Transesterification of triacetin and castor oil with methanol catalyzed by supported polyaniline-sulfate. A role of polymer morphology Original Research Article

Polyaniline-sulfate deposited on three different carriers was studied for transesterification of triacetin and castor oil with methanol at mild reaction conditions (temperature of 55 °C). Multi-wall carbon nanotubes (CNT), carbon and silica were coated with polyaniline sulfate (ca. 20 wt%) during polymerization of aniline. Because of different textural and hydrophobic properties of the carriers, the polymer coatings of various morphologies were obtained as evidenced by the electron microscopy technique. A uniform coating of CNT with polymer resulted in the most extended polymer structure. Nanorods of polymer forming branched dendritic structures appeared in the other two carbon and silica carriers. The acid capacity and the strength of acid sites were similar in all studied catalysts. All the samples were found to be active solid acid catalysts in methanolysis of both studied triglycerides and CNT-coated polyaniline sulfate exhibited the highest activity. The course of reaction during methanolysis of triacetin on CNT-containing catalyst was similar to that in the presence of soluble sulfuric acid. On the other hand, a partial blockage of active sites was observed in carbon and silica coated with polyaniline sulfate. A blockage effect was ascribed to strong interaction of acid sites with more polar reagents among them diacetin and glycerol. These interactions were facilitated by aggregated fibriral morphology of the polymer coating resulting in locally high density of acid sites.