碳纳米管和纳米纤维素晶体对超滤膜性能的提升研究

发布时间：2018-01-10 09:24

  本文关键词：碳纳米管和纳米纤维素晶体对超滤膜性能的提升研究　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

  更多相关文章： 碳纳米管 纳米纤维素晶体 表面涂覆改性 共混改性 膜污染 超滤膜机械强度

【摘要】：超滤技术能够有效保障饮用水生物安全性。超滤工艺占地面积小、易于实现模块化、自动化程度高。超滤过程不发生化学反应、不产生二次污染、环境友好。超滤技术现已大规模应用在水处理中。限制超滤技术发展的瓶颈问题主要包括膜污染现象、膜材料亲水性弱、超滤膜机械强度不足。这些问题均直接与超滤膜本身性质相关。为了解决以上问题,提升超滤膜性能,本论文从膜改性角度出发,采用表面涂覆改性和共混改性两种方法,选取碳纳米管(CNTs)和纳米纤维素晶体(CNCs)两种纳米材料作为改性材料,对聚醚砜(PES)超滤膜进行改性。系统考察CNTs表面涂覆改性对膜污染控制及膜阻力分布的影响并探讨其机理;研究并比较CNTs和CNCs共混改性对纳米复合膜形貌、亲疏水性和机械强度的影响及其机理。本论文以实际水体作为水源,首先考察运行工况优化对膜污染的控制效果。膜池内污染物分析结果表明,超滤过程中非溶解性颗粒物质、溶解性有机物和天然有机物在膜池内发生污染累积。为了减缓污染物累积产生的膜污染,考察了过滤模式、水力反洗、排空反洗液等条件对超滤膜跨膜压力的影响并得到最优工况参数;考察排泥周期对膜污染控制效果及对超滤工艺产水率的影响。结果表明,优化运行工况能够通过降低浓差极化污染和滤饼层污染,从而起到控制可逆污染的效果。缩短排泥周期能够减缓松散滤饼层向压实滤饼层的转化,间接降低弱吸附污染,从而缓解部分不可逆污染。缩短排泥周期导致超滤净产水量下降,排泥周期为24、12和6 h条件下,超滤工艺产水量分别为96.31%、92.61%和85.23%。运行工况优化对可逆污染有较好控制效果,但对不可逆污染控制效果微弱。从根本上解决膜污染问题,尤其是不可逆膜污染问题,仅凭优化运行工况的角度是不够的。控制超滤膜膜污染方面,采用多壁碳纳米管(MWCNTs)表面涂覆改性方法。制备功能化碳纳米管并根据官能团种类命名为Raw-MWCNTs、COOH-MWCNTs和PEG-MWCNTs。材料表征结果显示,功能化碳纳米管表面含有大量亲水基团;相同pH条件下,表面电负性关系为COOH-MWCNTsPEG-MWCNTsRaw-MWCNTs;水溶液中粒径分布大小规律为:Raw-MWCNTsCOOH-MWCNTsPEG-MWCNTs。表面涂覆改性后,根据涂覆材料将超滤膜依次命名为Control-M、Raw-M、COOH-M和PEG-M。相比于对照膜,改性膜的纯水通量略有下降。四种超滤膜表面粗糙度关系为:Raw-MCOOH-MPEG-MControl-M。以模型污染物作为天然水体有机污染物代表物,考察原始及功能化碳纳米管表面改性对膜污染的控制效果并分析其机理。腐殖酸过滤试验显示,Raw-M、COOH-M和PEG-M分别降低不可逆污染68.8%、75.0%和93.8%。表面负电性增强和表面亲水性增加是主要控制因素;牛血清蛋白过滤试验显示,Raw-M、COOH-M和PEG-M分别降低不可逆污染81.0%、90.5%和66.7%。表面电负性和表面粗糙度是主要控制因素;海藻酸钠过滤试验显示,Raw-M、COOH-M和PEG-M分别降低了不可逆污染69.4%、93.1%和98.3%。表面负电性增强和表面亲水性增加是主要控制因素。在超纯水反洗和污染物滤过液反洗条件下,三种改性膜中碳纳米管脱附含量关系为:PEG-MCOOH-MRaw-M。提升超滤膜亲水性和机械强度方面,采用CNTs和CNCs作为添加材料的共混改性方法。材料表征结果显示,CNTs和CNCs表面均含羟基,均为亲水材料。分别以0.5 wt%、1.0 wt%和2.0 wt%共混含量,制备0.5 CNTs-M、0.5 CNCs-M、1.0 CNTs-M、1.0 CNCs-M、2.0 CNTs-M和2.0 CNCs-M。未添加纳米材料的对照膜命名为Control-M。分别考察CNTs和CNCs对超滤膜形貌、结构及孔隙率的影响。结果显示,Control-M活性层中聚合物排列密实,孔隙结构很少;CNTs-M和CNTs-M活性层聚合物排列松散,有明显的孔隙结构后;CNTs-M和CNCs-M的平均孔隙率、表面孔隙率、平均孔径显著增加;表面粗糙度轻微增加。Control-M表面成疏水性;CNTs-M和CNTs-M表面呈亲水性,相同共混含量下,CNCs-M亲水性强于CNTs-M。改性纳米复合膜过水通量随纳米材料共混含量增加而提升,原因是改性膜亲水性增强和孔隙率提升。相同共混含量下,CNCs-M过水通量高于CNTs-M。改性膜机械强度研究结果显示,CNTs和CNCs均能提升纳米复合膜刚性性质,原因是纳米复合膜继承了共混材料自身机械性质。相同共混含量下,CNTs-M的杨氏模量和最大拉伸应力均高于CNCs-M。提高CNCs共混含量1倍,可以使CNCs-M达到或高于CNTs-M的刚度强度。结合环境影响和经济成本方面的考虑,在增加超滤膜亲水性和机械强度方面,CNCs有取代CNTs的可行性。
[Abstract]:Ultrafiltration can effectively protect drinking water biological safety. Ultrafiltration technology, small footprint, easy to realize modular, high degree of automation. The ultrafiltration process does not react, does not have two pollution, environmental friendly. Ultrafiltration technology has been widely applied in water treatment. The bottleneck of development of ultrafiltration technology including membrane fouling the phenomenon of weak hydrophilic membrane material, membrane, insufficient mechanical strength. These problems are directly related with the membrane itself properties. In order to solve the above problem, this paper improve the properties of UF membrane, membrane modification from the point of view of the surface coating modification and blending modification of two kinds of methods, selection