Abstract
Egyptian kaolinite was applied in the synthesis of zeolite-A by conventional hydrothermal and alkali fusion methods, resulting in two forms of zeolite-A: the hydrated phase (H.ZA) and the dehydrated phase (DH.ZA). The DH.ZA phase exhibits an enhanced surface area (488 m(2)/g), total basicity (7.73 mmol OH/g), high sodium content (20.2%), and a narrow particle size distribution (5 to 25 mu m) as compared to the H.ZA phase (423 m(2)/g surface area, 5.88 mmol OH/g total basicity, 13.3% sodium content, and 10 to 45 mu m particle size distribution). DH.ZA exhibits enhanced catalytic activity, achieving a biodiesel yield of 96.8% after 60 min at 60 degrees C, while the application of H.ZA resulted in a 95.8% yield after 120 min at 80 degrees C. The controlled transesterification mechanism in the presence of H.ZA and DH.ZA involved robust base-catalyzed reactions. The reactions follow the pseudo-first-order kinetics, and the rate constants (K-c) were determined at three different temperature values (40, 50 and 60 degrees C). The activation energies using H.ZA (35.9 kJ center dot mol(-1)) and DH.ZA (32.714 kJ center dot mol(-1)) demonstrates their efficiencies in mild conditions. The thermodynamic parameters of enthalpy (33.23 kJ center dot mol(-1) (H.ZA) and 30.03 kJ center dot mol(-1) (DH.ZA)), Gibb's free energy (65.164 kJ center dot mol(-1) (H.ZA) and 65.268 kJ center dot mol(-1) (DH.ZA)), and entropy (-195.59 J center dot K-1 center dot mol(-1) (H.ZA) and -195.91 J center dot K-1 center dot mol(-1) (DH.ZA)) demonstrate the spontaneous and endothermic behaviours of these reactions. The obtained biodiesel matches the physical properties of the international standards, and the recyclability properties of the two zeolite phases demonstrate their suitability for commercial-scale applications.