DE1014550B - Process for the isomerization and disproportionation of methylphenols - Google Patents

Description

Process for isomerization and disproportionation of methylphenols The invention relates to a process for isomerization and disproportionation in the vapor phase of those methylphenols which have no more than three methyl radicals, d. H. Cresols, xylenols and trimethylphenols.

Cresols, xylenols and trimethylphenols occur in the simmering tears, the products of carbohydrates, shale oils, some petroleum raw materials, lignite tears and the like. In the unrefined state, they exist as mixtures of the isomers in different proportions. The distribution of the isomers in each Raw material is often unfavorable; H. certain of the valuable isomers are in small amounts are present while other, less valuable isomers are in the mixture prevalence. It is often desirable to check the isomer distribution of the methylphenols by selectively converting the less desirable isomers to more valuable isomers to change.

The present invention is particularly for the conversion of o-cresol into a mixture of m- and p-cresols with a high ratio of m- to p-cresol valuable.

According to the invention, methylphenols with no more than three methyl groups are used in the vapor phase through a bed of silica-alumina catalyst on which a layer of carbon was deposited, at least 5 percent by weight of the fresh catalyst. The conversion reaction will carried out at about 232 to 371 ° and preferably at atmospheric pressure, although the partial pressure of the methylphenols due to the addition of inert gases such as nitrogen, Exhaust gases and the like, can be reduced.

The literature known so far indicates that methylphenols are isomerization reactions in the liquid phase, where elevated pressures were applied under Use of expensive and complicated equipment. Long dwell times, which required by these reactions in liquid phase decreased the throughput this procedure.

It is also known that reactions in the vapor phase with silicon dioxide-aluminum oxide catalysts for isomerization and dealkylation of alkylphenols on such alkylphenols are applicable which have alkyl substituents with 3 or more carbon atoms (See U.S. Patents 2,516,152 and 2,514,960). The products of such Dealkylations are a phenol and a straight or branched chain olefin. These Accordingly, reactions take place with hydrogen exchange. A corresponding dealkylation of methyl-substituted phenols is a hydrogen-consuming reaction, which cannot be carried out without supplying hydrogen from the outside.

Fresh silica-alumina catalysts have a high Activity and a low selectivity towards methylphenols, d. i.e., with fresh Catalyst high conversions are achieved (high activity), but very little des converted material is a desirable product (low selectivity); instead of of this, most of the converted material is carbon and a high boiling point Residue which is essentially less valuable than the original methyl phenols.

Silica-alumina became largely economical as a catalyst for the conversion of hydrocarbons and especially petroleum hydrocarbons usually used in the vapor phase at temperatures from 427 to 4e2 "and higher.

Through these reactions, some of the feed becomes carbon converted, which is deposited on the catalyst and d its activity is essential reduced. This strong reduction in activity makes regeneration in these cases of the catalyst required before the carbon content is 0 / o of the weight of the Silica-alumina reached. The regeneration consists in the settled Substantially completely burn carbon to increase catalyst activity restore.

It has been found that high conversions of methylphenols with corresponding high selectivity can be achieved when on the surface of a silica-alumina catalyst deposited a layer of carbon that is at least 501o by weight of the fresh catalyst. aside from that will be with the new procedure worked at 232 to 371 °, a temperature range well below that the usual vapor phase processes catalyzed by silica-alumina be, lies.

Those suitable for use in the method of the invention Silica-alumina catalysts are used in cracking hydrocarbons used known silica-alumina catalysts. They exist in generally consisting essentially of 1 to 50 percent by weight aluminum oxide and 99 to 50 percent by weight silicon dioxide and preferably from 1 to 200 / o aluminum oxide and 99 to 80% silica. It should be mentioned that smaller amounts (up to about 10 Percent by weight) of other oxides may be present, with essentially equivalents Results are obtained. At, aim for other oxides that may be present siiid magnesium oxide, boron oxide and zirconia.

The invention will now be based on the following description and the Drawing will be explained in more detail.

