【作者】 赵姗姗；

【导师】 王鹏； 郑彤；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2013， 博士

【摘要】 高温凝结水是石油化工企业生产过程中，蒸汽经换热冷凝后形成，具有较高的热量和回收价值。通常经过简单软化处理后凝结水可回用于锅炉补给水，但是由于生产设备和管线的泄漏与腐蚀，凝结水中油和铁浓度超标。净化和回用高温凝结水，不仅可以实现水资源和能源的二次利用，而且可以减少污染物排放，减轻后续污水处理负荷，具有很好的社会效益和经济效益。本文研制了抗污染性较好的耐高温超滤膜和荷正电纳滤膜，建立了超滤-纳滤膜分离组合工艺用于高温凝结水的净化与回用。选择耐热性树脂聚醚砜酮（PPESK）为膜材料，采用相转化法制备了耐高温PPESK/TiO₂复合超滤膜。研究了铸膜液组成和成膜条件对超滤膜结构和性能的影响。采用SEM、XRD、AFM、TGA、万能材料试验机、水接触角和超滤实验研究了TiO₂含量对复合膜孔结构、耐热性、亲水性、机械性能和抗污染性能的影响。研究结果表明，最佳PPESK超滤膜制备条件为：PPESK浓度为16wt.%，最优添加剂为水溶性高分子PEG4000，浓度为8wt.%，溶剂挥发时间为20s，凝胶浴温度为25℃。加入纳米TiO₂后，膜断面亚层贯通的大孔结构发展受到抑制，海绵状孔结构得到发展，皮层厚度增加。复合膜的热稳定性、亲水性、渗透性和机械性能显著提高。将PPESK/TiO₂复合膜用于模拟高温凝结水处理，采用通量模型、阻力串联模型和MFI膜污染指数考察膜污染情况。研究发现，复合膜的抗污染能力提高，过滤阻力和MFI值明显减小，通量恢复率高。当TiO₂浓度为2wt.%时，制备的PPESK/TiO₂复合膜的结构和性能最佳，可以有效用于高温凝结水的净化处理。针对高温凝结水中的二价或多价阳离子，以P84聚酰亚胺超滤膜为基膜，支化聚乙烯亚胺（PEI）为交联剂，采用交联改性的方法制备了荷正电纳滤膜。采用SEM、ATR-FTIR、XPS、水接触角和纳滤实验等表征方法，研究了交联时间和PEI分子量对纳滤膜表面和断面孔结构、表面亲水性、表面带电性和分离性能的影响。研究结果表明，改性纳滤膜表面孔密度和孔径减小，断面致密层厚度增加，海绵状孔孔隙率减少，表面亲水性显著提高。最佳改性条件为：交联时间60min，PEI分子量25000g·mol-1。此条件下制备的纳滤膜水接触角最小为35±1.2°；MWCO为436g·mol-1，孔径分布最窄。在pH<10的条件下，纳滤膜表面荷正电，对不同盐的截留率顺序为MgCl2>MgSO4≈NaCl>Na2SO4。改性膜在不同pH溶液中表面荷正电强度不同，影响膜对离子的截留率。当pH<8时，膜表面带正电，对Na+的截留率几乎不变；当pH从8升高到10时，膜表面正电性减弱，截留率降低。当pH=10时，膜表面呈中性，此时只有筛分作用，对NaCl的截留率最低。针对炼油厂高温凝结水中疏水性油滴、铁腐蚀产物和Ca2+、Mg2+等阳离子，建立了超滤-纳滤膜分离组合工艺对其进行净化处理与回用。以模拟高温凝结水为处理目标，分别研究了超滤过程中过膜压差（TMP），原水温度和pH，初始油和铁浓度等五个参数，以及纳滤过程中运行时间、操作压力、进水温度和pH等四个参数对膜渗透通量和污染物去除效果的影响。研究结果表明，超滤过程中，TMP越高，膜污染越严重，通量下降率越大，最佳TMP为0.1MPa；原水温度和pH影响铁的水解形态，强酸溶液中，铁离子水解受到抑制，去除率为0。温度升高，促进铁离子水解形成更多具有三维空间立体网孔结构的聚合态铁，可以将油滴网捕卷扫下来形成絮凝物，减少其在膜表面的吸附，减轻膜污染；初始油浓度增加，加剧膜表面污染。复合膜耐油和铁的冲击负荷能力较强。纳滤过程中，运行30min后，通量稳定，最佳操作压力为0.6MPa；渗透通量随着进水温度和pH的升高而增加，纳滤膜耐高温性能良好，进水温度对Ca2+、Mg2+离子去除率影响不大。pH增大，膜表面正电性强度减弱，出水Ca2+、Mg2+浓度略有增加，硬度升高。针对油滴和铁水解产物在超滤膜表面形成的滤饼层污染，以氢氧化钠，乙醇，草酸和盐酸为清洗剂，优化了超滤膜的清洗方法。最佳清洗条件为0.01mol·L-1NaOH和30%的乙醇联合清洗，膜通量恢复率在95%以上。某炼油厂实际高温凝结水经UF和NF组合工艺处理后，浊度完全去除，NF渗透出水达到《火力发电机组及蒸汽动力设备水汽质量》（GB/T12145-2008）标准，可以回用于锅炉补给水。UF和NF膜分离组合工艺净化回用炼油厂高温凝结水，具有操作简单、占地面积小、分离效率高、运行费用低、节能环保等优点，易实现自动控制和工业化推广。本文的研究结果为炼化企业高温凝结水回用提供了一条有效解决途径。研制的耐高温PPESK/TiO₂复合超滤膜和荷正电纳滤膜具有综合优异性能，在其它饮用水处理和废水处理领域具有广阔的应用前景。更多还原

【Abstract】 High temperature condensed water condensed from steam by heat exchange inthe petrochemical production process has a great value of recovery, for example, itcan be used as boiler makeup water. However, excess oil and iron contaminants incondensed water due to leakage and corrosion of production equipment andpipelines make it difficult to be reutilized directly. Therefore, purification of hightemperature condensed water is necessary for further usage. Moreover, such successwould increase both social and economic benefits in terms of reusage of water andenergy as well as reduction of pollutant discharge amount and the following sewagetreatment load. In this thesis, an ultrafiltration （UF） and nanofiltration （NF）combination separation process was established to remove oil, iron contaminantsand decrease hardness in high temperature condensed water. Meanwhile, athermostable UF membrane and a positively charged NF membrane were prepared.Thermostable resin poly（phthalazinone ether sulfone ketone）（PPESK） waschosen as the membrane material, and thermostable PPESK/TiO₂composite UFmembrane was prepared by using phase inversion method. The effects of castingsolution