Abstract
The work presents the results of studies on α-pinene oxidation over the TS-1 catalysts with different Ti content (in wt%): TS-1_1 (9.92), TS-1_2 (5.42), TS-1_3 (3.39) and TS-1_4 (3.08). No solvent was used in the oxidation studies, and molecular oxygen was used as the oxidizing agent. The effect of titanium content in the TS-1 catalyst, temperature, reaction time and amount of the catalyst in the reaction mixture on the conversion of α-pinene and the selectivities of appropriate products was investigated. It was found that it is most advantageous to carry out the process of α-pinene oxidation in the presence of the TS-1 catalyst with the titanium content of 5.42 wt% (TS-1_2), at the temperature of 85 °C, for 6 h and with the catalyst TS-1 content in the reaction mixture of 1 wt%. Under these conditions the conversion of α-pinene amounted to 34 mol%, and the selectivities of main products of α-pinene oxidation process were: α-pinene oxide (29 mol%), verbenol (15 mol%) and verbenone (12 mol%). In smaller quantities also campholenic aldehyde, trans-pinocarveol, myrtenal, myrtenol, L-carveol, carvone and 1,2-pinanediol were also formed. These products are of great practical importance in food, cosmetics, perfumery and medicine industries. Kinetic studies were also performed for the studied process.
Highlights
Accepted: 13 December 2021Titanium-silicate catalysts, both microporous (TS-1, TS-2, Ti-BETA, Ti-MWW) and mesoporous (Ti-MCM-41, Ti-MCM-48, Ti-SBA-15, Ti-SBA-16), enjoy the constant interest of researchers
Based on our results presented in the above-mentioned reference [6], we decided to check how the process of α-pinene oxidation would be affected by introducing the oxidant in the form of oxygen from the cylinder to the reaction environment—such studies on the oxidation of α-pinene have not been described in literature so far
Comparing the results obtained in our research with the results presented in the literature for such catalysts as carbon-supported Pt catalysts [52], it can be said that the use of TS-1 catalysts in the oxidation of α-pinene allows to obtain a lower summary selectivity of transformation to verbenol and verbenone than that obtained on carbon-supported Pt catalysts
Summary
Accepted: 13 December 2021Titanium-silicate catalysts, both microporous (TS-1, TS-2, Ti-BETA, Ti-MWW) and mesoporous (Ti-MCM-41, Ti-MCM-48, Ti-SBA-15, Ti-SBA-16), enjoy the constant interest of researchers. The first group of catalysts mentioned above is used mainly in reactions involving small size organic molecules, while the second group has found applications in reactions involving large and branched organic molecules—it is mainly related to the pore diameter of these catalysts The advantage of these catalysts is that they can be separated from the post-reaction mixture and can be used multiple times in the process. Research is being carried out on new methods of synthesis these catalysts, for example by introducing an additional step of crystallization during the synthesis of these materials, with the previously obtained porous structure dissolving earlier—an example may be the hollow TS-1 catalyst (HTS-1) [1]. In order to dissolve the originally obtained TS-1 porous structure, organic and inorganic
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