WO2002072508A1

WO2002072508A1 - HYDROGENATION OF α-PINENE

Info

Publication number: WO2002072508A1
Application number: PCT/FI2002/000159
Authority: WO
Inventors: Antero Laitinen; Olli Aaltonen; Juha Kaunisto
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 2001-03-09
Filing date: 2002-03-01
Publication date: 2002-09-19
Also published as: FI20010472A; FI20010472A0; WO2002072508A8; FI111160B; AU2002235961A1

Abstract

α-pinene-containing raw material is led, together with hydrogen, into a reactor which is packed with a Ruthenium-containing catalyst. In the continuous reactor α-pinene is hydrogenated selectively to cis-pinane under elevated pressure and temperature. The sulphur content of the feed raw material is below 5 ppm.

Description

HYDROGENATION OF α-PINENE

TECHNICAL FIELD

The invention belongs to the field of terpene chemistry. More specifically the invention concerns the hydrogenation of α-pinene selectively to cw-pinane in a continuous reactor.

BACKGROUND ART α-pinene (boiling point 156 °C) belongs to monoterpene hydrocarbons which are widely found in essential oils and rosin obtained from plant materials. Crude turpentine, which is obtained from pine, typically contains 50 - 80 % α-pinene. The commercially most interesting turpentine components, α- and β-pinene, can be separated from other terpenes, such as 3-carene, limonene and camfene, by vacuum distillation. Pure α- and β-pinene can be used as feedstock for making relatively expensive aroma compounds and fragrance components, such as linalool, dihydromyrcene, nerol or geraniol. One important method for making such compounds is to first hydrogenate the double bond in α-pinene to cω-pinane which can be used as raw material in subsequent reactions. For example, it is possible to make linalool by first oxygenating cw-pinane to pinane hydroperoxide, reducing the obtained product to pinalol and pyrolyzing pinalol to linalool. Trans-pinane is not a favourable hydrogenation product because its selective oxygenation to hydroperoxide proceeds considerably slower than the oxygenation of cw-pinane.

The selective hydrogenation of α-pinene to s-pinane has been a target of development work for a long time. US 4,018,842 [Canova] discloses the hydrogenation of α-pinene to cw-pinane batchwise by using a modified, nickel-containing catalyst. According to the patent text the selectivity to cw-pinane depends on temperature and on reaction time. Relatively low temperature and long reaction time favour reaction selectivity, α-pinene is preferably hydrogenated to cw-pinane at 50 - 80 °C temperature, most preferably at about 50 °C. According to examples it is possible to produce cw-pinane at 97 - 98 % selectivity, in 30 - 96 °C reaction temperature and under 15 - 40 bars hydrogenation pressure provided that reaction time is several hours. Even reaction time exceeding 30 hours is possible. The patent text states that hyrogenation pressure does not have an effect on cis /trans -selectivity.

US 4,310,714 [Pavlin] teaches the selective hydrogenation of α-pinene to cw-pinane by using a ruthenium-containing catalyst in batch equipment. According to the patent examples 94 - 99 % selectivity to cz^'s-pinane can be achieved under 4 - 30 bars hydrogenation pressure and in 20 - 90 °C reaction temperature with 1 - 6 hours reaction time. In the method which is described in the patent, catalyst and starting material are mixed together and are brought to contact with hydrogen. After the reaction the catalyst is separated from the reaction mixture by filtering, for example, and it is regenerated by washing. After this the catalyst may be reused. If the starting material is free from catalyst poisons, there is no need to regenerate the catalyst.

In US 4,018,842 and US 4,310,714 the effect of hydrogenation temperature on reaction selectivity is explored instead of its effect on catalyst lifetime.

Neither of the patent texts describe a continuous method even though in US 4,310,714 it is stated that catalyst may be reused after regeneration or filtration. It has not been possible to build continuous reactors because, according to the present knowledge, the catalyst lifetime is not long enough to make a continuous reactor reasonable. The major, although not the only, reason for catalyst deactivation is that the commercial α-pinene feedstock contains catalyst poisons. Sulphur is the most important of such poisons. Turpentine, which is obtained as side product from kraft pulping, always contains sulphur impurities. Using specific unit operations, such as adsorption with activated coal, hypochlorite treatment or hydrogen peroxide treatment, it is possible to produce a pinene-containing product which is almost sulphur-free [J.O. Bledsoe, Terpenoids, in: J. I. Kroschwitz, M. Howe-Grant (Eds.), Kirk-Othmer encyclopedia of Chemical Technology, 4th ed., John Wiley & Sons, 1997, vol. 23, p. 833]. One apparent alternative is to select sulphur-free gum turpentine for the raw material.

DESCRIPTION OF THE INVENTION

General description

A method in accordance with claim 1 has been invented which makes it possible to hydrogenate α-pinene selectively and continuously to m-pinane. In the present method hydrogenation occurs in a much more compact flow reactor the reaction time being only a few minutes.

In the continuous reactor experiments, which have been done at VTT, it has been found that under specific conditions the catalyst becomes deactivated despite of using a raw material which is from catalyst poisons free turpentine. Based on the experiments there is reason to assume that catalyst bed deactivation is not only caused by catalyst poisons in the raw material, but also because under certain conditions reactive species are deposited on catalyst surface causing catalyst deactivation in a catalyst bed which is observed as a decrease of conversion with time.

We have unexpectedly found in our experiments that when using a sulphur-free or low-sulphur raw material, the deactivation of a ruthenium-containing catalyst bed decreases stepwise when hydrogenation temperature is increased above a certain value which, according to experiments, is about 90 - 120 °C. The invention makes it possible to build a continuous α-pinene hydrogenation process. The experimental set-ups which were used in the findings related to the present invention are presented in Example 1 and in Table 1.

