Research On Performance Of Protic Ionic Liquid-based Membranes For Selective Separation Of CO₂ And CO

Fossil fuels still play dominant roles in the current energy industry,the production and consumption of fossil fuels are accompanied by the generation of CO₂(fossil fuel combustion)and CO(partial oxidation of fossil fuel and steam reforming).The greenhouse effect caused by CO₂ emission poses a serious threat to human survival,and CO is also a highly toxic gas harmful to human body.From the perspective of resource utilization,both CO₂ and CO are extremely important feedstock in C1 chemistry.Therefore,green and sustainable development in the future necessitates efficient capture and separation of CO₂ and CO from different gas sources.Membrane separation is an emerging green separation technology.However,commercial polymer membranes are subject to Robeson Upperbound,makeing it difficult to achieve high separation performance of CO₂ and CO.Ionic liquids(ILs)are a class of low volatile solvents with good affinity to gases.The combination of ionic liquids and membrane separation technology offers a new way to prepare high-performance membranes for gas separation.However,IL-based membranes are still difficult to meet the practical industrial requirements due to their high costs and low separation performance.In order to overcome the problems above,a series of protic ionic liquids-based(PILs-based)membranes were designed and prepared for selective separation of CO₂ and CO.The detailed researches and results are summarized as follows:(1)A series of fluorinion-based protic ionic liquids(FPILs)were designed in this work,and the supported ionic liquid membranes(SILMs)containing FPILs were prepared for selective separation of CO₂.The permeability of CO₂ in aqueous FPIL solutions was high up to 2572 barrers(40°C,0.1 bar),and the ideal selectivities of CO₂/N₂ and CO₂/CH₄ were up to 774 and 387,respectively.FPIL solutions facilitated the transport of CO₂,and the mechanism was further studied through NMR.The inhibition of permeation of N₂ and CH₄ by salting-out effect was found via measuring gas solubilities in aqueous FPIL solutions.This work provides an alternative strategy for designing efficient IL-based membranes.(2)Epichlorohydrin(ECH),a cheap and easily available crosslinking agent,was exploited for crosslinking with 3-(dimethylamino)-1-propylamine methoxyacetate([DMAPAH][MOAc])to synthesize ECH_n-[DMAPAH][MOAc],which are a class of crosslinked protic ionic liquids(CPILs).By monitoring the kinetic information of the crosslinking reaction and characterizing the structure of the products,the occurrence of the crosslinking was proved and a possible crosslinking mechanism was proposed.In addition,gel transition property of ECH-DMAPA was confirmed.Sol-gel membranes impregnated with CPILs were further fabricated.The gas permeation tests showed that the ideal selectivities of CO₂/N₂ and CO₂/CH₄ were up to 409.8 and 248.2(0.05 bar,40°C),respectively,and the maximum pressure resistance was increased to 3.5 bar.In addition,salting-out effects of CPILs on N₂ and CH₄ as well as the facilitated transport of CO₂ were found.A method of adjusting the acid-to-amine molar ratio to optimize CO₂ separation performance was further proposed.This work demonstrated the potential of ECH-crosslinked CPILs in the preparation of IL-based membranes for selective separation of CO₂.(3)In order to prepare CPIL-based membranes with higher crosslinking degree and mechanical properties,ECH was used to crosslinking with tetraethylenepentamine-based(TEPA-based)PILs and supported gel membranes(SGMs)were prepared.Scanning electron microscopy(SEM)characterization showed that the surfaces of prepared gel membranes were flat and dense,and these gel membranes stay stable under the transmembrane pressure difference of 5 bar.The CO₂ permeability in the gel membranes can reach 361.5 barrers(40°C,0.025 bar),and the ideal selectivity of CO₂/N₂ is as high as 294.8.In addition,we investigated the effect of acid-to-amine molar ratio and the content of added PEG 600 on the separation performance.There still exists a large space for optimizing the performance of this type of gel membranes,which possess the potential for industrial application.(4)In order to enrich the limited types of IL-based membranes for selective separation of CO,protic chlorocuprate ionic liquids(PCILs)were designed and immobilized into PES membrane to fabricate SILMs in this part of the work.The separation performances of PCILs in separating CO,H₂,N₂ and CO₂ were investigated.It is found that PCILs facilitated the transport of CO,and the permeability of CO and CO/N₂ selectivity are up to 178.3 barrers(40°C,0.05 bar)and 26.2,respectively.In addition,PCILs also shows good separation performance toward H₂,and the separation performance of CO over H₂ can be selectively controlled by altering operation temperature.This work provides a new way to prepare high-performance membrane for selective separation of CO.In this thesis,a series of low-cost ionic liquid-based membranes were prepared based on protic ionic liquids for the separation of CO₂ and CO,enriching the types of ionic liquid-based membranes.It will also provide new methods and strategies for the preparation of membranes with efficient performance for selective separation of CO₂and CO.