Researchers at Argentina’s Instituto de Investigaciones en Catlisis y Petroquímica (INCAPE) are working to lower the cloud point of biodiesel by using solid acid catalysts in the production process.
The cloud point of a fuel is the temperature at which crystals of paraffin wax—which will plug up filters—first appear. Crystals can be detected by cloudiness of the fuel. Biodiesel cloud point (as well as other properties such as kinematic viscosity and cetane number) are dependent on the composition of the esters, and can range from around -3° C to +11° C—much higher than the cloud point of petroleum diesel.
Blending biodiesel into petroleum diesel raises the overall cloud point of the blend. Furthermore, Ultra Low-Sulfur Diesel (ULSD) already has a higher cloud point that its higher-sulfur predecessors.
Thus, devising ways to lower the cloud point in biodiesel would prove extremely useful in promoting higher blends of the fuel in cold weather operation.
The INCAPE team isomerized soy biodiesel in the liquid phase at temperatures ranging from 125° C to 275° C using solid acid catalysts (SO42--ZrO2 and H-mordenite) to inhibit the formation of crystals. They then analyzed the crystallization by measuring the cloud point.
Reaction temperatures about 200° C resulted in decreasing the cetane number and increasing coke deposits.
While reacting biodiesel at 150°-200° C, a small decrease (4°-6.5° C) of the cloud point was obtained without a meaningful decrease of the cetane index. Best results were obtained with SO42--ZrO2 at 125° C.
Isomerization had both positive and negative effects on fuel properties: it reduced the cloud point but also increased the viscosity and decreased the cetane index.
“Depression of the Cloud Point of Biodiesel by Reaction over Solid Acids”; Juan C. Yori, Miguel A. D’Amato, Javier M. Grau, Carlos L. Pieck, and Carlos R. Vera;; Energy Fuels, ASAP Article 10.1021/ef060245i S0887-0624(06)00245-3