Sustainable biodiesel production using lignin-derived sulfonated carbon aerogels catalyst

In response to the energy crisis and the need for carbon neutrality, developing green heterogeneous catalysts for converting waste vegetable oils into biodiesel is promising for reducing carbon emission and pollution. This study introduces a novel sulphonated lignin-based carbon aerogel catalyst, synthesised through a sol-gel process to form a lignin-based hydrogel, followed by solvent exchange, supercritical CO₂ drying, carbonisation at 400°C in an N₂ atmosphere and sulphonation with sulphuric acid. The catalyst, LCA-S1:10(10), features a nanostructured morphology with a high specific surface area of 78.16 m²/g and a strong -SO₃H acidic intensity of 2.81 mmol g−1. Response Surface Methodology (RSM) was used to optimise reaction conditions, employing a central composite rotatable design (CCRD) with a two-factor, five-level approach. Optimal conditions included 10 wt% catalyst loading, an oil-to-methanol molar ratio of 1:45, a reaction temperature of 65°C, and a reaction time of 5 hours, achieving a maximum biodiesel conversion of 91.3%. The biodiesel produced met ASTM D6751 and EN 14214 standards, highlighting its potential for broader application.