Sulfonated Carbon Aerogel as Strong Solid Acid Catalyst for Esterification of Oleic Acid-Methanol

Biodiesel is a promising alternative energy source instead of fossil fuels that can be produced by the esterification process, which is the reaction of the production of ester compounds by reacting the alcohol with fatty acids in the presence of acid catalysts. In this work, a solid acid catalyst was prepared from cellulose aerogel, which is subsequently pyrolyzed into carbon aerogel before being sulfonated. Cellulose aerogel was derived from coir fiber in the system of NaOH-urea crosslinking solution at −14 °C. Carbon aerogel was produced through pyrolysis at 700 °C for 2 h. The sulfonation process was carried out by adding H2SO4 at a temperature of 100 °C for 5 h under atmospheric N2 conditions. Sulfonated carbon aerogel was characterized by acid density, SAA, SEM, and FTIR analysis. Carbon aerogel obtained by pyrolysis has a larger surface area of 1655.10 m² g⁻¹ than the initial cellulose aerogel of 430.52 m² g⁻¹. A solid acid aerogel catalyst with a surface area of 1322.93 m² g⁻¹ and an acid density of 3.29 mmol g⁻¹ was obtained after the sulfonation process. Esterification reaction involving oleic acid−methanol reactants with molar ratio of 1:9 was carried out at a temperature of 65 ℃. Oleic acid conversion of 90.21% was achieved at a catalyst dose of 5% for 2 h.