E220 SULPHUR DIOXIDE

E220 Sulphur dioxide or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula SO
2. 
E220 Sulphur dioxide is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. 
E220 Sulphur dioxide is released naturally by volcanic activity and is produced as a by-product of metals refining and the burning of sulfur-bearing hydrocarbon fuels.

CAS:    7446-09-5
MF:    O2S
MW:    64.06
EINECS:    231-195-2

Synonyms
Sulfur dioxide,liquid;sulfurous acid gas;Sulfur dioxide;Sulfur dioxide Standard;siarkidwutlenek(polish);SO2;Sulfur oxide;Sulfur oxide (SO2)
CAS:    7446-09-5

E220 Sulphur dioxide is somewhat toxic to humans, although only when inhaled in relatively large quantities for a period of several minutes or more. 
E220 Sulphur dioxide was known to medieval alchemists as "volatile spirit of sulfur".
E220 Sulphur dioxide is a compound formed by the combination of the elements sulfur and oxygen. 
On a weight basis, the proportion of the elements is about I part sulfur to I part oxygen, or more exactly, 50.05 percent to 49.95 percent, respectively. 
At standard conditions of temperature and pressure, E220 Sulphur dioxide is a colorless gas with a characteristic pungent odor. 
E220 Sulphur dioxide may be cooled and compressed to a colorless liquid, which, at one atmosphere pressure, boils at 14°F (10.0°C) and freezes at -104.6°F (-75.9°C). 
E220 Sulphur dioxide is heavier than water, and has a specific gravity of 1.436 at 32°F (0°C). 
As a gas, E220 Sulphur dioxide is more than twice as heavy as air; its relative density is 2.2638 at atmospheric pressure and 32°F (0°C).
E220 Sulphur dioxide is not flammable or explosive in either the gaseous or liquid state. 
E220 Sulphur dioxide is a relatively stable chemical. 
Temperatures above 3632°F (2000°C) are required to bring about detectable decomposition of sulfur dioxide. 

Dry E220 Sulphur dioxide (less than 100 ppm water) is not corrosive to ordinary metals. 
However, in the presence of even small amounts of water, E220 Sulphur dioxide becomes corrosive to most metals, with exceptions including lead, Type 316 stainless steel, and certain alloys. 
Glass and certain plastics are also resistant to moist sulfur dioxide.
E220 Sulphur dioxide is a sulfur oxide. 
E220 Sulphur dioxide has a role as a food bleaching agent, a refrigerant and an Escherichia coli metabolite.
E220 Sulphur dioxide also known as sulphur dioxide, is a widely used food additive known for its preservative and antioxidant properties. 
E220 Sulphur dioxide is a natural preservative used since ancient times in the Roman Empire and ancient Egypt. 
E220 Sulphur dioxide is a colorless gas obtained by burning sulfur.
E220 Sulphur dioxide helps maintain the appearance, taste, and longevity of various food products, making it an essential component in the food industry.

E220 Sulphur dioxide is a colorless gas with a pungent, suffocating odor, commonly associated with volcanic eruptions and industrial processes. 
E220 Sulphur dioxide is a significant atmospheric pollutant, primarily produced from the burning of fossil fuels and the smelting of metal ores. 
SO₂ is highly soluble in water, forming sulfurous acid (H₂SO₃), which contributes to acid rain. 
The gas is characterized by its ability to act as a reducing agent and is used in various applications, including as a preservative in food and beverages, a bleaching agent, and in the production of sulfuric acid. 
In terms of health effects, exposure to sulfur dioxide can irritate the respiratory system, leading to symptoms such as coughing and shortness of breath, particularly in individuals with pre-existing respiratory conditions. 
Environmental regulations often aim to limit SO₂ emissions due to its role in air pollution and its contribution to the formation of fine particulate matter. 
Overall, E220 Sulphur dioxide is a crucial compound in both environmental chemistry and industrial applications, necessitating careful management to mitigate its impacts.

Structure and bonding
SO2 is a bent molecule with C2v symmetry point group. 
A valence bond theory approach considering just s and p orbitals would describe the bonding in terms of resonance between two resonance structures.
The sulfur–oxygen bond has a bond order of 1.5. 
There is support for this simple approach that does not invoke d orbital participation.
In terms of electron-counting formalism, the sulfur atom has an oxidation state of +4 and a formal charge of +1.

