Carbon dioxide is formed by combustion and by biological processes including decomposition of organic material, fermentation and digestion.  It combines with water in air to form carbonic acid which corrodes metals, limestone and marble.  Large quantities are produced by lime kiln operation, ammonia production and magnesium production from dolomite. 

While most newly-formed carbon dioxide enters the atmosphere, the oceans contain a much higher percentage of the Earth's total inventory of CO₂ than the atmosphere.  (The US National Oceanic and Atmospheric Administration estimates the oceans contain about 50 times more CO₂ than the atmosphere)  

The concentration of CO₂ in air is not high enough to make its recovery commercially feasible. Producing carbon dioxide as a commercial product requires that it be recovered and purified from a relatively high-volume, CO₂-rich gas stream, generally a stream which is created as an unavoidable byproduct of a large-scale combustion or biological process.  In almost all cases, carbon dioxide which is captured and purified for commercial applications would be vented to the atmosphere at the production point if it were not recovered for transport and use at other locations. 

The most common operations from which commercially-produced carbon dioxide is recovered are industrial plants which produce hydrogen or ammonia from natural gas, coal, or other hydrocarbon feedstock, and large-volume fermentation operations in which plant products are made into ethanol for human consumption, automotive fuel or industrial use.  Breweries producing beer from various grain products are a traditional source.  Corn-to-ethanol plants have been the most rapidly growing source of feed gas for CO₂ recovery. 

CO₂-rich natural gas reservoirs found in underground formations found primarily in the western United States and in Canada are another source of recoverable carbon dioxide.  CO₂ from both natural and industrial sources is used to enhance production of oil from older wells by injecting the carbon dioxide into appropriate underground formations.  Carbon dioxide is used in selectively, primarily in wells which will benefit not only from re-pressurization, but also from a reduction in viscosity of the oil in the reservoir caused by a portion of the CO₂ dissolving in the oil.  (The extent to which carbon dioxide will dissolve in the oil varies with the type of petroleum present in the reservoir.  If the viscosity reduction effect will be minimal, nitrogen, which is usually less expensive, may be used as the pressurant instead.)

Carbon dioxide will not burn or support combustion.  Air with a carbon dioxide content of more than 10% will extinguish an open flame. Air containing more than 10% CO₂, if breathed, can be life-threatening.  Such concentrations may build up in silos, digestion chambers, wells, sewers and the like. Caution must be exercised when entering these types of confined spaces.

CO₂ gas is 1.5 times as heavy as air, thus if released to the air it will concentrate at low elevations. Carbon dioxide will form "dry ice" at -78.5ºC (-109.3º F).  One kg of dry ice has the cooling capacity of 2 kg of ordinary ice.  Gaseous or liquid carbon dioxide, stored under pressure, will form dry ice through an auto-refrigeration process if rapidly depressured.

Carbon dioxide is commercially available as high pressure cylinder gas, relatively low pressure (about 300 psig or 20 barg) refrigerated liquid, or as dry ice. Large quantities are produced and consumed at industrial sites making fertilizers, plastics and rubber.

Carbon dioxide is a versatile material, being used in many processes and applications - each of which takes advantage of one or more these characteristics:  reactivity, inertness and/ or coldness.  Common uses include the consumption of carbon dioxide as a raw material for production of various chemicals; its application as a working material in fire extinguishing systems; carbonation of soft drinks; freezing of food products such as poultry, meats, vegetables and fruit; chilling of meats prior to grinding; refrigeration and maintenance of ideal atmospheric conditions during transportation of food products to market; enhancement of oil recovery from oil wells; and treatment of alkaline water.

The concentration of CO₂ in the Earth's atmosphere has been increasing at a noticeable rate for much of the past century, There is much interest and concern over the inter-relationship between the levels of carbon dioxide in air and the subject of global warming,

Carbon dioxide plays a major role as a component of the carbon cycle in which carbon is exchanged between the atmosphere, the terrestrial biosphere (which includes freshwater systems and soil), the oceans, and sediments (including fossil fuels). These interactions are complex and widespread.  They undoubtedly can be, and are, influenced by many types of human activities, but the extent to which humans have impacted these processes, and will impact them in the future, remains the subject of much research and debate.

Much of the rise in CO₂ in the Earth's atmosphere over the past 11,000 years (the warmer period following the end of the last major glacial period) occurred prior to the industrial revolution; and much of that rise has been attributed to release of CO₂ from the oceans as they gradually warmed following the end of the last glacial period.  The amount of CO₂ that the oceans can hold is temperature dependent; and changes in the average temperature of the oceans occur much more slowly than changes in temperature at the surface of the Earth. 

