Rcscarch On The Properties And Synthesis Of Microporous Materials Based On The CH₄/N₂Adsorption Separation In The Low Enriched Coalbed Methane

Gas energy is a clean and low-carbon fuels, which becomes an promising energy form of energy in the world now and in the future. Nowdays a variety of unconventional gas (such as coalbed methane and shale gas) have been developed, however, there is scientific problems and the technical bottleneck in terms of purification separation, enrichment, storage and transportation. For example, it is extremely difficult to separate methane and nitrogen under low concentration of coalbed methane enrichment conditions.(1) We prepared several different surfaces on small pore zeolites by hydrothermal synthesis and ion exchange (Li+, Na+and Ca2+) based on three basic gas diameter grade structures of zeolites:KFI (3.9×3.9A), CHA (3.8×3.8A) and LEV (3.6×4.8A), which were characterized by XRD, SEM, and elemental analysis. The surface area was calculated using the D-R equation based on CO2adsorption at273K. The CHA was synthesized with lower Si/Al and the surfaces were changed greatly by ion exchange. KFI had higher Si/Al and the scope of the surface could be kept smaller. Focusing on the CH4and N2adsorption isotherms at high pressure (1MPa), we found that the samples were exchanged by Li+and Na+with bigger surfaces and greater adsorption volumes. From the viewpoint of the separate adsorption equilibria:Na-zeolites for CO2/N2and CO2/CH4, followed by Li-zeolites, which only had a strong adsorption potential of CO2; K-zeolites had the highest data adsorption separation factor of CH4/N2, based on the strong adsorption of CH4, and followed with Na and Li-zeolites. Conclude that the order of adsorption potential was K-zeolites> Na-zeolites> Li-zeolites, so the bigger ions had a stronger affinity. Divalent ions were less likely to be captured in the structures than univalent ions, so their separation was somewhat poorer.(2) Three hydrophobic microporous high-silica zeolites:DDR (8-membered ring), silicalite-1(10-membered ring) and Beta (12-membered ring) were synthesized, and characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, water vapor adsorption and volumetric nitrogen adsorption. They were tested for their CH4and N2adsorption properties at pressures of up to1MPa in the288-303K temperature range after activation, and the relationship between their separation factor (calculated from pure components) for CH4/N2and their microporous structures were analyzed. Compared with low-silica zeolites-5A, MIL-101and active carbon under the same conditions, the experimental results showed that the silicalite-1had the most suitable orifices for methane adsorption and the highest separation facter of CH4/N2. The mixed gas penetrating separation experiments also show that high silicon Silicalite-1having better separation efficiency.(3) Adsorption of CH4and N2was measured in two differently spaced flexible layer metal-organic frameworks (MOFs),[Cu(dhbc)2(bpy)](kitagawa S,2003) and [Cu(BF4)2(bpy)2](ELM-11, Kaneko K,2002), using a gravimetric method at temperatures of77K,195K,273K and298K with a high pressure2MPa. It was found that the gate-opening pressure was much lower at reduced temperatures in the flexible layer MOFs. Gas molecules were easily adsorbed into the widely spaced layers, but the organic ligands which play a supportive role in the layers prevent the spread of more molecules, because more of the space between the layers was occupied. The experimental results also showed the gate phenomenon and implied that these materials would be applicable for gases separated, especially the adsorption ratio of CH4/N2in [Cu(dhbc)2(bpy)] was up to42at normal pressure when the temperature decreased to195K.(4) High pure metal-organic framework chromium terephthalate (MIL-101) was synthesized from TMAOH-Cr(NO3)3-H2BDC-H2O for the first time. Typical synthesized samples were characterized by X-ray diffraction, scanning electron microscopy and thermal gravimetric analysis. CH4adsorption isotherms of the material were studied at273K and303K. The results showed that CH4adsorption was up to132.5cm3/g at273K and92.5cm3/g at303K under1.8MPa which was bigger than the value of MIL-101F-(115cm3/g-273K and89.6cm3/g-303K). It was confirmed that alkaline medium played an important role in this study, on the one hand, it promoted dissolution of the raw material H2BDC in water in the system and the pure sample was obtained easily, on the other hand, the pure sample which was more beneficial was used as the CH4storage material.