Abstract
Limonene belongs to a group of very important intermediates used in the production of fine chemicals. This monoterpene compound can be obtained from peels of oranges or lemon which are a (biomass) waste from the orange juice industry. Thus, limonene is a renewable, easy available and a relatively cheap compound. This work presents preliminary studies on the process of limonene epoxidation over zeolite type catalysts such as: TS-1 and Ti-SBA-15. In these studies methanol was used as a solvent and as an oxidizing agent a 60 wt % hydrogen peroxide solution was applied. The activity of each catalyst was investigated for four chosen temperatures (0 °C, 40 °C, 80 °C and 120 °C). The reaction time was changed from 0.5 to 24 h. For each catalyst the most beneficial conditions (the appropriate temperature and the reaction time) have been established. The obtained results were compared and the most active catalyst was chosen. These studies have also shown different possible ways of limonene transformation, not only in the direction of 1,2-epoxylimonene and its corresponding diol, but also in direction of carveol, carvone and perillyl alcohol—compounds with a lot of applications. The possible mechanisms of formation of the allylic oxidation products were proposed.
Highlights
Limonene belongs to a group of very important intermediates for the production of fine chemicals.This monoterpene compound can be obtained from peels of oranges or lemon which are a waste produced by the orange juice industry
The studies on the influence of the temperature and the reaction time on the course of limonene epoxidation over the TS-1 and Ti-SBA-15 catalysts are presented in Table 1 and
The comparison the results obtained over the mesoporous Ti-SBA-15 catalyst shows that independent of the temperature of the process 1,2-epoxylimonene, its diol, carveol which very undergoes oxidative dehydrogenation to carvone and perillyl alcohol which is very stable under the reaction conditions and does not react to perillyl aldehyde are present in the post-reaction mixture
Summary
Limonene belongs to a group of very important intermediates for the production of fine chemicals. Liquid phase oxidation of olefinic compounds by hydrogen peroxide or t-butyl hydroperoxide (TBHP) in the presence of heterogeneous catalysts is a very interesting way of obtaining very valuable, oxygenated products from olefins. The studies on the epoxidation of limonene over the Ti-MCM-41 catalyst were mainly performed with help of hydrogen peroxide or TBHP as the oxidizing agents. Abovementioned Ti-MCM-41 catalysts were performed at temperatures of 70–85 °C, for a molar ratio of limonene/hydrogen peroxide = 3.7:1 and for the reaction time of 0.5–7 h (in one case from 1 h to h [18]). Epoxidation of limonene over the Ti-MMM-2 catalyst was performed in acetonitrile as the solvent, at a temperature of 60 °C and with a limonene/H2O2 molar ratio of 1:2 [11] These studies showed that the amount of the epoxide compound obtained was three times higher than that of the other products. The possibility of the obtaining of various products in this process was shown and possible mechanisms were proposed for formation of the allylic oxidation products
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