Optimized Preparation Of MOFs-based Adsorbent Materials And Its Competitive Adsorption Mechanism For Coal Mine Gases

Gas is a companion to coal.Its main component is methane.It is a non-renewable clean energy.At the same time,gas is the main source of disasters for the safe production of coal mines in China and a strong greenhouse gas second only to CO₂.Therefore,the realization of efficient emission reduction of coal mine gas is of great significance for increasing energy supply and ensuring safe production and environmental protection of coal mines.However,,in the process of coal mine gas drainage,a large amount of air?such as N₂,O₂,CO₂,water vapor,etc.?is mixed due to the leakage of coal body cracks due to the geological conditions of coal seams and the limitation of extraction technology.The low content of CH₄ in the gas seriously restricts the safe transportation and subsequent resource utilization of gas containing gas in coal mines.The adsorptive separation technique is a technical means that has proven effective in the separation of mixed gases among the numerous gas purification methods.However,the key to adsorption separation is the preparation of high-efficiency adsorbents and their competitive adsorption mechanism for multi-component mixed gases.In this thesis,MIL-101 with good methane adsorption performance in MOFs was synthesized by using experimental methods and MOFs materials.It was modified by different methods such as loading Mg²⁺and adding activated carbon.Obtaining the reasons for the improvement of microstructure and adsorption performance after modification by the pore structure test,micromorphology characterization,surface chemical structure analysis and X-ray diffraction measurement.The ideal adsorption solution theory?IAST?was used to predict the adsorption of mixed components based on the test of single component gas adsorption.The results show that the modified material has excellent methane adsorption performance and separation performance of mixed gas in gas-containing?CH₄?gas adsorption separation compared with the original MIL-101 and other traditional adsorbent materials,which provides the theoretical basis and guidance of large-scale application for its large-scale application.The full text of the research results are as follows:?1?The selection of MOFs adsorbent materials in many adsorbent materials was analyzed through the comparison of structure and adsorption characteristics,and the theoretical basis and realistic basis for selecting MIL-101 as modified matrix materials were clarified.Explaining the modification mechanism of Mg²⁺and activated carbon on MOFs such as MIL-101.MIL-101@Mg and MIL-101@AC composites were prepared by loading Mg²⁺and adding activated carbon under different conditions,and the structural evolution characteristics of the modified materials were analyzed.It was found that the modified material had a specific surface area of up to 58.2%,a micropore volume increased by 72.9%,and a micropore size decreased by 100-200 nm,while maintaining the basic skeleton structure of MIL-101.Its pore structure is more conducive to methane adsorption.?2?The synthetic preparation conditions of the modified materials were optimized based on the high temperature and high pressure gas adsorption experiments.The saturated adsorption amount of M@19.2%Mg increased by 60.9%,the saturated adsorption amount of M@12.8%Mg increased by 46.0%,and the saturated adsorption amount of M@DfAC increased by 23.5%compared with the original MIL-101 material.However,the effect of adsorption of nitrogen by modification measures is weak,which provides good conditions for adsorption and separation.Regression analysis was carried out on the methane adsorption-desorption curve of modified materials,and the parameters such as adsorption-desorption hysteresis rate were introduced to characterize the hysteresis of adsorption and desorption of modified materials.The results show that the adsorption hysteresis rate of M@12.8%Mg is only0.3%,the adsorption desorption curve is highly coincident,and it has good adsorption and desorption performance.?3?The thermodynamic characteristics of methane adsorption of the original MIL-101 and modified materials were studied based on the high temperature and high pressure gas adsorption experiments at different temperatures.The results show that the adsorption heat of the material to methane adsorption significantly increases by loading of Mg²⁺and activated carbon,and the interaction between the adsorbent and the gas molecules is obviously enhanced.The parameters characterizing the surface uniformity of the material are defined through the volatility analysis of the same amount of adsorption heat.The closer the value is to 1,the more uniform the surface of the adsorbent.Studies have shown that the value of M@12.8%Mg exceeds 0.97,which means that the surface structure of the modified material is more uniform.?4?The separation of gas-containing gas competitive adsorption under different conditions?methane nitrogen molar ratio of 3:7,2:8,and 1:9?was predicted and analyzed based on the IAST theory and the adsorption characteristics of single-component methane and nitrogen.The results show that as the adsorption pressure increases and the proportion of methane in the mixed components increases,the adsorption separation coefficient increases.The adsorption separation coefficient of M@12.8%Mg to methane vs nitrogen is 4.55 at a temperature of 303K,a maximum adsorption pressure of 6 MPa,and a methane/nitrogen molar ratio of 3:7,which is significantly higher than that of conventional adsorbent materials.