【作者】 周媛；

【导师】 奚旦立；

【作者基本信息】 东华大学 ， 环境工程， 2007， 博士

【摘要】 本论文针对聚偏氟乙烯（PVDF）中空纤维膜性能中存在的问题,制备了一种新型的PVDF/热塑性聚氨酯（TPU）共混中空纤维膜。基于"利用PVDF和TPU的相容性来改善分离膜结构与性能"的设计理念,对PVDF和TPU的共混相容性、以及PVDF/TPU共混中空纤维膜的成膜工艺进行了较为全面的研究;同时将其应用于印染废水的处理,采用水解酸化-一体式膜生物反应器（SMBR）处理工艺,并投加絮凝剂聚合硫酸铝铁（PAFS）,考察了PVDF/TPU共混中空纤维膜在印染废水MBR处理工艺中的实际应用情况。通过混合焓值、Flory-huggins相互作用参数、稀溶液粘度法（Dilute SolutionViscosity）、差示扫描量热法（Differential Scanning Calorimetry）、红外光谱法（FTIR）等理论和试验方法,对PVDF/TPU的相容性进行了预测和分析。研究结果表明:PVDF与TPU具有部分相容性,且相容性与混合比、浓度等因素有关,PVDF含量)60%的体系相容性优于PVDF含量＜60%的体系,PVDF富相的相容性优于TPU富相的相容性。通过考察铸膜液中聚合物浓度以及PVDF/TPU共混比对铸膜液运动粘度、相容性、浊点数据、凝胶值的影响,从热力学以及传质动力学的角度对DMAc-PVDF/TPU-H₂O体系膜孔形成机理进行了研究。研究结果表明,随着PVDF/TPU浓度的增加,粘度增大,溶剂与非溶剂交换速率变小,有利于发生延迟相分离,大孔减少,孔隙率、水通量降低。聚合物浓度增加,聚合物与溶剂间的相互作用增强,分子链的运动能力减弱,铸膜液粘度急剧增大,使凝胶过程中铸膜液内的溶剂和凝胶介质之间的传质阻力增大,凝胶速度降低,膜孔隙率降低。铸膜液中聚合物浓度比较低时,体系粘度低,在动力学因素影响下,溶剂和非溶剂间交换速率快,凝胶值小,液液分相较早出现,从开始出现液液分相到最后聚合物浓相固化之间有较长的时间使得稀相孔长大,因而所成膜有较大的孔。但是聚合物浓度低导致膜的机械强度变差。浊点实验说明随着共混比的增大,少量的非溶剂就可以使铸膜液沉淀分相。PVDF与TPU共混比逐渐降低时,体系粘度逐渐增高,相容性变差,加入少量非溶剂就可以加速这种分离倾向,但是膜的机械性能大大提高。膜结构也说明随着TPU的含量增高,相分离严重,膜孔径变大,孔隙率增大,水通量增大,截留率迅速减小。按添加剂功能的不同,将添加剂区分为高分子有机添加剂与无机添加剂。通过热力学、动力学因素,DSC热焓分析,FTIR-ATR的PVDF晶型转化分析、SEM观察、水通量、截留率和机械强度的实验,对膜的性能与结构进行比较。结果表明,添加剂影响溶剂的化学位,改变了铸膜液中PVDF/TPU大分子的溶解状态。影响凝胶过程中溶剂和水之间的互散速度,进而影响凝胶过程,改变膜结构。在致孔添加剂-DMAc-PVDF/TPU-水的体系中,PVP（K30）是一种比较复杂的改良剂,可以制备不同性质的膜。由于其高分子量的特性,浓度增大,反而会抑制大孔的形成。因为它使铸膜液的粘度变化极为显著,粘度造成的动力学引发膜分相的作用大于热动力学造成的铸膜液相分离的因素,体系需要提供部分热动力驱动力来引发相分离,相分离延迟时间较长,最终发生铸膜液延迟液液分相。形成较致密的皮层,导致膜的结晶度先降低后升高,水通量也随之由高变低。在高分子添加剂中以PVPK30和PEG6000这两种添加剂的膜的PVDF结晶减少最为显著,表现为膜结构的孔的连通性比较好,膜的过滤性能及机械性能都优于其他添加剂。纺丝工艺包括凝胶浴的组成和温度、芯液的组成和流量、干纺程长度等,在以上因素的共同作用下,同铸膜液结构一起决定了膜的结构与性能。以动力学扩散对膜结构与性能影响的讨论为主。以溶剂DMAc的水溶液作凝胶浴时,凝胶浴的凝固能力降低,降低了溶剂与非溶剂扩散传质的化学势变化,容易发生延迟相分离,断面结构从指状向海绵状转变。以水为凝胶浴介质,因为扩散速度快,脱溶剂迅速,更易实现瞬间相分离,有利于大空腔结构的生成,提高膜的水通量。凝胶浴温度影响溶剂-非溶剂扩散。在25℃时,水通量和截留率得到最大值。当芯液选择酒精水溶液时,内、外凝固速率的差别对海绵层位置有明显的影响,浓度增大,海绵层逐渐外移,最终形成贯穿整个膜的大孔,水通量急剧增大。对其他纺丝工艺参数的研究中,确定当干纺程在14cm,芯液为水,流量为2.5-3ml/min时,可以制备出通量较大,截留性能较好的共混膜。选择不同pH值次氯酸钠（NaClO）溶液对PVDF/TPU中空纤维膜进行后处理。研究表明NaClO溶液可以明显地改善共混膜的表面微孔,提高膜的水通量。同时不同pH值的NaClO溶液随时间变化对膜的截留率的影响不大,均处于82-89%之间,表明NaClO溶液对膜孔径并没有显著影响。PVDF/TPU/PVP共混膜经酸碱浸泡处理后,失重比率在3%内,膜的机械强度影响不大,说明它可以在较宽的pH值范围内应用,具有较好的耐酸碱及氧化性能力。在超滤装置中,组件对活性艳兰KN-R的透过速率在60min后达到稳定,随着操作压力的增大,通量有所提高,压力过大会影响膜的寿命,在0.1MPa下,可以保持较高的通量。运行后的膜用清水冲洗,污染恢复率明显高于未添加PVP的PVDF/TPU共混膜,说明添加亲水性物质PVP后可以提高膜的抗污染能力。实验表明PVDF/TPU/PVP共混膜由于具有良好的抗酸碱性,耐污染性能强,在工业水处理应用中应会有良好的前景。通过平行对比试验,以生物相、颗粒粒径分布混合液特性指标,研究了PAFS对膜污染的缓解作用。投加PAFS后,活性污泥中会存在大量原生、后生动物,生物相变得更加丰富;混合液颗粒平均粒径显著增大,同时小于15μm的颗粒所占的比例显著减小;粒径增大说明加入PAFS后对缓解膜污染是有利的。在PVDF/TPU共混膜在活性染料废水处理的应用中,以水解酸化-一体式膜生物反应器（SMBR）组合工艺,对以活性艳兰KN-R和聚乙烯醇（PVA）为主的印染废水进行处理,水解酸化池-SMBR各段作用不同,起初水解酸化完成染料脱色,并且提高废水的可生化性,SMBR主要起去除COD的作用。随着系统运行时间的延长,使得更多的染料被絮凝在活性污泥中,强化了脱色细菌培养和驯化,使得脱色细菌慢慢适应了在Fe、Al存在的状况下生长,SMBR对色度的去除率有所增加。废水中不可生物降解物质的COD占总COD的7.6%左右。通过MBR处理印染废水的以COD为底物浓度的动力学模式、最短生物固体平均停留时间,说明水解酸化-SMBR工艺优于传统的厌氧工艺和厌氧-好氧工艺。污泥层沉积和凝胶层增厚是导致膜污染的主要原因。工艺选择NaOH清洗膜组件,电镜观察可知,活性污泥在膜表面得沉积也得到了缓解,保证系统长期稳定运行。实验结果表明水解酸化-PAFS-SMBR组合工艺是处理活性染料和PVA为主的印染废水的高效工艺。更多还原

