Study Of A Novel Hydrate-based Hybrid Hydrogen Storage Technology

Hydrate based hydrogen storage is a hydrogen storage technology with large scale industrial application prospects.For further improving hydrogen storage properties,there are three generations of hydrate based hydrogen storage technology have been developed.However,the common issue is the storage properties decline with gentler working condition of hydrate based hydrogen storage.Aiming at this issue,this thesis studies a novel hydrate-based hybrid hydrogen storage technology:hydrate hybrid with other hydrogen storage technology.Hydration-chemical and hydration-adsorption with carbon nanotube hybrid hydrogen storage were studied by high pressure experiment,Raman spectroscopy characterization and in-situ Raman dissociation experiment,which to achive the goal of lower working pressure and higher hydrogen storage density.In this work,tert-butyl alcohol?tBA?was choosen as chemical hydrogen storage material for hydration-chemical hybrid hydrogen storage.The phase equilibrium data of tBA-methane-hydrogen-water quaternary system were measured in hydrate reactor.The microstructure and dissociation process of the system were studied by Raman spectroscopy.The results shown that 2.8mol%tBA and 5.6mol%tBA could move phase equilibrium line about 4K and 5K towards higher temperature,respectively.Raman spectroscopy shown that the thermodynamic promotion mechanism was that tBA and water molecules form metastable hydrate cages through hydrogen bonds between hydroxyl groups,then form stable sII hydrates with the help of methane molecules and play a role in thermodynamicly promoting the formation of hydrogen hydrates.The?equivalent?capacity of hydrogen storage in a 450ml hydrate reactor at 273K and 20MPa could reach 5.51wt%,which hydrogen content is 0.12wt%,and the time required to reach 95%of the hydrogen storage capacity t95 is 36min.When the concentration of tBA was reduced to 2.8 mol%,Raman spectroscopy showed that methane began to occupy 5¹²6⁴ cages?large cages?and changed lattice parameters of sII hydrates,which lead to lose hydrogen storage ability.Therefore,the concentration of Tba solution for hydration-chemical hybrid hydrogen storage should be 2.8mol%-5.6mol%.Then in-situ Raman spectroscopy dissociation process of hydrates obtained in hydration-chemical hybrid hydrogen storage experiments were studied.When the hydrogen in the hydrate phase was about to be dissociated completely,the crystal structure and lattice parameters of the sII hydrate will change slightly,which results in self-preservation effect of hydrogen molecules in hydrate.Meanwhile by analyzing cage occupancies of methane it was found that there was secondary formation of methane in hydrate phase.Raman spectra data shown that hydrogen storage?equivalent?capacity of the hydrate obtained from the experiment of?75mol%?H₂/CH₄ storaged in 5.6 mol%tBA solution was 7.2 wt%,in which the hydrogen content was 0.31 wt%.In this work,multi-walled carbon nanotubes?MWCNTs?were selected as the physical adsorption medium for hydrogen storage,and the hydration-adsorption hybrid hydrogen storage of carbon nanotube suspension and carbon nanotube ice powder were studied.MWCNTs can not only absorb and store hydrogen,but also have hollow structure and hydrophobic surface which open a path for gas to enter the liquid phase.Hexagonal structure formed by carbon atoms can be used as a template to promote gas hydrate nucleation.Adding 1wt%MWCNTs to water can increase gas storage capacity from 0V/V to 20V/V,adding 1wt%MWCNTs to ice powder can increase both gas storage capacity and the maximum rate by 6.4 times and 5.5 times,respectively.The storage capacity of MWCNTs ice powder system was 2⁸ times higher than that of MWCNTs suspension system under the same conditions within 10 minutes.MWCNTs ice powder hydration-adsorption hybrid hydrogen storage system will be a more efficient solution.In order to further reduce the pressure of hydrate based hybrid hydrogen storage,the promotion effect of dichlorofluoroethane?HCFC-141b?and chloroform?CHCl₃?on hydrate based hydrogen storage was studied.Halogen group?-Cl or-F?in halohydrocarbons enhances the van der Waals force between guest molecules and water.The phase equilibrium line of hydrogen hydrate shifts 10K?HCFC-141b?and 5K?CHCl₃?toward higher temperature respectively.Hydrogen storage capacity of 5.6 mol%HCFC-141b can reach 50 V/V at 273 K and 12 MPa,while that of 5.6 mol%CHCl₃ is only 9.4 V/V at the same condition.Finally,Aspen Plus was used to simulate the novel hydration-chemical hybrid hydrogen storage process with tBA.The results show that the energy consumption of compression hydrogen storage is 4.9 kWh/kgH₂,the energy consumption of hydration-chemical hybrid hydrogen storage process without LNG cold energy is 4.3 kWh/kgH₂,and the energy consumption of hydration-chemical hybrid hydrogen storage process with LNG cold energy is3.1 kWh/kgH₂.Compared with the unused LNG cold energy process,the energy consumption is reduced by about 30%,and it is only 63%of the energy consumption of hydrogen storage by compression.