INTERACTIONS BETWEEN N-ALKANES AND CLOUD POINT COLD FILTER PLUGGING POINT DEPRESSANTS IN A DIESEL FUEL - A THERMODYNAMIC STUDY

Using several experimental techniques such as differential scanning calorimetry (d.s.c.), thermomicroscopy and isoperibolic calorimetry, a thermodynamic study has been carried out on the interactions between n-alkanes and cloud point (CP) and cold filter plugging point (CFPP) depressants. The mode of action of CP additive has been explained by a change in the thermodynamic functions of the solubility equilibrium. Lowering of CP depends on the interactions between long chains of n-alkanes and additives in the fuel, leading to solute complexes. CFPP depressant also causes weak interactions in the fuel but it cannot strongly modify the solubility of n-alkanes. In this case, the mode of action can be characterized by a decrease of the size of n-alkane crystals. Precipitation rate, k, has been evaluated using a germination-growth equation, and a change is observed when a significant lowering of CFPP is reached. It has been shown that the efficiency of CP and CFPP depressants can be evaluated using d.s.c. and thermomicroscopy results.