How to prepare anhydrous sodium sulfite

Method 1: A simple method for producing medicinal auxiliary anhydrous sodium sulfite, the process steps include:

(1) Use distilled water to prepare a certain concentration of sodium bisulfite solution. At a certain reaction temperature, add a certain concentration of sodium hydroxide solution while stirring to control the pH value of the reaction end to be alkaline. Stir the reaction for about 20 minutes;

(2) After the reaction is completed, continue to stir to control the pH value of the reaction end point in the range of 12.0～12.30;

(3) The reaction solution is vacuum-distilled under reduced pressure and evaporated until a large amount of crystals appear in the reaction solution, and then cooled, centrifuged, and the solid crystals are dried. The obtained product is analyzed and tested. The qualified product is anhydrous sodium sulfite, a pharmaceutical auxiliary.

Method 2: A method for producing anhydrous sodium sulfite by smelting flue gas, characterized in that the purified SO 2 -containing flue gas and caustic soda solution are reversely absorbed in an absorption tower to generate sodium sulfite and sodium bisulfite, and then neutralized by liquid caustic soda After dehydration to produce anhydrous sodium sulfite, the preparation process is as follows:

a. The prepared sodium hydroxide alkali solution with a weight concentration of 10%-13% is sprayed downward from the top of the absorption tower;

b. The purified SO2 flue gas is counter-currently contacted with the lye from the bottom of the absorption tower, the process control temperature is 40 ℃ -60 ℃, the lye is cyclically absorbed until the pH value reaches 5.0 to 6.0;

c. After the completion of step b, add 10%-13% sodium hydroxide solution to the absorption liquid, adjust the pH value of the solution to 9-10, control the temperature of the solution 80 ℃ ~ 95 ℃, the solution contains sodium sulfite weight concentration 20 %～25%;

d. Sodium sulfide is added to the solution to remove iron impurities. The amount of Na2S added is 8%-12% of the theoretical amount of total reaction with iron, and the solid-liquid separation is performed to obtain sodium sulfite solution;

e. The filtered sodium sulfite solution is evaporated to a solid-liquid mixed concentrated phase containing 42% to 45% by weight of sodium sulfite, and the concentrated phase is centrifuged to obtain a crude product of sodium sulfite containing 5% to 8% water;

f. Dry and dehydrate the crude sodium sulfite product by contacting with hot air at 120 ℃ ~ 160 ℃ through the vibration vulcanization bed or airflow drying system to prepare anhydrous sodium sulfite;