Acid decomposition reactions heat requirement

Spent acid burning is actually a misnomer, for such acids are decomposed to SO2 and H2O at high temperatures in an endothermic reaction. Excess water in the acid is also vaporized. Acid decomposition and water vaporization require considerable heat. Any organic compounds present in the spent acid oxidize to produce some of the required heat. To supply the additional heat required, auxiUary fuels, eg, oil or gas, must be burned. When available, sulfur and H2S are excellent auxiUary fuels. 

This reaction completes the process of urea decomposition, transforming the isocyanic acid into further ammonia delivered to the SCR reactor. The reaction enthalpy of hydrolysis indicates that the reaction is exothermic, bringing a heat generation of 95.9 kJ per mole. This aspect is important, since it can be a consistent contribution to the heat request of reaction 17.30, reducing to less than half the heat required by the thermal decomposition. The global process, therefore, can be seen as the reaction ... 

The same reactants are used for manufacture as for sodium fluoride. An excess of acid is required to crystallize the bifluoride. The crystals are dewatered, dried, sized, and packaged. Cooling of the reaction is necessary to avoid over-heating and decomposition. Reactors and auxiUary equipment are the same as for sodium fluoride. 

Red mercuric oxide generally is prepared in one of two ways by the heat-induced decomposition of mercuric nitrate or by hot precipitation. Both methods require careful control of reaction conditions. In the calcination method, mercury and an equivalent of hot, concentrated nitric acid react to form... 

Thermal decomposition of spent acids, eg, sulfuric acid, is required as an intermediate step at temperatures sufficientiy high to completely consume the organic contaminants by combustion temperatures above 1000°C are required. Concentrated acid can be made from the sulfur oxides. Spent acid is sprayed into a vertical combustion chamber, where the energy required to heat and vaporize the feed and support these endothermic reactions is suppHed by complete combustion of fuel oil plus added sulfur, if further acid production is desired. High feed rates of up to 30 t/d of uniform spent acid droplets are attained with a single rotary atomizer and decomposition rates of ca 400 t/d are possible (98). 

The reaction is endothermic, and heat transfer to the reactor is required in order to accomplish the decomposition of the acetylated oil, to liberate acetic acid vapour. The example has been considered previously by Perona (1972), Smith (1972), Cooper and Jeffreys (1971) and Froment and Bischoff (1990), although their solution procedures differ from that here. Data values are based on those used by Froment and Bischoff. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C and is usually a vapor phase reaction. In the laboratory this is done by using a glass tube in the heating zone of a small furnace. The vapors of the reactant are swept through the hot chamber by an inert gas and into a cold trap. Similar reactions occur with esters derived from long-chain acids. If the boiling point of the ester is above the decomposition temperature, the reaction can be carried out in the liquid phase, with distillation of the pyrolysis product. 

---