Molecular Simulation And Experimental Study Of CO₂ Separation From Natural Gas Using MOF-74

With the adjustment of China’s energy structure,the application proportion of natural gas as clean energy in primary energy is increasing year by year.Accelerating the development of natural gas is an important way to solve the shortage of clean energy.Purification and decarbonization of natural gas is a key link in the process of natural gas development.The purification effect is related to the quality of natural gas and the life of equipment.Adsorption decarburization has been widely studied in offshore and armored applications due to its simple installation and low energy consumption.The development of CO₂ adsorbent is still the core of this method.In this paper,metals such as Ni,Mg,Fe,Cr,Co,Mn are used as the metal center of MOF-74,and the adsorbent is M-MOF-74.Firstly,GCMC and MD methods were used to simulate the adsorption of CO₂ and CO₂/CH4 mixed gas in M-MOF-74 and the diffusion of CO₂ and CH4 in M-MOF-74 respectively.Comparing the adsorptive capacity,adsorptive energy,selectivity and regeneration of adsorbents,it is concluded that Ni-MOF-74 has the best adsorption and separation performance.However,the selectivity of Ni-MOF-74 decreases with the increase of adsorption amount and CO₂ content in the mixed gas,which affects the adsorption separation efficiency.In order to solve this problem,Ni-MOF-74 was modified with various groups such as-CH3,-NH2,-F and-O-Li.The simulation results show that the CO₂ adsorption capacity,adsorption energy and diffusion coefficient of the modified adsorbent increase,while the difference of electrostatic potential distribution in the framework results in the different selectivity of the modified adsorbent.The CO₂ adsorption amount of Li-Ni-MOF-74 modified by-O-Li group is increased by 26.95%,selectivity increased by more than twice compared with Ni-MOF-74,and the shortcomings of selectivity reduction in the process of Ni-MOF-74 adsorption were improved.So it is considered that Li-Ni-MOF-74 is more efficient in the adsorption and separation of CO₂ from natural gas.Secondly,Ni-MOF-74 and Li-Ni-MOF-74 were synthesized by hydrothermal synthesis and their microstructure was characterized.The two adsorbents have the same framework structure,but the specific surface area and pore volume of Li-Ni-MOF-74 are increased by162.03% and 86.42%,respectively,compared with Ni-MOF-74.Finally,a gas adsorption experimental device was built and dynamic penetration experiments were carried out to study the adsorption performance of the two adsorbents at different flow rates and multiple uses.The penetration time and separation factor of the modified adsorbent were greater than those of the modified adsorbent at the same flow rate and the same use times,which is consistent with the previous simulation results that Li-Ni-MOF-74 has better separation efficiency for mixed gases.Due to the better microstructure and gas separation performance of Li-Ni-MOF-74,it can be used as a high-efficiency adsorbent for the separation and separation of CO₂ from natural gas.