It can be also seen that a higher sulfuric acid concentration
in methanol results in a lower recoveries of FAMEs. However,
when methanol to rice bran ratio of 20 mL/g was used, the FAMEs
obtained at a sulfuric acid concentration in methanol of 1.5% (v/v)
was not significantly higher than that obtained at a sulfuric acid in
methanol of 5% (v/v). Moreover, using low acid amount (0.01, 0.05,
0.5, and 1% (v/v) sulfuric acid in methanol) in the in situ esterification
of rice bran resulted in less FAMEs produced (Yustianingsih
et al., 2009).
The purity of FAMEs remains stable with increasing sulfuric
acid concentration and reaction time as shown in Fig. 2. This was
because the separation process of biodiesel can remove the significant
unwanted compounds, such as polar compounds. Moreover,
using larger sulfuric acid catalyst concentration (5% (v/v) sulfuric
acid in methanol) resulted in bran darkening and an increase in bran