(649d) Precipitate Formation Above Cloud Point In Soy-, Cottonseed-, And Poultry Fat-Based Biodiesel Blends
The formation of precipitates in biodiesel blends may have serious implications for diesel engine fuel delivery systems, such as filter plugging and deposits on injectors and other critical fuel system components. The amount of precipitates is usually measured according to ASTM D2274 or D4625, subjecting the sample to high temperature and/or oxidation treatment. Here we report our findings on precipitates formation after low temperatures storage of three types of biodiesel blends: Soybean oil (SBO), cottonseed oil (CSO), and poultry fat (PF). Three series of biodiesel/ULSD blend samples: B0, B2, B5, B10, B20, B50, B70, and B100 were subjected to low temperature storage at either 4 or -15°C for 24 hours. The time to filter and precipitate mass were then measured after the samples had been returned to room temperature. Fourier transform infrared (FTIR), and matrix-assisted laser desorption/ionization (MALDI) were used to elucidate the nature of precipitates. Precipitates was observed in B5, B10, B20, and B50 after stored at 4 ºC, the temperature of which is substantially higher than the cloud point of biodiesel blends. Similarly, precipitates were observed in B5, B10, B20, B50, B70, and B100 after stored at -15 ºC. On the other hand, no precipitates were observed on the control experiment maintained at room temperature. For soy-based biodiesel, longer filtration times and higher amount of precipitate were measured for B20 as compared to B100 at 4°C. Moreover, two different formation kinetics were observed for the precipitates from B20 and B100. On the other hand, CSO- and PF- based biodiesel had a lower amount of precipates observed than the SBO-based. The cloud point (CP), pour point (PP), and cold flow plugging point (CFPP) increased with concentration for SBO-based, CSO-based, and PF-based biodiesel. The CFPP for B20 of SBO-based biodiesel is almost the same as the cloud point; whereas for the CSO- and PF-based biodiesel, the CFPP was 4 ºC and 2 ºC lower than cloud point, respectively. Thus, the CFPP was be a better indicator of the relative extent of the precipitates formation at low temperatures. The MALDI spectra shows the molecular weight distribution of precipitates is very different among from SBO-, CSO-, and PF-based biodiesel, and even between B20 and B100 of SBO-based biodiesel, suggesting different nature of precipitates. FTIR spectra indicated that the precipitates possess -OH groups. Together with our oxidized studies with filtrated biodiesel, it is concluded that precipitates formation may not be attributed to dimers, trimers, tetramers of oxidative products. Sterol glycosides may be the cause of precipitates formation. In summary, the formation of precipitates during cold temperature storage is dependent on the feedstock and blend concentration. The insolvency effects of biodiesel/petrodiesel blends are greater at low temperature than at room temperature leading to a higher amount of precipitates formed.