Fluorocarbons as Aerosols and Refrigerants

 
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Fluorocarbons are a class of chemicals commonly identified as organofluorine compounds. These compounds are organic and contain a carbon-fluorine bond that is represented by the formula Cx Fy. Fluorocarbons are applied in a variety of fields ranging from industrial to consumer and medical applications. More precisely, they are used for production refrigerants and air conditioning equipment, aerosols propellants, and plastic. They are applied as solvents in non-stick cookware, used in fire suppressors, as well as metered dose inhalers. As such, fluorocarbons are a part of daily human activities and their application cannot be easily avoided. Nonetheless, the chemical has attracted lots of antagonistic opinions with a particular focus on fluorocarbon as aerosols and refrigerators, and their impact on the environment and people’s health. There is need to conduct an analysis of fluorocarbons with an evaluation of their properties, industrial manufacture, application, and their effects in order to provide an informed insight on their importance.

Overview of Fluorocarbons and Their Relationship with Chlorofluorocarbons

Fluorocarbons, also known as per-fluorocarbon, are man-made organic compounds. To be more precise, they are hydrocarbons with heteroatoms, where the C-H bonds have been synthetically replaced with the C-F bonds, thereby giving rise to manmade organic chemistry (Ebnesajjad, 2013). As a result, they can be fluoroalkenes, fluoroalkynes, and flouroalkanes among other compounds. The C-H bonds have an average energy of 480 KJ/mol, which is higher than most carbons bonds, such as the C-Cl, which has an average energy of 320 KJ/mol (Ebnesajjad, 2013). Therefore, it is categorized among the strongest bonds. Additionally, the compound has different molecular weights, which allows it to exist in various state, including gas, solid, wax, and liquid forms. In conjunction with fluorocarbenes, fluoropolymers, hydrofluorocarbons, and perfluorinated compounds, fluorocarbon is referred to as organofluorines, as it contains the elements of fluorine and carbon (Koren, 2016). A fluorocarbon compound is used in combination with a variety of elements, such as hydrogen, chlorine, and bromine. For instance, and according to Koren (2016), when combined with the bromine, the fluorocarbon is referred to as a Hhalon, while when combined with hydrogen and chlorine it is referred to as hydrochlorofluorocarbon (HCFC), but when combined with only chlorine it is referred as a chlorofluorocarbon (CFC).

The main difference between fluorocarbons and chlorofluorocarbons is that the CFC is a combination of carbon, fluorine, and chlorine while a fluorocarbon is a combination of fluorine and carbon only. The chlorofluorocarbons are volatile substances and only exist in solid form as raw materials. Otherwise, they are produced as byproducts of methane and ethane with a composition of the formulas CClm F4-m and C2Clm F6-m respectively, whereby m is not equal to zero (Ibeh, 2014). Fluorocarbons differ from chlorofluorocarbons in their reactivity, while CFC’s emit chlorine gas into the atmosphere.

A deeper evaluation on the reasons behind replacement of chlorofluorocarbon despite of their wide use in the 1930s as a non-toxic and a non-flammable alternative to harmful elements, such as ammonia, revels that they resulted in the depletion of the ozone layer in the upper atmosphere. Additionally, chlorine gas produced and its compounds significantly contributed to the wearing out of the ozone. Koch (2012) asserts that this can be best outlined through the reaction of the C-Cl bond given by the formula CCl3F → CCl2F + Cl. As a result of the harmful properties of CFC’s upon reactivity, the need to replace them was inevitable. For this reason, fluorocarbons served to replace them with compounds, which would be less harmful to the environment in accordance with the Montreal Protocol.

History of Fluorocarbons

The history of fluorocarbons dates back to the end of the 18th century. The first case of hydrogen fluoride was reported by Scheele, a pharmaceutical chemist, illustrated that an acid was produced when sulfuric acid is heated with a fluorite in glass in 1771. The discovery of this acid, fluoric acid, sparked interest in chemistry due to its strangeness and as a result, Dumas and Peligot synthesized an organofluorine compound described as fluromethane (CH3F) in 1836 (Lindstrom, Strynar, & Libelo, 2011).  Further progression in this field resulted in Moissan preparing and isolating molecular elemental fluorine gas (F2) in 1886. However, the primary consideration on the foundations of the chemistry behind organofluorines is credited with Swarts, who studied simple aliphatic fluorocarbons between 1890 and 1938 (Lindstrom et al., 2011). He prepared the first CFC, Freon-12 (CF2Cl2) and various similar compounds. During the 1930’s Midgley and Henne investigated Swarts’ findings and exchange reaction mechanisms, which led to the discovery of cooling properties of CFC’s (Lindstrom et al, 2011). This gave rise to the use of these compounds are refrigerants.

