Systematic production of biodiesel fuel from palm oil over porous K2O@CaO catalyst derived from waste chicken eggshell via RSM/kinetic/thermodynamic studies

Abstract

Sustainable synthesis of biodiesel fuel or fatty acid methyl ester (FAME) was studied via transesterification of palm oil (PO) over green/low-cost heterogeneous alkali (waste chicken eggshell/WCE) catalyst. The porous K2O@CaO catalyst was effectively prepared via one-pot hydration-dehydration-incorporation process. The following reformations of catalyst properties were characterized by BET, XRD, SEM-EDX, TGA, FT-IR and CO2-TPD techniques. As obtained results, the as-modified catalysts with characteristic properties such as stronger basic site, higher basicity and surface area were successfully achieved when compared with pristine/commercial CaO, resulting in more facile upgrading of PO to FAME product. An integration between 2k factorial process with Box-Behnken model found that significant factors was in the order of catalyst loading amount > reaction time > reaction temperature. Meanwhile, the obtained optimal conditions were catalyst loading amount = 3 wt% of oil, molar ratio of methanol to oil = 15:1, reaction temperature = 80 °C and reaction temperature = 2 h, imparting a maximum FAME yield of 87.5%. For kinetic and thermodynamic studies of 10%KI/CaO catalyzed transesterification of PO, the important parameters such as Ea, A, ΔH, ΔS and ΔG were found to be 40.04 kJ/mol, 2.85 × 102 min−1, 37.24 kJ/mol, − 172.61 J/mol.K and 60.97 kJ/mol, respectively. The calcium glyceroxide was easily formed during reusability test, resulting in a significant reduction of FAME yield. Thus, regeneration-calcination process at 800 °C was applied to fully recover its properties and catalytic performance. This work provided the eco-friendly strategy for FAME production which could be possibly applied in practical process.