CH620186A5 - Process for preparing o-cresol and 2,6-xylenol - Google Patents

Abstract

A process is described in which phenol and methanol in the form of a gaseous stream are reacted at 200-400 DEG C in a fluidised bed of granular eta , gamma or chi -alumina having a surface area of 100 to 500 m<2>/g and a total pore volume of 0.3 to 0.6 ml/g, the said alumina having been pretreated for at least 2 hours with an inert gas stream at a temperature above 450 DEG C but below 550 DEG C. The process would allow improved control of the progress of the reaction and would reduce the need for frequent catalyst regenerations.

Description

The present invention relates to the preparation of o-cresol and 2,6-xylenol by contact of a gaseous flow containing phenol and methanol with particles of a catalyst.

The methylated derivatives of phenol are useful in the art as they are used in the preparation of resins, plasticizers, antioxidants, disinfectants and chemicals for agriculture.

More recently 2,6-xylenol has found application in the synthesis of valuable polymeric products such as polyphenylene oxide.

The methylated derivatives of phenol can be obtained as by-products in the manufacture of coke and in the oil refining treatments, or they can be synthesized by alkylation of the phenol with methanol by operating in the gas phase or in the liquid phase.

In the gas phase processes, to which the invention relates, a gas flow containing phenol and methanol is fed onto a catalyst consisting of a granular metal oxide in the form of a fixed bed, while reaction temperatures of 175 to 500 ° C are maintained about.

In particular, the conditions can be controlled to mainly produce anisol (British patent 600 837), o-cresol and 2,6-xylenol (British patents 600 837, 600 839 and 602 257 and J. Chem. Soc. 1145, 84), or more highly methylated products up to hexamethylbenzene (British patent 600 898).

In the gas phase processes it is difficult to control the progress of the reaction, also in consideration of the high exothermicity.

It follows that abundant formation of by-products occurs and furthermore the catalyst is rapidly deactivated, so that frequent regenerations are required and this makes the process difficult to apply on an industrial scale.

In any case, the separation of the useful products from the by-products is onerous, especially when a high purity is required, for example in the case of 2,6-xylenol suitable for producing polyphenylene oxide. It has now been found that it is possible to prepare o-cresol and 2,6-xylenol, avoiding the drawbacks of the prior art, or at least substantially reducing these drawbacks.

According to the present invention, o-cresol and 2,6-xylenol are prepared by a process which consists in contacting, under fluidization conditions and at temperatures from 200 to 400 ° C, a gaseous flow containing phenol and methanol with granular alumina, said alumina having a crystallographic form age (tj), gamma (y), or chi (x), a surface area from 100 to 500 mVg or an overall pore volume from 0.3 to 0.6 ml / g, called alumina having been pretreated for at least 2 hours with an inert gas flow at temperatures above 450 ° C and below 550 ° C.

As is known, in the reaction between phenol and methanol the formation of the intermediate anisole and then of the methylated products with a degree of methylation gradually increases.

Therefore, according to the present invention, in the production of o-cresol, anisole can be present in the gaseous flow feeding the catalyst.

Furthermore, in the production of 2,6-xylenol, in addition to anisole, o-cresol may also be present in said gaseous flow, together with phenol and methanol.

The alumina particularly useful for the purposes of the present invention is the alumina age (ij), with an overall pore volume of 0.3 to 0.5 ml / g and a surface area of 250 to 400 m2 / g, in the which at least 90% of said volume is attributable to pores with a radius of less than 40 Angstroms and at least 90% of said area is attributable to pores with a radius of less than 30 Angstroms.

The best results are obtained with alumina age (tj), having a global pore volume of the order of 0.4 ml / g, at least 90% of said volume being attributable to pores with a radius of less than 30 Angstroms and a surface area in the order of 350 m2 / g, at least 90% of said area being attributable to pores with a radius of less than 20 Angstroms.

It is known that the alumina age (ij), which can be obtained for example by heating the bayerite in air (ß • A1203 • 3H20) at temperatures from 250 to 500 ° C, crystallizes in the cubic system (spinel).

The other characteristics reported for alumina can be determined by the known B.E.T. methods, by absorption of nitrogen, at the temperatures of liquid nitrogen (-195 ° C).

According to the process of the present invention, o-cresol and 2,6-xylenol are prepared, operating with the fluidized catalyst.

