Regeneration Theory

Nyquist, H. (1932) Regeneration Theory, Bell System Technical Journal, 11, pp. 126-147. 

Nyquist, H. Bell System Tech. J. II (1932) 126. Regeneration theory. 

Hydroquinone and A -methyl-/j-aminophenol (Metol) form a superadditive mixture which was shown by Tausch and Levenson [47] to involve the consumption primarily of hydroquinone with the preservation of Metol. This led to the regeneration theory proposed by Levenson, that Metol was acting as the developing agent at the silver halide surface and that oxidized Metol was reduced back to Metol by hydroquinone as outlined in Eqs. (30)-(33). 

The regenerator theory was mainly developed by H. Hausen [1.10]. As it includes a number of complicated calculations of processes that are time dependent no further study of the theory will be made here. The summary by H. Hausen [1.7] and the VDI-Warmeatlas [1.11] are suggested for further study on this topic. 

The rate of mass transfer in the liquid phase in wetted-waU columns is highly dependent on surface conditions. When laminar-flow conditions prevail without the presence of wave formation, the laminar-penetration theory prevails. When, however, ripples form at the surface, and they may occur at a Reynolds number exceeding 4, a significant rate of surface regeneration develops, resulting in an increase in mass-transfer rate. 

There are several theories about the chemistry of vanadium poisoning. The most prominent involves conversion of VjOj to vanadic acid (H-iVO ) under regenerator conditions. Vanadic acid, through hydrolysis, extracts the tetrahedral alumina in the zeolite crystal structure, causing it to collapse. 

NOTE Hydrochloric acid is usually employed as a regenerant to avoid risks of calcium sulfate formation when using sulfuric acid. (lfH2S04 is used, it must not exceed 0.8% w/w strength.) HCl can be used at 120% of theoretical to obtain the maximum capacity and quality, but at the expense of some mineral acidity during the early part of the run. Therefore it is prudent to operate at only 100% of theory, which provides minimal alkalinity leakage and loss of capacity. 

Sutton Regeneration Partnership (1999). Mentoring - an interactive guide to theory and practice, CD-ROM. 

Rates of addition to carbonyls (or expulsion to regenerate a carbonyl) can be estimated by appropriate forms of Marcus Theory. " These reactions are often subject to general acid/base catalysis, so that it is commonly necessary to use Multidimensional Marcus Theory (MMT) - to allow for the variable importance of different proton transfer modes. This approach treats a concerted reaction as the result of several orthogonal processes, each of which has its own reaction coordinate and its own intrinsic barrier independent of the other coordinates. If an intrinsic barrier for the simple addition process is available then this is a satisfactory procedure. Intrinsic barriers are generally insensitive to the reactivity of the species, although for very reactive carbonyl compounds one finds that the intrinsic barrier becomes variable. ... 

Translated by Mike Brenner. Copyright Mike Brenner 1997. "Analyzes the natural and supernatural birth, destruction, and regeneration of the symbolic Child. Introduces the theory and practice of how to quest for and manufacture the Philosopher s Stone. Includes applications and explanations of verses by the famous Swedish [sic] Adept Norton, from an ancient manuscript. Now, for the first time, revealed according to mystical tradition and esoteric enlightenment. Includes the qabbalistic signs of Solomon, explained by a master- student of nature. With 12 emblematical figures with... 

Jacobson-Stockmayer theory (L2.). Usually transfer and termination reactions in polymerization have energies of activation higher than propagation. Thus, we attempted coupling reactions at temperatures lower than usually applied. In order to assure the access of dichlorosilane to the surface of the sodium, the dispersion was continuously regenerated by ultrasonication. 

Debierne (1914) was the first to suggest a radical reaction theory for water radiolysis (H and OH). In various forms, the idea has been regenerated by Risse (1929), Weiss (1944), Burton (1947, 1950), Allen (1948), and others. Platzman (1953), however, criticized the radical model on theoretical grounds and proposed the formation of the hydrated electron. Stein (1952a, b) meanwhile had suggested that both electrons and H atoms may coexist in radiolyzed water and proposed a model in which the electron digs its own hole. Later, Weiss (1953, 1960) also favored electron hydration with ideas similar to those of Stein and Platzman. In some respects, the theoretical basis of these ideas is attributable to the polaron (Landau, 1933 Platzman and... 

