水包油乳化超滤：陶瓷和聚合物膜对比Ultrafiltration of oil-in-water emulsion Comparison of ceramic and polymeric membranes.docx

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1、Ultrafiltration of oil-in-water emulsion: Comparison of ceramicand polymeric membranes水包油乳化超滤：陶瓷和聚合物膜比照Abstract 摘要Ultrafiltration has been recognized as a highly attractive technique for the treatment of stable oil-in-water emulsions. This technique has proved to be more effective then conventional

2、methods, since it may produce a water phase of higher quality and an oil phase which can be recycled. However, low permeate fluxes due to membrane fouling still represent one of the main limitations fbr its extensive application. The aim of this paper is to further contribute to the investigations o

3、f mass transfer characteristics during ultrafiltration of oil-in water emulsions. The performances of a polymeric (polyaryletherketone) membrane and a ceramic (zirconia) membrane were compared under different parameters of the ultrafiltration process. The comparison experiments were carried out at o

4、ptimal operation conditions for each of the membranes in order to maximise their performances. The results suggest that only comprehensive approach taking into account cross-flow and permeate hydrodynamics and interactions between membrane material and oil droplets can lead to the overall improvemen

5、t of the process.公认超滤是极具吸引力稳定水包油乳化处理技术。证明由于可更高质量的水相和可回 收利用的油相，这一技术比传统方法更有效。但是，膜污染导致的低渗透通量依然是其广 泛应用的主要限制之一。本文的目的是进一步研究水包油乳化超滤过程中传质特征。比照 了不同超滤工艺参数下聚合物(聚方基甲酮)膜和陶瓷(氧化错)膜的性能。比照实验是 在每种膜的最正确操作条件下进行，以最大限度地提高其性能。结果说明，只有考虑错流和 渗透流体动力学以及膜材料和油滴之间相互作用综合方法才能导致整体工艺改进。Keywords: Cross-flow ultrafiltration; Oil-in-wat

6、er emulsion; Polyaryletherketone; Zirconia 1. Introduction 弓 | 言但是，中等TMP （粗体值）时，油的去除非常好，渗透液中的油浓度远低于使用聚合物 膜取得的值。最正确操作条件的最终选择必须考虑表1和图2、3中给出的所有结果。表2 是之前结果的总结，显示了不同错流流速下的限制通量值，以及相应的TMP、E和渗透 油浓度。Table 2 Membrane performances at different operation conditions,不同操作条件下 的膜性能Ceramic membrane 陶瓷膜Cross-flow vel

7、ocity错流流速 m s-1TMPlim 限 值kPaFluxlim 通量 限值L m-2 h1Elim kWh m-3Permeate oil cone. 渗透液油浓度 mgL10.610045L31051.2150902.2211.81801203.439 - 2503.03202005.6732 - 1000Polymeric membrane 聚合物膜Cross-flow velocity错流流速 m s-1TMPlim 限值kPaFluxlim 通量 限值L m 2 h1Elim kWh m-3Permeate oil cone. 渗透液油浓度 mgL10.6100251.080

8、-2201.2200601.51.82001001.73.02001703.9Highlighted rows of the Table 2 represent the most favourable membrane performancestaking into consideration membrane productivity, energy consumption and selectivity. The optimal operation conditions were chosen to be: a flow rate of 150 L h1 (1.2 m s-1) and a

9、 TMP of 150 kPa fbr the ceramic ZrCh membrane and a flow rate of 300 L h-1 (1.8 m s) and a TMP of 200 kPa for the polymeric PAEK membrane.表2中突出显示的行代表考虑膜产量、能耗和选择性的最有利的膜性能。选择的最 佳操作条件为：陶瓷ZrO2膜的150 L h-1 (1.2 m s-1)流量和150 kPa的TMP和聚合物 PAEK 膜的 300Lh-i (1.8 ms/)和 200 kPa 的 TMP。3.2 Volumetric concentration

10、of oil-in-water emulsion 油包水乳化体积浓缩Volumetric concentration of the feed solution was carried out at actual operation conditions fbr each of the tested membranes. The variations of permeate flux and specific energy during feed concentration.consumption are shown in Fig. 4, while the Fig. 5 shows the v

11、ariation of the permeate oil concentrationVCF在每种膜的实际进料条件下，进行乃至溶液的体积浓缩。产水通量和单位能耗的变化 见图4所示，图5那么显示了进料浓缩过程中产水油浓度的变化。Fig. 4. Permeate flux (A) and specific energy consumption (B) as a function of VCF for ceramic ZrOz and polymeric PAEK membrane.陶瓷膜 ZrCh 和聚合物 PAEK 膜渗透 通量(A)和比能耗(B)与VCF关系Fig. 4 shows that s

