Difluoromethane

Difluoromethane, also called HFC-32 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.[1]

Difluoromethane
Difluoromethane-2D-skeletal
Spacefill model of difluoromethane
Names
Systematic IUPAC name
Difluoromethane[1]
Other names
Carbon fluoride hydride

Methylene difluoride
Methylene fluoride

Freon-32
Identifiers
3D model (JSmol)
Abbreviations HFC-32

R-32
FC-32

1730795
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.764
EC Number
  • 200-839-4
259463
MeSH Difluoromethane
RTECS number
  • PA8537500
UNII
UN number 3252
Properties
CH2F2
Molar mass 52.024 g·mol−1
Appearance Colorless 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
Safety data sheet See: data page
MSDS at Oxford University
R-phrases (outdated) R11
S-phrases (outdated) S9, S16, S33
NFPA 704 (fire diamond)
Flammability code 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. propaneHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
4
1
0
648 °C (1,198 °F; 921 K)
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Uses
Atmospheric concentration of difluoromethane at various latitudes since year 2009.

Difluoromethane is a molecule used as refrigerant that has excellent heat transfer and pressure drop performance, both in condensation and vaporisation.[2] It has a 100-year global warming potential (GWP) of 675 times that of carbon dioxide, and an atmospheric lifetime of nearly 5 years.[3] It is classified as A2L - slightly flammable by ASHRAE,[4] and has zero ozone depletion potential (ODP).[5] Difluoromethane is thus a relatively low-risk choice among HFC refrigerants, most of which have higher GWP and longer persistence when leaks occur.

Difluoromethane in a zeotropic (50/50 mass%) mixture with pentafluoroethane (R-125) is known as R-410A, a common replacement for various chlorofluorocarbons (aka 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 with chlorotrifluoromethane (R13).

Difluoromethane is currently used 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.[6] 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.[7]

Environmental Fate

Difluoromethane gas will degrade in the atmosphere by reaction with photochemically-produced hydroxyl radicals. This process will form carbonyl difluoride.[1] The half-life for this process is estimated to be 4 years.

References
  1. "Difluoromethane - Compound Summary". The PubChem Project. USA: National Center of Biotechnological Information.
  2. 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.
  3. May 2010 TEAP XXI/9 Task Force Report
  4. 2009 ASHRAE Handbook
  5. "R32".
  6. 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.
  7. 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.
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