Method for preparing limonene and composition containing limonene

Abstract

A continuous process for producing limonene is proposed, characterized in that β-pinene or a starting material containing β-pinene isomerized in a trickle bed reactor in the presence of an acid catalyst.

Description

Technical Field

[0001] The present invention belongs to the field of terpene compounds and relates to a method for catalytically rearranging beta-pinene into limonene. Background Art

[0002] Limonene is a natural substance of monocyclic terpenes and exists in two enantiomers.

[0003]

[0004] (R)-(+)-limonene (also referred to as D-(+)-limonene or (+)-limonene) and (S)-(-)-limonene [also referred to as L-(-)-limonene or (-)-limonene or]. The racemates of the two enantiomers are also called dipentene.

[0005] Limonene is the most common monoterpene in plants. (R)-(+)-limonene is found especially in bitter orange peel oil, caraway oil, dill oil, coriander seed oil, lemon oil (about 65%) and orange oil (usually >90%). It has an orange-like aroma. In contrast, (S)-(-)-limonene is found in tall fir and peppermint oils and has a turpentine-like smell. Racemic limonene is found especially in pine oil, Siberian pine needle oil, neroli oil, nutmeg oil and camphor oil.

[0006] The biosynthesis of limonene starts from geranyl pyrophosphate (GPP).

[0007]

[0008] Limonene is an important raw material for the fragrance industry and a starting material for a variety of applications and products. In particular, it has recently been used as a "green" solvent and a replacement for the environmentally problematic BTX solvent.

[0009] While β-pinene is a readily available source for the production of limonene, the difficulty with the acid-catalyzed isomerization of β-pinene is the potential for forming a broad spectrum of products of bicyclic, tricyclic, and monocyclic terpenes through a series of equilibrium reactions that must be avoided to achieve high limonene selectivity. A selection of possible product ranges is shown below.

[0010]

[0011] Related prior art The earliest relevant publications include two patents US 3,780,124 (DAVIS) and US 3,780,125 (TAKACS) from 1973, which proposed the application of iodine to zeolites to rearrange α-pinene.

[0012] US 4,508,930 (WIDEMANN) discloses the rearrangement of terpenes to limonene at elevated temperatures in the presence of supported alkali metal sulfide catalysts.

[0013] The isomerization of pinene to limonene and other by-products in the presence of zeolites is known from US Pat. No. 3,270,075 (GLIDDEN). The reaction is carried out in the liquid phase at 65° C. to 110° C. The catalyst is generally described as Me x / n[(AlO2)x(SiO2) y ]*zH2O and specifically mentions: Na 86 [(AlO2) 86 (SiO2) 106 ]*267 H2O.

[0014] Two Chinese patents CN 102126904B and CN 102343277B from Dalian University also describe the isomerization of pinene to limonene in the presence of a heterogeneous acid catalyst. The catalyst used is an acidic molecular sieve that has been post-treated with a halide and a base.

[0015] References are also made to MICROPOROUS AND MESOPOROUS MATERIAL 237, pp. 180-188 (2017) by Ma et al. and CHEM.REV.115, s.3141-3196 (2017) by Golets et al.

[0016] The disadvantage is that the processes known from the prior art are not economically viable alternatives in terms of yield or selectivity. These processes also usually operate at very high temperatures, require the use of toxic solvents, cannot be carried out continuously, and have an insufficient catalyst life. In addition, the reaction products usually contain undesirable by-products, such as, in particular, terpinenes, in amounts which can have an adverse effect on the product quality.

[0017] Purpose of the Invention

[0018] Therefore, a first object of the present invention is to provide a process for the continuous isomerization of β-pinene to limonene with a yield and selectivity of at least 65%, preferably at least 75%, and with camphene being produced as a by-product in large part (i.e. about 15% to 20% by weight). In particular, limonene should be obtained in the form of the L-isomer (>90% by weight).

[0019] Another object of the invention is to run the process avoiding, if possible, completely or at least partially, the use of toxic solvents, in particular those from the BTX series. The reaction should also be possible at temperatures below 100° C. and the catalyst should have a sufficiently long service life to allow it to be used and recycled several times without aftertreatment. Summary of the invention

[0020] The present invention firstly provides a continuous method for producing limonene, which is characterized in that β-pinene or a starting material containing β-pinene isomerized in a trickle bed reactor in the presence of an acid catalyst.

