WO2013120932A1

WO2013120932A1 - Method for production of cymene

Info

Publication number: WO2013120932A1
Application number: PCT/EP2013/052938
Authority: WO
Inventors: Jörg BRÜCHER; David BLOMBERG SAITTON
Original assignee: Holmen Ab
Priority date: 2012-02-14
Filing date: 2013-02-14
Publication date: 2013-08-22
Also published as: SE537147C2; SE1250119A1

Abstract

The present invention relates to a method for production of cymene comprising the following steps: a) providing a solution comprising cyclic monoterpenes having the formula C₁₀H₁₆ b) addition of a catalyst comprising Fe³⁺ and/ or Fe²⁺ ions c) addition of sulphur dioxide to the solution d) incubation of the solution mixture from step c) for a reaction time at a reaction temperature such that at least part of the cyclic monoterpenes are converted to cymene such that a solution comprising cymene is obtained.

Description

METHOD FOR PRODUCTION OF CYMENE

Technical field

The present invention relates to a method for production of cymene, in particular it relates to a method for production of cymene from a solution comprising monoterpenes.

Background

Cymene is a naturally occurring aromatic organic compound which structure consists of a benzene ring substituted with a methyl group and an isopropyl group. The structure of cymene is similar to the numerous monoterpenes containing a cyclohexene or cyclohexadiene ring but in contrast to those and other monoterpenes, cymene is a stable compound not undergoing the typical reactions of terpenes. The most common geometric isomer is p-cymene, in which the alkyl groups are para-substituted. There also exists two less common geometric isomers; o-Cymene, in which the alkyl groups are ortho-substituted, and m-cymene, in which they are meta-substituted. p-cymene and m-cymene are valuable base chemicals which for example are used in fragrances, pharmaceuticals, herbicides, dyes, and heat transfer media. One other industrially important use of p-cymene is as a starting material for p- cresol production via the Hock- Lange synthesis pathway (1-4). Furthermore, p- cymene has also been proposed as a suitable ingredient in aviation fuel formulations. Compared to other aromatics used in automotive formulations, such as benzene, toluene or ethyl benzene, cymene has lower toxicity and is degraded easier in both aquatic and terrestrial systems.

Turpentine from boreal hard- and softwood species is a complex mixture of different terpenes with a- pinene, β- pinene and carene as main constituents. As sterical strained, unsaturated hydrocarbons, terpenes are highly reactive easily undergoing rearrangements, di-or trimerisation or oxidation reactions. During the sulphate pulping process, terpenes stay unaltered and are condensed together with methanol from the off- gases. The turpentine is separated from other liquids by decantation, forming the typical crude sulphate turpentine (CST). Dominating impurities in CST are methanol along with organic sulphur compounds, polysulphides, and elementary sulphur. Turpentine is almost insoluble in water and thus CST and other turpentines generally contains only small amounts of water, such as less than 1 %.

Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula Ci₀Hi₆. Monoterpenes may be linear (acyclic) or contain rings. Biochemical modifications such as oxidation or rearrangement produce the related monoterpenoids.

Summary of the present disclosure

It has been described that cymene can be produced by alkylation of toluene with either propylene or isopropyl alcohol. A number of Friedal-Crafts catalysts, such as FeS0₄-HCI, AICI₃, BF₃ or H2SO4 have been used for toluene

isopropylation and solid acid catalysts has been used to produce p-cymene via alkylation of toluene with isopropyl alcohol (1-4). Methods for direct conversion of terpenes into cymene have also been described. These methods include for example conversion by acidic clays, oxidation with Cr (VI) compounds and transition metal based reactions. Vapour reactions using pure terpenes and Pd catalysts (Roberge, 2001 ) or Zn/ Cr catalysts (Al- Wadani, 2009) have been reported.

