Chitosan-supported calcium hydroxide hybrid material as new, efficient, and recyclable catalyst for biodiesel production.

• One-step synthesis of sub-micrometric Calcium Hydroxide/Chitosan hybrid catalyst • Biodiesel production with yield up to 98 % and recyclability up to 10 cycles • No calcination step was required for catalyst preparation. • Kinetics and mechanistic insights were provided for heterogeneous catalysis. • Full characterization demonstrated high Ca loading onto the biopolymer. In this work, a novel supported catalyst was prepared starting from calcium chloride and chitosan flakes using a very mild approach in an aqueous medium without final calcination at high temperatures. The as-prepared catalyst was fully characterized by thermogravimetric analysis (TGA), attenuated total reflectance Fourier transform infrared (ATR-FTIR), and X-ray photoelectron (XPS) spectroscopies, transmission and scanning electron microscopies (TEM, SEM), Energy Dispersive X-ray Spectroscopy (EDS), demonstrating that it consists of calcium hydroxide particles of about 200 nm supported on chitosan micrometric structures. The most crucial parameters in the transesterification process were investigated. A methanol/oil ratio of 6:1, a reaction time of 6 h, and a temperature of 60 °C were found to lead to complete conversion. A reaction on a gram scale using waste oil as a starting material was also tested, and excellent results were achieved. Moreover, the catalyst proved to be very robust, since even after the 10th recycle, the conversion rate remained at around 90 %. Spectroscopic analyses showed minimal leaching of material without modification of chemical composition. The kinetic behavior (activation energy, E a) of the catalyst was also studied, which resulted in similar outcomes to Ca-based systems present in the literature, but without the need for costly preparations and with superior recycling resistance. An E a value of 63.25 kJ·mol−1 was found, which agrees with data reported in the literature. [Display omitted] [ABSTRACT FROM AUTHOR]