Membrane technology characteristics

The catalytic esterification of ethanol and acetic acid to ethyl acetate and water has been taken as a representative example to emphasize the potential advantages of the application of membrane technology compared with conventional distillation [48], see Fig. 13.6. From the McCabe-Thiele diagram for the separation of ethanol-water mixtures it follows that pervaporation can reach high water selectivities at the azeotropic point in contrast to the distillation process. Considering the economic evaluation of membrane-assisted esterifications compared with the conventional distillation technique, a decrease of 75% in energy input and 50% lower investment and operation costs can be calculated. The characteristics of the membrane and the module design mainly determine the investment costs of membrane processes, whereas the operational costs are influenced by the hfetime of the 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. 

Since their introduction in the 1960s, membrane technologies have been utilized in food industries because they provide a unique opportunity for accomplishing both the fractionation and the concentration of components in liquid systems without phase change, while retaining desirable physical and chemical characteristics of key food components. Two of such food commodities with various components of desirable functional properties and health-enhancing effects, especially when utilized in purified form, are milk and whey [4—6]. 

Koyuncu, I., An advanced treatment of high-strength opium alkaloid processing industry wastewaters with membrane technology Pretreatment, fouling and retention characteristics of membranes. Desalination, 155, 265, 2003. 

A new variation related to the FT-30 membrane is being developed-the NF-50 composite membrane-which would appear to occupy a unique place in membrane technology. The NF-50 membrane has approximately the same characteristics as NTR-7250 and NF-40, but possesses an extremely high water flux. Reverse osmosis operation in large systems at a pressure of 35 to 50 psi is possible. The NF-50 membrane thus becomes the first example of a reverse osmosis membrane capable of operation at ultrafiltration membrane pressures. 

Childress A.E., Elimelech M. (1997), Effects of natural organic matter and surfactants on the surface characteristics of low pressure reverse osmosis and nanofiltration membranes, Proc. A WA Membrane Technology Conference, New Orleans, Feb. 97, 717-725. 

Jacangelo J.G., Cummings E.W., Cote P., Mallevialle J. (1993), Influence of feedwater characteristics on ultrafiltration and nanofiltration permeate water quality, Proc. of AWWA Membrane Technology Conf, Baltimore, Aug 93, 293-322. 

Zander A.K., Cleveland C., Curry N.K. (1995), Measurement of membrane surface hydrophobicity and charge as affected by solution characteristics, Proc. AWWA Membrane Technology Conf., Reno, Nevada, Aug 95, 609-619. 

Since membrane lungs as extracorporeal devices are in wide use, thoughts have turned to an implantable artificial lung prosthesis based on membrane technology. Developing such a device with the adequate characteristics and long-term reliability is a much more difficult task than encountered with the extracorporeal device developed for intermittent use. However, a small prototype device made of porous Teflon has been fabricated and tested by Richardson and Galletti. ... 

Membrane technology has been applied to a number of separation processes, each using a membrane but differing in the details of the method. Membranes suited for technical applications may be classified by the following characteristics [64,65] ... 

Membrane technology is presently an established part of several industrial processes. Well known is its relevance in the food industry, in the manufacture of dairy products as well as in the automotive industry for the recovery of electropainting baths. Membranes make possible the water supply for millions of people in the world and care for the survival of the large number of people suffering from kidney disease. The chemical industry is a growing field in the application of membranes, which, however, often requires membrane materials with exceptional stability. The first part of the book will discuss the currently available membranes for different processes, which are suitable for the chemical industry. Information on different methods of membrane preparation will be given. Different materials will be compared, taking into account physical characteristics and chemical stability. 

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