composition and membrane forming condition on the structure andproperties of UF membrane were investigated and optimized. The influences of TiO₂concentration on composite membrane pore structure, thermostability, hydrophilicity,mechanical properties and anti-fouling property were studied by SEM, XRD, AFM,TGA, electron-mechanical universal material testing machine, water contact angleand ultrafiltration experiments. The results show that the optimal membranepreparation condition was listed as follows: PPESK concentration was16wt.%, thebest additive was a water-soluble polyethylene glycol （PEG）4000with aconcentration of8wt.%, solvent evaporation time was20s and coagulation bathtemperature was25°C. With the addition of TiO₂, the penetrated finger-likestructure in sublayer is suppressed, while sponge-like structure begins to bedeveloped, and the skin layer thickness is increased. Thermostability, hydrophilicity,permeability and mechanical property of composite membranes are significantlyenhanced. The flux model, resistance in series model and membrane fouling index（MFI） were used to investigate membrane fouling in purifying simulated hightemperature condensed water by PPESK/TiO₂composite membranes. In comparisonwith parent membrane, the composite membrane showed enhanced anti-foulingproperty, decreased filtration resistance and MFI as well as higher flux recovery rate.When TiO₂concentration was2wt.%, PPESK/TiO₂composite membrane hasoptimal structures and properties, which can be effectively used for high temperature condensed water purification.To remove divalent and multivalent cation in high temperature condensed water,a positively charged NF membrane was prepared by cross-linking of hyperbranchedpolyethyleneimine （PEI） with P84polyimide UF membrane. The influences ofcross-linking time and PEI molecular weight on surface and cross-section porestructure, hydrophilicity, surface charge and separation performance of NFmembrane were studied by SEM, ATR-FTIR, XPS, water contact angle andnanofiltration experiments. The results show that the surface pore density and poresize of modified NF membrane decreases, the thickness of dense layer increases andporosity of sponge-like pore structure decreases. The hydrophilicity of modified NFmembrane is also improved. The optimal modification condition was confirmed: thecross-linking time is60min and PEI molecular weight is25000g·mol-1. Theprepared NF membrane under above condition behaves the smallest water contactangle of35±1.2°, a narrower pore size distribution and MWCO of436g·mol-1. TheNF membrane surface is positively charged when solution pH <10, and therejections of different salts show the sequence: MgCl2> MgSO4≈NaCl> Na2SO4.The surface charge intensity of modified NF membrane was affected by pH ofsolution, which could further influence the ions rejection of membranes. When pH <8, the membrane surface is positively charged, Na+rejetions keep constant; whilepH increases to10, Na+rejetion decreases due to the decrease of surface positivecharge intensity. Especially, the rejection of NaCl is the lowest at pH=10, ascribingto the sieving effect on neutral membrane surface.An UF and NF combination membrane separation process is established forremoval of hydrophobic