Preparation Of Nano Boron Nitride And Boron Carbon Nitride Materials And Adsorption And Separation Performances For CH₄/N₂

The development and utilization of coalbed methane is of great significance to alleviate the energy shortage situation in China and improve the quality of the atmospheric environment.Due to the huge methane content in low-and medium-concentration gas,it has considerable economic value,so the development of CH₄/N₂ separation technology is the key to realize the industrialized and efficient utilization of coal bed methane.The pressure swing adsorption separation method has the advantages of relatively mature technology and simple operation,which has caused widespread concern in the separation and purification of mine methane.However,because the physical and chemical properties of CH₄ and N₂ are very similar,it is difficult to make breakthrough progress in the research of CH₄/N₂adsorption separation.The main reason is that the existing adsorbent is difficult to achieve the separation effect required by the industry.Therefore,the development of an adsorbent with excellent adsorption separation effect,simple synthesis steps,and stable physicochemical properties is the focus of research in this field.Hexagonal boron nitride,as a new type of porous material,due to its well-developed pore structure,excellent thermal stability and chemical inertness,high specific surface area and other excellent physical and chemical properties,it has been used in water purification,catalysts,hydrogen storage,etc In order to explore the application of nano boron nitride and nano carbon boron nitride material as adsorbents,the purification of methane in low and medium concentration gas pressure swing adsorption.In this paper,nano-boron nitride with high specific surface area and rich pores was prepared by template-free method.At the same time,in order to achieve the carbonization of boron nitride,a series of nano-BCN materials were prepared by changing the reaction conditions based on the preparation of nano-boron nitride.In addition,the selective adsorption performance of BN and BCN materials in CH₄/N₂mixed system was further studied.The main research contents and results are as follows:?1?Nine boron nitride materials with high specific surface area were prepared by using boric acid as boron source,biuret and urea as compound nitrogen source and adjusting a series of experimental parameters such as reactant ratio,heating rate,holding time and reaction temperature.The results showed that the specific surface area,total pore volume,average pore diameter,specific surface area and micropore volume were 1360m²/g,1.28 cm³/g,1.88nm,1142m²/g and 0.83 cm³/g respectively.?2?The breakthrough experiment results of BN samples prepared under different conditions show that pressure has an important influence on the breakthrough separation effect.The increase in pressure will promote the better the effect of breakthrough separation,but the excessively high pressure leads to the longer time required for the breakthrough of CH₄ and N₂,so the optimal pressure is determined to be 0.3MPa.At the same time,with the increase of CH₄ concentration in the mixed system,the breakthrough time of the two gases of samples BN-1050-3.5?H:U:B=1:3:5?and BN-1050-3.5?H:U:B=1:2:5?will be extended.In addition,the results of atmospheric pressure static adsorption experiments show that the adsorption selection parameter S_CH4/N2H4/N2 of sample BN-950-3.5 is 17.8,which has certain research value in the field of CH₄/N₂ pressure swing adsorption separation..?3?In order to realize the carbonization of BN nanomaterials,seven kinds of porous BCN nanomaterials were prepared on the basis of BN nanomaterials preparation by changing the parameters of glucose addition ratio,reaction temperature and retention time.The optimal specific surface area of the sample is 1258m²/g,the total pore volume is 1.12 cm³/g,the average pore diameter is 1.78nm,the specific surface area of micropores is 935m²/g,and the volume of micropores is 0.82 cm³/g.The results of breakthrough experiments show that the sample BCN-1050-3.5 has a relatively good separation effect at 0.3MPa.In addition,the results of isothermal adsorption experiments at atmospheric pressure show that BCN-950-3.5 has the best separation coefficient,adsorption capacity selection coefficient and adsorption selection parameter,but there is a certain gap compared with BN-950-3.5This paper has 75 figures,23 tables and 78 references.