Design And Synthesis Of Pillared Ultra-Microporous Materials For Carbon Capture And Hydrocarbons Adsorptive Separation

The efficient separation of gas mixtures with similar structural properties is a significant challenge in chemical separation,and it is also a prerequisite for efficient carbon capture and alkene/alkane separation processes.As a high-efficiency and mild separation technology,the core of adsorption separation lies in designing efficient adsorbents.The development of adsorbents with high adsorption capacity,good separation selectivity,and meeting the requirements of applications is challenging.The pillared ultra-microporous materials with adjustable pore size,modifiable pore surface environment,and easily constructed pore structure are expected to enhance recognition of comparable gas molecules through pore structure orientation design.In this paper,a series of novel highstability ultra-microporous materials were constructed based on the coordination characteristics of multiple ligands,and the effects of organic ligands and pillar-type on the pore channels were systematically explored.On this basis,combined with gas molecules,the effect of pore channel properties on gas adsorption and separation performance was revealed,and efficient carbon capture and olefin/alkane separation processes are realized,which provides a theoretical basis for the design of adsorbents and the advancement of separation technology.The main research contents include:One of the key directions in the development of adsorbents is highly customizable pore structures and high stability based on structural chemistry.In this paper,tiny oxygen/nitrogen-containing pillars were incorporated into the framework and oxygen/nitrogen atoms were coordinated with metal endpoints to generate stable ultramicroporous materials.The findings demonstrated that materials made up of oxygencontaining pillars had thermal decomposition temperatures higher than 330℃.The hydrophobic methyl groups and nitrogen heterocyclic rings improved water resistance and stability in air,water,acid,and base solutions.The structural analysis demonstrated the pore channels contained high-density electronegative oxygen/nitrogen atomic functional sites that could enable the effective capture of polar small molecules.Additionally,through changing the pillars,the finely controlled pore size(3.40 A to 3.96 A)and pore shape of the materials were achieved which serve as a crucial foundation for the highly selective separation of molecules with identical structural properties.It is difficult to design physical adsorbents for carbon dioxide(CO2)capture under high temperature and high humidity conditions.In this paper,a novel oxalic acid pillared ultra-microporous material ZnMtzOx(ZU-301,Mtz=3-methyl-1H-1,2,4-triazole,Ox=oxalate)with one-dimensional quasi-discrete pore channels was designed.The highdensity hydrophobic methyl functional groups and oxalate anion inside the pore,together with the adequate pore window size(3.8 ?),enable the highly selective capture of CO2 from methane(CH4)and nitrogen(N2).The adsorption isotherms of ZU-301 were collected,and the selectivity was calculated.The breakthrough experiments were conducted to investigate CO2 capture performance.The results indicated that at 373 K,ZU-301’s CO2 adsorption capacity was still 2.13 mmol g-1,just 11%lower than at 273 K.Under 298 K-323 K，the IAST selectivity of ZU-301 for CO2/CH4 and CO2/N2 was 90111 and 846-19000.The breakthrough experiments demonstrate that ZU-301 can still effectively capture CO2 in high-temperature and humidity environments.The singlecrystal X-ray diffraction and simulation calculations revealed that the high-density hydrogen bond interaction and electrostatic interaction between the ZU-301 and CO2 are the keys to achieving efficient CO2 capture.The ability of materials to recognize propylene(C3H6)/propane(C3H8)can be enhanced by using the difference between gas molecules.In this paper,a novel carbonated pillared ultra-microporous material ZnATACO3(ZU-701,ATA=5-Amino-1H-tetrazole)was designed by synergistically modulating the pore structure and functional sites to achieve efficient separation of C3H6/C3H8 through a thermodynamic-kinetic synergistic separation mechanism.The results of the adsorption isotherms and dynamic adsorption curves of ZU-701 for C3H6 and C3H8 indicated that the capacity ratio for C3H6 and C3H8 was 4.27 at 298 K,and the diffusion coefficient of C3H6 in ZU-701 was high(2.329 × 1011 m2 min-1).The thermodynamic and kinetic combined selectivity of ZU-701 for C3H6/C3H8 separation was up to 2089.ZU-701 demonstrated good C3H6/C3H8 separation performance and a limited range of C3H6 mass transfer over a wide range of flow velocity,temperature,and humidity in fixed bed breakthrough experiments.According to the molecular simulation results,the high density of oxygen and nitrogen atoms on the surface of ZU-701 had a stronger affinity for C3H6 and achieves thermodynamic preferential adsorption of C3H6.Adsorbent adsorption and desorption behavior are critical to achieving an efficient PSA separation process,yet both are frequently difficult to perform.This study revealed the feasibility of controlling the adsorption and desorption behavior of porous materials at the molecular level by co-regulating the pore size/pore chemical environment and the flexibility of the framework.Using CPL-I-CH3(ZU-901)as the adsorbent,the adsorption isotherms of ethylene(C2H4)and ethane(C2H6)were collected.The C2H4 showed an "S"type adsorption isotherm,which realized the efficient and energy-saving separation of C2H4/C2H6.At 273 K,ZU-901 had a high C2H4 working capacity(1.36 mmol g-1)and negligible C2H6 capacity.An adsorbents selection parameter for C2H4/C2H6 was up to 65,and the heat of adsorption for C2H4 was 24.85 kJ mol-1 at zero loading.Low C2H4 capacity in the low-pressure region,promotes quick desorption.Through 50-cycle breakthrough experiments,the separation performance of the C2H4/C2H6 of ZU-901 remains unchanged.The high-purity C2H4(99.51%)was obtained by the two-bed pressure swing adsorption process,and the associated energy(2.03 kJ mol-1)was only 1/10 of the traditional distillation process.In addition,the large-scale preparation of ZU-901 was achieved by green aqueous-phase synthesis and mother liquor circulation process with 99%yield.