Purification Of Natural Gas By Adsorption On Cyclodextrin-based MOFs And Porous Carbons

In the face of energy shortage and environmental crisis,increasing attention has been paid to cleaner and more economical natural gas resources.However,the natural gas obtained by direct exploitation is usually mixed gas,which can only be utilized after preliminary processing,such as hydrocarbon removal and decarbonization.However,the current separation methods have some limitations,such as high energy consumption,high cost and harsh operating conditions.In this paper,in order to provide a new choice for natural gas purification,cyclodextrin MOFs(CDMOFs)and polyvinylidene chloride resins derived carbons were synthesized around the difficulty of natural gas purification,and their adsorption separation performance for methane/ethane/propane and methane/carbon dioxide/nitrogen were explored.?-CDMOF-1 and?-CDMOF-2 were synthesized by slow diffusion method,and PXRD,TGA and N₂adsorption tests at 77 K were performed.The results show that the materials have good phase purity and thermal stability.The adsorption separation performance of CDMOFs for CH₄,C₂H₆ and C₃H₈ were compared,and potential effect of the materials was investigated by fixed-bed breakthrough experiments.The results show that the IAST selectivity of?-CDMOF-2 for C₂H₆/CH₄(50/50)and C₂H₆/CH₄(50/50)is 190.1 and 22.5,which is inferior to that of?-CDMOF-1(988 and 29.7),but still superior to most reported MOFs.The fixed-bed breakthrough experiments show that both?-CDMOF-1 and?-CDMOF-2 have excellent separation performance on C₂H₆/CH₄(50/50),C₃H₈/CH₄(50/50)and C₃H₈/C₂H₆/CH₄(5/10/85)mixtures.The dynamic adsorption capacity of?-CDMOF-1in C₃H₈/CH₄breakthrough experiment is as high as 2.66 mmol/g.At the same time,both?-CDMOF-1 and?-CDMOF-2 show excellent recycling performance on C₃H₈/C₂H₆/CH₄(5/10/85).A series of C-PVDC-T microporous carbons were prepared by a one-step self reduction method and high temperature activation using bulk PVDC resins as the precursor.PXRD and SEM results showed that PVDC resins were transformed into amorphous carbons,donated as C-PVDC-T(T=700,800,900 and 1000),under high temperature pyrolysis,which not only retained the intact morphology of precursors,but also had abundant micropores on the surface.N₂ adsorption isotherms at 77 K show that C-PVDC-800 has high pore volume and BET surface area,reaching up to 0.37cm³/g and 1211 m²/g.The single-component static adsorption experiments show that the adsorption capacity at 298 K,0.04 bar and 1.0 bar for C-PVDC-800 were measured to be 3.74 mmol/g and 5.19 mmol/g,and the isosteric adsorption heat for C₃H₈ was 78.1 kJ/mol at zero loading,which indicated that the C-PVDC-800 skeleton had a strong interaction of C₃H₈.In addition,the IAST selectivity of C-PVDC-800 for C₃H₈/CH₄(50/50)and C₂H₆/CH₄(50/50)was as high as 3387 and 74.9.The breakthrough experiment shows that the dynamic adsorption capacity of C-PVDC-800 for C₃H₈/C₂H₆/CH₄(5/10/85)ternary mixture is 3.02 mmol/g,and the cycling breakthrough experiments show that C-PVDC-800 has excellent regeneration performance.The adsorption and separation potential of C-PVDC-T for CO₂/CH₄ and CO₂/N₂ were further investigated.The adsorption capacity of C-PVDC-T for CO₂ is significantly higher than that of CH₄ and N₂,and the adsorption curve of CO₂ is relatively steeper in the low pressure region,and the Q_st value for CO₂ is the highest(>23.8 kJ/mol),which indicates that the interaction of carbon materials for CO₂ is greater than that of CH₄(>19.5 kJ/mol)and N₂(>14.6 kJ/mol).At 298 K and 1.0 bar,the adsorption capacity of C-PVDC-700 for CO₂ is4.23 mmol/g,and the IAST selectivity for CO₂/CH₄(50/50)and CO₂/N₂(15/85)is 5.3 and29.6,showing excellent separation potential.In addition,the fixed-bed breakthrough experiments show that the C-PVDC-T can selectively capture CO₂ from CH₄/CO₂ and CO₂/N₂ mixture and obtain high purity N₂ or CH₄.