Sodium Metabisulphite is a white or yellowish solid with a strong odor of sulfur dioxide that gradually oxidizes to Sodium Sulfate in the air. It is mainly used in tanning, printing and dyeing, mineral processing, pharmaceutical, food and other industries. The production of Sodium Metabisulfite usually has two methods: Wet and Dry. Experimental analysis found that several indexes of the quality of Sodium Metabisulfite, with Sodium Carbonate/Soda Ash as raw material to synthesize SMBS, almost all the iron, heavy metals in raw materials with Sodium Metabisulphite precipitation, and only a small amount of chlorinated substances precipitation.
There are different quality indexes of Sodium Metabisulphite for different purposes. The quality indexes of products mainly include main content (% Na2S2O5) and impurities. The main sources of impurities in Sodium Metabisulphite synthesized from Sodium Carbonate are as follows: chloride, iron and heavy metal are mainly from Soda Ash; Sulfate only comes from the oxidation of S in the production process; Thiosulfate is mainly produced by the reaction of Sulfur and Sodium Sulfite in sulfur dioxide flow. The content of Sodium Sulfite is related to the PH value of the solution when Sodium Metabisulphite is precipitated.
Through repeated experiments, we come to the conclusion that raw material purity and oxidation are the two main factors affecting the quality of Na2S2O5. The Fe content is a very important factor affecting the quality of Sodium Metabisulfite. Iron content is not tight affect the quality of Na2S2O5, but also affect the product whiteness of the main cause. The iron in SMBS mainly comes from SO2 raw gas,Corrosion of steel equipment and steel pipes has the greatest impact on the system. Controlling the iron content in SO2 raw gas can effectively improve the product whiteness.
1. Bring in SO2 raw material gas
The SMBS enterprise uses sulfur-rich mineral powder to prepare SO2 raw material gas, which contains sulfur, iron, arsenic, zinc, lead, organic matter and so on. The ore powder is incinerated to produce raw gas with SO2=10%-16%. The raw gas is purified by the purification system and qualified SO2 raw gas, then synthesis of Sodium Metabisulfite. Therefore, the function of iron removal purification system is particularly important.
In the process of toptionchem.com SMBS production, multiple purification of SO2 raw gas was carried out to effectively reduce the iron content.
The process is as follows:
SO2 raw gas Cyclone Dust Removal Electrostatic Dust Removal Dynamic Wave Dust Removal Packed Tower Washing Cold water tower washing Electric De-fogging SO2 Fan Pressurized Purified SO2 Gas
2. Bring in raw Soda Ash
In theory, the production of 1MT sodium metabisulfite needs to consume about 600KG soda ash. The Fe in raw Soda Ash is 27-32mg/kg, and the actual amount of iron brought into raw soda ash is 18.29mg/kg by taking the average value calculation.
3. Bring in the supply water
There are four types of system water supply, including water in raw soda ash, steam, water for washing equipment and fresh brine removal. It was measured that the iron content introduced by the replenished water was about 0.44mg/kg.
4. Steel equipment and steel pipes are corroded.
The author visited more than a dozen manufacturers of Sodium Metabisulphite in China, and it is calculated that the iron content brought in by corrosion of equipment and pipes is about 44mg/kg, which affects the whiteness of products.
In summary, the author believes that iron content has a more prominent impact on the quality of Sodium Metabisulfite products, especially the whiteness. The sources of iron in SMBS mainly come from SO2 raw gas, corrosion of steel equipment and steel pipes, raw soda ash and water supply, among which the amount of iron brought by the corrosion of SO2 raw gas, steel equipment and steel pipes accounts for a large proportion. Under the circumstance that the main equipment cannot be replaced completely, controlling the iron content in the raw gas is the key measure to improve the whiteness of the product. In actual production, some enterprises, such as TOPTIONHEM(toptionchem.com), work more carefully in the main process route, equipment materials and raw gas pretreatment process. They can avoid or reduce the participation of iron from the source, or intercept iron in the middle link, so as to achieve the purpose of improving product quality.
Post time: Nov-28-2022