In the drawing, Fig. 1 shows a schematic flow sheet of the invention Method and Figure 2 is a graphical representation of the effect of carbon content of the catalyst to the rate at which carbon is removed from the feed materials is discontinued.

According to the flow diagram of FIG. 1, vaporized methylphenols are through passed a catalyst bed contained in a reaction vessel. The contact bed contains a silica-alumina catalyst with at least 50 /, of the weight of which was coated in carbon. The bed is at a temperature held from about 232 to 371 °. Inert gases such as nitrogen, carbon dioxide, carbon monoxide, Flue gases and the like can be added to the vaporized methylphenols in order to to reduce their partial pressure to a value of 0.1 to 1.0. Steam can too can be used as a diluent in the process, despite its more well known Ability to poison silica-alumina catalysts. The hourly The flow rate of the methylphenols in the reaction is preferably 0.1 to 5.0 volumes of liquid per volume of reaction vessel.

The vapors of the reaction product are removed from the reaction vessel and condensed to isolate the converted methylphenols therefrom. Not implemented Methylphenols are returned to the reaction zone.

To start the reaction, a carbon coating is put on the fresh catalyst deposited by evaporated hydrocarbons through the Catalyst passed at elevated temperature until the silica-alumina has absorbed at least 50 /, of its weight as deposited carbon. For example, vaporized o-cresol can through the fresh catalyst at 232 to 371 ° to create a carbon coating on the particles of the fresh Knock down catalyst. Optionally, the carbon-depositing vapors be a fraction of the acidic distillate of coal tar, such as cresol blends and Xylenol mixtures or creosote, heavy distillable coal tar oils, distillable Petroleum fractions, gas oils, heating oils and the like. Inert, gaseous diluents can also be used can be used to reduce the partial pressures of these carbon deposition vapors lower to a uniform carbon deposition on the entire catalyst surface to secure.

The vaporized methylphenols are coated by the carbon Catalyst at a temperature temperature from 232 to 371 °. A small part of the Methylphenols are decomposed and act as additional carbon on the catalyst dejected. The conversion to carbon, which occurs on fresh silica-alumina takes place at great speed, but is based on silica-alumina, on the surface of which 5 or more 0 /, carbon are deposited, very reduced, as will be explained further below in connection with FIG. The continued passing of methylphenols through the catalyst bed gradually increases the carbon content of the catalyst and thereby increases the selectivity of the conversion. The activity of the catalyst sinks - albeit only slightly - with the increased carbon content of the Catalyst. If the activity of the catalytic converter falls to a certain minimum permissible value has fallen, the current of the Methylphennle is interrupted to to enable the regeneration of the catalyst. The maximum allowable carbon content of the catalyst or the minimum permissible catalyst activity results from economic considerations. It has been found to be economically satisfactory Conversions are achieved even when the catalyst is 15 weight percent or more Contains carbon on the catalyst.

The catalyst is regenerated by burning the deposited carbon with air at controlled temperatures. In the case of batch The carbon can be burned by the catalyst, and after each work Regeneration is a new carbon layer from a cheap hydrocarbon distillate, such as fuel oil, creosote or the like, as mentioned above, on the regenerated silicon dioxide-aluminum oxide generated.

By using several reaction vessels connected in parallel with fixed bed can be a continuous conversion of methylphenols by successive Working of the vessels can be achieved, with at least one of the vessels as Conversion vessel works while the others are being regenerated or a fresh one Carbon layer is generated on the regenerated catalyst.

Continuous conversion can also be achieved using the fluidized bed process can be achieved with the carbon content of the catalyst in the reaction vessel is maintained between 5 and about 20 weight percent of the fresh catalyst. The regeneration can be done by burning off all the carbon with subsequent Redeposition of the carbon take place. To dilute the in the isomerization reaction Introduced methylphenols, exhaust gas from the regenerator can be used.

