Products Description
Sodium metabisulfite (chemical formula Na₂S₂O₅) is a white crystalline powder with strong reducing properties and a pungent odor. It mainly exerts preservative, antioxidant and bleaching effects by releasing sulfur dioxide (SO₂). In the food industry, it is widely used for the preservation and freshness of products such as dried fruits, wine, and fruit juice, inhibiting the growth of microorganisms and preventing Browning. It is used as a bleaching agent in starch products and sugar processing to improve color. In addition, it is also applied in pharmaceutical antioxidation, water treatment dechlorination and chemical reduction reactions. Despite its diverse functions, its use must strictly follow safety standards. Excessive amounts may cause allergies (especially in asthma patients) or destroy nutritional components. Regulations in various countries have limits on the residual amount of sulfur dioxide in food (for example, in China, it is stipulated that the sulfur dioxide residue in dried fruits should be ≤0.1g/kg), and it is mandatory to label the presence of sulfite components to ensure consumers' right to know.
DESCRIPTION
Basic Information
| Category | Parameter | Value/Description | Remarks |
|---|---|---|---|
| Basic Info | Chemical Name | Sodium Metabisulfite | - |
| Chemical Formula | Na₂S₂O₅ | Contains two sodium ions and one disulfite group (S₂O₅²⁻) | |
| CAS Number | 7681-57-4 | - | |
| Molecular Weight | 190.10 g/mol | - | |
| Structural Formula | Structural formula of sodium metabisulfite | Composed of two SO₃ groups linked by a sulfur-sulfur bond |
Physical Properties
| Category | Parameter | Value/Description | Remarks |
|---|---|---|---|
| Appearance | Color & Form | White or slightly yellow crystalline powder | Easily oxidized and discolored when exposed to air |
| Odor | - | Strong pungent sulfur dioxide (SO₂) odor | More noticeable in humid environments |
| Solubility | Water Solubility (20℃) | 54 g/100 mL water | Aqueous solution is acidic (pH 4–5) |
| Other Solvent Solubility | Slightly soluble in ethanol, insoluble in ether | - | |
| Density | Solid Density | 1.48 g/cm³ | - |
| Melting Point | - | 150°C (Decomposes) | Releases SO₂ and Na₂SO₃ upon decomposition |
| Stability | Hygroscopicity | Highly hygroscopic, store sealed | Releases SO₂ when decomposed in humid air |
Chemical Properties
| Category | Parameter | Value/Description | Remarks |
|---|---|---|---|
| pH Compatibility | Optimal Working pH | Acidic to neutral (pH 3–7) | Ineffective in strong alkaline environments |
| Reactivity | Key Reactions | Reacts vigorously with strong oxidizers (e.g., Cl₂, H₂O₂), releasing SO₂ | Avoid contact with oxidants and acids |
| Decomposition | Thermal Decomposition | Produces SO₂ and Na₂SO₃ at high temperatures (>150°C) | - |
Main application fields
Application Parameters
| Category | Parameter | Value/Description | Remarks |
|---|---|---|---|
| Food Industry | Maximum Residue Limit (as SO₂) | - Dried fruit: ≤0.1 g/kg (China GB 2760) - Wine: ≤250 mg/L (International standard) |
Must be labeled as "Contains Sulfur Dioxide" |
| Typical Usage Levels | - Preservative: 0.01%–0.1% - Bleaching: 0.1%–0.5% |
Soaking time: 10–30 minutes for dried fruits | |
| Pharmaceutical | Antioxidant in Injections | 0.01%–0.05% | Must comply with Chinese Pharmacopoeia purity ≥95% |
| Water Treatment | Dechlorination Dosage Ratio | Cl₂ : Na₂S₂O₅ ≈ 1 : 0.56 (by mass) | Reaction: Cl₂ + Na₂S₂O₅ + H₂O → 2HCl + Na₂SO₄ + H₂SO₃ |
| Chemical Reduction | Dye Reduction Dosage | 1%–5% (by total system mass) | Typically heated to 80–100°C |
Food Industry
In the food industry, there are strict requirements for the content of sodium metabisulfite. The concentration is usually low (0.01% to 0.1%) or high (0.1% to 0.5%). At low concentrations, it is typically used for preservation and antioxidant purposes, while at high concentrations, it is usually used for bleaching powder products. Its processes mainly include direct addition, soaking/fumigation, and spraying/film removal. In terms of application, it is mainly used as a preservative and antioxidant (E223), effectively inhibiting the growth of microorganisms (molds, yeasts) and extending the shelf life. It can also be used as a bleaching agent and is usually applied to the decolorization treatment of white sugar and starch products (such as vermicelli and vermicelli). The main application scenarios are in wine and dried fruits. It can effectively help wine inhibit miscellaneous bacteria, protect its flavor, and help dry fruits prevent mold.