However, these methods suffer from deactivation by sulphur compounds and thus none of the methods are applicable on CST or other sulphur rich turpentine starting materials. Furthermore, the reported reactions usually take place at high temperatures, such as above 300 °C. Both sensitivity to sulphur

contamination and high operating temperatures makes the prior art methods unsuitable for operation at sulphate- or sulphite pulp mills. The present inventors have realized that there is a need for improved methods of cymene production. Significant amounts of turpentine are produced at pulp mills. For example, in the sulphate pulping of hard wood, about 0.5 kg turpentine /adt (air-dry tonne pulp) is formed. Since the prior art methods of producing cymene from terpenes are sensitive to sulphur contamination and generally demands high reaction temperatures, the present inventors have realized that there is a particular need for improved methods for production of cymene from sulphur rich turpentine such as CST.

The inventors have discovered that cymene can be produced from a solution comprising cyclic monoterpenes (e.g. CST) by a method including oxidation of the cyclic monoterpenes with sulphur dioxide in the presence of a catalyst comprising Fe³+ and/or Fe²⁺ ions.

Thus, in a first aspect the present invention relates to a method for production of cymene comprising the following steps:

a) providing a solution comprising cyclic monoterpenes having the formula b) addition of a catalyst comprising Fe³⁺ and/ or Fe²⁺ ions

c) addition of sulphur dioxide to the solution

d) incubation of the solution mixture from step c) for a reaction time at a reaction temperature such that at least part of the cyclic monoterpenes are converted to cymene such that a solution comprising cymene is obtained.

In contrast to the methods described in the prior art, the method according to the present invention does not need reaction temperatures above 180 °C and it is insensitive to high sulphur contents. The method according to the present invention is thus particularly suitable for production of cymene from sulphur rich turpentine such as e.g. CST.

Brief description of the figures

Figure 1 a shows a GC/MS chromatogram of an untreated crude sulphate turpentine. The Y-axis shows relative abundance and the X-axis shows the retention time in minutes. Figure 1 b shows a GC/MS chromatogram of a crude sulphate turpentine treated with S0₂ in the absence of catalyst comprising Fe³⁺ and/ or Fe²⁺ ions. The Y-axis shows relative abundance and the X-axis shows the retention time in minutes.

Figure 1 c shows a GC/MS chromatogram of a crude sulphate turpentine treated with Fe2(S0₄)3 in the absence of SO₂. The Y-axis shows relative abundance and the X-axis shows the retention time in minutes.

Figure 1 d shows a GC/MS chromatogram of a crude sulphate turpentine treated with Fe₂(S0₄)₃ in the presence of S0₂. The Y-axis shows relative abundance and the X-axis shows the retention time in minutes.

Detailed description

A first aspect of the present invention relates to a method for production of cymene comprising the following steps:

c) addition of sulphur dioxide to the solution

The inventors have surprisingly discovered that monoterpenes can be oxidized to cymene by sulphur dioxide in the presence of Fe³⁺ and/ or Fe²⁺ ions, whereas no significant amounts of cymene is produced in the absence of catalyst.

Neither are any detectable amounts of cymene produced by treatment with Fe³⁺ and/ or Fe²⁺ ions in the absence of sulphur dioxide. Without being bound by theory, it is likely that the catalyst comprising Fe³⁺ and/ or Fe²⁺ catalysis an isomerisation of the monoterpenes to an isomer which subsequently can be oxidised to cymene by the sulphur dioxide. The addition of Fe3⁺ and/ or Fe²⁺ does not lead to any significant polymerization of monoterpenes into dimers, oligomers or polymers and thus the yield of cymene can be high. This is surprising since other Lewis acids, such as e.g. AICI3 and mineral acids have been reported to polymerize monoterpenes in to oligomers and polymers. For several reasons, it is also surprising that sulphur dioxide can be used to oxidize monoterpenes into cymene. First of all sulphur dioxide is usually regarded as a reducing agent and thus it is surprising that it is such a competent oxidation agent for oxidation of monoterpenes into cymene. The ability of several other oxidation agents, including sulphuric acid and sulphurous acid, to oxidize monoterpenes to cymene in the presence of Fe²⁺ and/or Fe³⁺ catalyst has also been investigated by the inventors, but they all gave rise to polymerization of the monoterpenes. Even though some cymene can be produced also by sulphurous acid in the presence of Fe2(S0₄)3, significant amounts of polymers were formed and thus sulphurous acid is less suitable as oxidation agent.

