Reaction #1442493

Reaction equation

sodium sesqui sulfate

sodium sulfate

→

H2SO4

sodium sulfate

Conditions

Workup

1. 1
   Otheris withdrawn together with evaporated water
2. 2
   OtherSolid sodium sesqui sulfate precipitates
3. 3
   Otheris separated from the reaction medium on
4. 4
   Filtrationa first filter 2
5. 5
   workup.ADDITIONcontaining sodium sulfate
6. 6
   Otherto form a slurry
7. 7
   Otheris separated from the aqueous solution on
8. 8
   Filtrationa second filter 4 on which the filter cake
9. 9
   Washis washed with sufficient water

Procedure

Referring to FIG. 1, sodium chlorate, sulfuric acid and methanol are supplied to a chlorine dioxide generator 1, preferably operated according to any of the SVP®-lite or the R8 processes. In the generator 1 an acid aqueous reaction medium containing sodium ions, sulfate ions and chlorate ions is maintained at subatmospheric pressure at a temperature sufficient to effect boiling. Chlorate ions are reduced by methanol to form chlorine dioxide gas which is withdrawn together with evaporated water. Solid sodium sesqui sulfate precipitates and is separated from the reaction medium on a first filter 2 and transferred to a mixing tank 3 in which it is contacted with an acid aqueous solution containing sodium sulfate to form a slurry, the acidity of the solution preferably being from about 5.5 to about 6.5 N. In the mixing tank 3 the solid sodium sesqui sulfate is partially converted to neutral sodium sulfate which is separated from the aqueous solution on a second filter 4 on which the filter cake is washed with sufficient water to obtain solid sodium sulfate containing less than about 2% by weight of H2SO4. The acid aqueous solution and the spent washing water are mixed to form an acid filtrate 5 which is transferred to a filtrate tank 6. An acid filtrate stream 7 is pumped to a device 8, for example a control valve, dividing the acid filtrate 7 to one stream 9 leading to the mixing tank 3, and another stream 10 leading back to the chlorine dioxide generator 1. The stream 10 preferably constitutes from about 10 to about 20% of the total acid filtrate stream 7. The amount of water added to the mixing tank 3 is preferably from about 0.28 to about 0.45 kg per kg sodium sesqui sulfate. The amount of water added to the second filter 4 for washing is preferably from about 0.04 to about 0.1 kg per kg sodium sesqui sulfate. Both the filters 2, 4 are preferably rotating drum filter operating with vacuum inside the drums. At least the second filter 4 is a bottom feed filter, preferably as shown in FIGS. 3 and 4, which can be operated without any cyclone or similar device for pre-concentrating the slurry, enabling more stable operation of the entire process than if a conventional top feed filter is used. Preferably also the first filter 2 is a bottom feed filter of similar construction. The entire process is preferably operated continuously.

Source