反渗透、超过滤过程中的浓差极化

浓差极化是反渗透、超过滤过程中的重要影响因素.为了合理进行装置设计,较准确地确定湍流状态下的浓差极化,作者通过推理分析和归纳,求得浓差极化比的计算公式.与前人工作的初步对比,本文公式具有一定的代表性,可用于较宽的F_w范围,特别是在较高的F_w下,能较好地反映真实规律.这对预估反渗透膜分离过程中的浓差极化有较大的参考价值.     

Potential Applications of Pulsed Flow for Minimizing Concentration Polarization in Ultrafiltration

Abstract

Various methods have been proposed to control or minimize concentration polarization and membrane fouling. A brief review of these alternatives is presented in this paper. Flow pulsation as a means of improving transmembrane flux has been studied experimentally by a few investigators. A mathematical model is developed to evaluate the performance of a tubular membrane module under oscillatory flow conditions. Besides the effect of osmotic pressure and axial pressure variation, the model considers the convective-diffusive mass transport without decoupling the momentum equation from the solute continuity equation. Model equations are solved by a finite difference method as part of an iterative solution. Model predictions of transmembrane flux with experimental data are found to be in good agreement. By flow pulsing, it is possible to improve the transmembrane flux by more than 68% at pulsing frequency of 60 cycles · min^?1. An analysis of extra power requirement for flow oscillation shows that the gain in transmembrane flux outweighs the cost of extra power, which is a minute fraction of the power required to maintain steady flow.     

超滤分离过程及浓差极化现象的理论分析

通过分析平板膜超滤分离过程,描述了超滤过程动量传递和质量传递的微分方程,求解方程得到速度分布和浓度分布曲线。对速度分布和浓度分布曲线的理论分析表明,超滤操作中的无因次常数Nf和α是决定浓差极化现象的两个重要参数。自制的平板超滤膜组件和聚醚砜超滤膜实验结果与理论分析计算结果基本吻合。     

微滤和超滤过程中浓差极化和膜污染控制方法研究

本文较全面的介绍了微滤和超滤过程中浓差极化和膜污染的各种控制方法,并比较了各种方法的优缺点。     

Concentration Polarization and Fouling during Ultrafiltration of Colloidal Suspensions and Hydrophobic Solutes

Abstract

Flux reductions experienced during ultrafiltration are due either to concentration polarization or fouling. It is usually difficult to distinguish between these two phenomena, but by using a turbulence-promoting module it is possible to determine the reversibility of a flux reduction, and thus distinguish between concentration polarization and fouling. By using a turbulence-promoting module, it is also possible to distinguish between different cases of fouling. In this paper, fouling caused by the deposition of material at the surface of the membrane is illustrated by results from tests with a silica sol, and fouling due to interactions in the membrane matrix is illustrated by results from ultrafiltration of a low-molecular organic solute.     

Concentration Polarization Effects in the Use of Micellar-Enhanced Ultrafiltration to Remove Dissolved Organic Pollutants from Wastewater

Abstract

Micellar-enhanced ultrafiltration (MEUF) is used to remove 4-tert-butylphenol (TBP) from aqueous solution, a separation for which traditional ultrafiltration is ineffactive. A micelle—forming surfactant is added to the solution. The micelles solubilize a high fraction of the TBP. The stream is then forced through an ultrafilter. Overall rejection of TBP was greater than 99%. under all conditions studied and did not decrease with increasing pressure drop. Micelles were completely rejected by membranes with pore size 10 000 Dalton MWCO and below. Concentration polarization affects MEUF fluxes under conditions of interest. Bel polarization theory does not completely explain MEUF flux behavior. Selection of optimum operating parameters in MEUF application are discussed.     

超滤膜在果汁加工中的应用研究

选用中空纤维PAN膜、羧基化改性的PAN板式膜、PS膜和PS-SPS膜四种国产膜材料对苹果汁进行超滤澄清处理,比较不同膜对苹果汁理化指标的影响以及处理果汁的最佳条件、最佳工艺。     

A Study of Concentration Polarization Phenomenon on the Surface of a Gas Separation Membrane

Abstract

Mass transfer coefficients on the surface of porous glass membrane were obtained from separation tests of H₂-CO mixtures. These data agree with the correlation presented by Ghosh and Upadhyay for mass transfer on an impermeable wall. In addition, effects of the selectivity of membrane and bulk composition on the concentration polarization phenomenon are discussed and the limiting permeability which is affected by the polarization is represented as a function of mass transfer coefficient.     

Concentration Polarization in the Baromembrane Process

Abstract

Equations correlating the flows of the components and concentration polarization in baromembrane process are developed and discussed.     

Concentration by Membrane Ultrafiltration of a Shear-Thinning Fluid

Abstract

Many commercial membrane processes involve fluids whose rheological properties are non-Newtonian. However, very little has been published on ultrafiltration of non-Newtonian fluids. The aim of this work is to show some experimental results concerning the concentration by membrane ultrafiltration of fluids whose viscosity is high and shear-thinning. Experiments were performed with xanthan solutions as model shear-thinning fluids. The variations of permeate flux with respect to the operating parameters show the unusual effects of some of these parameters. It is shown that when the feed solution in an ultrafiltration process has shear-thinning properties, those properties have an enormous influence in determining the operation efficiency.     

