Sodium metabisulfite stability and synthesis method

Synthesis method of sodium metabisulfite

　　 1. Feed crushed sulfur into the combustion furnace, and pass the artificial compressed air about twice the theoretical amount, spontaneous combustion at 600 ~ 800 ℃. After cooling and dust removal and water washing, it is sent to a multi-stage reactor for reverse absorption with sodium carbonate solution; the temperature of the absorption liquid is controlled at about 45°C. The crystal slurry flowing out of the multi-stage reaction is centrifugally separated and dried below 160°C to be the finished product.

　　 2. Add a certain amount of soda ash to the sodium bisulfite solution to produce a suspension of sodium sulfite. Sulfur dioxide is introduced to form sodium metabisulfite crystals, which are obtained by centrifugal separation and drying. Or use sodium carbonate solution to absorb sulfur dioxide gas to generate sodium bisulfite solution. When the reaction ends, it is precipitated from the saturated solution of sodium bisulfite, dehydrated by centrifugation and dried.

　　 3. Install the glass wool in the lower part of the ordinary glass drying tower, and then fill the mixture of NaHCO3 and broken glass flakes, and pass the SO2 gas from the lower part of the tower under negative pressure until no more carbon dioxide escapes. The water generated during the reaction is concentrated at the bottom of the tower, and the resulting salt is actually dry. Sieve out the broken glass pieces and put them in a closed bottle. Then, the anhydrous salt is burned in a large porcelain crucible at 500 to 600°C for 2 to 3 hours. The burning is performed until the precipitate formed by the reaction of the aqueous solution of the preparation sample and AgNO3 is pure white (not light yellow).

　　 4. Under the condition of maintaining the temperature at about 30 ℃, pass SO2 gas into the 30% sodium carbonate solution until there is a strong SO2 smell. Put this solution in a desiccator with concentrated sulfuric acid as the desiccant, keep the temperature above 25 ℃, let stand until the crystals precipitate. Filter with suction and wash the crystals with ethanol, and dry in a stream of nitrogen or hydrogen, isolated from air to save.

　　 5. Use absorption method. The food grade soda ash solution absorbs sulfur dioxide to produce sodium pyrosulfate, which is refined and decontaminated, filtered and dried to obtain edible grade sodium metabisulfite.

　　 6. Pass the washed sulfur dioxide gas into the sodium bicarbonate solution with a content of about 15% to carry out the reaction until the carbon dioxide gas no longer escapes. Equal volume of ethanol was added to precipitate crystals. Filter with suction and dry to obtain analytically pure product.

Sodium metabisulfite properties and stability

1. It is easy to decompose when exposed to moisture. When exposed to air, it is easily oxidized to sodium sulfate. Irritating.

2. In contact with strong acids, sulfur dioxide is released to form corresponding salts. Heated to 150 ℃ decomposition. The white powder with strong SO2 smell loses SO2 in the air and absorbs O2 to be converted into Na2SO4. It is easily soluble in water, and the aqueous solution is acidic. When the solution is heated above 65℃, it is decomposed into Na2SO3 and SO2.