Liquid carbon dioxide
Liquid carbon dioxide is the liquid form of carbon dioxide. At normal atmospheric pressure, carbon dioxide can only exist as a gas or solid, and is ordinarily found as a trace gas in Earth's atmosphere. Its liquid state can exist at pressures above, between the temperatures of its triple point, and its critical point,. Solid, known as dry ice, occurs at low temperatures, and has commercial applications. Dry ice sublimes above at atmospheric pressure—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
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 and above . The chemical symbol remains the same as gaseous carbon dioxide. It is transparent and odorless, and its density is 1101 kg/m3 when the liquid is at full saturation at.The solubility 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. The solubility turned out to be very low: from 0.02 to 0.10 %.
Image:Carbon dioxide pressure-temperature [phase diagram.svg|thumb|Carbon dioxide pressure-temperature phase diagram]
Uses
Uses of liquid carbon dioxide include the preservation of food, in fire extinguishers, and in commercial food processes. For food preservation, 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, but also cools the burning surface to avoid further damage. Solvent extraction using compressed liquid can be used in industrial processes such as removing caffeine from coffee or improving the yield of olive oil production.Liquid carbon dioxide is being considered as a means of CO2 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.
is also used in large-scale air-to-water heat pumps for district heating, replacing less-environmentally-friendly refrigerants. The changes phases between liquid and gaseous in the process.