Turpentine retrieved from a sulphate or sulphite pulp mill generally comprises high levels of sulphur. Therefore a catalyst comprising sulphur such as sulphate ions is suitable in the method according to the present invention. Fe₂(S0₄)₃ is a particularly suitable catalyst since it also is relatively cheap. Therefore, in one embodiment the catalyst added in step b) is Fe2(S0₄)3. In one embodiment at least 0.05 % (w/w), such as 0.05%-10 % (w/w) such as 0.1-1 % (w/w) such as 0.5-1 % (w/w) Fe₂(S0 )₃ is added in step b). In this context addition of at least 0.05 % (w/w) means that at least 0.05 g Fe₂(S0₄)₃ is added / 100 g of solution comprising cyclic monoterpenes. Other catalysts comprising Fe³⁺ and/ or Fe²⁺ are also suitable in the method according to the present invention and the optimal concentration of these catalyst can easily and without undue burden be optimized by a skilled person.

In one embodiment, at least 0.1 % (w/w), such 0.1-60% such as 1-50 % (w/w) such as 10-40 %(w/w), such as 15-30 % (w/w) sulphur dioxide is added to the solution in step c). In this context "addition of at least 0.1 % (w/w) sulphur dioxide" means that at least 0.1 gram sulphur dioxide is added per 100 gram of solution comprising cyclic monoterpenes. Since sulphur dioxide is a gas the reaction is preferably performed in a closed container such that the gas is retained in the reaction vessel after addition. The sulphur dioxide is preferably bubbled into the solution such that the gas is mixed with the solution. To keep the sulphur dioxide in the solution during the oxidation step, addition of sulphur dioxide and the oxidation in step d) is preferably performed at overpressure, for example at a pressure above 1 bar such as above 1.2 bar, such as above 1.5 bar, such as above 2 bar. As an alternative of bubbling the sulphur dioxide into the solution the sulphur dioxide can also be added at a temperature below its boiling point i.e. at a temperature below -10 °C. In one embodiment the reaction temperature in step d) is in a range between 50°C - 500°C, such as 100°C - 350°C, such as 150 - 200 °C.

In step d), small amounts of cymene will start to be formed almost immediately and usually 20 minutes incubation is sufficient for an overall recovery of about 75 %. Therefore, in one embodiment the reaction time in step d) is above 30 seconds, such as between 30 seconds and 12 hours, such as between 1 minute and 10 hours, such as between 2 minutes and 1 hour such as between 5 minutes and 30 minutes. In one embodiment the solution comprising cyclic monoterpenes is turpentine. In one embodiment the turpentine is retrieved from a pulping process in a pulp mill. In one embodiment the turpentine is crude sulphate turpentine (CST), turpentine from a thermo mechanical pulping process (TMP turpentine) or turpentine from a sulphite pulping process ( sulphite turpentine). The present inventors have discovered that the method according to the present invention, in contrast to other methods for producing cymene from monoterpenes described in the prior art, is insensitive to high levels of sulphur. The method according to the present invention is thus particularly suitable when the solution comprising cyclic monoterpenes comprises relatively high levels of sulphur, such as more than 0.1 % (w/w), such as more than 0.5 % (w/w), such as more than 1 % (w/w), such as more than 5 %, such as more than 10 % (w/w). CST and sulphite turpentine comprises high levels of sulphur and thus, in a preferred embodiment the solution comprising cyclic monoterpenes is CST or sulphite turpentine. In a most preferred embodiment the solution comprising cyclic monoterpenes is CST.

