Kinerja Resin Kopolimer Poli(stirena-co-divinilbenzena) Sulfonat sebagai Katalis Heterogen dalam Sintesis Biodiesel dari Asam Oleat melalui Reaksi Esterifikasi

Abstract

This study aims to synthesize and evaluate the performance of sulfonated poly(styrene-co-divinylbenzene) copolymer resin as a heterogeneous catalyst in the esterification reaction of oleic acid with methanol for biodiesel production. The copolymer resin was synthesized through the polymerization of styrene and divinylbenzene monomers using benzoyl peroxide (BPO) as a catalyst and subsequently functionalized with sulfonate groups (-SO₃H). Physicochemical characterizations of the resin were performed using FTIR to identify functional groups, XRD to determine crystallinity patterns, TGA to analyze thermal stability, and Surface Area Analyzer (SAA) to investigate the textural properties of the obtained resin. Catalytic performance testing was conducted through the esterification reaction of oleic acid by varying the molar ratio of methanol to oleic acid (6:1, 9:1, and 12:1) and the catalyst mass (0, 1, 3, 5, and 7 wt.%) under predetermined temperature and reaction time conditions. The results indicated successful sulfonation, evidenced by the appearance of a broad O–H stretching peak at 3438 cm-1, asymmetric and symmetric S=O stretching vibrations, and O=S=O stretching vibrations from sulfonate groups observed at 1214, 1032, and 1161 cm-1 in the FT-IR spectra. XRD patterns revealed that both resins were amorphous, with an increased degree of amorphousness after sulfonation, demonstrated by a broad diffraction peak at 2θ = 19.62° for the sulfonated resin. TGA analysis showed that the sulfonated resin catalyst was thermally stable within a temperature range of 100 °C to 150 °C, making it suitable for esterification processes. SAA analysis found that the sulfonated resin had a surface area of 2.037 m²/g, pore volume of 0.001 cc/g, and an average pore diameter of approximately 3.5 nm. The optimal esterification conditions were achieved at a molar ratio of methanol to oleic acid of 12:1, resulting in a conversion of 72%, while a catalyst mass variation of 7 wt.% achieved a biodiesel conversion of up to 92%. Reusability tests demonstrated a gradual decline in catalytic activity from a conversion rate of 76% in the first cycle, decreasing to 45% by the third cycle. This study confirms that sulfonated poly(styrene-co-divinylbenzene) copolymer resin has potential as a heterogeneous catalyst for biodiesel synthesis, although further optimization is necessary to enhance catalyst stability and efficiency.