Difluoromethane

Overview

Difluoromethane, also called HFC-32 or R-32, is an organic compound of the dihalogenoalkane variety. It is based on methane, except that two of the four hydrogen atoms have been replaced by fluorine atoms, hence the formula is CH2F2 instead of CH4 for normal methane.

With its remarkable thermodynamic properties, difluoromethane is commonly used as a coolant and is an ideal substitute for the second generation of ODS. The ODP (Ozone Depletion Potential) of difluoromethane is 0, and its GWP (Global Warming Potential) is 0.12. It is a colorless, odorless gas under normal temperature and pressure. It can be easily compressed into colorless and transparent liquid. It is nontoxic, non-flammable, soluble in oil, insoluble in water. It is used usually with other HFC products in the mixture working medium such as R407 and R410 according to the different content of components.

Physical and Chemical Properties

Physical State: Colorless transparent odorless liquefied gas.
Density:  0.961 at 25 deg C; 1.052 at 0 deg C (liquid)
Melting point：−136 °C (−213 °F; 137 K)
Boiling point：−52 °C (−62 °F; 221 K)
Solubility：In water, 1.285X10+4 mg/L at 25 deg C (est)
In water, 0.44% at 25 deg C
Soluble in ethanol
Vapor Pressure：1.26X10+4 mm Hg at 25 deg C
Difluoromethane is a colorless odorless gas. Insoluble in water and has a high thermal stability. Its vapors are heavier than air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Contact with the unconfined liquid can cause frostbite. Used as a refrigerant.

Toxicological Information

Human exposure and toxicity: There are no data available.
Animal studies: Acute inhalation toxicity on rats，LC：>52pph /4H, on mice, LC50：1810mg/m3.
 HFC32 is slightly maternally and developmentally toxic at 50,000 ppm in rats(inhalation), but not in rabbits. No evidence of teratogenicity was noted in rats or rabbits.

Halohydrocarbons

CFCs, shortly for chlorofluorocarbons, are considered to be the main substances that destroy the atmospheric ozone layer and produce global warming effects. The international community has decided to ban the use of CFCs. In several alternatives, fluorocarbons (HFCs or HCFCs) are the preferred alternatives.
(HFC-32) is one of the components of mixed refrigerants. It is a freon substitute with excellent thermodynamic performance. It has lower boiling point (-51.6 ℃), lower pressure ratio and high refrigeration coefficient, with ODP of 0 and low GWP.

Application

• Refrigerant, as substitute for R-502, or used respectively with HFC-134a,HFC-152a to form mixed refrigerants in replace of HCFC-22.
• Dry etching agent.

Synthesis

The synthesis of difluoromethane mainly includes dichloromethane fluorination method, hydrochloroflurocarbon hydrogenolysis reduction method, formaldehyde fluorination method, trioxane method.
In dichloromethane fluorination method, dichloromethane react with HF or KF. When KF is used, ω-fluorine, chlorine, hydrogen-3-oxa-polyfluoroalkyl sulfonyl fluoride or sulfonyl chloride will be needed as a catalyst, and the synthesis will become lack of versatility. So HF is usually chosen to react with dichloromethane in the industry synthesis.
The main reaction formulas in dichloromethane fluorination method:

