WO2003042146A1

WO2003042146A1 - Process for the preparation of hydroxylated aromatic compounds

Info

Publication number: WO2003042146A1
Application number: PCT/EP2002/012169
Authority: WO
Inventors: Daniele Bianchi; Rino D'aloisio; Roberto Tassinari
Original assignee: Polimeri Europa S.P.A.
Priority date: 2001-11-15
Filing date: 2002-10-30
Publication date: 2003-05-22
Also published as: ITMI20012410A1; TW200407289A

Abstract

A process is described for preparing hydroxylated aromatic compounds by means of the direct oxidation of an aromatic substrate with hydrogen peroxide in a triphasic reaction system, in the presence of a TS-1 zeolitic catalyst.

Description

PROCESS FOR THE PREPARATION OF HYDROXYLATED AROMATIC COMPOUNDS

The present invention relates to a process for the preparation of hydroxylated aromatic compounds by means of the direct oxidation of an aromatic substrate with hydrogen peroxide .

More specifically, the invention relates to an improved process for the preparation of hydroxylated aromatic compounds in which the oxidation reaction with hydrogen peroxide is carried out in a triphasic system, in the presence of a TS-1 zeolitic catalyst.

Hydroxylated aromatic compounds are used as intermediates for ^■ the production of phyto-medicines, dyes, pharma- ceutical compounds, antioxidants, synthetic resins and insecticides .

Among hydroxylated aromatic compounds of major interest from a commercial point of view, phenol can be mentioned, which is currently industrially produced from cu- ene . Various processes for the direct oxidation of aromatic substrates, with hydrogen peroxide in the presence of suitable catalytic systems, are known in the art.

These processes are generally carried out in an or- ganic solvent capable of improving the contact between the organic substrate and hydrogen peroxide.

The solvents commonly used are selected from alcohols such as methanol, ethanol or isopropyl alcohol, ketones such as acetone, methylethylketone, or acetic acid or ace- tonitrile as described in U.S. patents 4,396,783, GB

2,116,974.

Improvements in the conversion and selectivities of the above processes can however be obtained by operating in the presence of particular solvents such as, for example, sulfolane (EP A 919531) .

A further process improvement can also be achieved through an activation treatment of the catalyst in an aqueous medium with hydrogen peroxide and in the presence of fluorine ions, as described in European patent application EP A 958861.

The processes of the known art are generally carried out in a (solid/liquid) biphasic system.

It has now been found that by operating in a triphasic reaction system consisting of solid catalyst/aqueous phase/organic phase (aromatic compound + solvent) instead of a biphasic system (solid catalyst/organic phase) , it is possible to increase the productivity of oxidation processes of aromatic substrates without jeopardizing the selectivity. Furthermore, by operating in this system, it is possible to significantly reduce the quantity of organic solvent and consequently the dimensions of the recovery section, whose cost greatly influences the overall cost of the process.

An object of the present invention therefore relates to a process for the preparation of hydroxylated aromatic compounds comprising the direct oxidation of an aromatic substrate with hydrogen peroxide, characterized in that the process is carried out in a triphasic reaction system comprising a first liquid phase consisting of the aromatic substrate and an organic solvent, a second liquid phase consisting of water and a solid phase consisting of a catalyst based on titanium silicalite TS-1.

The triphasic reaction system is reached when operating with a^" controlled quantity of water which is such as to cause the demixing of the liquid phase and prevent the aggregation of the catalyst .

It is convenient to operate with a water concentration ranging from 5 to 60% by weight, preferably using concentrations ranging from 10 to 40%. The organic solvent can be selected from the solvents commonly used in oxidation processes described in the known art such as methanol, ethanol, isopropyl alcohol, acetone, methylethylketone, acetic acid or acetonitrile.

The process is preferably carried out in the presence of solvents having formula (I)

0 o

wherein: R_x, R₂, R₃ and R₄, the same or different, are hydrogen atoms or alkyl groups with from 1 to 4 carbon atoms, or among the compounds having general formula (II)

wherein R and R' , the same or different, represent an alkyl radical with from 1 to 4 carbon atoms, described in European patent^' application EP A 919531. Particularly preferred for the purposes of the present invention are compounds having general formula (I) and, among these, sulfolane is preferred.

The solvent is used in quantities ranging from 20 to 80% by weight with respect to the reaction mixture. Quantities ranging from 40 to 60% are preferably used. The catalysts used in the process of the present invention are selected from those having general formula (III) : xTi0₂-(l-x)Si0₂ (III) wherein: x ranges from 0.0001 to 0.04, preferably from 0.02 to 0.03.

