Abstract
Vegetable oils are produced form plants, their burning leads to a complete recyclable CO_2. The oil use as diesel fuel was limited due to its high viscosity (near 10 times of the gas oil). In order to adapt the fuel to the existing engines the vegetable oils had to be modified. The transesterification of vegetable oil with short-chain alcohols, in the presence of base- catalyst, by means of low frequency ultrasound was studied to produce clean fuel for global warming and emission of air pollutants. Rapeseed oil was converted to ethylester by transesterification with ethanol in the presence of potassium hydroxide (KOH) as catalyst. Thirty grams (0.03mol) of rapeseed oil was added 8.52g (0.18mol) of ethanol dissolved 0.03g of KOH, and mixed at 40℃ by ultrasonic irradiation at 19.5kHz or mechanical stirring at 500rpm. Fig. 1 shows the experimental set-up for ultrasonic irradiation. Samples were taken 1 mL and neutralized to add 0.1 mL of acetic acid to stop the reaction. Ethyl ester (ethyl oleate) in the samples were analyzed by gas chromatography with flame ionization detector. Fig. 2 shows the comparison of sonication and stirring. In the samples reacted at 20〜30mm, ethyl ester yield was 48〜49% by sonication and 40〜43% by mechanical stirring. The higher yield of methyl ester by sonication is assumed to result from vigorous mixing by ultrasonic vibration.
