Castor-Based Ester Oil Production Using SnCl₂/HZSM-5 Catalyst for Sustainable Transformer

Istiqomah (Transmission and Distribution Department, PLN Research Institute, Jakarta 12760)
Widayat Widayat (2) Department of Chemical Engineering, Faculty of Engineering, Diponegoro University, Semarang 50275, Indonesia. 3) Advanced Materials Laboratory, Diponegoro University, Semarang 50275)
John Philia (Advanced Materials Laboratory, Diponegoro University, Semarang 50275)
Sriyono (Transmission and Distribution Department, PLN Research Institute, Jakarta 12760)
Kevin Gausultan Hadith Mangunkusumo (Transmission and Distribution Department, PLN Research Institute, Jakarta 12760)
Aji Suryo Alam (Transmission and Distribution Department, PLN Research Institute, Jakarta 12760)
Hadiyanto (2) Department of Chemical Engineering, Faculty of Engineering, Diponegoro University, Semarang 50275, Indonesia. 4) Center of Biomass and Renewable Energy (CBIORE), Diponegoro University, Semarang 50275)

Emerging Science Journal
Vol. 10 No. 2 (2026): April

Mineral oil remains the most common insulating fluid in power transformers; nevertheless, its non-biodegradable nature and carbon-based emissions have prompted the quest for environmentally safer alternatives. Castor oil, a sustainable and non-edible derivative, provides a promising source for high-performance ester-based insulating lubricants. This study investigates the synthesis and process optimization of castor-based polyol esters via esterification with trimethylolpropane using a heterogeneous SnCl₂/HZSM-5 catalyst. The alcohol-to-oil molar ratio, temperature, and catalyst loading were among the critical reaction parameters that were modeled and optimized using response surface methods with a central composite design. Under optimized conditions of 130°C and 2.207 wt% catalyst, an ester yield of 81.77% was obtained. The resulting ester oil demonstrated advantageous characteristics, such as acceptable color and dielectric performance, while viscosity and acidity were improved by a two-step process to comply with the IEC 62975:2021 standards for distribution transformer insulating oils. The statistical study validated the model's reliability, with ANOVA indicating a substantial quadratic regression (R² = 0.952). The key novelty of this work lies in demonstrating the potential of SnCl₂/HZSM-5 to catalyze the synthesis of castor-derived polyol esters with tailored physicochemical properties, supporting their future scalability and use as sustainable insulating oils.