Product name: Sulfur dioxide

CAS: 7446-09-5

Molecular formula: O2S

Molecular weight: 64.06

EINECS: 231-195-2

Sulfur dioxide Chemical Properties

State and Color: Colorless gas under standard conditions.

Odor: Strong, pungent odor, irritating to the respiratory tract.

Solubility: Easily soluble in water. At room temperature and pressure, approximately 40 volumes of SO₂ can be dissolved in 1 volume of water. Its aqueous solution is sulfurous acid (H₂SO₃).

Boiling Point and Liquefaction: Boiling point is approximately -10°C. It is easily liquefied (can be converted to liquid by pressurization or cooling). Liquid SO₂ can be used as a refrigerant.

Sulfur dioxide Use

1. Industrial Sulfuric Acid:

This is one of the primary uses of sulfur dioxide. Industrially, sulfuric acid is produced via the contact process: sulfur dioxide reacts with oxygen in the presence of a catalyst (such as vanadium pentoxide) and heat to form sulfur trioxide (2SO₂ + O₂ ⇌ [catalyst, △] 2SO₃). Sulfur trioxide then reacts with water to form sulfuric acid (SO₃ + H₂O = H₂SO₄).

2. Bleaching Agent:

Utilizing its bleaching properties, sulfur dioxide can be used to bleach pulp, wool, silk, straw hats, and other materials. The bleaching principle is that it combines with colored substances to form an unstable colorless substance. This process is reversible (for example, a bleached straw hat will return to its original color after prolonged use). Therefore, it is not suitable for applications requiring permanent bleaching.

3. Preservative and Fungicide:

Sulfur dioxide has a certain bactericidal effect and can inhibit microbial growth. Therefore, it is often used as a preservative in the food and beverage industry (such as wine, dried fruit, and candied fruit) to extend the shelf life of products. However, usage must be strictly controlled to avoid any impact on human health.

4. Refrigerant:

Because sulfur dioxide readily liquefies (with a boiling point of approximately -10°C), liquid sulfur dioxide was once used as a refrigerant. However, with the emergence of safer and more efficient refrigerants (such as CFC substitutes), its use in this field has gradually declined.

5. Chemical Synthesis Raw Material:

It can be used to produce chemical products such as sulfites (such as sodium sulfite and sodium bisulfite) and thiosulfates, which are widely used in the papermaking, printing and dyeing, and pharmaceutical industries.

6. Environmental Protection Applications:

In some industrial exhaust gas treatment processes, sulfur dioxide can be used as a reducing agent to remove heavy metal ions (such as chromium ions) from wastewater or to treat chlorine-containing waste gases.