The Earth has experienced a number of glacial / interglacial cycles in its history.  They have tended to occur on a reasonably regular cycle for more than 400,000 years.  At the end of the last glacial period, about 11,000 years ago, the CO₂ level in the atmosphere was about 200 ppm.  Around the year 1800, near the end of the 300-years-long "Little Ice Age" period, and before the industrial revolution, the CO₂ level in the atmosphere was about 280 ppm. 

In 1960, the concentration of CO₂ in air had risen to 315 ppm. Since the middle of the Twentieth Century, the level of carbon dioxide in the Earth's atmosphere has increased at an average annual rate greater than 1 ppm per year due to a combination of natural processes and increased combustion of fossil fuels. The concentration of carbon dioxide in the atmosphere currently averages between about 380 and 385 ppm.  The rate of increase in carbon dioxide content of air is currently more than 2 ppm annually. 

(Much more on CO₂ in air can be found on our "Air" page).  

Carbon dioxide in solid and in liquid form is used for refrigeration and cooling.  It is used as an inert gas in chemical processes, in the storage of carbon powder and in fire extinguishers. 

Metals Industry:

Carbon dioxide is used in the manufacture of casting molds to enhance their hardness. 

Manufacturing and Construction Uses:

Carbon dioxide is used on a large scale as a shield gas in MIG/MAG welding, where the gas protects the weld puddle against oxidation by the surrounding air.  A mixture of argon and carbon dioxide is commonly used today to achieve a higher welding rate and reduce the need for post weld treatment. 

Dry ice pellets are used to replace sandblasting when removing paint from surfaces.  It aids in reducing the cost of disposal and cleanup.

Chemicals, Pharmaceuticals and Petroleum Industry Uses:

Large quantities are used as a raw material in the chemical process industry, especially for methanol and urea production.

Carbon dioxide is used in oil wells for oil extraction and maintain pressure within a formation.. When CO₂ is pumped into an oil well, it is partially dissolved into the oil, rendering it less viscous, allowing the oil to be extracted more easily from the bedrock.  Considerably more oil can be extracted from through this process.

Rubber and Plastics Industry Uses:

Flash is removed from rubber objects by tumbling them with crushed dry ice in a rotating drum.

Food and Beverages Uses for Carbon Dioxide:

Liquid or solid carbon dioxide is used for quick freezing, surface freezing, chilling and refrigeration in the transport of foods. In cryogenic tunnel and spiral freezers, high pressure liquid CO₂ is injected through nozzles that convert it to a mixture of CO₂ gas and dry ice "snow" that covers the surface of the food product.  As it sublimates (goes directly from solid to gas states) refrigeration is transferred to the product.

Carbon dioxide gas is used to carbonate soft drinks, beers and wine and to prevent fungal and bacterial growth.

Liquid carbon dioxide is a good solvent for many organic compounds.  It is used to de-caffeinate coffee.

It is used as an inert “blanket”, as a product-dispensing propellant and an extraction agent. It can also be used to displace air during canning. 

Supercritical CO₂ extraction coupled with a fractional separation technique is used by producers of flavors and fragrances to separate and purify volatile flavor and fragrances concentrates.

Cold sterilization can be carried out with a mixture of 90% carbon dioxide and 10% ethylene oxide, the carbon dioxide has a stabilizing effect on the ethylene oxide and reduces the risk of explosion.

Health Care Uses:

Carbon dioxide is used as an additive to oxygen for medical use as a respiration stimulant.

Environmental Uses:

Used as a propellant in aerosol cans, it replaces more environmentally troublesome alternatives.

By using dry ice pellets to replace sandblasting when removing paint from surfaces, problems of residue disposal are greatly reduced.

It is used to neutralize alkaline water.

Miscellaneous Uses for Carbon Dioxide (CO₂):

Liquid carbon dioxide's solvent potential has been employed in some dry cleaning equipment as a substitute for conventional solvents.  This use is still experimental - some types of soil are more effectively removed with traditional dry cleaning equipment, and the equipment is more expensive. 

Yields of plant products grown in greenhouses can increase by 20% by enriching the air inside the greenhouse with carbon dioxide.  The target level for enrichment is typically a carbon dioxide concentration of 1000 PPM (parts per million) - or about two and a half times the level present in the atmosphere. 

More on Carbon Dioxide in Air and its Recovery as an Industrial Gas:

Properties, Applications and Uses of Other Industrial Gases:

Information on Technology, Product Supply Optimization, UIG Plants & Services: