![Liquid carbon dioxide jets 02](https://upload.wikimedia.org/wikipedia/commons/d/db/Liquid_carbon_dioxide_jets_02.png)
Liquid carbon dioxide is the liquid state of
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
(), which cannot occur under atmospheric pressure. It can only exist at a pressure above , under (temperature of
critical point) and above (temperature of
triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the subli ...
). Low-temperature carbon dioxide is commercially used in its solid form, commonly known as "
dry ice
Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily a ...
". Solid
sublimes at at Earth
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
— that is, it transitions directly from solid to gas without an intermediate liquid stage. The uses and applications of liquid carbon dioxide include decaffeinating coffee, extracting virgin olive oil from olive paste, in fire extinguishers, and as a coolant.
Properties
![A container of liquid carbon dioxide](https://upload.wikimedia.org/wikipedia/commons/2/2a/A_container_of_liquid_carbon_dioxide.jpg)
Liquid carbon dioxide is a type of liquid which is formed from highly compressed and cooled gaseous carbon dioxide. It does not form under atmospheric conditions. It only exists when the pressure is above 5.1 atm and the temperature is under (temperature of
critical point) and above (temperature of
triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the subli ...
). The chemical symbol remains the same as gaseous carbon dioxide ().
It is transparent and odorless and the density of it is 1101 kg/m
3 when the liquid is at full saturation at .
The
solubility
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubil ...
of water in liquid carbon dioxide is measured in a range of temperatures, ranging from to . At this temperature, the pressure is measured in a range from 15 to 60 atmospheres.
Uses
![Fire extinguisher](https://upload.wikimedia.org/wikipedia/commons/0/0c/Fire_extinguisher.jpg)
Uses of liquid carbon dioxide include the preservation of food, in fire extinguishers, and in commercial food processes. For
food preservation
Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
, liquid carbon dioxide is used to refrigerate, preserve, store and soften. In a fire extinguisher, the is stored under pressure as a liquid to act as an anti-flammable.
The liquid carbon dioxide not only reduces combustion by displacing
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
, but also cools the burning surface to avoid further damage.
Solvent extraction
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
using compressed liquid can be used in industrial processes such as removing
caffeine
Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine t ...
from
coffee
Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulant, stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world.
S ...
or improving the yield of
olive oil
Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: f ...
production.
Liquid carbon dioxide is being considered as a means of CO
2 transportation for underground or subsea storage purposes. Due to its high density as a liquid, it is much more feasible to ship than as a gas.
See also
Other chemical compounds and elements are commonly used for commercial and research purposes in their liquid state:
*
Liquid oxygen
Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an applica ...
*
Liquid nitrogen
Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wide ...
*
Liquid helium
Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity.
At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temp ...
*
Liquid hydrogen
Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.
To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully li ...
References
{{Oxides
Carbon dioxide