Perfluorocarbon PFC: generally refers to carbon tetrafluoride
Carbon tetrafluoride (Carbontetrafluoride), the molecular formula is CF4, also known as perfluorocarbon
Chemical Properties
Carbon tetrafluoride is a colorless, odorless, non-flammable, easily compressible gas with high volatility. It is one of the stable organic compounds and is not easily soluble in water. At 900°C, it does not react with copper, nickel, tungsten, and molybdenum. It only decomposes slowly at carbon arc temperature and is slightly soluble in water. Its solubility is 0.0015% (weight ratio) at 25°C and 0.1Mpa. However, it does not react with flammable When sexual gas burns, it decomposes to produce toxic fluoride.
Environmental Impact
Carbon tetrafluoride is a gas that contributes to the greenhouse effect. It is very stable and can remain in the atmosphere for long periods of time, making it a very powerful greenhouse gas. Its lifetime in the atmosphere is about 50,000 years, and its global warming (global warming) coefficient is 6,500 (carbon dioxide’s coefficient is 1). Although similar in structure to hydrofluorocarbons, carbon tetrafluoride does not destroy the ozone layer. This is because the chlorine atoms in chlorofluorocarbons, which cause the destruction of the ozone layer, break apart when hit by ultraviolet radiation. The carbon-fluorine bond is relatively strong and therefore less likely to separate.
Synthesis method
1. By the reaction of carbon and fluorine, or the reaction of carbon monoxide and fluorine, or the reaction of silicon carbide and fluorine, or the reaction of fluorite and petroleum coke in an electric furnace, or the reaction of difluorodichloromethane and hydrogen fluoride, or the reaction of carbon tetrachloride and fluoride Silver reaction, or the reaction of carbon tetrachloride and hydrogen fluoride, can produce carbon tetrafluoride. The reaction between carbon tetrachloride and hydrogen fluoride is carried out in a high-temperature nickel tube filled with chromium hydroxide. The reacted gas is washed with water and alkali to remove the acid gas, then frozen, and the moisture in the gas is removed with silica gel, and then rectified. And get the finished product.
2. Weigh 5 to 10g of silicon carbide powder and 0.1g of elemental silicon powder in advance and place them in a nickel plate. After the silicon and silicon carbide are fully contacted, put the nickel plate into the Monel alloy reaction tube and insert it into the reaction tube. Introduce fluorine gas. The fluorine gas first reacts with elemental silicon. After the reaction is exothermic, fluorine begins to react with silicon carbide. An equal volume of dry nitrogen is introduced to dilute the fluorine gas to allow the reaction to continue. The generated gas is cooled by liquid nitrogen. After the nickel trap is condensed and then slowly vaporized, it is passed through a scrubbing bottle filled with sodium hydroxide solution to remove silicon tetrafluoride, and then passed through a silica gel and phosphorus pentoxide drying tower to obtain the final product.
3. Prepared by fluorination reaction using activated carbon and fluorine as raw materials. In the reaction furnace equipped with activated carbon, high-concentration fluorine gas is slowly introduced, and the reaction temperature is controlled through heater heating, fluorine supply rate and reactor cooling. The product is dusted and washed with alkali to remove HF, CoF2, SiF4, CO2 and other impurities, and then dehydrated to obtain a crude product with a content of approximately 85%. The crude product is introduced into a low-temperature distillation kettle for intermittent crude distillation. By controlling the distillation temperature, O2, N2, and H2 are removed to obtain high-purity CF4.
Security
The consequences of inhaling carbon tetrafluoride are concentration-dependent and include headache, nausea, dizziness and damage to the cardiovascular system (mainly the heart). Prolonged exposure can cause serious heart damage.
Carbon tetrafluoride has a relatively high density and can fill the floor space, causing suffocation in unventilated areas.
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