【Abstract】 In order to provide practical and theoretical solutions to the problems faced to Polyvinylidene fluoride （PVDF） hollow fiber membranes, preparing a novel PVDF/ Thermoplastic polyurethane （TPU） hollow fiber membrane, based on the design concept that the membrane structure and performance could be improved by adjusting the compatibility between PVDF and TPU blends, some aspects were studied, which included the studies on the compatibility of polymer blends, preparation and characterization of PVDF/TPU hollow fiber membranes, the effects on casting dope, membrane process, and influence factor in spinning and precipitation process; secondly, PVDF/TPU blend membrane applied in Hydrolysisacidrogenesis-sub membrane bioreactor process was used to treat reactive blue KN-R wastewater with addition of PAFS. A study on submerged membrane bioreactor （SMBR） with PVDF/TPU blend hollow fiber membranes for dyeing wastewater was carried out.For the first time the compatibility of PVDF and TPU was predicted and analyzed by means of calculation ofΔHm, Flory-huggins interaction parameters, Differential Scanning Calorimetry method and Dilute Solution Viscosity method respectively. It was demonstrated that PVDF and TPU possessed partial compatibility which was depended on and influenced by blend ratio, concentration of polymers in solution, temperature, etc. The compatibility of the systems with the percentage of PVDF in blends more than 60% was superior to systems with the percentage less than 60%. The compatibility in PVDF-rich phase was greater than in TPU-rich phase.The influence of the polymer concentration and PVDF/TPU ratio on such items was studied, as the viscosity of the casting solution, the compatibility, the cloud point, the gelation value, while as far as the system of DMAc-PVDF/TPU-H₂O was concerned, the formation mechanisms of the membrane were studied and explained based on thermodynamics and mass transfer dynamics. It was found that with the increase of polymer concentration, the viscosity of casting solution increased, the velocity of mass transfer between solvent and non solvent slowed down, which happened delay phase separation easily. Fewer big pores observed in the membrane structure, flux and porosity decreased. Due to the enhanced mutual function, molecule chain moved slowly. The diffusion was inhibited by TPU in the casting dope and the porosity reduced with the increase of the viscosity. The decrease of polymer concentration also reduced the viscosity of casting dope. Diffusion mass transfer between solvent and nonsolvent fasted, inducing spontaneous demixing and developing larger pores, while low polymer concentration resulted in poor mechanical properties. Cloud points experiments showed that with the increase of blends ratios, a very little amount of non-solvent can induce phase separation. When blends ratio reduced, the viscosity of casting dope increased, whereas the compatibility of the system reduced. Adding TPU to the casting dope can improve the membrane’s mechanical properties. High concentration of TPU in casting dope made the separation too serious, water flux and porosity increased, while retention decreased sharply.According to the function of additives, it could be classified into high molecular weight organic additives and inorganic additives. In the system of Additives-DMAC-PVDF/TPU-H₂O, PVP