Preparation And Gas Separation Performance Of Mixed Matrix Carbon Molecular Sieve Membranes Doped With Nitrogen-Containing Carbon Materials

With the rapid development of economy,a large number of CO₂ from fossil energy consumption has destroyed the carbon balance of the global atmosphere,which causes global warming and threatens human survival.Under the background of climate issues,the recovery and utilization of the greenhouse gas CO₂ have become the current global consensus.Membrane separation technology exhibit a large amount of advantages such as high separation,low energy consumption and environmental friendly,thus it has attracted much attention.The polymer membrane materials are largely limited to their applications of gas separation,due to their disadvantages such as lower acid and alkaline resistance,poor temperature resistance.As a new type of inorganic membrane,the carbon molecular sieve membranes（CMSMs）are formed by high temperature pyrolysis and carbonization of carbonaceous materials.In order to further improve the gas separation performance of CMSMs,the mixed matrix membrane（MMMs）doped with nitrogen-containing carbon materials is used as the precursor of CMSMs to adjust the pore structure and affinity of CO₂ of the as-prepared CMSMs.The specific research contents are as follows:（1）Melamine is selected as the additive,which is introduced into pyromellitic anhydride-4,4?-diaminodiphenyl ether（PMDA-ODA）type polyamic acid polymer membrane to prepare the mixed matrix membranes.Then,the nitrogen-doped mixed matrix carbon molecular sieve membranes are prepared by pyrolysis carbonization.The structure of the membrane is characterized by Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,Brunauer Emmett Teller（BET）,CO₂ adsorption and desorption curve;the effects of pyrolysis temperature,thermal soak time,melamine doping amount and different inorganic fillers on the separation performance of membranes are systematically discussed.Simultaneously,the separation performance of different dynamic diameter gases and mixed gas,the aging performance of the membranes are investigated.The results show that the mixed matrix CMSMs doped with 5wt%melamine shows the excellent CO₂/N₂ separation performance at 25℃and1 bar under pure gas conditions.Its CO₂ permeability and CO₂/N₂ selectivity are94 Barrer and 193,respectively.This is due to the in-situ formation of g-C₃N₄during membrane carbonization,which increase diffusion of gas molecules at the presence of the g-C₃N₄ sheet material.On the other hand,the strong interaction between triazine unit and CO₂ molecules enhanced the adsorption selectivity of CO₂,thus providing a certain adsorption selectivity for the prepared nitrogen doped CMSMS.The durability test of nitrogen-doped CMSMs shows the excellent CO₂/N₂ selectivity for 70 days.（2）The melamine-modified glucose-carbon sphere is prepared by hydrothermal method firstiy.After that,the precursor is actived to produce pores,and then added to the PMDA-ODA type polyamic acid membrane to prepare the mixed matrix membrane.The mixed matrix CMSMs doped with nitrogen-containing carbon spheres are prepared by pyrolysis at 650℃.The effects of activation time,activation temperature,KOH dosage and NPC loading on gas separation performance are investigated.At the same time,gas permeability performance with different dynamic radii,aging performance and mixed gas performance are studied systematically.When the NPC loading is 5 wt%,the CO₂permeability and the CO₂/N₂ selectivity of the mixed matrix CMSMs are 826Barrer and 87,respectively.This is due to the following two respects.On the one hand,the presence of porous carbon spheres provides the additional gas transmission channels for mixed matrix carbon molecular sieve membranes.On the other hand,the active sites of carbon spheres can increase the interaction with acid gases,providing a certain adsorption selectivity for mixed matrix CMSMs.Therefore,the selectivity of the mixed matrix carbon molecular sieve membrane is improved.The mixed gas test show that when the NPC loading reaches 5 wt%,the CO₂ permeability and CO₂/N₂ selectivity are 807 Barrer and 83,respectively.More importantly,the durability test of CMSMs doped with 5 wt%NPC shows that it can maintain excellent CO₂/N₂ selectivity for about 70 days.