The present invention is directed to a process for the manufacture of ortho-cresol (o-cresol) by reacting phenol with methanol in the gas phase and in the presence of a catalyst, whereby the catalyst comprises gallium oxide, which preferably further contains magnesium oxide. In a preferred embodiment of the present invention, the catalyst consists of gallium oxide and magnesium oxide. The term "consisting of" in the context of the present invention means that the total amount of gallium oxide and magnesium oxide ideally sums up to 100 weight-%. It is, however, not excluded that small amounts of impurities (such as e.g. any other metal) or non- reactive additives may be present in amounts of less than 5 weight-%, preferably less than 1 weight-%, more preferably less than 0.5 weight-%, based on the total weight of the methylation catalyst. The term "gallium oxide and magnesium oxide" also encompasses mixed oxides of gallium and magnesium, as well as any mixture of Ga ₂ C>3 and MgO, and mixtures of any modifications thereof. Preferably the catalyst comprising Ga ₂ 0 ₃ and MgO has a weight ratio of Mg to Ga from 1 : 1 to 15: 1 .

Ortho-cresol is an important intermediate for TMHQ (2,3,5-trimethylhydrochinone) being itself one of the building blocks of Vitamin E. The reaction sequence starting from o-cresol to 2,6-xylenol is disclosed by T. Mathew at al. in Trans IChemE 2003, Vol 81 , Part A, 265-270. The further reaction of 2,6-xylenol leading to TMHQ is e.g. described in WO 2012/025587 A1 .

The process of the present invention is now further described in more detail below.

Catalyst

In an embodiment of the present invention the catalyst comprises gallium oxide.

In a preferred embodiment of this embodiment the catalyst further comprises magnesium oxide. Thus, a catalyst comprising gallium oxide and magnesium oxide may also be used. The term "gallium oxide and magnesium oxide" also

encompasses mixed oxides of gallium and magnesium, as well as any mixture of Ga ₂ C>3 and MgO, and mixtures of any modifications thereof. These (mixed) oxides of gallium and magnesium do not have a spinel structure.

In a further embodiment of the present invention the catalyst consists of gallium oxide. The term "consisting of" in the context of the present invention means that the total amount of gallium oxide ideally is 100 weight-%. It is, however, not excluded that small amounts of impurities (such as e.g. any other metal) or non- reactive additives may be present in amounts of less than 5 weight-%, preferably less than 1 weight-%, more preferably less than 0.5 weight-%, based on the total weight of the catalyst.

In another embodiment of the present invention the catalyst consists of gallium oxide and magnesium oxide. Hereby also mixed oxides of gallium and magnesium are encompassed, as well as any mixture of Ga ₂ 0 ₃ and MgO, and mixtures of any modifications thereof. The term "consisting of" in the context of the present invention means that the total amount of gallium oxide and magnesium oxide ideally sums up to 100 weight-%. It is, however, not excluded that small amounts of impurities (such as e.g. any other metal) or non-reactive additives may be present in amounts of less than 5 weight-%, preferably less than 1 weight-%, more preferably less than 0.5 weight-%, based on the total weight of the catalyst.

In preferred embodiments of the present invention the catalysts either comprising gallium oxide/s and magnesium oxide/s or consisting of gallium oxide/s and magnesium oxide/s have a weight-ratio of magnesium to gallium in the range of from 1 : 1 to 15:1. Especially preferred are those catalysts where the weight-ratio of magnesium to gallium is either 2 : 1 or 6 : 1 or 10 : 1.

In a preferred embodiment of the present invention the catalyst with all

preferences and limitations as given above does not contain iron oxide in contrast to the catalysts disclosed in EP-A 019 476.

In a further preferred embodiment of the present invention the catalyst consisting of gallium oxide with all preferences and limitations as given above does neither contain titanium oxide nor indium oxide in contrast to US 5,245,089 and US

3,418,379, respectively.

Process for the manufacture of the catalysts

Usually the catalysts are prepared as follows:

a) dissolving gallium nitrate and optionally magnesium nitrate in the desired ratio in water;

b) providing a sodium carbonate solution with a concentration in the range of 0.3 to 2 M (preferably with a concentration in the range of 0.8 to 1.5 M) and a pH value in the range of 7.5 to 10 (preferably a pH value in the range of 8 to 9), whereby the molar ratio of sodium carbonate to the sum of gallium nitrate and optionally magnesium nitrate is 5 : 1 ;

c) dropping the solution obtained in step a) into the solution obtained in step b) under stirring, while adjusting the pH to a value in the range of 6 to 8 (preferably to a value in the range of 6.5 to 7.5) and keeping the temperature in the range of 50 to 60°C;

d) filtering the solution obtained in step c) to obtain the solid catalyst;

e) washing the solid catalyst obtained in step d) with water;

f) drying the solid catalyst obtained in step e);

g) calcinating the dried solid catalyst obtained in step f) in air.

