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(C7H12O),methylcyclohexane(C6H11-CH3),1,1-dimethylcyclohexane(1,1-C8H16)and 1,2-dimethylcyclohexane(1,2-C8H16),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-C8H16,1,2-C8H16,C6H11-CH3,and C7H12O.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-C8H16 and 1,2-C8H16)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-C8H16 requires lower pressure condition(60 MPa)as a macromolecular promoter than 1,2-C8H16(100 MPa).In hydrogen and methane mixture hydrates,1,1-C8H16 requires higher temperature condition(270 K)than 1,2-C8H16(260 K)and lower pressure condition(20 MPa)than 1,2-C8H16(40 MPa)as a macromolecular promoter.
H-type hydratesmacromolecular promotersbi-guest small moleculeshydrogen storagemolecular dynamics
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