Plant Biomass-Derived Sulfonated Carbon Catalysts for Biodiesel Production from Waste Cooking Oil: A Systematic Review

Abstract

Growing interest in sustainable fuels has prompted research into biodiesel production from used cooking oil as a means of converting waste into a renewable energy resource. This review systematically examines plant biomass-derived sulfonated carbons as heterogeneous catalysts for this process. Fifteen selected studies were assessed in terms of biomass feedstock, catalyst preparation and characterization, reaction parameters, biodiesel quality, and catalyst reusability. Across these studies, lignocellulosic biomass emerged as the predominant precursor owing to its ability to yield carbon frameworks suitable for functionalization with catalytically active sulfonic acid groups (–SO₃H). Advances in catalyst synthesis methods show a shift from conventional two-step pyrolysis toward more energy-efficient approaches through process intensification, such as ultrasonic irradiation and microwave-assisted methods, which can significantly reduce reaction time. In general, optimal esterification conditions are achieved at 50 – 70 °C, a methanol-to-oil molar ratio of 18:1 – 22:1, and a reaction time of 1 – 4 h, resulting in biodiesel yields of 80 – 99.7%. Most biodiesel products meet the ASTM D6751 standard, although compliance with EN 14214 remains variable. Catalyst stability is generally moderate to good after several reuse cycles. Overall, this catalyst shows significant potential for industrial-scale biodiesel production, although the decline in catalytic activity due to –SO₃H group leaching and surface fouling requires further investigation.