Difluoromethane

Last updated
Difluoromethane
Difluoromethane-2D-skeletal Difluoromethane-2D-skeletal.png
Difluoromethane-2D-skeletal
Spacefill model of difluoromethane Difluoromethane-3D-vdW.png
Spacefill model of difluoromethane
Names
Preferred IUPAC name
Difluoromethane [1]
Other names
Carbon fluoride hydride

Methylene difluoride
Methylene fluoride

Freon-32[ citation needed ]
Identifiers
3D model (JSmol)
AbbreviationsHFC-32

R-32
FC-32

1730795
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.764 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 200-839-4
259463
MeSH Difluoromethane
PubChem CID
RTECS number
  • PA8537500
UNII
UN number 3252
  • InChI=1S/CH2F2/c2-1-3/h1H2 Yes check.svgY
    Key: RWRIWBAIICGTTQ-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/CH2F2/c2-1-3/h1H2
    Key: RWRIWBAIICGTTQ-UHFFFAOYAC
  • FCF
Properties
CH2F2
Molar mass 52.024 g·mol−1
AppearanceColourless 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)
log P -0.611
Vapor pressure 1,518.92 kPa (220.301 psi) (at 21.1 °C [70.0 °F; 294.2 K])
Hazards
GHS labelling:
GHS-pictogram-flamme.svg
Danger
H220
P210, P377, P381, P403, P410+P403
NFPA 704 (fire diamond)
NFPA 704.svgHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
4
0
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 their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Difluoromethane, also called difluoromethylene, HFC-32Methylene Fluoride or R-32, is an organic compound of the dihalogenoalkane variety. Invented in 1964 by Hoechst AG (not Daikin) 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, the Clean 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.

Contents

R32 - Difluoromethane R32 - Difluoromethane.png
R32 - Difluoromethane

Synthesis

Difluoromethane is primarily synthesized via batch processes, by the reaction of dichloromethane and hydrogen fluoride (HF), in the liquid phase using SbCl5 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 for constant flow of difluoromethane production through an isolated chamber. [4]

Applications

HFC-32 measured by the Advanced Global Atmospheric Gases Experiment (AGAGE) in the lower atmosphere (troposphere) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in parts-per-trillion. HFC-32 mm.png
HFC-32 measured by the Advanced Global Atmospheric Gases Experiment (AGAGE) in the lower atmosphere (troposphere) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in parts-per-trillion.


Difluoromethane is often used as a fire extinguishant due to its ability to undergo endothermic processes. [5] Atmospheric concentration of difluoromethane at various latitudes since the year 2009 are shown to the left.

Atmospheric concentration of difluoromethane at various latitudes since year 2009. BK HFC32.jpg
Atmospheric concentration of difluoromethane at various latitudes since year 2009.

Difluoromethane is a molecule used as refrigerant that has prominent heat transfer and pressure drop performance, both in condensation and vaporization. [6] It has a 100-year global warming potential (GWP) of 675 times that of carbon dioxide, and an atmospheric lifetime of nearly 5 years. [7] It is classified as A2L - slightly flammable by ASHRAE, [8] and has zero ozone depletion potential (ODP). [9] Difluoromethane is thus a relatively low-risk choice among HFC refrigerants, most of which have higher GWP and longer persistence when leaks occur.

The common refrigerant R-410A is a zeotropic, 50/50-mass-percent mixture of difluoromethane and pentafluoroethane (R-125). Pentafluoroethane is a common replacement for various chlorofluorocarbons (i.e Freon ) in new refrigerant systems, especially for air-conditioning. The zeotropic mix of difluoromethane with pentafluoroethane (R-125) and tetrafluoroethane (R-134a) is known as R-407A through R-407F depending on the composition. Likewise, R-504 is the azeotropic (48.2/51.8 mass%) mixture of difluoromethane and chlorotrifluoromethane (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 for R-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 of R-410A under 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]

Environmental effects

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 form carbonyl difluoride. The half-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 not bioaccumulate 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]

The global 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 of VOCs supplied in the United States Clean Air Act due to the ODP 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 ]

Toxicity

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]

Related Research Articles

<span class="mw-page-title-main">Chlorofluorocarbon</span> Class of organic compounds

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and propane.

