Desulfurization of Model Fuel Oil Using Modified Lignin@S-g-C3N4: Optimization via Response Surface Methodology

Abstract

This work reports the oxidative desulfurization of dibenzothiophene in model fuel using Kraft Lignin doped S-graphitic carbon nitride (Fe@KL/S-g-C₃N₄), a newly synthesized and eco-friendly catalyst. Thus, the formation of the composite was confirmed using other characterization techniques such as Energy-Dispersive X-ray Spectroscopy (EDX), Raman Spectroscopy, UV-Visible Spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The result further showed that Kraft lignin (KL) was well adsorbed on to the S-g-C₃N₄ surface. New functional groups created through Kraft lignin adsorption increase surface coverage, add new active sites and improve S-g-C₃N₄ dispersion. The combined action inside the Fe@KL/S-g-C₃N₄ composite enhances its reactivity and also broadens the optical adsorption range. Optimizing the catalyst's effectiveness and assessing the impact of crucial variables on dibenzothiophene conversion. The following parameters were found to be ideal for maximal sulfur removal (98.37% conversion from 200 ppm): 42.5 °C, 0.3 g of catalyst, 32.5 minutes of reaction time, and 1 ml of H2O₂ as the oxidant. The quadratic model was shown to be very accurate (R2 = 0.9905), with a negligible lack of fit (p-value = 0.6671) when compared to the pure error, according to statistical analysis using ANOVA. The heterogeneous catalyst showed exceptional longevity by retaining both its structural integrity and its catalytic properties across five consecutive reuse cycles, proving to be a sustainable choice for desulfurization operations.