Sulfonated Carbon Catalyst Prepared from Calcination of Lignin for Ethyl Levulinate Synthesis via Ethanolysis of Levulinic Acid

Abstract

Ethyl levulinate (EL) is known as a platform bio-based chemical utilized for various applications, specifically as biofuel additives. Ethyl levulinate is synthesized via ethanolysis of levulinic acid (LA) in the presence of heterogeneous acid catalysts. In this study, sulfonated lignin-based carbon (LCS) was used as a solid acid catalyst to synthesize and achieve high EL yield. The lignin-based carbon (LC) precursor was prepared by the calcination of lignin at different temperature ranges (400–600 °C) for the selected time (1 and 2 h). The modification of LC was carried out by sulfonation at 120 °C for 15 h to prepare acid catalysts for ethanolysis. Ion-exchange titration was used to determine the total acid density of all the prepared catalysts. Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption-desorption analysis, and scanning electron microscopy-energy dispersive X-ray were conducted for selected samples to study their physical and chemical properties. The ethanolysis reaction of LA was conducted in a batch process at 80 °C for 3 h with 10 wt% of catalyst loading and 1:10 of LA-to-ethanol molar ratio. The results show that the LCS catalysts have good physical and chemical properties for ethanolysis. The highest EL yield of 71.5 mol% was achieved for the reaction using the LCS prepared at the calcination temperature of 400 °C and calcination time of 1 h (LCS-400-1). The LCS-400-1 has the highest acidity of 0.96 mmol/g with surface area of 43.3 m²/g. The finding also shows that different calcination temperatures and times influence the preparation of LCS and contribute to different catalytic effects on the ethanolysis of LA.