DE2430478A1 - PROCESS FOR MANUFACTURING CYCLOALIPHATIC HYDROCARBONS - Google Patents

Description

Bayer Aktiengesellschaft 2430478

Central area of patents, trademarks and licenses

509 Leverkusen, Bayerwerk

Dz / Cr

Process for the production of cycloaliphatic hydrocarbons.

The present invention relates to a process for the preparation of oycloaliphatic hydrocarbons by catalytic hydrogenation of aromatic hydrocarbons.

There are already known processes according to which aromatic Hydrocarbons by catalytic hydrogenation into the corresponding cycloaliphatic hydrocarbons can be converted. It is known, for example, that benzene converts to cyclohexane, toluene converts to methylcyclohexane, and xylenes to dimethylcyclohexanes, ethylbenzene to ethylcyclohexane, isopropylbenzene to isopropylcyclohexane, naphthalene to tetra * and / or decahydronaphthalene, methylnaphthalene can be hydrogenated to methyltetra- and / or methyldecahydronaphthalene. In some of these processes the hydrogenation is carried out in the liquid phase, in others it is carried out in the gaseous phase hydrogenated. There are also combinations of gas and liquid phase hydrogenations has been described.

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All previously known processes for the hydrogenation of However, aromatic hydrocarbons have a number of disadvantages.

To the extent that the processes are carried out in the gas phase, the disadvantages in the German Patent 1,184,756, which describes a process for the catalytic hydrogenation of aromatic hydrocarbons has made the following statements:

"The processes carried out in the gas phase provide practically only a low yield per unit volume of the reaction zone, not only because of the low density of the treated product, but also because of the difficulty to effectively cool this zone. This either leads to the use of large-scale equipment that is quite large and contain expensive internal cooling lines, but without to be able to avoid local heating of the catalyst, which reduces its effectiveness; or it leads to too strong Dilution of the aromatic hydrocarbons, e.g. with the corresponding hydrogenation products. This means that for the hydrogenation products are again provided for recirculation systems, which means that the facility is only minimal Yields. "(German Patent 1,184,756, column 1, lines 26 to 42).

For example, gas phase hydrogenation is used to convert benzene to cyclohexane in the presence of nickel catalysts in U.S. Patent 3,146,187, the Benzene in dilute form in two reactors arranged one behind the other with recycling of unreacted feedstock is hydrogenated. The implementation of this procedure is

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because of the large amount of equipment and the diverse Separation and return processes as well as extremely difficult because of working under increased pressure.

According to the method of US Pat. No. 3,070,640, aromatic hydrocarbons are at pressures from 300 to 600 p.s.i. (about 21 to 42 bar) in the presence of platinum, nickel, palladium, rhodium, iron and / or Ranney nickel, if necessary on supports, hydrogenated as a catalyst, whereby two different catalyst systems are used one after the other, which differ in their metal content. The conduct of the reaction is also not uniform in that to control the reaction temperature initially with a dilute catalyst mass, i.e. with a less active one Catalyst, and later worked with a more active catalyst (USA patent 3,070,640, column 2, lines 41 to 54) This method is therefore also associated with considerable effort in its implementation.

When carrying out the hydrogenation of aromatic hydrocarbons In the liquid phase, the catalyst is in suspended form and must therefore be continuous introduced into the reaction and discharged from the reaction vessel again (DAS 1.116.218).

The disadvantages associated with the gas phase and liquid phase hydrogenation of aromatic hydrocarbons also occur with a combination of ATbBITSWeISe ₇ in gas and liquid phase (German patent specification 1.1.4.756).

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A process for the hydrogenation of Bezol hydrocarbons in the trickle phase is described in DOS 1.443.888, with Noble metals, in particular platinum, rhodium and ruthenium, are used as catalysts, which are based on alkaline earth carbonates and sulfates, silicic acid, silicates and aluminum oxide are applied as carrier material. Although to carry out this process only requires one reactor unit and thereby a considerable advantage over the other processes for the catalytic hydrogenation of aromatic hydrocarbons is achieved, the process of DOS 1.443.888 is not satisfactory, since the catalysts after a relatively short time Run time lose their activity and cannot be regenerated. Unsatisfactory runtimes are also with the so far to record known hydrogenations which are carried out in the liquid phase and in which catalysts of the Raney type be used in suspended form (e.g. DAS 1.116.218).

Finally, there is a further considerable disadvantage of all the catalytic processes for hydrogenation that have become known to date aromatic hydrocarbons that they are carried out under increased pressure. In addition to the patents mentioned In this context, reference should also be made to DAS 1.203.257 and the USA patent specification 3.432.565.

