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From liquid CO2 into dry ice
Carbon Dioxide has 3 physical states of gas, liquid and solid which depend on temperature and pressure.
The relationship between the 3 states is shown on the pressure-temperature phase diagram beside.
Where does CO2 come from?
CO2 is derived from a number of sources including combustion of carbonaceous fuels, fermentation, natural wells, and as a by-product of industrial processes such as ethylene oxide and bioethanol production and ammonia synthesis.
The Solid State (Dry Ice):
Below the triple point (5.18 bar, - 56.6 °C) (7'512,96 psi, - 69,88 °F) CO2 can only appear in its solid and gaseous state. Dry ice is the common trade name for solid CO2 . At atmospheric pressure it has a temperature of approx. -79 °C (-110,2 °F). The solid CO2 changes directly into its gaseous state. This evaporation (sublimation) does not leave any residues. Dry ice is non-toxic, non-inflammable, inert, without smell and bacteriostatic. It is white and has a density of approx. 1'500 kg/m3 (93,64 lb/ft3) in its compact state. Dry ice is an ideal refrigerant which qualifies especially well for various applications. It has a high cooling capacity and heat transfer is very high when in direct contact with the cold material.
ASCO has the best range of dry ice machines for dry ice production.
The Liquid State:
Within a temperature range between -56.6 °C (-69,88 °F) and 31 °C (87,8 °F) and pressure greater than 5.2 bar and less than 74 bar (1'073,28 psi) respectively CO2 is in its liquid state except at very high pressures. This means that, below 5.2 bar (754,20 psi), CO2 exists only in its solid or gaseous state. At 5.2 bar (754,20 psi) and - 56.6 °C (- 69,88 °F) all three states (solid, liquid and gas) are present. This is called the triple point.
The critical point of CO2 lies at a temperature of approx. 31 °C (87,8 °F) and a pressure of approx. 74 bar (1'073,28 psi). Normal CO2 liquid can only be formed at temperatures below 31 °C (87,8 °F). Above the critical point there is no physical difference between the liquid and gaseous phase. This supercritical state is also called „Fluid“. The liquid state is important for the storage and transportation of CO2 as well as during cooling and freezing applications. During release of the liquid CO2 to atmosphere a temperature of -79 °C (-110,2 °F) is reached. This is associated with a high cooling capacity due to the evaporation heat which is extracted from the environment when releasing the liquid CO2 .
The Gaseous State:
CO2 gas has a density of approx. 1.9 kg/m3 (0,12 lb/ft3) at atmospheric pressure and +15 °C (+ 59 °F). CO2 has many unique and beneficial features which make it valuable in the preservation of packaged food, in explosion and fire protection, in pest control and as protective gas in inert-gas-welding. In all these applications it is important for the CO2 gas to drive out and replace the atmospheric oxygen. Moreover, CO2 gas is used for enriching the atmosphere in greenhouses, in storing fruits and vegetables and for pH control when treating potable and waste water.