[0021] In particular, a method is required, comprising or consisting of the following steps:

[0022] (a) providing β-pinene or a starting material containing β-pinene;

[0023] (b) providing a trickle bed reactor equipped with a fixed bed of catalyst;

[0024] (c) filling a reactor fixed bed with a heterogeneous acid catalyst;

[0025] (d) applying the starting material to the top of the reactor and passing the starting material through the fixed bed of catalyst;

[0026] (e) discharging limonene or a limonene-rich fraction at the reactor outlet.

[0027] Surprisingly, it has been found that the process using a trickle bed reactor with an integrated fixed catalyst bed allows the continuous isomerization of β-pinene to limonene with a selectivity of more than 65%. Process management in a fluidized bed reactor allows kinetic control of the selectivity by establishing an optimal residence time in the catalyst bed. This avoids the establishment of equilibrium, which, for example, occurs in batch processes, leading to the formation of thermodynamically more stable but undesirable isomers. This also makes it possible to largely avoid the production of oligomeric or even polymeric by-products in the continuous reaction, which would otherwise lead to premature deactivation of the catalyst. In comparison with conventional fixed bed reactors, fluidized bed reactors achieve overall higher catalyst service lives.

[0028] It is worth noting that β-pinene can exist in two enantiomeric forms, namely (S, S) and (R, R). Therefore, in the context of the present invention, the term "β-pinene" should be understood to include both forms or mixtures thereof. The preferred starting material is (1S, 5S) β-pinene, also known as (-)-β-pinene. At the same time, (1R, 5R)-β-pinene, also known as (+)-β-pinene, is particularly preferred because this allows enantiomerically pure D-limonene to be obtained.

[0029] catalyst

[0030] According to the present invention, the isomerization is carried out in the presence of a solid acid; the heterogeneous catalyst used is preferably or Lewis acids. Particularly suitable for this purpose are zeolites, especially those selected from the group consisting of the Y, H-beta, ZSM-5 and MMW types. MWW zeolites of the MCM-22 or PSH-3 type are particularly preferred.

[0031] The term "MWW" is understood to refer to the type of zeolite produced as shown in the following diagram (see pubs.acs.org / doi / abs / 10.1021 / jp972319k):

[0032] Zeolites consist of two mutually separated ten-ring pore systems. A distinction is made between variants A and B, in which the cavities are connected linearly and sinusoidally, respectively.

[0033] It is preferred to use MWW zeolites which have been previously calcined and / or acid activated. Particularly preferred zeolites are MCM-22 or PSH-3 type zeolites conforming to the following formula

[0034] M2 / n O*Al2O3*(20-150)SiO2

[0035] and is known, for example, from EP 0 064 205 B1 (BAYER).The MMW zeolite is preferably calcined and / or activated by acid treatment before use.

[0036] The calcination can preferably be carried out at a temperature of about 400° C. to about 1000° C., in particular 400° C. to 600° C., for about 1 to about 10 hours, preferably 4 to 6 hours. Nitric acid is particularly suitable for acid activation. Very particular preference is given to MCM-22 zeolite previously activated with calcination and nitric acid.

[0037] Trickle Bed Reactors and Reaction Management

[0038] Trickle bed reactors are generally known from wastewater treatment. In the process according to the invention, the starting materials are introduced from the top of the reactor and then trickle through the catalytic fixed bed, where the isomerization takes place. It has further proved to be advantageous to carry out the reaction in the presence of an inert gas, in particular nitrogen, which flows in cocurrent but preferably in countercurrent, since this avoids oxidative decomposition reactions and increases the service life of the catalyst.

[0039] The process according to the invention can be carried out with or without a solvent. However, the use of a solvent increases the selectivity and increases the service life of the catalyst and is therefore preferred. Suitable solvents are aprotic solvents, such as C6-C8-alkanes, in particular heptane, 1,4-dioxane or C1-C4-alkyl acetates, especially ethyl acetate. The mass ratio of solvent to β-pinene is preferably between 90:10 and 50:50, preferably a ratio of about 80:20.