12、imilar values of the permeate flux and the energy consumption were obtained despite the ceramic membrane has operated at 50% lower cross-flow velocity and around 30% lower TMP compared to the operation conditions of the polymeric membrane. Although efficient operation at lower velocities and pressur

13、es certainly is in favour of the ceramic membrane, this membrane showed unexpectedly poor oil rejection during feed concentration experiment (Fig. 5). Different patterns of the variations of the oil concentrations indicate different membrane fouling mechanisms. The polymeric membrane showed expected

14、 oil rejection variation consistent with formation of the surface layer of the oil droplets, while the ceramic membrane showed poor oil rejection at the beginning of the operation (up to VCF of 1.5). To confirm this, Fig. 6 shows the oil concentration in the permeate samples taken during the both ex

15、periments.o o o o o o3 2 1 q MLUO一 pguxluclo三 Inouo。-一o 一图4说明，与聚合物膜的操作条件相比，尽管陶瓷膜以低50%的错流流速和低约30% 的TMP下操作，但是，依然取得了相似的 渗透通量和能耗值。尽管较低流速和压力下 的高效操作肯定有利于陶瓷膜，但是，这种 膜在进料浓缩实验期间表现出出乎意料的油 去除差(图5)0油浓度变化的不同特征说明 不同的膜污染机理。聚合物膜显示出与油滴a o 外表层形成一致的预期油去除变化，而陶瓷 膜在操作开始时显示较差的油去除(高达1.5的VCF)。为了证实这一点，图6显示了在两种实验期间采集的渗透液样品中的油浓

16、 度。Fig. 5. Total oil concentration in the permeate vs. VCF for ceramic ZrO2 and polymeric PAEK membrane.陶瓷ZrOz和聚合物PAEK膜渗透液中总油浓度与VCF的关系。Moderate variations of the oil concentrations in the permeate samples for the polymericmembrane proves that the surface layer and the concentration polarisation dete

17、rmine the membrane rejection properties. Contrary to the polymeric membrane, the ceramic membrane showed poor oil rejection at the beginning of the operation. After initial oil penetration, the membrane has shown continuous increase in oil rejection slowly approaching the values fbr the polymeric me

18、mbrane. It can be assumed that the hydrophobic nature and the bigger pore sizes of the ceramic membrane facilitated initial oil permeation. One of the approaches is to coat a ceramic membrane with a polymeric layer. Wang et al. 16 coated a porous ceramic membrane with the polyamide/PVA composite thi

19、n top-layer. The prepared membrane showed a good performance for treating the O/W microemulsions with a mean diameter of about 2.4(im; the oil rejection was always higher than 98.5% from the beginning throughout the operation. However, since the polymer coating of the ceramic membranes diminishes th

20、e mojor advantages ofonLL- co-dLUBS。-BOLUJOClQL= u - oUOJ 二oonLL- co-dLUBS。-BOLUJOClQL= u - oUOJ 二oceramic membranes such as thermal and chemical resistance, modification of a ceramic membrane itself appears as an interesting solution 17,18. Our results suggest that initial oil penetration through t

21、he ceramic membrane could be reduced if the experiment is performed in the recirculation mode until the surface layer is formed and the pseudo-steady stateconditions are reached. More practical approach could be alteration of the system hydrodynamics in such way drag away the large oil droplets from

22、 the membrane surface. Use of centrifugal forces already proved effective fbr achieving a high VCF of the oil emulsions 13Fig. 6. Oil concentration in the permeate sample vs. VCF for ceramic ZrO2 andpolymeric PAEK membrane.陶瓷ZrO2和聚合庙PAEK膜的渗透液样品中油浓度与VCFo聚合物膜渗透液样品中油浓度的中等变化证明了外表层和浓差极化决定膜的去除性 能。与聚合物膜相反，

23、陶瓷膜在操作开始时表现出较差的油去除。在最初的油渗透后，膜 显示出油去除率连续增加，缓慢接近聚合物膜的值。可以认为陶瓷膜的疏水性和较大的孔 径促进初始油渗透。一种方法是陶瓷膜的聚合物涂层。多孔陶瓷膜涂层采用聚酰胺/PVA复 合薄表层。制备的膜平均直径约为2.4 U m,显示处理O/W微乳化的良好性能；在整个操作过程中，油去除率始终高于98.5%。但是，由于陶瓷膜的聚合物涂层削弱了陶瓷膜的主 要优点，如热和化学耐受性，陶瓷膜本身的改性似乎是一种值得关注的解决方案。结果表 明，如果以再循环模式下进行实验，直到表层形成和到达拟稳态条件，那么可以减少通过陶 瓷膜的初始油渗透。更实用的方法可能是改变系统

