Sulfur Dioxide
Sulfur dioxide (SO2) is a chemical compound which is formed by various industrial processes and is also created in nature by volcanoes. Since coal and petroleum often contain sulfur compounds, their combustion will generate SO2 unless the sulfur compounds are removed before the fuel is burned.
Further oxidation of sulfur dioxide, usually in the presence of a catalyst such as NO2, forms H2SO4, an acid that forms acid rain. SO2 emissions are also a precursor to particulates in the atmosphere. Both of these effects are cause for concern over the environmental impact of these fuels.
Specifications
| Gas | Sulfur Dioxide | Gas Density | 2.26 |
|---|---|---|---|
| Chemical Symbol | SO2 | Detection Principle | Electrochemical |
| PEL (ppm) | 2 | LEL (%) | |
| IDHL (ppm) | 100 | UEL (%) | |
| Industries | Chemical Processing, Glass Manufacturing, Pulp & Paper Industry, Water Treatment | description | |
| applications |
Products
Industrial Applications
Precursor to sulfuric acid
Sulfur dioxide is an intermediate in the production of sulfuric acid, being converted to sulfur trioxide, and then to oleum, which is made into sulfuric acid. Sulfur dioxide for this purpose is made when sulfur combines with oxygen. Sulfur dioxide is converted to sulfuric acid by means of a method called the contact process. Several billion kilograms are produced annually for this purpose.
As a preservative
Because of its antimicrobial properties, sulfur dioxide is sometimes used as a preservative, sometimes called E220, for dried fruits. As a preservative, it maintains the appearance of the fruit and prevents rotting.
In winemaking
Sulfur dioxide is an important compound in winemaking, and is designated as parts per million in wine, E number: E220. It is present even in so-called unsulfurated wine at concentrations of up to 10 milligrams per litre. It serves as an antibiotic and antioxidant, protecting wine from spoilage by bacteria and oxidation. It also helps to keep volatile acidity at desirable levels. SO2 is also a very important compound in winery sanitation. Wineries and equipment must be kept clean, and because bleach cannot be used in a winery, a mixture of SO2, water, and citric acid is commonly used to clean and sanitize equipment.
As a reducing agent
Sulfur dioxide is also a good reductant. In the presence of water, sulfur dioxide is able to de-colorize substances. Specifically it is a useful reducing bleach for papers and delicate materials such as clothes. In municipal wastewater treatment sulfur dioxide is used to treat chlorinated wastewater prior to release. Sulfur dioxide reduces free and combined chlorine to chloride.
As a reagent and solvent in the laboratory
Sulfur dioxide is a versatile inert solvent that has been widely used for dissolving highly oxidizing salts. It is also used occasionally as a source of the sulphonyl group in organic synthesis. Treatment of aryl diazonium salts with sulfur dioxide and cuprous chloride affords the corresponding aryl sulphonyl chloride, for example.