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
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
AppearanceColorless 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 1518.92 kPa (at 21.1 °C)
Hazards
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-bottle.svg
Danger
H220, H221, H280
P210, P377, P381, P403, P410+P403
NFPA 704 (fire diamond)
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. It has the formula of CH2F2. It is a colorless gas in the ambient atmosphere and is slightly soluble in the water, with a high thermal stability. [2] [ failed verification ] Due to the low melting and boiling point, (-136.0 °C and -51.6 °C 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

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 synthesis was developed. The new synthesis 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.
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 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.

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 kilotons 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. Therefore, tropospheric ozone is not likely to be produced from this molecule. Tropospheric ozone may lead to adverse health effects such as respiratory, cardiac or neurological damage. [3] Additionally, ozone can affect plant and vegetation by inducing the bronzing of leaves. [3]

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 commonly used as refrigerants

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. They are also commonly known by the DuPont brand name Freon.

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

A refrigerant is a working fluid used in the refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are heavily regulated due to their toxicity, 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, Freon 134a, Forane 134a, Genetron 134a, Green Gas, Florasol 134a, Suva 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).

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, sold under the trademarked names AZ-20, EcoFluor R410, Forane 410A, Genetron R410A, Puron, and Suva 410A, is a zeotropic but near-azeotropic mixture of difluoromethane (CH2F2, called R-32) and pentafluoroethane (CHF2CF3, called R-125) that is used as a refrigerant in air conditioning and heat pump applications. R-410A cylinders were colored rose but are no longer specially color-coded, now bearing a standard light gray color.

A zeotropicmixture, or non-azeotropic mixture, is a mixture with liquid components that have different boiling points. For example, nitrogen, methane, ethane, propane, and isobutane constitute a zeotropic mixture. Individual substances within the mixture do not evaporate or condense at the same temperature as one substance. In other words, the mixture has a temperature glide, as the phase change occurs in a temperature range of about four to seven degrees Celsius, rather than at a constant temperature. On temperature-composition graphs, this temperature glide can be seen as the temperature difference between the bubble point and dew point. For zeotropic mixtures, the temperatures on the bubble (boiling) curve are between the individual component's boiling temperatures. When a zeotropic mixture is boiled or condensed, the composition of the liquid and the vapor changes according to the mixtures's temperature-composition diagram.

<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.

Natural refrigerants are 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 are non-synthetic and can be found in nature. The most prominent of these include various natural hydrocarbons, carbon dioxide, ammonia, and water. Natural refrigerants are preferred to their synthetic counterparts for their 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 the formula CH2=CFCF3. It is also designated R-1234yf as the first of a new class of refrigerants: it is marketed under the name Opteon YF by Chemours and as Solstice YF by Honeywell.

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

1,1-Dichloro-1-fluoroethane is a haloalkane with the formula C
2
H
3
Cl
2
F
. It is one of the three isomers of dichlorofluoroethane. 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.

R-407A is a mixture of gasses used as a refrigerant. It is a zeotropic blend of difluoromethane (HFC-32), pentafluoroethane (HFC-125) and 1,1,1,2-tetrafluoroethane (HFC-134a). R-407A was developed as a close match to R-22's capacities and flow rates, making it well suited as an energy efficient retrofit for R-22 in medium and low temperature refrigeration systems for supermarket and food storage applications, but not for air conditioning systems or those with flooded evaporators. It must be used with synthetic oils. Its global warming potential is 2107.

<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">Hydrofluoroolefin</span> Class of chemical compounds

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

<span class="mw-page-title-main">1,3,3,3-Tetrafluoropropene</span> Chemical compound

1,3,3,3-Tetrafluoropropene (HFO-1234ze(E), R-1234ze) 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 (GFA). 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 and lower toxicity). In open atmosphere however, HFO-1234ze actually might form HFC-23 as one of its secondary atmospheric breakdown products. HFC-23 is a very potent greenhouse gas with a GWP100 of 14,800. The secondary GWP of R-1234ze would then be in the range of 1,400±700 considering the amount of HFC-23 which may form from HFO-1234ze in the atmosphere. Besides the global warming potential, when HFOs decompose in the atmosphere, trifluoroacetic acid (TFA(A)) is formed, which also remains in the atmosphere for several days. The trifluoroacetic acid then forms trifluoroacetate (TFA), a salt of trifluoroacetic acid, in water and on the ground. Due to its high polarity and low degradability, it is difficult to remove TFA from drinking water (ICPR 2019).

Fluorinated gases (F-gases) are chemical compounds containing fluorine that are gases near room temperature.

Barbara Haviland Minor is an American chemical engineer who has worked at DuPont and Chemours. She develops new refrigerants to be used in air conditioning and refrigeration systems, in Europe, North America, Australia and other countries. As of 2018, 50% of all new vehicles produced by original equipment manufacturers (OEMs) are believed to use her refrigerant, HFO-1234yf, an important contribution to countering global warming.

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.

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.

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

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  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 9 "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