Synthesis of N, N(1,3-phenylene)dimethanimine: A useful resource for the removal of free fatty acid in waste vegetable oil

Abstract

Developing an efficient material for the removal of free fatty acids (FFAs) in waste vegetable oil is a challenge in the refining of vegetable oil in food and oleochemical industries. In response to this, N,N(1, 3-phenylene)dimethanimine (NPD) was synthesized via green reaction route without involving solvent. NPD was characterized using Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric (TG) analysis, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). NPD was then applied as a material for the removal of FFA from waste cooking oil (WCO). The synthesis process gave a high yield of 95% of NPD. The FTIR result revealed different functional groups in NPD, the TG showed mass loss at diverse temperature range revealing loss at 80–150, 180–250, 250–410 and 410–600 °C while loss above 600 °C was assigned to loss of char. while TEM revealed the surface of NPD to be smooth with an irregular shape. EDX results further demonstrated the presence of oxygen, nitrogen and carbon in NPD. Removal of FFA from WCO may be described by pseudo-second-order with an adsorption capacity of 42.30 L kg-1. The process obeyed Langmuir isotherm with ?H of -0.679 kJ mol-1 and ?S of -0.049 kJ mol-1 K-1 while ?G increased with increase in temperature. The Density Functional Theory (DFT) concept was used to explain the action of NPD as an adsorbent with the aid of lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). It revealed the mechanism of removal of FFA from WCO by NPD to be via nucleophilic interaction.