PEI-based聚醯胺複合薄膜鑑定與奈米過濾效能之研究

Study on characteristic and nanofiltration performance of PEI-based polyamide composite membranes

唐嘉璘(Chia-Lin Tang)

指導教授 ： 李魁然 ； 黃書賢

中原大學/工學院/化學工程研究所/碩士(2019年)

https://doi.org/10.6840/cycu201900562

摘要

本研究以聚碸(Polysulfone，PSf)作為製備基材膜之高分子，選用胺類單體聚乙烯亞胺(Polyethylenimine，PEI)分別與三種化學結構相異的醯氯單體(Trimesoyl chloride (TMC)、Isophthaloyl chloride (IPC)以及Succinyl chloride (SCC))，於基材膜的表面進行界面聚合反應，以製備聚醯胺(PA)/PSf複合薄膜，應用於奈米過濾程序，分離氯化鎂、氯化鈉、硫酸鎂與硫酸鈉等四種鹽類水溶液。
本研究亦使用全反射式傅立葉轉換光譜儀(ATR-FTIR)分析薄膜表面之化學結構，以場發式電子顯微鏡(FE-SEM)觀察薄膜表面以及截面的結構與形貌，利用原子力顯微鏡(AFM)觀察薄膜表面的粗糙程度，使用接觸角測量儀(WCA)量測薄膜表面之親水性質。
為了選定最佳的基材膜，本研究以不同濃度之聚碸高分子，並分別添加PEG 20k作為造孔劑，以濕式相轉化法，製備非對稱且多孔隙之PSf基材膜，探討高分子濃度對基材膜結構之影響，並以純水通量測試作為挑選基材膜的依據，最後選定PSf的濃度為18 wt%，並添加50 wt%的PEG 20k作為製備基材膜的條件。
藉由界面聚合反應製備聚醯胺選擇層於基材膜表面上，並探討醯氯單體化學結構以及聚合條件(水相溶液濃度、有機相溶液濃度、水相溶液接觸時間與有機相溶液聚合時間)對複合薄膜奈米過濾效能的影響。實驗結果顯示，由奈米過濾的測試結果得知，TMC為本實驗中最理想之醯氯單體，將PSf基材膜與0.8 wt%的PEI水相溶液接觸9分鐘，再與0.2 wt%的TMC有機相溶液進行界面聚合反應30秒，所製得之PEI-TMC/PSf 複合薄膜，具有較好的奈米過濾分離效能，於6 bar的操作壓力下，進行1000 ppm 的氯化鎂水溶液分離程序，此複合薄膜的純水透過量與阻鹽率分別為29±3 LMH與71±2 %。
為提升薄膜的分離效能，進一步改質上述聚醯胺複合膜，在其PEI水相溶液中分別添加辛基硫酸鈉(Sodium octyl sulfate，SOS)、十二烷基苯磺酸鈉(Sodium dodecylbenzenesulfonate，SDBS)以及十二烷基硫酸鈉(Sodium dodecyl sulfonate，SDS)等三種界面活性劑，以期望奈米過濾效能可以再次提升。實驗結果顯示，當SDS添加量為0.5 wt %時，複合膜的純水通量可由29±3 LMH提高至44±3 LMH，同時薄膜對氯化鎂的阻鹽率也由71±2 % 提高至94±2 %，由於適量之界面活性劑可有效增加基材膜對於胺類單體的吸附量，因此可使薄膜的表面的親水性提升，提高複合膜的純水透過量，亦可使薄膜表面之正電荷密度增加，提高薄膜對多價離子之阻擋率，以此複合膜進行四種不同鹽類水溶液的測試，薄膜對鹽類的阻擋率由高至低依序為MgCl2 (94%) > MgSO4 (93%) > Na2SO4 (92%) > NaCl (47%)，此結果顯示，此複合膜具有良好的奈米過濾分離能力。

關鍵字

聚乙烯亞胺 ； 聚醯胺 ； 界面活性劑 ； 界面聚合 ； 薄膜 ； 奈米過濾

並列摘要

In this study, polysulfone (PSf) was used as the membrane support. The asymmetrical and porous PSf support was prepared by wet phase inversion method with different concentrations of PSf and pore forming agent, polyethylene glycol (PEG 20k). The best support was prepared with 18wt% PSf and 0.5% PEG 20k, and it had the highest pure water flux. This support was used for interfacial polymerization. Polyethylenimine (PEI) as amine monomer was reacted through interfacial polymerization with different acyl chloride, such as trimesoyl chloride (TMC), isophthaloyl chloride (IPC) and succinyl chloride (SCC). After reaction, a polyamide (PA)/PSf thin film composite (TFC) membranes were obtained.
Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy determined the chemical structure of membrane. Membrane morphology and surface roughness were examined using scanning electron microscope (SEM) and atomic force microscopy (AFM). Water contact angle (WCA) measurements were used to analyze the hydrophilicity of composite membrane. Anton Parr SurPASS was used to characterize the membrane surface charge density.
The effects of acyl chloride monomer chemical structure and polymerization conditions (the monomer concentrations of aqueous and organic solutions, immersion time of aqueous solutions and polymerization time of organic solutions) on the nanofiltration performance were investigated. According to nanofiltration test, TMC as organic monomer offered better nanofiltration efficiency than that of SCC and IPC. The optimum interfacial polymerization conditions are as follows: 0.8 wt% aqueous PEI solution; 8 min contact time of PSf with PEI solution; 0.2 wt% TMC/hexane solution; and 0.5 min reaction time. PEI-TMC/PSf composite membrane exhibited high pure water flux of 29 ± 3 L/m2 h and MgCl2 rejection of 71 ± 2 %, operating at 6 bar with feed concentration of 1000 ppm salt solution.
In order to improve further the PEI-TMC/PSf composite membrane, different surfactants were added in aqueous PEI solution. These surfactants are sodium octyl sulfate (SOS), sodium dodecylbenzenesulfonate (SDBS) and sodium dodecyl sulfonate (SDS). The results shows that addition of 0.5 wt% SDS in aqueous solution enhanced the pure water flux from 29 ± 3 LMH to 44 ±3 LMH, and the rejection of MgCl2 increased from 71±2% to 94±2%. Because adding the surfactant can effectively increase the adsorption of the PEI on the PSf support, thus the hydrophilicity of the surface and pure water flux were enhanced. Moreover, the membrane surface charged become more positive, thus the rejection of multivalent ions increased. The salt rejection of membrane was as follows: MgCl2 (94%) > MgSO4 (93%) > Na2SO4 (92%)> NaCl (47%). This results show that the TFC membrane has good nanofiltration performance.

並列關鍵字

polyethyleneimine ； polyamide ； surfactants ； interfacial polymerization ； membrane ； nanofiltration

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