管式正滲透薄膜之開發

內部濃差極化是正滲透(forward osmosis, FO)膜需面臨的主要現象。為了克服這個現象，設計具有高孔隙率和高孔隙連通性的基材薄膜以防止溶質積聚是至關重要的。因此本研究進行管式聚醯胺(polyamide, PA)/聚碸(polysulfone, PSf) 正滲透複合薄膜之開發。先於PSf鑄膜液中加入添加劑，以增加PSf管狀薄膜表面孔洞及結構之連通性，再藉由界面聚合法提供一緻密PA選擇層於PSf管狀薄膜外表面，過程中探討改變不同單體結構、水相單體濃度、反應時間及熱處理溫度等對於所製備PA/PSf管狀複合薄膜FO效能之影響。添加LiCl和不同分子量之PEG至PSf鑄膜液中有助於提高薄膜表面孔洞之尺寸，同時使其皮層轉為雙連續之結構，且巨型孔洞由較深處位置開始生成並幾乎成長至基材膜底部，使改質過基材膜的連通性較高，而純水通量可由未改質前的86.48 LMH上升至719.72 LMH，有利於降低正滲透過程中內部濃度極化之問題，而此部分亦透過掃描式電子顯微鏡(SEM)、黏度計、光學顯微鏡、水接觸角儀等來探討成膜過程對於其結構型態及膜親水性之影響。界面聚合的部分，首先使用不同結構之胺單體如m-phenylenediamine (MPD)、p-phenylenediamine (PPD)、o-phenylenediamine (OPD)和醯氯單體Trimesoyl chloride (TMC)、Isophthaloyl chloride (IPC)製備一系列PA/PSf管狀複合膜，主要探討胺單體的官能基位置和醯氯基團數量對於界面聚合層及正滲透效能之影響，並透過傅利葉轉換紅外光譜(FTIR)和SEM進行鑑定。結果顯示MPD為所使用之三種胺單體中最適合的，因其具有適中的擴散速度，不會像OPD生成過厚的聚醯胺層，同時其化學結構較PPD為非線性，因此形成之聚醯胺層較為鬆散，但又能保有一定的阻鹽率。而將醯氯單體TMC和IPC進行比較， IPC為雙官能基，所產生的聚醯胺結構為線性的，因此其自我抑制能力較弱，導致生成較厚的聚醯胺層，增加薄膜的質傳阻力。因此，MPD-TMC為本研究之最佳界面聚合單體組合。將MPD-TMC/PSf管狀複合膜進行FO效能測試，在使用2M NaCl汲取液和蒸餾水做為進料液時，具有最高的水通量及可接受之鹽逆擴散，其值分別為39.53 LMH和7.05 GMH。而以此單體組合做進一步的界面聚合條件優化，如胺單體濃度、反應時間和熱處理溫度。由正滲透實驗結果顯示，採用2wt% MPD濃度、30秒的反應時間及50℃熱處理10分鐘，可製備穩定且高效能之聚醯胺超薄複合正滲透膜。提高汲取液濃度有助於提升膜兩端之滲透壓差，因此當NaCl汲取液濃度從0.5M上升至2.0M時，PA/PSf管狀複合膜FO水通量可從10.75 LMH上升至39.53 LMH，同時鹽逆擴亦隨之增加。然而若採用多價鹽Na2SO4作為汲取液時，由於Na2SO4的滲透壓較高且水合半徑較大，所以初始水通量可提升至49.61 LMH，而鹽逆擴散量則從7.05 GMH降至3.21 GMH。

關鍵字

管狀薄膜；正滲透

並列摘要

Internal concentration polarization is the major problem in forward osmosis membrane. To overcome this problem, it is essential to design a membrane support with high porosity and high pore connectivity to prevent the solute accumulation. In this study, high porosity and lower tortuosity tubular polysulfone (PSf) support was fabricated by adding LiCl and different molecular weight of polyethylene glycol (PEG) in PSf solution. The membrane formation of PSf solution containing different additives were investigated through optical microscope and rheometer. Moreover, the formed PSf supports were characterized by field emission scanning electron microscope (FE-SEM) and water contact angle measurement. According to cross-sectional images of the modified PSf support, lacy structure was formed between the skin layer and macrovoids, and the macrovoids were formed from tip to the bottom part. Furthermore, the surface became more porous. Thus, compared to pristine PSf support (PWF = 86.48 LMH), modified PSf had better pure water flux of 719.72 LMH. PA/PSf thin film composite tubular membranes were fabricated using various water-soluble amine monomers (e.g., m-phenylenediamine (MPD), p-phenylenediamine (PPD) and o-phenylenediamine (OPD)) and various organic-soluble monomers (e.g., trimesoyl chloride (TMC) and isophthaloyl chloride (IPC)). The effect of chemical structure and the amount of chloride groups on membrane property and forward osmosis performance were investigated systematically. The fabricated PA/PSf membranes were characterized by FE-SEM and FTIR. The results revealed that MPD-TMC/PSf had the highest water flux with acceptable reverse salt flux. This was because of the moderate diffusion rate and nonlinear structure of MPD. Moreover, MPD-TMC/PSf had thinner polyamide layer than that of OPD-TMC/PSf, and had lower packing density compared to PPD-TMC/PSf. Comparing TMC and IPC, IPC just has two chloride groups, the polyamide layer of MPD-IPC/PSf is linear. Thus, self-limiting is not severe during the IP process. This means that IPC can easily pass through the initial polyamide layer and keep reacting with TMC, which results in the thick selective layer of MPD-IPC/PSf, leading to an increased in mass transfer resistance and decreased in water flux. Further optimization was done for the interfacial polymerization between MPD and TMC. Several parameters were varied: different aqueous monomer concentration, reaction time and curing temperature. At optimum condition the initial water flux was 39.53 LMH when the selective layer was oriented towards a 2M NaCl draw solution. Moreover, increasing the solute concentration of draw solution could increase the osmotic pressure. When the concentration of NaCl increased from 0.5M to 2.0M, the water flux increased from 10.75 LMH to 39.53 LMH, respectively. In addition, the reverse salt flux increased from 1.91 GMH to 7.05 GMH, respectively. However, when Na2SO4 was chosen as draw solute, the water flux reached up to 49.61 LMH, and the reverse salt flux declined to 3.21 GMH. This was due to the higher osmotic pressure and larger hydration radius of Na2SO4.

並列關鍵字

tubular membrane ； forward osmosis

參考文獻

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管式正滲透薄膜之開發

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