of carbon nanotubes (CNTs) and nano crystalline cellulose (CNCs) of two kinds of nano materials as the modified material of polyethersulfone (PES) ultrafiltration membrane was modified. The system of CNTs surface coating modification of control and membrane fouling resistance distribution Influence and to explore its mechanism; to study and compare the CNTs and CNCs blend modification on the morphology of nano composite film, effects of hydrophobicity and mechanical strength and mechanism. In this paper, the actual water as water source, first examine the operation optimization of membrane pollution control effect. The analysis results of pollutants in the membrane pool showed that insoluble in the process of ultrafiltration of particulate matter, dissolved organic matter and natural organic matter in the membrane pool. In order to reduce pollution accumulation of membrane pollution accumulation of pollutants generated, investigated the filtration mode, hydraulic backwash effect, anti emptying lotion and other conditions on the membrane of the transmembrane pressure and the optimal working parameters of mud cycle on membrane; the pollution control effect and influence on ultrafiltration water production rate. The results show that the optimal operating conditions can reduce the concentration polarization and the pollution of the cake layer pollution so as to control the pollution effect. Shorten the mud cycle can be transformed into the slow loose cake layer to the compaction of the cake layer, indirectly reduce the weak adsorption of pollution, so as to alleviate some of the irreversible fouling. Shorten the mud cycle leads to ultrafiltration water production decreased, mud cycle is 24,12 and 6 h under the condition of ultrafiltration water yield were 96.31%, 92.61% and 85.23%. operation optimization has better control effect on pollution, but the irreversible pollution control effect is weak. To solve the problem of membrane fouling fundamentally, especially the irreversible membrane fouling problem, only by optimization of the operating condition of the angle is not enough. The control of membrane fouling, multi walled carbon nanotubes (MWCNTs) by surface coating the modified method. The preparation of functionalized carbon nanotubes and according to the type of functional groups named Raw-MWCNTs, COOH-MWCNTs and PEG-MWCNTs. characterization results show that functionalized carbon nanotube surface contains a large number of hydrophilic groups; the same Under the condition of pH, the surface electronegativity of COOH-MWCNTsPEG-MWCNTsRaw-MWCNTs in aqueous solution; size distribution rule: Raw-MWCNTsCOOH-MWCNTsPEG-MWCNTs. surface coating modification, coating material according to the ultrafiltration membrane are named Control-M, Raw-M, COOH-M and PEG-M. compared to control membrane, pure water flux of the modified membrane decreased slightly. Four kinds of ultrafiltration membrane the relationship between surface roughness is Raw-MCOOH-MPEG-MControl-M. to model natural water pollutants as organic