[0040] It has proven possible and advantageous to carry out the process under mild conditions, ie in a temperature range from 50 to 120° C., in particular about 70 to 80° C., and at a pressure of 1 to 10 bar, in particular about 2 to 4 bar.

[0041] Solvent preparation

[0042] The present invention further provides a solvent composition obtainable by the method, which consists of the following components

[0043] (a) about 70% to about 80% by weight of limonene

[0044] (b) from about 15% to about 20% by weight of camphene

[0045] Provided that the reported amounts, optionally with pinene, terpinene and terpinolene, sum to 100% by weight.

[0046] Industrial Applicability

[0047] The invention finally also provides the use of MMC-22 zeolite, optionally after calcination and / or acid activation, as catalyst for the rearrangement of β-pinene to limonene in a process as described above. Example

[0048] Examples 1 to 11

[0049] Continuous Isomerization of β-pinene

[0050] A commercially available continuous 1″ flow-through reactor apparatus (Parr Instruments) made of titanium with a length of 60 cm and equipped with a two-zone heating jacket and an internal temperature sensor was used for the experiments. Liquid and argon were metered into the top of the reactor by HPLC pumps and mass flow controllers, respectively. Temperature, pressure and flow were monitored and adjusted by the accompanying software. Granular catalyst was filled to the middle of the reactor tube. The empty reactor volume above and below the catalyst bed was filled with inert corundum particles. 5 g of solid acid catalyst (particle size 0.3-0.7 mm) was placed in the middle of the reactor between the corundum particle beds. 109.6 g of commercial β-pinene was dissolved in 400 g of solvent and then pumped onto the catalyst bed at the desired temperature using an HPLC pump. At the same time, an argon flow was metered into the reactor at a rate of 50 ml / min at a pressure of 2 bar. After depressurization of the product mixture, samples were taken regularly downstream of the reactor outlet and analyzed by off-line gas chromatography. Other experimental conditions for other examples can be seen in Table 1. Zeolite Y catalyst was obtained from Zeolyst, and the abbreviation TOS stands for time on stream.

[0051] It is also possible to use β-pinene directly as feed without solvent (Example 10).

[0052] In long-term tests (Example 11, Figure 1 ), the activity and selectivity of the MCM-22 catalyst were determined at two different pumping rates (see Figure 2) for a total of 225 hours. After 225 hours, the yield of limonene was determined to be 67% at a conversion of 97%.

[0053]

Claims

1. A continuous method for producing limonene, characterized in that β-pinene or a β-pinene-containing starting material is isomerized in a trickle bed reactor in the presence of MCM-22 or PSH-3 zeolite, wherein the reaction is carried out at a temperature in the range of 50° C. to 120° C. and at a pressure of 1 to 10 bar.

2. The method according to claim 1, comprising or consisting of the following steps: (a) providing β-pinene or a starting material containing β-pinene; (b) providing a trickle bed reactor equipped with a fixed bed of catalyst; (c) filling a reactor fixed bed with MCM-22 or PSH-3 zeolite; (d) applying the starting material to the top of the reactor and passing the starting material through the fixed bed of catalyst; (e) discharging limonene or a limonene-rich fraction at the reactor outlet.

3. The method according to claim 1, characterized in that Zeolites are used which have previously been calcined and / or acid-activated.

4. The method according to claim 2, characterized in that Zeolites are used which have previously been calcined and / or acid-activated.

5. The method according to claim 3, characterized in that MCM-22 zeolite was used which had been previously calcined and activated with nitric acid.

6. The method according to claim 4, characterized in that MCM-22 zeolite was used which had been previously calcined and activated with nitric acid.

7. The method according to any one of claims 1 to 6, characterized in that The reaction is carried out in the presence of an aprotic solvent.

8. The method according to claim 7, characterized in that The solvent used is selected from C6-C8-alkanes, 1,4-dioxane or C1-C4-alkyl acetates.

9. The method according to claim 7, characterized in that The β-pinene and the solvent are used in a weight ratio of 90:10 to 50:

50.

10. The method according to claim 8, characterized in that The β-pinene and the solvent are used in a weight ratio of 90:10 to 50:50.

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