Additionally, per-fluorinated compounds which constitute fully chlorinated organic compounds were developed around the same period. In this case, and according to Lindstrom et al. (2011), Lebeau and Damiens made carbon tetrafluoride (CF4). Earlier on, domestic refrigerators relied on methyl chloride and ammonia as coolants. However, in the 1930’s, dichlorodifluoromethane (CCl2F2) was discovered to be a safe gas with optimal stability, whereby its liquefied state was associated with low compressibility (Hibbs, Hoch, & Cumberland, 2016). In addition, it was inflammable. For this reason, it was adopted as a refrigerant. Moreover, the fluorocarbons were later discovered to have unique properties that enhanced their use as aerosols. In this case, they were discovered to be inert gases, implying that they could not react with the atmospheric constitutions, particularly the ozone. Besides, it was realized that these chemicals could the potential for a diversity of applications. For instance, they were used as cleaning agents and chemical reagents as in the case of monomers.

Therefore, concerns for the detrimental effects of accumulations of CFC compounds in the atmosphere to the environment led to the introduction of fluorocarbons, especially hydrofluorocarbons (HFC’s) and hydrochlorofluorocarbons (HCFC’s). Particularly, in the later years of the 20th century, HFC’s and HCFC’s have been embraced to replace the CFC’s in their use as refrigerants and aerosols (Jones, Selby, Sterling, & the Institute for Environment and Development, 2010). Therefore, fluorine chemistry has significantly evolved since then.

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Properties of Fluorocarbons

Fluorocarbons have various physical and chemical properties that facilitate their use as aerosols and refrigerants. These properties range from non-flammability, non-reactivity, and low toxicity to stability at high temperatures. The section below describes these properties in detail.

Non-Flammability

Most fluorocarbons are non-flammable in nature. It indicates that they do not support combustion and this is a favorable feature, which allows for their use in making fire extinguishers. This property is ascribed to fluorocarbons’ high heat capacity that enables them to derive heat from fire (Dinçer, Midilli, & Kucuk, 2014). They, therefore, enhance safety and have a wide range of application including theatres, stores, and tall buildings.

Non-Reactivity

One important chemical property of fluorocarbons is that they are inert. Considering that they have elevated cracking temperatures of above 400°C, they are not affected by either oxidizing or reducing agents. Additionally, the high electronegative characteristic of fluorine minimizes the fluorocarbon’s polarity (Dinçer et al., 2014), which makes it unreactive. Additionally, fluorocarbons are neither affected by highly concentrated acid nor they are hydrolyzed by undiluted alkalis. Therefore, fluorocarbons are unreactive to several chemical compounds. As a result, they can be efficiently used as aerosols and refrigerants.

Toxicity

Fluorocarbons are characterized by lower toxicity compared to other halogen compounds, such as bromine and chlorine. Taking into account that toxicity increases with a corresponding increase in the mass number of the halogen atoms, fluorocarbons exhibit less-toxic properties (Dinçer et al., 2014). This low toxicity property facilitates their application as aerosols and other sprays since they cause fewer negative effect on the ozone layer.

Stability at High Temperatures

The melting and boiling points of fluorocarbons are similar with those of the hydrocarbon analogues. Particularly, their polymers have strong bonds that facilitate the withstanding of very high temperatures. In addition, fluorocarbons can only be decomposed, when mixed with potassium or sodium under the temperatures above 500°C (Dinçer et al., 2014). The implication is that fluorocarbons are very stable at high temperatures due to their inability to be decomposed.

