Figure 8 represents the effect of reaction time on the yield
of biodiesel over egg shell-based CaO catalyst. Longer reaction
time increased the contact period between methanol
and oil molecules on basic sites of catalyst and brought more
chances for the reaction [30]. The yield increased progressively
from 43.85 to 95.05% as the reaction time increased
from 30 to 180 min. For the operation beyond 3 h, the yield
decreased slightly, which may be due to the longer reaction
time that resulted in the hydrolysis of esters and caused
more fatty acids to form soap [31].