分子模拟研究N_(2)在5A分子筛上的吸附和扩散  

MOLECULAR SIMULATION STUDY ON ADSORPTION AND DIFFUSION OF N_(2)ON 5A MOLECULAR SIEVE

作　　者：白彪坤 BAI Biaokun(College of Petroleum and Chemical Engineering,Lanzhou University of Technology Lanzhou 730050,China)

机构地区：[1]兰州理工大学石油化工学院,兰州730050

出　　处：《离子交换与吸附》2020年第5期458-467,共10页Ion Exchange and Adsorption

摘　　要：分子模拟技术广泛应用于从微观尺度上研究分子、原子等粒子的结构和行为,从而模拟宏观性质。为探究低温吸附剂分子筛在低压下的吸附和扩散性质,采用分子模拟软件搭建5A分子筛的晶体模型,基于巨正则蒙特卡洛法和分子动力学方法模拟N_(2)分子在5A分子筛中的吸附和扩散行为,获得分子筛在低温低压下对N_(2)分子的吸附曲线,探讨不同温度下的吸附热,分析不同温度和压力下N_(2)分子在5A分子筛中的扩散过程,并计算得到自扩散系数。研究结果表明,模拟谱图对比标准谱图,5A分子筛的骨架模型合理。平衡压力在10^(-4)~10^(3)Pa范围内,5A分子筛对N_(2)分子的吸附分子数随平衡压力的升高而增大。温度在77K、87K、97K、107K和117K下,吸附分子数随温度的升高而减少。吸附热随吸附分子数的增加,呈现先减小后增大的趋势,且吸附温度越高,吸附初始阶段的吸附热越大。N_(2)分子在5A分子筛中的吸附位随温度的升高从能量较低的吸附位转向能量较高的吸附位。此外,分子动力学研究表明,N_(2)分子在5A分子筛中的自扩散系数随温度的升高而增大,随压力的升高而减小。Molecular simulation technology is widely used to study the structure and behavior of molecules,atoms and other particles on a microscopic scale,thus simulating macroscopic properties.In order to investigate the adsorption and diffusion properties of low temperature adsorbent molecular sieves at low pressure,a crystal model of 5A molecular sieve was built by molecular simulation software.The adsorption and diffusion of N_(2)in 5A molecular sieve were simulated based on Grand Canonical Monte Carlo and Molecular Dynamics.The adsorption curves of molecular sieves on N_(2)at low temperature and low pressure were obtained.The adsorption heat at different temperatures was discussed.The diffusion process of N_(2)in 5A molecular sieves under different temperatures and pressures was analyzed,and the self-diffusion coefficient was calculated.The results showed that compared with the standard XRD,5A molecular sieve structure was reasonable.In the equilibrium pressure range of 10^(-4)~10^(3) Pa,the adsorbed N_(2)in 5A molecular sieve increased with the increase of equilibrium pressure.At 77 K,87 K,97 K,107 K and 117 K,the adsorbed molecules decreased with the increase of temperature.As the adsorbed molecules increased,the adsorption heat first decreased then increased,and the higher the adsorption temperature,the greater the adsorption heat in the initial stage of adsorption.The adsorption sites of N_(2)in 5A molecular sieve shifted from the lower energy adsorption sites to the higher energy adsorption sites as the temperature increases.In addition,Molecular dynamics studies showed that the self-diffusion coefficient of N_(2)in 5A molecular sieve increased as temperature increased and decreased as pressure increased.

关 键 词：分子模拟 5A分子筛 蒙特卡洛 吸附 吸附热 扩散 

分 类 号：TQ424.25[化学工程] O647.3[理学—物理化学]