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<p>Despite extensive research on biodiesel production, few studies have been reported on optimal reduction of high free fatty acid (FFA) of blended oils using process intensive technique and ethanol to achieve high conversion efficiency. This study investigates ultrasound-assisted esterification of a blended low-cost feedstock comprising rice bran acid oil (RBAO; 30 vol%; FFA: 81.27%) and waste cooking oil (WCO; 70 vol%; FFA: 2.58%). The aim was to reduce the FFA content below 2%, enabling efficient transesterification process. Experiments were carried out in a glass reaction vessel with a 750 W ultrasonic processor (20&#xa0;kHz) set to 80% amplitude and a 60% duty cycle. A Box–Behnken design within the RSM framework was applied to the esterification step, and the process parameters (molar ratio (E:O), catalyst amount, and sonication time) were found optimal at 11.5:1, 4.7% (w/w), and 67&#xa0;min, respectively, resulting in a maximum predicted and experimental FFA conversion of 94.35% and 94.18 ± 0.5%, respectively. The low-FFA oil was subsequently converted into biodiesel via transesterification, achieving a yield of 97.5 ± 0.1%. Kinetic modeling indicated reduced activation energy (35.07&#xa0;kJ/mol) compared to conventional mechanical stirring. Ultrasonication significantly enhanced mass transfer between immiscible phases, accelerated reaction rates, and lowered energy requirements. Thermodynamic analysis showed the process is endothermic and not spontaneous; the biodiesel complied with EN 14214/ASTM D6751 ester-content criteria (≥ 96.5%) and exhibited physicochemical properties suitable for commercial applications. This work demonstrates ultrasound-assisted esterification using ethanol as a promising strategy to convert high-FFA feedstocks into sustainable biodiesel, supporting circular economy and clean energy goals.</p>

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Ultrasound assisted esterification reaction of pre-blended high free fatty acid rice bran acid oil and waste cooking oil: process optimization, thermodynamic and kinetic modelling

  • 期刊论文

  • 发表日期：

    2026年2月26日

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  • Samay Sagar Patel,
  • Nirav Prajapati,
  • Surendra Singh Kachhwaha,
  • Pravin Kodgire

摘要

Despite extensive research on biodiesel production, few studies have been reported on optimal reduction of high free fatty acid (FFA) of blended oils using process intensive technique and ethanol to achieve high conversion efficiency. This study investigates ultrasound-assisted esterification of a blended low-cost feedstock comprising rice bran acid oil (RBAO; 30 vol%; FFA: 81.27%) and waste cooking oil (WCO; 70 vol%; FFA: 2.58%). The aim was to reduce the FFA content below 2%, enabling efficient transesterification process. Experiments were carried out in a glass reaction vessel with a 750 W ultrasonic processor (20 kHz) set to 80% amplitude and a 60% duty cycle. A Box–Behnken design within the RSM framework was applied to the esterification step, and the process parameters (molar ratio (E:O), catalyst amount, and sonication time) were found optimal at 11.5:1, 4.7% (w/w), and 67 min, respectively, resulting in a maximum predicted and experimental FFA conversion of 94.35% and 94.18 ± 0.5%, respectively. The low-FFA oil was subsequently converted into biodiesel via transesterification, achieving a yield of 97.5 ± 0.1%. Kinetic modeling indicated reduced activation energy (35.07 kJ/mol) compared to conventional mechanical stirring. Ultrasonication significantly enhanced mass transfer between immiscible phases, accelerated reaction rates, and lowered energy requirements. Thermodynamic analysis showed the process is endothermic and not spontaneous; the biodiesel complied with EN 14214/ASTM D6751 ester-content criteria (≥ 96.5%) and exhibited physicochemical properties suitable for commercial applications. This work demonstrates ultrasound-assisted esterification using ethanol as a promising strategy to convert high-FFA feedstocks into sustainable biodiesel, supporting circular economy and clean energy goals.