| High purity hydrogen isotopes have been widely applied in nuclear fusion reactor,hydrogen nuclear magnetic resonance spectroscopy,illumination,isotope tracer,neutron scattering and other fields.The natural abundance of deuterium in the ocean is approximately 0.015%,extraction of deuterium from hydrogen is crucial.As consequence of the identical size,shape,and thermodynamic properties,large-scale industrial separation of hydrogen isotopes is difficult.It is a simple and efficient separation method to separate hydrogen isotopes with nano-porous materials by quantum sieving effect.Researches on porous materials are mainly carried out at ultra-low temperature（20～50 K）,and the refrigeration process consumes a large amount of energy.Therefore,it is recognized that the development of adsorbents with good separation effect of hydrogen isotopes at temperatures above 77 K and suitable for industrial application is a development direction.Metal-Organic Frameworks（MOFs）exhibit unique properties due to their highly harmonizable and engineered pore structures.Although the numerous connection modes between metal ions and organic ligands endow MOFs a broad application prospect in the separation of hydrogen isotopes,relevant studies are mainly focused on theoretical calculation,and carried out under ideal conditions.Limited experimental studies only investigate the separation performance of hydrogen isotopes by MOFs,while the structure-activity relationship between the material structure and the actual separation effect is unclear.Therefore,rationally designing and controlling the microstructure of MOFs materials,and exploring its internal mechanism for the separation of hydrogen isotopes,is not only one of the key scientific issues of whether such materials can enter practical engineering applications,but also a research hotspot in this field.In this thesis,based on the existing research results,Ni-based MOFs were taken as the research object,and the influence and mechanism of the pore size of MOFs and the different coordination forms of Ni（II）at open metal sites on the separation of hydrogen isotopes were discussed,and the separation performance of MOFs@γ-Al2O3as column packing for hydrogen isotopes under working conditions was investigated.The main research progress of this thesis is as follows:（1）With the same configuration and decreasing pore size,Ni（bdc）（ted）0.5,Ni（ndc）（ted）0.5and Ni（adc）（ted）0.5were synthesized with terephthalic acid（H2bdc）,1,4-naphthalenedioic acid（H2ndc）and 9,10-anthracene diacid（H2adc）as ligands（L）,respectively.The H2/D2separation performance was investigated by adsorption isotherm experiment and cryogenic thermal desorption spectroscopy.The adsorption capacities of D2and H2are related to temperature and pressure.At the same temperatures,with the increase of pressure,the adsorption capacity of H2and D2increase accordingly.At the same temperature and pressure,the adsorption capacity of D2is greater than that of H2,showing obvious quantum sieving effect.With the increase of adsorption temperature,the adsorption capacity of H2and D2decrease accordingly.The selectivity of H2/D2is related to the pore size and adsorption temperature,which means that at the same adsorption temperature,the smaller the material pore size is,the better the selectivity is.With the increase of adsorption temperature,selectivity decreased,and Ni（adc）（ted）0.5still showed good selectivity separation for H2/D2separation at 77 K.（2）Three Ni（L）（ted）0.5@γ-Al2O3column packing were prepared by loading the above MOFs onγ-Al2O3respectively,and the separation performance of H2/D2binary mixture and H2/HD/D2ternary mixture were investigated at 77 K.The three kinds of packing showed good separation performance for H2/D2,and the separation effect is related to carrier gas flow rate and injection ring pressure.When the carrier gas flow rate is 80 m L/min and the injection ring pressure is 5 k Pa,Ni（bdc）（ted）0.5@γ-Al2O3,Ni（ndc）（ted）0.5@γ-Al2O3and Ni（adc）（ted）0.5@γ-Al2O3can all achieve baseline separation of H2/D2.Among them,the separation effect of Ni（adc）（ted）0.5@γ-Al2O3is the best.When the carrier gas flow rate is 40 m L/min,the separation resolution of H2/D2is up to 3.34,which can realize the quantitative analysis of H2/D2mixture.However,as H2and HD are isomers,it is difficult to achieve baseline separation of H2and HD.In addition,the separation performance of Ni（ndc）（ted）0.5@γ-Al2O3with different load times for the H2/HD/D2ternary mixture was investigated,but increasing of load times did not significantly improve the separation resolution of each component.