was a complicated improver, which can prepare membranes with different property due to its high molecular weight. The separation property, microstructure and crystalline phase of membranes were characterized by bovine serum albumin （BSA） retention experiments, mechanical property scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy- attenuated total reflection （FTIR-ATR）and differential scanning calorimetric （DSC）, respectively. The results showed that additives can affect Chemical Potential of solvent, change PVDF/TPU macromolecule soluble state. Additives also can affect the diffusion velocity between solvent and nonsolvent, forming different membrane structure. High PVP concentration would suppress macrovoid formation. PVP can not come to terms with the demixing enhancement, it was not because the PVP fails to induce thermodynamic enhancement but because it was overwhelmed by kinetic hindrance. Due to the increase of the dope viscosity, affected the exchange between Water and DMAc during the phase inversion and phase separation time increased and demixing delayed. Thus firstly the water flux increased while Crystallinity decreased, then flux reduced while crystallinity increased. PVP K30 and PEG6000 can reduce crystallinity of membrane significantly. Membranes added PVP K30 and PEG6000 possessed good retention and mechanical properties because the pores in membranes connected well. The membranes with 5 wt% content of PVP, comparing membranes without additive, flux improved from 9.25 L/m²·h to 346.73 L/m²·h, retention was from 82.54% to 86.88%, which can prepare excellent blend membranes with high water flux and retention..The influences of various parameters on the spinning technology included coagulation bath agent, coagulation bath temperature, bore liquid agent, bore liquid velocity, dry spinning gap distance, etc. Structure and performance of membranes were affected by spinning condition and the casting dope content. The dynamic diffusion was discussed. DMAc solvent as a coagulation bath, resulting in concrete slowing, chemical potential of diffusion mass transfer between solvent and non-solvent changed, which induced delay demixing, membrane structure changed from finger-like structure to spongy structure. Diffusion velocity increased with water as a coagulation bath. It is easy to desolventize and induce spontaneous demixing. Water flux increased with the development of macrovoid. The temperature of coagulation also effected solvent and non-solvent diffusion. At 25℃water flux and retention reached to their maximum. EtOH as bore liquid, different internal and external concerted velocity resulted in spongy layer location. With the increase of ethanol concentration, spongy layer removed to membrane outboard, finally forming macrovoid from the underneath of membrane skin to the bottom of a sublayer with water flux increase quickly Considering for other factors, when dry spinning gap distance being 14cm, water as bore liquid and velocity 2.5-3 ml/min, it can prepare excellent blend membranes with high water flux and retention.PVDF/TPU blends hollow fiber membranes with NaClO solvent post-treatment