Quaternary Diffusion Coefficients in Liquids from Microfluidics and Raman Microspectroscopy: Cyclohexane + Toluene + Acetone + Methanol

Abstract

Diffusion data in multicomponent liquids are scarce, because these diffusion measurements are time-consuming and laborious. Most diffusion data are therefore available for binary mixtures. While there are at least some data on ternary diffusion, the data on quaternary diffusion are very limited. Therefore, experimental data on multicomponent diffusion are the bottleneck for modeling and understanding mass transport in chemical, biological, and physiological multicomponent systems. In this work, we present the first measurement of quaternary diffusion coefficients using Raman microspectroscopy in a H-cell microchannel. This measurement method provides access to quaternary diffusion coefficients even from a single experiment. Three experiments are sufficient for good precision and low uncertainty. The presented measurement method reduces the experiment time, the sample volume, and the number of experiments. Diffusion coefficients are reported for the quaternary system cyclohexane + toluene + acetone + methanol and its ternary subsystem cyclohexane + toluene + methanol at 298.15 K. For both systems, significant cross-diffusion coefficients were observed even at low concentrations. Despite the molecular interactions, adding acetone as further component to the system reduced the cross-diffusion coefficients by almost 1 order of magnitude showing the complex behavior of multicomponent diffusion.

Molecular Modeling and Simulation: Model Development, Thermodynamic Properties, Scaling Behavior and Data Management

“…However, because of the lack of experimental data, only consistency test could be performed for the predicted diffusion data. Here, the Fick diffusion coefficient matrix for the mixture cyclohexane + toluene + acetone + methanol, which was recently studied with Raman spectroscopy [54], was successfully predicted solely with molecular simulation techniques.…”

“…Predictive equilibrium MD simulations of diffusion coefficients and the thermodynamic factor of the quaternary mixture cyclohexane (1) + toluene (2) + acetone (3) + methanol (4) were carried out at 298.15 K and 0.1 MPa for one composition that was studied experimentally [54], i.e. x 1 = x 2 = x 3 = 0.05 mol mol −1 .…”

Thermodynamic Theory of Diffusion and Thermodiffusion Coefficients in Multicomponent Mixtures

“…A classical monatomic gas is the gas with the heat capacities c V = 3 2 R and c P = 5 2 R. Waldmann [54] postulates the energy emission for such gas E to be 1 4 C ⋅2P. While the multiplier 1 4 C is of the same nature as for the mass transfer (energy of the Knudsen gas is only transferred with the flowing molecules), the multiplier 2P is less trivial.…”

“…The first step is to define the mass emission functions Γ i . It may be tempting to postulate that they are equal to 1 4 ρ i C i , as for the ideal gas case (and as applied in [51,52]). However, such a form is inconsistent with Statement 1, since for non-ideal mixtures the values of ρ i may not only be dependent on ν i , but also on other potentials ν j .…”

“…For practical applications, it is important to have model expressions making it possible to evaluate these coefficients based on the thermodynamic properties of a mixture. Modeling is essential, since experimental data are scarce and difficult to obtain, and only a few experimental values are available for mixtures containing more than two components [1,2]. The transport coefficients may also be accessed by molecular dynamics simulations, which are outside of the scope of the present work (see, e. g., the reviews in [3][4][5]).…”