張海珍, 周秉武, 湯永健, 許振良
(化學(xué)工程聯(lián)合國(guó)家重點(diǎn)實(shí)驗(yàn)室, 華東理工大學(xué) 化學(xué)工程研究所 膜科學(xué)與工程研發(fā)中心,上海 200237)
PES中空纖維含哌嗪-氟單體聚酰胺納濾膜制備及耐氯性能
張海珍, 周秉武, 湯永健, 許振良
(化學(xué)工程聯(lián)合國(guó)家重點(diǎn)實(shí)驗(yàn)室, 華東理工大學(xué) 化學(xué)工程研究所 膜科學(xué)與工程研發(fā)中心,上海 200237)
以聚醚砜(PES)-N,N-二甲基乙酰胺(DMAc)-PEG200為鑄膜液體系,制備了PES中空纖維超濾膜,討論了空氣段間距和芯液組成對(duì)PES中空纖維超濾膜的影響。選用PESUFB90中空纖維超濾膜為基膜,以0.5%(w/v)哌嗪(PIP)和0.5% (w/v) 2,2-二(1-羥基-1-三氟甲基-2,2,2-三氟乙基)-4,4-亞甲基雙苯胺(BHTTM)為水相溶液,0.15%(w/v)均苯三甲酰氯(TMC)為油相溶液,采用界面聚合法制備了PES中空纖維復(fù)合納濾膜,利用SEM、AFM和動(dòng)態(tài)接觸角等表征了PES基膜和納濾膜的性能,討論了操作壓力和鹽濃度對(duì)PES納濾膜分離性能的影響,測(cè)定了納濾膜的孔徑,考察了膜的耐氯性能。結(jié)果表明,界面聚合后PES膜的表面粗糙度提高;PES基膜的接觸角大于納濾膜的接觸角,納濾膜親水性較好;納濾膜的有效孔徑約為0.5 nm;0.6 MPa下,純水通量為31.2 LMH,對(duì)硫酸鹽的截留率在90% 以上。此外,經(jīng)1000 ppm NaClO處理18 h后,膜通量和截留無(wú)明顯變化,顯示良好的耐氯性能。
中空纖維;混合二胺;納濾膜;制備;性能
通常,納濾膜是一種介于超濾和反滲透之間以壓力為驅(qū)動(dòng)力的分離膜,孔徑小于2 nm,同時(shí)具有Donnan效應(yīng)和尺寸篩分效應(yīng),可選擇性分離一價(jià)、二價(jià)離子且對(duì)小分子量(200~1000)中性有機(jī)物具有較好的截留效果。納濾膜在硬水軟化、海水淡化、地表水脫色與除雜等方面的應(yīng)用受到極大關(guān)注[1~5]。在對(duì)含鹽、含染料等廢水的處理及回用方面,目前使用的納濾膜大部分為平板膜[6,7]。相對(duì)于平板膜,中空纖維膜具有填充密度高、有效面積大、易清洗等優(yōu)點(diǎn),中空纖維納濾膜以其優(yōu)勢(shì)廣泛關(guān)注。目前,納濾膜的主要制備方法為界面聚合[8~11]。在應(yīng)用過(guò)程中,納濾膜對(duì)目標(biāo)物的截留效果及長(zhǎng)期運(yùn)行穩(wěn)定性至關(guān)重要,目前關(guān)于納濾膜運(yùn)行穩(wěn)定性的研究較少,且運(yùn)行時(shí)間普遍較短[12,13]。此外,水處理過(guò)程中,常用NaClO和Cl2等進(jìn)行殺菌消毒,水中余氯的存在使得膜的耐氯性能研究十分必要。
在前文基礎(chǔ)上[10,14],本文以聚醚砜(PES)-N-N-二甲基乙酰胺(DMAc)-PEG200為鑄膜液體系,制備了PES中空纖維超濾基膜,討論了空氣段間距和芯液組成對(duì)PES中空纖維超濾基膜的影響。選用PESUFB90中空纖維超濾膜為基膜,以0.5%(W/V)哌嗪(PIP)和0.5%(W/V)含氟二胺(BHTTM)混合單體為水相,通過(guò)界面聚合法制備PES中空纖維納濾膜,探討了操作壓力與鹽溶液濃度對(duì)納濾膜純水通量與截留性能的影響,尤其納濾膜對(duì)不同無(wú)機(jī)鹽及有機(jī)物的截留性能,討論了1000 mg·L-1NaClO溶液浸泡時(shí)間的納濾膜耐氯性能。
2.1 原料與試劑
聚醚砜(PES,E6020P),德國(guó)BASF應(yīng)用化學(xué)有限公司;均苯三甲酰氯(TMC)、N,N-二甲基乙酰胺(DMAc)、哌嗪(PIP)、聚乙二醇200(PEG200)、聚乙二醇400(PEG400)、聚乙二醇20000(PEG20K)、牛血清蛋白(BSA)、正己烷、硫酸鈉(Na2SO4)、硫酸鎂(MgSO4)、氯化鎂(MgCl2)、氯化鈉(NaCl)、硫酸鈉(Na2SO4)、硫酸鎂(MgSO4)、氯化鎂(MgCl2)葡萄糖、蔗糖和棉子糖,分析純,國(guó)藥集團(tuán)化學(xué)試劑有限公司;2,2-二(1-羥基-1-三氟甲基-2,2,2-三氟乙基)-4,4-亞甲基雙苯胺(BHTTM,純度 > 98%),實(shí)驗(yàn)室自制。
