One-step synthesis of a heterogeneous catalyst by the hydrothermal carbonization of acai seed

Abstract

Carbon-based catalysts functionalized with sulfonic groups are candidates for replacing homogeneous catalysts such as H2SO4. Mainly due to their high structural stability under hydrothermal reaction conditions, their easy preparation, their efficient catalytic performance, their easy separation from the reaction medium and their low cost. In general, lignocellulosic biomass residues are common precursors used in the manufacture of carbon material, reinforcing the ecologically correct character of its production. Acid catalysts derived from biomass residues can be synthesized by two methods of insertion of sulfonic groups into their structure. The first manner is postgrafting functionalization and the second is in-situ functionalization. In this study, a solid acid catalyst was developed, which used the acai seed residue as a precursor, and the in-situ functionalization method. This sulfonation route has the advantage of carbonizing and sulfonating the material simultaneously, and avoids wasting time and energy. Catalyst samples were prepared at different time and temperature of hydrothermal treatment. The HTAS6-130 sample, simultaneously carbonized and sulfonated at 130 °C for 6 h, showed better performance in the esterification reaction of oleic acid and methanol with a 95% conversion at a reaction temperature 100 °C, reaction time of 1 h, catalyst loading of 3 wt% and 12:1 methanol to oleic acid molar ratio. The recyclability of HTAS6-130 was satisfactory, reducing conversion only 18% after the five reaction cycles. In summary, the in-situ functionalization method brought together the advantages of rapid synthesis, low energy consumption and high density of active acid sites after use in five consecutive reaction cycles. © 2021, Akadémiai Kiadó, Budapest, Hungary.