Bio-esters formation in transesterification and esterification reactions on carbon and silica supported organo-sulfonic acids-polyaniline solid catalysts

Polyaniline doped with methanosulfonic (MSA) or camphorosulfonic (CSA) acid was deposited on silica and carbon support during polymerization of appropriate aniline salt carried out in the presence of immersed carriers. The activity of obtained catalysts was examined in the transesterification of triglycerides (triacetin and castor oil) and esterification of ricinoleic acid with methanol. The textural (specific surface area, porosity, pore diameter), morphological and acid (concentration and strength of acid centers) properties of catalysts were studied by number of techniques. The activity of acid sites in the silica and carbon supported MSA- and CSA-polyaniline catalysts was observed to be distinctly higher than activity of their counterparts with alkyl-free sulfuric acid-polyaniline coatings. A role of the type of support (carbon, silica), textural characteristics (porous structure), morphology of the polymer coating and the type of organo-sulfonic acid was studied. An enhancement in catalytic performance (higher activity, lower active sites blockage) due to organic group in close proximity to the SO3H sites varied depending on the type of reaction, being the highest in reactions with bulky reactants such as triglycerides from castor oil and ricinoleic acid. Among all catalysts, silica coated with methanosulfonic acid-polyaniline (SiO2-pani-MSA) exhibits the best catalytic performance in all tested reactions.