According to the phase where the reactions take place, difluoromethane fluorination method is divided into liquid phase fluorination, gas phase fluorination and sectionally continuous fluorination method.
Liquid phase method: The process parameters for the synthesis of difluoromethane in liquid phase are as follows: the reaction pressure is 1~10 kg/cm2 in the presence of hydrogen fluoride and fluorination catalyst, the reaction temperature is 50~150 ℃ (the selected temperature at which the hydrogen fluoride is not liquefied). It is characterized in that in the reactor, the HF is essentially in gaseous form and the CH2 Cl2 is in excess and mainly in the liquid phase. The catalyst used is SbClXFy (x + y = 5, y = 1 to 4, preferably y = 2 to 3). The fluorination catalyst is used in an amount such that the molar content of the catalyst in the liquid reaction mixture is from 10% to 90%. At 10% or less, the residence time of the reaction gas is long, the impurities of the R40 are generated in large amount and the yield is lowered. In the case of 90% or more, due to the small amount of organic substances in the reactor, and the amount of catalyst entrained in the atomization is large enough to jam the piping. Above all, the concentration is preferably 40 to 70%.
Gas phase fluorination method uses gaseous chloralkane (such as CH2Cl2, CF3CH2Cl and CH3CCl3, etc.) or olefins (Cl2C = CCl2 and Cl2C = CHCl, etc.) and anhydrous HF as raw materials in fixed bed reactor. Hydrofluoroalkane  are prepared on the surface of the catalyst by fluorine-chlorine exchange reaction using solid particles of oxides, fluorides or oxyfluorides of Cr and other additives as catalysts.
Sectional continuous fluorination process: The first stage is a gas phase reaction in which HF reacts with difluoromethane in the presence of a composite catalyst consisting of chloride, hydroxide oxide or fluoride of Al and Cr. The second stage is a liquid phase reaction in which the product from the first stage is directly introduced into the liquid phase reactor in the presence of the chlorides of Sb or their mixture with Sn chlorides as catalyst. The method has a long process pipeline, and has the problems of low utilization rate of raw materials and high energy consumption.

Health Hazard

Excerpt from ERG Guide 115 [Gases-Flammable (Including Refrigerated Liquids)]: Vapors may cause dizziness or asphyxiation without warning. Some may be irritating if inhaled at high concentrations. Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite. Fire may produce irritating and/or toxic gases. (ERG, 2016)

Fire Hazard

Excerpt from ERG Guide 115 [Gases-Flammable (Including Refrigerated Liquids)]: EXTREMELY FLAMMABLE. Will be easily ignited by heat, sparks or flames. Will form explosive mixtures with air. Vapors from liquefied gas are initially heavier than air and spread along ground. CAUTION: Hydrogen (UN1049), Deuterium (UN1957), Hydrogen, refrigerated liquid (UN1966) and Methane (UN1971) are lighter than air and will rise. Hydrogen and Deuterium fires are difficult to detect since they burn with an invisible flame. Use an alternate method of detection (thermal camera, broom handle, etc.) Vapors may travel to source of ignition and flash back. Cylinders exposed to fire may vent and release flammable gas through pressure relief devices. Containers may explode when heated. Ruptured cylinders may rocket. (ERG, 2016)

Chemical Properties

Difluoromethane is a colorless and flammable gas that has a light ethereal odor with poor warning properties.

Uses

Difluoromethane is use as refrigerant, as an important component in some refrigeration mixtures, and as a reactive ion etching gas in semiconductor materials processing applications.

Preparation

Difluoromethane(HFC-32) is manufactured in closed systems. Possible routes are hydrodechlorination of chlorodifluoromethane (HCFC-22) and hydrofluorination of dichloromethane.

Definition

ChEBI: Difluoromethane is a member of fluoromethanes. It has a role as a refrigerant.

General Description

A colorless odorless gas. Insoluble in water and has a high thermal stability. Its vapors are heavier than air. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Contact with the unconfined liquid can cause frostbite. Used as a refrigerant.

Air & Water Reactions

Highly flammable. Insoluble in water. Easily ignited by heat, sparks or flames. Forms explosive mixtures with air

Reactivity Profile

Difluoromethane can react with some metals to form dangerous products. May react violently with aluminum. Incompatible with strong oxidizing and reducing agents. Also incompatible with many amines, nitrides, azo/diazo compounds, alkali metals, and epoxides.

Health Hazard

Vapors may cause dizziness or asphyxiation without warning. Some may be irritating if inhaled at high concentrations. Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite. Fire may produce irritating and/or toxic gases.

Fire Hazard

EXTREMELY FLAMMABLE. Will be easily ignited by heat, sparks or flames. Will form explosive mixtures with air. Vapors from liquefied gas are initially heavier than air and spread along ground. CAUTION: Hydrogen (UN1049), Deuterium (UN1957), Hydrogen, refrigerated liquid (UN1966) and Methane (UN1971) are lighter than air and will rise. Hydrogen and Deuterium fires are difficult to detect since they burn with an invisible flame. Use an alternate method of detection (thermal camera, broom handle, etc.) Vapors may travel to source of ignition and flash back. Cylinders exposed to fire may vent and release flammable gas through pressure relief devices. Containers may explode when heated. Ruptured cylinders may rocket.