Development of lignin based heterogeneous solid acid catalyst derived from sugarcane bagasse for microwave assisted-transesterification of waste cooking oil

Abstract The production of biodiesel by using homogeneous or heterogeneous catalysts is not favourable due to difficult catalyst recovery, purification of the product in case of homogeneous catalysts and longer reaction time, severe reaction conditions and high production cost are the drawbacks of heterogeneous catalysts. Different sulfonated catalysts were synthesized to overcome these problems and their feasibility on industrial scale. Therefore, the focus of this study was to synthesize a sulfonated catalyst using activated carbon produced from the lignin extracted from sugarcane bagasse and used in the transesterification of waste cooking oil with methanol using microwave as heating source. The catalyst was prepared by varying the sulfonation temperature (140–220 °C) for 120 min and characterized by using thermogravimetric analysis (TGA), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FT-IR), surface area (BET) and elemental analysis by CHNS analyzer. The catalyst prepared at 180 °C for 2 h showed excellent characteristics in terms of surface area i.e., 30.31 m2. g−1, acidic density 4.74 mmol. g−1, pore volume 0.03 cm3 g−1, pore size of 9.44 nm, functional groups attachments, surface morphology and crystallographic structure. The process of transesterification was optimized by varying reaction time (5–25 min), methanol to oil molar ratio (6:1–24:1), catalyst loading (5–20 wt% to oil) and temperature (40–70 °C). The maximum yield (89.19%) of biodiesel was achieved after 15 min with a methanol to oil molar ratio of 18:1 at 60 °C and 15 wt% of catalyst. The reusability and stability of the prepared catalyst up to six cycles with minor loss in its activity i.e., 8% for low-grade feedstocks having higher value of free fatty acid content (FFA) was studied.