Difluoromethane

Synthesis

Difluoromethane is produced by the reaction of dichloromethane and hydrogen fluoride (HF) using SbF5 as a catalyst. :

Applications

Difluoromethane is used as refrigerant that has prominent heat transfer and pressure drop performance, both in condensation and vaporization.

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. 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.

Other uses of difluoromethane include its use as aerosol propellant and blowing agent.

Environmental effects

The global warming potential (GWP) of HFC-32 is estimated at 677 on a 100-year time window. This is lower than the GWP for HFC refrigerants that it is replacing, but remains sufficiently high to spur continued research into using lower-GWP refrigerants.

Difluoromethane is excluded from the 1963 list of VOCs restricted by the United States Clean Air Act due to the ODP being zero.

European Union phase-out

In order to reduce greenhouse gas emissions, the European Union passed a law aiming at phasing out several high-GWP hydrofluorocarbon refrigerants, including R-32. Sale of R-32-based domestic refrigerators are banned from 1 January 2026, and air conditioners and heat pumps from 2027 to 2030, depending on capacity and equipment type.

Replacements being considered arehttps://www.daikin.eu/en_us/press-releases/an-outlook-from-daikin-on-refrigerant-alternatives-in-europe.html:

• R-290 (propane) – highly flammable and not suitable for many residential installation. Manufacturers are also trying to restrict DIY installations of it, which increases costs.
• R-454C – a mix of 21.5 percent R-32 and 78.5 percent R1234yf. This is under the GWP limit of 150, but has a worse COPhttps://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=3481&context=iracc. Additionally R1234yf can decompose into the highly toxic forever chemical TFA.
• R-744 (carbon dioxide) – engineering challenges remain because the cost is too high for residential use.

References

References

1. "Difluoromethane – Compound Summary". National Center of Biotechnological Information.
2. "Regulation (EU) 2024/573 of the European Parliament and of the Council of 7 February 2024 on fluorinated greenhouse gases".
3. (2000). "Ullmann's Encyclopedia of Industrial Chemistry".
4. (2015). "HFC32 vaporisation inside a Brazed Plate Heat Exchanger (BPHE): Experimental measurements and IR thermography analysis". International Journal of Refrigeration.
5. (2016). "HFC32 and HFC410A flow boiling inside a 4 mm horizontal smooth tube". International Journal of Refrigeration.
6. (2018). "The development of environmentally acceptable fluorocarbons". Critical Reviews in Toxicology.