Absorption exothermic type

Quantitative analysis of the peroxy group of macroinitiators is performed by iodometry [38] and that of the azo group is done by ultraviolet (UV) spectrometry. Recently, type II MAI composed of PU was determined of its azo concentration by UV [20]. When the UV absorption spectral peak of the azo group overlaps other peaks, DSC is available by determining the azo group from the exothermal peak area [1IJ. 

Two types of situation may generally arise in respect of this equation. In the first, the enthalpy of the products exceeds that of the reactants (AH is positive), while in the second the converse happens (AH is negative). A reaction that conforms to the former situation is called an exothermic reaction and a reaction that corresponds to the latter situation is called an endothermic reaction. An exothermic reaction is accompanied by evolution of heat. An endothermic reaction, in contrast, occurs with absorption of heat. Enthalpy changes are... 

Recently, a chain type of reaction lias been postulated for the oxidation of ethylene.20 In highly exothermic vapor phase reactions such as the homogeneous oxidation of olefinic hydrocarbons conditions are particularly favorable for chain type reactions. The initial reaction in such transformations results in the formation of a molecule with excess energy and capable of readily reacting further with another molecule of the hydrocarbon to continue the cycle. Secondary processes such as absorption of the excess energy by a wall or surface, or destruction of the molecule by further oxidation serve to break the chain of reactions. The relative rates of formation and destruction of the active centers determine the speed of the reaction. Obviously, if the number of chains started is more than the number broken, the reaction becomes very rapid and explosion results. If the two rates are very nearly equal, the reaction proceeds with a measurable rate, the speed of which depends upon chain length. In general, the concentration of the reactants in the mixture determines the rates of formation and destruction of the chains and, hence, determines the rate of the reaction.27 The first step in the chain would be the formation of an unstable peroxide which could then react with another molecule of ethylene to form an unstable hydroxylated molecule to continue the chain reaction. Further oxidation of the peroxide first formed, however, would end the chain. Supplementary data and additional evidence that this type of reaction occurs have been supplied by Spence and Taylor.241... 

Here we will pay attention to the gas-liquid reactors. The reaction takes place usually in the liquid phase. Three main types of contact may be distinguished following the phase ratio (1) gas bubbles dispersed in liquid, (2) liquid drops dispersed in gas, and (3) gas and liquid in film contact. In the first category we may cite gas-liquid bubble columns, plate or packed absorption columns, agitated tanks, agitated columns, static mixer columns, pump-type reactors. As examples in the second class we may name spray columns or liquid injection systems. The third category can be used with very exothermic reactions or viscous liquids. 

After cooling, chlorine gas is dried by contact with concentrated sulfuric acid, a powerful desiccant over which the vapor pressure of contained water is very low. Other drying processes have been suggested from time to time, but none has had wide commercial success. The absorption of water by sulfuric acid is highly exothermic (more than 3 MJ kg ), and many combinations of feed and spent acid strengths can result in boiling if the heat is not removed. This section covers the amounts of acid required, equilibrium considerations in the process, the types of apparatus used, and the handling of the acid. 

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