Hydrofluorocarbons HFCs in Modern Chemistry

Before starting with the HFC meaning, let us discuss the HFC full form. HFC full form is hydrofluorocarbons. HFC is a type of halocarbons. These molecules are carbon-based molecules that have chlorine, fluorine, or bromine in them. In these molecules, the carbon to fluorine bonds oscillate and hence absorb, the wavelengths around the 9 micrometres. HFC gas is environmentally important not only because they contribute to global warming but also because chlorine and bromine atoms that find their way into the stratosphere have the ability to destroy ozone catalytically. The HFCs meaning represents that it is made up of hydrogen, fluorine, and carbon atoms.

Hydrofluorocarbons are the subcategories of halocarbons. These molecules are like CFCs but do contain hydrogen. HFC gas differs from all of the other radiatively active gases in that they do not occur naturally and their presence in the atmosphere is due entirely to human activities. Other important halocarbons include carbon tetrachloride (CCl₄), methyl chloroform (CH₃CCl₃), and methyl bromide (CH₃ Br). 

HFC Greenhouse Gas Composition

Hydrofluorocarbons (HFCs) gas molecules do not contain any chlorine atoms. So they are even better than HCFCs. In terms of stratospheric ozone depletion protection HFCs are better than the other halocarbons like HCFCs and CFCs. The hydrofluorocarbons CH₂FCF₃ is quickly becoming the refrigerant of choice for automobile air conditioners and refrigeration equipment. Even this chemical, however, has a sizable atmospheric lifetime. The atmospheric lifetime of the HFCs is 14.6 years, which contributes to its rather significant global warming potential. 

Halocarbon Numbering System

The HFCs are identified by a simple numerical designation as well as a chemical formula. The HFCs are referred to using a number system developed years ago by DuPont. For example, trichlorofluoromethane, CFCl₃ is CFC-11, and the hydrochlorofluorocarbon CHF₂Cl is HCFC-22. 

To determine the chemical formula from a fluorocarbon number, begin by adding 90 to the number and then interpret the three-digit result as follows: the leftmost digit is the number of carbon atoms, the middle digit is the number of hydrogen atoms, and the right digit is the number of fluorine.

To determine the number of chlorine atoms, begin by visualising molecules in which each carbon atom forms four single bonds to other atoms (if the other atoms are all hydrogens, this is the familiar alkane series: methane, ethane, and propane). A single carbon atom has four sites to fill, two carbon atoms have six sites, and so forth. All of the sites will be occupied by hydrogen, fluorine, or chlorine. So, to find the number of chlorines, just subtract the number of hydrogens and fluorine, or chlorine. 

For example, to figure out what CFC-12 is, add 90 to 12, giving 102. So, there is one carbon, no hydrogens, and two fluorines. With one carbon there are four sites available, two of which are taken by fluorine, leaving two for chlorine. Thus CFC-12 is CF₂Cl₂. The halones also have a number system, but this one is not so complicated. Halones are given a four-digit designation, with the leftmost digit being the number of carbons. The second is fluorine, the third is chlorines, and the fourth is bromine. For example, H-1211 is CF₂ClBr.

Radiative Forcing of the Halocarbons

The total direct radiative forcing associated with halocarbons since the preindustrial period is 0.28 W/m². This contribution is 11 percent of the direct forcings of the greenhouse gases (carbon dioxide, methane, nitrous oxide, and halocarbons). Of that amount, CFC-11 is responsible for about 0.06 W/m², CFC-12 contributes 0.14 W/m2, and most of the remaining 0.08 W/m2 is associated with carbon tetrachloride (CCl₄), hydrochlorofluorocarbons (HCFC-22), and chlorofluorocarbons (CFC-113). These data are for the direct radiative forcing, which is positive and do not include the negative forcing that results from the indirect greenhouse gas effect of halocarbons.

Since HFCs induce the loss of ozone in the lower stratosphere, and ozone is a greenhouse gas, the net forcing of HFCs is reduced by about 0.1 W/m².

Structure of HFCs

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The above structure of HFCs represents the bonds between carbon, fluorine, and hydrogen atoms. The structure hydrofluorocarbons show that the HFC is made up of three elements. These three elements are hydrogen, carbon, and fluorine atoms. These atoms are attached to each other by the covalent bonds. Only single (sigma) bonds are present in the CFCs molecule. No double bond (pi bond) is formed between any atoms. 

