The Design Of Functional Metal-organic Frameworks Materials And Their Application In Gas Adsorption And Separation

There are many important gas separations in the field of petrochemical industry,such as hydrocarbon gas,rare gas,isotope gas and corrosive gas mixture.Their efficient separation is of great practical significance to the petrochemical industry,energy and environment.Compared with other methods(including cryogenic distillation and liquid-absorption),the predominant characteristic of adsorption-separation method based on porous materials are high selectivity,less pollution and less energy consumption.The key is to find the materials with high efficiency.As a new type of nano-micro structure porous material,metal-organic frameworks(MOFs)have attracted more and more attention in recent years.MOFs are three-dimensional porous materials,which are bridged by inorganic metal nodes called secondary building units(SBU)and organic ligands.The high specific surface area,larger porosity,rich functional groups and highly adjustable pore size and structure make it have a wide application prospect in many fields.Based on this,a series of MOF and composites based on MOF with excellent separation performance for a variety of important separation were obtained through theory and experiment,which considered the structure and properties of guest molecules.This provides the material foundation for efficient gas separation.The main work includes:1.The existence of heavy hydrocarbons in natural gas will affect the calorific value and safe transportation of methane.So,it is necessary to separate heavy hydrocarbons from methane efficiently.For the C3/C1 mixture with the difference of molecular size,the van der Waals interactions was adjusted by changing the specific surface area and pore size of MOF materials through the pre-modification based on UiO-66.The effect of van der Waals interactions on the adsorption and separation performance was systematically studied.The results show that the material with larger specific surface area,the larger pore volume and the weaker van der Waals interaction shows the greater adsorption capacity of C3,such as Zr-BPDC(the adsorption capacities of C3 are about 7.14 mmol/g);the material with stronger van der Waals interaction have higher selectivity for C3/C1,such as Zr-FUM(SC3H8/CH4=292;SC3H6/CH=242).2.Ammonia(NH3)capture can not only reduce its threat to human health,but also make its resource utilization.Therefore,ionic liquid@MOF composites with high NH3 capture efficiency were developed.Based on the polarity of NH3 molecule,an ionic liquid(IL,[BOHmim][Zn2Cl5])with multisites for adsorption was designed.MIL-101(Cr)with mesoporous,as the support of ILs,is stable under alkaline conditions.Constructed IL@MIL-101(Cr)composite with strong adsorption sites,large BET and high porosity,which are conducive to the diffusion,adsorption and storage of NH3 molecules.The experimental results show that the NH3 adsorption capacity in IL@MIL-101(Cr)composite can reach to 24.12 mmol/g under dry condition,which was 1.7 times higher than that of MIL-101(Cr).Such the adsorption capacity is higher than that of all porous materials reported in the literature.Even under humid conditions,the composite still has good adsorption capacity(23.55 mmol/g).In addition,the material has good regeneration performance after 5 adsorption/desorption cycles.3.H2O capture bases on solid adsorbents from the air has great application potential in the field of adsorption heat pump and clean water.At present,it is still a challenge to find adsorbents with high water absorption capacity,low regeneration temperature and high energy efficiency.For the application of H2O capture,the designed[BOHmim][Zn2Cl5]@MIL-101(Cr)composite has a confinement and non-confinement switching effect to the adsorption of H2O because of the characteristics of high polarity and low-boiling point of H2O.In other words,confined ILs in the composite will be dissolved in the adsorbed H2O and become non-confined ILs,which could flow out of the pores of the material.Such effect overcomes the limitation of the material pore volume and increase the H2O capacity.During the process of desorption,the non-confined ILs will gradually deposit on the material with the-release of H2O molecules and become the confined ILs.The experimental results show that:the adsorption capacity of IL@MIL-101(Cr)-60%reach to 477 wt%at 298 K and 95%RH.More importantly,about 97%of the adsorbed H2O can be desorbed under relatively mild conditions(40%RH and 313 K).4.In order to meet the great demand of national carbon neutralization,it is urgent to develop efficient carbon dioxide(CO2)capture materials.For CO2 capture,a kind of IL-ZIF-IL composite with shell-interlayer-core structure was prepared by[TETA]L and ZIF-8 inspiring by the separation principle of gradually enhance separation performance in distillation column.The composite can realize the stepwise separation of CO2/CH4 and CO2/N2 mixtures.The structure of the material was proved by TEM,FT-IR and EDS.The experimental results show that the obtained IL-ZIF-IL composite exhibits the high selectivities for CO2 capture(SCO2/CH4=1990;SCO2/N2=5572),while maintaining a high CO2 adsorption capacity(1.53 mmol/g).In addition,it can achieve complete separation through dynamic breakthrough test.5.High purity hydrogen isotopes are widely used in nuclear power,isotope tracer technology and other fields.Because hydrogen isotope molecules have almost the same physicochemical properties,it is difficult for conventional methods and materials to achieve high separation selectivity.Based on the principle of quantum sieving,high throughput screening of MOF materials for hydrogen isotope separation was carried out.The target material SIFSIX-3-Zn was obtained through high throughput screening based on the MOF material database according to the following factors:pore size,?ZPE,pore structure and material stability.More importantly,the results base on advance cryogenic thermal desorption system(ACTDS)show that the selectivity of D2/H2 mixture in SIFSIX-3-Zn is greater than 35.0 at 20 K and in the whole test pressure range(1-25 kPa).The selectivity can reach to 53.8 at 25 kPa.The separation selectivity is one order of magnitude higher than that of ultra-low temperature distillation(3.0 at 20 K)and superiors to other separation materials reported in the literature.The mechanism analysis shows that the excellent separation performance depends on the synergistic effect of F functional groups and ultramicropore.