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.