DE2005153C3 - Process for the isomerization or disproportionation of methylphenols - Google Patents

Description

The invention relates to isomerization or disproportionation of o-cresol, xylenols and mixtures thereof or of phenol methylation products.

Methyl substituted phenols can easily be prepared by the catalytic methylation of phenol. Because of the increasing demand for o-cresol and 2,6-xylenol, processes have been developed which favor the o-methylation of phenols (see US-PS 24 48 942, 24 77 091 and 33 47 926). With Such a process a methylated product is obtained, the main components of which are o-cresol and 2,6-xylenol. In general, m-creso is obtained as by-products! and p-cresol, usually in quantities, which are less than 5% by weight of the total product. As also for m- and p-cresol with a high If the meta to para ratio is in great demand, it would be desirable if the methylated one was used Product or at least the fraction rich in o-cresol and / or 2,6-xylenol as desired in m- and Could convert p-cresol, so that no further, special process for the production of m- and p-K resol would be necessary.

It is already known to convert methyl-substituted phenols into a mixture of m- and p-cresol with one to convert high ratio of m- to p-cresol (see GB-PS 6 95 464 and US-PS 27 77 881 as well the DT-AS 1014 550). This can be done either through catalytic isomerization or disproportionation or both methods can be achieved. As a catalyst, for. B. silica-alumina catalysts are used will. Unfortunately, a large amount of carbon is obtained using the commercially available silica-alumina catalysts used. In the British patent 6 95 464 the addition of water vapor is described to the formation of coal-like Avoid substances. The US-PS or the corresponding DT-AS teaches that at least 5 wt% carbon must be deposited on the catalyst before the desired conversion is carried out.

According to the invention there is now a method for conversion of methyl-substituted phenols to m- and p-cresol with high conversion rates and yields and indicated with a high ratio of meta- to para-cresol, at which it is not necessary is to add water vapor or provide for a pre-deposit of coal, as in the preceding Patent specifications described.

The invention relates to a process for isomerization or disproportionation of o-cresol, xylenols and mixtures thereof or of Phenolmetliylierungsprodu cycle in the vapor phase at high temperatures in the presence of a silica-alumina catalyst, which is characterized in that the methylphenols at temperatures of about 375 to 525 C with a silica-alumina catalyst in contact, which consists of about 1 to 30 wt .-% alumina and about 99 to 70 wt .-% silica and a surface area in the range between 10 and 200 m ² / g owns
According to one embodiment of the invention, the reaction is carried out at temperatures of about 425 to 475 ° C. in the presence of a catalyst which consists of about 1 to 20% by weight of alumina and 99 to 80% by weight of silica

The methylphenol used is preferably a phenol methylate which contains o-cresol or o-cresol and 2,6-xylenol as the predominant components. According to another embodiment of the invention, the methylphenol consists predominantly of o-cresol or of 2,6-xylenol. The end product can contain a mixture of m-cresol and p-cresol as the predominant component, it being possible in particular for a raw ratio of m-cresol to p-cresol to exist.
The silica-alumina catalysts to be used according to the invention are not the known silica-alumina catalysts which are used for cracking hydrocarbons. These catalysts have a relatively large surface, ie over 300 mVg. The silica-alumina catalysts to be used according to the invention have a smaller surface area, ie less than 200 m ² / g. They have practically the same composition as the usual cracking catalysts, namely 1 to 30% by weight of alumina and 99 to 70% by weight of silica and preferably 1 to 20% of alumina and 99 to 80% of silica. Virtually the same results are achieved when small amounts (up to about 10% by weight) of other oxides are present. Such oxides are z. B. magnesium oxide, boron oxide and zirconium oxide. The catalysts to be used according to the invention can be prepared by customary processes.

