Preparation And CO₂ Separation Performance Of 6FDA-TrMPD Mixed Matrix Membranes Filled With CHA-type Zeolites

Excessive CO₂ emissions will cause a series of environmental problems.Therefore,how to capture and recover CO₂ gas has become one of the major issues in the field of environment and energy.Conventional CO₂ separation and capture technologies mainly include cryogenic distillation,chemical absorption,physical adsorption and membrane separation technologies.Among them,membrane technology has become a competitive CO₂ separation method due to its low investment and operating costs,energy saving,easy operation and environmental friendliness.However,currently commercial separation membrane materials are mainly polymer materials,which usually show the trade-off limit in selectivity and permeability at the same time.That is,when the selectivity increases,the permeability usually decreases,and vice versa.Adding inorganic particles into polymer matrix to prepare the mixed matrix membranes（MMMs）can have both the ease of processing of polymer materials and the high selectivity of inorganic materials.Zeolites are considered to be attractive fillers for the preparation of mixed matrix membranes due to their excellent thermal stability and mechanical properties,as well as their high porosity,high specific surface area and good CO₂ adsorption performance.Therefore,this thesis mainly studies the preparation of mixed matrix membrane filled with CHA-type zeolites and uses it for CO₂ separation.The research content mainly includes the following three parts:（1）The polymer 6FDA-TrMPD matrix was synthesized by a two-step condensation method,two CHA-type zeolites（SSZ-13 and SAPO-34）were used as fillers,and the mixed matrix membranes（MMMs）with different zeolite loadings were prepared by solution casting,and the morphology and microstructure of the（MMMs）was investigated.The gas separation performance of CO₂,N₂,CH₄ on the synthesized membrane was studied.For the 6FDA-TrMPD/SSZ-13 mixed matrix membranes,as the loading increased,the single gas permeability of the membrane continuously increased,when the loading was 20 wt.%,the permeability of the membrane reached its maximum value,which was 1363 Barrer,which was 200%higher than that of pure PI membrane,and the ideal selectivity was also improved.For the 6FDA-TrMPD/SAPO-34 mixed matrix membranes,the CO₂ permeability increased significantly with the increase of the loading,when the loading was 40wt.%,the permeability increased from 751 Barrer of pure PI membrane to 1663Barrer,an increase of 120%,and the ideal selectivity remained almost stable.（2）In view of the fact that the zeolite in（1）was easy to agglomerate in the matrix,the dispersant polyvinylpyrrolidone（PVP）was added during the membrane synthesis to improve the gas permeation of the membrane.The morphology and microstructure of the modified membrane were characterized and the single gas performance test was carried out.The results showed that the addition of PVP could improve the distribution of zeolite particles in the matrix under low loading,reduce non-selective pores in the membrane,and effectively improve the gas separation performance of the membrane.When the loading was 5 wt.%,compared to the pure membrane,the selectivity of the CO₂/CH₄ gas pair increased from 15 to 36,an increase of 140%,while the permeability was basically unchanged.（3）Surface functionalization of Zn APO-34 zeolite by imidazole group,a new material Zn APO-34-m IM was synthesized,the physical and chemical properties of the prepared composite materials was characterized through X-ray diffraction（XRD）,field emission scanning electron microscope（SEM）,Fourier transform infrared absorption spectrometer（FT-IR）.The results showed that Zn APO-34 and-m IM（imidazole group）were successfully combined into Zn APO-34-m IM through Zn-N bond,and this combination had almost no effect on its morphology.Subsequently,Zn APO-34 and Zn APO-34-m IM were used as fillers and 6FDA-TrMPD as the matrix to synthesize mixed matrix membrane with a loading amount of 10 wt.%.The morphology and microstructure of the synthesized membrane were characterized,and the results showed the filler had been successfully doped,and Zn APO-34-m IM showed better compatibility with the matrix.Finally,a single-gas separation test was performed on the synthetic membrane.The results showed that the doped filler Zn APO-34-m IM had better separation performance than the filler Zn APO-34.When the loading was 10 wt.%,surface functionalization of Zn APO-34 zeolite could increase the CO₂ permeability from the original 445 Barrer to 1662 Barrer,an increase of 273%,while the CO₂/CH₄ and CO₂/N₂ selectivity remained basically stable.