IT8319727A1 - PROCESS FOR THE PRODUCTION OF ORTHOCRESOL AND PARACRESOL - Google Patents

Description

"PROCESS FOR THE PRODUCTION OF ORTHOCRESOL AND PARACRESOL"

Summary

Process for the production of o-cresol and p-cresol, by alkylation of phenol with methanol, according to molar phenol: methanol ratios between 0.1 and 10, possibly in the presence of a diluent, characterized in that the alkylation is carried out between 220 and 400? C in the presence of a zeolite of the ZSM type, having a structural molar ratio SiO: A10 between 13 and 500 (with crystal dimensions less than or equal to 5 ^ \ m and possibly in mixture with an inert binder) at speed? space between 0.5 and 25 Kg / h of phenol per Kg of zeolite.

The invention relates to a process for the production of o and p-cresol, according to the equation:

C6H5OH CH3OH? 5> C6H4 (CH3) OH H2O

The synthesis of cresols by alkylation of phenol with methanol is usually carried out in the liquid phase, in the presence of ZnBr HBr mixtures, at 200-250 ° C and at pressures higher than 2000 KPa; see, for example, the following patents: U.K. 1,060,036 and 1,125,077, D 1,265,755, FR 1,478,038, NL66 / 03749 and 68/02166. If the cat? Lysis? of acid type, mixtures of cresols, x? lenols, polyalkylates and anisole are obtained, while if the catalysis? of basic type, o-cresol and 2,6-xylenol are obtained with good selectivity. By carefully choosing the parameters of the operating conditions,? possible to obtain a reaction effluent with few traces of the pi isomer? unwanted (m-cresol) and containing, next to the ortho isomer, considerable quantities? of the isomer pi? desirable and what? of p-cresol, a very useful intermediate in various organic syntheses, such as for example the synthesis of 2,6-di-tert-butyl-p-cresol, known commercially by the acronym BHT. The good yields of p-cresol are however accompanied, as long as the alkylation occurs in the liquid phase, by not a few drawbacks; we cite in particular the obligation of having to resort to high pressures, in the presence of highly corrosive solutions, and of having to proceed with an annoying and difficult recovery of the catalyst, which involves the use of bulky and complex equipment. Yup ? why? tried for some time to make phenol and methanol react in the gaseous phase, but yes? noted, similarly to what happens for the liquid phase, that a basic catalysis markedly favors only the alkylation in the ortho position, giving rise, depending on the reaction conditions, to o-cresol and / or 2, 6-xylenol; see, for example, the following patents or patent publications:

Patent <1>? Catalyst

CH 620186

USA 4283574 (MgO + Ti02 + U 0g + Cr203) JA 81/55327 (Cr 0 SnO Cu 0)

JA 81/43229 (Cr 0 MnO)

? 3

Yup ? then tried to send gaseous phenol and methanol onto solid acid catalysts as described in the following patents and articles:

Patent number UK 1063028 lumino-silicate catalyst

UK 1125087 amphoteric oxides

USSR 784906 alumino-silicates modified with H? P0,

3 4

Articles

Kaspri J et al. "Heterogenous Catalysis by solid superacids 4. Methylation of Phenols with Methyl Alcohol and th? Rearrangements of Aniso.le and Mehty.l-anisoles over a Perfluorinated Resin Sulfonic Acid Catalyst", J. Org. Chem. Vol. 43, No. 16 page 3U 2 (1978).

Even in this case, however, despite the presence of appreciable quantities? of p-cresol, the results were not at all satisfactory, so much so that today, to our knowledge, there are no industrial plants that implement this method; the inconvenience this time? *? represented by a very high percentage of unwanted products (m-cresol, xylenols and, above all, polyalkyl phenples). We note incidentally that the anisole, always present, also in quantity? relevant, isn't it? to be considered completely undesirable, as it can? be usefully recycled to the synthesis reactor, where the alkylation conditions favor its conversion into o- or p-cresol. Recently Seitaro Namba et alii / "Selective Formation of p-cresol by Alkylation of Phenol with Methanol over Y Type Zeolites1 ', p. 105, Catalysis by Zeolites; Elsevier Se. Pubi. (1980) Amsterdam / have suggested a catalysis of gas synthesis with zeolites of type Y, but also this method could not be implemented, because, alongside the other drawbacks mentioned above, it presents a rapid decay of the catalyst (a few minutes).

A purpose of the invention? to avoid such drawbacks and to obtain mixtures of o- and p-cresol free from meta isomer (and from other by-products difficult to separate) and rich in para isomer; other objects will become apparent from the following description.

In its pi? in general, the invention relates to a process for the production of o-cresol and p-cresol by alkylation of phenol with methanol, according to molar ratios of phenol: methanol between 0.1 and 10 and preferably between 0.5 and 4, optionally in the presence of an inert diluent, characterized in that 1 <1> alkylation is carried out between 220 and 400 ° C (preferably between 230 and 380 ° C) in the presence of a catalyst based on ZSM type zeolites (preferably selected from ZSM 5 and ZSM 11 / with structural molar ratio SiO: A1 0 between 13 and 500 (preferably between 20 and 200) and with 2 2 3

crystal size less than or equal to 5 yum (preferably 0.5 ^ m) and possibly in mixture with an inert binder / at speed? space between 0.5 and 25 (preferably between 1 and 10) Kg / h of phenol per Kg of pure ZSM zeolite (binder excluded).

