Synthesis of nanomagnetic sulphonated impregnated Ni/Mn/Na2SiO3 as catalyst for esterification of palm fatty acid distillate

Abstract

The deterioration of the environment due to anthropogenic disturbances has become a major concern to scientists and engineers. This study responds to the concern by developing a novel nanomagnetic carbonaceous solid acid catalyst using empty fruit bunches (EFBs) as a precursor. The EFB was sulphonated to obtain acidic EFBs (AEFBs). The impregnation method was performed to incorporate metal oxides, namely, NiO, MnO and Na₂SiO₃, on the AEFBs. This process resulted in three nanomagnetic catalysts, namely, Na₂SiO₃–NiO–MnO/AC, NiO–MnO/AC and NiO/AC. According to X-ray diffraction analysis, the crystal size of the NiO/AC, NiO–MnO/AC and Na₂SiO₃–NiO–MnO/AC catalysts were 13.87, 28.38 and 39.64 nm, respectively, whereas their Brunauer–Emmett–Teller surface areas were 23.78, 12.69 and 16.8 m² g⁻¹, respectively. To confirm the incorporation of active metallic species (Ni, Mn, Na and SiO) into the carbon surface, we performed X-ray photoelectron spectroscopy. TPD-NH₃ absorption showed that the Na₂SiO₃–Ni–MnO/AC catalysts substantially increased in the active sites and exhibited higher acidity. FESEM images showed the morphology of the surface, pore sizes and agglomeration of the catalysts. Moreover, the vibrating sample magnetometer depicted that the Na₂SiO₃–Ni–MnO/AC catalyst was ferrimagnetic with magnetisation and magnetic saturation values of 40.27 and 86.04 emu g⁻¹, respectively. The optimal reaction conditions were as follows: PFAD/methanol ratio of 16 : 1, 2 wt% mass of the catalyst, temperature of 120 °C and time of 4 h. Using the synthesised nanomagnetic catalyst exhibited 96% conversion of PFAD to methyl esters. Furthermore, the Na₂SiO₃–Ni–MnO/AC catalyst was easily separated from the reaction mixture using an external magnet and was recycled six times. The modified nanomagnetic catalyst could be an efficient catalyst for discarded feedstocks for biodiesel production.