Membrane Process Modelling

Liposomes have been widely used as model membranes and their physicochemical properties have therefore been studied extensively. More recently, they have become important tools for the study of membrane-mediated processes (e.g., membrane fusion), catalysis of reactions occurring at interfaces, and energy conversion. Besides, liposomes are currently under investigation as carrier systems for drugs and as antigen-presenting systems to be used as vaccines. 

It has been proposed " that the mechanism(s) of action of gymnemic acids and ziziphins is a biphasic, model-membrane penetration-process. The model suggested that the modifier molecules interact first with the receptor-cell plasma-membrane surface. It was postulated that this initial interaction involves a selective effect on taste perception, including the transduction and quality specification of the sweet stimuli, and selective depression of sweetness perception. Following the initial interaction, the modifier molecules interact with the membrane-lipid interior to produce a general disruption of membrane function and a nonselective effect on taste... 

Reverse osmosis membrane process, 27 637 Reverse osmosis membrane cleaning citric acid application, 6 647 Reverse-osmosis membranes, 75 811, 825 development of, 75 797 Reverse osmosis models, 27 638-639 Reverse osmosis permeators, 76 19 Reverse osmosis seawater desalination process, 26 85 Reverse osmosis systems blending in, 26 80-81 brackish and nanofiltration, 26 80-83 Reverse osmosis technology... 

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. 

An important approach to the study of biological membranes has been the preparation and study of model membranes. According to current usage, model membranes include lipid bilayers and lipid bilayers into which have been incorporated additional components such as one or more membrane proteins. It is through the study of such model membranes that one has the best opportunity to isolate and study fundamental physical chemical and biophysical processes, and it is for this reason that the present report emphasizes these systems. A discussion of model membranes necessarily starts with a description of the chemical compositions and physical properties of lipid molecules. 

All four systems illustrated in Fig. 4 exhibit properties differing from those of cell membranes. Methods a-c have no influence on the head groups and preserve physical properties, such as charge, charge density, etc. The fluidity of the hydrocarbon core, however, is drastically decreased by the polymerization process. In case d, fluidity is not affected, but there is no free choice of head groups. In comparison to biomembranes, all polymerized model membrane systems will show an increase in viscosity and a decrease in lateral mobility of the molecules. 

C. Kleinstreuer and G. Belfort, Mathematical Modeling of Fluid Flow and Solute Distribution in Pressure-driven Membrane Modules, in Synthetic Membrane Processes,... 

The formation of concentration gradients caused by the flow of ions through a single cationic membrane is shown in Figure 10.8. As in the treatment of concentration polarization in other membrane processes, the resistance of the aqueous solution is modeled as a thin boundary layer of unstirred solution separating the... 

Carrier facilitated transport involves a combination of chemical reaction and diffusion. One way to model the process is to calculate the equilibrium between the various species in the membrane phase and to link them by the appropriate rate expressions to the species in adjacent feed and permeate solutions. An expression for the concentration gradient of each species across the membrane is then calculated and can be solved to give the membrane flux in terms of the diffusion coefficients, the distribution coefficients, and the rate constants for all the species involved in the process [41,42], Unfortunately, the resulting expressions are too complex to be widely used. 

Other processes that lead to nonlinear compartmental models are processes dealing with transport of materials across cell membranes that represent the transfers between compartments. The amounts of various metabolites in the extracellular and intracellular spaces separated by membranes may be sufficiently distinct kinetically to act like compartments. It should be mentioned here that Michaelis-Menten kinetics also apply to the transfer of many solutes across cell membranes. This transfer is called facilitated diffusion or in some cases active transport (cf. Chapter 2). In facilitated diffusion, the substrate combines with a membrane component called a carrier to form a carrier-substrate complex. The carrier-substrate complex undergoes a change in conformation that allows dissociation and release of the unchanged substrate on the opposite side of the membrane. In active transport processes not only is there a carrier to facilitate crossing of the membrane, but the carrier mechanism is somehow coupled to energy dissipation so as to move the transported material up its concentration gradient. 

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