Advanced reactor design for biodiesel synthesis: evaluating a smooth periodic constriction reactor with sunflower oil and eggshell-derived CaO

Depleting fossil fuels and growing environmental pressures highlight the need for sustainable, renewable energy. Biodiesel, a biodegradable and eco-friendly fuel, is a viable solution, but its production faces challenges, including lengthy reaction times, high methanol consumption, and reliance on chemically homogeneous catalysts. This study investigates optimizing biodiesel production in a smooth periodic constriction (SPC) reactor by analyzing the effects of residence time, temperature, molar ratio, and catalyst concentration on conversion efficiency. The SPC reactor’s oscillatory flow and periodic constrictions enhance mixing, improving mass transfer and reaction kinetics. Using response surface methodology (RSM), the following optimal conditions were determined: 51.08 °C, 26 min, 7.1:1 molar ratio, and 5.82% catalyst concentration, yielding a 91.94% conversion efficiency. These conditions surpass conventional reactors, which require 60–100 °C and hours-long processes, reducing energy consumption. The biodiesel met most American Society for Testing and Materials (ASTM) D6751 standards, with minor deviations in water content and iodine value. With sunflower oil as feedstock, the SPC reactor proved highly efficient under milder conditions, highlighting its potential for energy-efficient biodiesel production. Furthermore, eggshell-based CaO catalysts promote sustainability by transforming waste into valuable catalytic material, supporting greener energy production and advancing environmentally responsible fuel alternatives.