Study On Fire-extinguishing Mechanism Of Environment-friendly Cyclic Olefins

Halon,as a high-efficiency chemical fire-extinguishing agent,is widely used in ships,aircraft,power plants and other important places.However,due to its destructive effect on the ozone layer,Halon has been clearly required to be eliminated within a limited time in recent years.Therefore,whether to develop and study a new generation of clean,efficient and low toxic fire-extinguishing medium to replace Halon as the fire-extinguishing agent in important places is one of the urgent problems to be solved in the field of fire protection in various countries.Based on the previous work of the research group,this paper studies the thermal decomposition and fire-extinguishing mechanism of cyclic olefins,improves the theory of the relationship between the molecular structure and fire-extinguishing performance of Halon substitutes,and further promotes the research on the screening of Halon substitutes.Firstly,the thermal decomposition mechanism of Octafluorocyclopentene(C5F8)and 1-Chloroheptafluorocyclopentene(C5ClF7)is studied by Gaussian package based on density functional theory(DFT).Four decomposition paths of Octafluorocyclopentene are found through calculation.It is found that the main pyrolysis products of Octafluorocyclopentene are CF3C≡CCF3 and CF3C≡CF,and the channel from Octafluorocyclopentene to CF3C≡CCF3 through IM4 is the main reaction path;At the same time,ten decomposition paths of monochloro heptafluorocyclopentene are found through calculation.It is found that the main decomposition products of 1-Chloroheptafluorocyclopentene are IM0,CF2=CFCl,CF≡CF,CF≡CCl,CF2=CF2 and CCl≡CCF3,in which the channel of 1-Chloroheptafluorocyclopentene to form IM0 is the main reaction path.Secondly,the reaction mechanism of Octafluorocyclopentene and 1-Chloroheptafluorocyclopentene and their thermal decomposition products(CF3C≡CCF3,CF3C≡CF and IM0)with active free radicals OH· and H· in flame is studied by density functional theory based on the investigation of thermal decomposition.Twelve reaction channels between Octafluorocyclopentene and OH· and seven reaction channels between Octafluorocyclopentene and H· are found through calculation,in which the channel generating the product P12a is the main reaction path;At the same time,six reaction channels between 1-Chloroheptafluorocyclopentene and OH·and seven reaction channels between 1-Chloroheptafluorocyclopentene and H·are found by calculation,among which the main reaction path is the channel generating the product P6a;In addition,seven reaction channels of the isomer IM0 of 1-Chloroheptafluorocyclopentene with OH·and eight reaction channels with H·are calculated,in which the channel generating the product P13a is the main reaction path.Finally,the fire-extinguishing concentrations of Octafluorocyclopentene and 1-Chloroheptafluorocyclopentene are measured by the cup-burner experiment.The fire-extinguishing concentrations of methane-air flame are 6.73 vol%and 5.37 vol%respectively,and the fire-extinguishing concentrations of propane-air flame are 7.74 vol%and 5.93 vol%respectively,which is equivalent to the fire-extinguishing concentration of HFCs fire-extinguishing agent,showing excellent fire-extinguishing performance,and the fire-extinguishing effect of 1-Chloroheptafluorocyclopentene is better than that of Octafluorocyclopentene.Based on the study of fire-extinguishing mechanism,it is found that 1-Chloroheptafluorocyclopentene contains Cl atoms and is asymmetric,and it has more decomposition paths and products,and more paths to capture free radicals,showing better fire-extinguishing performance,which is also verified by the experimental results.Based on the research results of thermal decomposition mechanism,fire extinguishing mechanism and characteristics,Octafluorocyclopentene and 1-Chloroheptafluorocyclopentene have excellent fire-extinguishing performance and can be used as Halon substitutes for further research.The research on the cyclic olefins with all halogen further improves the structure-activity relationship theory of Halon substitutes,which is conducive to promoting the research on the screening of Halon substitutes.