DOI: https://doi.org/10.61435/ijred.2026.61945
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Methyl ester production from high free fatty acid content with Ce/Zeolite bifunctional catalyst

1Department of Chemical Engineering, Universitas Diponegoro, Jl. Prof. Sudarto, SH, Tembalang, Semarang, 50275, Indonesia

2Department of Mechanical Engineering, Faculty of Engineering, Diponegoro University, Jl. Prof. Soedharto, S.H. Tembalang Semarang 50275, Central Java, Indonesia

3Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor,, Malaysia

Received: 4 Nov 2025; Revised: 16 Feb 2026; Accepted: 10 Mar 2026; Available online: 15 Mar 2026; Published: 1 May 2026.
Editor(s): Editor Office
Open Access Copyright (c) 2026 The Author(s). Published by Centre of Biomass and Renewable Energy (CBIORE)
Creative Commons License This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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Abstract

The production of methyl esters from high free fatty acid (FFA) feedstock remains a critical challenge in biodiesel processing, particularly when using Palm Acid Oil–waste cooking oil (PAO–WCO) with an initial FFA content of 53.21%. Such high FFA content significantly reduces reaction efficiency and necessitates a conventional two-step process involving esterification to lower the FFA level followed by transesterification to convert triglycerides into methyl esters. This multistep approach limits process efficiency and increases operational complexity for high-FFA feedstock. This study investigates the use of a bifunctional Ce/Zeolite catalyst to enable simultaneous esterification and transesterification in a single-step process for high FFA content oil. The zeolite support was synthesized from geothermal waste, and cerium was incorporated via impregnation. The catalyst was characterized using SEM–EDX, X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface area analyses. The reaction was conducted under various operating conditions, including different temperatures and catalyst loadings. The Ce/Zeolite catalyst exhibited effective bifunctional activity, enhancing the simultaneous conversion of FFAs and triglycerides in high FFA content feedstock. The optimum conditions were a methanol-to-oil molar ratio of 12:1, 4 wt% catalyst loading, and a reaction temperature of 50 °C for 180 min. Under these conditions, FAME concentration of 91.5% was obtained, with FFA conversion of 25.31% (reduction of 13.47% FFAs from initial 53.21%) achieved in a single-step transesterification process. These results demonstrate that Ce/Zeolite is a promising bifunctional catalyst for the efficient processing of high FFA content oil, offering a simplified and more sustainable pathway for industrial biodiesel production.

Keywords: bifunctional catalyst; Ce/Zeolite; methyl ester; high free fatty acid; esterification; transesterification

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Section: Int Conf. of Chemical and Material Engineering 2025
Language : EN
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