Membranes, characteristics ultrafiltration

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

Three different membrane processes, ultrafiltration, reverse osmosis, and electrodialysis are receiving increased interest in pollution-control applications as end-of-pipe treatment and for inplant recovery systems. There is no sharp distinction between ultrafiltration and reverse osmosis. In the former, the separation is based primarily on the size of the solute molecule which, depending upon the particular membrane porosity, can range from about 2 to 10,000 millimicrons. In the reverse-osmosis process, the size of the solute molecule is not the sole basis for the degree of removal, since other characteristics of the... 

The magnitude of the Peclet number indicates the importance of the convective relative to the diffuse process for solute transport. The solute concentration profiles for representative values of Pe are illustrated in Fig. 12.2 according to Bungay [7]. When diffusion is dominant (Pe 0) the concentration varies nearly linearly in z. For large absolute values of the Peclet number, diffusion is significant only in a thin zone adjacent to the low pressure face of the membrane in which the concentration profile is very steep. For micro- and ultrafiltration membranes, the solute concentration varies little from the value at high pressure face. For nanofiltration the Peclet number can vary considerably depending on membrane characteristic almost dense or porous membranes. 

Filtration protocols are described in the relevant chapters, microfiltration, ultrafiltration and nanofiltration, respectively. Membrane characteristics such as suifiace charge and morphology are also presented in these chapters. 

In ultrafiltration, analyte molecules are basically carried along with the flow of water and electrolytes. The factors determining recovery in ultrafiltration are membrane characteristics, temperatme, and chemistry of the analyte. Unlike microdialysis, recovery is not dependent on flow rate, membrane surface area, or probe size. Recovery tends to be higher than for dialysis, since there is no perfusion medium to dilute the collected analyte. Ultrafiltration recovery rates are typically in the 90-100% range. This high recovery rate simplifies determination of in vivo analyte concentrations. Table I illustrates some in vitro recoveries obtainable with ultrafiltration probes. 

Susanto, H. and Ulbricht, M. (2005) Influence of ultrafiltration membrane characteristics on adsorptive fouling with dex-trans. Journal of Membrane Science 266, 132-142. 

Examination of the results for the conventimial parameters tested in the feed and permeate (Table 3) provides some insight into the separation mechanism. High concentrations of oil and grease found in the feedwater suggests that cmisiderable oil remained in a dispersed or colloidal form. This oil would be removed by a membrane with ultrafiltration or hyperfiltration characteristics. Since the PAHs are more soluble in oil than in water, concurrent removal of the PAHs entrained within the oil may have occurred. The phenols with relatively high solubility in water are, also as expected, removed more poorly. This also is reflected in the poor rejections calculated for TOC and COD. Other contaminants, not quantified by the semivolatile analysis, also may contribute to the high TOC and COD in the permeate. 

The subsequent improvement of the physical and chemical characteristics of these membranes, their incorporation into machines, and the development of procedures to prevent or clean surface-fouling films were the principal areas of significant advancement. By 1990, the industrial ultrafiltration market had grown to an estimated (90-100) x 10 . ... 

Nonselective membranes can assist enantioselective processes, providing essential nonchiral separation characteristics and thus making a chiral separation based on enantioselectivity outside the membrane technically and economically feasible. For this purpose several configurations can be applied (i) liquid-liquid extraction based on hollow-fiber membrane fractionation (ii) liquid- membrane fractionation and (iii) micellar-enhanced ultrafiltration (MEUF). 

Ultrafiltration of micellar solutions combines the high permeate flows commonly found in ultrafiltration systems with the possibility of removing molecules independent of their size, since micelles can specifically solubilize or bind low molecular weight components. Characteristics of this separation technique, known as micellar-enhanced ultrafiltration (MEUF), are that micelles bind specific compounds and subsequent ultrafiltration separates the surrounding aqueous phase from the micelles [70]. The pore size of the UF membrane must be chosen such, that the micelles are retained but the unbound components can pass the membrane freely. Alternatively, proteins such as BSA have been used in stead of micelles to obtain similar enan-tioselective aggregates [71]. 

B. Production and Rejection Characteristics of S-Layer Ultrafiltration Membranes (SUMs)... 

Nakao, S-I Nomura, T Kumura, S, Characteristics of Macromolecular Gel Layer Formed on Ultrafiltration Tubular Membrane, AIChE Journal 25, 615, 1979. 

Generally, the effectiveness of the separation is determined not by the membrane itself, but rather by the formation of a secondary or dynamic membrane caused by interactions of the solutes and particles with the membrane. The buildup of a gel layer on the surface of an ultrafiltration membrane owing to rejection of macromolecules can provide the primary separation characteristics of the membrane. Similarly, with colloidal suspensions, pore blocking and bridging of... 

Table 10 Ultrafiltration Characteristics of Do Wastewater Using Different Membranes...

Membrane extraction offers attractive alternatives to conventional solvent extraction through the use of dialysis or ultrafiltration procedures (41). The choice of the right membrane depends on a number of parameters such as tlie degree of retention of the analyte, flow rate, some environmental characteristics, and tlie analyte recovery. Many early methods used flat, supported membranes, but recent membrane technology has focused on the use of hollow fibers (42-45). Although most membranes are made of inert polymers, undesired adsorption of analytes onto the membrane surface may be observed, especially in dilute solutions and when certain buffer systems are applied. 

The polyamide membranes prepared from aromatic diamines and aliphatic dichlorides, or from aliphatic diamines and aromatic dichlorides may be feasible for ultrafiltration as well as aliphatic polyamide membranes. Ohya 57) investigated the separation characteristics of asymmetric poly(xylyleneadipamide) (72) membrane under severe conditions of high temperature and high (or low) pH. 

Y. Nakagawa, K. Edogawa, M. Kurihara and T. Tonomura, Solute Separation and Transport Characteristics Through Polyether Composite (PEC)-1000 Reverse-Osmosis Membranes, in Reverse Osmosis and Ultrafiltration, S. Sourirajan and T. Matsuura (eds), ACS Symposium Series Number 281, American Chemical Society, Washington, DC, pp. 187-200 (1985). 

Bae, T.H. and Tak, M.T. (2005) Interpretation of fouling characteristics of ultrafiltration membranes during the filtration of membrane bioreactor mixed liquor. Journal of Membrane Science, 264 (1-2), 151-160. 

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