One typical source creating huge amounts of spent acid is nitration technology. Using a mixture of sulfuric acid and nitric acid in the process diluted spent sulfuric acids contaminated with nitric acid, nitrous acid and organic compounds are received. These acids can be denitrated, recovering the dissolved nitric acid and organic compounds, in many cases. Using the Pfaudler HoSA® process, concentrated sulfuric acid is recovered for recycling in the process.
Main applications are the production of nitro-esters, like nitroglycerine, nitrocellulose, and so on, the production of nitro-aromatic compounds, like nitrobenzene as a pre-product of aniline and MDI, and the production nitrotoluenes, where Di-Nitrotoluene (DNT) as a pre-product of TDI is one core product.
Based on decades of experience with these acids, Pfaudler offers safe treatment procedures that are customized and adapted to their respective contaminants. This is especially required when treating spent acid that originates from the production of explosives. Other sources for spent sulfuric acid are gas drying processes, like chlorine drying, where diluted sulfuric acid is generated, which has to be reconcentrated and recycled.
Mixtures of sulfuric acid with hydrochloric acid or hydrofluoric acid require a special know-how in material selection, which Pfaudler offers, with a vast portfolio on corrosion resistant materials.
Pfaudler has developed a special thermal oil heated, glass-lined steel Pfaudler HTX Heat Exchanger which allows for acid temperatures up to 250 °C. If sulfuric acid is contaminated with stable organic compounds, oxidative high temperature treatments can solve the task and provide the required acid purification.