24、流体动力学，从而使大油滴脱离膜外表。 也证明使用离心力可有效实现油乳化的高VCFo.Our volumetric concentration experiments showed one of the advantages of the ceramic membrane over the polymeric membrane; similar permeate fluxes were obtained at similar energy consumption but at significantly lower cross-flow velocity and transmembrane pr

25、essure. Further investigations will show if the poor oil rejection of the ceramic membrane at the beginning of the operation can be reduced without losing proved advantages of ceramic membranes over polymeric membranes.体积浓缩实验显示陶瓷膜相对聚合物膜的优势之一；以相似能消耗取得相似的渗透通 量，但错流流速和跨膜压力显著降低。进一步的研究将说明，是否可见减少运行开始时陶 瓷膜的

26、较差油去除，而不影响得到证明的陶瓷膜相对聚合物膜的优点。4. Conclusions结论The comparison experiments certainly showed the advantage of the ceramic membrane over the polymeric one in the area of membrane productivity. Bigger pore sizes with better module hydrodynamics provided similar permeate fluxes at considerably lower pressur

27、es and flow rates. The oil rejection of the ceramic membrane was not at the satisfactory level due to initial oil penetration to the permeate.比照实验肯定地说明陶瓷膜膜产率方面优于聚合物膜。更大的孔径和更好的模块流体 动力学以相当低的压力和流量提供相似的渗透通量。由于初始的油渗透到渗透液中，陶瓷 膜的油去除没有到达令人满意的水平。The results showed that the choice between a ceramic and a poly

28、meric membrane for the particular application depends on better understanding of membrane fouling mechanisms. Operation at optimal operation conditions is also essential, especially in the case of ceramic membranes. It seems that ceramic membranes with their limited availability of the pore sizes an

29、d hydrophobic nature of membrane material require more “tailoring” in order to provide optimal performances in the case of filtration of the aqueous solutions. However, once the right membrane is chosen for the particular application and its operation optimised, better thermal, mechanical and chemic

30、al stability, as well as easy of use represent obvious advantage of ceramic membranes over polymeric membranes.结果说明，特定应用的陶瓷膜和聚合物膜之间选择取决于膜污染机理的更好认识。最 佳操作条件下的操作也很重要，尤其是对于陶瓷膜。膜材料可行和疏水性质适用性有限, 陶瓷膜更多需要“定制”，从而提供水溶液过滤时的最正确性能。但是，一旦为特定应用选 择了正确的膜且优化其操作，更好的热、机械和化学稳定性以及易于使用是陶瓷膜相对聚 合物膜的明显优势。Oil-in-water emulsion

31、s are generated by various industries and subsequently discharged into the natural environment creating a significant ecological problem. The conventional methods for treatment of oil-in-water emulsions can be classified as chemical, mechanical and thermal. However, these methods have shown several

32、disadvantages, such as low efficiency, operational difficulties and high operation costs. To address this problem, membrane processes, such as microfiltration, ultrafiltration, nanofiltration and reverse osmosis have been investigated. These processes have proved to be more effective than convention

33、al methods, because they can produce a water phase of higher quality and oil phase which can be recycled, at low operating costs. Ultrafiltration, especially a cross-flow mode of operation, has been extensively investigated. For more than 25 years, this process has been considered as an attractive m

34、ethod fbr the separation of stable oil-in-water emulsions. The use of cross-flow ultrafiltration employing both polymeric and ceramic membranes has been reported in many articles 1-8. Nevertheless, membrane fouling which lead to the permeate flux decline and reduced membrane selectivity has been rec

35、ognised as a main limitation of this process. Oil-in water emulsions induce three types of fouling mechanisms: oil droplet deposit, concentration polarisation and adsorption of dissolved organic compounds 9.不同的行业产生水包油乳化，随后排放到自然环境，造成严重的生态问题。处理水包 油乳化的常规方法可分为化学、机械和热法。但是，说明这些方法存在效率低、操作困难、 运行本钱高等缺点。为了解决这

36、一问题，研究了微滤、超滤、纳滤和反渗透等膜工艺。证 明由于可以较低的运行本钱生产更高质量水相和可回收的用油相，这些方法比传统方法更 有效。广泛研究了超滤，尤其是错流运行模式。25年多来，这一工艺一直视为一种具有吸 引力的别离稳定水包油乳化方法。很多文章都报告了采用聚合物膜和陶瓷膜错流超滤应用。 但是，一直公认导致渗透通量下降和膜选择性降低的膜污染为这一工艺的主要限制。水包 油乳液导致三种污染机理：油滴沉积、浓差极化和溶解有机化合物吸附。In order to reduce membrane fouling and to improve the permeate flux different a

