分子筛吸附C_4F_7N/CO_2混合绝缘气体及其分解产物的理论研究
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摘要
鉴于环保混合气体C_4F_7N/CO_2(g~3)的分解产物对其绝缘与安全性能均有重要影响,研究了g~3气体分解产物与分子筛吸附剂的相互作用,为设计适于g~3工程应用的吸附剂提供理论依据。采用巨正则系综MonteCarlo方法与分子动力学模拟研究了g~3及其13种分解产物CO、CF_2=CFCN、COF_2、C_2F_6、C_3F_8、C_2F_5CN、CF_3CN、C_2F_4、(CN)_2、HF、(CF_3)_2CHCN、(CF_3)_2C=CF_2、(CH_3)_2Si F_2在Na-4A分子筛中的吸附特性,获得了饱和吸附量、吸附等温线、吸附自由能、吸附结构、扩散系数等关键参数。分子筛的每个α笼可以吸附2个C_4F_7N分子,饱和吸附量(质量摩尔浓度)为1.18 mol/kg。当与CO_2混合后,C_4F_7N的吸附量显著降低至0.22 mol/kg。分子筛对全氟代烷烃与烯烃的吸附能力较弱,更易于优先且高效吸附各种剧毒性分解产物,按吸附量高低依次为HF>COF_2>(CN)_2>CF_3CN>C_2F_5CN。鉴于吸附量仅为1.99 mol/kg且自由能较高,分子筛并不适合用于吸附CO。
Decomposed gaseous products of the C_4F_7 N/CO_2(g~3) mixture play an important role in the dielectric and safety issue. Interaction of the gases with zeolite is crucial to provide theoretical guidance to the design of the specific sorbents for industrial use of g~3. We employed Gibbs-ensemble Monte Carlo and molecular dynamics simulations to investigate the adsorption of g~3 and its thirteen decomposition products including CO, CF_2=CFCN, COF_2, C_2 F_6, C_3 F_8, C_2 F_5 CN, CF_3 CN,C_2 F_4,(CN)_2, HF,(CF_3)_2 CHCN,(CF_3)_2 C=CF_2 and(CH_3)_2 Si F_2 in zeolite Na-4 A. Adsorption capacities, isotherms, free energies, density profiles, and diffusion coefficients were obtained. Two C_4F_7 N molecules can be absorbed into one α cage of Na-4 A, leading to an absorption capacity of 1.18 mol/kg. For the binary C_4F_7 N/CO_2 mixture, the selective adsorption of CO_2 over C_4F_7 N leads to the significant reduction(0.22 mol/kg) of the latter. Na-4 A prefers to adsorb the highly toxic compounds in the order HF > COF_2 >(CN)_2 > CF_3 CN > C_2 F_5 CN, whereas the adsorption of the perfluorinated alkanes and alkenes is less favorable. Na-4 A is not an appropriate sorbent for CO in view of the extremely low adsorption capacity(1.99 mol/kg) and the highest free energy.
Decomposed gaseous products of the C_4F_7 N/CO_2(g~3) mixture play an important role in the dielectric and safety issue. Interaction of the gases with zeolite is crucial to provide theoretical guidance to the design of the specific sorbents for industrial use of g~3. We employed Gibbs-ensemble Monte Carlo and molecular dynamics simulations to investigate the adsorption of g~3 and its thirteen decomposition products including CO, CF_2=CFCN, COF_2, C_2 F_6, C_3 F_8, C_2 F_5 CN, CF_3 CN,C_2 F_4,(CN)_2, HF,(CF_3)_2 CHCN,(CF_3)_2 C=CF_2 and(CH_3)_2 Si F_2 in zeolite Na-4 A. Adsorption capacities, isotherms, free energies, density profiles, and diffusion coefficients were obtained. Two C_4F_7 N molecules can be absorbed into one α cage of Na-4 A, leading to an absorption capacity of 1.18 mol/kg. For the binary C_4F_7 N/CO_2 mixture, the selective adsorption of CO_2 over C_4F_7 N leads to the significant reduction(0.22 mol/kg) of the latter. Na-4 A prefers to adsorb the highly toxic compounds in the order HF > COF_2 >(CN)_2 > CF_3 CN > C_2 F_5 CN, whereas the adsorption of the perfluorinated alkanes and alkenes is less favorable. Na-4 A is not an appropriate sorbent for CO in view of the extremely low adsorption capacity(1.99 mol/kg) and the highest free energy.
引文
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[5]高克利,颜湘莲,王浩,等.环保型气体绝缘输电线路(GIL)技术发展[J].高电压技术,2018,44(10):3105-3113.GAO Keli,YAN Xianglian,WANG Hao,et al.Progress in environment-friendly gas-insulated transmission line(GIL)[J].High Voltage Engineering,2018,44(10):3105-3113.
[6]KIEFFEL Y.Characteristics of g3-an alternative gas to SF6[C]∥IEEE International Conference on Dielectrics.Montpellier,France:IEEE,2016:880-884.
[7]OWENS J G.Greenhouse gas emission reductions through use of a sustainable alternative to SF6[C]∥IEEE Electrical Insulation Conference.Montreal,Canada:IEEE,2016:535-538.
[8]YU X,HOU H,WANG B.Mechanistic and kinetic investigations on the thermal unimolecular reaction of heptafluoroisobutyronitrile[J].Journal of Physical Chemistry A,2018,122(38):7704-7715.
[9]JARAMILLO E,CHANDROSS M.Adsorption of small molecules in LTA zeolites.1.NH3,CO2 and H2O in zeolite 4A[J].Journal of Physical Chemistry B,2004,108(52):20155-20159.
[10]DEMIR B,SALMAS R E,AHUNBY M G,et al.Monte Carlo simulations of HCN adsorption in LTA zeolites[C]∥International Conference on Innovations in Chemical Engineering and Medical Sciences.Dubai,United Arab Emirates:IEEE,2012:11-15.
[11]YANG J,REN Y,TIAN A,et al.COMPASS force field for 14 inorganic molecules,He,Ne,Ar,Kr,Xe,H2,O2,N2,NO,CO,CO2,NO2,CS2 and SO2 in liquid phases[J].Journal of Physical Chemistry B,2000,104(20):4951-4957.
[12]FAUX D A,SMITH W,FORESTER T R.Molecular dynamics studies of hydrated and dehydrated Na+-zeolite-4A[J].Journal of Physical Chemistry B,1997,101(10):1762-1768.
[13]SALMAS R E,DEMIR B,YILDIRIM E,et al.Silver-sodium ion exchange dynamics in LTA zeolite membranes[J].Journal of Physical Chemistry C,2013,117(9):1663-1671.
[14]GARCíA-SANCHEZ A,VAN DEN BERGH J,CASTILLO,J M,et al.Influence of force field parameters on computed diffusion coefficients of CO2 in LTA-type zeolite[J].Microporous Mesoporous Mater,2012,158(1/2):64-76.
[15]ZITO P F,CARAVELLA A,BRUNETTI A,et al.Light gases saturation loading dependence on temperature in LTA-4A zeolite[J].Microporous Mesoporous Mater,2017,249(1/2):67-77.
[16]ZHU W,GORA L,VAN DEN BERGH A W C,et al.Water vapour separation from permanent gases by a zeolite-4A membrane[J].Journal of Membrane Science,2005,253(1/2):57-66.
[17]EAGAN J D,ANDERSON R B.Kinetics and equilibrium of adsorption on 4A zeolite[J].Journal of Colloid and Interface Science,1975,50(3):419-433.