For this purpose, microspheroidal alumina or in any case in granules, with an average diameter preferably in the order of

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50 microns, in which the granules with a diameter greater than 100 microns and less than 20 microns are absent.

The fluidization of this alumina is achieved with a minimum linear velocity of the gaseous flow of the order of 0.2 cm / second, a value easily achievable in industrial reactors. The maximum speed preferably does not exceed 40 cm / sec.

Preferably, molar ratios between the phenol (or the sum of the phenol with any anisol and o-cresol) and the methanol from 1/1 to 1/2 are maintained in the feed gas flow.

It is possible, even if not convenient, to dilute the gas flow with inert gases, such as nitrogen. Furthermore, the reaction temperature is preferably maintained in the range from 250 to 300 ° C, choosing the highest temperatures when it is intended to direct the reaction towards the prevailing formation of the product with a higher degree of methylation.

The contact times in the reaction conditions can take values from 1 to 35 seconds.

It should be noted that linear speed and contact times refer to the empty reactor (without catalyst), in the temperature and pressure conditions of the reaction, the pressure being normally atmospheric, even if it is possible to operate at pressures higher or lower than that Atmospheric.

The alumina is thermally pretreated before its use by making air or other inert gas, such as nitrogen, flow through an alumina bed, while temperatures between 450 and 550 ° C are maintained. Preferably one operates under the fluidization conditions.

The pre-treatment times can vary from 2 to 6 hours. Times of less than 2 hours are insufficient for the purposes to be achieved, while times of more than 6 hours are useless.

By operating according to the process of the present invention it is possible to produce o-cresol and 2,6-xylenol from methanol and phenol (and possibly also from its methylated derivatives) under perfectly controllable conditions and with high values of activity and selectivity, as will result more evident from the experimental examples that follow.

The reaction products can be easily recovered from the gaseous flow leaving the reactor by cooling followed by the normal solvent extraction, distillation or crystallization treatments.

A fundamental advantage of the process of the present invention consists in the long life of the catalyst in the conditions of use without the need for regeneration.

The best results are obtained with age alumina (tj) while somewhat lower results are obtained with the use of gamma alumina (7) or chi (jc).

Other types of alumina, such as alpha (a) or gamma alfa (7 + a) alumina do not demonstrate appreciable activity in the process according to the invention.

Example 1

A glass tubular reactor with an internal diameter of 25 mm is used, equipped with an external cavity for the exchange of heat and a porous septum at the bottom. 160 grams of alumina in granules of 20 to 100 microns having the following characteristics are loaded into the reactor:

- crystallographic form: age (tj);

- overall pore volume: 0.4 ml / g;

(25% of said volume is due to pores with a radius of less than 12 Angstroms and 90% to pores with a radius of less than 30 Angstroms);

- surface area: 300 m2 / g;

(25% of this area is due to pores with a radius less than

11 Angstroms or 90% pores with a radius of less than 21

Angstrom);

- pile density: 1.25 g / ml;

- average diameter of the granules; 50 microns.

5 Air is sent to the foot of the reactor, which is made to flow into the reactor at a speed of 5 cm / second, while the temperature is brought to about 500 ° C.

It is maintained at this temperature and in the fluidization conditions for 4 hours.

10 After this activation treatment the air is replaced with nitrogen while the temperature is lowered to 250 ° C and the nitrogen flow is then gradually replaced with a gaseous flow of phenol and methanol in a 1/1 molar ratio.

In particular, 0.35 volumes of the mixture fe-15 nol and methanol (considered as liquid) are fed for each hour and for each volume of the fluidized catalyst. The reaction temperature is 250 ° C and the contact time of 7 seconds.

The products of the reaction, recovered at the head of the reactor, 1 are subjected to analysis, which results in a 20 molar conversion of 50% with respect to the fed phenol. Furthermore, the selectivity with respect to the reacted phenol is equal to 40%; molar for anisole, 40% molar for o-cresol and 20% molar for 2,6-xylenol.

By leaving the other conditions unchanged, the reaction temperature is increased to 300 ° C and a conversion of the phenol of 60% is obtained, and the following values for selectivity; anisol 3%, o-cresol 50%, 2,6-xylenol 47%.

30 Example 2

The procedure is similar to Example 1 by feeding phenol and methanol in a 1/2 molar ratio to the reactor.

By operating at 250 ° C, 55% of the phenol is converted, with the following selectivities: anisole 47%, o-cresol 30%, 2,6-xyl-35 hire 15%.

