Physical and Chemical Characterization of Lignin-Based Carbon as Acidic Catalyst

Abstract

Lignin, one of the interesting carbon sources which underutilized, gives great interest in transforming into value-added material, specifically as a solid acid catalyst. In this study, lignin undergoes heat treatment at temperatures 400–600 °C for 1 and 2 h, followed by sulfonation on a 1:10 (carbon-to-acid, g/mL) ratio in a reflux setup at 150 °C for 15 h to produce lignin carbon acid catalysts. The characterization of the catalysts was performed by the elemental analyzer, N2 adsorption-desorption, Fourier transform infrared (FTIR), and acid density calculation. The effects of lignin carbon preparations on the catalyst's physiochemical properties as well as the effectiveness of sulfonation were evaluated. The selected catalyst was tested in levulinic acid esterification at selected fixed conditions; 1:10 molar ratio of levulinic acid-to-ethanol, 10 wt.% of catalyst loading, for 3 h of reaction at 80 °C and 200 rpm in a batch reaction system. At higher heat treatment temperatures and time of carbon preparation, the surface area of the catalysts was recorded to increase resulting in the acid density reduction. For the catalytic activity, 62.36 mol% (Batch 1) and 61.64 mol% (Batch 2) of ethyl levulinate yield were obtained over LCS-400-1 with a good acid density of 0.0223 mmol/m2 and a surface area of 43.28 m2/g. The results of this study show that the conditions for carbon preparation significantly influence the catalyst's physical and chemical characteristics.