製備顆粒型聚偏二氟乙烯薄膜及薄膜蒸餾之應用

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Title:	製備顆粒型聚偏二氟乙烯薄膜及薄膜蒸餾之應用
Other Titles:	Preparation of particulate polyvinylidene fluoride membranes and their application in membrane distillation processes
Authors:	楊承道;Yang, Cheng-Dau
Contributors:	淡江大學化學工程與材料工程學系碩士班鄭廖平;Cheng, Liao-Ping
Keywords:	顆粒型薄膜;直接接觸式薄膜蒸餾;聚偏二氟乙烯;particulate membrane;DCMD;PVDF
Date:	2015
Issue Date:	2016-01-22 15:02:30 (UTC+8)
Abstract:	DMF/PVDF 製膜液融解在不同溫度(50、60、70 和80 oC)，浸入正辛醇沉澱槽，製備出多孔型PVDF 薄膜，其代號分別為FO50、FO60、FO70 及FO80，薄膜結構對稱，結晶顆粒尺寸均一，孔洞與孔洞互通貫穿整張薄膜。當製膜液融解溫度為50 oC，顆粒尺寸只有1um，相對的當融解溫度為提高至80 oC，顆粒尺寸成長到2um。四種薄膜孔隙度為66%，結晶度55%，接觸角133o(上表面)、126o(下表面)，抗張強度隨著顆粒尺寸增加而降低，因為顆粒間的連結減少所造成。薄膜測試直接接觸式薄膜蒸餾(DCMD)，其阻隔率大於99%，操作條件：3.5 wt%NaCl(aq)；Tfeed = 52 oC；Tproduct = 18 oC；進料與產物流速皆為0.7 L/min；FO60、FO70 及FO80 有較高的通量(12、14、16 LMH)，然而FO50 通量只有2.7 LMH。當進料溫度或流速提升，通量也隨之提高。另一方面增加NaCl 氯化鈉水溶液濃度，通量下降。FO60 薄膜測試DCMD 48 小時，通量從11.6 降低至10.5 LMH，阻隔率仍維持在99%以上。DMF/PVDF 製膜液融解在不同溫度(50、60、70 和80 oC)，浸入正辛醇沉澱槽，製備出多孔型PVDF 薄膜，其代號分別為FO50、FO60、FO70 及FO80，薄膜結構對稱，結晶顆粒尺寸均一，孔洞與孔洞互通貫穿整張薄膜。當製膜液融解溫度為50 oC，顆粒尺寸只有1um，相對的當融解溫度為提高至80 oC，顆粒尺寸成長到2um。四種薄膜孔隙度為66%，結晶度55%，接觸角133o(上表面)、126o(下表面)，抗張強度隨著顆粒尺寸增加而降低，因為顆粒間的連結減少所造成。薄膜測試直接接觸式薄膜蒸餾(DCMD)，其阻隔率大於99%，操作條件：3.5 wt%NaCl(aq)；Tfeed = 52 oC；Tproduct = 18 oC；進料與產物流速皆為0.7 L/min；FO60、FO70 及FO80 有較高的通量(12、14、16 LMH)，然而FO50 通量只有2.7 LMH。當進料溫度或流速提升，通量也隨之提高。另一方面增加NaCl 氯化鈉水溶液濃度，通量下降。FO60 薄膜測試DCMD 48 小時，通量從11.6 降低至10.5 LMH，阻隔率仍維持在99%以上。 Microporous PVDF membranes were prepared by immersion-precipitation of DMF/PVDF solutions dissolved at different temperatures (50, 60, 70, and 80 oC) in 1-octanol bath. The membranes formed (termed FO50, FO60, FO70, and FO80) exhibited a symmetric structure, consisting of nearly equal-sized crystalline particles that interlinked into a continuous matrix, in which porous channels dispersed. When the dope was dissolved at 50 oC, the particles were only ~1 micron; in contrast, the particles expanded significantly to ~3 microns, if dissolution was carried out at 80 oC. All membranes had a similar porosity of ~66%, crystallinity of ~55%, and water contact angles of 133o (top surface) and 126o (bottom surface). The tensile strength decreased with increasing particle size, due to reduced and particle-particle interconnection. The membranes were tested for performance in desalination via direct contact membrane distillation (DCMD). High rejections (> 99%) were attained for all membranes operated under the conditions: feed concentration = 3.5% NaCl(aq), Tfeed = 52 oC, Tproduct = 18 oC, and circulation rates = 0.7 L/min for both feed and product streams. The permeation fluxes for the membranes FO60, FO70, and FO80 reached high IV values of 12, 14, and 16 LMH, respectively; however, that for FO50 was only 2.7 LMH, consistent with the morphologies of these membranes. As the feed temperature or the circulation rate was raised, the permeation flux increases as well. On the other hand, raising the salt concentration in the feed caused decrement of the permeation flux. For the membrane FO60 operated over the period of 48 h., the flux decreased slightly from 11.6 to 10.5 LMH, rejection >99%.
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