Industrial Manufacture of Fluorocarbons

Due to their synthetic nature, fluorocarbons can be manufactured industrially through various processes. For example, a hydrocarbon can directly react with active metal fluorides to generate a fluorocarbon. In addition, the hydrogen exchange method can be used to prepare a fluorocarbon, whereby a halogen, for example chlorine, is replaced by fluorine under special conditions. These two methods are discussed in detail in the section below.

The Fowler Process

This process entails substituting the hydrogen element from a hydrocarbon in a reaction with an active metal fluoride of silver, lead, or cobalt. The reaction occurs as illustrated in the following chemical equations, whereby cobalt fluoride is used as the active metal fluoride:

  1. 2CoF2 + F2 → 2CoF3
  2. RH + 2CoF3 → RF + 2CoF2 + H

In this case, R represents the hydrocarbon chain. This reaction occurs in two steps. First, fluorine is passed through the metal salt at high temperatures to generate the active metal fluoride as depicted in the first equation (Koch, 2012). Secondly, the starting material is passed over the fluoride at high temperatures to facilitate fluorination as shown in the second equation. The heat generated for each C-F bond formed is 46 k cal/mol, which implies that high yield is realized considering that a lot of heat results in low yield of the fluorocarbon. It is imperative to note that the reactivity of the active metal fluorides is ascribed to the oxidation potentials of their metal ions. Therefore, the highest form of reactivity is experienced by the active metal fluoride with the highest potential. For instance, the effectiveness of fluorination is higher, when lead fluoride is used instead of cobalt fluoride (Koch, 2012). It is because the lead ion (Pb2+) has a higher oxidation potential in the electrochemical series compared to the cobalt ion (Co2+). The Fowler process of preparing fluorocarbons usually yields saturated fluorocarbons. Other than active metal fluorides, it can also be instrumental in fluorinating polychlorohydrocarbons, whereby fluorine replaces hydrogen and chlorine. This method is, therefore, useful in preparing fluorocarbons from polychlorohydrocarbons and hydrocarbons by reacting them with active metal fluorides.

The Halogen Exchange Method

Another method of preparing fluorocarbons involves replacing chlorine with fluorine, particularly when preparing aliphatic fluorocarbons. The primary commercial reagent used, in this case, is a fluoride of antimony. For example, antimony trifluoride reacts with other compounds of carbon with the general structural formulas of RCX2R and RCX3, where R represents hydrogen or an alkyl group, while X denotes a halogen. It is imperative to consider that the fluoride of antimony cannot replace a single atom of a halogen bound to carbon or radical (Ibeh, 2014). In this case, a more effective and useful reagent is generated from the pentavalent antimony chloride, as in the fluorination of chloroform illustrated in the following equations:

  1. SbCl5 + 3HF → SbCl2F3 + 3HCl
  2. SbCl2F3 + CHCl3 → SbCl4F + CHClF2
  3. SbCl4F + 2HF → SbCl2F3 + 2HCl

These reactions ensure that there is a continuous regeneration of the fluorination agent. Other than the agents prepared from the pentavalent antimony chloride, other inorganic fluorides such as sodium chloride and potassium chloride are more effective in preparation of fluorocarbons using the halogen exchange method. For instance, potassium fluoride can replace vinyl chloride under conditions such as the presence of a polar medium. In this case, sulfones and amides are the examples of suitable polar media (Ibeh, 2014). However, metal halides, such as those of mercury and lead, hinder halogen exchange, when used as reagents. Additionally, they fluorinate the unsaturated bonds in halogenated olefins. Consequently, mercury fluoride and lead fluoride are ineffective when used as reagents in the preparation of fluorocarbons in the halogen exchange method.

Considering that the fluoride ion (F) exhibits strong nucleophilic properties in many reactions, it can interact with fluoro-olefins to facilitate reversible addition, thereby generating a fluorocarbanion. This fluorocarbanion may acquire a proton from the solvent to form an additional hydrogen fluoride product. Therefore, the halogen exchange method is an effective industrial process of manufacturing fluorocarbons, particularly those with aliphatic properties.

Fluorocarbons as Aerosols and Refrigerants

The properties of fluorocarbons discussed above associate them with characteristics that are favorable for their wide application. For instance, they can be used as fire extinguishers, in aerosols, and refrigerants. Their use as aerosols and refrigerants is described in detail in the following section.