The drawings are intended to explain the present invention in more detail. Is in them

1 shows a schematic drawing of a device suitable for the method according to the invention and

Fig. 2 is a graph showing the influence of the catalyst surfaces on the yield of m- and shows p-cresol and carbon deposition. According to Fig. 1, methylphenols are in the Vapor phase passed through a catalyst bed located in a reactor. As a charge suitable methylphenols are generally phenol methylation products, which contain o-cresol and 2,6-xylenol and other methylphenols. these can easily by converting methanol and phenol in the vapor phase via an activated alumina

catalyst can be produced under the following conditions:

temperature
pressure
LHSV

Methanol / phenol molar ratio

275 to 375 C
practically atmospheric
0.5 to 6.0
0.75 to 1.25

However, the process according to the invention is not restricted to mixtures of methylphenols. You can use o-cresol or 2,6-xylenol, as described later carried out, optionally also converted separately to m- and p-cresol.

The contact bed in the reactor contains a silica-alumina catalyst with a surface area between 10 and 200 m ² / g of the composition described above. A particularly suitable catalyst contains 87% by weight of silica and 13% by weight of alumina. The bed is ^{maintained at} a temperature of about 375-525C. Inert gases such as nitrogen, carbon dioxide, carbon monoxide, exhaust gases can be added to the methylphenols in order to reduce their partial pressure to 0.1 to 1.0. Steam cannot be used in this process because it is known to poison silica-alumina catalysts. The liquid hourly space velocity (LHSV) of the reaction is preferably 0.1 to 2.0.

The products are discharged from the reactor in vapor form, condensed and separated to convert the To obtain methylphenols. Unconverted methylphenols are returned to the reaction. Part of the methylation product decomposes to carbon, which is deposited on the catalyst. The conversion to carbon, the over fresh silica-alumina catalysts with a relatively large surface area quickly takes place, isl when using silica-alumina catalysts with smaller surface area, much less, as will be shown in the discussion of FIG. 2 below. When the activity of the catalyst (which depends on the carbon content) on one

Table 1

Influence of the catalyst surface area

predetermined minimum value has fallen, the supply of methylphenols is stopped so that the Catalyst can be regenerated. The regeneration can be done by burning the deposited carbon with air at controlled temperatures. Examples are the conversions according to the invention explain and the usefulness and efficiency of the method according to the invention prove. The catalyst that

ίο in the examples listed in the tables below, contained about 87% by weight silica and 13% by weight alumina. The abbreviation LHSV means liquid hourly space velocity, ie volume of liquid (before evaporation) per volume of catalyst per hour. Table 1 shows the effect of the catalyst surface area on the conversion to m- and p-cresol and the carbon deposition on the catalyst when using a feed consisting of the fraction of the methylation product boiling below 250 ° C., the fraction being replaced by those described above Conversion of methanol and phenol in vapor phase had been obtained. The composition of the charge can be found in the second column of the table. The term "Cq _s " refers to trimethylated phenols that do not correspond to those specifically defined. The analysis of the feeds and the products obtained is based on the boiling points so that in some cases a mixture of compounds is identified as a single component because their boiling points are very close to one another. The first paragraph contains the preparation conditions. The second paragraph contains the raw composition of the end product including the unconverted charge, the distillable portions being divided into those boiling below 250 ° C and those boiling above 250 ° C. The third paragraph lists the composition of the charge and the composition of the distillable product boiling below 250 ° C. (also containing unconverted charge). The fourth and last paragraph shows the carbon deposition on the catalyst in% by weight of the catalyst.

Approach no. 17th B. 40 C. D. E. F. A. 468 468 (Comparison) 0.5 0.5 conditions 12th 12th 70 115-120 190 315 Catalyst surface (m ² / g) 468 468 468 468 Temperature (C) 94.8 91.0 0.5 0.5 0.5 0.5 LHSV (hour ¹ ) 4.9 X, 4 12th 12th 12th 12th Time (hours) 0.2 0.2 Products (wt .-%) 0.1 0.4 85.2 86.2 83.8 83.2 Fraction boiling up to 250 C. 13.9 12.6 13.4 13.1 Fraction boiling above 250 C. 0.3 0.4 0.8 0.9 gas 0.6 0.8 2.0 2.8 coke

continuation

Feeding seed / no.

