence, vapor permeation operation was used to prevent the high swelling degree of membrane at the high alcohol concentration of feed solution. Compared with pervaporation, vapor permeation effectively increases the permselectivity of water. In addition, the pervaporation and vapor permeation performances of a 90wt% aqueous alcohol solution through the polyamide membrane shows that an increase in the separation factor and a decrease in the permeation rate occur as the number of carbon atoms in the alcohol increases.These results can be explained by the diversity of molecular size and the solubility parameters difference between the feed solutions and the membranes. The affinity between feed solution and membrane increases with the solubility parameter difference decreases. On the other hand, alcohol with higher numbers of carbon atom has larger molar volume and enhances the diffusion resistance and diffusivity selectivity.
The wet phase inversion method was used to understand the effects of coagulation media on the membrane morphology, membrane porosity and the vapor permeation performance of aqueous ethanol mixtures through wet phase inversion prepared asymmetric polyamide membrane were investigated. The membrane morphology and membrane formation properties were characterized SEM, FT-IR microscopy, FT-IR ATR, Light transmission experiment, penetration test and clouding point measurement. The Young’s modulus increases and membrane porosity of the asymmetric polyamide membrane decreased with increasing the molar volume of coagulation medium. The diffusivity of coagulation medium ranks in the following order: water＞methanol＞ethanol＞n-propanol. The optimum vapor permeation results, a separation factor of 21 and permeation rate of 657 g/m2h, were obtained with the asymmetric polyamide membrane prepared from the ethanol.
At last, the polyamide/clay and polyimide/clay hybrid nanocomposite membrane were prepared by direct polycondensation in the presence of organo-modified montmorillonite in N-methyl-2-pyrrolidinone (NMP) and tested with alcohol solution by pervaporation. The organo-modified montmorillonite (organo-clay) was prepared by using sodium dodecyl sulfate as a swelling agent in silicate layers of monrillonite. The morphology of the nanocomposite membranes were characterized by using Wide-Angle X-ray Diffraction (XRD) and Transmission electron microscopy (TEM), which indicated that the organo-clay existing intercalated and exfoliated in the nanocomposite membranes. The nanocomposite membranes showed superior properties in the thermal stability and mechanical properties comparing with pristine membrane. The glass transition temperatures of nanocomposite membranes were higher than pristine membrane. The effects of the organo-clay concentrations, feed solution composition and the degree of swelling on the pervaporation performances in aqueous alcohol mixtures through the polyamide/clay nanocomposite membranes were also investigated. It shows that the permeation rates decreased and separation factors increased as the clay content lower than 2wt% in the polyamide/clay hybrid membranes.

並列關鍵字

vapor permeation ； pervaporation ； polyimide ； polyamide

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