Effects of Chemical Reactions

The standard Gibbs-energy change of reaction AG° is used in the calculation of equilibrium compositions. The standard heat of reaclion AH° is used in the calculation of the heat effects of chemical reaction, and the standard heat-capacity change of reaction is used for extrapolating AH° and AG° with T. Numerical values for AH° and AG° are computed from tabulated formation data, and AC° is determined from empirical expressions for the T dependence of the C° (see, e.g., Eq. [4-142]). 

In any event the value of iri the presence of a chemical reac tion normally is larger than the value found when only physical absorption occurs, 7c . This has led to the presentation of data on the effects of chemical reaction in terms of the reaction factor or enhancement factor defined as... 

The effect of chemical reaction in reducing the effect of variation of the liquid rate on the rate of absorption in the laminar-flow regime was illustrated by the evaluation of the rate of absorption of chlorine in ferrous chloride solutions in a wetted-waU column by Gilliland, Baddoiir, and White [Am. In.st. Chem. Eng. J., 4, 323 (1958)]. 

Gutknecht, J. Tosteson, D. C., Diffusion of weak acids across lipid membranes Effects of chemical reactions in the unstirred layers, Science 182, 1258-1261 (1973). 

Now consider the effect of chemical reaction. If the reaction is fast, its effect is to reduce the liquid-film resistance. The result is an effective increase in the overall... 

Major DT, Gao J (2007) An integrated path integral and free-energy perturbation-umbrella sampling method for computing kinetic isotope effects of chemical reactions in solution and in enzymes. J Chem Theory Comput 3 949—960... 

Gaussian PDFs are found for homogeneous inert scalar mixing in the presence of a uniform mean scalar gradient. However, for turbulent reacting flows, the composition PDF is usually far from Gaussian due to the non-linear effects of chemical reactions. 

Unlike presumed PDF methods, transported PDF methods do not require a priori knowledge of the joint PDF. The effect of chemical reactions on the joint PDF is treated exactly. The key modeled term in transported PDF methods is the molecular mixing term (i.e., the micromixing term), which describes how molecular diffusion modifies the shape of the joint PDF. 

This is rarely done in practice. For example, all commonly used models ignore possible effects of chemical reactions on the scalar-mixing process. Compare this with the flamelet model, where mixing and reactions are tightly coupled. 

Unlike Lagrangian composition codes that use two-equation turbulence models, closure at the level of second-order RANS turbulence models is achieved. In particular, the scalar fluxes are treated in a consistent manner with respect to the turbulence model, and the effect of chemical reactions on the scalar fluxes is treated exactly. 

The Effect of Chemical Reactions Coupled to Electron Transfers... 

FIGURE 5.14 Effect of chemical reaction rates on detonation structures as viewed on Hugoniot... 

SuperChems Expert 161 is a code developed by Arthur D Little Inc. for risk assessment consequence analysis, which also has a relief system sizing option. The code has a physical properties package that can handle highly non-ideal properties. It can also consider the effect of chemical reaction in the relief system piping. The code uses the DIERS drift flux methods for level swell and has the option of a rigorous two-phase slip model for the. relief system capacity. 

A laboratory test apparatus for measuring thermal effects of chemical reactions. 

Another experimental example of the effect of chemical reactions on voltammetry in resistive media is given by the reduction of tetracyanoquinodi-methane (TCNQ) in acetonitrile. At high ionic strength, voltammograms of TCNQ have two one-electron waves of equal amplitude [75]. The waves correspond to the following electrochemical processes ... 

The choice of the temperature of the initial reactive mass (75 - 90°C) is dictated by two requirements firstly, the reactive mass must be liquid secondly, the reaction rate in this temperature range must be negligible. It was established in preliminary experiments that the temperature of the heater surface needs to be 75 - 125°C higher than the initial temperature of the reactive mass. The necessary operation period for the heater depends on the initial temperature of the reactive mixture and its reactivity (i.e., on its composition). The temperature of the heater does not influence the properties of the final product or the stationary kinetics of the process. The local temperature increase inside the adjoining layer must be supplemented by a heater for 30 - 50 min. This is the time required to set up the reaction front after that, the front exists by itself and propagates due to the exothermal heating effects of chemical reaction and crystallization. 

Usually the effect of chemical reactions in RA processes is advantageous only in the region of low gas-phase concentrations, due to limitations stemming from the reaction stoichiometry or equilibrium (20). Further difficulties of RA applications may be caused by the reaction heat through exothermic reactions and by relatively difficult solvent regeneration (21,22). Most RA processes are... 

Absorption is another important unit operation process involved in the chemical, petrochemical, and a number of other processing industries. Since the discovery of the major effect of chemical reaction in promoting absorption, especially after the establishment of the systematical analysis method by Denckwerts [70], chemical absorption has been more widely applied industrially. It is clear that whenever an absorption treatment is needed in the processing industries, people always prefer where possible to employ chemical absorption. Of course, in the application of impinging streams in the area of absorption, what we are most concerned with is its application in chemical absorption too. This is the focal point of the discussion in this chapter. 

As indicated in Chapter 1, principally, the reactions may be conjugated, when one of them slows another one down, and somewhat inhibits it. The mechanism of slowing down the secondary reaction may have different origins (e.g. if the target reaction is of the catalytic type, and intermediate products (IP) poisoning the catalyst are formed in the primary reaction). Another possible case is realized when IP of both reactions recombine or disproportionate (active sites are eliminated). Such negative effects of chemical reactions allow us to... 

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