carbon dioxide

Carbon Dioxide

Carbon dioxide (CO2) is a slightly toxic, odorless, colorless gas with a slightly pungent, acid taste. Carbon dioxide is a small but important constituent of air. It is a necessary raw material for most plants, which remove carbon dioxide from air using the process of photosynthesis.

A typical concentration of CO2 in air is about 0.038% or 380 ppm. The concentration of atmospheric carbon dioxide rises and falls in a seasonal pattern over a range of about 6 ppmv. The concentration of CO2 in air has also been steadily increasing from year to year for over 60 years. The current rate of increase is about 2 ppm per year.


Carbon dioxide is formed by combustion and by biological processes. These include decomposition of organic material, fermentation and digestion. As an example, exhaled air contains as much as 4% carbon dioxide, or about 100 times the amount of carbon dioxide which was breathed in.

Large quantities of CO2 are produced by lime kilns, which burn limestone (primarily calcium carbonate) to produce calcium oxide ( lime, used to make cement); and in the production of magnesium from dolomite (calcium magnesium carbonate). Other industrial activities which produce large amounts of carbon dioxide are ammonia production and hydrogen production from natural gas or other hydrocarbon raw materials.
The concentration of CO2 in air and in stack gases from simple combustion sources (heaters, boilers, furnaces) is not high enough to make carbon dioxide 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 chemical production process or some form of 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 was not recoved for transport and beneficial 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.

Carbon dioxide will not burn or support combustion. Air with a carbon dioxide content of more than 10% will extinguish an open flame, and, 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 in the Earth’s Atmosphere

Carbon dioxide in air is considered to be a greenhouse gas because of its ability to absorb infrared light.

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.

Applications :

Multi-Industry Uses for Carbon Dioxide (CO2):
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.

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