Characterization of Precipitate Formed Above and Below the Cloud Point of Palm Oil Biodiesel

Abstract

Annual biodiesel production has increased due to policies that promote the use of alternative and renewable energy; however, precipitate formation well above the cloud point temperature has limited biodiesel acceptance. Precipitate formation is expected to be accelerated when biodiesel is subjected to low temperatures. However, temperature may affect not only the amount of precipitate but also its physical and chemical nature. Therefore, the nature of precipitate formed above and below the cloud point of palm oil biodiesel (POB) was investigated in this study. POB was incubated at 18 and 4 °C for 16 h and then analyzed to determine the precipitate content and the cold soak filtration time (CSFT) in accordance with the ASTM D7321 and D7501 Standard Tests Methods. Precipitate was isolated and then analyzed using SEM/EDS, FTIR, and DSC. SEM analyses revealed that precipitates isolated from these biodiesels were physically equal. Although differing from each other in their elemental composition, corrugate spherical structures incorporated into a network of snowflake-like structures surrounded by amorphous structures were observed in the precipitates. FTIR spectra suggested that the precipitates were composed of the same compounds, namely FSG and monoglycerides. However, peaks characteristic of FSG were more intense in the spectrum of the precipitate formed at 4 °C. Crystallization and melting profiles obtained by DSC were similar to each other; however, crystallization and melting temperatures and enthalpies of crystallization and fusion were lower for the precipitate formed at 18 °C. Thus, the nature of POB precipitate was not found to be significantly affected by temperature because there were no marked differences in morphology, chemical constitution, and thermal profile between precipitates formed above and below the cloud point.