第一代制冷剂是CFC（氯氟烃），它们是含有氯、氟和碳原子的合成化合物。 它们的通式为 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是整数1。
最常用作制冷剂的 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. 及其在通用汽车和 Frigidaire 的同事于 20 世纪 20 年代和 1930 年代开发，作为当时使用的有毒易燃制冷剂（如氨、二氧化硫和氯甲烷）的替代品3。
CFC作为制冷剂具有许多优点，如稳定性高、毒性低、不易燃、沸点低、汽化潜热高以及与润滑油和金属相容等。 它们还广泛用于其他应用，例如气溶胶推进剂、泡沫发泡剂、溶剂和灭火器5。
然而，氟氯化碳也会对环境产生严重影响，因为它们是强效温室气体，会导致全球变暖和臭氧层消耗。 氟氯化碳可以在大气中保留数十年或数百年，当它们到达平流层时，它们会被紫外线辐射分解，释放出氯原子，从而催化臭氧分子的破坏。
保护地球免受有害紫外线辐射的臭氧层的消耗可能会造成各种负面影响，例如皮肤癌、眼白内障、免疫系统紊乱、农作物受损和海洋生物破坏等。
全球氟氯化碳的生产和消费在 20 世纪 70 年代末和 1980 年代初达到顶峰，然后由于科学证据的不断增加和公众对其环境危害的认识而开始下降。 1987年，197个国家签署了《蒙特利尔议定书》，同意在具体期限内逐步淘汰氟氯化碳和其他消耗臭氧层物质的生产和使用。
《蒙特利尔议定书》被认为是最成功的国际环境协定之一，有效减少了氟氯化碳等消耗臭氧层物质的排放，为臭氧层的恢复做出了贡献。 根据联合国最新评估，臭氧层预计到本世纪中叶将恢复到1980年的水平。
氟氯化碳的逐步淘汰还刺激了替代制冷剂的开发和采用，例如 HCFC（氢氯氟碳化合物）、HFC（氢氟碳化合物）、HFO（氢氟烯烃）和天然制冷剂（如氨、二氧化碳、碳氢化合物和水）。 这些替代品的臭氧消耗潜势较低或为零，但它们可能具有其他缺点，例如全球变暖潜势高、易燃性、毒性或效率低。
因此，制冷剂的选择和开发是一个复杂的动态过程，涉及热力学、物理、化学、安全、经济和环境等多个因素。 理想的制冷剂应该具有高性能、低环境影响、低成本和广泛的可用性。
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.