<span class="mw-page-title-main">Heat pump</span> System that transfers heat from one space to another

A heat pump is a device that consumes energy to transfer heat from a cold heat sink to a hot heat sink. Specifically, the heat pump transfers thermal energy using a refrigeration cycle, cooling the cool space and warming the warm space. In cold weather, a heat pump can move heat from the cool outdoors to warm a house ; the pump may also be designed to move heat from the house to the warmer outdoors in warm weather. As they transfer heat rather than generating heat, they are more energy-efficient than other ways of heating or cooling a home.

<span class="mw-page-title-main">Refrigerant</span> Substance in a refrigeration cycle

A refrigerant is a working fluid used in cooling, heating or reverse cooling and heating of air conditioning systems and heat pumps where they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are heavily regulated because of their toxicity and flammability and the contribution of CFC and HCFC refrigerants to ozone depletion and that of HFC refrigerants to climate change.

1,1,1,2-Tetrafluoroethane (also known as norflurane (INN), R-134a, Klea 134a, Freon 134a, Forane 134a, Genetron 134a, Green Gas, Florasol 134a, Suva 134a, HFA-134a, or HFC-134a) is a hydrofluorocarbon (HFC) and haloalkane refrigerant with thermodynamic properties similar to R-12 (dichlorodifluoromethane) but with insignificant ozone depletion potential and a lower 100-year global warming potential (1,430, compared to R-12's GWP of 10,900). It has the formula CF3CH2F and a boiling point of −26.3 °C (−15.34 °F) at atmospheric pressure. R-134a cylinders are colored light blue. A phaseout and transition to HFO-1234yf and other refrigerants, with GWPs similar to CO2, began in 2012 within the automotive market.

<span class="mw-page-title-main">1,1-Difluoroethane</span> Chemical compound

1,1-Difluoroethane, or DFE, is an organofluorine compound with the chemical formula C2H4F2. This colorless gas is used as a refrigerant, where it is often listed as R-152a (refrigerant-152a) or HFC-152a (hydrofluorocarbon-152a). It is also used as a propellant for aerosol sprays and in gas duster products. As an alternative to chlorofluorocarbons, it has an ozone depletion potential of zero, a lower global warming potential (124) and a shorter atmospheric lifetime (1.4 years).

<span class="mw-page-title-main">Chlorodifluoromethane</span> Chemical propellant and refrigerant

Chlorodifluoromethane or difluoromonochloromethane is a hydrochlorofluorocarbon (HCFC). This colorless gas is better known as HCFC-22, or R-22, or CHClF
2. It was commonly used as a propellant and refrigerant. These applications were phased out under the Montreal Protocol in developed countries in 2020 due to the compound's ozone depletion potential (ODP) and high global warming potential (GWP), and in developing countries this process will be completed by 2030. R-22 is a versatile intermediate in industrial organofluorine chemistry, e.g. as a precursor to tetrafluoroethylene.

R-410A is a refrigerant used in air conditioning and heat pump applications. It is a zeotropic but near-azeotropic mixture of difluoromethane (CH2F2, called R-32) and pentafluoroethane (CHF2CF3, called R-125). R-410A is sold under the trademarked names AZ-20, EcoFluor R410, Forane 410A, Genetron R410A, Puron, and Suva 410A.

<span class="mw-page-title-main">Vapor-compression refrigeration</span> Refrigeration process

Vapour-compression refrigeration or vapor-compression refrigeration system (VCRS), in which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. Cascade refrigeration systems may also be implemented using two compressors.

