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Sulfuric Acid Production

Process Monitoring with LiquiSonic®

Sulfuric acid (H2SO4) is one of the most important basic chemicals. Steady demand grows because it‘s favorable properties make it useful in preparing a variety of products.


Sulfuric acid production

The LiquiSonic® analyzer can easily be integrated into different process stages. The rapid, robust sensing technology improves asset utilization, process safety and product yield.

Sulfuric acid production | 4 MB

Several applications for LiquiSonic® analyzer measurements of sulfuric acid and oleum concentrations are:

  • H2SO4 and oleum production
  • fertilizer production
  • synthesis gas drying
  • etching and pickling baths
  • mine-ore processing
  • refinery catalysis
  • production of various chemicals

Two main H2SO4 production processes include, first of all, “double contact double absorption” (DCDA) - a process featuring a vanadium pentoxide (V2O5) catalyst to produce highly concentrated H2SO4 and oleum. A second application developed in 1980 removes sulfur from various process gases in an approach known as “wet sulfuric acid” (WSA) process. The analyzer can easily be integrated into the process stages. LiquiSonic‘s® rapid, robust sensing technology improves asset utilization, process safety and product yield.

Advantage of sonic velocity over conductivity and density

Double contact double absorption process

DCDA uses a variety of starting materials which synthesize into sulfur dioxide during different reactions. Initially, SO2-containing gas enters a drying tower for removal of its water content. Next, the gas encounters three catalyst beds in the converter where SO2 oxidizes into SO3:

SO2 + 0.5 O2 → SO3

SO3 then enters the intermediate absorption tower (IAT). Although absorption of SO3 in a water solution is possible, such a strong exothermal reaction could corrode and destroy the plant. Instead, SO3 reacts with the water content of 98 wt% H2SO4 to form super-concentrated H2SO4:

SO3 + H2O → H2SO4

To avoid environmental pollution, SO2-containing exhaust air leaving the IAT passes the converter again to prepare SO3 for processing into concentrated H2SO4 in the final absorption tower (FAT). DCDA processing forms oleum as an intermediate product, consisting of 100 wt% H2SO4 enriched with SO3 – also known as fuming sulfuric acid or disulfuric acid. Applications include:

  • production of highly concentrated H2SO4
  • manufacturing of caprolactam and nylon
  • nitration process in combination with nitric acid

Oleum is produced by the absorption of SO3 in an oleum-absorption tower. LiquiSonic® sensors provide excellent process control in oleum concentration ranges of 20 - 30 wt% and 50 - 60 wt%. LiquiSonic® sensors may be installed in feed and return lines of absorption towers and after the dilution unit.

Wet sulfuric acid process (WSA)

Originally, the WSA process was developed to remove sulfur components from the exhaust gases of various industrial manufacturing processes with a wide spectrum of starting materials which can result in SO2. Unlike for DCDA, water vapor remains in the SO2 gas. By virtue of a special vanadium-containing catalyst, the vapor has no negative impact on the catalytical oxidation from SO2 to SO3 in the converter. LiquiSonic® measuring points in the WSA process Finally, the SO3 gas enters the WSA condenser, where water vapor condenses to change SO3 into H2SO4. Product concentrations of 98 wt% H2SO4 are typical. Measuring the concentration inline, the LiquiSonic® sensors are installed in the exit lines for both the WSA condenser and the dilution unit.

Customer value

With the high sensitivity of sonic velocity to sulfuric acid concentration, the LiquiSonic® sensors can achieve an unmatched accuracy of ± 0.03 wt%. LiquiSonic® overcomes the dual sensitivities of both conductivity and density by generating a clear signal in the concentration range of 80 - 100 wt% H2SO4 as graphed below to offer reliable, real-time process data. In the event of acid degradation to a highly corrosive level under 95 wt%, LiquiSonic® detects that critical acid “runaway” to curb the probability of heat-exchanger or other component damage, enhancing process safety and control.
The inline LiquiSonic® analyzer reduces manual laboratory measurements, saving labor and material costs in a typical laboratory titration budget for sulfuric acid measurement:  

  • sampling time: 15 minutes
  • sampling frequency: 6 times per day
  • investment payback within 13 months  

Additional benefits of LiquiSonic® measuring systems include:

  • easy, user-friendly installation (plug&play)
  • excellent long-term stability
  • one sensor for all applications (reduced investment costs)
  • comprehensive diagnostic capabilities
  • suitability for all needed concentration ranges with high accuracy
  • enhanced process control and safety