Introduction
Chlorine dioxide can be generated by use of many different processes. The most common processes, for instance the different SVP® processes or the Mathieson process, use purchased sodium chlorate as raw material. Depending on prevailing conditions, it can be advantageous to produce chlorate in direct connection with the chlorine dioxide generation in spite of the much larger investment required.
This is particularly valid where the electrical power cost is low, where a by-product free process is preferred or where it is difficult to get a reliable and low cost supply of sodium chlorate. As the integrated process is a consumer of chlorine, the process is also of interest in order to adjust the chlorine/caustic soda balance, in cases where there is an on-site chlor-alkali plant.
Process Description
Process Block Diagram
The Integrated chlorine dioxide plant is subdivided into the following sections which are interrelated with each others according to the above block diagram:
- Chlorate Electrolysis
- ClO2 Generation and Absorption
- Hydrochloric Acid Synthesis
Chlorate Electrolysis
Through Eka Chemicals, being the biggest manufacturer of chlorate in the world, Eka Engineering has access to several different chlorate technologies. Depending on the required production capacity, the local situation and the client's special needs, the most suitable technology will be selected.
Chlorine Dioxide Generation and Absorption
To produce chlorine dioxide (CIO2) by the integrated process, sodium chlorate is reduced with hydrochloric acid by the two reactions:
NaCIO3 + 2 HCI → ClO2 + 1/2 Cl2 + NaCl + H2O
NaCIO3 + 6 HCI → 3 Cl2 + NaCl + 3 H2O
The latter reaction is an undesirable secondary reaction which must be suppressed in favor of the first.
As described under "SVP®-Processes" the SVP® Total HCl process is suitable for integration with chlorate electrolysis. The basic features of the integrated SVP® process are listed below:
Comparison with other integrated processes
One stage reactor (Single Vessel), easy to operate
Crystallized NaCl returned to electrolysis after dissolving
Safe ClO2 conc. by vacuum operation meaning less risk for decompositions
No dilution air required giving large hydrogen excess in HCl-system and no risk for emission of chlorine
Suitable for larger capacities (There are SVP® plants in operation up to 70 TPD in one line)
Comparison with non-integrated SVP® process