Effective esterification of sewage sludge lipid feedstock into biodiesel using sulfated-based ZrO2 – SiO2 nanocomposite

A novel sulfated ZrO2-SiO2 nanocomposite has been synthesized using the impregnation process and rigorously evaluated for its efficacy in biodiesel generation by the esterification of either pure free fatty acid (stearic acid) or mixed fatty acids (sewage sludge) as a promising lipid feedstock. The synthesized catalysts were distinguished by SEM, EDX, FT-IR, XRD, N2 adsorption-desorption, (NH3-TPD) analysis, and FT-IR following pyridine adsorption. The outcomes of these analyses revealed that sulfated silica was successfully modified with zirconia, resulting in both the largest production of strong acidic sites and the highest number of Brønsted and Lewis acid sites. The most promising catalyst was the sulfated silica treated with 0.2 % zirconia, where the percentage of the esterification of sewage sludge lipid feedstock and stearic acid at the optimum condition rises to almost 94.5 % and 92 %, respectively. Thermodynamic, pseudo-first order kinetic characteristics and the reusability for fourth runs of sewage sludge esterification onto the optimized zirconia catalyst were examined. Modelling of the sewage sludge esterification via response surface methodology was investigated. The esterification mechanism between the fatty acid and the most effective catalyst was illustrated through the use of a computational chemistry study.