Synthesis Of Metal-Organic Frameworks And Their Application In Purification Of Natural Gas

The world energy crisis and environmental pollution problem is increasingly serious,low-carbon and economic natural gas resources have attracted wide attention.Freshly mined natural gas,mixed with many gas impurities,needs to be purified by pickling,de-carbonization and dehydrocarbon-removal processes before initial use.Current industrial separation technologies are limited by high energy consumption,high costs,and harsh environmental conditions of use,so it is necessary to develop new separation technol-ogy to reduce energy consumption.Pressure swing adsorption technology（PSA）based on porous materials has low equipment requirements and simple operation,which can effectively improve the separation efficiency and reduce the cost.As a new generation of porous materials,metal-organic frameworks（MOFs）have been widely studied in the field of gas adsorption,but due to the large preparation cost of MOFs,it is difficult to apply them on a large scale in industry.This paper focuses on the main difficulties of low separation efficiency of small and medium molecular gas impurities in the purification of natural gas,and the high cost of MOFs ligands.Indium fumarate,copper isonicoti-nate and zirconium fumarate MOFs were synthesized by using fumarate or isonicotinate acid as ligands,and their separation capacities for methane/ethane/propane,carbon diox-ide/methane and methane/nitrogen systems were investigated respectively.（1）In-FA-M and In-FA-E isomeric MOFs were synthesized using fumaric acid as ligands.After the materials were characterized by PXRD,BET and FTIR,the pure com-ponent isotherm adsorption experiments of MOFs were carried out to compare the ad-sorption and separation performance of propane,ethane and methane.According to the results,the In-FA-E to C₃H₈saturated adsorption amount of up to 70.8 cm³g^-1at 298K and 1 bar,and the adsorption heat of C₃H₈is 49.1 k J mol^-1,indicating strong inter-action of the In-FA-E pore structure with C₃H₈.In addition,the selectivity of In-FA-M for C₃H₈/CH₄（50/50）and C₂H₆/CH₄（50/50）is 68.9 and 17.3,respectively,which is lower than that of In-FA-E（118 and 18.9,respectively）,showing its good C₃H₈/CH₄and C₂H₆/CH₄separation performance.Meanwhile,the thermogravimetric experiment and C₂H₆adsorption cycle experiment show that In-FA-E will have more stable separation performance and application potential.（2）Cu INA-DH,a microporous MOF material with one-dimensional pore channels,was synthesized using isonicotinic acid as the ligand.After the material was character-ized,the adsorption and separation properties of CO₂/CH₄（50/50）were studied by pure component gas adsorption and desorption experiments.The saturation adsorption of CO₂by Cu INA-DH is 47 cm³g^-1,which is much larger than that of the adsorption of CH₄(3cm³g^-1)at 298 K and 1 bar,and the adsorption heat for CO₂is as low as 38 k J mol^-1.The IAST selectivity results show that the CO₂/CH₄（50/50）selectivity gradually increases with pressure up to 394,which is better than most MOFs materials,indicating its good CO₂/CH₄adsorption separation performance.The GCMC simulation results show that the exposed hydrogen atoms under the suitable microporous structure of Cu INA-DH en-hanced the adsorption of CO₂by MOF,which led to the good CO₂/CH₄separation per-formance of Cu INA-DH.（3）Zr-FA-1 and Zr-FA-2 were synthesized based on zirconium oxygen clusters as metal centers and fumaric acid as ligands.The structure analysis shows that the formate in Zr-FA-2 was used as an auxiliary ligand to bring about a denser pore structure.After the material was characterized by PXRD,BET,etc.,the adsorption properties of CH₄/N₂were investigated by static adsorption experiments on MOFs of Zr-FA-1 and Zr-FA-2.It was calculated that the selectivity of CH₄/N₂at 298 K of Zr-FA-1 is 4.3.The selectivity of Zr-FA-2 with more compact structure is 13.1,and the saturation adsorption capacity of CH₄is 27.5 cm³g^-1,which is higher than most MOFs with a certain adsorption capac-ity.The adsorption heat of 28 k J mol^-1indicates that Zr-FA-2 interacts well with CH₄.The mechanism and adsorption sites of Zr-FA-2 were analyzed by GCMC simulation.The results show that the adsorption site of CH₄is derived from the-CH???πinteraction between the MOF skeleton and CH₄,making Zr-FA-2 exhibit good CH₄/N₂separation performance.