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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.

In the present work catalytic reactivity of polyaniline protonated with organo-sulfonic acids, namely methanosulfonic (MSA-Pani), camphorosulfonic (CSA-Pani) and lignosulfonic (LG-Pani) acids was evaluated for the transesterification of triglycerides (triacetin, castor oil) and esterification of fatty acid (ricinoleic) with methanol. Their reactivity was also compared with previously studied alkyl-free polyaniline-sulfate (S-Pani) catalyst. The textural and acid properties of the catalysts before and after catalytic tests were characterized by BET, FT-IR, XRD, SEM, thermogravimetric and ammonia sorption techniques. It was observed that acid characteristics, namely concentration and the strength of acid sites as well as chemical properties of the surface e.g. the type of organo-sulfonic acid played an important role in catalytic performance of studied samples. In all tested reactions, the MSA- and CSA-doped polyanilines exhibited the highest initial activity referred to the acid site capacity. However, too weak acid sites in these catalysts resulted in their partial blockage during methanolysis of triglycerides. This was not observed in the esterification reaction. Among all studied samples, the LG-Pani (commercial reagent) and MSA-Pani catalysts seem to be the most promising owing to their high activity and good stability in reaction mixture, in particular during methanolysis of triglycerides. In contrast to the MSA-Pani catalyst (thermally stable up to 260 °C), lower stability of LG-Pani catalyst (up to ca. 120 °C) may limit its application.

Methanolysis of natural oil, i.e. castor oil and triacetin, a model compound for the transesterification of triglycerides in biodiesel production was studied under atmospheric pressure at temperature of 50–60 °C. As-received zinc hydroxy nitrate Zn5(OH)8(NO3)2×2H2O (Zn-5) and samples obtained by thermal treatment of Zn-5 for 2 h in the temperature range of 105–300 °C were used as the catalysts. The catalysts were characterized by thermogravimetric (TG) analysis, X-ray powder diffraction (XRD), infrared spectroscopy (FTIR), nitrogen sorption (BET) and scanning electron microscopy (SEM). The effect of thermal treatment of Zn-5 salt on the activity and reusability in methanolysis of triglycerides was studied. During thermal treatment of as-received Zn-5 salt a gradual decomposition via various hydroxy nitrates intermediates such as Zn5(OH)8(NO3)2 and Zn3(OH)4(NO3)2 to ZnO occurred. This was accompanied by significant morphological and textural changes. Plate-like particles of Zn-5 salt reorganized into spherically shaped particles of ZnO. Moreover, decrease in specific surface area and porosity occurred. In methanolysis of both triglycerides, the activity of Zn-catalysts gradually decreased as the temperature of thermal treatment increased and the activity of ZnO, a final product of thermal decomposition was very low. The most active was as-received Zn-5 salt and its morphological/chemical properties did not change during methanolysis reaction performed at temperature of 50–60 °C. Moreover, the activity of original Zn-5 salt was fully restored after methanol/THF washing of spent catalysts. The activity of as-received Zn-5 catalyst was preserved under successive use in catalytic tests. The activity of thermally treated Zn-5 salt (at 140 °C) did not restore after methanol/THF washing and during subsequent use of Zn-5-140 catalyst its activity successively decreased.