Fluorocarbons as Aerosols

Fluorocarbons are used in a myriad of aerosols, owing to their compressible capacities and environment-friendly nature. Aerosol sprays facilitate a dispensing system, whereby the fluorocarbons are mixed with other compounds to form a mist of liquid particles under high pressure (Elges, 2017). These sprays are contained in a can with a payload, propeller, and a valve. Aerosols have a wide range of applications. For instance, they are used in insecticide sprays, whereby they are mixed with chemical compounds that are toxic to insects. Additionally, they are used to make inhalants, for example epinephrine, which are important for enhancing relaxation of the respiratory tract muscles upon irritations and related problems, which facilitates clearing of the airway (Elges, 2017). Moreover, aerosols are also used to make body sprays and colognes, whereby fluorocarbons are mixed with scented components in aerosol cans. These sprays are important in maintaining an appealing body fragrance.

Fluorocarbons as Refrigerants

Apart from making aerosols, fluorocarbons are also used in making refrigerants. Considering that they are non-flammable, non-toxic, thermodynamic, and less corrosive, fluorocarbons have been used widely as ideal refrigerants (Elges, 2017). In this case, they are applied in making freezers, refrigerators, and air conditioners. The fluorocarbon’s properties of high vaporization heat and low boiling points enhances their use as refrigerants in numerous industries apart from domestic purposes.

Effects of Fluorocarbons

In as much as the fluorocarbons exhibit favorable properties that enable them to be used as environmental-friendly refrigerants and aerosols, they are associated with various effects to the world population. The section below describes these effects in detail.

Damage to the Immune System

Fluorocarbons were shown to affect the immune system, particularly in children, whereby they weaken their immune responses to certain infectious agents. According to Grandjean et al. (2012), a research carried out on children, who had been exposed to perfluorinated compounds, displayed significant effects on their immunity against various diseases. For instance, the participants were unable to respond to tetanus and diphtheria inoculations. This, therefore, creates concern for the use of fluorocarbons as aerosols and refrigerants, since widespread applications may result in hazardous effects on the world population by damaging the immune system, which makes it unable to respond to diseases that are detrimental to human health.

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Perfluorinated compounds also pose cancerous health risks due to their polluting effect on the atmosphere. According to Bonefeld-Jorgesen et al. (2011), a case control study on individuals in Greenlandic Inuit revealed that fluorocarbons have a negative effect on human health, as they pose harmful effects, which can finally result in breast cancer. The implication is that the compounds of fluorocarbons are harmful for human health in the context of posing cancer-related risks.

Decreased Fertility in Women

The use of fluorocarbons in making aerosols and refrigerants has also impacted remarkably the world health, particularly in women, by decreasing their fertility rates. Fel et al. (2009) discuss a case, when women predisposed to compounds of fluorocarbons, experienced decline in fertility, which indicated declined levels of human reproduction capacities. According to the study, the quantities of the fluorocarbon compounds in blood of these women were proportional to the decline in the level of fertility (Fel et al., 2009). In this case, those with higher levels of fluorocarbon blood concentration showed delayed in conception. Therefore, fluorocarbons can contribute to risks associated with decreased fertility in women.

Conclusion

Fluorocarbons are chemical compounds, which consist of fluorine and carbon as the only elements components. These substances are synthetic and they were developed due to the need to replace the harmful CFC’s, which are environmentally-unfriendly by depleting the ozone layer. Perfluorocarbons differ from chlorofluorocarbons by the absence of the chlorine element in their structural composition, which forms the basis for their difference in chemical properties as discussed. The history of fluorocarbons reveals notable figures, who participated in the synthesis of these compounds. For instance, Swarts is credited for synthesizing Freon-12, while Lebleau and Damiens have contributed by forming tetrafluoride. As noted, fluorocarbons have various properties that facilitate their application as aerosols and refrigerants. These include their inflammability, inertness, low toxicity, and stability at high temperatures. Moreover, the Fowler process and the halogen exchange method have been described as some ways of manufacturing fluorocarbons. Besides, the uses of fluorocarbons as aerosols and refrigerants have been evaluated including their effects on human health.