Apparatus with a high pressure cell for textile cleaning using liquid CO2: (a) general overview; (b) open high pressure cell with puddles for applying mechanical stress while washing (marked with a yellow frame).
As of October 2010, carbon dioxide (CO2) in the Earth’s atmosphere is at a concentration of 388 ppm by volume. Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the Northern Hemisphere. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay. Taking all this into account, the concentration of CO2 grew by about 2 ppm in 2009. Carbon dioxide is a greenhouse gas as it transmits visible light but absorbs strongly in the infrared and near-infrared.
Before the advent of human-caused release of carbon dioxide to the atmosphere, concentrations tended to increase with increasing global temperatures, acting as a positive feedback for changes induced by other processes such as orbital cycles.
Carbon dioxide is soluble in water, in which it spontaneously interconverts between CO2 and H2CO3 (carbonic acid). The relative concentrations of CO2, H2CO3, and the deprotonated forms HCO3− (bicarbonate) and CO2−3(carbonate) depend on the pH. In neutral or slightly alkaline water (pH > 6.5), the bicarbonate form predominates (>50%) becoming the most prevalent (>95%) at the pH of seawater, while in very alkaline water (pH > 10.4) the predominant (>50%) form is carbonate.
Carbon dioxide is used by the food industry, the oil industry, and the chemical industry. It is used in many consumer products that require pressurized gas because it is inexpensive and nonflammable, and because it undergoes a phase transition from gas to liquid at room temperature at an attainable pressure of approximately 60 bar (59 atm), allowing far more carbon dioxide to fit in a given container than otherwise would.
Liquid CO2 cleaners as a nontoxic dry-cleaning alternative use the same process as standard dry cleaning except that liquid carbon dioxide is used as the solvent, which eliminates the need for toxic cleaning chemicals.
The goal of the experiments is to elucidate the mechanisms behind particle and oily stain removal in dry-cleaning process and in a dry-cleaning apparatus.
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