oil droplets, iron corrosion products, Ca2+and Mg2+in hightemperature condensed water. The effects of five operation parameters in UF process（transmembrane pressure （TMP）, temperature and pH of feed water, initial oil andiron concentration） and four operation parameters in NF process （operating time,pressure, temperature and pH of feed water） on the permeate flux and removalefficiencies of contaminants were investigated in detail. The result reveals thathigher TMP aggravates membrane fouling, resulting in the increase of flux declinerate.0.1MPa is chosen as the optimal TMP. The temperature and pH of feed wateraffect ferric hydrolysate species. In strong acidic solution, the hydrolysis of ironions is inhibited, and the iron removal efficiency is almost zero. Hydrolysis of ironions is accelerated by high temperature and more polymeric species are formed. Thehigh polymeric species with a three-dimensional stereoscopic porous like structurecan sweep down the oil drops to form floccules. These floccules can be easily sweptaway by the hydraulic flush rather than be adsorbed on the membrane surface. Inthis process, the membrane fouling is mitigated. The composite membrane showshigh resistance towards oil and iron concentration. It can be seen that the optimal operating pressure is0.6MPa in NF process. The permeate flux increases with theincrease of temperature and pH of feed water. The NF membrane behaves a goodthermostability, and the removal efficiencies of Ca2+and Mg2+are not affected muchby the feed water temperature. When pH increase, a slight increase of Ca2+, Mg2+concentrations was found and this may be because of the lower positive chargedensity on the membrane surface.To remove cake layer pollution formed by accumulation and deposition of oildroplets and iron hydrolysate, four kinds of chemcial cleaning agents includingsodium hydroxide, ethanol, oxalic acid and hydrochloric acid were used, and thecontaminated UF membrane cleaning method was optimized. The result shows that0.01mol·L-1NaOH solution cleaning combination with30%ethanol solutioncleaning is the best method with over95%flux recovery rate. Actual hightemperature condensed water from refinery can be efficiently treated using UF andNF combined separation process. The turbidity is completely removed and thecontaminants concentrations in NF permeate solution satisfy the Quality Criterion ofWater and Steam for Steam Power Equipment （GB/T12145-2008, China）. The NFpermeate solution can be potentially used as boiler makeup water.Realization of UF and NF combination membrane separation process promisesa great many advantages for refinery high temperature condensed water purificationand recycling, like simple operation, small occupied area, high separation efficiency,low operational costs, energy saving and environmental protection and possibility toachieve automatic control and industrial extension. This study provides an effectivesolution for high temperature condensed water recycling for refinery enterprises.The presented thermostable PPESK/TiO₂composite UF membrane and positivelycharged NF membrane show comprehensive excellent performance, which isexpected to have wide application in other drinking water treatment and wastewatertreatment fields.更多还原