Some conversion examples, which according to the inventive method carried out are intended to prove its usefulness and effectiveness to serve. For the following examples, the catalyst for each feed was specific made by adding fresh (i.e. carbon content = zero) silica-alumina in contact with the feed material concerned under reaction conditions was brought until enough charge had decomposed to coat a carbon corresponding to provide at least 5 percent by weight of the silica-alumina. The fresh silica-alumina contained about 88 percent by weight silica and about 12 weight percent alumina. The conversions were carried out by passing vaporized methylphenols downward through a fixed bed of catalyst became.

(The abbreviation VMSV means the rate of passage of the vapors per minute, ie the volume of the steam per volume of catalyst per minute.) Table I Cresols Approach no. 1 2 1 3 1 4 1 Charging (cresol) .......................... ortho ortho orth meta para Temperature, ° C ................................ 288 343 399 343 343 Partial pressure, atm ............................. 0.93 0.42 0.43 0.40 0.40 VMSV 1, 4 1.4 7.45 8.1 7.3 7.0 Results: Conversion (weight percent of feed) ..... 40.2 50 66 43 87 Yield of liquid reaction products (weight percent converted feed) .............. 93.8 91.2 92.6 93.6 96.6 Yield in percent by weight of the converted Feed: Neutral parts .................................. 0.0 0.5 1.3 2.5 0.5 Phenol ........................................ 31.5 27.8 25.8 17.3 20.4 Isomerization products (cresols) ......................... 24.7 29.0 27.2 35.2 39.4 Other disproportionation products ........... 33.1 28.7 22.3 17.2 21.9 Remainder ................. .................. .......... 4.2 4 , 9 15.9 21.4 14.0 Gas ............ ............. ........ 0.0 0.1 0.2 0.0 0.0 Carbon ..................................... 6.2 8.7 7.2 6.4 3.4 Ratio of m- to p-cresol .............. .. 2.48 3.08 3.18 - - Table I shows the desired conversions obtained in the process of the invention and its versatility. The conversion of each of the cresol isomers is indicated. Considerable sales are accompanied by high liquid yields. The insignificant amount of neutral product indicates that in fact no cleavage of the hydroxyl group of the cresols occurs during the process. Batch 3 with o-cresol at 399 ° further shows the significant increase in the residue when temperatures above 371 ° are used.

Significant amounts of valuable phenol (i.e. demethylated cresol) arise almost exclusively from disproportionation; this results from the fact that there are almost no gaseous by-products and that the Yield of other disproportionation products (i.e. xylenols and trimethylphenols) corresponds to the phenol yield.

Figure 2 shows the effect of the carbon content of the catalyst on the rate at which fresh cresol breaks down into additional carbon will. The data from which the curve of FIG. 2 emerges was obtained during the treatment of o-cresol at 343 ° over a silica-alumina catalyst at several Values for deposited carbon determined.

The hourly rate of passage was 0.73 volumes of o-cresol per volume of catalyst.

The curve in FIG. 2 shows the significant drop in speed the deposition of carbon on the catalyst, which occurs when the carbon substance content of the catalyst occurs. If the catalyst is less than about 5% Contains carbon, substantial amounts of that are used as the feed Cresol decomposes by converting it to carbon instead of being converted into carbon Conversion into desired isomers can be refined. With a catalyst that is more than 50% carbon, however, only small amounts of it are used as feed used cresol decomposed to carbon. A similar relationship exists for the other methylphenols.

The rate of conversion for cresol drops slightly with one Increase in the carbon content of the catalyst, although economically acceptable Conversions are achieved when the catalyst has a carbon content of 150 /, or owns higher. The yield of liquid reaction products increases with increasing Carbon content of the catalyst. With increasing carbon content of the catalyst the isomerization is increased and the disproportionation is decreased. Furthermore the ratio of m to p-cresol of the converted o-cresol increases with increasing Carbon content of the catalyst.

In Table II, for comparison purposes, the results are which can be obtained with three different catalysts. Approach 6 is same as run 2 in Table I. Each of the runs given in Table II was carried out with o-cresol, which with nitrogen to a partial pressure of 0.42 atm was diluted. The hourly throughput was 0.39 volume of o-cresol per volume Catalyst.

