Central Composite Design Optimization of Friedel-Crafts Benzylation of Toluene over Fe3+/Zn2+-Doped Coconut Shell Biochar

Background and Objective: The Friedel-Crafts benzylation of toluene is an important industrial reaction for producing diarylmethanes, requiring efficient and environmentally benign heterogeneous catalysts. This study evaluated the catalytic performance of Fe³⁺/Zn²⁺ doped coconut shell biochar and optimized the reaction conditions using Response Surface Methodology (RSM) based on a Central Composite Design (CCD). Materials and Methods: Fe³⁺/Zn²⁺-doped coconut shell biochar was synthesized and applied as a heterogeneous catalyst for the Friedel-Crafts benzylation of toluene. Preliminary single-factor experiments were conducted to investigate the effects of the toluene-to-benzyl chloride stoichiometric ratio, reaction temperature, and catalyst loading. Subsequently, CCD was employed to optimize the reaction conditions and develop a quadratic polynomial model for predicting benzyl chloride conversion. Results: The quadratic model showed excellent agreement with the experimental data, with a coefficient of determination (R²) of 0.986. The optimized reaction conditions were a toluene chloride molar ratio of 16.71:1, a reaction temperature of 69.15°C, and a reaction time of 134.57 min, yielding a predicted benzyl chloride conversion of 91.64%. Experimental validation under the optimized conditions achieved a conversion of 93.01±1.68%, confirming the reliability and predictive capability of the developed model. Conclusion: Fe³⁺/Zn²⁺-doped coconut shell biochar is an effective heterogeneous catalyst for the Friedel-Crafts benzylation of toluene. Optimization using RSM-CCD successfully identified the optimum reaction conditions, and the developed quadratic model accurately predicted benzyl chloride conversion, demonstrating its potential for efficient process optimization and industrial application.