Abstract
The present work unlocks the full potential of sulfonated lignin-based carbon (SLBC) catalyst in the esterification of levulinic acid (LA) with different alcohols such as methanol, ethanol, and n-butanol to alkyl levulinates (ALs), followed by liquid product analysis and product separation. Lignin was calcined to produce carbon material, modified into the SCLB catalyst by hydrothermal sulfonation, and finally characterized. The reaction was performed over SLBC catalyst in selected reaction conditions of 6 molar ratio of alcohol-to-LA, 0.3 g catalyst, and 5 h at respective alcohol reflux temperatures. The liquid products were examined by acid-base titration and then quantified using gas chromatography coupled with mass spectrometry (GC-MS) for comparison of data. The separation of the synthesized ALs and simulated ALs-LA mixture was conducted via liquid-liquid extraction, utilizing 9:1 hexane-water (v/v) mixture as the extraction solvent. The SLBC catalyst successfully yielded ALs (methyl, ethyl, and butyl levulinates) of 73.5–83.3 mol%. The hexane-water mixture was able to extract ALs from the liquid mixtures and the percentage extraction increased for longer alkyl chains of ALs. The acid-base titration demonstrated a minimal percentage difference with GC-MS data for LA conversion and could be suggested as a reliable liquid product analysis, especially for LA esterification reaction.
