<![CDATA[Used cooking oil contains free fatty acids (FFAs), which can increase due to hydrolysis and repeated heating, thereby limiting its further use. This study descriptively evaluated the effects of reaction temperature (40 and 60 °C) and the volume of phosphoric acid catalyst (4 and 8 mL) on the reduction of FFAs through esterification with methanol. Each reaction used 100 mL of pretreated used cooking oil, 20 mL of methanol, and 85% H?PO? for 60 minutes at 500 rpm. FFA content was determined by alkalimetric titration, while FTIR was used for supporting qualitative characterization. The density and viscosity of the new oil and used oil were also compared. The initial FFA content was 2.11%. After esterification, the FFA contents were 1.33%, 0.88%, 0.70%; and 0.33% under the conditions of 4 mL–40 °C, 4 mL–60 °C, 8 mL–40 °C, and 8 mL–60 °C, with reported conversion rates ranging from 37.02% to 84.55%. The lowest FFA content was obtained at 60 °C with 8 mL of H?PO?. The FTIR spectra before and after treatment showed similar C=O and C–O ester bands because the triglycerides already contained ester groups; therefore, FFA titration was used as the primary indicator of esterification progress. Within the range of conditions tested, higher temperatures and catalyst volumes were associated with greater reductions in FFA.]]>
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