pollutant, and investigate the original functionalized carbon nanotube surface modification effect on membrane fouling and analyze its mechanism. Humic acid filtration test showed that Raw-M, COOH-M and PEG-M respectively to reduce the irreversible pollution 68.8%, increased 75% and 93.8%. surface electronegativity enhanced and surface hydrophilicity is the main control factor; bovine serum albumin filtration test showed that Raw-M, COOH-M and PEG-M were not reduced The inverse pollution 81%, 90.5% and 66.7%. surface electronegativity and the surface roughness is the main control factor; sodium alginate filtration test showed that Raw-M, COOH-M and PEG-M were decreased by irreversible pollution 69.4%, increased 93.1% and 98.3%. surface electronegativity enhancement and surface hydrophilicity is the main control factor. In ultrapure water backwashing and pollutant filtration backwash under the condition of three kinds of modified carbon nanotube membrane desorption content relationship: PEG-MCOOH-MRaw-M. enhance ultrafiltration membrane hydrophilicity and mechanical strength, using CNTs and CNCs as the material blending addition modification method. Characterization results show that the CNTs and CNCs surfaces are hydrophilic materials containing hydroxyl group, respectively with 0.5 wt%. 1, wt% and 2 wt% blend content, preparation of 0.5 CNTs-M, 0.5 CNCs-M, 1 CNTs-M, 1 CNCs-M, 2 CNTs-M and 2 CNCs-M. control film without adding nano material named Control-M. CNTs and CNCs were investigated respectively. The effect of ultrafiltration membrane morphology, structure and porosity. The results showed that the activity of Control-M in dense polymer layer, the pore structure of CNTs-M and less; CNTs-M active layer polymer arranged loosely, pore structure obviously after CNTs-M and CNCs-M; the average porosity, surface porosity, average pore size increased significantly; the surface roughness increased slightly a hydrophobic.Control-M surface; hydrophilic CNTs-M and CNTs-M surface, blending the same content, CNCs-M strong hydrophilicity of CNTs-M. modified nano composite membrane water flux with the increase of the content of nano materials was promoted, the reason is to change the hydrophilic membrane and enhanced porosity improvement. The same blend content, water flux CNCs-M the research results of mechanical strength higher than that of CNTs-M. film shows that CNTs and CNCs can enhance the rigidity properties of nanocomposite films, because nano composite film inherited its mechanical properties of blends. The same blend content, the young's modulus and the maximum tensile stress of CNTs-M was higher than that of CNCs-M. CNCs was increased in 1 times, the stiffness and strength of CNCs-M can be reached or higher than that of CNTs-M. Combined with the environmental impact and economic cost, the increase in membrane hydrophilicity and mechanical strength, CNCs has replaced the feasibility of CNTs.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU991.2
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本文编号：1404724