For the production of polyurethanes, two different monomers (polyisocyanates and polyols) are linked together. In this polyaddition, polyether polyol and toluene-2,4-diisocyanate (TDI) are often used. The production can be divided into 3 areas:
- Production of polyether polyol
- Production of toluene-2,4-diisocyanate
- Polyaddition
TDI is produced by phosgenation from 2,4-toluenediamine (TDA). In the event of an accident, the unconsumed phosgene must be absorbed because it is extremely toxic. Therefore, it is only used in hermetically sealed circuits. The neutralization of the gas to sodium chloride (NaCl) and sodium carbonate (Na2CO3) takes place in the gas scrubber with caustic soda.
Sound velocity measurement with LiquiSonic® 40
Application
In the gas scrubber, a washing liquid is brought into contact with the gas stream to be cleaned, whereby certain gaseous, liquid, and solid components are absorbed by the liquid. The circulating washing liquid (NaOH) must be kept within the range of maximum absorption. To ensure this, the concentration of NaOH as well as the salts NaCl and Na2CO3 must be monitored.
The LiquiSonic measurement system®enables concentration measurement in 3-component liquids. By measuring two physical quantities such as sound velocity and conductivity, two concentrations can be determined simultaneously: the caustic soda and the salts NaCl and Na2CO3. If the NaOH content is too low, it must be adjusted. If the salt content is too high, it is removed because otherwise it would crystallize in the system.
Installation
The LiquiSonic® immersion sensors can be easily installed directly into the pipeline. A common installation site is in the pipelines (DN80) from the gas scrubber to the regeneration tank. The LiquiSonic® Controller 40 is connected to the LiquiSonic® sensor and the measuring unit for the second physical quantity. The controller displays the concentration of the caustic soda and the salts in the main menu.
Typical measuring range:
Concentration range NaOH: 5 to 20 wt%,
Concentration range Na2CO3/NaCl: 5 to 30 wt%
Temperature range: 30 to 60 °C
Customer benefits
The robust sensor design and the choice of special materials, such as HC2000, ensure long system uptime. LiquiSonic®reduces time-consuming laboratory measurements:
- Time required: 1 hour per day
Avoiding over- and under-dosing leads to savings in material costs.
LiquiSonic® ensures precise concentration measurement with continuous data recording. This enables automatic control of the caustic soda in the area of maximum absorption or maximum efficiency of the gas scrubber.
