DE1293731B - Process for the catalytic demethylation of methyl-substituted aromatic hydrocarbons - Google Patents

Description

aromatic hydrocarbons is a series of io methylnaphthalene, dimethylnaphthalene, methylane demethylation processes known. In the case of enthracene, methylphenanthrene and their mixtures.

as

drive U.S. Patent 2,734,929
Catalyst activated alumina used. Other processes lead to the demethylation of methyl-substituted, aromatic hydrocarbons in the presence of chromium oxide and molybdenum oxide, aluminum oxide, silicon dioxide, nickel on aluminum and silicon oxide as catalysts, cf. US Patents 2,773,917,

shaped reaction vessel or a fluidized bed reaction vessel carried out with equal success will.

Any known dehydrogenation catalyst, such as iron oxide - potassium oxide, magnesium - iron oxide - Potassium carbonate, aluminum oxide — silicon dioxide— Nickel can be used in the practice of the invention. However, in general with

The process of the invention is carried out at atmospheric pressure operated. The application of pressure does not improve the results.

For practical reasons, water vapor is preferably in the range between about 1 and 5 kg each 1 kg of methyl substituted aromatic feed used.

The size of the reaction vessel has no impact

2,786,876, 2,970,954. These procedures are so fluent on the operation of the procedure of the Erfin-Presence of hydrogen, at high pressures and manure, however, the optimal size is expedient carried out at extremely high temperatures. to achieve a suitable residence time like them

From US Pat. No. 2,436,923, a process for the demethylation of coal is also commonly used in this type of demethylation reaction. In the same way, the structure of hydrogen in the presence of water is known, irrelevant for a reaction vessel. The invention which the reaction mixture at a temperature can in a fixed bed reaction vessel, a tube of about 180 to 350 ⁰ C in the presence of an active
Hydrogenation catalyst is implemented. These
However, the mode of operation is also not yet satisfactory. For example, at the time of 30
methylation of toluene at 263 to 266 ° C in
Presence of a nickel-diatomaceous earth containing
Catalyst obtained only a product with only 6% benzene.

The object of the invention is therefore to create 35 activated iron oxide due to its potassium a technically usable process for de-activity and selectivity is preferred. Others apply methylation of methyl-substituted, aromatic bare dehydrogenation catalysts are catalysts Hydrocarbons, which under moderate temperature- which iron and zinc oxides as main components conditions and at atmospheric pressure under and smaller amounts of copper, potassium or sodium run of good yields contain 40 salts, as well as catalysts which can and especially for the production of benzene iron oxide as the main component and copper and from toluene is suitable.

The process according to the invention is characterized in that the methyl-substituted aromatic hydrocarbon is mixed with about 0.5 to 10 kg of water vapor per 1 kg of aromatic charge over a dehydrogenation catalyst at temperatures of about 500 to 1000 ^° C., especially between about 650 and 850 ° C, conducts.

The particular advantage of the process of the invention consists in the unexpectedly high conversion steel carried out for low pressure, which essentially and the good yields of benzene in a tubular 0.91 m high reac demethylation process, which works with an atmospheric vessel with a diameter of 6.35 cm pressure and avoids extremely high temperatures as well as those cooled by running tap water. In the demethylation of toluene, the conversion is 50% with a condenser and a graduated receptacle. The method of the invention stood. The reaction vessel with about 2200 g is also very advantageous from an economic point of view, pelletized catalyst with a content of pressure vessels which are expensive for the production of benzene from toluene or 86.8% iron oxide, 1.6% chromium oxide and 11.9% other demethylations Potassium, calculated as potassium carbonate, is charged, and devices are no longer required. 60 A stream of steam and toluene in one By using a dehydration catalyst weight ratio of 1.6: 1, the process costs of the process of the speed of about 750 g per hour in the Reak invention are compared with those of the previously carried out tion vessel introduced and significantly reduced by the process carried out at a temperature. catalyst bed temperature of about 75O ⁰ C held

The process of the invention is directed to the demethyl 65. In the reaction vessel, atmospheric pressure of both monomethyl-substituted and spherical pressures was practically maintained. The outflowing, also of polymethyl-substituted aromatic gases, became applicable to hydrocarbons thanks to the water-cooled cooler. At the latter 72O ⁰ C and the product in the receiving

Potassium oxides or magnesium and potassium oxides or chromium and potassium oxides than those in lesser ones Contain quantities of ingredients present.

The invention is explained in more detail below with the aid of examples.

example 1
The demethylation of toluene was carried out in one

Vessel collected in which the organic and aqueous layers were separated. Analysis of the organic Layer found that 37.65% toluene had been converted to benzene and that in the product The benzene yield obtained was 87.5% of theory.

Example 2

An experiment according to Example 1 was repeated using a ratio of steam to toluene of 1.1: g per hour 1, a feed rate of 342, and repeats a reaction temperature of 74o C ^0. The conversion of toluene into benzene in this case was 49.6% and the benzene yield was more than 95% of theory.

Example 3

The demethylation of xylene was carried out using the same apparatus, catalyst and procedure as indicated in Example 1. Water vapor, and mixtures of xylenes were mixed in a weight ratio of 4.1: g 1 in the reaction vessel at a rate of 516 per hour introduced and passed through the held at a temperature of 65O ⁰ C the catalyst bed, as about 8.3% of the fed xylenes converted into benzene while 14.0% was converted into toluene. The yield of benzene and toluene from the xylene stream was calculated to be above 90% of theory.

Example 4

A reaction vessel, as used in Example 1, was charged with 2200 g of catalyst which consisted of 56.6% magnesium oxide, 14.0% iron oxide, 3.3% potassium oxide, 2.3% cuprooxide and 2.2% aluminum oxide. The catalyst was heated to a temperature of about 74o C ^0, and a mixture of water vapor and toluene in a weight ratio of 1.1: 1 grams per hour through the catalyst bed at a rate of about 342nd The conversion of toluene to benzene and the benzene yield achieved are comparable to those given in Example 2 above.

From the above examples it can be seen that benzene is made from toluene and xylene at atmospheric Pressures and moderate temperatures on an industrial scale in the presence of steam below Can be prepared using a conventional dehydrogenation catalyst. It is not another Feed material such as diluent gas, e.g. hydrogen, nitrogen or propane, is required. the However, supply of steam with the toluene or xylene is necessary to achieve adequate conversions to achieve.

Claims (2)

Patent claims: 1. A process for the catalytic demethylation of methyl-substituted, aromatic hydrocarbons in the presence of water at atmospheric pressure and elevated temperatures, characterized in that the methyl-substituted, aromatic hydrocarbon together with about 0.5 to 10 kg of water vapor per 1 kg of aromatic charge over a dehydrogenation catalyst Temperatures from about 500 to 1000 ⁰ C, especially from about 650 to 850 ° C conducts. 2. The method according to claim 1, characterized in that one is used as a catalyst Potassium activated iron oxide dehydrogenation catalyst with a low content of chromium oxide used.