2.2 PES中空纖維超濾基膜及納濾膜制備
2.2.1 PES中空纖維超濾基膜
將一定量的DMAc與PEG200加入錐形瓶中攪拌1 h,而后加入經(jīng)干燥處理的PES,常溫下攪拌12 h形成透明均勻的17%(wt) PES鑄膜液,靜置脫泡24 h后紡絲、純水清洗和備用。不同空氣段間距(0、5、10和20 cm) PES超濾膜分別以PESUFA00、PESUFA05、PESUFA10和PESUFA20標(biāo)記。不同芯液組成(H2O:DMAc = 100:0、50:50、25:75和10:90) PES超濾基膜分別以PESUFA00、PESUFB50、PESUFB75和PESUFB90標(biāo)記。
2.2.2 PES中空纖維納濾膜
將PES基膜從去離子水中取出,晾至表面無(wú)明顯液滴,將兩端密封后的膜浸入水相(0.5%(W/V))PIP和0.5%( W/V) BHTTM),2 min后取出,用壓縮氣體吹掃膜表面液滴后置于0.15%( W/V) TMC正己烷溶液中,15 s后將膜取出放入80℃ 烘箱熱處理[10,11]。制備的PES納濾膜標(biāo)記為PESNFB。
2.3 膜形貌結(jié)構(gòu)FE-SEM表征
FE-SEM(Nova NanoSEM 450)觀察膜的表面形貌與斷面結(jié)構(gòu)。
2.4 膜性能評(píng)價(jià)
2.4.1 純水通量
采用自制的中空纖維膜性能測(cè)試裝置對(duì)膜的純水通量進(jìn)行測(cè)試,將納濾膜裝入組件密封后,分別在0.1和0.6 MPa下測(cè)定PES基膜和納濾膜的通量,純水預(yù)壓30 min,待通量穩(wěn)定后進(jìn)行測(cè)試,每個(gè)樣品測(cè)試3次,取平均值。計(jì)算公式如下:
式中,Q表示水的滲透體積(L);A表示膜的有效面積(m2);t表示滲透體積為Q時(shí)對(duì)應(yīng)的時(shí)間(h)。
2.4.2 截留率和脫鹽率
PES基膜的截留率分別用500 mg·L?1的BSA和PEG20K溶液測(cè)定。分別用500 mg·L?1的PEG200、PEG400、葡萄糖、蔗糖、棉子糖水溶液和2000 mg·L?1的Na2SO4、MgSO4、NaCl、MgCl2測(cè)定納濾膜的截留性能和脫鹽率。一定壓力下預(yù)壓30 min,待流量穩(wěn)定后,測(cè)定透過(guò)液及原料液的濃度。截留率與脫鹽率的計(jì)算公式如下:
其中,R為截留率或脫鹽率(%);Cf為原料液的濃度(mg·L?1);Cp為透過(guò)液的濃度(mg·L?1)。
雷磁數(shù)顯電導(dǎo)率儀(DDS-307A)和總有機(jī)碳分析儀(TNM-1,SHIMADZU)分別用于測(cè)定無(wú)機(jī)鹽和有機(jī)物的濃度。
2.4.3 納濾膜耐氯性能
3000 mg·L?1NaClO溶液浸泡納濾膜1 h后,用純水清洗待用;討論1000 mg·L?1NaClO溶液浸泡時(shí)間對(duì)納濾膜性能的影響,并檢測(cè)不同浸泡時(shí)間下納濾膜的純水通量與Na2SO4截留性能,以此考察其耐氯性能。
3.1 PES中空纖維超濾膜性能
超濾膜的制備條件及親水性與強(qiáng)度的測(cè)試結(jié)果見表1??諝舛伍g距及芯液組成對(duì)膜滲透與截留性能的影響如圖1所示。由圖1可知,隨空氣段間距增加純水通量先提高再下降,而BSA和PEG20K的截留率先下降而后趨于穩(wěn)定。由圖2可知,隨芯液中DMAc含量增加純水通量先提高再下降,而BSA和PEG20K的截留率先下降再提高。PESUFB90膜的BSA和PEG20K截留率分別為95.9% 和71.8%,是8種PES中空纖維超濾膜中最高的。此外,PESUFB90膜純水通量90.0 L·m-2·h-1(0.1 MPa)。同時(shí),空氣段間距和芯液組成對(duì)中空纖維基膜靜態(tài)接觸角和機(jī)械強(qiáng)度的影響見表1,PESUFB90膜的靜態(tài)接觸角為75.1°。因此,選取PESUFB90中空纖維超濾膜作為納濾膜基膜。
