Carbon dioxide (carbon dioxide), a carbon oxide compound, has a chemical formula of CO2 and a chemical formula of 44.0095. At room temperature and pressure, it is a colorless, odorless or colorless and odorless (no smell) but slightly acidic gas. A common greenhouse gas is also a component of air (0.03% -0.04% of the total atmospheric volume). In terms of physical properties, the melting point of carbon dioxide is -78.5 ° C, the boiling point is -56.6 ° C, the density is greater than the density of air (under standard conditions), and it is soluble in water. In terms of chemical properties, the chemical properties of carbon dioxide are inactive and have high thermal stability (only 1.8% decomposition at 2000 ° C). They cannot be burned and generally do not support combustion. They are acid oxides and have the generality of acid oxides. Since carbonic acid is formed by reaction with water, it is an anhydride of carbonic acid.
Carbon dioxide is generally produced by calcining limestone at high temperatures or by reacting limestone with dilute hydrochloric acid. It is mainly used in refrigerated and perishable foods (solid), as a refrigerant (liquid), in carbonized soft drinks (gaseous), and as a solvent for homogeneous reactions ( Supercritical state) and so on. With regard to its toxicity, research has shown that low concentrations of carbon dioxide are not toxic, and high concentrations of carbon dioxide can poison animals.
High-purity carbon dioxide is mainly used in the electronics industry, medical research and clinical diagnosis, calibration gas for carbon dioxide lasers, testing instruments, and other special mixed gas preparations. It is also used as a regulator in the polymerization of polyethylene.
Solid carbon dioxide is widely used in refrigerated dairy products, meat, frozen foods, and other perishable foods in transit. It is used as a refrigerant in many industrial processes, such as crushing heat-sensitive materials, rubber polishing, metal cold processing, shrink assembly of mechanical parts. , Vacuum cold trap, etc.
Gaseous carbon dioxide is used for carbonized soft drinks, pH control of water treatment processes, chemical processing, food preservation, inert protection of chemical and food processing processes, welding gases, plant growth stimulants, used in hardening molds and cores in casting and for Pneumatic device, also used as a thinner for germicidal gas (that is, a mixed gas of ethylene oxide and carbon dioxide is used as sterilization, insecticide, fumigant, widely used in sterilization of medical devices, packaging materials, clothing, fur, bedding, etc. , Bone meal disinfection, fumigation of warehouses, factories, cultural relics, books).
Liquid carbon dioxide is used as a refrigerant, low temperature tests for aircraft, missiles and electronic components, to improve oil well recovery, rubber polishing, and to control chemical reactions. It can also be used as a fire extinguishing agent.
Carbon dioxide in the supercritical state can be used as a solvent for dissolving non-polar, non-ionic and low molecular weight compounds, so it is widely used in homogeneous reactions.