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题名: 醋酸纤维素正渗透膜的制备及其应用研究
作者: 李国亮
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 栾兆坤
关键词: 正渗透,醋酸纤维素,膜性能,SiO2掺杂,浓差极化 ; Forward Osmosis, Cellulose Acetate, Membrane Performance, SiO2 doping, Concentration Polarization
其他题名: Fabrication and Application of Cellulose Acetate Forward Osmosis Membrane
学位专业: 环境工程
中文摘要:     正渗透作为一种新型的水处理技术,由于具有能耗低、回收率高、操作简单以及对组件要求低等特点,在污水处理、食品加工、苦咸水和海水淡化、医药以及极端环境应急水处理等领域具有广阔的应用前景。然而,目前的正渗透技术仍处于试验探索的初步阶段,距离大规模应用仍存在许多关键技术需要解决,如正渗透膜的研发、汲取体系及分离技术的研究等。制备具有较小内浓差极化效应的正渗透膜是实现正渗透技术应用的关键因素之一。理想正渗透膜的特点如下:具有较薄的膜致密分离层和多孔的支撑层,具有较高的机械强度,具有较好的物化稳定性和抗污染性能等。本研究以醋酸纤维素为膜材料,结合支撑体系和膜改性技术,制备了多种醋酸纤维素正渗透膜,采用多种表征手段,系统考察了制膜工艺和正渗透分离过程对膜渗透分离性能的影响,进一步完成无机掺杂改性正渗透膜的制备与性能研究,并对正渗透膜的应用进行了初步研究,取得了如下成果:
1.以醋酸纤维素为膜材料,系统考察了溶剂、支撑材料、铸膜液浓度和温度,以及挥发、凝胶和热处理过程对成膜性能的影响,得到了最佳的制膜工艺:以 NMP为溶剂,丙酮为添加剂,配制  18  wt.%的 CA铸膜液,在室温静置  24  h脱气;以 150目涤纶网为支撑刮膜,在  50℃的恒温恒湿环境中挥发 60  s后,转至 5℃的凝胶浴中浸泡 18 h;初生膜在 70℃的水中继续浸泡 1 h,制得醋酸纤维素正渗透膜。
2.制备的   CA-PET膜呈“三明治”结构,厚度在  120 μm左右,上下表面均较平滑,具有较高的机械强度  (37.86  N)、较好的亲水性  (51.4°)和较高的孔隙率(74.2%)。以此为研究对象,对影响膜分离过程的研究表明:以水为原料液时,在 PRO模式时的水通量   (9.83 L•m-2•h-1)高于   FO模式   (6.63  L•m-2•h-1),而以模拟污水为原料液时,水通量降低,PRO和  FO模式时的水通量分别为  7.68和   5.03L•m-2•h-1;体系温度升高会提高膜的渗透性能,而对分离性能不利,汲取液一侧温度对膜渗透分离性能的影响大于原料液一侧;适当提高膜面流速可显著降低外浓差极化效应;水通量随着汲取液浓度升高而升高,相同浓度时,不同类型汲取液产生的渗透压不同,从而影响膜的水通量。
3.以最佳制膜工艺为基础,制备了   SiO2纳米粒子掺杂醋酸纤维素膜。结果表明,SiO2的掺杂   (由未掺杂升高至掺杂量为 0.4%)对膜上表面影响不大,而增加了下表面粗糙度(Ra由  1.95升至  9.93 nm)、亲水性  (接触角由 50.3°降至  42.2°)和孔隙率  (74.2%增至 81.1%);掺杂对致密分离层孔径影响不大  (0.3  nm左右),而使孔径分布稍向大孔方向偏移;SiO2的掺杂提高了膜的渗透性能,而分离性能基本稳定。
4.制备的   CA-PET膜具有较好的耐酸耐碱性,在  pH  2~11的范围内具有较稳定的渗透分离性能,FO和PRO模式时的渗透通量分别为 6.55±0.57和   9.45±0.5L•m-2•h-1;而 SiCA-0.2膜耐碱性差,在  pH  2~8的范围内较稳定,FO和PRO模式时的水通量分别为 8.6±0.24和  12.34±0.59  L•m-2•h-1。经 5.5 d的运行后清洗,CA-PET膜在 FO和  PRO模式时的通量恢复率分别为 97.6%和 94.3%,而  SiCA-0.2膜两种模式时的通量恢复率分别为 97.2%和 93.2%,说明污染层易清洗,形成的污染为可逆污染。
5.所制备的两种膜与   HTI (CA-ES)膜均具有较高的截盐率,三种膜对 NaCl的截留率为 96%左右,对 MgSO4的截留高达  99%。经 SiO2纳米粒子掺杂后,膜对橙汁的浓缩效率为未掺杂时的约 1.5倍,运行过程中产生的污染经清洗后具有较高的通量恢复率  (CA-PET:  94.4%,SiCA-0.2: 92.2,HTI(CA-ES):  96.1%),说明形成的污染为可逆污染,膜具有较好的抗污染性能。制备的膜具有较小的内浓差极化效应。
英文摘要:     Forward  osmosis  (FO),   a  novel  technology   for  water  treatment,  has   broad prospect of  applications in  waste water  treatment, food  process, brackish  water and seawater  desalination,   drugs   and  emergency   drinking  water   supply  in   extreme environment  due  to  its  superiority  such  as   low  energy  consumption,  high  water recovery,  easy  operating   and  low  requirements  for  the   modules  and  equipment. However,  FO is  still  in its  primary  exploring  stage as  some  key  technologies still needs  to   be  overcome,  such   as  the  FO   membranes,  the  draw   solution  and  its separation   technology.    An   FO   membrane    with   small    internal   concentration polarization  (ICP)  effect   is  one  of  the  key  points   for  FO  applicatio.  The   ideal membranes  fit  for  the   FO  process  should  have   such  advantages:  thin  active  or selective   layer,    porous    support   layer,    high   mechanical    strength,    and   well physicochemical  and fouling  resistance.  In this  study, serious  FO  membranes were fabricated via  a phase inversion  process using  cellulose acetate (CA),  support layers and   additives.  The   membranes   were  characterized   and   the   parameters  of   the
fabrication  and  the operation  process  were  studied.  In  addition,SiO2  doping  CA membranes were fabricated as well  as the membrane applications were studied in this work.