表1 空氣段間距和芯液組成對(duì)中空纖維基膜靜態(tài)接觸角和機(jī)械強(qiáng)度的影響Table 1 Effects of air-gap distances and bore fluid composition on static contact angle and mechanical properties of the PES hollow fiber UF membranes
圖1 空氣段間距對(duì)PES中空纖維超濾膜純水通量和截留率的影響Fig.1 Effects of air-gap distance on the flux and rejection of PES hollow fiber UF membrane
圖2 芯液組成對(duì)PES中空纖維超濾膜純水通量和截留率的影響Fig.2 Effect of bore liquid composition on the flux and rejection of the PES hollow fiber UF membrane
3.2 PESUFB 90中空纖維基膜與納濾膜結(jié)構(gòu)
如圖3A中,PES納濾膜外表面存在明顯聚合物層。與PESUFB90中空纖維基膜相比,納濾膜表面有大量的微納結(jié)構(gòu),這是界面聚合反應(yīng)形成的典型聚酰胺層結(jié)構(gòu)[15]。根據(jù)文獻(xiàn)[14]的PES基膜與納濾膜表面形貌及粗糙度,PESUFB90 (文獻(xiàn)[14]的M)中空纖維基膜的表面較為光滑平整,界面聚合后,膜的表面(文獻(xiàn)[14]的MPB)粗糙度增加。這是因?yàn)镻IP與TMC間的反應(yīng)較為劇烈,使得生成的聚酰胺來(lái)不及有序排列,從而形成粗糙的膜面結(jié)構(gòu)。這說(shuō)明AFM測(cè)得的膜面粗糙度直觀上與SEM圖片的結(jié)果一致。
圖3 PESUFB90中空纖維基膜與納濾膜的SEM圖Fig.3 SEM images of PESUFB90 hollow fiber support membrane and NF membranes A. enlarged cross section near outer surface B. cross-section C. outer surface[14]
3.3 PES中空纖維納濾膜截留分子量和分離性能
由圖4可見,所制備的納濾膜純水通量為 (31.2±0.2) L·m-2·h-1(0.6 MPa),對(duì)無(wú)機(jī)鹽的截留順序?yàn)椋篘a2SO4(99.7%) > MgSO4(92.3%) > NaCl (43.6%) > MgCl2(28.2%),表明此膜表面帶負(fù)電。同時(shí)PESNFB對(duì)于不同小分子有機(jī)物的截留率分別為:PEG200 71.7% (Mw= 200 Da)、PEG400 94.0% (Mw= 400 Da)、棉子糖97.1% (Mw= 504 Da和r= 0.538 nm)、蔗糖 94.1%(Mw= 341 Da和r= 0.471 nm)、葡萄糖70.6% (Mw= 180 Da和r= 0.359 nm)。由有機(jī)物的分子量和斯托克斯半徑可知[16],納濾膜的有效孔徑約為0.5 nm。
圖4 納濾膜純水通量、不同無(wú)機(jī)鹽和有機(jī)物的截留性能Fig.4 Pure water permeation (PWP) and rejection of the NF membrane for inorganic salts and low molecule-weight organics
圖5 不同壓力下納濾膜的滲透通量與截留率Fig.5 Pure water permeation (PWP) and rejection of the NF membrane at different operation pressures
3.4 操作壓力和鹽濃度對(duì)PES中空纖維納濾膜性能的影響
由圖5可見,0.2 MPa時(shí)膜通量為5.20 L·m-2·h-1,對(duì)Na2SO4的截留率為94.3%;隨著操作壓力的增大,膜通量和截留率均增加,0.6 MPa時(shí)膜純水通量和截留率分別為31.2 L·m-2·h-1和99.7%;操作壓力繼續(xù)增加時(shí),膜通量緩慢增加而截留率基本不變。其原因如下:操作壓力增大有利于膜純水通量的增加,由于膜孔大小不一,通量測(cè)試過(guò)程中,不同操作壓力下膜的固有阻力不同,且壓力持續(xù)增大會(huì)造成膜絲的形變,這兩方面因素共同影響導(dǎo)致膜的純水通量先快速增加而后緩慢增大[17]。
