Accompanied by Chemical Reaction

Many separations which would be difficult to achieve by conventional distillation processes may be effected by a distillation process in which a solvent is introduced which reacts chemically with one or more of the components to be separated. Three methods are presented for solving problems of this type. In Sec. 8-1, the 0 method of convergence is applied to conventional and complex distillation columns. In Sec. 8-2, the 2N Newton-Raphson method is applied to absorbers and distillation columns in which one or more chemical reactions occur per stage. The first two methods are recommended for mixtures which do not deviate too widely from ideal solutions. For mixtures which form highly nonideal solutions and one or more chemical reactions occur per stage, a formulation of the Almost Band Algorithm such as the one presented in Sec. 8-3 is recommended. 

8-1 APPLICATION OF THE THETA METHOD OF CONVERGENCE TO DISTILLATION COLUMNS IN WHICH CHEMICAL REACTIONS OCCUR 

The 0 method of convergence, which was originally formulated for the solution of distillation problems in which chemical reactions did not occur, is extended to include the case where one or more chemical reactions occur on each stage of a distillation column. The computational time of the 0 method, which is one of the fastest known methods for solving distillation problems, is not significantly increased by the inclusion of one or more chemical reactions per stage. In the 

In recent years, several calculational procedures have been proposed for solving distillation problems in which a chemical reaction occurs on each plate. Suzuki, et al.24 used a procedure based on Muller s method whereas, Jelinek and Hlavacek14 used a relaxation method. Komatsu and Holland17 and Nelson19 proposed different formulations of the Newton-Raphson method. 

Consider the case of an existing column such as the one shown in Fig. 2-3. Suppose that the specifications are taken to be (1) the total number of stages and the location of the feed plate, (2) the complete definition of the feed (the total-flow rate, composition, and thermal condition), (3) the reflux rate, (4) the distillate rate, (5) the column pressure, and (6) the type of condenser (total or partial). On the basis of this set of specifications, it is desired to find the resulting compositions of the distillate and bottom products. 

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Another assumption, which is commonly made when the diffusion is accompanied by chemical reaction, is that the effect of the heat of reaction is negligible. 

In the instances so far considered, the process of absorption of the gas in the liquid has been entirely a physical one. There are, however, a number of cases in which the gas, on absorption, reacts chemically with a component of the liquid phase(36). The topic of mass transfer accompanied by chemical reaction is treated in detail in Volume 1, Chapter 10. 

In case of mass transfer accompanied by chemical reactions in gas-liquid systems the mass flux of the absorbed component is usually formulated as the product of an enhancement factor Ea and the mass flux corresponding to physical absorption at the same bulk concentration ... 

M. Nativ, S. Goldstein, and G. Schmuckler, Kinetics of ion-exchange processes accompanied by chemical reactions, J. Inorganic Nuclear Chem., 37 (1975), p. 1951. 

Two of this year s articles discuss the fluid-mechanical aspects of systems where material transfer may occur, accompanied by chemical reaction or heat transfer. Fulford analyzes thin-film flow in terms of the flow regimes and of surface disturbances, and relates recent experimental findings to the theoretical framework. Rietema discusses segregation phenomena in heterogeneous reactions, in relation to conditions of flow and of mass transfer. 

The partial differential equation for unsteady-state diffusion accompanied by chemical reaction is derived in Volume 1 as equation 10.170... 

Suzaki, Yagi, Kamatsu, and Hirat, "Calculation of Multicomponent Distillation Accompanied by Chemical Reaction", J. Chem. Eng. (Japan), vol 4, no 1, p 26, (1971)... 

In aqueous electrolytes, simple exchange of one or two electrons and protons is observed at many electrode surfaces. In anodic reactions, however, radical intermediate formation may also occur, as for example in the Kolbe reaction [525], The order in which electron and proton exchange occur, whether accompanied by chemical reactions or not, can often be characterized by standard electrochemical analysis. Radical ion formation is mostly involved in electro-organic reactions in aprotic non-aqueous... 

T he solubility data of gases in aqueous mixed-salt solutions are funda-mentally important in research on liquid-gas mass transfer and in designing gas-liquid contacting operations, especially gas absorption accompanied by chemical reaction. 

As the potential is increased, there is a point at which no equilibrium state is reached, but instead, an appreciable steady current flows which will obey Ohm s law over a reasonable range of applied potential. The potential at which this steady current is observed is called the decomposition potential because it is accompanied by chemical reaction (electrolysis) at the electrode surfaces. These electrode reactions are quite generally the oxidation (anode) and reduction (cathode) of ionic or molecular species present in the solution. If the reactions at the electrodes are reversible, then the decomposition potential Ed is related by the Nernst equation to the free energy changes of the electrode reactions... 

For the case of absorption accompanied by chemical reaction, Q(0) is deduced from solution of the equation... 

There are understandably some difficulties in describing reaction kinetics during microbiological conversions. Unlike chemical reactions, transport of components into and out of cells is involved. The cell population itself is in a dynamic state, and processes occurring within the cells may be accompanied by chemical reactions in the surrounding medium. 

In general, metal ion exchange by a chelating resin is intraparticle diffusion controlled (IPDC) accompanied by chemical reaction (chelation).Both Pick s law and Nernst-Planck have been used to describe... 

A model for multistage separation accompanied by chemical reactions must include a term in the component material balance. Equation 13.2 or 13.49, to represent the change in the number of moles of component i on stage j due to chemical reaction. This term is expressed as... 

Simultaneous absorption and desorption of several gases occurs, followed by chemical reaction the absorption of NO2, N2O3, and N2O4 is accompanied by chemical reactions, whereas the desorption of NO, NO2, and HNO2 is preceded by chemical reactions. (4) Equilibria prevail between various components in each phase. (5) Heterogeneous equilibria also prevail between the gas phase and liquid phase components. Sherwood et al. (1975) and Joshi et al. (1985) have reviewed NO absorption. 

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