Measurements and modelling of wax formation in diesel fuels

Wax formation in hydrocarbon fluids at low temperatures is one of the haras sing problems faced by the petroleum industry. The prevention of wax format ion, the production of diesels more resistant at low temperatures and the d esign of new and better additives requires a good understanding of the crys tallisation behaviour of the paraffin molecules. Better experimental techni ques to study the wax formation and reliable thermodynamical models, able t o predict the solid-liquid equilibrium of petroleum fluids, would help to p revent and overcome many of the problems associated with wax deposition. Here, an equilibrium cell previously used with synthetic mixtures is applie d to study the influence of the desulphuration on the low temperature behav iour of a Petrogal diesel. The compositions of the solid and liquid phases in equilibrium and the fraction of solids in partly crystallised solutions were measured between - 5 and - 20 degrees C. The latter was also measured by DSC, The experimental data was modelled using the Predictive UNIQUAC mod el. It is shown that the model provides an excellent description of the mea sured phase behaviour for these diesels. The desulphuration of the diesel s eems to make it slightly heavier and to increase its wax appearance tempera ture (WAT). (C) 2000 Elsevier Science Ltd. All rights reserved.