The Synthesis Of Two MOFs Materials And Their Adsorptive Separation Performance For C1-C3 Light Hydrocarbons

In petrochemical industry,separation and purification is a critical value-added process,efficient separation of C1-C3 light hydrocarbons has also become a research topic attracting much attention.Due to the disadvantages of traditional C₂H₄-selective adsorbents like larger adsorbents amount required for crack gas separation and higher complexity of process flow to produce C₂H₄,as well as low C₂H₆ adsorption capacity and poor moisture stability of reported C₂H₆-selective adsorbents,this work synthesized C₂H₆-selective MOFs with high stability and studied its adsorption phase equilibrium and separation mechanism of C₂H₆/C₂H₄.Because of low C₂H₆ adsorption capacity under low pressure and poor C2/C1 separation selectivity of existing materials,this work designed MOF material that can efficiently recover low-concentration C₂H₆ and purify CH₄ in natural gas.Therefore,this thesis has great research value and application significance.This work studied a highly stable Y-TATB MOF material and its C₂H₆/C₂H₄ separation performance and mechanism.The isotherms revealed that Y-TATB preferentially adsorbed C₂H₆.At 298 K and 100 k Pa,the adsorption capacity for C₂H₆ and C₂H₄ were 4.33 mmol/g and2.98 mmol/g,and the uptake ratio of C₂H₆/C₂H₄ reached 1.45,which surpassed the majority of the reported MOFs materials.What’s more,Y-TATB had remarkable thermal stability（below550°C）and moisture stability.Three consecutive breakthrough tests showed that Y-TATB possessed excellent dynamic separation performance and regeneration stability.Simulation calculation revealed that Y-TATB contains trigonal bipyramid cages,in which C₂H₆ and C₂H₄were adsorbed near 6-connected and 12-connected Y（III）clusters,respectively.For C₂H₆,three tightly-surrounded TATB^3-ligands that coordinated with 6-connected clusters can corporately provide 5 C-H…πvan der Waals interactions for C₂H₆.Due to structure matching between C₂H₄and four symmetrical TATB^3-ligands,C₂H₄ tends to approach 12-connected Y（III）clusters with larger pore volume,further interaction distance greatly weakens the adsorption affinity of C₂H₄.Therefore,the adsorption affinity of C₂H₆ is stronger than that of C₂H₄,which makes Y-TATB can preferentially adsorb C₂H₆ and exhibits excellent C₂H₆/C₂H₄ adsorption separation performance.In this work,Cu-IPA porous MOF was designed and synthesized for the first time,and its C1/C2/C3 separation performance was studied.At 298 K,100 k Pa,the adsorption capacities of C₃H₈,C₂H_6,and CH₄ on Cu-IPA were 3.10 mmol/g,2.57 mmol/g and 0.81 mmol/g,respectively.Especially,C₂H₆ uptake for Cu-IPA has reached 1.33 mmol/g at 10 k Pa.For C2/C1（10:85,v:v）mixture,Cu-IPA exhibited remarkable IAST selectivity of 35,outperforming most of the benchmark adsorbents.After three consecutive breakthrough experiments,Cu-IPA remained excellent dynamic separation performance and recyclability.According to molecule simulation,Cu-IPA contains both triangular channels with a smaller pore size（site I）and hexagonal channels with a larger pore size（site II）.Because of stronger interaction,Site I mainly affect the C1/C2/C3 separation performance of Cu-IPA.Within the in the channel of site I,a large number of oxygen atoms with strong electronegativity enables the framework to form stronger C-H…O van der Waals interaction with C₂H₆ and C₃H₈ with higher polarizability.Due to the appropriate pore size of site I,C₂H₆ and C₃H₈ are adsorbed in the center of site I and can interact with oxygen atoms in all directions evenly,forming 6 and 8 C-H…O van der Waals interactions,respectively.However,CH₄ with a smaller size only forms two C-H…O van der Waals interactions,resulting in its weaker adsorption affinity.Therefore,the large difference between C₂H₆ and CH₄ resulted in remarkable C2/C1 separation selectivity of Cu-IPA.