was studied and the results indicated that post-treatment with NaClO can enlarge the micropore on membrane surface, increase water flux significantly. NaClO had no distinct influence on membrane aperture size, which resulted in retention remained stable between 82% and 89%. PVDF/TPU/PVP blends hollow fiber membrane weight loss was below 3%, after membrane dipped in both acid and alkaline solution. Acid and alkaline soak had little effect on mechanical property. The results showed that PVDF/TPU blend hollow fiber membranes owned good ability of resistance to acid and alkali in the broad pH range. The membranes flux declined as the filtration time increased, followed by 60 minutes with a steady value. Reactive sapphire KN-R dyeing fluxes can be improved through increasing driving force, but excessive driving force would affect the membranes natural life, In the experiment, we would take 0.1 MPa as the transmembrane pressure, which also can remain high flux. Fouled membranes cleaned by water, membrane added PVP flux recovery higher than membrane free of PVP, It showed that PVP can improve hydrophilicity of membranes. Membranes modified by PVP had a more favorable antifouling performance and can be applied in wastewater treatment.Based on parallel experiment including biomorphic variety, particle diameter distributing in mixing sludge solution, PAFS addition can reduce membrane fouling. When PAFS was added in suludge, different kinds microorganism such as protozoan, metazoan had exited in sludge. Particle diameter increased, microorganism with particle diameter less than 15μm increased obviously, which can reduce membrane fouling and improve sludge characteristic. While the PVDF/TPU hollow fiber membrane was used in submerged membrane bioreactor （SMBR） process, Hydrolysisacidrogenesis-sub membrane bioreactor process was used to treat reactive sapphire KN-R and Polyvinyl Alcohol （PVA） dyeing wastewater. It showed different function. The results showed that decolorization was accomplished hydrolysisacidroginesis process in the beginning. COD was removed by SMBR system mostly. With the increase of running period, more and more coloring matter was flocculate in the sludge, which strengthened decolor bacteria culture, decolor bacteria can exist in the ferriferous and aluminous sludge, which resulted in the increase of color reduction. Based on the calculation result of dyestuff degradation dynamics parameters, COD of non-degradable pollutants account was only 7.6 % of the total COD. Based on the calculation result of dyestuff degradation dynamics parameters and the shortest bio-solid residence time, it can draw the conclusion that hydrolysisacidrogenesis-PAFS-SMBR process superior than anaerobic process and anaerobic-aerobic process. The fouling of membrane was mainly formed by gel polarity and sludge sediment. The alkali cleaning can reduce activated sludge sediment on the surface of membranes, which can ensure that SMBR system run stably for long time. It showed that a combined Hydrolysisacidroginesis-membrane bioreactor process adding flocculant PAFS was considered as a high efficient combination.更多还原