Synthesis and Initial Evaluation of Solid Acid Catalyst Derived from Spent Coffee Grounds for the Esterification of Oleic Acid and Methanol

Abstract

Spent coffee grounds (SCGs) were utilized in the synthesis of a solid acid catalyst (SAC) through a carbonization–sulfonation process performed at low temperatures (350–500 °C for carbonization and 50–150 °C for sulfonation) and short processing times (1–10 h). The best SAC from the process was able to convert more than 90% of oleic acid to methyl oleate during esterification with methanol (10 mol OA/mol methanol, 80 °C, 7 h, 10%w/w catalyst loading). It was obtained by carbonizing SCG at 400 °C for 2 h and then sulfonating the biochar at 100 °C for 1 h. The reusability tests performed in 4 cycles at the same esterification conditions reveal loss of activity of about 70% of its original state, corresponding to a decrease in total acid and sulfonic acid densities from 4.22 and 3.36 mmol H+/g to 1.33 and 1.16 mmol H+/g, respectively. This process is a considerable improvement from that reported in previous works, having no activating agents in the carbonization process and with significantly shorter times for processing.