不同离子浓度条件下典型有机物对不同超滤膜的吸附特性研究

发布时间：2018-07-22 16:35

【摘要】：近年来,超滤技术在水处理领域应用逐渐变得非常广泛。但由于超滤膜易污染,使用成本较高,使得其在推广过程中受到了极大的限制。本文首先论述了三种自制超滤膜的性能及微观结构,后讨论了在不同离子种类(Na+、Ca2+),离子浓度下牛血清蛋白(BSA)对三种膜材料(PVDF、PES和EVOH)的污染规律,并结合石英晶体微天平(QCM-D)等尖端分析手段,对膜污染机制进行了探讨。实验结果表明:(1)三种膜材料亲水性大小依次为EVOHPESPVDF,膜的亲疏水性与膜的被污染能力有关,当膜亲水时,相比疏水性的膜,不易被污染,因此三种膜的污染严重程度依次为EVOHPESPVDF。对于膜孔较大的PVDF膜和EVOH膜,由于BSA分子为均匀的椭球体结构,分子之间不但不容易互相穿插,且单个分子更容易透过膜面进入膜孔内,BSA分子容易流失,因此这两种膜的BSA截留率比PES低。因此这三种膜中PES膜对BSA的截留能力最强。三种膜中对BSA吸附量最大的是PVDF膜,其次是PES膜,EVOH膜对BSA在无离子共存条件下的吸附量最小。(2)三种膜在Na+离子共存条件下的BSA截留率,就整体情况看,PES膜的截留率最高,EOVH的截留率次之,PVDF膜最低。同种超滤膜材料都表现出一致的规律,即Na+离子浓度越高,BSA的截留率越低,对于PVDF膜和EVOH膜,当Na+离子浓度为100mmol/L时,几乎不能截留BSA。这可能是由于牛血清蛋白分子与膜表面形成的水合力,使得牛血清蛋白分子很难相互聚集,且它本身分子量较小,反而易于穿过膜孔而使截留率降低。通量恢复率表现为,随着离子浓度增大而降低,离子浓度增大到一定程度,通量恢复率反而升高。Na+离子浓度为0mmol/L,1mmol/L,10mmol/L,100mmol/L时,三种超滤膜在对BSA的吸附过程中,污染过程初期,吸附速率非常快,形成刚性吸附薄层,而到一定时间后,吸附层开始展现出粘弹性,吸附量不再增加,吸附过程达到吸附平衡。当离子浓度增大,吸附量越来越大,但当离子浓度增大到一定程度,水合作用力成为主导作用力时,由于水合排斥力增加,吸附量反而开始降低。(3)Ca2+离子共存时,在进行膜通量衰减实验、BSA截留率测定实验、膜通量恢复率测定实验、BSA在三种材质超滤膜上的吸附行为研究实验时,发现了与Na+离子共存时相类似的污染规律,即Ca2+离子浓度越高,BSA的截留率越低,对于PVDF膜和EVOH膜,当Ca2+离子浓度为100mmol/L时,几乎不能截留BSA。通量恢复率表现为,随着离子浓度增大降低,离子浓度增大到一定程度,通量恢复率反而升高,吸附行为规律也与Na+离子共存时类似。主要由于二价Ca2+离子与一价Na+离子同为阳离子,因此其与带负电的BSA会形成静电屏蔽效应,使得静电排斥力减小,膜污染加重。而由于二价Ca2+离子还存在络合作用,其对膜通量衰减造成的影响较Na+离子略大。
[Abstract]:In recent years, ultrafiltration technology has been widely used in the field of water treatment. However, the UF membrane is easy to pollute and its cost is high, so it is restricted greatly in the process of popularization. In this paper, the properties and microstructure of three kinds of self-made ultrafiltration membranes are discussed, and then the contamination of bovine serum protein (BSA) to three kinds of membrane materials (PVDF, PES and EVOH) under different kinds of ions (Na ~ (2 +) and ion concentration is discussed. The mechanism of membrane fouling was discussed by means of quartz crystal microbalance (QCM-D). The results showed that: (1) the hydrophilicity of the three membrane materials was EVOHPESPVDF.The hydrophobicity of the three membranes was related to the fouling ability of the membrane. When the hydrophilic membrane was hydrophilic, the hydrophobic membrane was not easy to be contaminated, so the serious pollution degree of the three membranes was EVOHPESPVDF. For PVDF and EVOH membranes with larger membrane pores, because the BSA molecule is a uniform ellipsoid structure, it is not easy for the molecules to intersect with each other, and it is easier for a single molecule to enter into the membrane pore through the membrane surface and the BSA molecule is easily lost. Therefore, the BSA retention rate of these two membranes is lower than that of PES. Therefore, PES membrane has the strongest retention ability to BSA. The highest amount of BSA adsorption was PVDF membrane, followed by PES membrane EVOH membrane under the condition of ion-free coexistence. (2) the BSA retention rate of the three membranes under Na ion coexistence condition. On the whole, the PES membrane had the highest rejection rate and the lowest EOVH membrane was PVDF membrane. The same ultrafiltration membrane material showed the same rule that the higher the concentration of Na ion, the lower the rejection rate of BSA. For PVDF membrane and EVOH membrane, when Na ion concentration was 100 mmol / L, BSAs could hardly be intercepted. This may be due to the water binding between bovine serum protein molecules and the membrane surface, which makes it difficult for the bovine serum protein molecules to aggregate with each other, and its molecular weight is small, which makes it easy to penetrate the membrane pore and reduce the rejection rate. The flux recovery rate decreases with the increase of ion concentration, increases to a certain extent, and increases to a certain extent. When the concentration of Na ion is 0 mmol / L ~ (-1) mol / L ~ (10) mmol / L ~ (10) mmol / L ~ (-1), the three kinds of ultrafiltration membranes are in the initial stage of fouling process in the process of adsorption of BSA. The adsorption rate is very fast and the rigid adsorption layer is formed. After a certain time the adsorption layer begins to show viscoelasticity and the adsorption amount does not increase and the adsorption process reaches the adsorption equilibrium. When the ion concentration increases, the adsorption capacity increases, but when the ion concentration increases to a certain extent and the hydration force becomes the dominant force, the adsorption capacity begins to decrease because of the increase of the hydration repulsion force. (3) when the Ca 2 + coexists, the adsorption capacity begins to decrease. In the experiments of membrane flux attenuation and membrane flux recovery, the adsorption behavior of BSA on three kinds of ultrafiltration membranes was studied, and the pollution law was found to be similar to that of Na ions. The higher the concentration of Ca 2 +, the lower the rejection rate of BSA. For PVDF and EVOH membranes, when Ca 2 + concentration is 100 mmol / L, BSAs can hardly be intercepted. The flux recovery rate shows that with the increase of ion concentration, ion concentration increases to a certain extent, the flux recovery rate increases, and the adsorption behavior is similar to that when Na ion coexists. Because the bivalent Ca2 + and monovalent Na are cations, the electrostatic shielding effect is formed with the negative BSA, and the electrostatic repulsive force decreases and the membrane fouling is aggravated. Because of the complexation of the bivalent Ca 2 +, the effect of Ca 2 + on the flux attenuation of the membrane is slightly greater than that of Na ion.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X703;TQ028.8

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