Chemical reactions semipermeable membrane

Two-Phase System with a Chemical Reaction and a Semipermeable Membrane... 

Phase equilibrium across semipermeable membranes is of special interest in biological applications. First, we will consider two-phase aqueous systems without chemical reactions, then introduce reactions, and finally electric potential differences between phases. The numbers of intensive degrees of freedom F and... 

When looking for an economically feasible enzymatic system, retention and reuse of the biocatalyst should be taken into account as potential alternatives [98, 99]. Enzymatic membrane reactors (EMR) result from the coupling of a membrane separation process with an enzymatic reactor. They can be considered as reactors where separation of the enzyme from the reactants and products is performed by means of a semipermeable membrane that acts as a selective barrier [98]. A difference in chemical potential, pressure, or electric field is usually responsible from the movement of solutes across the membrane, by diffusion, convection, or electrophoretic migration. The selective membrane should ensure the complete retention of the enzyme in order to maintain the full activity inside the system. Furthermore, the technique may include the integration of a purification step in the process, as products can be easily separated from the reaction mixture by means of the selective membrane. 

It may be noted that we define AG such that it equals the chemical potential of the substrate minus the chemical potential of the product. We noted above that the possibility of free-energy dissipation drives a reaction. Free-energy differences like ACr and A/tg in the above equation embody such a possibility they act as forces that drive the reaction. Other examples are the contractile force on a muscle the voltage drop across an electrical resistance the osmotic pressure on a semipermeable membrane. The dissipation function consists of the sum of the products of fluxes (currents) and the (thermodynamic) forces that drive them [4]. 

What makes the sodium-sulfur cell possible is a remarkable property of a compound called beta-alumina, which has the composition NaAlnOiy. Beta-alumina allows sodium ions to migrate through its structure very easily, but it blocks the passage of polysulfide ions. Therefore, it can function as a semipermeable medium like the membranes used in osmosis (see Section 11.5). Such an ion-conducting solid electrolyte is essential to prevent direct chemical reaction between sulfur and sodium. The lithium-sulfur battery operates on similar principles, and other solid electrolytes such as calcium fluoride, which permits ionic transport of fluoride ion, may find use in cells based on those elements. 

A chemical destruction method that has been used for the treatment of PCBs in contaminated dielectric liquids or soil is based on the reaction of a polyethylene glycol/potassium hydroxide mixture with PCBs (De Filippis et al. 1997). This method can be used successfully for the destruction of higher chlorinated PCBs with an efficiency of >99%, but was found to be unsuitable for the treatment of di- and trichlorobiphenyls due to low destruction efficiencies (Sabata et al. 1993). Irradiation of PCBs in isooctane and transformer oil by y-radiation resulted in degradation of PCBs to less chlorinated PCBs and PCB-solvent adducts (Arbon et al. 1996). Supercritical fluid technology has shown promise as a method for extraction of PCBs from soils, coupled with supercritical water oxidation of the extracted PCBs (Tavlarides 1993,1998a). Hofelt and Shea (1997) demonstrated the use of semipermeable membrane devices to accumulate PCBs from New Bedford Harbor, Massachusetts water. Another method showing... 

Consider a reaction that occurs in a vessel containing a semipermeable membrane that allows only one of the components to pass through it (for example, a small molecule such as hydrogen) but will not allow the passage of large molecules. With such a membrane, the chemical potential of the permeable component can be kept constant in the reaction vessel. 

Consider the membrane separation shown in Figure 3.8. An isothermal rigid vessel, initially contains pure component B at pressure Po and temperature To. it is. separated by a semipermeable membrane from a source of pure component A at pressure Fe. The membrane is permeable to component A but not component B. The system undergoes chemical reaction... 

Transport problems in discontinuous (heterogeneous) system discuss the flows of the substance, heat, and electrical energy between two parts of the same system. These parts or phases are uniform and homogeneous. The two parts make up a closed system, although each individual part is an open system, and a substance can be transported from one part to another. There is no chemical reaction taking place in any part. Each part may contain n number of substances. For example, thermal diffusion in a discontinuous system is usually called thermal osmosis. If the parts are in different states of matter, there will be a natural interface. However, if both parts are in liquid or gas phases, then the parts are separated by a porous wall or a semipermeable membrane. 

This chapter focuses on two types of biocatalyst membrane reactors, namely, enzymatic membrane reactors and cell-immobilized membrane reactors. The fundamental characteristic of an enzymatic membrane reactor is the separation of enzymes (biopolymers) from products and/or substrates by a semipermeable membrane (Jochems et al, 2011 Lopez et al, 2002). Permeable substrates and products can be selectively separated from the reaction mixture by the action of a driving force across the membrane (chemical potential, pressure, electric field) that causes the movement (diffusion, convection, electrophoretic migration) of solutes. In an enzymatic membrane reactor, the biocatalyst (enzyme) is retained within the system by... 

Hornung, U. and Jager, W. Diffusion, convection, adsorption, and reaction of chemicals in porous media, J. Diff. Equat. 92, 199-225, 1991 Hornung, U. and Jager, W. and Mikelic, A. Reactive transport through an array of cells with semipermeable membranes, R.A.LR.O. Mathematical Modelling and Numerical Analysis, 28, 59-94, 1994... 

We may need to evaluate the entropy of a nonequilibrium state. To do this, we imagine imposing hypothetical internal constraints that change the nonequilibrium state to a constrained equilibrium state with the same internal structure. Some examples of such internal constraints were given in Sec. 2.4.4, and include rigid adiabatic partitions between phases of different temperature and pressure, semipermeable membranes to prevent transfer of certain species between adjaeent phases, and inhibitors to prevent chemical reactions. 

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