The above titanium silicalites can be prepared according to the method described in U.S. patent 4,410,501 in which their structural characteristics are also described. The titanium silicalites can also be subjected to activation treatment as described in patent EP A 958861.

Titanium silicalites in which part of the titanium is substituted by other metals such as boron, aluminum, iron or gallium, can also be used. These substituted titanium silicalites and the methods for their preparation are described in European patent applications 226,257, 226,258 and 266,825.

The catalyst is generally used in quantities ranging from 2 to ^"60% by weight with respect to the aromatic sub- strate.

Quantities of catalyst ranging from 5 to 40% by weight with respect to the aromatic substrate are preferably used.

The hydrogen peroxide is added to the reaction mixture in quantities ranging from 5 to 50% in moles with respect to the aromatic substrate, preferably from 10 to 30% in moles .

Solutions of hydrogen peroxide with a concentration ranging from 10 to 60% by weight, preferably from 15 to 60% by weight, are conveniently used. Aromatic substrates which can be used in the process of the present invention can be selected from benzene, toluene, ethylbenzene, chloroben- zene, anisole, phenol and naphthol.

The aromatic substrate is generally used in quantities ranging from 20 to 80% by weight with respect to the reac- tion mixture.

Quantities of aromatic substrate ranging from 30 to 60% by weight with respect to the reaction mixture are preferably used.

The oxidation reaction is carried out at temperatures ranging from 50° to 110°C, preferably from 70° to 100°C.

The reaction time necessary for the complete use of the hydrogen peroxide depends on the reaction conditions used.

At the end of the reaction, the reaction products and non-reacted aromatic substrate are recovered by means of the conventional techniques such as fractionated distillation and crystallization.

The process of the present invention can be carried out in reactors of the semi-batch type (with hydrogen per- oxide feeding) or of the CSTR type (continuous stirred batch reactor) with continuous feeding of the hydrogen peroxide and benzene/solvent mixture.

When operating in a continuous process, the aqueous phase (in which the catalyst is selectively distributed) , is kept inside the reactor removing the organic phase to a quiet non-stirred area in which the de ixing takes place. In this way, only one phase is obtained at the outlet, containing: an aromatic compound, a solvent, a hydroxy- aromatic compound and the by-products. When operating under the process conditions of the invention, it is also possible to operate at 100°C obtaining an increase in the catalytic activity (TN Ti) without a loss in selectivity, as would normally happen when operating in a double phase. The following examples, whose sole purpose is to describe the present invention in greater detail, should in no way be interpreted as limiting the scope to the invention itself.

The experimentation was carried out using a jacketed, AISI 316 steel reactor having a capacity of 600 ml, equipped with a mechanical stirrer, feeding lines of the reagents, temperature control and reflux condenser cooled to 0°C.

The solution of H₂0₂ and, in the case of a continuous functioning, the benzene/solvent mixture, were fed by means of piston pumps.

EXAMPLE 1

Activation of the catalyst

3.0 g (1.43 mmoles of Ti) of TS-1 catalyst (EniChem, Ti = 2.29% by weight) and 0.11 g of NH₄HF₂ (average titer 92.5%) in 35 ml of water, corresponding to a molar ratio F/Ti = 2.5, are charged into a 100 ml glass flask, equipped with a mechanical stirrer, reflux condenser, thermometer and oil-circulation thermostat. The aqueous suspension of the catalyst, maintained under mechanical stirring, is heated to 60°C. 1.6 ml of H₂0₂ at 30% by weight, equal to a molar ratio H₂0₂/Ti = 11, are subsequently added, and the suspension is maintained under stirring at 60°C for 4 hours. After cooling, the solid is separated from the mother liquor (pH 4.3) by filtration on a porous septum, repeatedly washed with deionized water and finally with acetone. The catalyst is then dried under vacuum at 40°C for 8 hours and subjected, at a heating rate of 50°C/h, to thermal treatment in air at 550°C for 4 hours. Titer of the activated catalyst = 1.49% of Ti. The dissolved titanium corresponds to 35% by weight. EXAMPLE 2

Comparative example : biphasic system (operating under the conditions described in patent EP A 958,861) An AISI 316 reactor (volume = 600 ml) is pressurized with nitrogen at a pressure of 5 atm. 100 g of benzene (1.28 moles), 200 g of sulfolane and 10 g of catalyst activated as described in Example 1 (equal to 3.1 mmoles of Ti) , are then charged. The liquid phase of the reaction mixture in this case is homogeneous . The temperature of the reactor is brought to 80°C. 14.5 g (128 mmoles of H₂0₂; H₂0₂/benzene = 0.1) of an aqueous solution of H₂0₂ at 30% w/w) are subsequently added over a period of two hours .

