Spent sulfuric acid handling

For the process step involving handling of spent sulfuric acid, several patents have been issued in which improvements in this step were a main claim. The azeotropic nitration of benzene essentially eliminates the need to reconcentrate sulfuric acid (10,11). The nitration step is carried out at higher than usual temperatures (120—160°C). Because excess benzene is used, the higher temperature allows water to be removed as a water—benzene azeotrope. The water is separated and the benzene phase, containing approximately 8% nitrobenzene, is recycled back into the reactor. The dry sulfuric acid is then reused continuously. 

In the gas cleaning sections of spent acid or metaUurgical sulfuric acid plants, the weak acid scmbbing circuit is typicaUy handled by plastic or glass fiber reinforced plastic (ERP) pipe. The contaminants in weak acid usuaUy vary too greatly to aUow use of an economical aUoy. 

The first commercial application of the Wellman-Lord process was at the Olin Corp. sulfuric acid regeneration plant in Paulsboro, N. J. This plant regenerates 700 tons of sulfuric acid/day and handles a variety of spent acids. The sulfur dioxide content of the tail gas varies as the blends of these acids change. 

In the production of sulfuric acid, including heat reconvert and the reconditioning and recycling of spent acids, it is necessary to handle acids at elevated temperatures and various concentrations. Corrosion damage that considerably impairs the availability of a plant has occurred in sulfuric acid coolers, for example. Damage of this kind can be prevented by anodic protection. 

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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