High Performance Of Mixed Matrix Membranes Synergistically Enhanced By Double Inorganic Fillers For CO₂ Separation

CO₂ capture technologies have become a key in mitigating the greenhouse effect.Compared with a variety of traditional separation technologies such as adsorption,adsorption and cryogenic distillation,membrane technology is more excellent due to its low energy consumption,high separation efficiency,operational simplicity and environmental friendliness.It has important practical significance in developing membrane materials with high permeability and high selectivity for CO₂ separation.In this work,double inorganic fillers were used to control styrene-butadiene-styrene triblock copolymer（SBS）membrane structure,a series of mixed matix membranes（MMMs）are designed and prepared,enhanced CO₂ separation performance.The main research contents are as follows:（1）In this chapter,sheet material metakaolin（MK）and tubular material multi-wall carbon nanotubes（MWCNTs）were introduced into SBS matrix to fabricate mixed matrix membrane.The structure of the mixed matrix membrane was characterized by XRD,SEM and ATR-FTIR.The effects of the mass ratio of MWCNTs to MK（MWCNTs/MK）,pressure and temperature on CO₂/N₂separation performance of membrane were studied.The results showed that the double inorganic fillers have good dispersibility in SBS matrix.The separation performance of the membrane with MWCNTs/MK of 0.15 is optimal.This membrane showed CO₂ permeability of 296 Barrer with good CO₂/N₂ selectivity of 40 at 25°C and 2 bar.MK provided longer and more tortuous pathways to improve CO₂/N₂ selectivity,whereas MWCNTs acted as gas transport highways to improve CO₂ permeability because of their extraordinary smooth walls and large diameter pores.The separation performance of MMM with MWCNTs/MK of 0.15 in simulated flue gas（CO₂/N₂=15/85 vol%）had excellent long-term operational stability for 360 h,and the CO₂ permeability and CO₂/N₂ selectivity of the membrane were 283 Barrer and 38,respectively.（2）In this chapter,ZIF-8 was modified with silane coupling agent3-aminopropyltriethoxysilane（APTES）to obtain ZnA.Then ZnA was grafted onto hydroxylated multi-wall carbon nanotubes（MWCNTs-OH）,which was added to the SBS matrix to prepare mixed matrix membrane.The chemical structure of the inorganic fillers was characterized by FTIR,and CO₂ adsorption performance of fillers was tested.The effects of the mass ratio of ZnA to MWCNTs-OH（ZnA/MWCNTs-OH）,pressure and temperature on CO₂/N₂separation performance of the membranes were investigated.The results showed that ZIF-8 was successfully grafted onto MWCNTs-OH and had good adsorption properties for CO₂.At 25°C and 2 bar,the MMM with the ZnA/MWCNTs-OH of 0.8 had the best CO₂/N₂ separation performance.This membrane showed CO₂ permeability of 420 Barrer with good CO₂/N₂ selectivity of 51.MWCNTs-OH acted as gas transport highways to improve permeability because of their extraordinary smooth walls and large diameter pores,whereas ZnA had molecular sieving effect on CO₂ and N₂,and the metal active sites and unsaturated 2-methylimidazole（Hmim）in ZnA have strong affinity for CO₂,which could enhance the CO₂/N₂ selectivity.And the double inorganic fillers synergistically improved the CO₂/N₂ separation performance of the MMMs.The separation performance of MMM with ZnA/MWCNTs-OH of 0.8 in simulated flue gas（CO₂/N₂=15/85 vol%）had excellent long-term operational stability for360 h,and the CO₂ permeability and CO₂/N₂ selectivity of the membrane were402 Barrer and 49,respectively.（3）In this chapter,Cu₃（BTC）₂ and ZIF-8 were modified by3-aminopropyltriethoxysilane（APTES）to obtain CuA and ZnA,which were introduced into SBS matrix to prepare mixed matrix membranes.The chemical structure of the inorganic fillers was characterized by FTIR.The effects of the mass ratio of ZnA to CuA（ZnA/CuA）,pressure and temperature on the separation performance of CO₂/N₂ were investigated.The results showed that the inorganic fillers were successfully prepared and modified.At 25°C and 2 bar,the MMM with the ZnA/CuA of 2 had the best CO₂/N₂ separation performance.This membrane showed CO₂ permeability of 389 Barrer with good CO₂/N₂selectivity of 60.Because CuA with large pore structure allowed gas to transport quickly,which could improve CO₂ permeability,whereas ZnA had molecular sieving effect on CO₂ and N₂,and the metal active sites in CuA and unsaturated Hmim in ZnA have strong affinity for CO₂,which could enhance the CO₂/N₂selectivity.The double nanofillers synergistically enhanced the gas separation performance of the MMMs.The separation performance of MMM with ZnA/CuA of 2 in simulated flue gas（CO₂/N₂=15/85 vol%）had excellent long-term operational stability for 360 h,and the CO₂ permeability and CO₂/N₂selectivity of the membrane were 380 Barrer and 58,respectively.