There has now been a process for the preparation of cycloaliphatic hydrocarbons by gas phase hydrogenation of aromatic hydrocarbons found in the presence of fixed palladium catalysts, which is characterized is that one uses palladium catalysts which contain the palladium applied to a support, which consists of aluminum oxide, which is at least 20%,

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moved to the weight of the carrier, in lithium aluminum spinel has been transferred, and that the gas phase hydrogenation is carried out practically without pressure.

The spinel to be used as a carrier according to the invention is obtained by reacting aluminum oxide with compounds of lithium. It is beneficial when going to spinel production starts from highly active aluminum oxide in lump form, which has a specific surface area of 200 to 350 m / g. But it is also possible to use aluminum oxide with lower specific Surface to be used as the starting material. All the forms can be used as aluminum oxides still have absorbency and form lithium-aluminum spinels when annealed in the presence of lithium compounds. The lumpy aluminum oxide, for example in the form of sausages, pills or preferably in spherical form in dimensions of 1 to 10 mm, is soaked or sprayed with a solution of a lithium compound and then dried. As lithium compounds can be used: lithium hydroxide, lithium salts of inorganic acids such as lithium nitrate and Lithium chloride and lithium salts of organic acids such as lithium formate and lithium acetate.

In the case of impregnation or spraying with lithium salts, these can be converted into lithium hydroxide or lithium oxide before spinel formation by chemical conversion or by heating. The spinel formation is carried out at 900 to 1300 ⁰ C, for which for example a time of 1 to 6 hours is required. Carriers with high mechanical strength are obtained in this way. If necessary, stoichiometric spinel formation can be achieved if the impregnation or spraying of the respective solution is carried out after intermediate drying and possible decomposition or conversion of the lithium compounds. The duration of the annealing process and the level of the annealing temperature

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an influence on the specific surface and the pore diameter the finished beam. Catalyst supports with an average pore diameter of 200 to 800 & as well as specific BET surfaces of 20 to 120 m / g have been proven.

The palladium can be applied to the carrier produced in this way in a known manner. For example, the palladium in Quantities from 0.1 to 5% by weight, preferably 0.5 to 2% by weight, based on the finished catalyst, applied to the carrier. For this purpose, the carrier is soaked or sprayed for example with an aqueous palladium salt solution. All commercially available palladium compounds are suitable for impregnation or spraying suitable. Before the reduction of the palladium compounds to metallic palladium, the palladium compounds can converted to palladium hydroxide or palladium oxide. The normally subsequent reduction of the palladium compounds to palladium can be carried out, for example, with formaldehyde and hydrazine in neutral or alkaline solution or with formic acid, hydrogen, carbon oxide or ethylene will. However, other reduction methods can also be used. It is advisable to use the Catalysts wash the anions contained in the production process with distilled water.

Any aromatic hydrocarbons are suitable as starting material for the process according to the invention. For example hydrocarbons of the benzene and naphthalene series can be used, through aliphatic side chains can be substituted. The aromatic nucleus can be replaced by one or more alkyl radicals having 1 to 4 carbon atoms be substituted. Suitable hydrocarbons for the process according to the invention are, for example, benzene, toluene,

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Ethylbenzene, n-propylbenzene, cumene, xylenes, naphthalene, methylnaphthalene and ethyl naphthalene.

In general, the process according to the invention is carried out ^{at temperatures of from 200 to 350 ° C. in the catalyst bed.} There is practically no pressure, since the dynamic pressure of the catalyst only has to be overcome when the material to be hydrogenated is passed through the reactor.

The aromatic hydrocarbon to be hydrogenated can be vaporized in front of or in the reaction vessel and brought to the desired reaction temperature to be brought. It can be advantageous not to use all of the hydrocarbon intended for hydrogenation to evaporate and deduct a small portion as a bottom product.

In general, the gaseous ^ feed mixture comes from aromatic Hydrocarbon and hydrogen preheated, e.g. to a temperature of 140 ° C, from below in a tubular reactor, in which the catalyst according to the invention is located. The catalyst can with 100 to 500 g, preferably 150 to 200 g of aromatic hydrocarbon per liter of catalyst and hour are loaded. The hydrogen is in 5- to A 15-fold molar excess, based on the aromatic hydrocarbon, was added. The hydrogen addition can take place anywhere in the reaction system. The hydrogen is preferably used after the aromatic hydrogen has been preheated Hydrocarbon, e.g. behind the evaporator, added. Of the After the hydrogenation, unconverted hydrogen can be wholly or partly recycled into the flow of the hydrogen used will.

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Conventional reactors can be used as reaction vessels. For example, reaction tubes with a length of 1 to 6 m and. a clear width of 25 to 75 mm, which can be surrounded by a cooling jacket through which the heat of reaction can be dissipated. The reaction mixture emerging at the upper end of the reactor is cooled to such an extent that the hydrogenated product is condensed as completely as possible. In general, temperatures of about 5-10 ^° C. are required for this.

