Exothermic process, thermal

Chlorine free radicals used for the substitutioa reactioa are obtaiaed by either thermal, photochemical, or chemical means. The thermal method requites temperatures of at least 250°C to iaitiate decomposition of the diatomic chlorine molecules iato chlorine radicals. The large reaction exotherm demands close temperature control by cooling or dilution, although adiabatic reactors with an appropriate diluent are commonly used ia iadustrial processes. Thermal chlorination is iaexpeasive and less sensitive to inhibition than the photochemical process. Mercury arc lamps are the usual source of ultraviolet light for photochemical processes furnishing wavelengths from 300—500 nm. 

The scale-up of exothermic processes is greatly enhanced through the use of the coefficient of thermal stability. Kafarov [2] defined this as the ratio of the slope (tan ttj) of the line representing the heat removal (due to the heat transfer medium and changes in enthalpy) to the slope (tan ttj) of the line representing heat generation (by the reaction) at the intersection of the two lines when plotted on the T versus Q coordinates. This is expressed as... 

Differential scanning calorimetry (DSC) experiments on the various dimeric carbocycles indicated that, depending on the length of the alkyl groups, thermal polymerization had occurred between 100 and 125°C as an abrupt, exothermic process. The narrow temperature range for each exotherm was suggestive of a chain reaction however, IR spectroscopy revealed the absence of acetylene functionalities in the polymerized material. Consequently, none of the substi-... 

The sample temperature is increased in a linear fashion, while the property in question is evaluated on a continuous basis. These methods are used to characterize compound purity, polymorphism, solvation, degradation, and excipient compatibility [41], Thermal analysis methods are normally used to monitor endothermic processes (melting, boiling, sublimation, vaporization, desolvation, solid-solid phase transitions, and chemical degradation) as well as exothermic processes (crystallization and oxidative decomposition). Thermal methods can be extremely useful in preformulation studies, since the carefully planned studies can be used to indicate the existence of possible drug-excipient interactions in a prototype formulation [7]. 

The formation of betaines in the reaction of silylenes (germylenes, stannylenes) Me2E14 (E14 = Si, Ge, Sn) with ylides H2C=E15Me3 (E15 = P, As) under gas-phase conditions occurs without a barrier as a strongly exothermic process. The thermal effects of the reactions are presented in Table XVII. 

The result obtained for Af//°[Cr(CO)6, cr)] is some 50 kJ mol-1 more positive than the recommended value, -980.0 2.0 kJ mol-1 [149], a weighted mean of experimental results determined with several types of calorimeter. The large discrepancy is not due to an ill-assigned thermal decomposition reaction but to a slow adsorption of carbon monoxide by the chromium mirror that covered the vessel wall. This is an exothermic process and lowered the measured Ar//°(9.13). 

In catalytic combustion or any exothermic decomposition, thermal aspects can dominate the continued reacting process particularly since the catalytic surface will also rise in temperature. 

Table I also presents the temperature at which this exothermal process starts (as Tg) and at which it ends (as Tg). The difference Tg- T can be considered as being the processing window of the thermally reactive oligomers, and is also listed in Table I.

Tg = Tg of a,u>-bis(hydroxyphenyl)PSU Tg = initial Tg of a,a)-bis(vinylbenzyl)PSU Tg = final Tg of the thermally cured a,co-bis(vinylbenzyl)PSU, i.e., constant value which does not increase by subsequent curing at 257°C Tg = temperature at which the exothermal process starts T = temperature at which the exothermal process ends. Does not reflect time necessary to complete reaction, only reflects length of time held at 257°C after the first heating run. 

On the basis of the above observation, Dahn and co-workers proposed a thermal reaction scheme for the coupling of carbonaceous anodes and electrolytes. The initial peak, which was almost identical for all of the anode samples and independent of lithiation degrees, should arise from the decomposition of the SEI because the amount of SEI chemicals was only proportional to the surface area. This could have been due to the transformation of the metastable lithium alkyl carbonate into the stable Li2C03. After the depletion of the SEI, a second process between 150 and 190 °C was caused by the reduction of electrolyte components by the lithiated carbon to form a new SEI, and the autocatalyzed reaction proceeded until all of the intercalated lithium was consumed or the thickness of this new SEI was sufficient to suppress further reductions. The corresponding decrease in SHR created the dip in the least lithiated sample in Eigure 35. Above 200 °C (beyond the ARC test range as shown in Eigure 35), electrolyte decomposition occurred, which was also an exothermic process. 

With an exothermic reaction, on the other hand, it may be necessary to remove heat to control the reaction and, if the reaction is reversible, to ensure a reasonable equilibrium conversion. The possibility of thermal runaway is always present with an exothermic process and this, with its implications for safety, must always be examined in any full reactor design. 

The ATR is carried out in the presence of a catalyst, which controls the reaction pathways and thereby determines the relative extents of the oxidation and SR reactions. The SR reaction absorbs part of the heat generated by the oxidation reaction, limiting the maximum temperature in the reactor. The net result is a slightly exothermic process. However, in order to achieve the desired conversion and product selectivity, an appropriate catalyst is essential. The lower temperature provides many benefits such as less thermal integration, less fuel consumed during the start-up phase, wider choice of materials, which reduces the manufacturing costs, and reduced reactor size and cost due to a minor need for insulation [22]. 

We can expect the entropy of the surroundings to increase when water freezes because freezing is an exothermic process, and the heat released passes into the surroundings. This heat stirs up the thermal motion of the atoms in the surroundings, which increases their disorder and hence their entropy (Fig. 7.15). 

JAP1090993). When the reaction is carried out on a large scale, heating the reactants to this temperature is sometimes enough to start a mild exothermal process further, thermally regulated by mere acetylene feeding. 

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