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| Names | |||
|---|---|---|---|
| Preferred IUPAC name Difluoromethane[1] | |||
| Other names | |||
| Identifiers | |||
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3D model (JSmol) | |||
| Abbreviations | HFC-32 R-32 | ||
| 1730795 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
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| ECHA InfoCard | 100.000.764 | ||
| EC Number |
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| 259463 | |||
| MeSH | Difluoromethane | ||
| RTECS number |
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| UNII | |||
| UN number | 3252 | ||
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| Properties | |||
| CH2F2 | |||
| Molar mass | 52.024 g·mol−1 | ||
| Appearance | Colourless gas | ||
| Density | 1.1 g cm−3(in liquid form) | ||
| Melting point | −136 °C (−213 °F; 137 K) | ||
| Boiling point | −52 °C (−62 °F; 221 K) | ||
| logP | −0.611 | ||
| Vapor pressure | 1,518.92 kPa (220.301 psi) (at 21.1 °C [70.0 °F; 294.2 K]) | ||
| Hazards | |||
| GHS labelling: | |||
 | |||
| Danger | |||
| H220 | |||
| P210,P377,P381,P403,P410+P403 | |||
| NFPA 704 (fire diamond) | |||
| 648 °C (1,198 °F; 921 K) | |||
| Safety data sheet (SDS) | MSDS at Oxford University | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Difluoromethane, also called difluoromethylene,HFC-32Methylene Fluoride orR-32, is anorganic compound of thedihalogenoalkane variety. Invented in 1964 by Hoechst AG, it has the formula of CH2F2. It is a colorless gas in the ambient atmosphere and is slightly soluble in water, with a high thermal stability.[2][failed verification] Due to the low melting and boiling point, (−136.0 and −51.6 °C [−212.8 and −60.9 °F; 137.2 and 221.6 K] respectively) contact with this compound may result in frostbite.[2][failed verification] In the United States, theClean Air Act Section 111 on Volatile Organic Compounds (VOC) has listed difluoromethane as an exception (since 1997) from the definition of VOC due to its low production of tropospheric ozone.[3] Difluoromethane is commonly used in endothermic processes such as refrigeration or air conditioning.
Difluoromethane is primarily synthesized viabatch processes, by the reaction ofdichloromethane andhydrogen fluoride (HF), in the liquid phase usingSbCl5 as a catalyst.[4] Due to hydrogen fluoride's hazardous properties, a new process (based on the same reaction) was developed. The new process allows forconstant flow of difluoromethane production through an isolated chamber.[4]
Difluoromethane is often used as a fire extinguishant due to its ability to undergo endothermic processes.[5]
Difluoromethane is a molecule used asrefrigerant that has prominent heat transfer and pressure drop performance, both in condensation and vaporization.[6] It has a 100-yearglobal warming potential (GWP) of 675 times that of carbon dioxide, and anatmospheric lifetime of nearly 5 years.[7] It is classified as A2L - slightly flammable by ASHRAE,[8] and has zeroozone depletion potential (ODP).[9] Difluoromethane is thus a relatively low-risk choice amongHFC refrigerants, most of which have higher GWP and longer persistence when leaks occur.
The common refrigerantR-410A is azeotropic, 50/50-mass-percent mixture of difluoromethane andpentafluoroethane (R-125).Pentafluoroethane is a common replacement for variouschlorofluorocarbons (i.eFreon) in newrefrigerant systems, especially for air-conditioning. Thezeotropic mix of difluoromethane withpentafluoroethane (R-125) andtetrafluoroethane (R-134a) is known asR-407A through R-407F depending on the composition. Likewise, R-504 is theazeotropic (48.2/51.8 mass%) mixture of difluoromethane andchlorotrifluoromethane (R13). In 2011 17,949,893 metric tons of difluoromethane were emitted into the atmosphere in the United States alone.[10]
Difluoromethane is currently used by itself in residential and commercial air-conditioners in Japan, China, and India as a substitute forR-410A. In order to reduce the residual risk associated with its mild flammability, this molecule should be applied in heat transfer equipment with low refrigerant charge such as brazed plate heat exchangers (BPHE), or shell and tube heat exchangers and tube and plate heat exchangers with tube of small diameter.[11]Many applications confirmed that difluoromethane exhibits heat transfer coefficients higher than those ofR-410Aunder the same operating conditions but also higher frictional pressure drops.[11]
Other uses of difluoromethane include its use as aerosol propellants, blowing agents, and solvents.[3]
Every year, approximately 15 kilotonnes of difluoromethane are produced.[3] In gas form, the compound will degrade in the atmosphere by reaction with photochemically-produced hydroxyl radicals. This process will formcarbonyl difluoride. Thehalf-life for this process is estimated to be 4 years.[3] Difluoromethane tends to enter the environment via the gas phase and accumulates there more commonly than in soils or sediments. Volatilization half-lives of this compound are about 45 minutes for rivers and 69 hours for lakes, difluoromethane does notbioaccumulate in aquatic areas well.[3]
HFC-32 released into the environment gets broken down into CF as an intermediate product. This goes on to create HF and CO2 by hydrolysis in atmospheric water.[3]
Theglobal warming potential (GWP) of HFC-32 is estimated at 677 on a 100-year time window.[12] This is far lower than the GWP for HFC refrigerants it is replacing, but remains sufficiently high to spur continued research into using lower-GWP refrigerants.
Difluoromethane is excluded from the list ofVOCs supplied in the United States Clean Air Act due to theODP being zero.[3] Therefore,tropospheric ozone is not likely to be produced from this molecule.[citation needed] Tropospheric ozone may lead to adverse health effects such as respiratory, cardiac or neurological damage. Additionally, ozone can affect plant and vegetation by inducing the bronzing of leaves.[citation needed]
Difluoromethane shows slight maternal and developmental toxicity at concentrations of approximately 50,000 ppm in rats, but not in rabbits. The exposure limitations set on difluoromethane for human use are 1,000 ppm, making exposure to dangerous levels unlikely.[3]
| Authority control databases: National |
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