Esterification of the trap grease resulted in the reduction
of acid value in all experiment runs as shown in Figure 3.
The acid value of trap grease was reduced to about 15.59±
5.10 mg KOH/g from 60.38 mg KOH/g by acid catalyzed
esterification with methanol to FFA ratio of 3:1 using H2SO4
catalysts. When the weight ratio of methanol increased to
5:1, acid value was reduced to 11.60±1.60 mgKOH/g suggesting
that higher methanol-to-FFA ratio could further improve
the reduction of acid value of trap grease. Similarly, Zhang
and Jiang (2008) reported that acid value of Zanthoxylum
bungeanum seed oil with initially high free fatty acid could
not go below 10 mg KOH/g after 60 min of reaction time at
60°C with a 4:1 methanol-to-oil molar ratio, but a further
increase of the methanol ratio to 24:1 reduced the acid value
to less than 2 mg KOH/g. Figure 3 also showed that catalyst
concentration has an influence on the ester content but in
different ways compared to the methanol ratio. It was found
that as the catalyst concentration increased from 2% to 5%
wt. H2SO4, the acid value in the final product was increased
from 10.79±1.08 to 16.39±4.14 mg KOH/g. Furthermore, increasing
reaction time did not promote any reduction of acid
value (Figure 3) corresponding to the results reported by
Zhang and Jiang (2008) who observed that increasing reaction