Preparation And Performance Study Of N₂/CH₄ Separation Membrane Based On Hollow SAPO-34 Molecular Siev

Under the pressure of energy crisis and environmental protection,natural gas,as a clean energy,has attracted people’s attention.Gas separation membrane materials show broad application prospects because of low cost,low energy consumption,simple operation and environmental friendliness.However,it is difficult to separate the N₂/CH₄mixture due to the similar dynamic diameter and properties,which is the technical bottleneck of the membrane purification of natural gas.Moreover,due to the limitations of the"trade-off"effect,the polymeric membranes are far from reaching the requirements of the large-scale application in terms of both the permeability coefficient and selectivity.The mixed matrix membrane is a hot topic in the scientific research because it combines the advantages of the filler and the matrix.This paper proposed the idea of the hollow molecular sieve as the filler to prepare the N₂/CH₄separation membrane.The research contents are as follows.Firstly,the SAPO-34 molecular sieve was used as the precursor to realize the cavitation of SAPO-34 molecular sieve by the etching treatment method.The effects of the etching temperature and time on the morphology and structure of the hollow SAPO-34 molecular sieve were investigated,and the N₂/CH₄adsorption test was carried out for the hollow SAPO-34 molecular sieve with good hollow structure.The results showed we could obtain the hollow molecular sieve with good hollow structure after being treated in tetraethyl ammonium hydroxide aqueous solution at60℃for 15 min.Further tests showed that the granularity of the hollow SAPO-34molecular sieve was about 370 nm,the shell thickness was about 30 nm,and the most measurable pore size of the shell was 0.47 nm.Compared with the solid SAPO-34molecular sieve,the hollow SAPO-34 has higher N₂/CH₄adsorption selectivity.Secondly,the hollow SAPO-34 molecular sieve was added into the poly（dodecafluoroheptyl methacrylate）matrix as fillers to prepare the mixed matrix membrane.The loading amount,the test temperature and pressure on the gas permeability of the hollow SAPO-34 molecular sieve were investigated.The results showed that the addition of hollow SAPO-34 molecular sieve could improve the permeability coefficient and solubility selectivity of the gas without sacrificing the gas selectivity.At 35℃,0.2 MPa,the N₂permeability coefficient was 366 Barrer and the N₂/CH₄selectivity was 1.6,which exceeded the upper bound of Robeson in 2008.At the same time,the mixed matrix membrane with the loading amount of 12 wt.%was tested at the variable temperature and pressure.The results showed that the mixed matrix membrane had the high sensitivity to the temperature and pressure.The gas permeability coefficient increased with increasing temperature,but the selectivity remained unchanged.As the pressure increased,the permeability coefficient decreased,and the selectivity was basically independent of the feed pressure.Finally,To improve the dispersion of the molecular sieve in the membrane,the amino-functionalization of the hollow SAPO-34 molecular sieve was synthesized,and the DFHMA-PETA-amino-functionalized hollow SAPO-34 molecular sieve copolymeric membranes was prepared by polymerization of the hollow SAPO-34molecular sieve with the DFHMA monomer and the PETA cross-linker by UV light.The dispersion of fillers and the mechanical strength of the membrane were improved,and the gas permeability showed a further increase to 496 Barrrer while maintaining the gas selectivity.The improvement of the gas permeability was mainly due to the increase of solubility coefficients of N₂and CH₄by the introduction of the amino group.