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1.
Effect of membrane morphology on rising properties of filtration resistance in microfiltration of dilute colloids
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Eiji Iritani Nobuyuki Katagiri Yuuki Yamashita 《American Institute of Chemical Engineers》2017,63(8):3511-3522
The effect of membrane morphology on the flux decline behaviors in dead‐end unstirred microfiltration of very dilute colloids of polystyrene latex was examined using mixed cellulose ester and cellulose acetate membranes with interconnected tortuous pores and track‐etched polycarbonate membranes with uniform straight cylindrical pores. The plots of reciprocal filtration rate against the filtrate volume per unit membrane area for the former two membranes exhibit concave downward curves in the initial period when the membrane pore blocking is significant, whereas the plot for the latter shows a concave upward curve in that period. The former results were described by a serial resistance model consisting of the initial membrane pore blocking followed by filter cake growth, and the latter was represented by a parallel resistance model in which the pore blocking and cake growth develop simultaneously from the beginning of filtration. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3511–3522, 2017 相似文献
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Kuo-Jen Hwang Chih-Sheng Chan Fung-Fu Chen 《Journal of the Chinese Institute of Chemical Engineers》2008,39(3):257-264
Hydrodynamic methods are used for mitigating particle fouling and for enhancing the filtrate flux in submerged membrane filtration. In the comparison membrane blocking-cake formation filtration system, the effects of filtration pressure, aeration intensity, backwash duration and stepwise increasing pressure on the filtration resistances and filtration flux are measured and discussed. Aeration is helpful for reducing particle deposition on the membrane surface, while stepwise increasing pressure can mainly mitigate internal fouling of the membrane. Periodic backwash can significantly reduce both the resistance caused by the membrane internal fouling and by cake formation; consequently, it can effectively recover the filtrate flux. In contrast, increasing the pressure in constant pressure filtration leads the flux to be decreased due to more severe membrane blockage. According to the comparison of the long-term flux and the received filtrate volume, among these hydrodynamic methods, the periodic backwash with longer duration is the optimal strategy for the filtration. 相似文献
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动态膜处理污水时阻力分布及污染机理 总被引:4,自引:0,他引:4
对高岭土动态膜处理污水过程中膜污染阻力分布及膜污染机理进行了研究。通过测定和计算得知不同操作条件下各部分阻力的比例及其变化情况。动态膜过滤污水的阻力主要由动态膜膜孔堵塞阻力和膜面污染层阻力所控制。随着错流速度的增大,总阻力减小,各部分阻力的比例有所变化,但动态膜膜孔堵塞阻力和膜面污染层阻力依然占主导地位。利用传统膜过滤时有关膜污染的堵塞模型和滤饼过滤模型对动态膜处理污水时的实验数据进行分析,结果表明,动态膜过滤污水过程中,过滤初期约10 min左右,污染以膜的微孔堵塞为主,此后,膜的污染情况因操作条件不同而有所差异,影响最显著因素为错流速度,当错流速度较小时,膜的污染以膜面沉积污染物为主,符合滤饼过滤模型。适当提高错流速度有利于减小过滤阻力。 相似文献
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动态膜的形成机理及其水处理性能研究 总被引:3,自引:0,他引:3
以陶瓷管为载体,对高岭土动态膜的形成及其污水处理性能进行了详细的研究.实验中采用错流过滤方式涂膜,考查了跨膜压差、涂膜液浓度、错流速度及涂制时间等对动态膜形成的影响.通过对实验数据分析可知,动态膜形成初期10~13 min,膜的形成过程可用标准过滤模型描述,在此期间颗粒堵塞载体膜管孔道,致使渗透液通量急剧减小;之后,膜的形成过程符合滤饼过滤模型,这一阶段颗粒主要在载体膜管内壁面沉积,渗透液通量缓慢下降直至基本稳定.制备的动态膜可用于处理城市污水厂二级出水,动态膜对浊度去除率基本上为100%,对COD也有一定的去除作用. 相似文献
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针对头孢菌素C(CPC)发酵液在工业生产中难过滤的问题,在收率衡算模型基础上,结合浓差极化机理引入时间参数,针对连续洗滤过程(CFD)建立考虑时间的膜分离过程估算式,并以最短膜处理时间tmin为目标进行了优化求解。结果表明,在优化的膜处理过程中,CPC收率从85%增长到95%所用时间占总处理时间的30%~40%;而前浓缩比a值在0.5~0.8范围内时,总膜过滤时间差别不大。在一个相对较宽的可操作范围内,适当调整前浓缩比或/和调整目标收率,可以对生产过程的时效性及CPC收率、滤液/保留液体积等生产指标进行优化与控制。 相似文献
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《分离科学与技术》2012,47(1):52-61
The sugars produced by enzymatic hydrolysis of rice straw are separated using cross-flow diafiltration in this study. The effects of membrane type, membrane pore size, cross-flow velocity and transmembrane pressure on the filtration flux, sugar rejection, and sugar mass flux transported to the filtrate are discussed. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. When the membrane made of mixed cellulose ester (MCE) is used, over 70% filtration resistances are caused by the membrane fouling; while the resistance due to virgin membrane is dominant when regenerated cellulose (RC) membranes are used. A force balance model is applied to relate the filtration flux and filtration resistance to operating conditions. The calculated data of filtration flux based on this model agree fairly well with experimental data. In addition, a theoretical model is used to explain the sugar transmission through the cake and membrane pores. The sugar rejection coefficient decreases with increasing cross-flow velocity because of the effect of cake reduction. This effect is more significant when the MCE membrane is used. Comparing the sugar mass flux transported into the filtrate, it is more effective for sugar purification by using 10 kD RC membrane and under higher transmembrane pressures. 相似文献