Table II o-cresol Approach no: 6 1 7 1 8 Temperature, ° C. ................. ............. 343 343 343 Catalyst. ................................... silicon dioxide- silicon dioxide- silicon dioxide- Alumina alumina-magnesia Zirconium oxide Approach no. 6 7 8 Results: Conversion (weight percent of feed) ............ 50.0 44.1 4.9 Yield of liquid reaction products (weight percent of the charge reversed) ............ 91.2 93.4 62.3 Yield in percent by weight of the converted feed: Neutral parts ....................................... 0.5 0.0 0.0 Phenol ............................................. 27.8 30 , 7 21.3 m-cresol ........................................... 22.0 17 , 1 12.9 p-cresol ........................................... 7.0 9 , 0 0.5 Xvlenol ............................................ 28.7 29, 1 0.0 Remainder ............................................... 4, 9 8.5 27.6 Gas ................................................ 0 , 1 0.1 0.0 Carbon ........................................ 8.7 6.5 37.7 m-zm p-cresol ...................................... 3.08 1.9 26.9 The silicon dioxide-aluminum oxide of batch 6 contained about 88% SiO2 and about 12010 Al2 03. The catalyst of batch 7 contained 5.44% ZrO2, 7.83% Al2O3 and 86.73% SiO2. In each example, before the reaction equilibrium conditions were established, the catalyst was coated with more than 5010 carbon deposited. The results of runs 6 and 7 indicate that silicon dioxide-aluminum oxide-zirconium oxide behaves towards o-cresol essentially in the same way as silicon dioxide-aluminum oxide.

The silica-magnesia of batch 8 contained about 88% SiO2 and about 12% MgO. The silica-magnesia catalyst (an acidic Oxide-type cracking catalysts, such as silica-alumina) gave markedly lower levels Conversions and lower yields of liquid reaction products compared with silica-alumina.

In general, the isomerization of o-cresol to m-cresol versus p-cresol by lower Table III xylenols Approach no. 9 l 10 11 12 to 13 Xylenol feed4) ............................... 2.6 2.4- 3.4- 2.5- mixture1) Temperature, ° C ..................................... 288 343 343 288 316 Partial pressure, atm .................................. 0.92 0.40 0.40 0.37 0 , 40 VMSV ............................................... 1, 28 7.0 7.0 12.1 7.0 Results: Sales (percent by weight of the charge) ............ 81.4 88 91 i 38.1 2) Yield of liquid reaction products (weight percent of the converted feed) ........... 96.0 92.4 92.7 96.8 93.5 Yield in percent by weight of the converted Feed: Neutral parts ....................................... 0.0 1.2 1.3 0 , 0 0.0 Phenol ....................................... 3.8 2.6 1.4 0 , 0 11.8 Cresols ....................................... 26.3 22.4 21.2 19 .5 20.93) Xylenols ....................................... 35.8 26.9 31.6 51 , 5 40.3 Trimethylphenols ....................................... 22.8 28.5 23.7 23 , 8 12.0 Remainder ................... .............. ......... 2.5 10.8 13 , 6 0.0 8.4 Gas .............. ........... .............. 0.05 0.0 0.0 0 , 1 0.0 Carbon ....................................... 3.9 7.6 7.3 3 , 1 6.5 Xylenol analysis, percent by weight of the xylenols obtained: 2,3-xylenol ....................................... 5.9 12.5 13.4 15.3 4.2 2,4-xylenol ....................................... 32.4 - 30, 3 46.4 - 2,5-xylenol ....................................... 31.9 35.8 28.3-16.4 2,6-xylenol ....................................... - 16.4 7, 4 7.3 7.9 3,4-xylenol ....................................... 20.2 10.4 - 15.7 6.0 3,5-xylenol ....................................... 9.6 24.9 20.6 15.3 5.8 1) 50 percent by weight 2,4-xylenol, 50 percent by weight cresol.

2) Conversion of o-cresol was 38.5%; of 2,4-xylenol 72.7 O / o.

3) 14.1% cresol, 6.8% p-cresol.

