Sulfuric Acid


Sulfuric acid concentration plants can be divided into three different fields of process technology. The differences are the potential operating conditions, the necessity of water vapor purification, and the applicable materials of construction (MoC).

Pre-Concentration of Sulfuric Acid up to 70 wt% H2SO4 – PoSA

The PoSA process can operate under vacuum or atmospheric conditions. Even in atmosphere, the boiling temperature of sulfuric acid of 70 wt% H2SO4 is about 166°C. This allows for the use of “normal “steam for evaporation. Heaters, evaporators, and piping can also be produced out of high-alloys or lined FRP. Due to the vapor pressure of H2SO4 an additional vapor treatment is usually not necessary.

Using the Pfaudler PoSA process, starting from very low concentrations of 3 to 20% H2SO4 up to approximately 75% H2SO4 where H2SO4 vapor pressure is quite low, multi-effect plants can be applied in relation to boiling temperatures.

Medium-Concentration of Sulfuric Acid up to 85 wt% H2SO4 – MoSA

The concentration of sulfuric acid up to 85 wt% can be used under vacuum or atmospheric conditions, depending on the available heating media and the required treatment steps. No additional vapor washing might be needed, since the vapor pressure of H2SO4 is in the range of 0.5 to 1 wt%.

Due to the strong corrosive behavior of sulfuric acid at the elevated temperature and concentration levels, corrosion-resistant materials like glass, glass-lined steel, and Tantalum must be used. The final selection of process conditions is reached in accordance with the client‘s site conditions and the requirements for product quality and effluents.

Using the Pfaudler MoSA process, starting from approximately 65 to 70% H2SO4 up to approximately 85% H2SO4 where H2SO4 vapor pressure is still low, vacuum concentration is applied in relation to boiling temperatures.

High-Concentration of Sulfuric Acid up to 96 wt% H2SO4 – HoSA®

The HoSA® process can be used, starting from approximately 80-85% H2SO4 up to 96 % H2SO4 – (for special requirements, even up to 98 wt% H2SO4), where vapor washing is required to reduce losses.

With the high-temperature treatment of sulfuric acid using the Pfaudler HTX Heat Exchanger, Pfaudler has developed a special thermal oil heated glass-lined steel heat exchanger which allows for acid temperatures up to 250°C.

The Pfaudler HTX Heat Exchanger is usually applied for the HoSA® process, in order to enable use at reasonable vacuum conditions, with regular cooling water for vapor condensation, but it is also applied to the MoSA process if high temperatures are required for acid purification.