Medicine and Cosmetics
In the fields of medicine and cosmetics, sodium metabisulfite is required to have the highest safety because it is used as an antioxidant in injections or oral medications and directly in skin products (to prevent the oxidation and failure of active ingredients), and is usually required to have an extremely low concentration (0.01% to 0.1%). Its process involves adding it in a sterile environment or using it in combination with other stabilizers (such as EDTA). Of course, in addition to acting as an antioxidant in drugs, it can also be used in disinfection and preservative products, which can be applied to the disinfection of medical instruments or the preservation of cosmetics.
Chemical engineering and Water Treatment
In the chemical and industrial fields, the content requirements for sodium pyrosulfite are not so strict. It is usually in high concentrations (such as 1% to 10%) and is mainly used as a reducing agent. It can participate in dye synthesis, rubber vulcanization termination and other reactions. The process is through high-temperature reactions. For example, in the dye industry, it needs to be heated to a specific high temperature, such as (80 to 100℃), to promote reduction reactions. It can also be added in batches. According to the reaction progress, it can be added in several times to control the reaction rate.
The required content of sodium pyrosulfite in water treatment is dynamically adjusted according to the residual chlorine in the water (usually 1-10mg/L), and it is added at a ratio of Cl₂:Na₂S₂O₅ ≈ 1:0.56 during dechlorination. The process lies between the continuous dosing system and can control the dosing amount in real time through the metering pump or adjust the pH. The reaction needs to be carried out under neutral or weakly acidic conditions (pH 5-7) to improve the dechlorination efficiency
Comparison with other sulfites
| Property | Sodium Metabisulfite (Na₂S₂O₅) | Sodium Sulfite (Na₂SO₃) | Sodium Bisulfite (NaHSO₃) |
|---|---|---|---|
| SO₂ Content | High (67.4%) | Low (50.8%) | Moderate (61.2%) |
| pH Compatibility | Acidic to neutral | Neutral to alkaline | Acidic |
| Main Applications | Food preservation, bleaching, water treatment | Textile dyeing, paper bleaching | Food preservation (short-term effect) |
Safety and Toxicology
| Category | Parameter | Value/Description | Remarks |
|---|---|---|---|
| Toxicity Data | Acute Oral Toxicity (LD₅₀, rats) | 820 mg/kg | Moderately toxic |
| Exposure Limits | Workplace Air (OSHA) | SO₂ concentration ≤5 ppm (8-hour TWA) | Use gas masks in industrial environments |
| Health Risks | Main Hazards | - Irritates eyes, skin, and respiratory tract - May trigger allergic reactions in asthmatics |
Rinse immediately with water if contact occurs |
Storage Conditions
| Category | Parameter | Value/Description | Remarks |
|---|---|---|---|
| Storage | - | Store in cool, dry, sealed conditions, away from oxidants and acids | Recommended: Temperature ≤25°C, RH ≤60% |
Epilogue
The application of sodium metabisulfite requires flexible adjustment of concentration and process according to industry demands, while strictly adhering to regulations in various fields to balance functionality and safety. For instance, the difference between low-concentration preservation in food and high-concentration reduction in industry is essentially the result of a trade-off between "safety first" and "efficiency first". If you have any questions, you can consult Eastar. We can explain them to you. At the same time, we would like to introduce our company to you at the end of the film. Eastar has been dedicated to the chemical industry for over 20 years and has proposed a complete supply chain system including R&D, manufacturing, inventory, logistics and export. We are committed to providing high-quality products and services. We strive to become an outstanding chemical supplier with international influence. If you have any needs, please contact us and we will reply to your requirements as soon as possible.
