| 题名 | PVDF中空纤维疏水膜制备及应用 |
| 作者 | 侯得印 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 王军 ; 栾兆坤 |
| 关键词 | 膜蒸馏 聚偏氟乙烯复合膜 力学性能 除硼 脱盐除氟 |
| 中文摘要 | 本文针对当前疏水膜通量较低、机械强度差等限制膜蒸馏技术应用的瓶颈问题，在深入探讨相转化法中空纤维膜成形机理的基础上，开展了纳米粒子改性力学增强型聚偏氟乙烯(PVDF)中空纤维复合膜制备工艺及膜蒸馏应用研究，取得了如下创新性成果： 1. 系统考察了溶剂、固含量、无机纳米粒子、非溶剂添加剂等因素对中空纤维膜结构及性能的影响，优化并确定了气隙长度、凝胶浴组成与温度等膜制备工艺条件，建立了基于无机-有机混合型添加剂的新型铸膜液体系，成功制备了通量较高、盐截留效果好、疏水性强的增强型PVDF中空纤维疏水复合膜，为疏水膜产业化提供了技术支撑。 2. 详细研究了无机纳米粒子加入量及不同后处理方式对PVDF复合膜结构特征与膜性能的影响，无机纳米粒子的加入可有效改善PVDF中空纤维膜的机械性能，复合膜的最大拉伸应变可达140.67%，抗拉强度提高到6.13 MPa，酸洗后处理具有一定的扩孔作用，可增加膜通量约15%；不同后处理过程对复合膜的机械性能影响轻微。 3. 研究分析了膜组件结构和流体技术参数变化对直接接触式膜蒸馏通量的影响。提高热侧进水温度、流速、并流运行方式等均有利于膜蒸馏通量的提高；随着膜组件长度及封装率的提高，膜通量呈下降趋势。膜组件中纤维膜束规则排列与随机排列相比，流体在组件壳程分布均匀，且不同区域内壳程流量差别不大，沟流效应得到有效抑制，可提高膜通量10.7-22.4%。 4. 系统开展了膜蒸馏除硼技术应用研究，重点考察了pH值、硼浓度、盐度等因素对膜蒸馏除硼过程的影响。与反渗透膜技术相比，膜蒸馏技术除硼效率高达99.9%以上，产水中硼浓度<20 μg/L，且进水pH值、硼浓度及盐度对其除硼效率的影响较小。 5. 依据膜蒸馏脱盐的技术优势，考察了高氟苦咸水膜蒸馏脱盐除氟效果及其浓缩过程中的膜污染现象。随着浓缩倍率的提高，浓水侧产生CaCO3沉淀，造成组件管程进水口堵塞、膜污染并润湿，脱盐效率下降。预酸化可有效防止CaCO3沉淀产生，连续运行300 h，膜通量保持稳定，产水率高达80%以上，产水电导率<4.0 μS/cm，实验研究结果为太阳能-膜蒸馏反应器奠定了技术研发基础。 |
| 英文摘要 | In this study, a novel casting dope with the mixture of inorganic salt and soluble polymer as non-solvent additive was introduced to fabricate hydrophobic hollow fiber membrane of polyvinylidene fluoride (PVDF) by phase inversion process. To improve the mechanical properties of the hollow fiber, hydrophobic inorganic nano-particles were added into the casting dope. As a result, the PVDF composite membrane exhibited excellent mechanical properties and good hydrophobicity. During boron removal and brackish groundwater concentration processes through direct contact membrane distillation (DCMD), the experimental results showed that the membrane had high permeate flux and solute rejection, indicating that the self-prepared membrane may be of great potential in prospective industrialization. The following results were obtained: 1. The influence factors on membrane structures, such as solvent, solid content, non-solvent additive, air gap distance, the temperature and components of coagulation bath were investigated. It was found that the PVDF hollow fiber membrane with the mixture of inorganic salt LiCl and soluble polymer polyethylene glycol (PEG) 400 as non-solvent additive had an ultra-thin skin, a porous support layer and a narrow pore size distribution. The membrane structure had the advantage of decreasing the vapor transport resistance, enhancing the permeate flux and keeping a high salt rejection. 2. The PVDF composite membranes were prepared by dispersing hydrophobic inorganic nano-particles in PVDF casting solutions. The addition of nano-particles could enhance tensile strength and stretching strain at break to 6.13 MPa and 140.67%, respectively. It was found that immersion cleaning of the composite membranes with dilute hydrochloric acid could enlarge the membranes pore size and improve the permeate flux about 15%, and not destroy the mechanical properties of hollow fiber membranes. 3. The influence of membrane module configuration and fluid parameter on permeate flux was investigated. It was beneficial to the permeate flux enhancement to improve the feed temperature and flow rate. Compared with cross-current flow, co-current flow can obtain higher permeate flux. With the increase of the module length and packing density, the permeate flux would decline. Regular packing of the hollow fibers in the module could weaken the channeling effect and enhance the permeate flux about 10.7-22.4%. 4. The removal of boron from aqueous solution by DCMD was studied with self-prepared PVDF membranes. The effect of pH, boron concentration, temperature and salt concentration of the feed on boron rejection was investigated. The experimental results indicated that boron rejection was less dependent on pH, boron and salt concentration of the feed. The model seawater primary reverse osmosis producing water containing 15 mg/L of boron was treated by DCMD. The permeate boron kept below 20 µg/L and the boron rejection was above 99.9%. 5. The concentration process of brackish groundwater was fully investigated and membrane fouling caused by inorganic salts crystallization was also deeply discussed. With the increase of concentration factor, the precipitation of CaCO3 would foul the hollow fibers and a rapid flux decline was observed. DCMD process could be efficiently used for production high-quality potable water from pre-acidified brackish groundwater with water recovery at as high as 80%. The experimental results were very useful for exploitation of solar-powered membrane distillation system. |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/35018]  |
| 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 | 侯得印. PVDF中空纤维疏水膜制备及应用[D]. 北京. 中国科学院研究生院. 2010. |
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