2.2. Procedures
The influence of low frequency ultrasound (28 and 40
kHz) versus traditional stirring on the bio-diesel production
from neat vegetable oil, at room temperature,
has been investigated. The reaction mixtures consisted in
vegetable oil, alcohol and alkaline catalyst. The molar
ratio of alcohol to oil was 6:1, and the quantity of catalyst
was 0.5%, 1.0% and 1.5% (wt/wt) to the oil respectively.
The hydroxide was dissolved into the alcohol prior to the
addition of vegetable oil. The silent reactions were performed
using a Matsushita Electric Ind., Model
SCV35W stirrer at 1800 rot/min. The ultrasonic reactions
were performed using Honda Electronics Ultrasonic
CleanersWS1200-28 andWS1200-40, with a total power
of 1200 W, working power being set at 60%.
After the complete conversion of the vegetable oil, as
determined by TLC analysis, the reaction was stopped
and the reaction mixture was allowed to stand for phase
separations: the ester mixture formed the upper layer
and glycerin formed the lower layer. The residual catalyst
and non-reacted alcohol were distributed between
the two phases: some traces into the ester layer and a
high amount in the glycerin layer (due to a high miscibility
of the alcohol with glycerin). After the phases
separation the traces of catalyst and alcohol were washed
out with water from the esters mixture and the
esters were dried over anhydrous calcium chloride. All
experiments were performed in an Erlenmeyer type flask
having 100 ml volume.