Abstract
The SO3H group-functionalized mesoporous zinc oxide catalyst (SO3H ZnO) was synthesized in order to catalyze the esterification of palm fatty acid distillate (PFAD) containing high free fatty acid (FFA-90%). In this regard, a mesoporous zinc oxide catalyst was hydrothermally fabricated and further functionalized by post-sulfonation treatment to apply -SO3H acid group on the mesopore walls. Structural, textural, physicochemical, thermal, and morphological properties of the synthesized catalysts were characterized by X-ray diffraction (XRD), surface area analysis (Brunauer-Emmett-Teller), Fourier transform infrared spectroscopy (FT-IR), ammonia temperature programmed desorption (NH3-TPD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The synthesized mesoporous SO3H-ZnO catalyst possessed unique characteristics such as high surface area of 305.62 m(2)g(-1), an average pore diameter of 3.16 nm, pore volume of 0.12 cm(3)g(-1), and high acid density of 1.72 mmolg(-1). The optimum esterification conditions were found as 9:1 of methanol to oil molar ratio, 2 wt% of catalyst concentration, 120 degrees C of temperature, and 90 min of reaction time to obtained 95.60% yield of PFAD methyl esters. Additionally, the recyclability experiments revealed that the spent catalyst was highly potential to be recycled for seven consecutive runs without further treatment. Furthermore, some important fuel properties of generated PFAD methyl ester such as density, kinematic viscosity, water content, acid value, could-, pour-, and flash -point were compared well with those of EN 14214 and ASTM D6751 specifications. (C) 2016 Elsevier Ltd. All rights reserved.