<span class="mw-page-title-main">Air source heat pump</span> Most common type of heat pump

An air source heat pump (ASHP) is a heat pump that can absorb heat from air outside a building and release it inside; it uses the same vapor-compression refrigeration process and much the same equipment as an air conditioner, but in the opposite direction. ASHPs are the most common type of heat pump and, usually being smaller, tend to be used to heat individual houses or flats rather than blocks, districts or industrial processes.

Natural refrigerants are considered substances that serve as refrigerants in refrigeration systems. They are alternatives to synthetic refrigerants such as chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) based refrigerants. Unlike other refrigerants, natural refrigerants can be found in nature and are commercially available thanks to physical industrial processes like fractional distillation, chemical reactions such as Haber process and spin-off gases. The most prominent of these include various natural hydrocarbons, carbon dioxide, ammonia, and water. Natural refrigerants are preferred actually in new equipment to their synthetic counterparts for their presumption of higher degrees of sustainability. With the current technologies available, almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants.

<span class="mw-page-title-main">2,3,3,3-Tetrafluoropropene</span> Chemical compound

2,3,3,3-Tetrafluoropropene, HFO-1234yf, is a hydrofluoroolefin (HFO) with molecular formula CH2=CFCF3. Its primary application is as a refrigerant with low global warming potential (GWP).

<span class="mw-page-title-main">Pentafluoroethane</span> Chemical compound

Pentafluoroethane is a fluorocarbon with the formula CF3CHF2. Pentafluoroethane is currently used as a refrigerant (known as R-125) and also used as a fire suppression agent in fire suppression systems.

<span class="mw-page-title-main">1-Chloro-1,1-difluoroethane</span> Chemical compound

1-Chloro-1,1-difluoroethane (HCFC-142b) is a haloalkane with the chemical formula CH3CClF2. It belongs to the hydrochlorofluorocarbon (HCFC) family of man-made compounds that contribute significantly to both ozone depletion and global warming when released into the environment. It is primarily used as a refrigerant where it is also known as R-142b and by trade names including Freon-142b.

<span class="mw-page-title-main">Hydrofluoroolefin</span> Class of chemical compounds

Hydrofluoroolefins (HFOs) are unsaturated organic compounds composed of hydrogen, fluorine and carbon. These organofluorine compounds are of interest as refrigerants. Unlike traditional hydrofluorocarbons (HFCs) and chlorofluorocarbons (CFCs), which are saturated, HFOs are olefins, otherwise known as alkenes.

<i>trans</i>-1,3,3,3-Tetrafluoropropene Chemical compound

trans-1,3,3,3-Tetrafluoropropene (HFO-1234ze(E), R-1234ze(E)) is a hydrofluoroolefin. It was developed as a "fourth generation" refrigerant to replace fluids such as R-134a, as a blowing agent for foam and aerosol applications, and in air horns and gas dusters. The use of R-134a is being phased out because of its high global warming potential (GWP). HFO-1234ze(E) itself has zero ozone-depletion potential (ODP=0), a very low global warming potential (GWP < 1 ), even lower than CO2, and it is classified by ANSI/ASHRAE as class A2L refrigerant (lower flammability (see below) and lower toxicity).

R-454B, also known by the trademarked names Opteon XL41, Solstice 454B, and Puron Advance, is a zeotropic blend of 68.9 percent difluoromethane (R-32), a hydrofluorocarbon, and 31.1 percent 2,3,3,3-tetrafluoropropene (R-1234yf), a hydrofluoroolefin. Because of its reduced global warming potential (GWP), R-454B is intended to be an alternative to refrigerant R-410A in new equipment. R-454B has a GWP of 466, which is 78 percent lower than R-410A's GWP of 2088.

