Abstract
Biodiesel can absorb about ten times more water than diesel, which makes it challenging to control its water content according to the specifications set by regulatory agencies. Therefore, efficient water removal from biodiesel is essential to ensure fuel stability and performance. The novelty of this work is the analysis of the effect of post-synthesis alkaline hydrolysis of chitosan-graft-polyacrylamide hydrogels, investigated by immersing the material in sodium hydroxide solution (0.5 M) at 75 °C for 18 h. The hydrolysis significantly enhanced hydrogel performance, increasing the swelling degree from 11 g·g?¹ to 139 g·g?¹ and the biodiesel dehydration efficiency from 47 % to 65 %. SEM, FTIR, and TGA analysis confirmed the hydrogel formation and incorporation of both chitosan and hydrolysed polyacrylamide onto the desiccant network. Batch experiments revealed that dehydration occurs via chemisorption, with both mono and multilayer sorption occurring simultaneously. The system reached kinetic equilibrium after 24 h, with an optimal hydrogel dosage of 0.5 g per 25 mL of saturated biodiesel. The material maintained stable efficiency over three reuse cycles, demonstrating potential for sustainable application. The hydrolysed chitosan-polyacrylamide hydrogel reduced the biodiesel water content from 1,700 to 567 mg·kg?¹, approaching the international specification limit (<500 mg·kg?¹). The results highlight the potential of chitosan-based hydrogels for biodiesel dehydration as a sustainable and reusable material that combine simple separation process with the advantages of renewable biopolymers to improve biofuel quality.
