Adsorption And Diffusion Of HCl And N₂in MCM-41

With the development of technology and human progress, gas separation technology is being applied in more wider occasions. With the increase in production and demand, people have invented a lot of new separation methods, in which a pressure swing adsorption separation is concerned more. In the study of pressure swing adsorption, reasonable development and efficient adsorbent is particularly important. In recent years, MCM-41as a polar adsorbent, has received widespread attention. This paper introduces that since it was firstly synthesized, the mesoporous molecular sieve MCM-41owning regular and larger pore size and specific surface area, has been widely used in drug delivery, desulfurization heavy fuel, petrochemical industry as a catalyst, adsorption separation etc. In this paper based on MCM-41as a model, use Materials Studio software and the computer simulation method including Grand Canonical Monte Carlo Simulation (GCMC) and molecular dynamics (MD) simulation, respectively analyze adsorption and diffusion properties of N2, HCl, and the mixed gas in the MCM-41mesoporous molecular sieve, discuss separation performance to the two kinds of gas under different temperatures.In terms of adsorption, respectively, simulate the adsorption condition of MCM-41mesoporous molecular sieve adsorbing N2, HCl, and the mixed gas at the temperature of83K,173K,298K under the pressure of100kpa to1000kpa and fit the data of simulation results respectively obtaining Langmuir adsorption isotherms. Simulation results show that for a single component gas adsorption, the adsorption quantity of HCl and N2at83K is much larger than that of HCl and N2at298K, and the adsorption quantity of HCl is larger than that of N2at the same temperature. For mixed gas adsorption, the adsorption quantity of HCl and N2at83K is also much larger than that of HCl and N2at298Kand as we can see from the adsorption quantity and adsorption heat, competitive adsorption occurs in the adsorption process of HCl and N2, in which HCl is preferentially adsorbed with much larger adsorption quantity than N2. According to the results of simulating adsorption, the separation factor relying on temperature is more obvious than that relying on pressure. In addition, The separation effect of low temperature is better. But when the temperature is83K(liquid nitrogen temperature), the adsorption quantity of two kinds of gas is large and can achieve saturated adsorption. At this time, separation coefficient is small, and therefore there is no realistic significance.In terms of diffusion, do a molecular dynamics simulation to stable adsorption configurations in the process of adsorption and analyze particle trajectories. Yet analyze the relation of mean square displacement of all adsorption configuration along with time changing and achieve diffusion coefficient of adsorption at298K under different pressure. The analysis results show that at298K the relation of diffusion coefficient:N2single component>N2mixed components>HCl single component>HCl mixed components. Obviously, in MCM-41, N2spreads faster than HCl. The causes of this phenomenon are that HCl is polar adsorbate which has a larger role with polar adsorbent MCM-41than N2. N2molecule is more beneficial to diffusion than HCl in the pores. In addition, diffusion coefficient of N2and HCl on the z axis is faster than other direction.