超滤压力对制备高浓度纳米香精性能的影响

采用超滤技术,对以壳聚糖-三聚磷酸钠为壁材,桂花香精、晚香玉香精为芯材的纳米香精胶囊进行浓缩。通过一系列单因素实验分析不同因素对纳米香精胶囊超滤时间、粒径、固含量、Zeta电位等的影响,获得优化制备条件。采用激光粒度仪(DLS)等对其性能进行检测。结果表明,对于桂花纳米香精,将原液浓缩一倍时,选择相对分子质量150 000的壳聚糖,0.3 MPa超滤压力,香精质量分数为0.5%时超滤综合效果最好;对于晚香玉纳米香精,将原液浓缩一倍时,选择相对分子质量150 000的壳聚糖,0.3 MPa超滤压力,香精质量分数为0.244%超滤综合效果最好。     

“患者”——伴有超滤的透析型人工肾系统双室模型的研究

本文建立了“患者”——伴有超滤人工肾系统的双室模型,该模型的解析解考虑了超滤对透析器溶质清除率和细胞外室体积变化的影响,具有较为普遍的意义.通过拟合犬-人工肾活体动物实验数据,对双室模型参数进行了辨识,获得了令人满意的结果.     

超滤处理含油废水的研究

采用KMS Spirapak膜组件用于超滤工艺,能有效处理含油废水。在合适的操作条件下,浓缩倍数可达71,膜通量保持在0.6～1L/(min·m~2)。处理后出水中的油脂浓度小于30mg/L;COD浓度为2000～2500mg/L;并且其可生化性有了大幅度提高。采用KMS KLD-Ⅱ型膜清洗剂,能有效恢复膜通量,减轻膜污染。     

Influence of Membrane Properties on System Performances in Pervaporation under Concentration Polarization Regime

Abstract

The concentration polarization phenomenon was studied in the case of the dehydration by pervaporation of octanol in relatively concentrated solutions (up to 47000 ppm of water in n-octanol). The dependence of the observed performances on the mass transfer properties of the membrane and the boundary layer is analyzed theoretically. Experiments performed with cellulose acetate membranes of different thicknesses at a variable stirring speed in an agitated cell allowed us to determine the parameters of the theoretical model. It appears that the selectivity in pervaporation may depend in a complex way on the mass transfer in the boundary layer due to the possible concentration-dependent coupling of fluxes in the membrane. Results of the simulations of situations in which the membrane characteristics as well as the mass transfer in the liquid phase were changed are given to illustrate the influence of different parameters on the observed performances.     

酸性气体膜吸收过程中浓差极化

用聚丙烯中空纤维膜吸收器，针对酸性气体膜吸收传质过程，根据浓差极化时存在局部高浓度区的特点，分别进行了SO2/空气混合气和CO2/空气混合气中酸性气体的选择性吸收实验. 实验测定了SO2和CO2两种不同酸性气体在不同浓度吸收液及不同液速下的总传质系数，比较了两种酸性气体在液相侧的传质特性，根据两组份间化学反应机理的不同，分析了浓差极化对膜吸收过程的影响.     

侧柏叶提取液超滤过程及修正凝胶极化模型

采用酶法提取、乙醇 水混合溶剂提取工艺提取侧柏叶有效成分,对提取液的超滤过程进行研究。建立了该体系超滤过程的修正凝胶化模型,对模型参数进行了关联。该模型可适用于整个超滤操作压力范围,计算值与实验值非常一致。     

超滤新技术应用于果汁澄清的研究

研究了采用内压聚偏氟乙烯超滤膜对果汁进行过滤澄清的可行性,考察了膜面流速和膜的操作压力对膜通量的影响。研究了膜对果汁中的色度、浊度、电导率和糖度的影响。结果表明,PVDF超滤膜可以较好的去除果汁的浊度,平均去除率为90%,其透过液在室温保存半年无沉淀生成。其对果汁的色度影响较小,平均去除率为20%,其对电导率和糖度基本没有影响。     

超滤法对清喉颗粒除杂效果的研究

目的：考察超滤技术对清喉颗粒的除杂效果。方法：以绿原酸、总黄酮、牛蒡子苷保留率及固形物减少率为指标,对膜分子量、药液比、温度、加水量等4因素进行考察。结论：确定超滤工艺为：药液比为1∶16（g/ml）的药液,在40℃条件下进行超滤（超滤膜的截留分子量为20万）,在超滤过程中补加5倍量水。采用超滤技术对药液进行除杂,能够有效去除药液中的热原,提高药液澄明度,较大程度保留有效成分。     

Temperature Effects on Concentration Polarization Thickness in Thin‐Film Composite Reverse Osmosis Membranes

Continuous research and development of reverse osmosis (RO) technologies has led to the production of membranes that are very effective with high salt rejection abilities. As temperature is one of the factors that affects salt rejection capabilities in membranes, this paper investigates the effect of temperature on the thickness of the concentration polarization layer (CPL) deposited on thin‐film composite seawater RO membranes. Two types of membranes were studied: those with ex situ macromolecules and those with in situ macromolecules. FilmTec's reverse osmosis system analysis design software was used to predict the variation of salt rejection and permeate flow rate with temperature. The impact of these variations on the thickness of the CPL was analyzed for different polyamide concentrations in the membrane.