Diffusion Coefficients in Mixtures of Poly(oxymethylene) Dimethyl Ethers with Alkanes

Poly(oxymethylene) dimethyl ethers (OME, CH₃O(CH₂O)_nCH₃) are new synthetic fuels that can be produced from renewable resources. An interesting application of OME fuels is the use of them in mixtures with hydrogenated vegetable oils (HVO), which mainly consist of alkanes. Data on diffusion coefficients of OME containing mixtures are lacking in the literature but are needed for modeling OME production processes and OME combustion. Therefore, in the present work, self-diffusion coefficients of binary mixtures of OME and alkanes were measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR). OME with chain lengths n = 1...4 were studied; the alkanes were n-dodecane (C12) and n-hexadecane (C16). The measurements in the binary mixtures were carried out at high dilution of the diffusing components and extrapolated to obtain the self-diffusion coefficients at infinite dilution that are identical with the mutual diffusion coefficient. For completeness, the self-diffusion coefficients of the pure components were also measured. The experiments were carried out at temperatures between 298.15 and 353.15 K at ambient pressure. The experimental data for the diffusion coefficients at infinite dilution were compared with the results from established prediction methods (SEGWE and Wilke and Chang), revealing considerable discrepancies. Furthermore, entropy scaling (ES) was applied here for the first time for modeling diffusion coefficients at infinite dilution. By coupling the results from entropy scaling with the Vignes equation, mutual diffusion coefficients in mixtures of OME and alkanes can now be predicted as a function of temperature, pressure, and composition for a wide range of conditions.