Life Cycle Climate Performance (LCCP) is an evolving method to evaluate the carbon footprint and global warming impact of heating, ventilation, air conditioning (AC), refrigeration systems, and potentially other applications such as thermal insulating foam. It is calculated as the sum of direct, indirect, and embodied greenhouse gas (GHG) emissions generated over the lifetime of the system “from cradle to grave,” i.e. from manufacture to disposal. Direct emissions include all climate forcing effects from the release of refrigerants into the atmosphere, including annual leakage and losses during service and disposal of the unit. Indirect emissions include the climate forcing effects of GHG emissions from the electricity powering the equipment. The embodied emissions include the climate forcing effects of the manufacturing processes, transport, and installation for the refrigerant, materials, and equipment, and for recycle or other disposal of the product at end of its useful life.

R-469A is a refrigerant blend consisting of 35% carbon dioxide (R-744), 32.5% difluoromethane (R-32), and 32.5% pentafluoroethane (R-125).

The Significant New Alternatives Policy is a program of the EPA to determine acceptable chemical substitutes, and establish which are prohibited or regulated by the EPA. It also establishes a program by which new alternatives may be accepted, and promulgates timelines to the industry regarding phase-outs of substitutes.

References

  1. ↑ "Difluoromethane - Compound Summary". The PubChem Project. US: National Center of Biotechnological Information.
  2. 1 2 "Editorial Board". Journal of Fluorine Chemistry. 241: 109706. January 2021. doi: 10.1016/s0022-1139(20)30404-8 . ISSN   0022-1139. S2CID   243320092.
  3. 1 2 3 4 5 6 7 8 "Stratospheric Ozone Protection: The Montreal Protocol and Title VI of the Clean Air Act Amendments of 1990". Air & Waste. 43 (8): 1066–1067. August 1993. doi: 10.1080/1073161x.1993.10467184 . ISSN   1073-161X.
  4. 1 2 Shen, Tao; Ge, Xin; Zhao, Hengjun; Xu, Zhixiong; Tong, Shaofeng; Zhou, Shaodong; Qian, Chao; Chen, Xinzhi (2020-07-01). "A safe and efficient process for the preparation of difluoromethane in continuous flow". Chinese Journal of Chemical Engineering. 28 (7): 1860–1865. doi:10.1016/j.cjche.2020.02.024. ISSN   1004-9541. S2CID   216394634.
  5. ↑ Blowers, Paul; Hollingshead, Kyle (2009-05-21). "Estimations of Global Warming Potentials from Computational Chemistry Calculations for CH 2 F 2 and Other Fluorinated Methyl Species Verified by Comparison to Experiment". The Journal of Physical Chemistry A. 113 (20): 5942–5950. Bibcode:2009JPCA..113.5942B. doi:10.1021/jp8114918. ISSN   1089-5639. PMID   19402663.
  6. ↑ Longo, Giovanni A.; Mancin, Simone; Righetti, Giulia; Zilio, Claudio (2015). "HFC32 vaporisation inside a Brazed Plate Heat Exchanger (BPHE): Experimental measurements and IR thermography analysis". International Journal of Refrigeration. 57: 77–86. doi:10.1016/j.ijrefrig.2015.04.017.
  7. ↑ May 2010 TEAP XXI/9 Task Force Report
  8. ↑ 2009 ASHRAE Handbook
  9. ↑ "R32".
  10. ↑ Galka, Michael D.; Lownsbury, James M.; Blowers, Paul (2012-12-04). "Greenhouse Gas Emissions for Refrigerant Choices in Room Air Conditioner Units". Environmental Science & Technology. 46 (23): 12977–12985. Bibcode:2012EnST...4612977G. doi:10.1021/es302338s. ISSN   0013-936X. PMID   23136858.
  11. 1 2 Longo, Giovanni A.; Mancin, Simone; Righetti, Giulia; Zilio, Claudio (2016). "HFC32 and HFC410A flow boiling inside a 4 mm horizontal smooth tube". International Journal of Refrigeration. 61: 12–22. doi:10.1016/j.ijrefrig.2015.09.002.
  12. ↑ IPCC AR4, summarized at https://www.ghgprotocol.org/sites/default/files/ghgp/Global-Warming-Potential-Values%20%28Feb%2016%202016%29_1.pdf

See also

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