37、pproaches have been investigated, including changing of operation conditions 10, alteration of membrane material characteristics 11,12 and using of different hydrodynamic methods such as air sparging 7,9, high-shear rotary ultrafiltration 13 or insertion of static turbulence promoters 14. Howell 10

38、has introduced a concept of critical flux suggesting filtration at low transmembrane pressure as a method fbr reduction of membrane fouling during microfiltration.This investigation showed that operation bellow certain value of the transmembrane pressure can eliminate or significantly reduce membran

39、e fouling leading to improved process performance over time despite low permeate flux values. Faibish and Cohen 11 have reported the increase of over 20% in oil rejection for a commercial cutting oil emulsion with polymer-modified zirconia-based ultrafiltration membrane compared to the native membra

40、ne. Ju at el. 12 have reported high flux increase and higher organic rejection in the case of coated polysulfbne membrane compared to the uncoated membrane. Viadero Jr. et al 13 have shown that high-shear rotary ultrafiltration allows concentration of oil beyond the typical operating limitations of

41、conventional ultrafiltration modules. Krstic et al. 14 have shown that the operation conditions should be selected properly in order to achieve significant increase in permeate flux with reduction in operating costs during ultrafiltration with inserted static mixer as a turbulence promoter为了减少膜污染和提高

42、渗透通量，研究了不同的方法，包括改变操作条件、改变膜材 料特性，以及采用不同的流体动力学方法，如空气喷射鼓泡、强-剪切旋转超滤或嵌入静态 湍流促进器。引入临界通量的概念，建议低跨膜压力下过滤作为减少微滤过程中膜污染的 方法。这一研究说明，低于特定跨膜压力值的操作可消除或减少膜污染，尽管渗透通量值 低，也导致工艺性能随着时间推移而提高。报告了与原始膜相比，采用聚合物-改性氧化- 错基超滤膜的商业切削油乳化的油去除率增加了 20%以上。报告了与未涂涂层膜相比， 涂层聚飒膜的通量增加大，有机物去除率更高。说明强-剪切旋转超滤允许油的浓度超出传 统超滤模块的典型操作限值。说明应正确选择操作条件，且在超

43、滤期间使用嵌入静态混合 器作为湍流启促进器，实现渗透通量显著增加运行本钱降低。Ceramic membranes have been extensively investigated fbr the treatment of oil emulsions. Ceramic membranes have gained popularity due to their better mechanical, thennal and chemical stability over polymeric membranes. However, hydrophobic nature of the ceramic

44、 membranes, high price and limited availability of pore size range are identified as their main disadvantages over polymeric membranes. The reported results 3,5 suggest that a high pressure and a high velocity represents the optimum operation conditions fbr a polymeric membrane. On the other hand, t

45、he fouling phenomena of ceramic membranes are very affected by the transmembrane pressure therefore the operation at a moderate pressure has been recommended 8,14.广泛研究老了油乳化处理陶瓷膜。由于与聚合物膜相比的更好机械、热和化学稳定性，陶瓷膜变得普遍。但是，确定了陶瓷膜的疏水性、高价格和有限的孔径范围与与聚合物膜 相比的主要缺点。报告的结果说明，高压和高速是聚合物膜的最正确操作条件。另一方面, 陶瓷膜的污染现象受跨膜压力影响很大，

46、因此推荐以中等压力下操作。The aim of this study was to compare the performances of a ceramic and a polymeric membrane during ultrafiltration of an oil-in-water emulsion. It was assumed that the membrane performances could significantly vary with operation conditions. In that case, comparison at the same operatio

47、n condition could mask the actual membrane performances. Therefore, the optimal operation conditions for both membranes were determined during permeate recirculation experiments, followed by the volumetric concentration experiments carried out at genuine optimal operation conditions for both polymer

48、ic and ceramic membrane.本研究的目的是比照水包油乳化超滤过程中陶瓷膜和聚合物膜性能。假设膜性能可能 随着操作条件而显著变化。在这种情况下，相同操作条件下的比照可能“掩盖”实际膜性 能。因此，在渗透液再循环实验期间，确定了两种膜的最正确操作条件，之后在聚合物膜和 陶瓷膜真正最正确操作条件下的体积浓缩实验。2. Materials and methods材料和方法The experiments were carried out in cross-flow mode using a conventional ultrafiltration set-up with two mo

49、dules installed: tubular single-channel module containing a ceramic zirconia (ZrO2)membrane (Exekia, Pall, USA) and a flat sheet polymeric polyaryletherketone (PAEK) membrane (BFM 70100-P, Germany) (Fig. 1). The ceramic membrane used had a nominal pore size of 20 nm9 diameter of 6.8 mm and the effective membrane area of 46.2 cm2? while t