In this study, a novel idea was proposed to convert the polyethylene terephthalate (PET) waste drinking-water bottles into activated carbon (AC) to use for waste cooking oil (WCO) and palm fatty acid distillate (PFAD) feasibility to convert into esters. The acidic and basic char were prepared by using the waste PET bottles. The physiochemical properties were determined by employing various analytical techniques, such as field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), Brunauer–Emmett–Teller (BET) and temperature-programmed desorption – ammonia/carbon dioxide (TPD-NH₃/CO₂). The prepared PET H₃PO₄ and PET KOH showed the higher surface area, thus illustrating that the surface of both materials has enough space for impregnation of foreign precursors. The TPD-NH₃ and TPD-CO₂ results depicted that PET H₃PO₄ is found to have higher acidity, i.e., 18.17 mmolg⁻¹, due to the attachment of phosponyl groups to it during pretreatment, whereas, in the case of PET KOH, the basicity increases to 13.49 mmolg⁻¹. The conversion results show that prepared materials can be used as a support for an acidic and basic catalyst for the conversion of WCO and PFAD into green fuel.

The main purpose of this manuscript is to report the new usage of tea waste (TW) as a catalyst for efficient conversion of palm fatty acid distillate (PFAD) to biodiesel. In this work, we investigate the potential of tea waste char as a catalyst for biodiesel production before and after sulfonation. The activated sulfonated tea waste char catalyst was characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffractometry (XRD), elemental composition (CHNS), nitrogen adsorption-desorption using Brunauer-Emmett-Teller (BET) and ammonia-temperature-programmed desorption (NH₃-TPD). The activated tea waste char catalyst shows higher acid density of 31 μmol g⁻¹ as compared to tea waste char of 16 μmol g⁻¹ and higher surface area of 122 m²/g. The optimum fatty acid conversion conditions were found that 4 wt % of catalyst loading with 9:1 of methanol:PFAD for 90 min of reaction time at 65 °C gives 97% free fatty acid (FFA) conversion. In conclusion, the sulfonated tea waste (STW) catalyst showed an impressive catalytic activity towards the esterification of PFAD at optimum reaction conditions with significant recyclability in five successive cycles without any reactivation step.