After step d), typically about 75 % of the cyclic monoterpenes have been converted to cymene. However there may still be quite high levels of terpenes present in the solution comprising cymene obtained in step d). Under

atmospheric pressure, the boiling points of these terpenes are typically about 155- 175 °C, and cymene has a boiling point of 177 °C. Hence, a mixture of terpenes and cymene is hard to separate by conventional distillation processes. Furthermore, elementary sulphur present in the solution comprising cymene obtained in step d) further complicates purification of the cymene present in the solution obtained in step d). To solve this problem the present inventors have designed a novel method for purification of cymene from a solution comprising cymene and at least one terpene. The present inventors have discovered that by addition of at least 0.5 % (w/w) sulphuric acid, such as 1-25 % (w/w) to such a solution, the terpenes react to high boiling dimers, trimers and/or other oligomers. Moreover, elementary sulphur reacts to high boiling polysulphides. Therefore by addition of sulphuric acid to the solution obtained in step d), pure cymene can easily be purified from remaining terpenes and elementary sulphur by a distilling process.

Thus, in one embodiment the method further comprising a step e) distilling the solution comprising cymene obtained in step d) such that a target chemical stream comprising more than 50 % of the cymene is obtained and separated from a residual stream comprising less than 50 % of the cymene. In one embodiment the target chemical stream obtained in step e) comprises at least 75 %, such as at least 90%, of the cymene present in the solution comprising cymene obtained in step d). In one embodiment step e) is performed in the presence of at least 0.5 % (w/w) sulphuric acid, such as 1 -25% (w/w). In one embodiment the solution comprising cymene obtained in step d) comprises elementary sulphur and at least part of the elementary sulphur reacts to form polysulphides in step e). In one embodiment the solution obtained in step d) comprises monoterpenes and at least part of the monoterpenes react to dimers, t rimers, oligomers and/or polymers in step e).

Sometimes it is preferred to perform the distillation process at a lower temperature. This can be achieved if the pressure is decreased in the distilling process. Thus, in one embodiment the distilling in step e) is performed at a distilling temperature below 170 °C , such as below 120 °C, such as 20°C- 120°C. In one embodiment the distilling in step e) is performed at a reduced pressure, such as at a pressure below 101 KPa, such as at a pressure between 1-50 kPA such as at a pressure between 5-10 KPa.

The cymene in the target chemical stream obtained in step e) may contain water and small amounts of sulphur compounds. The cymene in the target chemical stream can be further purified by removal of water and sulphur contents. This can be achieved by addition of a dehydrating agent. Therefore, in one embodiment the method further comprises a step f) removing water from the target chemical stream obtained in e) by addition of a dehydrating agent. In one embodiment the dehydration agent is selected from a substance

comprising CaO, anhydrous MgSO4, anhydrous Na2SO₄ and/or anhydrous CaCI₂. In a preferred embodiment the dehydration agent comprises CaO. In one embodiment the CaO in added to a concentration of 1-25 % (w/w), such as 2-10 % (w/w).

In one embodiment at least part of the cyclic monoterpenes in step a) is a- pinene, β-pinene, caren, sabinene, a-thujene, β-thujene and/or limonene. A CST often mainly consists of a-pinene, β-pinene, and careen. Therefore, in a preferred embodiment at least part of the cyclic monoterpenes in step a) is a- pinene, β-pinene, and/or caren, and in a most preferred embodiment the majority of the cyclic monoterpenes in step a) are a-pinene, β-pinene and/or carene. In one embodiment the cymene obtained in step d) is para-cymene. Detailed description of exemplary embodiments Example 1

1 % (w/w) Fe₂(S0₄)₃ was added at room temperature to a crude sulphate turpentine in a micro wave vial. The temperature of the liquid was lowered to -15 °C and sulphur dioxide was condensed into the liquid, in an amount corresponding to 35 % (w/w) of the crude sulphate turpentine. The solution was thereafter heated to 170 °C for 20 minutes using microwave irradiation. The solution was subsequently cooled to room temperature and analysed by GC/MS. As shown in figure 1 d, high amounts of cymene were formed during the reaction. The yield obtained was in the range of 50- 80 % of the theoretical amount. A GC/MS chromatogram of an untreated crude sulphate turpentine is shown in figure 1 a. Example 2

