Spent Acids


Spent Acid, which is normally a mixture of sulfuric acid, nitric acid, water, and the related organic compound is generated mainly through nitration processes. Recycling these spent acids is either mandatory for cost-efficient procedures or required by environmental protection regulations. Our process engineers deliver high-value, customized spent acid recovery units used to regenerate pure acid for many different chemical processing plants. Depending on the type of production used, the spent acid treatment requires several process systems, such as:

  • Stabilization, to secure safe storage and destroy unstable organic components
  • Separation of nitric acid and sulfuric acid
  • Denitration of sulfuric acid
  • Purification, which is a thermo-chemical pre-treatment under atmospheric conditions

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.