In this research, a greener heterogeneous catalyst (named TPC) was obtained from 'Ponkan' tangerine (Citrus reticulata Blanco) peel ashes. TPC was efficient for biodiesel production through the methyl route using refined soybean oil and waste cooking oil as raw materials in a biorefinerybased approach. Eight catalyst samples were prepared via calcination of the ashes at 700 °C (TPC7), 800 °C (TPC8) and 900 °C (TPC9), and blends of TPC7 with CaCO 3 and K 2 CO 3 . All the catalysts were employed in preliminary tests for the transesterification reactions. A set of characterization techniques such as Fourier transform infrared and spectroscopy, X-ray diffractometry, X-ray fluorescence, field emission gun scanning electron microscopy, energy-dispersive X-ray, CO 2 -desorption at programmed temperature, thermogravimetric analysis/derivative thermogravimetry (DTG), N 2 adsorption-desorption isotherms, and the Hammett basicity test were performed for catalysts assessment. The X-ray diffractometry patterns showed peaks associated with characteristic phases of K 2 CO 3 , CaCO 3 , K 2 Ca(CO 3 ) 2 , MgO and CaO, confirmed by Fourier transform infrared spectroscopy spectroscopy and X-ray fluorescence. CO 2 -desorption at programmed temperature data demonstrated the presence of basic sites in the TPC catalysts. The experimental evaluation by response surface methodology using the D-Optimal design showed that the reaction time effect (F = 19.04, P-value = 0.0005) and its interaction with the molar ratio effect are the most significant parameters to improve the yield of refined soybean oil biodiesel. The selected reaction conditions promoted a methyl ester conversion higher than 92%, as calculated from 1 H NMR data. Furthermore, the production of waste cooking oil biodiesel was effective using TPC7 and TPC8 catalysts, allowing a sustainable and economic feasibility process.

No abstract