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采用湿式催化氧化/膜过滤组合工艺,以Mo-Zn-Al-O粉末作为催化剂降解阳离子红GTL模拟染料废水,探讨在膜过滤过程中平均孔径为0.1 μm的微滤和0.022 μm的超滤聚偏氟乙烯(PVDF)中空纤维膜的过滤机理。实验结果表明,两种膜过滤组合工艺对染料的降解效果均优于单独湿式催化氧化,0.01 MPa恒压条件下运行120 min后微滤和超滤的膜通量分别衰减了26.63%和16.48%,其原因是粉末催化剂可在微滤膜孔内部沉积形成中间阻塞过滤,后在表面形成滤饼层;而在超滤膜表面仅形成滤饼层。通过实验结果对膜阻力进行计算,可知在相同反应过程后微滤膜产生的不可逆阻力大于超滤膜。在不同反应条件下,催化剂的沉积量与膜阻力呈现线性相关。 相似文献
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根据使用陶瓷膜中存在的问题,并以非对称陶瓷膜结构特点为基础,提出了以陶瓷膜支撑层(深层)与膜层共同作为过滤介质的一种新的陶瓷膜错流深层过滤方式。用非均粒径高岭土悬浮液,经过自行设计的实验流程和错流过滤器,进行了陶瓷膜错流深层过滤等实验。对取得的实验数据进行分析对比,得到了在相同操作条件下新方式比传统错流膜过滤的过滤阻力... 相似文献
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Modulation of electrical conductivity in kaolin/kerosene suspensions was examined as a means for the attenuation of fines retention in trickle‐bed reactors. The suspension stability was remarkably enhanced through ON‐OFF concentration modulation of an electrolyte‐based kerosene conductivity improver and resulted in an efficient bed‐cleaning strategy under operating conditions. Periodic additions of the conductivity improver enabled fines and deposits to gain momentarily large and similar electrical charges undoing, or impeding, multilayer deposition. The time evolution of the two‐phase pressure drop and specific deposit with/without conductivity improver was monitored, as well as the corresponding local deposition structure via electrical capacitance tomography (ECT). Electrical conductivity modulation was found to reduce the bed‐specific deposit by an order of magnitude and the bed pressure drop increment by a factor 14. ECT imaging evaluated the efficacy of this modulation strategy in mitigating deposition and in preventing filtration‐induced flow maldistribution. © 2010 American Institute of Chemical Engineers AIChE J, 2011 相似文献
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Cross-flow filtration is a filtration process for separation of a disperse phase from liquids. Suspension flows tangentially to a membrane and the filtrate is drawn off perpendicular to the direction of flow. Formation of a filter cake on the membrane is thus prevented, reduced, or its composition, modified. The principle of the separation is based on tow opposing effects: on the one hand, the particles are transported by the filtration flux to the membrane where they cause and increase in concentration; on the other hand, concentration differences are again reduced by the turbulence of the cross-flow and by Brownian motion of the particles. The two mechanisms compete with each other and depend upon particle size in different ways. An energetic comparison of the two effects yields the separation law of cross-flow filtration as a steady state solution of the Fokker-Planck equation. The separation law has an exponential form and assigns each particle size a separation probability with which it reaches the membrane. Once on the membrane the particles may form a filter cake, flow through the pores or return to the bulk flow. If the particles remain on the membrane the ranges of layer-free and cake-forming filtration can be calculated from the hydro-dynamic and geometric conditions of the cross-flow filter. Conventional cake filtration is regarded as limiting case. In continuous cross-flow filtration process a low separation probability through the filtration pressure on selection of the filter medium resistance. 相似文献
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《分离科学与技术》2012,47(7):1813-1825
