Membrane process principles

Jelen, P. 1992. Pressure-driven membrane processes principles and definitions. In New Applications of Membrane Processes , IDF Special Issue 9201, pp. 7-14. 

The fourth fully developed membrane process is electrodialysis, in which charged membranes are used to separate ions from aqueous solutions under the driving force of an electrical potential difference. The process utilizes an electrodialysis stack, built on the plate-and-frame principle, containing several hundred individual cells formed by a pair of anion- and cation-exchange membranes. The principal current appHcation of electrodialysis is the desalting of brackish groundwater. However, industrial use of the process in the food industry, for example to deionize cheese whey, is growing, as is its use in poUution-control appHcations. 

An electrochemical membrane process can, in principle, perform the entire sequence in a single step while enriching the process gas slightly with H2. If the H2S could be electronated at a suitable cathode ... 

In this paper an overview of the developments in liquid membrane extraction of cephalosporin antibiotics has been presented. The principle of reactive extraction via the so-called liquid-liquid ion exchange extraction mechanism can be exploited to develop liquid membrane processes for extraction of cephalosporin antibiotics. The mathematical models that have been used to simulate experimental data have been discussed. Emulsion liquid membrane and supported liquid membrane could provide high extraction flux for cephalosporins, but stability problems need to be fully resolved for process application. Non-dispersive extraction in hollow fib er membrane is likely to offer an attractive alternative in this respect. The applicability of the liquid membrane process has been discussed from process engineering and design considerations. 

The process design principles of SLM, non-dispersive extraction, and hybrid hquid membrane systems need to be understood through bench scale experiments using feed solution of practical relevance. While the economic analysis of an ELM process can be performed from small scale experiments, such an analysis is difficult for other LM systems. In particular, availability and cost of hollow fiber membranes for commercial application are not known apriori. A simple rule of thumb for cost scale-up may not be apphcable in the case of an HE membrane. Yet we feel that the pilot plant tests would be adequate to make realistic cost benefit analysis of a liquid membrane process, since the volume of production in )8-lactam antibiotic industries is usually low. 

Membranes are semipermeable barriers that permit the separation of two compartments of different composition or even condition, with the transport of components from one compartment to another being controlled by the membrane barrier. Ideally, this barrier is designed to let pass selectively only certain target compounds, while retaining all others—hence the denotation semipermeable . Membrane separations are particularly suitable for food applications because (1) they do not require any extraction aids such as solvents, which avoids secondary contamination and, hence, the necessity for subsequent purification (2) transfer of components from one matrix to another is possible without direct contact and the risk of cross-contamination (3) membrane processes can, in general, be operated under smooth conditions and therefore maintaining in principle the properties and quality of delicate foodstuff. 

Naturally, there exist a variety of membrane separation processes depending on the particular separation task [1]. The successful introduction of a membrane process into the production line therefore relies on understanding the basic separation principles as well as on the knowledge of the application limits. As is the case with any other unit operation, the optimum configuration needs to be found in view of the overall production process, and combination with other separation techniques (hybrid processes) often proves advantageous for large-scale applications. 

In bioprocesses, a variety of apparatus that incorporate artificial (usually polymeric) membranes are often used for both separations and bioreactions. In this chapter, we shall briefly review the general principles of several membrane processes, namely, dialysis, ultrafiltration (UF), microfiltration (MF), and reverse osmosis (RO). 

Churchill, London (1946), Chapter 1 8) H.S, Harned, ChemRevs 40, 461-522 (1947) (Quantitative aspect of diffusion in electrolytic solutions) 9) R.B. Dean, ChemRevs 41, 503-23(1947) (Effects produced by diffusion in aqueous systems containing membranes) 10) D.A. Hougen K.M. Watson, "Chemical Process principles , Part 3, "Kinetics Catalysts , Wiley, NY (1947), Chap 20 11) Perry (1950), pp 522-59 (by... 

This concentration method uses a polymeric semipermeable membrane and principles of RO to effect separation of water from the organics in drinking water samples. In this process, a water sample is recirculated past the semipermeable membrane while hydraulic pressures exceeding the osmotic pressure are maintained. Water is transported through the membrane under these conditions (permeation). The concentration of solutes continues to build as water is removed from the system. 

In order to obtain potable water from sea water, one must either remove good watex from the solution or remove salt from the solution, leaving the good water behind. Most well known desalinization processes work on the principle of removing good water from solution the ion membrane process is the notable exception. It seems obvious that, since sea water is 96.5% water and only 3.5% salt, it would be preferable to remove the salt. Such processes received special attention in the work reported here. 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

Principles and applications of electrochemical remediation of industrial discharges are presented by Pallav Tatapudi and James M. Fenton. Essentials of direct and indirect oxidation and reduction, membrane processes, electrodialysis, and treatment of gas streams, and of soils, are complemented by discussions of electrode materials, catalysts, and elements of reactor design. 

Other monographs of note include Membrane Separations Technology Principles and Applications (Noble and Stern, 1995), Membrane Processes in Separation and Purification (Crespo and Boddeker, 1993), Membrane Separations in Chemical Processing (Flynn and Way, 1982), and Membrane Separation Processes (Meares, 1976). Additional references may be found at the end of the chapter. 

In industrial plants, ceramic membrane modules are arranged in different ways based on the general principles used for the design of membrane processes. The simplest module implementation is the dead-end operation mode. Here, the feed is forced through the membrane, which implies that the concentration of rejected components on the feed side of the membrane increases continuously and consequently the quality and the flux of permeate decrease with time. The main advantage of the dead-end... 

X. J. Chai, G. H. Chen, P. L. Yue, and Y. L. Mi, Pilot scale membrane separation of electroplating waste water by reverse osmosis. Journal of Membrane Science 123,235-242 (1997). J. D. Seader and E. J. Henley, Separation Process Principles, John Wiley Sons, New York, 1998. 

Fig. 7 Principle of the membrane process for chlor-alkali electrolysis [14, p. 441],...

Membrane processes are UNIT OPERATIONS. Regardless of what chemicals are being separated, the basic design principles for different types of membrane separations are always similar. 

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