Bentonite pillarization using sonication in a solid acid catalyst preparation for the oleic acid esterification reaction

Abstract

Bentonite is one of the abundant non-metallic minerals and still was not used optimally. Bentonite could be tailored into a high-value material, one of which is a solid catalyst for a particular reaction. In general, the modification of bentonite is by the pillarization process, which is exchanging cations between the alumina-silicate layers of bentonite with a single or mixture of metal oxide, thereby modifying the distance between the layers and its physicochemical properties from the original bentonite. However, the conventional pillarization process is usually time-consuming, especially during on aging process (almost one day). Using sonication during the pillarization process could prepare the pillarization process to become shorter, at least eliminating the aging process. Thus, this study investigated the sonication effect on the pillarization process of bentonite, especially its physicochemical properties. A solid acid catalyst is prepared by the pillarization method with or without the sonication. Zirconium (Zr) and titanium (Ti) are used as the pillared metals. In the bentonite pillarization process using sonication, the amplitude of the ultrasonic probe will be varied at 30, 50, and 70% with a sonication time of 20 min, respectively. The prepared solid acid catalysts are tested for their catalytic activity in the esterification reaction of oleic acid to methyl oleate. Several characterization techniques are also conducted on the prepared solid acid catalysts to obtain information on their physicochemical properties, such as N2 gas adsorption, XRD, NH3-TPD, XRF, and SEM. Conversion of the esterification reaction is verified by calculating the acid value and GC–MS analysis. It is found that the surface area increased after the pillarization process for Ti-PILC and Zr-PILC catalysts, with/without the sonication. The XRD results also confirmed that the basal spacing shifted after the pillarization for both prepared catalysts. It is assumed that the pillarization is prepared successfully by using sonication. Furthermore, the surface area of Zr-PiLC catalysts was significantly enhanced when using sonication, however, not observed for the Ti-PiLC catalyst. The N2 gas adsorption results disclosed that the sonication effects extensively enlarge the pore volume. Similar results are described in the NH3-TPD analysis that the acidity of the prepared catalysts also increased due to the sonication. Therefore, the conversion of the esterification reaction of oleic acid also increased. The maximum value of oleic acid conversion obtained in this study was 62.66% for the solid acid catalyst Ti/PILC, with an amplitude of 70%. It is achieved that using the sonication in the bentonite pillarization process could reduce the pillarization time drastically and cause the prepared material to become more porous.