Abstract The objective was to quantify the importance of operational conditions, aeration, and physico‐chemical conditioning on membrane fouling intensity. The suspension filterability was also analysed by using frontal filtration and a cake filtration model. Results pointed out the moderated role of aeration to reduce compound accumulation on the membrane surface. It did not appear as a determining criterion to prevent membrane fouling. In contrast, the physico‐chemical conditioning appeared as a determining criterion to increase critical flux. According to the experimental conditions 200 l/m2/h/bar membrane permeability could be maintained transmembrane pressure (TMP) when filtering stored rainwater. This permeability value was 2–3 times higher than the values obtained without conditioning. Moreover, according to the low turbidity of such stored rainwater and because of the high selectivity of the membrane, the coagulation step, a very low amount of 10 mg/l FeCl3, was sufficient to intensify the filtration step. This conditioning interest appeared less significant when filtering salted water in immersed membrane systems, but a 20 mg/l FeCl3 addition appeared sufficient to double the value of critical flux. Nevertheless filtration in frontal mode pointed out the significant impact of physico‐chemical conditioning in reducing the cake deposit hydraulic resistance. 相似文献
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《分离科学与技术》2012,47(12):1689-1697
The tubular membrane filtration system is widely applied to solid-liquid separation processes. Any improvements to the filtration module would increase separation efficiency, thus reducing operating costs. In this experiment, PMMA powder with an average particle diameter of 0.8 µm was filtered by a ceramic tubular membrane with an average pore size of 0.2 µm, and the impacts of the operating variables, such as suspension concentration, the filtration pressure, and the crossflow velocity on the permeate flux were discussed. In order to understand the increased permeate flux, the proposed module is comparable to the tubular membrane filtration module, but with an additional side stream under the same filtration mass flow rate. In addition, variations of shear force on the membrane surface are analyzed by CFD simulation, and the influence of backwash operations on the permeate flux is discussed. The results show that the side stream membrane filtration increased the shear force on the membrane surface, reduced fouling on the membrane surface, and increased the permeate flux. Furthermore, a backwash operation with a side stream flow channel could effectively clean the particles deposited in the module, thus, increasing the permeate flux. 相似文献
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D. B. Patience R. W. Hartel D. Illingworth 《Journal of the American Oil Chemists' Society》1999,76(5):585-594
Melt crystallization of anhydrous milk fat and subsequent filtration of the slurry is a common process for obtaining milk
fat fractions with different physical and chemical properties. The crystallization mechanism is very complex and little is
known about how the crystallizer conditions and the crystal size distribution (CSD) affect the filtration process. The objective
of this study was to characterize the fractionation process and determine which geometric parameters of the crystallizer affect
the filtration step. Two scales of fractionation were studied, 0.6 L and 3.6 L, with crystallization at 28°C. The slurry was
pressure-filtered after 24 h at 500 kPa in a 1-L chamber. Impeller diameters and speeds were varied for both scales. Photomicroscopy
and spectrophotometry were used to characterize the crystallization process, and filtration rates were measured by weighing
the amount of filtrate passing through the filter. Filtration resistance values, calculated using the constant pressure filtration
equation, as well as photomicroscopy results indicated that the agglomerates and crystals that formed had different morphological
characteristics for the different mixing and flow regimes in the crystallizer. Crystallization conditions that provide an
optimal filtration time, a solid fraction with minimal liquid entrainment, and a CSD with an intermediate range of sizes (80–500
μm) having good packing properties for filtration were found. 相似文献
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在液体燃料合成浆态搅拌反应器中设置了以金属烧结板为过滤介质的内过滤器,实现固液分离。研究了压降、温度、搅拌转速、固含率、过滤介质孔径及颗粒粒径对过滤速率的影响。实验结果表明:在浆态反应器中进行内过滤可以得到澄清稳定的滤液;随着操作进行,滤饼厚度达到动态平衡,过滤速率最终趋于稳定;过滤速率随着压降、温度、过滤介质孔径、颗粒粒径的增大及搅拌转速、固含率的减小而增大。应用因次分析法建立过滤模型,通过麦夸特算法对实验数据进行最优拟合得到模型的参数值,统计检验以及模型计算值与实验值的比较表明该模型可靠。 相似文献
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不同过滤方式下过滤速率衰减模型研究 总被引:7,自引:3,他引:4
对真空死端过滤、气压死端过滤、轴向流十字流过滤、旋转流十字流过滤等不同过滤方式下的过滤速率衰减行为进行了系统的研究,建立了相应的过滤速率衰减模型、以及相应模型系数与悬池液浓度、操作压力、雷诺数和欧拉数等影响因素的关系式。结果表明,死端过滤速率衰减模型中过滤速率与时间呈幂函数关系、而十字流过滤速率衰减模型中过滤速率与时间则呈一次函数关系,死端过滤时悬浮液浓度和气压过滤压力对其过滤速率衰减模型系数的影响均呈三次函数关系,在十字流过滤时悬浮液浓度、操作压力以及雷诺数对模型系数b的影响均呈线性关系,轴向流十字流过滤速率衰减模型系数b与欧拉数呈反比,而旋转流十字流过滤时则模型系数a与欧拉数呈反比关系。十字流过滤中,旋转流方式同轴向流方式相比,过滤速率衰减趋势较陡,但其初始通量高,在较长时间内都能以高于轴向流过滤通量的状态运行。 相似文献