On Degradation And Resource Utilization Of SF₆ And Other Fluorinated Gases

Since the industrial revolution,the increasing human production capacity has led to the continuous growth of various greenhouse gas emissions.Due to its extremely long lifetime（3200 y）and high GWP（GWP=23900）,sulfur hexafluoride（SF₆）has become one of the greenhouse gases restricted by the Kyoto Protocol.It has excellent insulation and arc extinguishing properties and is widely used in electrical equipment,magnesium smelting,semiconductor manufacturing and other industries.According to statistics,the annual worldwide emissions of SF₆ are 9.04±0.35 Gg y^-1,which is equivalent to 200million tons of CO₂ emissions,therefore,it is urgent to reduce the SF₆ emissions.Firstly,the mechanochemical reaction products and reaction mechanism between graphite and SF₆ were investigated and a new method for the mechanochemical degradation of SF₆ was developed.The method avoids the high temperature conditions of the conventional thermal degradation process,as well as the harmful HF by-products,while also converting graphite into the high-value chemical sulfur-containing fluorinated graphite material（SFGCM）.The degradation under different ball milling conditions was investigated.The higher the rotational speed,the higher the ball-to-material ratio and the longer the reaction time,the better the degradation of SF₆ and the maximum unit degradation of graphite of 0.95 g/（g graphite）could be achieved.At the same time,the free radical mechanism of the mechanochemical reaction between SF₆and graphite was elucidated.It is shown that SFGCM is a novel fluorinated graphite with abundant functional groups,multi-atom doping and good thermal stability at sub-micron level,and has good adsorption performance on heavy metals and dyes in water as a multifunctional adsorbent for wastewater treatment.Further,the mechanochemical reaction of calcium carbide（CC）with SF₆was studied to produce submicron Ca F₂ and sulfur-containing alkyne carbon materials.The maximum unit degradation of SF₆ per gram of calcium carbide is up to 0.75 g/（g CC）.This method is suitable for the efficient degradation of a wide range of fluorinated greenhouse gases,such as CF₄,CClF₂CH₃,CF₃Br,etc.,and offers better versatility compared to conventional methods.Finally,the SF₆ and CF₄ degradation experiments are summarized and concluded.In addition,the mechanochemical reaction of difluoromethane chloride（R22）with alkaline substances is explored,providing a new approach for the preparation of metal fluorides.In conclusion,this study provides a novel method for degrading SF₆ and other fluorinated gases under mechanochemical conditions for the first time,based on the concept of"turning waste into treasure".This study has achieved a high value utilization of fluorine resources while alleviating the greenhouse effect,and has good prospects for industrial applications.