After 15 minutes of conditioning at a constant tem- perature, under stirring, the reaction mixture is cooled to 20°C and the catalyst is separated by filtration on a porous septum.

The solution is analyzed by means of HPLC revealing the formation of the following products: phenol 7.5 g (79.8 mmoles) hydroquinone traces (0 mmoles) catechol traces (0 mmoles)

The reaction mixture was then evaporated at reduced pressure obtaining 1.2 g of polyphenol pitches (correspond- ing to 10.9 mmoles of C₆H₆0₂ monomer), as boiler residue.

The reaction performances are consequently as follows: benzene conversion (Cl) = 7.1% (in moles);

H₂0₂ conversion (C2) = 99% (in moles) ; selectivity to phenol (SI) = 88% (in moles) ; - selectivity with respect to H₂0₂ (S2) = 63% (in moles) ; hourly turnover (TOF) = 11 (phenol moles/Ti moles per hour) phenol concentration in the final reaction mixture = 2.38% (by weight) .

Operating under these conditions, during the recovery and purification phase of the reaction products, it is necessary to evaporate 41.0 Kg of solvent (sulfolane and non- reacted benzene) per Kg of phenol. EXAMPLE 3

Comparative example: biphasic system

The same procedure is adopted as described in Example 2, but adding 21.75 (192 mmoles of H₂0₂; H₂0₂/benzene = 0.15) of an aqueous solution of H₂0₂ at 30% w/w; in 1 hour at a temperature of 100°C.

The solution is analyzed by means of HPLC revealing the formation of the following products: phenol 9.64 g (102.6 mmoles) hydroquinone 286 mg (2.6 mmoles) catechol 429 mg (3.9 mmoles)

The reaction mixture was then evaporated at reduced pressure obtaining 2.46 g of polyphenol pitches (corresponding to 22.4 mmoles of C₆H₆0₂ monomer), as boiler residue. The reaction performances are consequently as follows: benzene conversion (Cl) = 10.3% (in moles); H₂0₂ conversion (C2) = 99% (in moles) ; selectivity to phenol (SI) = 78% (in moles) ; selectivity with respect to H₂0₂ (S2) = 54% (in moles) ; hourly turnover (TOF) = 33 (phenol moles/Ti moles per hour) phenol concentration in the final reaction mixture = 3.00% (by weight) . Operating under these conditions, during the recovery and purification phase of the reaction products, it is necessary to evaporate 32.3 Kg of solvent (sulfolane and non- reacted benzene) per Kg of phenol. EXAMPLE 4 Triphasic system under semi-batch conditions

An AISI 316 reactor (volume = 600 ml) is pressurized with nitrogen at a pressure of 5 atm. 100 g of benzene (1.28 moles), 180 g of sulfolane 43 g of water and 10 g of catalyst activated as described in Example 1 (equal to 3.1 mmoles of Ti) , are then charged. The liquid fraction of the reaction mixture in this case is biphasic. The temperature of the reactor is brought to 80°C. 14.5 g (128 mmoles of H₂0₂; H₂0₂/benzene = 0.1) of an aqueous solution of H₂0₂ at 30% w/w) are subsequently added over a period of two hours. The reaction mixture is then cooled to 20°C and the catalyst is separated by filtration on a porous septum.

The liquid phase is analyzed by means of HPLC revealing the formation of the following products: phenol 8.7 g (92.4 mmoles) hydroquinone 264 mg (2.4 mmoles) catechol 385 mg (3.5 mmoles)

The reaction mixture was then evaporated at reduced pressure obtaining only traces of polyphenol pitches as boiler residue. The reaction performances are consequently as follows: benzene conversion (Cl) = 7.7% (in moles) ;

H₂0 conversion (C2) = 95% (in moles) ; selectivity to phenol (SI) = 94% (in moles) ; selectivity with respect to H₂0₂ (S2) = 76% (in moles) ; hourly turnover (TOF) = 15 (phenol moles/Ti moles per hour) phenol concentration in the organic phase = 3.11% (by weight) . Operating under these conditions, during the recovery and purification phase of the reaction products, it is necessary to evaporate 31.2 Kg of solvent (sulfolane and non- reacted benzene) per Kg of phenol. EXAMPLE 5 Triphasic system under semi-batch conditions The same procedure is adopted as in Example 4, but adding 21.75 (192 mmoles of H₂0₂; H₂0₂/benzene = 0.15) of an aqueous solution of H₂0₂ at 30% w/w, in 2 hours at a temperature of 80°C. The solution is analyzed by means of HPLC revealing the formation of the following products : phenol 12.7 g (135.0 mmoles) hydroquinone 660 mg (6.0 mmoles) catechol 990 mg (9.0 mmoles) The reaction mixture was then evaporated at reduced pressure obtaining only traces of polyphenol pitches as boiler residue.

