Synthesis and IR Characterization of Activated Carbon Acid Catalysts from Cassava Peels and their Use in Esterification of Free Fatty Acid in Palm Kernel oil

Abstract

The present study reports the preparation of four solid acids (CS, CPS, CAS and CPAS) from cassava peels and investigates their catalytic activities in the esterification of free fatty acid (FFA) in palm Kernel oil (PKO). The activated carbon obtained from carbonization was directly sulfonated with sulfuric acid (CS) or treated first with phosphoric acid before sulfonation (CPS). Another part of activated carbon was pyrolyzed at 800°C and treated as in the two previous cases (CAS and CPAS). The FTIR spectra of CS, CPS, CAS and CPAS showed characteristic absorption peaks of functional groups such as O=S=O (1031 cm-1), OH (3849 and 3405 cm-1), C=C (1555-1574 cm-1), S=O (1042,1031 cm-1) and P=O (754 cm-1), which confirm the presence of sulfonic, carboxylic and phosphoric groups on the surface of the activated carbon acids prepared. The total acid densities of the catalysts range from 2.26 to 3.49 mmol/g whereas the -SO3H densities were from 0.92 to 2.20 mmol/g. Amongthe four catalysts prepared, their effectiveness in the esterification of free fatty acid in palm kernel oil with a conversion rate from 70 to 90%, depended mostly on the sulfonic acid density on the catalyst, CPS showed the highest total and –SO3H acid densities with 3.49 and 2.2 mmol/g respectively and a highest free acid fatty conversion rate of 90%. Thus, CPS was more efficient than CS, CPAS and CAS. All the catalysts prepared could be reused in the esterification reaction with a mild decrease in the conversion rate.