How thinner can you? use water, nitrogen, helium, argon or other inert gas. The zeolitic catalysts can be used as such or mixed with a suitable quantity? of inert agent, for example SiO2 j which acts as a binder and / or as a support. The reaction products can be easily recovered by cooling the flow leaving the alkylation reactor and resorting to the normal separation treatments (solvent extraction, distillation, crystallization, selective absorption or other); in the case of distillation, the unreacted phenol and anisole distill at the top of the column and can be advantageously recycled to the alkylation reactor, which can be recycled to the alkylation reactor. be a fixed or fluidized bed, depending on convenience

According to a preferred form of the invention, the catalytic system? consisting of zeolites used in their acid form (H-ZSM 5 or H-ZSM 11). In the preparation of the catalyst yes? noticed an improvement in the properties? catalytic, both in terms of conversion and selectivity, if the transition from the raw form of the zeolite, obtained by thermal decomposition of an organic cation (for example at 540? C), to the acid form (HZSM 5 or H -ZSM 11) is made by exchange with a mineral acid, such as for example hydrochloric acid; in principle it is suggested to use 1 molar solutions of HC1 at a temperature of about 80 ° C. The effect of the acid? that of cleaning the zeolithic structure from any polluting substances, which can be incorporated in the synthesis phase and which can act as non-selective catalysts for the ortho and para alkylation.

The global pressure used in the tests? slightly higher than atmospheric, but the partial pressure of phenol and methanol, given the presence of diluents (N, HO, He, Ar, etc.)? generally sub-atmospheric; obviously, however, lower or higher pressures can be used. The persistence of the activity? catalytic, with high selectivity? and productivity ?,? a fairly critical factor in the process; ? it is therefore important to regenerate the catalyst when said characteristics fall below the admissible levels. An excellent regeneration? consisting of an air treatment for a few hours between 300 and 600 ° C. Even the initial activation of the catalyst? an important factor; in general, an activation in air between 450 and 600 and preferably between 500 and 550 ° C is recommended. The invention? illustrated, for example, of course in non-limiting form, by Figure 1, following which, it can be seen that an alkylation reactor is fed with a mixture of phenol, methanol, recycle anisole and N. The effluent from the reactor is distilled; 1 <1> anisole and phenol and, on the side, o-cresol are obtained. The low cuts of the distillation column, rich in the product more? (p-cresol) The remainder (generally from 3 to 15% by weight) being substantially m-cresolq7, can be fractionated by selective absorption, for example on type Y zeolites, following the teachings of US patents 4-356.331 or 3-969-422.

The following examples further illustrate the invention, without however limiting its scope in any way.

EXAMPLES 1 and 2

2.3 g of zeolite H-ZSM 5 / <"> prepared (in crude form) according to example 24 of US patent 3-702.886, exchanged with HCl (1 M) at 80 ° C and having dimensions less than 0, 5 / <?? / are mixed with 1 g of binder (SiO ^ Jj activated in air for 2 hours at 540 ° C and then loaded into a microreactor, thermostated at 350 ° C, continuously fed with a gaseous mixture of phenol, methanol and nitrogen; the molar ratio of phenol: methanol? 2: 1 and the molar ratio of phenol: N? 1: 1. The pressure is slightly above atmospheric and the space velocity is 2.6 kg / h of phenol per kg of pure H-ZSM 5 (binder excluded); table 1 shows the operating methods and the excellent results obtained. The percentage of m-cresol is very low and the not excessive amount of anisole does not constitute a loss, as 1 The anisole itself can be separated by distillation and recycled to the reactor, as raw material, in a mixture with fresh phenol and unreacted phenol; the heavy tails of distillation are or consisting substantially of 2,4-xyl <e> freight.

EXAMPLES 3 and 4

Examples 1 and 2 were repeated, using a zeolite of the same type (H-ZSM 5)> having for? an average crystal size between 3 ^ 4 ^ * m; as can be seen from the results in table 1, the conversion significantly decreases.

EXAMPLES 5 and 6

Examples 1 and 2 were repeated, using a H-ZSM 11 zeolite, prepared (in crude form) according to example 8 of US patent 3709979) exchanged with HCl (1 M) at 80 ° C, having a molar ratio of SiO: At 0 equal to 80 and an average crystal size of about 0.5 / * ni; the results, similar to the results of examples 1 and 2, are in table 1, next to the modalities? operational.

EXAMPLES 7 and 8

Examples 1 and 2 were repeated by reducing both the speed? spatial that the alkylation temperature and obtaining extremely low meta isomer percentages; mode? operational and results are reported in table 2. Note that the gi? low percentage of meta isomer, both in these and in the other examples, tends to disappear with the passage of time.