In some reactions involving gases, the rate of reaction estimated by the simple collision theory in terms of the usually infened species is much lower than observed. Examples of these reactions are the oxidation of H2 and of hydrocarbons, and the formation of HC1 and of HBr. These are examples of chain reactions in which very reactive species (chain carriers) are initially produced, either thermally (i.e., by collision) or photochemically (by absorption of incident radiation), and regenerated by subsequent steps, so that reaction can occur in chain-fashion relatively rapidly. In extreme cases these become explosions, but not all chain reactions are so rapid as to be termed explosions. The chain... 

The impact which was made by the writer s revival of the old ester mechanism in the context of polymerisations is attested by the number of polymer chemists who set about examining the validity of the theory experimentally. For example, Bywater in Canada confirmed that during the progress of a polymerisation of styrene by perchloric acid the acid could not be distilled out of the reaction mixture, but after exhaustion of the monomer it could be. This regeneration of the initiating acid after the consumption of the monomer is an often attested characteristic of pseudocationic polymerisations with many different protonic acids it is most simply explained by the decomposition of the ester to an alkene and the acid, i.e., a reversal of the initiation, when the monomer has been consumed. Enikolopian in the USSR found that the effect of pressure on the rate of polymerisation in the same system was not compatible with the propagation step involving an ion, and... 

However, we have to reflect on one of our model assumptions (Table 5.1). It is certainly not justified to assume a completely uniform oxide surface. The dissolution is favored at a few localized (active) sites where the reactions have lower activation energy. The overall reaction rate is the sum of the rates of the various types of sites. The reactions occurring at differently active sites are parallel reaction steps occurring at different rates (Table 5.1). In parallel reactions the fast reaction is rate determining. We can assume that the ratio (mol fraction, %a) of active sites to total (active plus less active) sites remains constant during the dissolution that is the active sites are continuously regenerated after AI(III) detachment and thus steady state conditions are maintained, i.e., a mean field rate law can generalize the dissolution rate. The reaction constant k in Eq. (5.9) includes %a, which is a function of the particular material used (see remark 4 in Table 5.1). In the activated complex theory the surface complex is the precursor of the activated complex (Fig. 5.4) and is in local equilibrium with it. The detachment corresponds to the desorption of the activated surface complex. 

C. D. Prater, J. Wei, V. W. Weekman, Jr., and B. Gross, A Reaction Engineering Case History Coke Burning in Thermofor Catalytic Cracking Regenerators Costei D. Denson, Stripping Operations in Polymer Processing Robert C. Reid, Rapid Phase Transitions from Liquid to Vapor John H. Seinfeld, Atmospheric Diffusion Theory... 

The reversibility of the sensing process is determined by the features of the (bio)chemical reaction, immobilized species (reagent and/or catalyst) and separation process involved. Very often, the slow kinetics of some such processes make them apparently irreversible in practice when in fact they are not in theory. Many of these sensors are of the irreversible-reusable type and require two steps (sensing and regeneration) for proper functioning. Only... 

The identification of a direct cardiac precursor within the bone marrow cell population opens up a vast number of possibilities for the field of cardiac regeneration. In theory, in vitro expansion of this type of cell would be therapeutically attractive. 

The notion of boundary is, in fact, one central concept in the theory of autopoiesis. Inside the boundary of a cell, many reactions and correspondingly many chemical transformations occur. However, despite all these chemical processes, the cell always maintains its own identity during its homeostasis period. This is because the cell (under steady-state conditions and/or homeostasis) regenerates within its own boundary all those chemicals that are being destroyed or transformed, ATP, glucose, amino acids, proteins, etc. 

In theory, an ideal catalyst would not be consumed but this is not always the case in practice. Owing to competing reactions, the catalyst undergoes chemical changes and its activity becomes lower (catalyst deactivation). Thus catalysts must be regenerated or eventually replaced [2]. 

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