Preparation Of Anion-pillared Ultramicroporous Materials And Their Application In Gas Separations

Light hydrocarbons including alkenes,alkynes and alkanes are important basic chemicals and clean energy.Separation and purification is the key technology in the efficient utilization of light hydrocarbons.Traditional separation methods such as cryogenic separation and solvent extraction have the disadvantages of high energy consumption and equipment investments,so new methods of high efficiency separation need to be developed urgently.Adsorption separation is a energy saving and high efficiency technology,and the key is to develop new porous adsorbents.Anion-pillared microporous materials is a new type of porous materials.they have high density strong basic inorganic anionic sites and their structures and apertures can be accurately designed,which contribute to display excellent performances in gas adsorption separation.This work focused on designing and preparing new types of anion-pillared ultramicroporous materials with different metal nodes,organic ligands and inorganic anions,and then investigated their adsorption equilibriums and separation performances of light hydrocarbons.Hydrothermally stable TiF62-pillared microporous materials-TIFSIX-2-Cu-i and TIFSIX-2-Ni-i(2=4-(2-pyridin-4-ylethynyl)pyridine,i=interpenetrated)were prepared.TIFSIX-2-Ni-i were prepared for the first time and single crystal sample was also prepared successfully.The crystal structure,pore size and thermal stability of TIFSIX materials were characterized.The adsorption equilibrium and separation properties of TIFSIX materials on C2H2 and C2H4 were systematically investigated.The modes and sites of interaction between C2H2/C2H4 and TIFSIX materials were obtained by DFT-D calculations.The dynamic C2H2/C2H4 gas mixtures separation performance of TIFSIX materials were evaluated by fixed bed breakthrough tests.Breakthrough tests for C2H2/C2H4 mixtures with trace water and the cycling performance of TIFSIX materials were also researched.The results indicated that the pore size of TIFSIX-2-Cu-i and TIFSIX-2-Ni-i were 5.05 A and 5.10 A and BET specific surface area of them were 320.4 m2/g and 480.5 m2/g,respectively.Their structures remained stable under high temperature(below 237? and 228?,respectively)or exposed to air(65%?75%humid)for 5 days.At 298 K and 1 bar,the C2H2 capacity of TIFSIX-2-Cu-i and TIFSIX-2-Ni-i were up to 4.16 mmol/g and 4.21mmol/g,which exceeded the benchmark material SIFSIX-2-Cu-i(4.02 mmol/g,SIFSIX = SiF62-).At the same time,they showed high separation selectivity of C2H2/C2H4.For the 1/99(v/v)mixtures,Ideal Adsorbed Solution Theory(IAST)selectivities were up to 30.9 and 22.7,respectively.The DFT-D results showed that C2H2 or C2H4 were bound by two diagonal TiF62-from adjacent nets simultaneously.The breakthrough results showed that TIFSIX materials could separate the gas mixtures efficiently and wouldn't be affected by trace water.TIFSIX materials also have good cycling performance and stability.we synthesized SIFSIX-14-Cu-i(14 = 4,4'-azopyridine)by using shorter linker-4,4'-azopyridine(9.0 A).The structure and physicochemical properties of SIFSIX-14-Cu-i were studied.The adsorption equilibrium and separation performance of SIFSIX-14-Cu-i on CO2 and CH4 were systematiclly measured.The results indicated that SiF62-interacted with the pyridine ring on ligand through strong hydrogen bond which induced the tilt of pyridine ring.As a result,a pocket type special structure with the narrow pore size of 3.4 A,which between the dynamic size of CO2 and CH4.SIFSIX-14-Cu-i realized the molecular sieving effect for CO2/CH4 separation and also had ultra high CO2 capacity.At 273 K,1 bar,the uptake of CO2 was up to 172.7 cm3/cm3,while the CH4 capacity was very low(3.8 cm3/cm3).The CO2/CH4 uptake ratio(selectivity)at 273 K and 298 K were up to 46.7 and 116.1,respectively.It was the highest selectivity in literature,at the same time,the CO2 capacity of SIFSIX-14-Cu-i ranked first in molecular sieve materials.DFT-D calculations showed that CO2 was adsorbed at SiF62-site and one cell could hold two CO2 molecules.The results of breakthrough tests demonstrated that SIFSIX-14-Cu-i could separate CO2/CH4(50/50)mixtures efficiently.What's more,the SIFSIX-14-Cu-i column could regenerate easily and its separation performance wouldn't decline after 5 cycling tests.The structure of anions was the key factor affecting the performance of anion-pillared microporous materials.TaF72-was used for the first time as inorganic anion part and new materials of TAFSEV-3-Cu,TAFSEV-3-Ni and TAFSEV-3-Co were successfully syhthsized.Adsorption equilibrium and separation properties of CO2 and CH4 on TAFSEV materials were investigated systematically.The dynamic separation performance of CO2/CH4 mixtures was evaluated by fixed bed breakthrough tests for TAFSEV-3-Ni with the best performance.The results showed that BET surface area of TAFSEV-3-Cu,TAFSEV-3-Ni and TAFSEV-3-Co were 149.17 m2/g,189.86 m2/g and 164.86 m2/g and they could maintain stable under 200?.The IAST selectivity of CO2/CH4(50/50)mixtures at 273 K and 100 kPa on TAFSEV-3-Cu,TAFSEV-3-Ni and TAFSEV-3-Co were calculated as 70.7,5245 and 2984,which were among the top level of reported MOFs.The results of breakthrough tests indicated TAFSEV-3-Ni could separate CO2/CH4 mixtures effectively and had good recycling performance.