Synthesis of Sulfonated Carbon Aerogel from Coir Fiber as Solid Acid Catalyst for Esterification

Abstract

The increasing human population drives up energy consumption, particularly in the transportation and industrial sectors. Due to the limited and non-renewable availability of fossil fuels encourages various technological developments in the field of renewable energy, including biodiesel. Biodiesel is a biodegradable, non-toxic, and environmentally favorable renewable fuel. One of typical technique of biodiesel production is involving esterification reaction between fatty acids and alcohols by addition acid catalyst to enhance reaction rate. Solid acid catalysts are widely utilized for esterification reaction due to their ability to overcome the drawback of homogeneous catalysts that are difficult to separate. Solid acid catalysts can be produced from cellulose aerogel derived from coir fiber, which is then pyrolyzed into carbon aerogel and sulfonated through grafting process. Although sulfuric acid is a common sulfonic agent used in the catalyst sulfonation process, it has a lengthy grafting time. The addition of 4-aminobenzenesulfonic acid (sulfanilic acid) as a sulfonic agent alternative for sulfuric acid was investigated in this work. This paper reports the methods for preparing cellulose aerogel derived from coir fiber, pyrolysis of cellulose aerogel into carbon aerogel, sulfonation of carbon aerogel into solid acid catalyst, and application of solid acid catalyst for ethyl acetate production. The solid acid catalyst characterization tests include acid density, adsorption-desorption nitrogen analysis, SEM, and FTIR analysis. According to the adsorption-desorption nitrogen analysis results, the sulfonated carbon aerogel catalyst has a specific surface area of 220.29 g/m2. Sulfonated carbon aerogel catalyst with acid density value of 2.81 mmol/g can be obtained at the mass ratio of sulfanilic acid to carbon substrates of 1:1 and pyrolysis temperature of 700°C. The esterification reaction was carried out at 80°C and reached a conversion of 31.37% after 4 h.