1. Cellulose  acetate was used  for the membrane  preparation and the  parameters such as the solvent, support layer, casting solution  concentration and temperature, and the evaporation,  coagulation  and annealing  processes were  all studied.  The  optimal process was  as follows: CA  solution of 18  wt.% was prepared  with NMP as  solvent and acetone as the additive. After deaerated at room temperature for 24  h, the solution was cast  with  a PET  net mesh  as the  support  layer. Then  undergoing a  continuous processes of evaporating  at 50℃  for 60  s, coagulating at  a 5℃  water bath for  18 h,and annealing at 70℃  water for 1 h, the membrane was obtained.
2. The  membrane showed  a sandwich  structure and the  thickness was  of about 120 μm. It  has high mechanical strength (37.86N),  high hydrophilia (contact angle of 51.4°) and  high  porosity (74.2%).  The membrane  separation  processes was  studied using  membrane as  prepared and  showed  as follows:  the  water flux  in  PRO mode(9.83 L•m-2•h-1) was  higher than that in  FO mode (6.63 L•m-2•h-1  ) when using water as the feed, while decreased using simulated water as the feed, and were 7.68 and 5.03 L•m-2•h-1 ,respectively. The raising system temperature favored the permeability while adversed  to the  selectivity, and  the  influence of  the draw  solution  temperature was greater  than   the  feed.   An  appropriate   flow   velocity  of   the  membrane   surface significantly  diminished   the  external   concentration  polarization.   The  water  flux increased as  the draw solution  concentration rises.  Different types  of draw solutions differ in osmosis pressure at the same concentration, and thus affect the water flux.
3.  The SiO2  nano-particles doping  cellulose acetate  membranes  were prepared based on  the optimized process  and the results  showed that the doping  of SiO2  (0 to 0.4%) has little effect on the top  surface, while increasing the roughness (Ra  increases from 1.95  to 9.93 nm), hydrophilia  (contact angle decreases  from 50.3°to 42.2°)  and the porosity  (increases  from74.2% to  81.1%) of  the bottom  surface.  The doping  of SiO2 has little effect on the pore size (around 0.3 nm), while promoted the  distribution to  the   large  side.  The   doping  increased  the   permeability  while  maintained   the separation property.
4.  The CA-PET  membrane  has high  physicochemical  resistance and  performs steady  at the  pH  2~11.  The water  flux  in  FO and  PRO  mode  was 6.55±0.57  and 9.45±0.5  L•m-2•h-1, respectively.  The SiCA-0.2  membrane  has low  alkali resistance and performs  steady at pH  2~8. The water  flux in  FO and PRO  mode was 8.6±0.24 and 12.34±0.59 L•m-2•h-1, respectively. The membranes were cleaned after 5.5 days of operation. The  water flux  recovery for  CA-PET in  FO and  PRO mode  were 97.6% and  94.3%, respectively.  While for  SiCA-0.2  were 97.2%  and  93.2%, espectively. This indicated that the fouling can be cleaned easily and was reversible.
5. The fabricated membranes  were compared with the commercial HTI (CA-ES)membrane. The study showed  that all the membranes have high  rejection for NaCl of around 96%, and for MgSO4  of around 99%. After doping of SiO2  nano-particles, the concentrating  efficiency  for  the  orange juice  was  about  1.5  times  of  the  original CA-PET membrane. The water flux recovery after cleaning was high to 94.4%,92.2% and 96.1%  for  CA-PET, SiCA-0.2  and HTI  (CA-ES), respectively,  which  indicated the fouling  was reversible  and the  membranes had  high fouling resistance property.The  fabricated   membranes  had  less   inner  concentration  polarization   effect  than commercial HTI (CA-ES) membrane.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36876
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
李国亮. 醋酸纤维素正渗透膜的制备及其应用研究[D]. 北京. 中国科学院研究生院. 2016.
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