The reaction performances are consequently as follows: benzene conversion (Cl) = 11.7% (in moles); - H₂0₂ conversion (C2) = 95% (in moles) ; selectivity to phenol (SI) = 90% (in moles) ; selectivity with respect to H₂0₂ (S2) = 74% (in moles) ; hourly turnover (TOF) = 22 (phenol moles/Ti moles per hour) phenol concentration in the final reaction mixture =

4.53% (by weight) .

Operating under these conditions, during the recovery and purification phase of the reaction products, it is nec- essary to evaporate 21.1 Kg of solvent (sulfolane and non- reacted benzene) per Kg of phenol.

EXAMPLE 6

Triphasic system under semi-batch conditions

The same procedure is adopted as in Example 4, but adding 21.75 (192 mmoles of H₂0₂; H₂0₂/benzene = 0.15) of an aqueous solution of H₂0₂ at 30% w/w, in 1 hour at a temperature of 100°C.

The solution is analyzed by means of HPLC revealing the formation of the following products: phenol 13.3 g (141.1 mmoles) hydroquinone 693 mg (6.3 mmoles) catechol 1034 mg (9.4 mmoles)

The reaction mixture was then evaporated at reduced pressure obtaining only traces of polyphenol pitches as boiler residue.

The reaction performances are consequently as follows: benzene conversion (Cl) = 12.2% (in moles);

H0₂ conversion (C2) = 98% (in moles) ; selectivity to phenol (SI) = 90% (in moles) ; - selectivity with respect to H₂0₂ (S2) = 75% (in moles) ; hourly turnover (TOF) = 46 (phenol moles/Ti moles per hour) phenol concentration in the final reaction mixture = 4.75% (by weight). Operating under these conditions, during the recovery and purification phase of the reaction products, it is necessary to evaporate 20.1 Kg of solvent (sulfolane and non- reacted benzene) per Kg of phenol.

A comparison between the results obtained in the biphasic and triphasic system, operating under semi-batch conditions, is provided in Table 1.

Table 1

Example Benzene Sulfolane H₂0 H2O2 T Conv. % Selec. % Selec. % TOF Cone. % Kg solv. nr. % w/w % w/w • % w/w (b) °C benzene benzene H2O2 (c) phenol Kgphenol

(a) (a) ' (a) (Cl) (SI) (S2) (d) (e)

2 33 67 0 10 80 7.1 88 63 11 2.38 41.0

3 33 67 0 15 100 10.3 78 54 33 3.00 32.3

4 31 56 13 10 80 7.7 94 76 15 3.11 31.2

5 31 56 13 15 80 11.7 90 74 22 4.53 21.1

6 31 56 13 15 100 12.2 90 75 46 4.75 20.1

(a) weight percentage with respect to the reaction mixture

(b) H2O2 moles/benzene moles

(c) hourly turnover of titanium (phenol moles/titanium moles per hour)

(d) wt % concentration of phenol in the final reaction mixture (in the triphasic system only the organic phase was considered)

(e) Kg of solvent to be evaporated in the recovery phase per 1 Kg of phenol produced.

EXAMPLE 7

Triphasic system under CSTR conditions (process in continuous)

An AISI 316 reactor (volume = 600 ml) was equipped with a column (material: AISI 316, internal diameter: 1 cm) , fixed at the head, and immersed in the reaction mixture. A non-stirred zone is created inside the column, in which it is possible to selectively remove the organic phase (light phase) . The reactor is pressurized with nitrogen at a pressure of 5 atm. 100 g of benzene (1.28 moles), 150 g of sulfolane 150 g of water and 50 g of catalyst activated as described in Example 1 (equal to 15.5 mmoles of Ti) , are then charged. The liquid fraction of the reaction mixture in this case is biphasic. The temperature of the reactor is brought to 100°C.

A mixture of benzene (38.3% by weight), sulfolane (57.5% by weight and H₂0₂ (solution at 60% w/w) is then fed in continuous (flow: 500 g/hour) . 766 g of benzene (9.82 moles) and 84 g of H₂0₂ (60% w/w; 1.48 moles), corresponding to a H₂0₂/benzene ratio = 0.15, are then fed over a period of 4 hours.

