CS266828B1 - Process for producing sodium dithionite - Google Patents

Abstract

During the reduction process of sulfur dioxide with zinc dust, circulation is introduced, and at the end of the reduction, the supply of sulfur dioxide is gradually interrupted.

Description

The present invention relates to a process for the production of sodium dithionite by reduction of sulfur dioxide with zinc dust in aqueous suspension.

The quality of zinc dust, its chemical composition, physical properties, size and distribution of its particles and the technological process are decisive for maximum yield.

The production of sodium dithionite is carried out batchwise in several operating processes. The first stage of production is a reduction operation, the result of which maximally affects the final yield of sodium dithionite. The reduction operation proceeds according to the formula

Zn + SO 2 -ZnS 2 O 2 by introducing 100% sulfur dioxide gas into the aqueous suspension of zinc dust with constant stirring and cooling. The result of the reduction operation is zinc dithionite, the yield of which determines the course and efficiency of other operations in the entire production process. The reduction is an exothermic operation and is therefore carried out with constant cooling.

In parallel with said main chemical reaction, other secondary, undesired chemical reactions take place, reducing the yield of the reduction operation and thus the yield of the final product. For example, ZnO in zinc dust reacts with ZnSO 2, air oxidation produces more ZnSO 2, decomposition with water produces ZnS ₂ Og and Zn (HSO 2) in the presence of SO 2 from 100% SC 2 produces ZnSO 2, etc. However, the most serious is the decomposition of ZnSO _2. O ^, because it deeply reduces the yield of the reduction operation.Decomposition is formed during the completion of the reduction operation by breaking the technological process, for example by not maintaining the temperatures and especially by overdosing 100% gaseous SO ₂ .

The size of the reduction vessel and the weight of the batches is constant. The reduction time is determined by the climatic conditions and the temperature of the cooling water, i.e. it lasts about 100 minutes in summer and 70 minutes in winter. The completion of the reduction process is determined by visual inspection of the appearance of the solution, which according to the regulatory regulation should be milky gray with the content of small flying residues of unreacted zinc. When this condition is detected, the supply of 100% SO ₂ is stopped and the circulation is started.

The process according to the invention substantially reduces the possibility of decomposition of zinc dithionite and at the same time allows the reaction of still reactive zinc dust particles, thus achieving the maximum possible yield. This method consists essentially in the introduction of a continuous circulation before completion of reduction operation, and successively feed interruption 100% gas of _{the second}

Example

Approximately 20 minutes before the end of the reducing operation is stopped, the lead 100% S0 _2, ^stop-cooling and the reaction mixture is brought into circulation. Circulation will already be left until the reduction process is completed. After 5 minutes, the 100% SO ₂ feed is resumed along with a continuous visual inspection of the solution. If there is a slight milky turbidity of the solution containing small residues of unreacted zinc, the supply of 100% SO _{2 is} stopped again, including the stopping of cooling. After 5 minutes, a visual evaluation is performed again and, if necessary, given the amount of flying zinc particles, a small amount of 100% SO ₂ is sensitively admitted with renewed cooling. 20-25 ° C. In this way, the undesired decomposition of znS ^^ is avoided and thus the maximum yield of the final product - sodium dithionite - is achieved.

Claims (1)

OBJECT OF THE INVENTION Process for the production of sodium dithionite by reduction of sulfur dioxide with zinc dust in aqueous suspension, characterized in that circulation is introduced during the reduction process, the reduction being terminated by gradually interrupting the sulfur dioxide supply and subsequently to 25 ° C.