E220 Sulphur dioxide Chemical Properties
Melting point: -73 °C (lit.)
Boiling point: -10 °C (lit.)
density: 1.25 g/mL at 25 °C (lit.)
vapor density: 2.26 (21 °C, vs air)
vapor pressure: 1779 mm Hg ( 21 °C)
FEMA: 3039 | SULFUR DIOXIDE
solubility: soluble in H2O, EtOh, ethyl ether,chloroform
form: colorless gas
color: colorless
Odor: Pungent odor detectable at 0.3 to 5 ppm
Odor Threshold: 0.87ppm
Water Solubility: %H2O: 17.7 (0°C), 11.9 (15°C), 8.5 (25°C), 6.4 (35°C); % other solvents: 25, alcohol; 32, methanol [MER06]
Thermal Conductivity: 0.009 W/(m·K)
Merck: 13,9061
BRN: 3535237
Henry's Law Constant: 1.3×10-2 mol/(m3Pa) at 25℃, Burkholder et al. (2019)
Exposure limits    TLV-TWA 2 ppm (～5 mg/m3) (ACGIH), 5 ppm (OSHA and MSHA); IDLH 100 ppm (NIOSH).
Dielectric constant: 17.6（-20℃）
Stability: Stable. Non-corrosive when dry to common materials except zinc; corrosive when wet. Incompatible with strong reducing or oxidizing agents, moisture, zinc and its alloys.
InChI: 1S/O2S/c1-3-2
InChIKey: RAHZWNYVWXNFOC-UHFFFAOYSA-N
CAS DataBase Reference: 7446-09-5(CAS DataBase Reference)
NIST Chemistry Reference: Sulfur dioxide(7446-09-5)
IARC: 3 (Vol. 54) 1992
EPA Substance Registry System: E220 Sulphur dioxide (7446-09-5)

E220 Sulphur dioxide is a noncombustible colorless gas at ambient temperatures with a characteristic, strong, suffocating odor. 
The Odor Threshold is 1.1ppm. 
Shipped as a liquefied compressed gas.
E220 Sulphur dioxide ,S02, also known as sulfurous acid anhydride,is a toxic, irritating, colorless gas. 
E220 Sulphur dioxide is soluble in water, alcohol, and ether, and boils at -10 °C. 
E220 Sulphur dioxide is used as a chemical intermediate, in artificial ice, in paper pulping,in ore refining,and as a solvent.
E220 Sulphur dioxide is a colorless gas. 
E220 Sulphur dioxide is stable, and non-corrosive when dry to common materials except zinc. 
E220 Sulphur dioxide is corrosive when wet and incompatible with strong reducing or oxidizing agents, moisture, zinc, and its alloys. 

E220 Sulphur dioxide has a large number of industrial applications. 
For instance, E220 Sulphur dioxide is used in the manufacture of sodium sulfi te, sulfuric acid, sulfuryl chloride, thionyl chloride, organic sulfonate,extensively as a bleaching agent, particularly in the bleaching of beet sugar, fl our, straw, textiles, and wood pulp. 
E220 Sulphur dioxide has industrial utility in the tanning of leather, in brewing and preserving. 
E220 Sulphur dioxide is a colorless gas with a characteristic and strong suffocating odor. 
E220 Sulphur dioxide gas is released primarily from the combustion of fossil fuels (75%–85% of the industrial sources), the smelting of sulfi de ores, volcanic emissions, and several other natural sources. 
E220 Sulphur dioxide is a US EPA priority air pollutant, but has many industrial and agricultural uses. 
E220 Sulphur dioxide is sometimes added as a warning marker and fi re retardant to liquid grain fumigants.

Physical properties    
Colorless gas; pungent suffocating odor; gas density 2.927 g/L at 20°C; heavier than air, vapor density 2.263 (air=1); condenses to a colorless liquid at -10°C; density of liquid SO2 1.434 g/mL; freezes at -72.7°C; critical temperature 157.65°C; critical pressure 77.78 atm; critical volume 122 cc/g; dielectric constant 17.27 at -16.5°C; dissolves in water forming sulfurous acid, solubility 22.97 g and 11.58 g/100mL water at 0° and 20°C, respectively, under atmospheric pressure; very soluble in acetone, methyl isobutyl ketone, acetic acid, and alcohol; soluble in sulfuric acid; liquid SO2 slightly miscible in water.

