Central composite design-based optimization for conversion of free fatty acids in oil extracted from coffee grounds into biodiesel
Abstract
At the present, the extracted oil from waste coffee grounds (WCGO) has proven to be a suitable sources to produce biodiesel. However, because of high free fatty acid (FFA) content in WCGO needs to be pretreated. In this study, the esterification reaction between FFA in extracted oil from coffee grounds with methanol was performed in a batch reactor. Response surface methodology (RSM) was applied to establish experiment, synthesize, evaluvate, and optimize the experiment results. The factors included: MeOH/WCGO molar ratio (5 – 10 mol/mol), H 2 SO 4 /WCGO catalyst content (1 – 10 wt.%), temperature (50 – 70 o C) and reaction time (60 – 120 min). The effects of these factors were evaluated and tested as per RSM. The regression model of conversion of FFA in WCGO to biodiesel was established with a high correlation coefficient (R 2 = 0.923). The FFA conversion of 90 % (final FFA content of 0.70 wt%) was achieved with the MeOH/WCGO molar ratio of 8.18 mol/mol, H 2 SO 4 /WCGO catalyst content of 8.74 wt.% for 90 min at 60 o C. Finally, some important properties of the esterified oil were checked and suitable for the next stage of biodiesel production.