A crude sulphate turpentine was added to a micro wave vial, the temperature of the crude sulphate turpentine was lowered to -15 °C and sulphur dioxide was condensed into the crude sulphate turpentine in an amount corresponding to 35 % (w/w) of the crude sulphate turpentine. The solution was thereafter heated to 170 °C for 20 minutes using microwave irradiation. The solution was

subsequently cooled to room temperature and analysed by GC/MS. As shown in figure 1 b no detectable cymene is formed in the absence of catalyst comprising Fe³⁺ and/ or Fe²⁺ ions. A GC/MS chromatogram of an untreated crude sulphate turpentine is shown in figure 1 a.

Example 3

1 % (w/w) Fe2(S0₄)3 was added at room temperature to a crude sulphate turpentine in a micro wave vial followed by heating to 170 °C for 20 minutes using microwave irradiation. The solution was cooled to room temperature and analysed by GC/MS. As shown in figure 1 c, no cymene is formed by this reaction in the absence of sulphur dioxide. However, some menthene type terpenes are formed. A GC/MS chromatogram of an untreated crude sulphate turpentine is shown in figure 1 a. REFERENCES

1. Ito et al., Hydrocarb. Process. 52 (8) (1973), 89.

2. Welstead et al., Encyclopedia Chem. Technol. 9 (1978), 544.

3. Derfer et al., Encyclopedia Chem. Technol. 22 (1978), 709.

4. Barman et al., Chemical Engineering Journal 114 (2005)

Claims

1 ) A method for production of cymene comprising the following steps:

c) addition of sulphur dioxide to the solution

2) Method according to claim 1 wherein the catalyst comprising Fe³⁺ and/ or

3) Method according to claim 2 wherein at least 0.05 %, such as 0.05 %-10 % (w/w) such as 0.1-1 % (w/w) such as 0.5-1 % (w/w) Fe2(SO₄)₃ is added in step b).

4) Method according to any one of the previous claims wherein at least 0.1 % (w/w) such as 0.1-60% such as 1-50 % (w/w), such as 10-40 %(w/w), such as

15-30 % (w/w) sulphur dioxide is added to the solution in step c).

5) Method according to any one of the previous claims wherein the reaction temperature in step d) is in a range between 50°C - 500°C, such as 100°C - 350 °C, such as 150 - 200 °C.

6) Method according to any one of the previous claims wherein the reaction time in step d) is above 30 seconds, such as between 30 seconds and 12 hours, such as between 1 minute and 10 hours, such as between 2 minutes and 1 hour such as between 5 minutes and 30 minutes. 7) Method according to any one of the previous claims wherein the solution comprising cyclic monoterpenes is selected from crude sulphate turpentine, TMP turpentine or sulphite turpentine. 8) Method according to claim 7 wherein the solution comprising cyclic monoterpenes is crude sulphate turpentine.

9) Method according to any one of the previous claims wherein the sulphur content of the solution comprising cyclic monoterpenes is at least 0.1 % (w/w), such as at least 0.5 % (w/w).

10) Method according to any one of the previous claims, further comprising the step:

e) distilling the solution mixture comprising cymene obtained in step d) such that a target chemical stream comprising more than 50 % of the cymene is obtained and separated from a residual stream comprising less than 50 % of the cymene.

11 ) Method according to claim 10 wherein step e) is performed in the presence of at least 0.5 % (w/w) sulphuric acid, such as 1-25% (w/w).

12) Method according to any one of the previous claims wherein at least part of the cyclic monoterpenes in step a) is a-pinene, β-pinene, carene, sabinene, a- thujene, β-thujene and/or limonene.

13) Method according to claim 12 wherein at feast part of the cyclic

monoterpenes in step a) is a-pinene, β-pinene, and/or carene.