Lubna Nusrat, Kamath Ganesh, Potoff Jeffrey J, Rai Neeraj, Siepmann J Ilja
Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, Michigan 48202, USA.
J Phys Chem B. 2005 Dec 22;109(50):24100-7. doi: 10.1021/jp0549125.
An extension of the transferable potentials for phase equilibria united-atom (TraPPE-UA) force field to thiol, sulfide, and disulfide functionalities and thiophene is presented. In the TraPPE-UA force field, nonbonded interactions are governed by a Lennard-Jones plus fixed point charge functional form. Partial charges are determined through a CHELPG analysis of electrostatic potential energy surfaces derived from ab initio calculations at the HF/6-31g+(d,p) level. The Lennard-Jones well depth and size parameters for four new interaction sites, S (thiols), S(sulfides), S(disulfides), and S(thiophene), were determined by fitting simulation data to pure-component vapor-equilibrium data for methanethiol, dimethyl sulfide, dimethyl disulfide, and thiophene, respectively. Configurational-bias Monte Carlo simulations in the grand canonical ensemble combined with histogram-reweighting methods were used to calculate the vapor-liquid coexistence curves for methanethiol, ethanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, 2-butanethiol, pentanethiol, octanethiol, dimethyl sulfide, diethyl sulfide, ethylmethyl sulfide, dimethyl disulfide, diethyl disulfide, and thiophene. Excellent agreement with experiment is achieved, with unsigned errors of less than 1% for saturated liquid densities and less than 3% for critical temperatures. The normal boiling points were predicted to within 1% of experiment in most cases, although for certain molecules (pentanethiol) deviations as large as 5% were found. Additional calculations were performed to determine the pressure-composition behavior of ethanethiol+n-butane at 373.15 K and the temperature-composition behavior of 1-propanethiol+n-hexane at 1.01 bar. In each case, a good reproduction of experimental vapor-liquid equilibrium separation factors is achieved; both of the coexistence curves are somewhat shifted because of overprediction of the pure-component vapor pressures.
本文介绍了将用于相平衡的可转移联合原子（TraPPE-UA）力场扩展到硫醇、硫化物、二硫化物官能团以及噻吩的情况。在TraPPE-UA力场中，非键相互作用由Lennard-Jones加固定点电荷函数形式控制。部分电荷通过对在HF/6-31g+(d,p)水平的从头算计算得出的静电势能面进行CHELPG分析来确定。四个新相互作用位点S（硫醇）、S（硫化物）、S（二硫化物）和S（噻吩）的Lennard-Jones阱深和尺寸参数分别通过将模拟数据拟合到甲硫醇、二甲基硫醚、二甲基二硫醚和噻吩的纯组分气-液平衡数据来确定。在巨正则系综中结合直方图重加权方法的构型偏置蒙特卡罗模拟被用于计算甲硫醇、乙硫醇、2-甲基-1-丙硫醇、2-甲基-2-丙硫醇、2-丁硫醇、戊硫醇、辛硫醇、二甲基硫醚、二乙基硫醚、甲乙基硫醚、二甲基二硫醚、二乙基二硫醚和噻吩的气-液共存曲线。与实验结果达成了极佳的一致性，饱和液体密度的无符号误差小于1%，临界温度的无符号误差小于3%。在大多数情况下，预测的正常沸点与实验值的偏差在1%以内，不过对于某些分子（戊硫醇），发现偏差高达5%。还进行了额外的计算，以确定373.15 K下乙硫醇 + 正丁烷的压力-组成行为以及1.01 bar下1-丙硫醇 + 正己烷的温度-组成行为。在每种情况下，都能很好地再现实验气-液平衡分离因子；由于对纯组分蒸气压的预测过高，两条共存曲线都有所偏移。
