Molecular Simulation Studies On H₂S Adsorption And Separation In Halogen-functionalized MIL-47?V?

H₂S is a trace but highly hazardous gas in natural gas and biomass syngas.It corrodes pipelines and jeopardizes the safety of operation.Its leak also causes environmental pollution and harm to human body.Currently,the method of liquid-phase chemical scrubbing with amines is used to remove H₂ S in the industry.However,this process is energy-greedy and the ammonia has short duration and cannot be recycled.Adsorptive separation technique is an alternative method.The key of this technology is the adsorbent material.Metal-organic framework?MOFs?can be the potential adsorbent material of H₂ S,due to their unique structures and properties.Experimental studies have shown that MIL-47?V?has high H₂ S adsorption capacity and can be recycled,but its moisture stability is poor.Experiments have shown that introducing halogen atoms to the ligands of MOFs can significantly improve the hydrophobicity.At present,the halogen-functionalized MIL-47?V?-X?X=F,Cl,Br?have been synthesized,but their H₂ S adsorption and separation properties have not yet been carried out.Therefore,it is necessary to perform systematic molecular simulation studies on their H₂ S adsorption and separation properties and reveal the impact of halogen functionalization on H₂ S adsorption and separation properties.This will provide useful theoretic guidance for the design of new H₂ S adsorption and separation materials and the on-going experiments.In this thesis,the grand canonical Monte Carlo?GCMC?molecular simulation method is performed to study the adsorption properties of single-component H₂ S,CH4,and N2 in MIL-47?V?and halogen-functionalized MIL-47?V?-X?X=F,Cl,Br?,as well as their adsorptive separation performances towards two-component gas mixture H₂S/CH4 and H₂S/N2.At first,the crystral structures of MIL-47?V?-X?X=F,Cl,Br?are constructed based on the crystal structure of MIL-47?V?.The accuracies of the constructed srystral structures and the chosed force field parameters and calcution methods are vertified by comparing the results of molecular simulation in this thesis with the results from experiments and the simulation results from other literatures.On this basis,the single-component H₂ S,CH4,and N2 adsorption isotherms in MIL-47?V?and MIL-47?V?-X?X=F,Cl,Br?are obtained by molecular simulation,which aims to study the effect of temperature,pressure,and halogen functionalization on the gas adsorption amount.In addition,isosteric heat and adsorption sites are also performed to reveal the mechanism of halogen functionalization impact.Furthermore,the adsorptive separation performances of the two-component gas mixture H₂S/CH4 and H₂S/N2 in MIL-47?V?and MIL-47?V?-X?X=F,Cl,Br?are simulated.The effects of temperature,pressure,mixture component,and halogen functionalization on adsorptive separation properties are discussed.The results show that these four MOFs all have a high H₂ S adsorption rate and ultra-high H₂ S adsorption amount.At 303 K,the saturated?excess?adsorption amount of H₂ S in MIL-47?V?and MIL-47?V?-X?X=F,Cl,Br?respectively is 11.83,10.79,9.89 and 8.97 mmol/g.The weight fraction of adsorbed H₂ S is 40.33%,36.76%,33.66% and 30.56%,respectively.These four MOFs also have a high CH4 adsorption capacity.At 303 K and 4.0 MPa,the weight fraction of adsorbed CH4 respectively is 8.58%,8.19%,8.04% and 7.63%.However,the N2 adsorption capacity is low.H₂ S adsorbs in these four MOFs by forming hydrogen bonds with the ?2-O atoms and halogen atom in the frameworks.Nevertheless,there are no special adsorption sites when CH4 and N2 adsorb in these four MOFs.These four MOFs also have good adsorptive separation performances of two-component gas mixture H₂S/CH4 and H₂S/N2.When the temperature rises,the H₂S/CH4 and H₂S/N2 adsorptive separation performances degrade.At the constant pressure,with the increase of H₂ S volume fraction in gas mixtures,H₂ S adsorption capacity of these four MOFs increases,but the adsorption selectivity reduces.When the H₂ S volume faction in gas mixtures is constant,with the increase of pressure,H₂ S adsorption capacity of these four MOFs also increases,but the adsorption selectivity reduces as well.Despite H₂S/CH4 and H₂S/N2 adsorptive selection coefficient are high at the low pressure and low H₂ S volume fraction,but the H₂ S adsorption amount is low.At 303 K and 4.0 MPa,when the H₂ S volume fraction in gas mixture was 10%,the adsorption amount of H₂ S adsorbed by these four MOFs from H₂S/CH4 mixture repectively is 7.46,7.15,6.73 and 6.13 mmol/g.H₂S/CH4 adsorptive selectivity is 30,34,34 and 40,respectively.At the same condiction,the adsorption amount of H₂ S adsorbed by these four MOFs from H₂S/N2 mixtures respectively is 8.75,8.15,7.84 and 7.07 mmol/g.H₂S/N2 adsorptive selection selectivity is 88,95,109 and 127,respectively.Halogen functionalization increases H₂ S,CH4 and N2 isosteric heat,thus improved the gas adsorption capacity of MOFs especially at low-pressure zone.Meanwhile,halogen functionalization increases the density of MOFs materials,H₂ S adsorption amount per unit mass will drop,but H₂ S adsorption amount per unit volume will increase.The halogen atoms in halogen-functionalizaed MOFs can form hydrogen bonds with H₂ S molecules and serve as H₂ S adsorption sites.Halogen functionalization improves the H₂S/CH4 and H₂S/N2 adsorptive separation selectivity of MOFs at the condition of low temperature,high pressure and high H₂ S volume fraction.Therefore,these four MOFs can be potential H₂ S and CH4 adsorptive storage material,as well as H₂S/CH4 and H₂S/N2 adsorptive separation material,expecially halogen-functionalized MIL-47?V?-X?X=F,Cl,Br?with good hydrophobicity.