Λ
(Wt .-%)

(Comparison)

Composition of under 250 (
boiling product (wt%)

water 0.1 1.7 1.6 3.9 2.4 3.1 '2.3 leader 0.4 0.8 1.5 2.6 2.3 3.0 2.9 Anisole 39.4 0.3 0.3 0.4 0.3 0.4 0.3 phenol 33.0 36.6 35.7 35.6 35.5 35.8 40.9 o-K resol 13.9 29.2 21.3 20.7 20.5 18.9 19.1 2,6-xyienoi 1.9 6.6 2.5 1.8 2.3 i, 9 ϊ, ό m- and para-cresol 4.0 8.7 20.2 20.2 21.1 22.4 21.0 2,4- + 2,5-xylenols 1.0 7.6 8.3 7.5 8.0 7.4 5.9 2,4,6-trimethylphenol 4.0 0.7 0.3 0.3 0.3 0.2 0.2 2,3-xylenol and 2,3,6- 4.2 4.8 4.3 4.6 4.3 3.4 Trimethylphenol 0.1 3,4-xylenol 2.1 1.0 1.5 1.2 1.3 1.3 1.0 0.1 2.5 1.9 1.4 1.3 1.2 1.4 Not identified 0.1 0.1 0.1 0.1 0.1 0.0

Carbon deposition
on the catalyst

(% By weight of the catalyst)

0.50

2.64

6.08

6.08

15.94

21.06

In FIG. 2, a bar diagram shows the influence of the catalyst surface on the yield of m- and p-cresol and the carbon deposition on the catalyst. The letters A to F represent batches A to F, the conditions and results of which are listed in Table 1. The black bar represents the m- and p-cresol content of the feed used in runs A through F. The empty bars A to F indicate the m- and p-cresol content of the products obtained in batches A to F. As the surface area increases, the m- and p-cresol content increases sharply, and the maximum yield is achieved with a relatively small surface area. The KohienstofTablagerung is only at a surface area of about 200 m ^J / g seriously.

The following table 2 contains the results and conditions of experiments, the invention

Table 2

o-cresol and 2,6-xylenol

Proper procedure using o-creso and 2,6-xylenol was performed. The in the An Silica-alumina catalysts used in sets A, B and D contained about 87% silica 13% clay and had different surface areas as indicated in the table. In approach C the silica-alumina catalyst contained about 45% silica and 53% alumina, the remainder being constant from the above-mentioned oxides. Approach C sol show that carbon deposition is increasing if a catalyst is used which contains too much clay although its surface area is favorable is. The data of Table 2 are arranged as in Table]. In addition, in the fourth paragraph are Conversion of o-cresol and the ratio before m- and p-cresol in the end product for some approaches specified.

Approach no. A

(Comparison)

conditions

feed

Catalyst surface (m ² / g)
Temperature (C)
LHSV (std.- ')
Time (hours)

Products (wt .-%)
Fraction boiling up to 250 C.
Fraction boiling above 250 C.
gas
coke

o-cresol o-cresol o-cresol 2,6-xylenol 40 75 100 70 468 468 468 468 1.0 1.0 1.0 0.5 12th 12th 12th 12th 96.3 93.4 94.4 77.8 3.5 6.2 4.4 19.9 0.1 0.2 0.4 1.1 0.1 0.2 0.8 1.2

