第一代制冷劑是CFC（氯氟烴），它們是含有氯、氟和碳原子的合成化合物。 它們的通式為 C<sub>n</sub>F<sub>2n+2</sub> 或 C<sub>n</sub>Cl<sub>x</sub>F<sub>2n +2-x</sub>，其中n和x是整數1。
最常用作制冷劑的 CFC 是 R11（三氯氟甲烷）、R12（二氯二氟甲烷）、R13（三氟氯甲烷）、R113（1,1,2-三氯-1,2,2-三氟乙烷）、R114（1,2-二氯- 1,1,2,2-四氟乙烷）和 R115（氯五氟乙烷）2。
CFC 最初由 Thomas Midgley Jr. 及其在通用汽車和 Frigidaire 的同事于 20 世紀 20 年代和 1930 年代開發，作為當時使用的有毒易燃制冷劑（如氨、二氧化硫和氯甲烷）的替代品3。
CFC作為制冷劑具有許多優點，如穩定性高、毒性低、不易燃、沸點低、汽化潛熱高以及與潤滑油和金屬相容等。 它們還廣泛用于其他應用，例如氣溶膠推進劑、泡沫發泡劑、溶劑和滅火器5。
然而，氟氯化碳也會對環境產生嚴重影響，因為它們是強效溫室氣體，會導致全球變暖和臭氧層消耗。 氟氯化碳可以在大氣中保留數十年或數百年，當它們到達平流層時，它們會被紫外線輻射分解，釋放出氯原子，從而催化臭氧分子的破壞。
保護地球免受有害紫外線輻射的臭氧層的消耗可能會造成各種負面影響，例如皮膚癌、眼白內障、免疫系統紊亂、農作物受損和海洋生物破壞等。
全球氟氯化碳的生產和消費在 20 世紀 70 年代末和 1980 年代初達到頂峰，然后由于科學證據的不斷增加和公眾對其環境危害的認識而開始下降。 1987年，197個國家簽署了《蒙特利爾議定書》，同意在具體期限內逐步淘汰氟氯化碳和其他消耗臭氧層物質的生產和使用。
《蒙特利爾議定書》被認為是最成功的國際環境協定之一，有效減少了氟氯化碳等消耗臭氧層物質的排放，為臭氧層的恢復做出了貢獻。 根據聯合國最新評估，臭氧層預計到本世紀中葉將恢復到1980年的水平。
氟氯化碳的逐步淘汰還刺激了替代制冷劑的開發和采用，例如 HCFC（氫氯氟碳化合物）、HFC（氫氟碳化合物）、HFO（氫氟烯烴）和天然制冷劑（如氨、二氧化碳、碳氫化合物和水）。 這些替代品的臭氧消耗潛勢較低或為零，但它們可能具有其他缺點，例如全球變暖潛勢高、易燃性、毒性或效率低。
因此，制冷劑的選擇和開發是一個復雜的動態過程，涉及熱力學、物理、化學、安全、經濟和環境等多個因素。 理想的制冷劑應該具有高性能、低環境影響、低成本和廣泛的可用性。
The first generation of refrigerants are CFCs (chlorofluorocarbons), which are synthetic compounds that contain chlorine, fluorine and carbon atoms. They have the general formula of C<sub>n</sub>F<sub>2n+2</sub> or C<sub>n</sub>Cl<sub>x</sub>F<sub>2n+2-x</sub>, where n and x are integers1.
The most common CFCs used as refrigerants are R11 (trichlorofluoromethane), R12 (dichlorodifluoromethane), R13 (chlorotrifluoromethane), R113 (1,1,2-trichloro-1,2,2-trifluoroethane), R114 (1,2-dichloro-1,1,2,2-tetrafluoroethane) and R115 (chloropentafluoroethane)2.
CFCs were first developed in the 1920s and 1930s by Thomas Midgley Jr. and his colleagues at General Motors and Frigidaire as alternatives to the toxic and flammable refrigerants used at that time, such as ammonia, sulfur dioxide and methyl chloride3.
CFCs have many advantages as refrigerants, such as high stability, low toxicity, non-flammability, low boiling point, high latent heat of vaporization and compatibility with lubricants and metals4. They are also widely used in other applications, such as aerosol propellants, foam blowing agents, solvents and fire extinguishers5.
However, CFCs also have serious environmental impacts, as they are potent greenhouse gases that contribute to global warming and ozone depletion. CFCs can remain in the atmosphere for decades or centuries, and when they reach the stratosphere, they are broken down by ultraviolet radiation, releasing chlorine atoms that catalyze the destruction of ozone molecules.
The depletion of the ozone layer, which protects the Earth from harmful ultraviolet radiation, can cause various negative effects, such as increased skin cancer, eye cataracts, immune system disorders, crop damage and marine life disruption.
The global production and consumption of CFCs peaked in the late 1970s and early 1980s, and then began to decline due to the growing scientific evidence and public awareness of their environmental hazards. In 1987, the Montreal Protocol was signed by 197 countries, which agreed to phase out the production and use of CFCs and other ozone-depleting substances by specific deadlines.
The Montreal Protocol is considered one of the most successful international environmental agreements, as it has effectively reduced the emissions of CFCs and other ozone-depleting substances, and has contributed to the recovery of the ozone layer. According to the latest assessment by the United Nations, the ozone layer is expected to return to its 1980 levels by the middle of this century.
The phase-out of CFCs has also stimulated the development and adoption of alternative refrigerants, such as HCFCs (hydrochlorofluorocarbons), HFCs (hydrofluorocarbons), HFOs (hydrofluoroolefins) and natural refrigerants (such as ammonia, carbon dioxide, hydrocarbons and water). These alternatives have lower or zero ozone depletion potential, but they may have other drawbacks, such as high global warming potential, flammability, toxicity or low efficiency.
Therefore, the selection and development of refrigerants is a complex and dynamic process that involves multiple factors, such as thermodynamic, physical, chemical, safety, economic and environmental aspects. The ideal refrigerant should have high performance, low environmental impact, low cost and wide availability.
