Additives for Improving the Cold Behavior of Diesel Fuel

4 Additives for Improving the Cold Behavior of Diesel Fuel (Coley, 1989) 

Straight run diesei fuels have a high paraffin content, which is desirable, incidentally, for obtaining high cetane numbers. The higher the distillation end point, the higher is the heavy paraffin content (with a carbon number greater than C24). 

The nature of these paraffins and their concentration in diesel fuel affect the three temperatures that characterize the cold behavior. The cloud point is the temperature at which crystals of paraffins appear when the temperature is lowered. The cold filter pluming point is defined as the temperature under which a suspension no ionger flows through a standard filter. Finally, the pour point is the temperature below which the diesel fuel no longer flows by simple gravity in a standard tube. These three temperatures are defined by regulations and the refiner has three types of additives to improve the quality of the diesel fuel of winter. 

Additives that affect the cloud point are no longer in frequent use however, it has been shown that certain polymers having branched paraffins can recognize paraffins of equivalent size and keep them in solution. It is therefore possible to complex the longest paraffins selectively and to decrease the cloud point by 3 to 4°C (Damin et al., 1986). 

Additives acting on the pour point also modify the crystal size and, in addition, decrease the cohesive forces between crystals, allowing flow at lower temperatures. These additives are also copolymers containing vinyl esters, alkyl acrylates, or alkyl fumarates. In addition, formulations containing surfactants, such as the amides or fatty acid salts and long-chain dialkyl-amines, have an effect both on the cold filter plugging point and the pour point. 

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