The level inside the reactor is kept constant by removing the organic phase which is separated in the quiet zone inside the tube immersed in the reaction medium. The organic phase is subsequently analyzed by means of HPLC revealing the formation of the following products : phenol 88.5 g (942 mmoles) hydroquinone 6.16 g (56 mmoles) catechol 9.24 mg (84 mmoles)

The reaction performances are consequently as follows: - benzene conversion (Cl) = 11.0% (in moles);

H₂0₂ conversion (C2) = 95% (in moles) ; selectivity to phenol (SI) = 87% (in moles) ; selectivity with respect to H₂0₂ (S2) = 67% (in moles) ; - hourly turnover (TOF) = 30 (phenol moles/Ti moles per hour) phenol concentration in the organic phase= 4.43% (by weight) .

Operating under these conditions, during the recovery and purification phase of the reaction products, it is necessary to evaporate 21.6 Kg of solvent (sulfolane and non- reacted benzene) per Kg of phenol.

Claims

1. A process for the preparation of hydroxylated aromatic compounds comprising the direct oxidation of an aromatic substrate with hydrogen peroxide, characterized in that the process is carried out in a triphasic reaction system comprising a first liquid phase consisting of the aromatic substrate and an organic solvent, a second liquid phase consisting of water and a solid phase consisting of a catalyst based on titanium sili- calite TS-1.

2. The process according to claim 1, wherein the quantity of water in the reaction system ranges from 5 to 60% by weight .

3. The process according to claim 2 , wherein the quantity of water ranges from 10 to 40%

4. The process according to claim 1, wherein the organic solvent is selected from solvents having formula (I)

wherein: Ri, R₂, R₃ and R₄, the same or different, are hydrogen atoms or alkyl groups with from 1 to 4 carbon atoms, or among the compounds having general formula (ID

wherein R and R', the same or different, represent an alkyl radical with from 1 to 4 carbon atoms .

5. The process according to claim 4, wherein the organic solvent is selected from the compounds having general formula (I) .

6. The process according to claim 5, wherein the organic solvent is sulfolane .

7. The process according to claim 1, wherein the organic solvent is used in quantities ranging from 20 to 80% by weight with respect to the reaction mixture.

8. The process according to claim 7, wherein the organic solvent is used in quantities ranging from 40 to 60%.

9. The process according to claim 1, wherein the catalyst is selected from those having general formula (III) :

^{• "'} xTi0₂-(l-x)Si0₂ (III) wherein: x ranges from 0.0001 to 0.04, preferably from

0.02 to 0.03.

10. The process according to claim 9, wherein the catalyst is used in quantities ranging from 2 to 60% with respect to the aromatic substrate.

11. The process according to claim 10, wherein the cata- lyst is used in quantities ranging from 5 to 40% with respect to the aromatic substrate.

12. The process according to claim 9, wherein the catalyst is subjected to activation treatment.

13. The process according to claim 1, wherein the hydrogen peroxide is added to the reaction mixture in quantities ranging from 5 to 50% in moles with respect to the aromatic substrate.

14. The process according to claim 13 , wherein the hydro- gen peroxide is added to the reaction mixture in quantities ranging from 10 to 30% in moles with respect to the aromatic substrate .

15. The process according to claim 1, wherein the hydrogen peroxide is used in a solution at a concentration ranging from 10 to 60% .

16. The process according to claim 15, wherein the hydrogen peroxide is used in a solution at a concentration ranging from 15 to 60% by weight.

17. The process according to claim 1, wherein the aromatic substrate is selected from benzene, toluene, ethylben- zene, chlorobenzene, anisole, phenol and naphthol .

18. The process according to claim 17, wherein the aromatic substrate is benzene.

19. The process according to claim 1, wherein the aromatic substrate is used in quantities ranging from 20 to 80% by weight with respect to the reaction mixture.

20. The process according to claim 19, wherein the aromatic substrate is used in quantities ranging from 30 to 60% by weight with respect to the reaction mixture.

21. The process according to claim 1, wherein the oxidation reaction is carried out at temperatures ranging from 50° to 110°C.

22. The process according to claim 21, wherein the oxidation reaction is carried out at temperatures ranging from 70° to 100°C.

23. The process according to claim 1, wherein the oxidation reaction is carried out in reactors of the semi- batch type, with feeding of hydrogen peroxide, or of the CSTR type (continuous stirred batch reactor) with continuous feeding of hydrogen peroxide and of the aromatic substrate/solvent mixture.