多孔膜的污染研究

【作者】 刘惠玉；

【导师】 吕晓龙；

【作者基本信息】 天津工业大学 ， 材料学， 2004， 硕士

【摘要】 本文就对多孔膜的污染问题进行了理论探讨，并针对多孔膜中硫酸钙垢的清洗作了一系列实验。找出了高效清洗多孔膜中的硫酸钙垢的试剂和优化条件。主要包括： 通过对三聚磷酸钠、六偏磷酸钠、乙二胺四乙酸二钠、乙二胺四乙酸四钠四种螯合剂对硫酸钙溶解性对比实验，最终选择乙二胺四乙酸二钠和乙二酸四乙酸四钠作为本实验清洗剂。 研究了反应浓度对Na₄EDTA和Na₂EDTA溶解硫酸钙的影响。在高反应浓度下，反应能够相对较快达到平衡。 初步拟合了20℃下，Na₄EDTA，Na₂EDTA和硫酸钙同为0.029mol时对硫酸钙溶解的反应速率公式：其中v为反应速率，mol／l·s，t为反应时间，s。 考察了在Na₄EDTA和Na₂EDTA溶解硫酸钙过程中，pH值的改变。发现1．等摩尔浓度的Na₄EDTA和Na₂EDTA的水溶液中，Na₄EDTA溶液的pH值高于Na₂EDTA的pH。2．对Na₄EDTA来说，溶液浓度越大，pH值越高，Na₂EDTA则相反。3．随着螯合反应的进行，pH不断下降。 考察了pH对Na₄EDTA和Na₂EDTA螯合性能的影响。考察了含盐量对Na₄EDTA和Na₂EDTA溶解硫酸钙性能的影响。随着NaCl盐浓度的增加，Na₂EDTA和Na₄EDTA对CaSO₄的溶解率缓慢上升。 在上述实验的基础上，参选出不同的因素水平，作出Na₄EDTA和Na₂EDTA对CaSO₄溶解的三因素四水平正交实验。通过极差和方差分析后，认为在Na₄EDTA溶解CaSO₄过程中，时间和pH对此反应有高度显著影响。在所选水平内，反应20min，pH=11时，效果最好。在Na₂EDTA溶解CaSO₄过程中，时间此反应有高度显著影响，pH有显著影响。在所选水平内，反应25min，pH=5时，效果最好。 最后，在前面实验的基础上，作出Na₄EDTA和Na₂EDTA对硫酸钙垢污染的PVDF微滤膜清洗后，相对通量恢复率的五因素三水平正交实验。通过正交实验的极差和方差分析认为，在Na4EDTA对污染膜的清洗过程中，浓度对清洗效果影响是高度显著的，pH和压力对清洗效果影响显著，而时间、温度则无明显影响。最优工程的操作条件为Na4EDTA浓度为4%wt，操作压力为0.IMPa，清洗pH=11。在NaZEDTA对污染膜的清洗过程中，浓度，时间对清洗效果影响是高度显著的，pH和压力对清洗效果影响显著，而温度则无明显影响。最优工程的操作条件为NaZEDTA浓度为4%wt，清洗时间为40min，操作压力为o.IMPa，清洗pH=11。 在综合考虑乙二胺四乙酸二钠和乙二胺四乙酸四钠对硫酸钙的溶解性实验及正交实验，和最后对污染膜清洗的正交实验可以看出，尽管最优工程选择中NaZEDTA清洗后膜的相对恢复率略高于Na4ED飞’A，但其要求条件相对苛刻，从溶解性实验也可看出，Na4EDrLA对硫酸钙的溶解相对稳定，溶解率高。可以得出结论，对于膜污染的硫酸钙垢，采用N粼EDTA可以达到最好的清洗效果，其最优清洗条件为:PH=11、操作压力为0.IMPa、浓度为4%wt。更多还原

【Abstract】 In this paper, theories of porous membrane fouling and cleaning were explored, and a series of experiments were especially done to clean CaSO4 scale in porous membrane. The high-efficiency cleaning agent and optimum conditions were chosen and it has some guiding significance on practice. The main tasks include:By the contrastive experiments of sodium tripolyhosphate, sodium hexametaphosphate, Na2EDTA and Na4EDTA dissolving CaSO4, Na2EDTA and N^EDTA were chosen as cleaning agents in this experiment.Effects of Na2EDTA and Na4EDTA’s concentration on dissolving CaSO4 were studied. The reaction rate was relatively easy to reach the balance when concentrations of cleaning agents were higher.The dissolving reaction rate was fitted under the experiment conditions when NNa2EDTA and NCaso4 is 0.029mol:where v is the reaction rate, mol/l-s; and t is the reaction time,s.The change of pH was examined in the process of Na4EDTA and Na2EDTA dissolving CaSO4. Some conclusions were obtained: 1. PH value of Na4EDTA solution was higher than that of Na4EDTA solution when the mol concentration of the both solutions is same.2. For Na4EDTA solution or for Na2EDTA solution, the higher the solution concentration, the higher pH value was, however, the Na2EDTA solution is adverse. 3. With the increasing of the chelating reactions, pH value decreased gradually.The effect of pH value on the chelating properties of Na4EDTA and Na2EDTA for CaSO4 was studied. For Na4EDTA, and the effect of ionic strength on the chelating properties of Na4EDTA and Na2EDTA for CaSO4 was reviewed. With the increasing of ionic strength, the chelating property increased.On the basis of above experiments, the different factors and levels were selected and thethree-factor-four-level orthogonal experiments of Na4EDTA and NaiEDTA were done. By range analysis and variance analysis, time factor and pH factor were considered that had high remarkable effects on the course of Na4EDTA dissolving CaSO4. In all selected levels, the dissolving effect is best when time=20rm’nand pH=ll. In the course of Na2EDTA dissolving CaSO4, time factor has high remarkable effect and pH has remarkable effect. The effect is best when time=25min and pH=5.At last, on the basis of above experiments, the five-factor-three-level orthogonal experiments on the relative flux recovery ratio after Na2EDTA and Na4EDTA cleaning PVDF microfiltration membrane that was fouled by CaSO4 were done. By range analysis and variance analysis, the effect of concentration, pH and pressure on the cleaning property of Na4EDTA to the fouled membrane were high remarkable, but, time and temperature did not affect much. The optimum condition was that Na4EDTA concentration is 4%wt, operating pressure is 0.1 Mpa and pH is 11. In the process of Na2EDTA cleaning the fouled membrane, concentration and time had high remarkable effects, pH and pressure had remarkable effects but temperature had not obvious effect. The optimum condition was that NaiEDTA is 4%wt, cleaning time is 40min, operating pressure is 0. IMpa and pH is 11.Integrating the dissolving experiments of Na2EDTA and Na4EDTA and the orthogonal experiments, we can conclude that the dissolving property of Na^EDTA is relatively more stable and higher than that of Na2EDTA in this experiment. And, the conclusion can be made that for the CaSO4 scale in membrane Na4EDTA has the best cleaning effect and the optimum condition is pH=11, operating pressure=0.1Mpa and concentration=4%wt.更多还原