LCVM型混合规则扩展用于多参数状态方程以关联混合物汽液相平衡

Extending LCVM-type Mixing Rule to Multi-parameter Equations of State for Vapor-liquid Equilibria of Mixtures

基于两参数状态方程提出的LCVM混合规则是将以无穷压力为参考态的HV混合规则与以零压力为参考态的MHV1混合规则线性结合而得的,尽管没有理论基础,但对于计算非极性、极性体系给出了较好的结果。因而研究借鉴获得LCVM混合规则的思路将LCVM混合规则扩展到多参数状态方程中,即将HVOS混合规则与MHV1混合规则进行线性结合,并通过引入两个对比参数λ0,λ∞给出了适合多常数状态方程的新LCVM型混合规则。在新的LCVM型混合规则中,参数δ决定了MHV1和HVOS混合规则的相对贡献,该参数可由模型在高压和低压下拟合二元混合物的泡露点得到,通过拟合得到的值约为0.21;混合规则中的活度系数模型可以利用由低压区关联出的GE模型。采用该新混合规则模型,在较宽的温度与压力范围内,结合Harmens-Knapp(HK)方程对包括非极性体系、极性体系等在内的20种二元混合物进行了相平衡计算。计算的结果与实验数据吻合得很好。该模型与采用VDW混合规则模型的相平衡计算结果比较表明,该模型的关联精度有了很大的提高,可以在较大的温度与压力范围内关联多种体系的汽液相平衡数据。但是在混合规则中,参数b,c是依赖于经验获得,因此还有待于进一步的研究。

The LCVM mixing rule, proposed for two-parameter cubic equations of state, is derived by the linear combination of av at infinite pressure and aM at zero pressure, and provides better results for calculating nonpolar and polar system mixtures. In this paper, the LCVM mixing rule was extended to couple with the multi-parameter equations of state by introducing reduced parameters λo and λ∞. In the new mixing rule, the pararneter δ which determines the relative contributions of zero pressure and infinite pressure mixing rules, was obtained by fitting the bubble point pressures for a variety of binary mixtures at high and low pressures. The new LCVM-type mixing rule, coupled with Harmens-Knapp（HK） equation of state was tested for vapor-liquid equilibria of different polar and nonpolar systems in which the NRTL activity coefficient model was used to calculate the excess Gibbs free energy. The tested results are in good agreement with the various existing experimental data within a wide range of temperatures and pressures. In comparison with the Van der Waals mixing rule, the new mixing rule gives much better results for the correlations of vapor-liquid equilibrium of nonpolar and polar systems. The parameters b, c for the mixing rules can only be obtained by empirical method at present time and this is a problem needed to be solved.