(25e) Solubility and Nucleation Kinetics of a Series of Representative Single and Mixed Diesel N-Alkanes in Dodecane and Toluene

The formation of n-alkane waxes in solution during cold weather is a recurrent problem in the automotive industry. In diesel fuels, crystallisation of long chains n-alkanes can result in the formation of large flat plate-like crystals leading to flow impairment, blockage of filters and engine fuel starvation. Clearly the unwanted formation of these waxes and their associated problems can cause significant issues for the manufacturer and end-users.

Current wax mitigation strategies involve the development of chemical additives to control or inhibit the nucleation and growth of crystals so that they no longer form large deposits or block filters. However, the variable nature of fuel composition, specifically the fractionation of the n-alkanes, results in a complex challenge for the additive provider to meet operational needs¹. In order to understand crystallisation of waxes in fuels, it is important to understand the crystallisation of n-alkanes in mixtures and singularly.

Here we present the results from an experimental study on the nucleation kinetics and solubility behaviour single and mixtures of 8 n-alkanes representative of diesel fuel, ranging from C₁₆H₃₄ to C₂₃H₄₈ in toluene and dodecane. Analysis of the experimental polythermal data making, use of the analytically derived KBHR approach^2–4 reveals, that in all bar two cases the preferred nucleation mechanism for single n-alkane solutions is instantaneous. i.e. all the nuclei are formed at once at a certain level of supersaturation, to further grow . Furthermore, the influence of chain length on solubility was observed between odd and even alkanes in both toluene and dodecane. By analysing the nucleation and solubility behaviour within the set of n-alkanes tested, suggestions of the factors controlling wax crystallisation in fuel systems are presented and discussed from first thermodynamic principles.

References

[1] A. R. Gerson; K. J. Roberts; J. N. Sherwood, Powder Technol., 65 (1991) 243.

[2] D. Kashchiev; A. Borissova; R. B. Hammond; K. J. Roberts, J. Cryst. Growth, 312 (2010) 698.

[3] D. Kashchiev; A. Borissova; R. B. Hammond; K. J. Roberts, J. Phys. Chem., 114 (2010) 5441.

[4] D. M. Camacho Corzo; A. Borissova; R. B. Hammond; D. Kashchiev; K. J. Roberts; K. Lewtas; I. More, CrystEngComm, 16 (2014) 974.