By operating at 300 ° C, 70% of the phenol is converted, with the following selectivities: 5% anisole, 30% o-cresol, 45% 2,6-xylenol.

40 Example 3

One works as in example 1 by activating alumina in granules, having a crystallographic form gamma (7), overall pore volume 0.4 ml / g and surface area 180 m2 / g. By making phenol and methanol interact under conditions similar to those of Example 45, the following results are obtained:

- at 250 ° C the phenol is converted for 20%, with the following selectivities: anisol 40%, o-cresol 40% 2,6-xylenol 10%;

- at 300 ° C the phenol is converted for 30%, with the following 50 selectivities: anisol 50%, o-cresol 30%, 2,6-xylene-

20%.

Example 4 (comparison)

The procedure is carried out as in example 3 by using gamma alumina 55 and crystallographic gamma alpha (7 + a), having a surface area of 40 m2 / g.

There is practically no interaction between phenol and methanol.

60 Example 5

The reactor of Example 1 is used in which 160 grams of granulated alumina, of crystallographic form age (tj), with surface area 350 m2 / g and overall pore volume of 0.38 ml / g are loaded, the other characteristics being similar 65 to those described for the alumina of Example 1.

It is activated by means of an air flow under the conditions of Example 1 and then a gaseous flow of phenol and methanol (molar ratio 1/1) is fed to the reactor at the rate of 0.35

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volumes (as liquid) per volume of fluidized catalyst and per hour.

It is also operated at 210 ° C and with a contact time of 5 seconds.

Under these conditions, 40% of the phenol is converted with a selectivity of 70% for the anisole and 30% for the o-cre-solo.

Example 6

The procedure is carried out as in example 5 by feeding phenol or methanol in molar ratio 111 to the reactor and maintaining the temperature at 250 ° C.

With the other conditions similar to those of Example 5, 60% of the phenol is converted and the selectivity is 50% for the anisole and 40% for the o-cresol.

5 Example 7

One works as in example 5 by feeding to the reactor, for each mole of methanol, a phenolic fraction consisting of 0.4 moles of phenol, 0.34 moles of anisole and 0.26 moles of o-cresol. Operating at 250 ° C, the overall conversion of the phenolic io fraction is 70% with a selectivity for 2,6-xylenol of 65%.

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Claims (9)

620186 1. Process for the preparation of o-cresol and 2,6-xi-lenol characterized by contacting, under fluidization conditions and at temperatures from 200 to 400 ° C, a gaseous flow containing phenol or methanol with granular alumina, called alumina having a crystallographic form age (ij), gamma (7) or chi (x), a surface area from 100 to 500 mV g and an overall pore volume from 0.3 to 0.6 ml / g, said alumina being it was pretreated for at least 2 hours with an inert gas flow at temperatures above 450 ° C and below 550 ° C. 2. Process according to claim 1, in which o-cresol is prepared and the feed gas flow contains only together with phenol and methanol. 2 3. Process according to claim 1, wherein 2,6-xylenol is prepared and the feed gas flow contains anisol and / or o-cresol together with phenol and methanol. Process according to claim 1, wherein the alumina has a crystallographic age (17), an overall pore volume of 0.3 to 0.5 ml / g and a surface area of 250 to 400 m2 / g, at least 90% of said volume being attributable to pores with radius less than 40 Angstrom, at least 90% of said area being attributable to pores with radius less than 30 Angstrom. 5. Process according to claim 1, in which the alumina has a crystallographic form age (77), a global pore volume of the order of 0.4 ml / g, at least 90% of said volume being attributable to pores with a smaller radius at 30 Angstroms, and a surface area of the order of 350 mVg, at least 90% of said area being attributable to pores with a radius less than 20 Angstrom. 6. Process according to claim 4 or 5, wherein the alumina is in the form of granules from 20 to 100 microns, with an average diameter of the order of 50 microns. 7. Process according to claim 1, wherein in the feed gas flow a molar ratio is maintained between the phenol (or the sum of phenol with any anisol and o-cresol) and methanol from 1/1 to 1/2 and it is operated at temperatures from 250 to 300 ° C. 8. Process according to claim 1, wherein the linear velocity of the gases through the fluidized bed of the alumina particles is maintained at values from 0.2 to 40 cm / second, with contact times of 1 and 35 seconds. 9. Process according to claim 1, wherein the alumina is pretreated by a flow of air or nitrogen at temperatures indicated for times from 2 to 6 hours.