EXAMPLE 9

Example 5 was repeated, reducing the phenol: methanol ratio and increasing the speed? space; the results, similar to the results of example 5, are shown in table 2, next to the modalities? operational.

E S E M P I O 7 8 9

CATALYST 1 H-ZSM 5 v. ex. 7 v. ex. 5

Crystal size <0.5 rn II IP SiO / Al 0 (molar) <1> 28 1! (1

1 ^

WHSW (h) The

1,4 2,4 Phenol: Methanol (molar) 2 11

0,5 Reaction temperature (? C) 250 250 350 Data recording after: 1 h 4 h 1 ti

THE RESULTS {% molar)

Phenol conversion 50.8 42.6 42.1 I Selectivity to anisole 50.5 55.6 20.9 | Selectivity to o-cresol 32.6 29.0 42.8 Selectivity? to m-cresol 1.0 0.5 6.4 Selectivity to p-cresol 14.5 H, i 20.0 Selectivity? a 2,4-xylenol 1,1 0,7 7,8 Selectivity to others 0.3 0.1 2.1

CRESOLI DISTRIBUTION

{mol%)

o-cresol 67.7 66.5 61.9 m-cresol 2.1 1.1 9.2 p-cresol 30.2 32.4 28.9

V.

Claims (14)

1) Process for the production of o-cresol and p-cresol by alkylation of phenol with methanol, according to molar phenol: methanol ratios between 0.1 and 10 and preferably between 0.5 and 4, possibly in the presence of a diluent , characterized in that the alkylation is carried out between 220 and 400 ° C (preferably between 230 and 380 ° C) in the presence of a catalyst based on ZSM 5 or ZSM 11 / zeolites with structural molar ratio SiO: Al 0 between 13 and 500 (preferably between 20 and 200), with crystal sizes less than or equal to 5 / Um (preferably 0.5 / tni). space between 0.5 and 25 (preferably between 1 and 10) Kg / h of phenol per Kg of pure ZSM zeolite. 2) Process according to claim 1, in which phenol and methanol are fed to the alkylation in the gas phase. 3) Process according to claim 2, in which the diluent? selected from N, He, Ar, HO and their mixtures. 4) Process according to claim 2, in which the inert binder? YesO. 5) Process according to claim 2, in which the zeolite is used in an acid form (H-ZSM 5 or H-ZSM 11), preferably obtained by exchanging a crude zeolite with HCl. 6) Process according to claim 2, in which the alkylation is carried out on a fixed catalytic bed. 7) Process according to claim 2, wherein the zeolite is activated in air between 450 and 500 and preferably between 500 and 550 ° C. 8) Process according to claim 2, in which the crude effluent coming from the alkylation is fractionated in a distillation column, the overhead product of which, substantially constituted by anisole and unreacted phenol, is recycled to the same alkylation. 9) Process for the production of mixtures of o-cresol and p-cresol, rich in para isomer and practically free of meta isomer, by alkylation of phenol with methanol in the gaseous phase, according to molar ratios phenol: methane. Or between 0.5 and 4, optionally in the presence of a diluent such as water or nitrogen, in which 1 <1> alkylation is carried out between 230 and 380? C, in the presence of a zeolite ZSM 5, with structural molar ratio SiO: A.10 between 20 and 200 and with di- Z ?? J crystal sizes less than or equal to 0.5 / tm (preferably mixed with SiO), at a speed? between 1 and 10 Kg / h of phenol per Kg of pure ZSM 5. 10) Process according to claim 9 in which a fixed bed of H-ZSM 5 (obtained from raw ZSM 5 by exchange with HCl) is used, pre-activated in air between 500 and 550 ° C. 11) Process according to claim 9, characterized in that the crude effluent, coming from the alkylation, is fractionated in a distillation column, the top product of which, substantially constituted by anisole and unreacted phenol, is recycled to the same alkylation. 12) Process for the production of mixtures of o-cresol and p-cresol, rich in para isomer and practically free from meta isomer, by alkylation of phenol with methanol in the gaseous phase, according to molar ratios phenol: methanol between 0.5 and 4 , possibly in the presence of a diluent such as water or nitrogen, in which the alkylation is carried out between 230 and 380 ° C, in the presence of a zeolite ZSM 11, with structural molar ratio SiO?: Al 0 between 20 and 200 and with 2 2 3 <'> crystal size less than or equal to 0.5 / <m (preferably in mixture with SiO), at speed? space between z 1 and 10 Kg / h of phenol per Kg of pure ZSM 11. 13) Process according to claim 12, in which a fixed bed of H-ZSM 11 (obtained from raw ZSM 11 by exchange with HCl) is used, pre-activated in air between 500 and 550 ° C. 14) Process according to claim 12, characterized by the fact that the crude effluent, coming from the alkylation, is fractionated in a distillation column, the overhead product of which, substantially constituted by anisole and unreacted phenol, is recycled to the alkylation itself .