Isomerization and Dehydroaromatization of R(+)-Limonene Over the Ti-MCM-41 Catalyst: Effect of Temperature, Reaction Time and Catalyst Content on Product Yield

Abstract

This work describes research on the isomerization of R(+)-limonene over the Ti-MCM-41 catalyst. The studies showed that the Ti-MCM-41 catalyst is an active catalyst in the isomerization of R(+)-limonene. As a result of the isomerization of this compound, it is possible to obtain α-terpinene, γ-terpinene, terpinolene and p-cymene. Terpinolene is the main product of this process, and p-cymene is formed by the alpha-terpinene, gamma-terpinene and terpinolene dehydrogenation. The aforementioned products are of great practical importance. The most favorable reaction conditions leading to the obtaining of limonene isomerization products is the use of the catalyst in an amount of 15 wt% and the temperature of 160 • C. Depending on whether the desired products are the isomers of limonene (γ-terpinene, α-terpinene and terpinolene) or the product of their dehydroaromatization (β-cymene), it is possible to shorten or extend the reaction time. The method for the isomerization of limonene on the Ti-MCM-41 catalyst makes it possible to obtain a significant yield of both the limonene and p-cymene isomers. Longer reaction time is conducive to obtain larger quantities of other reaction products and less desirable products that constitute impurities (oxidized products and polymeric compounds).Currently, among the mesoporous titanium-silicate catalysts, great attention is paid to the Ti-MCM-41 catalyst. This catalyst can be obtained in a simple way. 1) By the hydrothermal method, crystallization of Ti-MCM-41 in the autoclave from the crystallization gel, 2) by the direct precipitation of Ti-MCM-41 from the crystallization gel at ambient temperature without the crystallization in the autoclave, or 3) by the impregnation of the previously obtained MCM-41 structure with an appropriate titanium source [3]. The first two methods allow the introduction of titanium to the entire catalyst structure (including the pores), while the third method allows the introduction of titanium, only on the surface of this material [4].Materials with MCM-41 structure (including Ti-MCM-41) are mesoporous materials having an ordered, two-dimensional structure with hexagonal pores. The MCM-41 structure resembles a honeycomb. These materials have a narrow pore size distribution (1.8 to 10 nm) that have p6mm symmetry. The size of the pores depends on the synthesis conditions, the composition of the crystallization gel, as well as on the length of alkyl chains of the surfactant used in the synthesis. The specific surface area of these materials is well developed and exceeds 1000 m 2 /g. These types of materials have walls with a thickness of 1 nm, which are made of amorphous silica, and their structure is characterized by a close-range order [5][6][7][8][9]. Thanks to this structure, Ti-MCM-41 materials are used as effective catalysts in the processes of epoxidation, oxidation and isomerization of olefins, e.g., allylic compounds (allyl alcohol [10], diallyl ether [11], allyl-glycidyl ether [12], and allyl chloride [13]) or olefins of natural origin (limonene [...

The isomerization of S-carvone over the natural clinoptilolite as the catalyst: the influence of reaction time, temperature and catalyst content

“…Fig. 8 The mechanism of the isomerization of S-carvone Taking into account the literature data [11,12] and our previous studies [27,29] on the isomerization of limonene we can proposed the following mechanism of the isomerization of S-carvone to carvacrol- Fig. 8.…”

The Limonene Biorefinery: From Extractive Technologies to Its Catalytic Upgrading into p-Cymene

“…Retajczyk et al carried out studies on the limonene isomerization process using Ti-SBA-15 and Ti-MCM-41 as catalysts, performing the limonene isomerization without any organic solvents [40]. The conversion of limonene increases by increasing both the reaction temperatures as well as the reaction time (Fig.…”

“…Finally, since the conventional p-cymene production occurs in a liquid phase, the separation of the reactants from the catalyst is an energy-intensive process [33][34][35]. Alternative methodologies for the production of p-cymene have been widely investigated including the use of renewable limonene also in consideration that a relatively low amount of p-cymene (4000 tonnes) is manufactured yearly [36][37][38][39][40].…”

“…Temperature effect on the isomerization of R-limonene. Reproduced with permission from Retajczyk et al[40]. Copyright (2019) MDPI.…”

Influence of Technological Parameters on the Isomerization of Geraniol Using Sepiolite

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