Investigation of ultrasound-assisted KOH and CaO catalyzed transesterification for biodiesel production from waste cotton-seed cooking oil: Process optimization and conversion rate evaluation

Abstract

Development of Ultrasound (US)-assisted biodiesel production from Waste Cotton-seed Cooking Oil (WCCO) is gaining importance due to significantly lower reaction time and high energy-efficiency. In the present novel work, a comprehensive experimental study for KOH and CaO catalyzed transesterification process with detailed process optimization was performed. Kinetic modeling, scalability and energy analysis were performed to confirm the relative importance of US compared to Mechanical Stirring (MS). The optimized process parameters for KOH and CaO catalyst conditions were determined as methanol/oil molar proportion: 6.1:1 and 10.9:1, catalyst amount (w/w) %: 0.46 % and 0.96 %, reaction temperature: 53.2 °C and 48.3 °C, and the corresponding yield: 97.76 % ± 0.03 and 96.16 % ± 0.03 respectively. Box-Behnken model exhibits a significant correlation with experimental results in case of KOH (R2 = 0.98) and CaO (R2 = 0.97) catalyzed conditions. Triglyceride conversion follows pseudo-first-order reaction kinetics. The activation energy calculated for KOH and CaO catalyzed conditions was 21.36 and 33.83 kJ/mol respectively, which is 1.5 – 1.7 times lower as compared to MS process. Energy analysis showed that dissipated energy in US process is higher compared to MS. The scalability effect (with tenfold batch size), and ultrasonic duty cycle analysis showed that the continuous sonication is more effective in comparison to pulse mode. Physicochemical properties of produced biodiesel were observed in accordance with fuel specification as prescribed by ASTM D6751. Outcomes of this study are useful for development of energy-efficient US-assisted biodiesel production process on industrial scale.