Sintesis Metil Oleat dari Asam Oleat dan Metanol pada Variasi Rasio Mol dan Katalis K2O/Zeolit Menggunakan Pengaduk Pendispersi Homogen

Abstract

The synthesis of methyl oleate was carried out through an esterification reaction between oleic acid and methanol using a K₂O/zeolite catalyst and a homogenizing disperser stirrer. The K₂O/zeolite catalyst was prepared via an impregnation process of potassium acetate into zeolite, followed by calcination at 500°C for 4 hours. The resulting catalyst was characterized using Fourier Transform Infrared (FT-IR) spectroscopy, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX). The esterification reaction was conducted under varying catalyst concentrations (6%, 9%, 12%, 15%, and 18% w/w) and oleic acid:methanol molar ratios (1:6, 1:9, 1:12, 1:15, and 1:18) with a reaction time of 45 minutes and a stirring speed of 5000 rpm. The percentage conversion of methyl oleate was determined through alkalimetric titration by measuring the acid value before and after the reaction based on ISO 660:2020, as well as through gas chromatography analysis and FT-IR functional group analysis. The highest conversion and yield of methyl oleate were 99.29% ± 0.14% and 84.62% ± 3.07%, respectively, achieved under the reaction conditions of a 1:15 molar ratio, 12% (w/w) catalyst loading, 45-minute reaction time, and 5000 rpm stirring speed. Gas chromatography analysis showed a methyl oleate conversion of 70.58%. FT-IR analysis revealed the presence of an ester -C=O stretching absorption band at 1744.4 cm⁻¹ and the disappearance of the broad -OH stretching vibration band (typical of carboxylic acids) in the 3400–2400 cm⁻¹ region. Additionally, characteristic -C-O-C- stretching bands appeared in the 1300–1000 cm⁻¹ region, with a significant increase in absorption intensity at the lower wavenumber end, indicating successful ester formation. These findings confirm the substitution of the -CH₃ group for the hydrogen atom in the -OH group of oleic acid. The K₂O/zeolite catalyst analysis showed oxide compositions of K₂O (9.02%), SiO₃ (15.95%), and Al₂O₃ (70.96%). FT-IR data indicated successful impregnation of K₂O into the zeolite structure, evidenced by a shift in peak positions to lower wavenumbers after impregnation, with the main peak located at 995 cm⁻¹, corresponding to asymmetric Si–O vibrations.