汽液相平衡计算混合法则中协体积项b的改进

Modification of co-volume parameter b in mixing rule for calculating vapor liquid equilibrium

混合物汽液相平衡通常需要引入合适的混合法则才能更好地进行关联。针对目前混合法则中协体积项b的改进提出了一种新的修正协体积项b的方法。该方法以Mie势能理论、London色散力理论为基础,同时引入Leach等分子形状系数进行修正,这样协体积项b中的交互作用参数lij形式上是纯组分分子形状系数θ和φ及临界参数的函数,无需实验数据拟合得到,从而真实反映了二元混合物的实际混合情况。将修正的协体积项b运用于MHV1、LCVM及HV混合法则并结合PR+NRTL模型对不同种类的16个体系汽液相平衡进行了计算,并与采用b=∑xibi的MHV1、LCVM及HV混合法则结合PR+NRTL模型计算的结果进行比较,结果表明运用修正的协体积项b的混合法则+PR+NRTL模型所得的计算结果精度优于采用b=∑xibi的MHV1、LCVM及HV混合法则+PR+NRTL模型的计算结果。

To get better correlation results of vapor liquid equilibrium（VLE） of mixture systems, it is usually necessary to select the suitable mixing rule. The modifications of force parameter a have obtained good results in both theory and application. However, the research on co-volume parameter b is less and usually empirical. A new modified method for co-volume b was presented. In the revised mixing rule, the molecular shape factors obtained from Leach et al were introduced to amend co-volume b on the basis of Mie potential-energy and London dispersion theory. Thus, the interactive parameter lij in co-volume b was dependent on the molecular shape factors θ, φ, and critical parameters of the components. Without experimental data, molecular shape factors and interactive parameter lij could be obtained, which could be used to reflect the actual situations of mixture systems. The VLE calculation results for 16 kinds of different systems were given by using modified co-volume parameter b in MHV1/LCVM/HV mixing rules combined with PR EOS and NRTL models, and the results were compared with the results of using b = ∑xibi in MHV1/LCVM/HV mixing rule combined with PR EOS and NRTL models. The models with the modified co-volume b were better than those with b = ∑xibi to some extent.