界面活性劑對薄膜液體貫穿壓力與薄膜蒸餾影響之實驗探討

從工業廢水或生活污水中回收產製再生水成為近年重要的議題，薄膜蒸餾用於水處理也漸被重視，但該操作中，若液體貫穿薄膜將使程序失效，所以膜材液體貫穿壓力(LEP)是薄膜蒸餾(MD)模組設計與操作條件選定之重要參考數據。該壓力值除受所選定之薄膜特性所決定外，膜面接觸溶液所含的成分如界面活性劑亦會有明顯影響。基於石化、紡織放流水及生活污水等常含有界面活性劑，考量未來以薄膜蒸餾進行這些廢水的再生操作，本研究進行溶液中含界面活性劑(SDS)及鹽類(NaCl)對LEP及薄膜蒸餾影響之實驗探討，選用平均孔徑0.1與0.2μm PTFE平板薄膜，而操作條件則含界面活性劑濃度、鹽濃度及溫度等的變化。結果顯示平均孔徑0.2 μm PTFE薄膜，接觸25℃水溶液含NaCl為250 ppm及SDS在0~1000 ppm範圍，LEP量測值由346.41降至142.29kPa；而同膜材但孔徑為0.1 μm者，LEP則由485.76降至 218.84 kPa。若25℃水溶液含SDS150 ppm，而NaCl濃度250~5000 ppm範圍， 0.2μm薄膜之LEP由328.75降至145.24 kPa；而0.1μm者於相同操作條件下，LEP則由440.62降至226.69 kPa。將測量之LEP、表面張力及接觸角等數據帶入Laplace方程式，可得膜材B/r_max 值(B為膜材形狀因子，r_max為薄膜最大孔半徑)，對選用之0.1及0.2μm PTFE膜，其B/r_max 值分別為4.9及6.5 〔 1/μm 〕，以此值所估算之LEP與實驗數據相較，對0.1μm薄膜兩者差距為1~11%；而0.2μm者之差距則為1~9%。使用0.2μm薄膜，進料濃度為SDS 150 ppm及NaCl 1000 ppm於25～50℃時隨溫度上升LEP由260.05下降至212.95kPa；而溫度於50～70℃時，LEP則約維持在221.95 ± 5 kPa之範圍內。另外在薄膜蒸餾實驗方面，進料端與滲透端為60℃與25℃，分別使用0.1與0.2μm PTFE薄膜，固定NaCl為1000ppm其對應之SDS臨界濃度，0.1μm者介於3250~3500ppm；0.2μm者介於700~900ppm。固定SDS為500 ppm其 NaCl臨界濃度0.1μm者介於5000~5250 ppm；0.2μm者介於1500~1750ppm。若將被潤濕後之薄膜清洗風乾後再進行薄膜蒸餾實驗，則會快速再被潤濕，說明若膜孔已被界面活性劑附著並產生潤濕之情形，即使經由沖洗與風乾，仍無法使薄膜恢復具MD之分離性能。

關鍵字

液體貫穿壓力；薄膜蒸餾

並列摘要

Water recovery from industrial wastewater or domestic sewage is an important issue for sustainable development, and the application of membrane distillation (MD) technology for wastewater treatment has been paid more attention in recent years. In order to prevent the wetting of membranes used for MD, the liquid entry pressure (LEP) is an important characteristic of membrane. In practice, the LEP depends not only on the membrane characteristics such as the hydrophobicity and maximum pore size, but also on the solution components such as surfactant and salt that affect the surface tension. It is noted these components are often present in the wastewater streams from petrochemical plant, textile mill and the domestic sewage etc.. This study investigates experimentally the effects of surfactant (SDS) and NaCl in aqueous solution on LEP of 0.1 0.2μm PTFE membranes and its MD performance. Experimental results show that, when the SDS concentration increases from 0 to 1000 ppm under 250 ppm NaCl, LEP value of 0.2μm PTFE membrane decreases from 346.41 to 142.29 kPa, while for 0.1μm PTFE membrane its LEP decreases from 485.76 to 218.84 kPa. If SDS is maintained at 150 ppm and the NaCl concentration is varied in a range of 250 to 5000 ppm, LEP values of 0.1 and 0.2μm membranes decrease from 328.75 to 145.24 kPa and 440.62 to 226.69 kPa, respectively. The B/rmax (ratio of geometry coefficient and maximum pore size of the membrane) in Laplace equation was also determined based on the measured LEP and, for the 0.1 and 0.2μm PTFE membranes used in the study the B/rmax value is 4.9 and 6.5 [1/μm], respectively. The relative difference between experimental data of LEP and that estimated based on the Laplace equation is 1~11% for the 0.1μm membrane, and 1~9% for the 0.2μm membrane under the conditions used in the study. About the influence of solution temperature on LEP, experimental results of 0.2μm PTFE membrane with the solutions containing SDS 150 ppm and NaCl 1000 ppm, showed that the LEP decreases from 260.05 to 212.95kpa when the temperature is increased from 25 to 50 ℃. However, the LEP is remained at 221.95± 5 kPa when the temperature is further increased to 70℃. Based on the increase in conductivity of the permeate, the critical concentration of SDS and NaCl in the feed for DCMD was also determined. When the feeds containing 1000 ppm NaCl, the critical SDS concentration is 3250~3500ppm and 700~900ppm, for 0.1 and 0.2μm membranes, respectively. When SDS remains at 500 ppm, the critical concentration of NaCl in feed for the two membranes is 5000~5250 ppm and 1500~1750ppm, respectively. It is noted that if the membrane is cleaned and dried after being wetted by surfactant solution during MD operation, it will be wetted quickly when the membrane is subjected to MD operation again.

並列關鍵字

Liquid entry pressure ； Membrane distillation

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界面活性劑對薄膜液體貫穿壓力與薄膜蒸餾影響之實驗探討

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