应用大分子促进剂的H型水合物储氢特性的分子动力学模拟

Molecular dynamics simulation of hydrogen storage characteristics of H-type hydrates using macromolecular promoters

纯氢气水合物形成的温压条件极为苛刻(低温高压),限制了其工业应用,而氢气和甲烷混合气水合物形成的温压条件相对温和。通过恒温恒压(NPT)系综分子动力学模拟,研究了环庚酮(C_(7)H_(12)O)、甲基环己烷(C_(6)H_(11)-CH_(3))、1,1-二甲基环己烷(1,1-C_(8)H_(16))和1,2-二甲基环己烷(1,2-C_(8)H_(16))4种大分子促进剂对H型纯氢气水合物以及氢气和甲烷混合气水合物稳定性的影响。结果表明,分别应用4种大分子促进剂的H型水合物牢笼稳定性从大到小依次为1,1-C_(8)H_(16)、1,2-C_(8)H_(16)、C_(6)H_(11)-CH_(3)和C_(7)H_(12)O。相比于纯氢气,氢气和甲烷混合气能够极大缓和热力学条件(温度升高,压力降低)。两种同分异构体(1,1-C_(8)H_(16)和1,2-C_(8)H_(16))作为大分子促进剂,对应的热力学条件表现出较大差异。在纯氢气水合物中,两种同分异构体作为大分子促进剂所需温度条件相近(270 K),而1,1-C_(8)H_(16)作为大分子促进剂所需压力条件(60 MPa)低于1,2-C_(8)H_(16)(100 MPa)。在氢气和甲烷混合气水合物中,1,1-C_(8)H_(16)作为大分子促进剂所需温度条件(270 K)高于1,2-C_(8)H_(16)(260 K),所需压力条件(20 MPa)低于1,2-C_(8)H_(16)(40 MPa)。

The temperature and pressure conditions for the formation of pure hydrogen hydrates are extremely harsh(low temperature and high pressure),limiting their industrial applications,whereas the temperature and pressure conditions for the formation of hydrogen and methane mixture hydrates are relatively mild.The effects of four macromolecular promoters,cycloheptanone(C_(7)H_(12)O),methylcyclohexane(C_(6)H_(11)-CH_(3)),1,1-dimethylcyclohexane(1,1-C_(8)H_(16))and 1,2-dimethylcyclohexane(1,2-C_(8)H_(16)),on the stability of H-type pure hydrogen hydrates and hydrogen and methane mixture hydrates were investigated by means of molecular dynamics simulations using a thermostatic constant pressure(NPT)system.The results show that the cage stability of H-type hydrates with the application of the four macromolecular promoters is,in descending order,1,1-C_(8)H_(16),1,2-C_(8)H_(16),C_(6)H_(11)-CH_(3),and C_(7)H_(12)O.The mixture of hydrogen and methane is able to greatly moderate the thermodynamic conditions(temperature increases and pressure decreases)compared to that of pure hydrogen.The two isomers(1,1-C_(8)H_(16) and 1,2-C_(8)H_(16))show large differences in thermodynamic conditions between them as macromolecular promoters.In pure hydrogen hydrate,both isomers require similar temperature condition(270 K)as macromolecular promoters,while 1,1-C_(8)H_(16) requires lower pressure condition(60 MPa)as a macromolecular promoter than 1,2-C_(8)H_(16)(100 MPa).In hydrogen and methane mixture hydrates,1,1-C_(8)H_(16) requires higher temperature condition(270 K)than 1,2-C_(8)H_(16)(260 K)and lower pressure condition(20 MPa)than 1,2-C_(8)H_(16)(40 MPa)as a macromolecular promoter.