Freezing point diesel fuel

Methanol has a very low freezing point which is essential for a practical fuel, and indeed, methanol was once used as an engine coolant antifreeze before better antifreeze compounds were found. While methanol s freezing point is much lower than gasoline and diesel fuel, this is no particular advantage to methanol since gasoline s freezing point is sufficiently low to prevent problems in vehicle fuel systems. 

Once the synthetic crude oils from coal and oil shale have been upgraded and the heavy ends converted to lighter distillates, further refining by existing processes need not be covered in detail except to note the essential character of the products. The paraffinic syncrude from oil shale yields middle distillates which are excellent jet and diesel fuel stocks. The principal requirements are removal of nitrogen to the extent necessary for good thermal stability of the fuels and adjustment of cut points to meet required pour or freeze points, limited by the presence of waxy straight-chain paraffins. The heavy naphtha from shale oil can be further hydrotreated and catalytically reformed to acceptable octane number, but with considerable loss of volume because of the only moderate content of cyclic hydrocarbons, typically 45-50%. On the other... 

The pour point (ASTM D-97, IP 15) is the lowest temperature at which the fuel oil will flow under specified conditions. The maximum and minimum pour point temperatures provide a temperature window where a petroleum product, depending on its thermal history, might appear in the liquid as well as the solid state. Pour point data can be used to supplement other measurements of cold flow behavior, and the data are particularly useful for the screening of the effect of wax interaction modifiers on the flow behavior of petroleum. The pour point should not be confused with the freezing point, which is an index of the lowest temperature at which the crude oil will flow under specified conditions. Test methods (ASTM D-2386, ASTM D-5901, ASTM D-5972, IP 434, IP 435) for the freezing point are not usually applicable to fuel oil but are more applicable to diesel fuel and aviation fuel. 

The hydrotreated shale oil is fractionated by distillation methods into gasoline, jet, diesel, and 650°F bottoms (residua). The jet and diesel fuel boiling ranges were determined experimentally to meet flash point and freeze or pour point requirements. Some of the residua was recycled back to the hydrotreater to increase jet and diesel fuel yields. 

Diesel fuel is not very volatile, so it does not evaporate in the intake air. In a diesel engine, the fuel is sprayed directly into the cylinder right at the top of the compression stroke. The hot, highly compressed air in the cylinder causes the fuel to burn quickly, swirling and vaporizing as it burns. Some of the alkanes in diesel fuel have fairly high freezing points, and they may solidify in cold weather. This partial... 

The freezing point (pour point, doud point, cold filter plugging) of jet fuel and diesel is the lowest temperature at which the fuel remains free of sohd hydrocarbon... 

Pour points are usually lower than freezing points, but exceptions have been encountered. In the jet fuel range, based mainly on the work of Frank Tsai, samples out of 107 deviated by more than 60°F (one high and one low), and, 10 samples deviated by more than 40 F. In the diesel fuel range, the adburacy is better with only 15 in more than 300 samples deviating by more than 15 F, Likewise, in the lube-oil range, about 13 of 165 samples deviated by more than 40°F. 

We apply Equations (6.25)-(6.28) to estimate the flash points and freezing points of diesel ful in MP HCR process and jet fuel in HP HCR process by models predictions on distillation curve, specific gravity, and MeABP. 

Section 6.4.6 demonstrates the updated correlations for predicting the flash point and freezing point of diesel fuel. Figures 6.43 and 6.44 illustrate model predictions on flash point and freezing point of diesel fuel. The AADs are 3.6 °C and 4.1 °C, respectively, which are about the same values as those obtained from correlating plant data. Applying the updated correlations demonstrated in Section 6.4.6, we find satisfactory predictions on the flash point and freezing point of diesel fuel. 

Figure 6.44 Predictions of the freezing point of diesel fuel (MP HCR).

The integrated HCR process models also gives good estimations on liquid product qualities - density, flash point and freezing point of diesel fuel (MP HCR) and jet fuel (HP HCR) - by using updated API correlations. 

---