Chitosan with Sulfonic Groups: A Catalyst for the Esterification of Caprylic Acid with Methanol

Esterification of caprylic acid with methanol was performed over chitosan with sulfonic acid groups, as a catalyst, at 60 °C. The sulfonic acid groups were introduced into chitosan (CH) by using chlorosulfonic acid. Catalysts were characterized by scanning electron microscopy (SEM), elemental analysis, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and acid-base titration. Catalytic activity increased with the amount of sulfonic acid groups present on chitosan. The 4-CH-SO₃H catalyst (chitosan with sulfonic acid groups-sample 4 prepared) showed the highest activity of all materials. The esterification of caprylic acid with methanol was optimized using a 4-CH-SO₃H catalyst. Under optimized reaction conditions, it was found that, at 60 °C, with 0.2 g of catalyst loading and with a molar ratio methanol to caprylic acid equal 1:95, a caprylic acid conversion of about 83%, after 4 h could be obtained. Catalytic stability of the 4-CH-SO₃H material was evaluated through consecutive batch runs. After the second batch, the catalytic activity stabilized.