（3）On the basis of the above studies,Ni3（pzdc）2（7Hade）2,Ni2Cl2BBTA and Ni-MOF-74 with open metal sites were selected as the research objects,and the selective separation of H2/D2by chemical affinity quantum screening effect at different adsorption temperatures was investigated by cryogenic thermal desorption spectroscopy.The experimental results show that due to the existence of open metal sites,the desorption peaks of H2and D2can still be observed above 77 K.The maximum temperature of thermal desorption peak of Ni3（pzdc）2（7Hade）2is 120 K due to the presence of tetra-coordination Ni（II）,and there is still a strong force on H2and D2at this temperature.However,due to the combined action of quantum effect and knudsen effect,the substitution of H2and D2is limited,and the selective separation of H2/D2is limited.Both Ni2Cl2BBTA and Ni-MOF-74 have pentagonal coordination with Ni（II）,and their topological structures are similar.However,due to the difference of coordination atoms with Ni（II）,the temperature of the maximum thermal desorption peak is different,which is 72 K and 100 K,respectively.Ni2Cl2BBTA and Ni-MOF-74 showed good selectivity for H2/D2separation at 77 K,with separation ratios of 2.5 and 8.4,respectively.These results suggest that there is an optimal operating temperature for hydrogen isotope separation using chemical affinity quantum screening effect,and MOFs with strong action sites and appropriate pore sizes are more favorable for hydrogen isotope separation.（4）Ni2Cl2BBTA@γ-Al2O3chromatographic column was prepared by loading Ni2Cl2BBTA onγ-Al2O3.The effects of load times,carrier gas flow rate and injection ring pressure on the separation of H2/HD/D2ternary mixture were systematically investigated at 77 K.The experimental results show that with the increase of loading times,and the decrease of the carrier gas flow and injection ring pressure,and the packing separation performance is better.When the load times were 3,the carrier gas flow rate was 40 m L/min,and the injection ring pressure was 5 k Pa,the separation degree of H2/HD was 1.57,and the baseline separation could be achieved within 11min.The quantitative analysis of each component in H2/HD/D2has good accuracy and stability.On the basis of this study,the difference between MOFs with open metal sites as stationary phase and conventional modified column packing for hydrogen isotope separation was also discussed.The innovation of this thesis is as follows:（1）By taking advantage of the design property of MOFs,isomorphic MOFs with different pore sizes were synthesized,and the effect of pore sizes on hydrogen isotope separation at different adsorption temperatures was systematically investigated for the first time.（2）MOFs were loaded intoγ-Al2O3to make chromatographic column packing.Through dynamic separation experiments,the structure-activity relationship between the material structure and the separation of H2/D2and H2/HD/D2in practical applications was explored for the first time.（3）The differences of affinity between open metal sites with different coordination forms and hydrogen isotopes are discussed for the first time.It is concluded that sites with strong effects on hydrogen isotopes and MOFs with appropriate pore sizes are more conducive to hydrogen isotope separation.（4）Chromatographic column packing prepared by loading MOFs with open metal sites into theγ-Al2O3,and used for the separation of H2/HD/D2ternary mixture for the first time,and the baseline separation of H2/HD is implemented.The quantitative analysis of HD in H2/HD/D2has carried with normalization method.This study lays a theoretical and experimental foundation for the separation and quantitative analysis of H2/HD/D2ternary mixture.Through the above research,a method for hydrogen isotope separation was established by controlling the length of ligands to regulate the pore size of MOFs.The effects of open metal sites with different coordination forms on the separation of hydrogen isotopes were systematically investigated.The practical application prospect of MOFs@γ-Al2O3as chromatographic column packing in hydrogen isotope separation engineering was also discussed.The research of this experiment has guiding significance for the design of new MOFs for hydrogen isotope separation and the application of MOFs in hydrogen isotope separation engineering.These results lay a foundation for the efficient separation and fast online analysis of hydrogen isotopes in the deuterium-tritium fuel cycle gas of fusion reactor in the future. |
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