由鹽通量計(jì)算公式Js=Kp(Cb-Cf)可知,鹽通量與操作壓力無(wú)關(guān),僅與膜兩側(cè)的鹽濃度差有關(guān),故操作壓力增加,鹽通量不會(huì)升高。但壓力導(dǎo)致的水通量的增加會(huì)提高膜的鹽截留率,致使膜兩側(cè)的鹽濃度差增大,而鹽濃度差的增大又會(huì)導(dǎo)致鹽通量的增加,從而降低鹽截留率。這兩方面因素共同作用導(dǎo)致膜對(duì)Na2SO4的截留先升高而后趨于穩(wěn)定。Na2SO4濃度對(duì)納濾膜通量和截留率的影響如圖6所示。Na2SO4濃度從500 ppm增加到2500 ppm過(guò)程中,膜通量基本不變,保持在30 L·m-2·h-1左右,Na2SO4截留率略有下降,從99.7% 降至98.5%。這是由于納濾膜對(duì)Na2SO4的截留過(guò)程中,隨Na2SO4濃度的增加,濃差極化作用增強(qiáng),納濾膜面處的鹽濃度升高;同時(shí),鹽濃度的增加使得離子在膜表面的吸附量增加,吸附的離子會(huì)屏蔽膜表面的電荷,使得膜表面所帶凈電荷降低,從而對(duì)離子的截留率下降。
圖6 納濾膜對(duì)不同Na2SO4濃度的滲透通量與截留率Fig.6 Permeation and rejection of the NF membrane with different Na2SO4concentrations
圖7 NaClO處理對(duì)納濾膜性能的影響Fig.7 Effects of the NaClO treatment on the NF membrane
3.5 納濾膜耐氯性能
在水處理工藝中,常用NaClO和Cl2等進(jìn)行消毒殺菌,而氯會(huì)破壞膜表面聚酰胺結(jié)構(gòu),損害膜性能,DOW納濾膜FILMTECTMNF270-400/34i和FILMTECTMNF90-400/34i要求進(jìn)水含氯小于0.1 ppm[10](如納濾膜壽命三年(20000 h)計(jì),則為2000 ppm·h Cl),因此納濾膜的耐氯性能研究至關(guān)重要。以純水通量和Na2SO4截留率來(lái)表征膜經(jīng)NaClO溶液處理后的納濾性能,結(jié)果如圖7所示。由圖7可知,經(jīng)1000 ppm NaClO處理18 h后(即18000 ppm·h NaClO,或8580 ppm·h Cl。)的膜通量和Na2SO4截留分別32.2 L·m-2·h-1和98.5%,與無(wú)NaClO處理的膜通量(31.2 L·m-2·h-1)和Na2SO4截留(99.7%)相比,無(wú)明顯變化。這是由于含氟單體中的強(qiáng)吸電子基團(tuán) -F可以和酰胺中的氮原子相互作用,防止酰胺被氯破壞,因此與DOW納濾膜相比,具有良好的耐氯性能[10]。
以PESUFB90中空纖維超濾膜作為納濾膜基膜,PIP和BHTTM混合二胺為水相單體、TMC為有機(jī)相單體,采用界面聚合法制備PES中空纖維納濾膜,并對(duì)所制備納濾膜的結(jié)構(gòu)及性能進(jìn)行了考察。結(jié)果表明,經(jīng)界面聚合后,PES中空纖維膜表面形成聚酰胺層結(jié)構(gòu),膜面粗糙度提高,親水性增強(qiáng)。滲透與截留測(cè)試結(jié)果表明,以混合二胺為水相制備的納濾膜PESNFB具有較好的滲透與截留性能。納濾膜的有效孔徑約為0.5 nm,對(duì)NaSO4和MgCl2的截留率達(dá)90% 以上。經(jīng)1000 ppm NaClO處理18 h后,納濾膜對(duì)Na2SO4的通量與截留基本未變,顯示較強(qiáng)的耐氯性能。
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Preparation and Chlorine-Tolerant Performance of Piperazine-Fluoropolyamide Contained PES Hollow Fiber Nanofiltration Membranes
ZHANG Hai-zhen, ZHOU Bing-wu, TANG Yong-jian, XU Zhen-liang
(State Key Laboratory of Chemical Engineering, Membrane Science and Engineering R&D Lab, Chemical Engineering Research Center, East China University of Science and Technology, Shanghai 200237, China)
