Tehnične zahteve za natrijev formaldehid sulfoksilat-Kitty
1.2Raw materials and technical requirements:
Sodium metabisulfite (Na2S2O5):Industrial Grade I with a content of >64% (in terms of SO2).
Industrial formaldehyde solution: first or second grade .
Zinc metal powder: 98% total zinc, not less than 94% zinc metal, zinc powder with grey appearance.
1.3 Production process and control
The production ofsodium formaldehydesulphoxylate by this method mainly includes three processes: dissolution-reduction addition reaction, solid-liquid separation and evaporation and crystallization.
(1) Dissolution-reduction addition reaction: the reaction is carried out in a porcelain-lined reactor with stirring.
According to a certain ingredient ratio, sodium metabisulphite, water, zinc powder and formaldehyde solution are added to the reaction kettle, and a certain amount of additives are added to speed up the reaction speed and the generation ofsodium formaldehydesulphoxylate. After all materials are added, the reaction is heated indirectly by steam in a closed stirred kettle with constant stirring and constant temperature when the temperature of the solution in the kettle rises to 95°C.
The materials are reactedaround2h and samples are taken for analysis.
The reaction equation was :
During the reaction, in addition to the output ofsodium formaldehydesulphoxylate, the zinc powder involved in the reaction is transformed into zinc oxide and zinc hydroxide.
As zinc powder is added in excess, there is still a small amount of metallic zinc and we call this solid matter zinc sludge.
(2) Solid-liquid separation: After the reaction is completed, indirect cooling is carried out with water.
The temperature of the material is reduced to below 50°C for solid-liquid separation. Because of the corrosive nature of the solution, the solid-liquid separation is carried out using a hydraulically pressurised plastic plate rubber frame filter. The filtrate is pumped to the qualified liquid storage tank. After the solution has been clarified in the reservoir for a certain time and then filtered a second time to provide a pure clear solution for evaporation and concentration.
(3) Evaporation and concentration, cooling and crystallisation: the sodium formaldehydesulphoxylate solution in the storage tank is pumped into the vacuum evaporation vessel by vacuum.
Indirectly heated by steam, the evaporation process controls the temperature below 65°C. When the concentration of the solution in the evaporator reaches the requirements, the concentrate is put into the crystalliser, cooled and crystallised at room temperature and the large pieces are crushed, then samples are taken and tested according to the standard, and the qualified products are packed.