Densities, Speeds of Sound, and Viscosities of Binary Mixtures of an n-Alkylcyclohexane (n-Propyl-, n-Pentyl-, n-Hexyl-, n-Heptyl, n-Octyl-, n-Nonyl-, n-Decyl-, and n-Dodecyl-) with n-Hexadecane

摘要

This work reports densities, speeds of sound, and viscosities of binary mixtures of n-alkylcyclohexanes (propyl- to dodecylcyclohexane) in n-hexadecane as a function of temperature. Isentropic bulk moduli for these mixtures were calculated from these speed of sound and density data. Mixture densities increased with increasing alkylcyclohexane concentration. As the alkyl-chain length on the alkylcyclohexane increased, the excess molar volume decreased, with n-propylcyclohexane and n-dodecylcyclohexane mixtures having positive and negative excess molar volumes, respectively. Molecular dynamics simulations accurately predict densities and isentropic bulk moduli of n-propylcyclohexane and n-dodecylcyclohexane mixtures, and suggest that the differences in excess molar volumes for different alkyl-chain lengths are related to changes in molecular packing. The speed of sound as a function of mole fraction was modeled using a second-order polynomial, and viscosities were modeled using the McAllister three-body equation. Excess speeds of sound and excess molar Gibbs energies of activation for viscous flow at 293.15 K were not statistically different from zero, which suggest ideal behavior. Many of these mixtures have densities similar to those of petroleum-based diesel and jet fuel and viscosities comparable to diesel fuel. The isentropic bulk modulus of jet fuel is best matched by mixtures of n-propylcyclohexane, while that of diesel fuel is matched by mixtures of n-decylcyclohexane or n-dodecylcyclohexane.