The steps are now described in more detail below. Step a)

This step is usually performed at room temperature, but may be also performed at temperatures above room temperature. It is only important that the salts, i.e. gallium nitrate and optionally magnesium nitrate, become dissolved. The pressure at which this step is performed is not critical. It is also possible to use other magnesium or gallium salts such as magnesium halogenides or gallium halogenides as long as the salts are removed by the calcination step g).

Step b) If needed the pH value is adjusted by means of concentrated HNO3. Other acids may also be suitable, if other salts of Ga and Mg are used. Thus, it is e.g. possible to use concentrated hydrogen chloride if Ga chloride and Mg chloride are used. Step c)

The pH is preferably adjusted with concentrated sodium hydroxide. Other bases such as other alkaline bases and earth alkaline bases may also be suitable as long as the formed salts are better soluble than MgO and Ga ₂ 0 ₃ . Stirring is continued for about 30 to 45 minutes.

Step d)

For filtering any suitable filter such as a Biichner filter may be used. Step e)

The washing with water is preferably continued until the elution water shows a pH value of 7.

Step f )

The drying may be carried out at a temperature in the range of from 100 to 150°C for 4 to 48 hours. In one embodiment of the process of the present invention the drying is carried out at 120°C for 4 hours, in another embodiment of the process of the present invention the drying is carried out at 110° C for 12 hours.

Step g)

The calcination is preferably carried out at a temperature in the range of from 400 to 600° C, for a time in the range of 4 to 15 hours. More preferably the calcination is carried out at 450° C for 8 hours.

The methylation reaction according to the present invention is now described in more detail below. The GHSV (gas hourly space velocity) is thereby in the range of from 3200 h ^"1 to 4000 h ^"1 , more preferably the GHSV is around 3600 h ^"1 . Process of the present invention

Preferably the reaction, i.e. the methylation of phenol to o-cresol, is carried out at a temperature in the range of from 250 to 600° C, preferably at a temperature in the range of from 400 to 500° C.

Preferably the molar ratio of phenol to methanol is in the range of from 1 : 1 to 1 :20, more preferably it is in the range of from 1 : 1 to 1 : 15, most preferably it is in the range of from 1 :2 to 1 :6.

Preferably the pressure is in the range of from 1 to 10 bara (bar absolute), more preferably it is 1 bara.

During the reaction water may also be present. Hereby the molar amount of water is at most 20 times the molar amount of phenol.

The invention is now further illustrated in the following non-limiting examples. Examples All examples have been carried out according to the general procedure. General procedure

In a typical experiment, 1 cm ³ of catalyst is loaded in the reactor, with particles having a size in the range of from 30 to 60 mesh, prepared by compressing the powder into particles, then crushed and sieved. The liquid mixture is then prepared, with the desired methanol/ phenolic compound molar ratio, loaded in the syringe and installed on the pump. The gas flow rate is then set up and regulated (typically N ₂ ), with a flow rate that is typically equal to 20 mL/min (when the reaction temperature is 400° C). The temperature of the reactor is then raised, and when the needed temperature is reached, the reaction time is started. Typical conditions are: 1 second of contact time (GHSV 3600 h ^"1 ), calculated on the basis of the overall gas/vapour flow. The overall content of organics in the inlet flow (phenol + methanol) is between 15 and 18 volume%; it may change within this interval because the N ₂ flow is changed in function of the reaction temperature used. Moreover, if also water is fed, by means of a second syringe and pump, the N ₂ flow is decreased proportionally, so to keep the overall flow of inert (after vaporisation of water) constant. The amount of organic fed (and vaporised) is typically 0.46 mL/h.

During the experiment, the outlet flow is made bubbling in a isopropanol solution, and the compounds which cannot be condensed are then sent to the vent. After 50 minutes of reaction time, the syringe is stopped, and the N ₂ is let flow for some minutes more. The isopropanol solution is transferred in a vessel, brought to 25 mL volume with isopropanol, then 20 microL of standard are added (n-decane), and then the mixture is analysed by GC (Thermo Instrumento, capillary column HP5, FID detector).

Examples 1 -3: Methylation of phenol to o-cresol

Example 1 : Use of Ga ₂ Q ₃ as catalyst

Selectivity = 86%

Conversion = 38%

Catalyst: Ga ₂ 0 ₃

Feed: Phenol/Methanol (1 :10) (molar ratio)

T = 400°C

Example 2: Use of Ga ₂ Q ₃ as catalyst

Selectivity: 66%

Conversion: 59%

Feed: MeOH/Phenol = 10 : 1 (molar ratio)

Temperature: 400° C Example 3: Use of a Mg-Ga-oxide-cata yst with a weight ratio of Mg to Ga of 10 to 1 Selectivity: 54%

Conversion: 9%

Feed: MeOH /water/ Phenol = 10 : 5 : 1 (molar ratio) Temperature: 400° C