Acid-activated pillar bentonite as a novel catalyst for the esterification of high FFA oil

The esterification reaction of methanol with oleic acid or high acid content refined palm oil catalyzed over sulfuric acid-activated pillar bentonite clay was performed. Pillar clay was synthesized using natural Na-bentonite as the raw material by cetyltrimethylammonium bromide and hexadecylamine surfactant intercalation, silica pillar polymerization (with tetraethylorthosilicate as the silica source) and then surfactant removal by acid–ethanol refluxing followed by calcination. The pillar bentonite samples were then acid-activated by refluxing with 0.5 M sulfuric acid. The characterization of the raw Na-bentonite, the sulfuric-acid-activated pillar bentonite and the intermediate pillar bentonites, was conducted by nitrogen adsorption-desorption, X-ray powder diffractometry and acid–base titration techniques. The results indicated that the pillar bentonite was successfully prepared and significantly increased the specific surface area 20-fold compared with the parent material. The catalytic activity was related to the acid value and the catalyst surface area, pore size and volume, and was improved by the use of both surfactants, surfactant removal by both acid–ethanol refluxing and calcination, and especially by sulfuric acid activation. The acid-activated pillar clay catalyst exhibited a 100% methyl oleate yield and 99% oleic acid conversion, which was higher than that obtained under the same conditions with the commercial Amberlyst-15 catalyst.

The natural bentonite was added by pillar formation via micelle surfactant intercalation and silica polymerization. After structure directing agents were removed, catalytic acidic site was modified. An enhanced acidic catalyst with high surface area 20-times compared to parent clay can be obtained. This acidic pillarized clay gave better performance in esterification for biodiesel production than commercial catalysts.Figure optionsDownload as PowerPoint slideHighlights
► Raw bentonite was increased in specific surface areas by porous pillar.
► Pillar bentonite material was acidic raised by sulfuric acid activation.
► Acidic pillar bentonite gave highest catalytic activity in biodiesel preparation.
► Acidic pillar bentonite is tolerant than Amberlyst-15 in reused catalyst testing.