Ultrafiltration (UF) membranes composed of polyethersulfone (PES) hollow fiber were fabricated using PES-DMAc-PEG200 as the dope solution. Effects of air-gap distance and bore liquid composition on the flux and rejection of the prepared membrane were discussed. PES hollow fiber nanofiltration (NF) membranes were prepared via interfacial polymerization using PESUFB90 hollow fiber UF membrane as support, 0.5% (W/V) piperazine (PIP) and 0.5% (W/V) 2,2'-bis(1-hydroxyl-1-trifluoromethyl-2,2,2- triflutoethyl)-4,4'-methylenedianiline (BHTTM) as the water phase solution and 0.15% (W/V) trimesoyl chloride (TMC) as the organic phase solution. The performance of the PES support and NF membrane were characterized by SEM, AFM and dynamic contact angle measurement. The effects of operation pressure and salt concentration on the performance of NF membrane were investigated and the pore size of the NF membrane was obtained. In addition, the chlorine tolerant property of NF membrane was evaluated. The results show that the surface roughness of the PES support increases after interfacial polymerization, and the contact angle of the PES NF membrane is lower than that of the PES support. The effective pore size of the NF membrane is about 0.5 nm. Pure water flux and the rejection for sulfates of the NF membrane are 31.2 LMH and over 90% under 0.6 MPa, respectively. Moreover, the flux and rejection have no obvious change after treated with 1000 ppm NaClO for 18 h, which shows good chlorine tolerant of the PES NF membrane.
hollow fiber; mixed diamines; nanofiltration membrane; preparation; performance
TQ 028.8
A
10.3969/j.issn.1003-9015.2016.06.024
1003-9015(2016)06-1405-06
2016-05-11
2016-07-20。
國(guó)家科技部支撐計(jì)劃項(xiàng)目(2014BAB07B01,2015BAB09B01);江蘇省科技支撐計(jì)劃(BE2013031);國(guó)家發(fā)改委能源局項(xiàng)目(2013-117)。
張海珍(1986-),女,江蘇徐州人,華東理工大學(xué)博士生。
許振良,E-mail:chemxuzl@ecust.edu.cn