4) The numbers in the table indicate the positions of the methyl groups where the hydroxyl group is in the l-position.

Reaction temperatures, e.g. B. 260 to 316 °, high partial pressure of the o-cresol loading, short contact times with the catalyst and catalysts with a higher carbon content, e.g. B. 10 percent by weight and more carbon favored.

Some runs using xylenols as a feed are given in Table III.

The catalyst used in the approaches was a silica-alumina catalyst, which contained about 880 / o SiO2 and about 120 / o Al205.

The data in Table III show the xylenol conversions which result from the method according to the invention. High conversion speeds are accompanied by high fluid yields.

Considerable amounts of both those valuable for resin manufacture 3, 5-xylenol as well as all other isomers are made from the less valuable 3,4-xylenol and 3,4-xylenol are produced. Phenol and cresols are used in considerable amounts Quantities generated mainly by the disproportionation reaction as by the Absence of gaseous by-products and the fact that the yield of phenol and cresols corresponds to the trimethylphenol yield. The negligible amount on neutral compounds indicates that there is no elimination of hydroxyl groups.

Run 13 was run with one feed, the same Amounts by weight of o-cresol and 2, 4-xylenol contained. The results indicate that this new process is able to isomerize mixtures of methyl-substituted phenols. The xylenol conversion was 72.7 01o, the cresol conversion 38.50 /.

It was also found that the desired cresol isomerization reaction can be increased by suppressing the disproportionation reactions.

By adding a significant amount of xylenols to the cresols the cresol disproportionation equilibrium is disturbed and the reaction as a result suppressed. In general, the cresols should be half to double their weight of xylenols are mixed, so that the increased isomerization is achieved. For example, Run 13 in Table III has been given equal amounts by weight 2, 4-xylenol and o-cresol processed. The product contains m-cresol, p-cresol and Phenol in an amount equal to 94.50% of the converted o-cresol. About that in addition, the amount of xylenols available for recycle is 72.1 0 / o of the xylenol introduced with the feed crepes.

The isomerization and disproportionation of the trimethylphenols according to the present invention is preferably carried out at temperatures in the lower part the temperature range from 232 to 371C carried out, e.g. B. about 260 ". In that Measures as the temperature rises past this point will be the cracking Methyl groups noticeable. The production of phenol, Cresols and xylenols is increased, when the conversion is carried out at the lower temperatures.

Claims (7)

PATENT CLAIMS 1. Isomerization and disproportionation processes of methylphenols with not more than three methyl substituents in the vapor phase, characterized in that their vapors at a temperature of 232 to 371C Passes over a silica-alumina catalyst on top of carbon deposited in an amount of at least 50% by weight of the catalyst and that the vapors of the reaction product are condensed. 2. The method according to claim 1, characterized in that the methylphenol vapor is diluted with an inert gas prior to contact with the catalyst. 3. The method according to claim 1, characterized in that the methylphenols consist of a mixture of cresols and xylenols. 4. The method according to claim 1, 2 or 3, characterized in that The catalyst consists essentially of 1 to 500/0 aluminum oxide and 99 to 500/0 silicon dioxide consists in which carbon has been deposited on the catalyst in an amount which is at least 50/0 of the weight of the silica-alumina. 5. The method according to claim 1, 2 or 3, characterized in that the catalyst consists essentially of 1 to 20 percent by weight aluminum oxide and 99 up to 80 percent by weight of silicon dioxide, with carbon on the catalyst deposited in an amount which is at least 50 ½ the weight of the silica and alumina is. 6. The method according to claim 1, characterized in that the starting material a mixture of cresols with 1/2 to 2 volumes of xylenols is used. 7. The method according to claim 1 to 6, characterized in that one the catalyst to avoid too high a carbon content from the reaction vessel withdraws the high carbon catalyst by essentially burning it all carbon deposited on it regenerated on this regenerated catalyst Carbon in an amount which is at least 50 / o of the weight of the catalyst, iind precipitates the carbon-coated regenerated catalyst in the reaction vessel returns .. Documents considered: U.S. Patent No. 2,551 628