Design And Fabrication Of Anion-pillared Hybrid Ultramicroporous Materials For Olefins Separation

Olefins separation and purification,one of the most important but energy-intensive processes in petrochemical industry,is of significance for the production of high-quality and high-value end chemicals.The analogous molecular structures,size and physical properties of light olefins exert great challenges on their separation.The trade-off between capacity and selectivity further sets barriers to design novel porous materials with high separation performance.Anion-pillared hybrid ultramicroporous materials(HUMs)with the merits of high density of basic anions,hyperfine-tuned pore size,designable and predictable frameworks,have exhibited advantages in gas separation.In this work,a series of HUMs were designed and synthesized via judiciously choosing anion-pillars,organic linkers and metal nodes.The adsorption and separation performances of HUMs for light olefins(C2-C4)were systematically investigated in sub-nano-confined space.With the aim of separating and purifying C4 olefins,interpenetrated HUMs were synthesized via altering the kinds of anions and organic linkers and then used for C4 olefins separation.The results showed that interpenetrated HUMs can efficiently separate C4 olefins by combing molecular recognition and size-sieving effects.The effects of anions and organic linkers on the structure and physicochemical properties of HUMs were studied.The adsorption and separation performance of HUMs for C4 olefins were investigated.The structure-property relationships were studied by DFT calculations.The results showed that the cavity size and functional site disposition location can be varied in 0.2 A increments by altering the anion pillars and organic linkers.The adsorption capacity of C4H6,n-C4H8 and iso-C4H8 on SIFSIX-2-Cu-i were 4.02?3.26 and 1.61 mmol g-1,respectively,and C4 olefins can be separated with high capacity and high selectivity.The rotation angle of organic linker in interpenetrated HUMs can be controlled,ZU-52(NbFSIX-2-Cu-i)with the rotation of pyridine ring for 15° captured 2.26 mmol g-1 n-C4H8 and rejected iso-C4H8 completely,however,ZU-33(GeFSIX-14-Cu-i,rotation angle:30 °)can adsorb 2.67 mmol g-1 C4H6 with n-C4H8 and iso-C4H8 excluded.HUMs with finely tuned pore dimensions were constructed,which exhibited the appropriate pore cavity matching trans-2-C4H8 molecular.Trans-/cis-2-C4H8 were efficiently separated by HUMs with high trans-2-C4H8 capacity and cis-2-C4H8 rejected.The influences of metal ions on pore dimensions and trans-/cis-2-C4H8 separation performances of HUMs were systematically investigated.The separation performances were evaluated by breakthrough tests.The results presented that ZU-36-Ni(GeFSIX-3-Ni)unexpectedly exhibited guest-adaptive pore channels for trapping trans-C4H8 with high adsorption capacity(2.45 mmol g-1)while effectively rejecting Cis-C4H8.DFT calculations suggested that the guest-adaptive behavior was derived from the organic linker rotation and the optimal pore dimensions,which not only improved the favorable adsorption of trans-C4H8 with maximum host-guest interactions,but also enhanced the size-exclusion of cis-C4H8.HUMs with suitable pore window size matching the cross section of olefins moleculewere judiciously fabricated with pyrazine as organic linker based on the molecular structures of light olefins and alkanes.The coordination ability between metal sites and organic linker played an important role in HUMs' stability,the stronger the coordination affinity between the metal sites and organic linker was,the more stable the HUMs were,and ZU-36-Ni can be stable until 340?.The adsorption and separation performances of HUMs for light olefins/alkanes were studied by single gas adsorption and breakthrough tests.ZU-36-Ni with suitable pore window of 4.42x4.42 A2 exhibited high capacity for n-C4H8,propylene,and ethylene(2.2?2.1 and 2.1 mmol g-1,respectively)and good separation selectivity for n-C4H8/n-C4H10,propylene/propane and ethylene/ethane.The breakthrough tests presented ZU-36-Ni can be appropriate for the above three mixtures separation.We for the first introduced flexible ligand containing electronegative S-S bridging group into HUMs to construct a robust HUM with more abundant binding sites in pore channels,which can maximize the host-guest interactions.The obtained pillar-sharing interlaced HUMs with one dimensional pore channels decorated by electronegative S and F atoms,were used for trace acetylene(1000 ppm and 1%)removal from ethylene,and the host-guest interactions were studied by DFT calculations.The electronegative atoms enriched pore channel and the optimized rhombic pore shape and size were beneficial to maximize the host-guest interactions of acetylene within the micropore,endowing the interlaced HUMs with enhanced acetylene recognition ability.HUMs exhibited ultrahigh acetylene capacity at low pressures(0.85 mmol g-1 at 0.001 bar),and high separation selectivity for 1/999 acetylene/ethylene mixtures(1225).Breakthrough tests showed that acetylene can be reatined for 310 min(688 min g-1)with a productivity of 828 mL g-1 for ethylene.