Preparation and characterization of bio-diesels from various bio-oils

Methyl, ethyl, 2-propyl and butyl esters were prepared from canola and linseed oils through transesterification using KOH and/or sodium alkoxides as catalysts. In addition, methyl and ethyl esters were prepared from rapeseed and sunflower oils using the same catalysts. Chemical composition of the esters was determined by HPLC for the class of lipids and by GC for fatty acid compositions. The bio-diesel esters were characterized for their physical and fuel properties including density, viscosity, iodine value, acid value, cloud point, pure point, gross heat of combustion and volatility. Methyl and ethyl esters prepared from a particular vegetable oil had similar viscosities, cloud points and pour points, whereas methyl, ethyl, 2-propyl and butyl esters derived from a particular vegetable oil had similar gross heating values. However, their densities, which were 2-7% higher than those of diesel fuels, statistically decreased in the order of methyl similar to 2-propyl > ethyl > butyl esters. Butyl esters showed reduced cloud. points (-6 degreesC to -10 degreesC) and pour points (-13 degreesC to -16 degreesC) similar to those of summer diesel fuel having cloud and pour points of -8 degreesC and -15 degreesC, respectively. The viscosities of bio-diesels (3.3-7.6 x 10(-4) Pa s at 40 degreesC) were much less than those of pure oils (22.4-45.1 x 10(-4) Pa s at 40 degreesC) and were twice those of summer and winter diesel fuels (3.50 and 1.72 x 10(-4) Pa s at 40 degreesC), and their gross heat contents of approximately 40 MJ/kg were 11% less than those of diesel fuels (similar to 45 MJ/kg). For different esters from the same vegetable oil, methyl esters were the most volatile, and the volatility decreased as the alkyl group grew bulkier. However, the bio-diesels were considerably less volatile than the conventional diesel fuels. (C) 2001 Elsevier Science Ltd. All rights reserved.