关键词: Gibbs蒙特卡洛模拟, 乙二醇/1,2-丁二醇, 汽液相平衡, 微观结构

Abstract: Gibbs ensemble Monte Carlo simulation(GEMC) method is used to investigate the vapor-liquid equilibria and microstructure of ethylene glycol(EG)/1,2-butanediol(1,2-BDO), EG/1,3-but-anediol(1,3-BDO) and EG/1,4-butanediol (1,4-BDO) mixtures. The simulation approach and OPLS-AA force field are proved to be adaptable to calculate the vapor-liquid equilibria by comparing the simulating results with experimental data or results calculated from Wilson EOS. Analyses of radial distribution functions for the mixtures above show that there is strong hydrogen-bonding interaction that is unrelated to the site of hydroxyl and Van der Waals interaction occurred in different regions among diol-mixtures. Statistics of the number of O-O atom pair and analyses of the hydrogen-bonding association structure reveal that with increasing EG in the mixture,the microstructure of the saturated liquid phase changes from the state consisting of many big BDO-BDO and EG-BDO hydrogen-bonding association structure(>6) to that composed of many small EG-EG and EGBDO hydrogen-bonding association structure(2~4) with decreased proportion of associated molecules. Molclus and Gaussian 09 are utilized to search for the stable structure of the EG,1,2-BDO small hydrogen-bonding configuration. Then,one possible reason is proposed to explain why the proportion of diols association structure changes in some law above. That is,1,2-BDO-1,2-BDO association structure behaves more stable than others,and,as the number of associated molecules grows,the associated structure changes to be more stable,while the difference between the stability of big EG-EG association structures and smaller EG-1,2-BDO association structures decreases.

Key words: Gibbs ensemble Monte Carlo simulation, ethylene glycol/1,2-butanediol(EG/1,2-BDO), vapor-liquid equilibrium, microstructure