continuation 20 05 0.9 also increase the 35 takes the optimal 153 8th C. I) ) 3.8: temperature has. To the be increased if c I 115-120? 7th 0.6 Carbon deposits on the catalyst. With a (Comparison 3.2; ■ a catalyst is selected at 500 C the only one small 468 ί
0.5 y 0.0 enlarged catalyst surface 1.7 ' Surface area Example can be good | Methylate B methylate A f 12 \ Approach no 50.7 Table 3 3.8 I. Conversion rates and when using ^ 115-120 Composition of below 250 C A. 4.58 Influence of temperature B. 1.0 1K9 I. a catalyst with a surface of 17m ² / gf 425
0.5 86.2 I. boiling product (wt%) 1.83 1.0 at i be achieved. 12th 12.6 water 0.1 \ 2% 0.4 leader Influence of tem- .30 conditions 16.7 20.2 93.3 0.8 Anisole 0.6 m . In feed 1.0 44.6 4.5 6.2 phenol 0.6 A silica-alumina catalyst was used for all batches Catalyst surface (m ² / g) 1.0 2.4 13.2 Approach no. 0.1 o-K resol 0.0 used sator, which is about 87% silica and about Temperature ( ⁰ C)
LHSV (Stdr ¹ ) track 21.6 3.3 A. B. 0.4 2,6-xylenol 12.5 Contained 13% clay. Time (hours) 14.8 7.2 13.6 m- and p-cresol 51.2 With rising temperatures Products (wt .-%) 51.7 0.2 Methylate A. 2.4 2,4- and 2,5-xylenol i, 7 Fraction boiling up to 250 ° C 2.4 3.2 115-120 2.3 2,4,6-trimethylphenol 23.6 Fraction boiling above 250C 18.7 1.0 400
0.5 0.3 5.8 gas 6.5 1.0 9.13 12th 1.0 35.5 0.1 coke 0.2 track 0.7 20.5 2,3-xylenol and 2,3,6-trimethylphenol 2,4 Composition of up to 250 ⁰ C feed 2.3 57.7 male temperature for the isomerization. On the other hand 96.2 0.1 3,4-xylenol boiling fraction (wt .-%) AWAY 0.8 can be the optimal 3.6 40.1 0.6 10.49 0.1 27.9 Not identified 0.1 track 0.1 o-cresol conversion (wt%) water 0.4 ' 51.7 Ratio meta: para leader 39.4 41.6 4.7 Carbon deposition on cat. Anisole 33.0 36.4 3.33 (% By weight of the catalyst) phenol The following Table 3 is the o-cresol 0.7 temperature to approaches A to C. 0.5 0.2 36.3 30.2

continuation

ίο

Charging approach no.

ABA

Composition of up to 250 C
boiling fraction (wt .-%)

2,6-xylenol 13.9 15.0 7.4 3.7 2.3

m- and p-K resol 1.9 1.0 8.4 13.1 21.1

2,4- and 2,5-xylenol 4.0 1.8 8.3 7.3 8.0

2,4,6-trimethylphenol 1.0 0.3 0.7 0.3 0.3

2,3-xylenol & 2,3,6-trimethylphenol 4.0 2.6 4.1 3.5 4.6

3,4-xylenol 0.1 0.9 1.0 1.3

1.3 1.3

Not identified 0.1 0.0 0.1 0.0 0.1

1.9 1.0 8.4 4.0 1.8 8.3 1.0 0.3 0.7 4.0 2.6 4.1 0.1 0.9 2.1 1.3 2.2 0.1 0.0 0.1 1.26 For this 2 sheets of drawings

Carbon deposition on catalyst
(Wt% of the catalyst) 1.26 2.61 6.36

Claims (2)

Patent claims: 1. A process for isomerization or disproportionation of o-cresol, xylenols and mixtures thereof or of phenol methylation products in the vapor phase at high temperatures in the presence of a silica-alumina catalyst, characterized in that the methylphenols at temperatures of about 375 to 525 C with a silica-alumina catalyst in contact, which consists of about 1 to 30 wt .-% alumina and about 99 to 70 wt .-% silica and has a surface area in the range between 10 and 200 m ² / g 2. The method according to claim 1, characterized in that the reaction is carried out at temperatures carried out from about 425 to 475 C in the presence of a catalyst, which from about 1 to 20 wt .-% Alumina and 99 to 80 wt .-% silica