These equations are valid only in the range of variables studied.
The statistical model obtained from coded levels can be represented
as dimensional surfaces, as shown in Figs. 1(b), 2(b),
3(b) and 4(b). These show the ester yield predicted for the experimental
range of temperature and initial catalyst concentration.
For the biodiesel yield the most significant factor is the catalyst
concentration except for UFO4%FFA content which is influenced
more by temperature. The catalyst concentration has a negative
influence on biodiesel yield for all the samples in the experimental
range studied. Temperature also has a negative effect on biodiesel
yield, except in the case of UFO1%FFA content which is positive and
with insignificant effect on the process. Therefore, an increase in
the catalyst concentration and temperature produces a decrease
in biodiesel yield for all the samples of UFO tested.
Sample of UFO4%FFA
The temperature influence is statistically significant in the
range studied. This effect has a negative influence on the response.
For this sample the temperature has an important effect compared
to other samples (0%, 1% and 2% FFA). The temperature effect is
twice the effect of catalyst concentration
As can be seen in Fig. 1(a) at low temperature an increase in
catalyst concentration decreases slightly the product yield from
(95–94.85%). However, when the temperature was set at high
value the increase of catalyst concentration also decrease the yield
from (94.8–94.6%).
Thus initial increases in one of these variables (T and C) at low
value of the second variable produce a slightly decrease in the biodiesel
yield. The maximum yield (95%) obtained from UFO4%FFA was
achieved working at low temperature and catalyst concentration
values (Fig. 1(b)).