The Chemical Decomposition And Adsorptive Separation Of NF₃ As A Novel Greenhouse Gas

Nitrogen trifluoride（NF₃）is being widely used in semiconductor industry as an etching and cleaning gas,and has an extremely high global warming potential（GWP）of 17200 and long atmospheric lifetime of 740 years.The gas emission is increasing year by year.Decomposition of NF₃ with metal oxides in the absence of water is an effective method for elimination of this waste gas,where the fluorine element in NF₃can be fixed by the formation of metal fluorides and the reactant of metal oxides are called as fluorine-fixed reagents.Considering the long-term impact of NF₃ on the environment,adsorptive separation and recovery is a more effective way of resourceful reduction.In this thesis,the research on decomposition without water and adsorptive seperation of NF₃ has been carried out.The decomposition of NF₃ on fluorine-fixed reagents of Al₂O₃@Mn₂O₃ and Co-Al₂O₃ was studied,and the capacities of MOF and carbon-based adsorbents for NF₃ adsorption were evaluated.The solid reagents and adsorbents were characterized by the techniques such as N₂ physisorption,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,infrared spectroscopy（FTIR）and thermal analysis（TA）.The research contents and conclusions are listed as follows:（1）Al₂O₃@Mn₂O₃ reagents were synthesized hydrothermally by using carbon-sphere as template for NF₃ decomposition.The effect of crystallizing temperatures on the reactivity of Al₂O₃@Mn₂O₃ reagents was investigated.The results show that the specific surface area and reactivity of Al₂O₃@Mn₂O₃ increased first and then decreased with the increase in the crystallization temperatures.Among the reagents,720 min of NF₃ full conversion on Al₂O₃@Mn₂O₃-160℃with 74.9%of utilization percentage was reached,which exceeds the reagents of Al-Mn complex oxides reported previously.（2）Co-Al₂O₃ homogeneous reagents were prepared by sol-gel method.The pore structure and reactivity of reagents were screened by changing the molar ratio of nitric acid and aluminum isopropanol in raw materials.The results show that the specific surface area,pore volume and reactivity of reagents increased first and then decreased with the increase in the molar ratio of nitric acid to aluminum isopropoxide from 2.20to 2.80.Among the reagents,700 min of NF₃ complete conversion over Co-Al₂O₃-2.45 with 72.9%of utilization percentage was obtained,which is superior to the reagents of Al-Co dual oxides reported in literatures.（3）Four functionalized 1,4-benzenedicarboxylate ligands bearing different groups,cobalt ions and TPP ligands were assembled together to form Co-Pacs-MOF materials under solvothermal conditions.The adsorption and separation properties for NF₃/N₂ were studied.The results show that the substituents can effectively control the adsorption and separation properties of adsorbents.As an example,1.52 mmol·g^-1 of equilibrium uptake for NF₃ and 10.11 of selectivity for NF₃/N₂（1/1）was obtained on the Co₃-DHBDC adsorbent at 298 K and 100 k Pa.In addition,the NF₃/N₂ mixture can be separated under flowing condition.（4）The commercial carbon was activated by KOH to prepare the carbon adsorbents.It is shown that the micro-pores of activated carbon treated by potassium hydroxide became smaller,and the adsorption capacity for NF₃ was greatly improved.Especially,a high equilibrium uptake of 2.13 mmol·g^-1 for NF₃ adsorption and selectivity of 34.99 for NF₃/N₂（1/1）was reached over the ACK-3 adsorbent at 298 K and 100 k Pa.The breakthrough experiment results show that the NF₃/N₂ mixture can be effectively separated under flowing condition.