Process auto-catalytic

Recently there has been an increasing interest in self-oscillatory phenomena and also in formation of spatio-temporal structure, accompanied by the rapid development of theory concerning dynamics of such systems under nonlinear, nonequilibrium conditions. The discovery of model chemical reactions to produce self-oscillations and spatio-temporal structures has accelerated the studies on nonlinear dynamics in chemistry. The Belousov-Zhabotinskii(B-Z) reaction is the most famous among such types of oscillatory chemical reactions, and has been studied most frequently during the past couple of decades [1,2]. The B-Z reaction has attracted much interest from scientists with various discipline, because in this reaction, the rhythmic change between oxidation and reduction states can be easily observed in a test tube. As the reproducibility of the amplitude, period and some other experimental measures is rather high under a found condition, the mechanism of the B-Z reaction has been almost fully understood until now. The most important step in the induction of oscillations is the existence of auto-catalytic process in the reaction network. 

Kinetic data on the thermal degradation of ABS and PC/ABS blends are available (130,131). Thermogravimetric analysis suggests that the kinetics of the thermal degradation can be modelled by an auto-catalytic process. 

If at the initial moment of time active sites, representing a catalyst of further substrate oxidation, are formed in the system, such processes are classified as auto-catalytic processes. 

In all the cases considered, auto catalytic processes must be present, whether linear or nonlinear. To understand the actual mechanism of autocatalysis for the Soai reaction, identification of the process at a molecular level is necessary, but is out of scope of the present review. 

Although these experiments did not provide the desired systems needed to amplify chirality, they were helpful in elucidating the stereochemical mechanism of the role played by additives in the early stages of crystal nucleation. This information was instrumental to the elaboration of appropriate model systems for the amplification of chirality, such as the generation of homochiral lysine via crystals of nickel/caprolactam [131] and the auto catalytic process of the spontaneous segregation of racemic enantiomers of amino acids in aqueous solutions assisted by centrosymmetric glycine crystals grown at interfaces. 

Electrochemical reduction of nickel(I)(salen) in the presence of benzal chloride at a carbon electrode in DMF leads to a variety of monomeric and dimeric products171. Cyclic voltammetric studies using benzylic halides showed that carbanions can bring about auto-catalytic processes by acting as electron-transfer catalysts (Scheme 16)172. 

The crystallization curve of the spontaneous system features an S shape, i.e., no X-ray-diffraction-detectable crystals exist in the synthetic system at the early stage of the crystallization period for a relatively long time, which is called the induction period subsequently, the crystallization rate gradually accelerates, which is called the auto-catalytic process finally, the crystallization rate gradually decreases at the last stage of the crystallization period, and the crystallization curve shows a gentle incline. 

This auto-catalytic process is characterized by a rather long induction period, which can be shortened by initiating the conversion by the introduction of small amounts (0.05 to 0.5 per cent weight in relation to the feed) of cumyl hydroperoxide or of its sodium salt Other initiators or oxidation catalysts are sometimes introduced these may be soluble salts of heavy metals (Mn, Co, Cu) or alkaline and alkaline earth derivatives of lead, bismuth, tin and antimony. "... 

We consider a simple test model which has the advantage that it can be studied analytically even for very large numbers of intermediates, which makes it suitable for the analysis of the interference between experimental errors with the errors due to linearization. This type of model, which is somewhat similar to Eigen s hypercycle model [26], has recently been introduced in connection with a population genetic problem [12]. The model used here is essentially a space-independent, homogeneous version of the model from [12]. We assume that there are two types of chemical species in the system, stable chemicals, A , v = 1,2,..., and active intermediates X , u = 1,2,..., and that there is a very large supply of stable species Ay, v = 1,2,..., and their concentrations ay, v = 1, 2,..., are assumed to be constant and only the concentrations Xu,u = 1,2,..., of the active intermediates are variable. We consider that the active intermediates replicate, transform into each other, and disappear through auto-catalytic processes moreover we assume that all active intermediates have the same... 

Bulk polymerization, which is an auto-catalytic process and rarely used commercially and is therefore not considered ... 

The sigmoidal behavior, which is a characteristic feature in auto-catalytic processes [37], can be explained by the role of HH crystals, which act apparently as seed ( catalyst ) promoting the transformation. After the initial formation of HH crystals these act as seed. Over time the surface of these crystals increases hence providing an increasing number of active surface sites for incorporation of ions into the crystal lattice structure. This results in acceleration of the conversion process until all DH has been converted to HH. 

Although the simple rate expressions, Eqs. (2-6) and (2-9), may serve as first approximations they are inadequate for the complete description of the kinetics of many epoxy resin curing reactions. Complex parallel or sequential reactions requiring more than one rate constant may be involved. For example these reactions are often auto-catalytic in nature and the rate may become diffusion-controlled as the viscosity of the system increases. If processes of differing heat of reaction are involved, then the deconvolution of the DSC data is difficult and may require information from other analytical techniques. Some approaches to the interpretation of data using more complex kinetic models are discussed in Chapter 4. 

One can see such frozen structures that were formed due to an auto-catalytic reaction in tektites.12 There are several other geological processes that show such freezing of nonequilibrium structures.13... 

Figure 4.7 shows that after reaching the maximum yield the consumption rate of vinylethylbenzenes decreases only slightly. This indicates deficient H202 concentration at the stage of divinylbenzene synthesis. The S-shape of the kinetic curves obtained testifies to the auto-catalytic type of the process with the autoacceleration period from the beginning of these curves to inflection points. 

A homogeneous catalytic process, developed by Oxirane, uses a molybdenum catalyst that epoxidizes propylene by transferring an oxygen atom from tertiary butyl hydroperoxide. This is shown by 8.28. The hydroperoxide is obtained by the auto-oxidation of isobutane. The co-product of propylene oxide, /-butanol, finds use as an antiknock gasoline additive. It is also used in the synthesis of methyl /-butyl ether, another important gasoline additive. The over-... 

Violation of the stability condition (3.5) is allowed in bimolecular auto catalytic reactions, where the reaction groups of the initial reactants and of transformation products are interrelated. Consider the simplest bimolec ular reaction of the autocatalytic formation of an intermediate Aj by the process similar to the considered one ... 

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