Uses    
E220 Sulphur dioxide has a wide range of industrial applications, the most notable being as an intermediate in producing sulfuric acid. 
E220 Sulphur dioxide is used to produce chlorine dioxide, sodium bisulfite, and sodium dithionate, which are all bleaching agents. 
Also, E220 Sulphur dioxide itself is a bleaching agent used in bleaching textile fibers, straw, glue, gelatin, and other substances. 
E220 Sulphur dioxide is used extensively in the food industry to preserve vegetables and dry fruits such as apricots and cherries; as a bleach and steeping agent for grains; to prevent growth of bacteria in processing soy proteins; in refining sugar; as an additive to wine to destroy molds, bacterias, and undesired wild yeast; to prevent formation of nitrosamines in beer in the malting process; and in producing highfructose corn syrups.
E220 Sulphur dioxide is used in removing oxygen in petroleum recovery processes to prevent corrosion in piping and storage systems. 

Also, E220 Sulphur dioxide is applied in water treatment to reduce residual chlorine.
In clay processing E220 Sulphur dioxide reduces iron compounds and other color-forming impurities.
Other uses are extracting sulfide ores; casting magnesium; catalyst modifier in certain organic oxidation reactions; and colorimetric analysis of sulfite ion in aqueous samples. 
In the chemical industry, E220 Sulphur dioxide is used as a reducing agent in a number of preparative and analytical reactions. 
E220 Sulphur dioxide is used as a solvent for sulfur trioxide in sulfonation.
E220 Sulphur dioxide occurs in nature in volcanic gases. 
E220 Sulphur dioxide is found in the upper atmosphere at varying but trace concentrations resulting from natural processes and human activities. 
E220 Sulphur dioxide occurs in the automotive exhausts and in many fire and stack emission gases. 
E220 Sulphur dioxide is produced from burning sulfur–containing fuels, such as coal and oil. 
Also, E220 Sulphur dioxide is produced in the petroleum refining process. 
E220 Sulphur dioxide is partly responsible for causing acid rain.

E220 Sulphur dioxide is used as a bleaching andfumigating agent; as a disinfectant, for treat ing wood pulp for manufacturing paper, inmetal refining, for preserving food and vegetables, and as a reducing agent. 
E220 Sulphur dioxide is a majorair pollutant and is produced when soft coal,oils, or other sulfur-containing substances areburned. 
Automobile exhaust gases also contribute to air pollution. 
E220 Sulphur dioxide in theatmosphere reacts with moisture to form sulfurous acid, or is oxidized to sulfur trioxide, which forms sulfuric acid, causing acid rain.
Preserving fruits, vegetables, etc.; disinfectant in breweries and food factories; bleaching textile fibers, straw, wicker ware, gelatin, glue, beet sugars. 
Solvent and reagent in organic synthesis.
Intermediate in the manufacture of E220 Sulphur dioxide and sulfite pulp; casting of nonferrous metal; used in the food industry as a biocide and a preservative.
E220 Sulphur dioxide is a preservative, being a gas that dissolves in water to yield sulfurous acid. 
sulfite salts, such as sodium and potassium sulfite, sodium and potassium bisulfite, and sodium and potassium metabisulfite, yield free sulfurous acid at low ph. 
E220 Sulphur dioxide pre- vents the discoloration of foods by combining with the sugars and enzymes. 
E220 Sulphur dioxide also inhibits bacterial growth. 
E220 Sulphur dioxide is used in beverages, cherries, wines, and fruits.

Materials Uses    
Service conditions must be defined to properly specifY materials of construction for handling sulfur dioxide. 
E220 Sulphur dioxide is customary, however, to use carbon steel for dry sulfur dioxide at ambient temperatures. 
Reference should be made to the latest edition of the ASME Code, Section VIlI, Division I for vessels, and to the latest edition of ANSI/ASME 831.3, Chemical Plant and Petroleum Refinery Piping for piping specifications.
Moist sulfur dioxide is corrosive to carbon steel; therefore, other materials of construction have to be considered in this case. 
A source of data on the corrosivity of sulfur dioxide to various materials is the Corrosion Data Survey, published by the National Association of Corrosion Engineers; suppliers of liquid sulfur dioxide are another source.