The method according to the present invention provides a more favourable and faster way to manufacture c s-pinane by hydrogenating α-pinene. In the present method a ruthenium- containing catalyst is advantageously situated on a support which is fixed in a reactor. The support can be organic or inorganic. The catalyst support can be an organic polymer fiber, which can e.g. be formed into a felt or a knit. The support can also be an inorganig matrix. Catalyst support is then fixed in the equipment so that the α-pinene-containing raw material and hydrogen flow through it. One advantage of the present invention is that there is no need to filter the catalyst from the reaction mixture, because the catalyst is on a solid catalyst bed instead of a slurry, which is the case in batch hydrogenation.

In the method according to the present invention the reaction temperature has to be at least 90 °C, preferably 120 - 200 °C to get sufficient catalyst lifetime. Pressure in the hydrogenation reactor may typically be 1 - 1000 bars. High pressure increases reaction rate but also increases equipment cost. In the present invention the hydrogenation pressure is advantageously 20 - 300 bars.

In the present invention the residence time in the reactor is typically 1 - 10 minutes, whereas in batch reactors the required reaction time is typically 1 - 30 hours, usually less than 6 hours. Very short reaction time means that the volume of a continuous reactor is very small compared with a batch reactor of same production capacity.

The hydrogenation reactor can e.g. be a tubular reactor, a multi-tube reactor or some other type of continuous reactor. The reactor can be equipped with thermal control to achieve optimum reaction temperature. The s-pinane-containing reaction product can be circulated back to reactor, if required. Hydrogen feed to the process can be directly into the hydrogenation reactor or into some other process technically suitable part of the equipment. The excess hydrogen, which comes out from the reactor, can either be circulated back to the reactor or it can be removed from the process. The reaction can be controlled with the amount of feed hydrogen, with temperature or with pressure.

Detailed description

A flowchart of a continuous process provided by the present invention is shown in Figure 1. Hydrogen is fed from reservoir 1, through control valve 2 into mixer 5, where α-pinene- containing raw material from tank 3 is also pumped with pump 4. The obtained reaction mixture flows into reactor 7, which is packed with a ruthenium-containing catalyst. The temperatures of the in- and out- flows are controlled with heat exchangers 6 and 8. The pressure of the reaction mixture is reduced in valve 9, and gaseous and liquid components are separated in separator 10. The product is collected in tank 11. The liquid and gaseous products from separator 10 may be circulated back to the reactor, if required.

The flowchart is in no way binding but many different technical alternatives as well are possible within the scope of the present invention.

EXAMPLES

1. Hydrogenation of α-pinene to cz pinane with a continuous reactor

α-pinene is continuously hydrogenated in an 8 mm diameter reactor . Catalyst is packed inside the reactor. The catalyst contains 0.5 weight-% ruthenium on carbon pellet support. The reactor is heated with electric resistors so that reaction temperature is 50 °C. Hydrogenation pressure is 150 bars, α-pinene-containing raw material is fed to the reactor with an HPLC pump with feed rate 30 g per hour. The feed is from gum turpentine, containing 96 % α-pinene and no sulphur according to analyses. Hydrogen flows directly from bottle, 1.1 g per hour, through a control valve which functions as pressure reducer, α-pinene and hydrogen flows are mixed in a static mixer before feeding into the reactor. The pressure of the flow out from the reactor is reduced in a pressure reducer whereby excess hydrogen separates from liquid products. The product is analyzed with GC. α-pinene is hydrogenated in the reactor to cw-pinane with a selectivity of 99 % and with initial conversion of 100 %. Catalyst deactivation is observed almost immediately from decreasing conversion.

All reaction experiments are carried out principally in the same way except that reaction parameters and starting materials are changed. Results are shown in table 1.

The raw materials used in the experiments are as follows: a) 96 % α-pinene from gum turpentine, no sulphur b) 98 % α-pinene, no sulphur c) 95 % α-pinene from crude sulphate turpentine, max. 5 ppm sulphur. d) 95 % α-pinene from crude sulphate turpentine, over 30 ppm sulphur.

The catalysts used in the experiments are: e) 0.5 weight-% Ruthenium on pelletized carbon carrier f) 10 weight-% Ruthenium on pelletized carbon carrier g) 0.5 weight-% Ruthenium on pelletized alumina carrier h) 10 weight-% Ruthenium on pelletized alumina carrier i) 5 weight-% Ruthenium on polyolefin fibre

Claims

1. A method for producing c/s-pinane by simultneously contacting α-pinene containing starting material and hydrogen with a ruthenium containing catalyst, under elevated pressure and temperature so that major part of the α-pinene in the mixture is hydrogenated to czs-pinane, characterized in that a) hydrogenation occurs in a flow-reactor, and b) the α-pinene-containing starting material originates from a process where sulphur chemicals are not used or the sulphur content of the α-pinene-containing starting material is less than 5 ppm, and c) hydrogen and the α-pinene-containing starting material are brought into contact with the catalyst at temperature above 90 °C, preferably at 120 - 200 °C, and d) under pressure of 5 - 600 bars , preferably under 20 - 300 bars.

2. A method according to claim 1 characterized in that ruthenium is immobilized on a support phase.

3. A method according to any of claims 1 - 2 characterized in that the support phase pellett consists of alumina or carbon or a mixture thereof.

4. A method according to any of claims 1 - 2 characterized in that the ruthenium-containing catalyst which is immobilized in pellets, forms a bed inside the reactor.