A comparative study of direct transesterification of camelina oil under supercritical methanol, ethanol and 1-butanol conditions

Abstract

Transesterifications of camelina oil under supercritical methanol, ethanol, and 1-butanol conditions are investigated and compared to find the suitable alcohols for the esters conversion process. The factors affecting the yields of fatty acid methyl esters (FAME), fatty acid ethyl esters (FAEE), and fatty acid butyl eaters (FABE), such as reaction temperature and time, are studied and discussed in detail. The increase of the reaction temperature and time is proved to be favorable to the production of FAME, FAEE, and FABE initially since the transesterification is a reversible, endothermal reaction; however, the persistent increase of reaction temperature and time will decrease the yield of the Camelina sativa biofuels due to their thermal instability. The composition and thermal stability of biodiesel produced under various supercritical alcohol conditions are characterized by gas chromatography-mass spectrometry and thermogravimetric analysis methods. The saturated degree of fatty acid esters in C. sativa oil decreases with the increase of the alkyl chain of the alcohols from methanol, ethanol, to 1-butanol. The physical properties of biodiesels including the specific gravity, viscosity, calorific value, cold properties, and cetane number are tested and compared with the American Society for Testing and Materials (ASTM) standards. According to the results, the specific gravity and the viscosity of the C. sativa biodiesels are comparable to the ASTM standards. The calorific value, cetane number, and cold properties of biodiesel are improved with the increase of the length of the carbon chain of alcohols, while they decrease with the increase of unsaturated degree of compositions of biodiesels.