Properties of  Hydrofluorocarbons (HFCs)

• Hydrofluorocarbons are used as refrigerants nowadays. A refrigerant is a substance or mixture, usually a fluid. HFCs are used in a refrigeration cycle. In most cycles, it undergoes phase transitions from a liquid to a gas and back again.

Refrigerant Chemical Composition

The refrigerant chemical composition is given below:

Carbon (C)

Hydrogen (H)

Chlorine (Cl)

Fluorine (F)

• These molecules exist in both forms (azeotropic refrigerants and zeotropic refrigerants). Azeotropic refrigerants are the mixture of two or more refrigerants whose vapour and liquid phases retain identical compositions over a wide range of temperature. In a zeotropic mixture, the composition in the liquid phase differs from that of the vapour phase. These mixtures do not boil at a constant temperature.

• HFC gas contains hydrogen (H), Fluorine (F), and Carbon (C). These gases are used extensively in everyday systems.

• There is no current ban upon these games, due to their composition and stability. But the responsible use and equipment inspection are mandatory.

• The HFC refrigerant gases have no ozone depletion potential. Some examples of HFC are R410A and R134.

• These gases do not contain chlorine in their composition. Therefore, making it safer for the environment and is now being used in place of R22.

Replacement of CFCs with HFCs

Until recently, most refrigerators, freezers, and automobile air conditioners used CFC-12 as the refrigerant, and large building air conditioning systems tended to use CFC-11. CFC refrigerants do not wear out, so as long as they are sealed into equipment the total emission rate can be small. Automobile air conditioners, however, tend to develop leaks that necessitate periodic recharging of their systems. In the recent past, when car air conditioners were serviced, the old refrigerant was usually vented to the atmosphere rather than being captured and recycled, which compounded the loss rate. 

As a result, automobile air conditioners used to contribute on the order of 20 percent of all emissions of CFCs in the United States. The Montreal Protocol and subsequent changes in the Clean Air Act have changed that picture significantly. Production and importation of CFCs ended in 1996, and air conditioners on new cars now tend to use HFC-134a, which contains no chlorine. Only licensed facilities that use CFC recycling equipment can service older automobile air conditioners.  

Environmental Regulation For the Ozone Layer Protection

Hydrofluorocarbons are used in other international agreements, unlike other greenhouse gases in the Paris Agreement. The New York Declaration on Forests, issued in September 2016, called for a global reduction in the use of HFCs. Due to the contribution of these chemicals to climate change, delegates from 197 countries met at a United Nations Environment Programme summit in Kigali, Rwanda on October 15, 2016, and reached a legally binding agreement (the Kigali Amendment) to phase out hydrofluorocarbons (HFCs) in an amendment to the Montreal Protocol. The Kigali Agreement has yet to be ratified by the United States. As of February 2020, 16 states in the United States have banned or are phasing out HFCs.

On December 21, 2020, the United States House of Representatives and Senate passed COVID-19 relief legislation, which included a provision requiring chemical manufacturers to phase out the production and use of HFCs.

Consequences of HFCs to the Environment

The earth's protective ozone layer is destroyed by chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons, which shield the earth from harmful ultraviolet (UV-B) rays emitted by the sun. CFCs and HCFCs also warm the earth's lower atmosphere, causing global climate change. Hydrofluorocarbons (HFCs) also contribute to global warming. The Minnesota Pollution Control Agency (MPCA) is collaborating with industry, citizens, and government to reduce the harm that CFCs, HCFCs, HFCs, and related chemicals cause to the ozone layer and global environment.

Did You Know?

• HFCs are the fastest-growing greenhouse gases in most of the world, with annual increases of 10-15%.

• These are man-made gases that were once thought to be sufficient to replace ozone-depleting substances but are no longer used in most industries, such as air conditioning, refrigeration, and foam insulation.

• HFCs are extremely strong greenhouse gases that trap thousands of times more heat per unit of mass in the atmosphere than CO₂. The most abundant and fastest-growing HFC is HFC-134a, which has a 13.4-year atmospheric lifespan and a GWP of 1,300.

• Though HFCs have contributed to just 1% of total global warming to date, their output, use, and emissions are increasing at a rate of 10-15% per year. Global HFC emissions could exceed 8.8 Gt CO2-eq by 2050, approximately equal to the combined carbon emissions of the United States and the European Union.

• By 2050, the HFC amendment could save about 100 Gt CO2-eq, and by 2100, it could save up to 0.5°C.