醋酸纤维素正渗透膜的制备及其应用研究
文献类型：学位论文
| 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. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/36876]  |
| 专题 | 生态环境研究中心_环境水质学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 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. |
入库方式： OAI收割
来源：生态环境研究中心
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