Reactions
Sulfites result by the action of aqueous base on sulfur dioxide:

SO2 + 2 NaOH → Na2SO3 + H2O
E220 Sulphur dioxide is a mild but useful reducing agent. 
E220 Sulphur dioxide is oxidized by halogens to give the sulfuryl halides, such as sulfuryl chloride:

SO2 + Cl2 → SO2Cl2
E220 Sulphur dioxide is the oxidising agent in the Claus process, which is conducted on a large scale in oil refineries. 
Here, sulfur dioxide is reduced by hydrogen sulfide to give elemental sulfur:

SO2 + 2 H2S → 3 S + 2 H2O
The sequential oxidation of E220 Sulphur dioxide followed by its hydration is used in the production of sulfuric acid.

SO2 + H2O + 1⁄2 O2 → H2SO4
E220 Sulphur dioxide dissolves in water to give "sulfurous acid", which cannot be isolated and is instead an acidic solution of bisulfite, and possibly sulfite, ions.

SO2 + H2O ⇌ HSO−3 + H+         Ka = 1.54×10−2; pKa = 1.81

Production    
E220 Sulphur dioxide is manufactured mostly by combustion of sulfur or its iron sulfide mineral, pyrite, FeS2 , in air. 
The flame temperatures for such combustion of sulfur in the air are usually in the range 1,200 to 1,600°C. 
Many types of sulfur burners are available and are used to produce E220 Sulphur dioxide. 
They include rotary-kiln, spray, spinning-cup and air-atomizing sulfur burners. 
Selection and design of burners depend on quality of sulfur to be burned, and rate and concentration of sulfur dioxide to be generated. 
Pyrites or other metal sulfides may be burned in air in fluid-bed roasters to form E220 Sulphur dioxide. 
Other sources of sulfur dioxide are flue gases and spent E220 Sulphur dioxide.
E220 Sulphur dioxide may be recovered from stack gases in smelting or power plants. 
Similarly, SO2 can be generated from spent sulfuric acid recovered from oil refineries. 
The spent acid is burned in a high temperature furnace above 900°C to form E220 Sulphur dioxide, water, and gaseous products.
Liquid E220 Sulphur dioxide can be produced by passing a stream of sulfur trioxide, SO3, through molten sulfur:
2SO3 + S → 3SO2
Trace sulfur trioxide in the product may be removed by passing the product sulfur dioxide through sulfuric acid.
E220 Sulphur dioxide can be made by burning sulfur, or by roasting sulfide ores such as pyrites, sphalerite, and cinnabar.

Toxicity    
E220 Sulphur dioxide is highly toxic. 
E220 Sulphur dioxide causes severe irritation of eyes, skin, and respiratory tract. 
Effects are coughing, suffocation, and bronchial constriction.

Preparation    
E220 Sulphur dioxide usually is prepared industrially by the burning in air or oxygen of sulfur or such compounds of sulfur as iron pyrite or copper pyrite. 
Large quantities of sulfur dioxide are formed in the combustion of sulfur-containing fuels. 
In the laboratory, the gas may be prepared by reducing sulfuric acid (H2SO4) to sulfurous acid (H2SO3), which decomposes into water and sulfur dioxide, or by treating sulfites (salts of sulfurous acid) with strong acids, such as hydrochloric acid, again forming sulfurous acid.

Production
E220 Sulphur dioxide is primarily produced for sulfuric acid manufacture (see contact process, but other processes predated that at least since 16th century). 
In the United States in 1979, 23.6 million metric tons (26 million U.S. short tons) of E220 Sulphur dioxide were used in this way, compared with 150,000 metric tons (165,347 U.S. short tons) used for other purposes. 
Most E220 Sulphur dioxide is produced by the combustion of elemental sulfur. 
Some E220 Sulphur dioxide is also produced by roasting pyrite and other sulfide ores in air.