Low Boiling Point Organic Amine-Catalyzed Transesterification for Biodiesel Production

Abstract

The transesterification of triacetin to methyl acetate catalyzed by 11 kinds of low boiling point amines was examined at subcritical methanol temperature as model reactions to simulate the biodiesel production. It was found that the branched amines showed higher yield of methyl acetate than normal amines. For normal amines, the yield of methyl acetate decreased with the increase of the carbon number of the amines. Three kinds of amines, i.e., isopropylamine, tert-butylamine, and triethylamine with boiling points lower than 90 °C and high activities in the above model reaction were, respectively, applied to the transesterification of rapeseed oil or soybean oil with methanol to produce biodiesel. The process conditions, such as molar ratio of methanol to oil, reaction temperature, catalyst usage, and water content were investigated. HPLC, GC, GC-MS, IR and 1H NMR were used to analyze the products. The results indicated that the yield of methyl ester increased with the increase of the molar ratio of methanol to oil from 4:1 to 20:1, the reaction temperature from 60 to 230 °C, and the catalyst content from 0 to 6 wt %. The increase of the water content in the oil had a negative effect on the yield of methyl ester. The yield of biodiesel could reach over 90% when the reaction carried out with a molar ratio of methanol to rapeseed oil of 20:1, a catalyst dosage of 3 wt %, and at the reaction temperature of 230 °C for 6 to 8 h when using the three kinds of amines as catalysts. The possible reaction between the amines with oil was also examined. It was found that small amounts of isopropylamine and tert-butylamine and trace amounts of triethylamine could react with oil under the reaction conditions studied in this paper.