Adsorption characteristics of Cu-BTC for trace SF6 and its fault decomposition products in SF6/N2 gas mixtures

Abstract

Replacing SF₆ in existing gas-insulated equipment with SF₆/N₂ is an effective means of reducing SF₆ use and emissions at this stage. This paper proposes the use of metal–organic skeleton material Cu-BTC for adsorption and separation of trace SF₆ and its faulty decomposition products in SF₆/N₂ gas mixtures, in order to achieve the effective separation and purification and recovery of trace SF₆ and its decomposition products in high-capacity SF₆/N₂ gases, and thus reduce the damage of SF₆ and its decomposition products to the human environment. The results show that: the high specific surface area and three-dimensional microporous structure of Cu-BTC endowed it with excellent adsorption capacity, and the adsorption of SF₆ reaches 4.6 mmol/g at 298 K and 100 bar, which is 7–9 times higher than that of the traditional molecular sieve (kdhF-03); the adsorption isotherms are in accordance with the characteristics of I-type, and the adsorption capacity decreases with the increase of temperature; CF₄ exhibits the widest range of adsorption sites due to the molecular size fit to the secondary window; SF₃ shows the highest adsorption activity due to the formation of chemical bonding (adsorption energy −1.375 eV) with the open metal site of Cu²⁺, whereas SO₂ and H₂S are directionally bonded to the Cu site through the sulphur atoms; the charge transfer and density of states analyses further reveal that the p-orbitals of the S, F atoms electronic coupling mechanism with Cu-BTC. This study provides a theoretical basis for the development of highly efficient SF₆ adsorbent materials with potential applications in reducing greenhouse gas emissions in power equipment. Firstly, the adsorption performance of Cu-BTC on SF₆ and its decomposition products (SO₂F₂, SOF₂, SOF₄, SO₂, NF₃, NO₂, NO, N₂O, HF, H₂S and CF₄) is systematically explored by using a grand canonical Monte Carlo method; and then, the parameters of adsorption energy, charge transfer and density of states of Cu-BTC for SF₆ and its main fault decomposition gases are further analysed in conjunction with the density functional theory, so as to investigate the adsorption properties and mechanisms of different gas molecules in Cu-BTC.