The cycloaliphatic obtained by the process according to the invention Hydrocarbons are so pure that they can be used directly in subsequent processes without intermediate cleaning. For example, the cyclohexane obtained from benzene can be used directly in the oxidation to cyclohexanone / cyclohexanol will.

If the unreacted hydrogen is returned to use as cycle gas and the cycle gas is inert gases, e.g. Methane, it is expedient to withdraw a partial stream from the cycle gas. This may be necessary, for example in order to obtain a feed hydrogen gas content of at least 85% by volume.

The method according to the invention is distinguished from the hitherto known catalytic process for the hydrogenation of aromatic hydrocarbons due to the following advantages the end:

1. Only a single reactor is required for implementation

2. The hydrogenation can be carried out without pressure

3. A recycle of unreacted aromatic hydrocarbon not necessary

4. A uniform catalyst system is used, which has long running times, complete conversions and high selectivities enables.

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Example 1 - Preparation of the catalyst

2.86 1 spherical aluminum oxide with a diameter of 4 to 6 mm and a specific surface area of approx. 250 m / g were ^{soaked at 30 °} C. with one liter of an aqueous solution in which 296 g of formic acid and 233 g of 54% strength were successively aqueous lithium hydroxide solution had been added. The impregnated alumina was dried at 150 ⁰ C in vacuum, with the same solution again soaked again and dried at 150 ° C in vacuo. The carrier material obtained in this way was then calcined to spinel ^{at 1050 ° C. for 6 hours.} The spinel formation was confirmed by an X-ray structure analysis. The finished support had a specific surface area of 25 m 2 / g and an average pore size of 700 A. After impregnation with a hydrochloric acid solution of 82.7 g of palladium-II-chloride hydrate and reduction with alkaline 20% formalin, the Chloride with distilled water and subsequent drying, the finished catalyst contained 1.8% by weight of palladium.

Example 2

2000 ml of the 1.8% strength palladium catalyst according to Example 1 were placed in a reaction tube with an internal width of 50 mm and a length of 1 m, which was provided with a cooling jacket filled with oil. After treating the catalyst with hydrogen at 150 to 200 ⁰ C over a period of about 24 hours, the cooling jacket was cooled to 110 to 12O ⁰ C then each hour 400 ml of benzene vapor together with 600 1 of hydrogen passed over the catalyst. The heat of reaction is absorbed and dissipated by the cooling jacket of the reaction tube. This raises a significant reaction zone which has a temperature maximum at about 240 to 250 ⁰ C. The molar ratio of benzene: hydrogen was 1: 6. 600 l / h

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Hydrogen were fed as cycle gas. The conversion, based on benzene, was 100–96. The selectivity was approximately 100, which thus corresponds to a yield of cyclohexane of approx. 100 % .

The obtained reaction product contained 99.9 % cyclohexane.

Example 3

If, as described in Example 2, 400 ml of vaporous toluene per hour are passed over the catalyst together with 600 l of hydrogen, a clear reaction zone is also established, which has a temperature maximum of about 230-240.degree. The molar ratio of toluene: hydrogen was 1: 7; 600 l / h of hydrogen were fed as cycle gas. The conversion, based on toluene, was 100 % with a selectivity of approximately 100 %, which thus corresponds to a yield of methylcyclohexane of approx. 100 % .

The reaction product obtained contained 99.9% methylcyclohexane .

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Claims (8)

Claims 1. "Process for the production of cycloaliphatic hydrocarbons by gas phase hydrogenation of aromatic hydrocarbons in the presence of fixed palladium catalysts, characterized in that palladium catalysts are used, which the palladium applied to a Contain carrier which consists of aluminum oxide, which is at least 20% by weight, based on the weight of the carrier, was converted into lithium-aluminum spine11, and that the Carries out gas phase hydrogenation practically without pressure. 2. The method according to claim 1, characterized in that the carrier consists of aluminum oxide, 80 to 100% by weight, based on the weight of the carrier, in lithium aluminum spinel has been convicted. 3. The method according to claim 1 and 2, characterized in that the catalyst 0.1 to 5 wt .-%, based on palladium the total weight of the catalyst. 4. The method according to claim 1 to 3, characterized in that the catalyst 0.5 to 2 wt .-%, based on palladium the total weight of the catalyst. 5. The method according to claim 1 to 4, characterized in that the carrier has an average pore diameter of 200 to 800 Å. 6. The method according to claim 1 to 5, characterized in that that <has. that the carrier has a specific surface area of 20 to 120 m / g Le A 15 655 -11- 509883/0952 7 · The method according to claim 1 to 6, characterized in that at temperatures vi
Catalyst bed works. that at temperatures of 100 to 300 ⁰ C, measured in 8. The method according to claim 1 to 7, characterized in that the aromatic hydrocarbons are passed in gaseous form in an ascending flow through the catalyst bed and in the vicinity of the gas inlet in the reactor temperatures in the range of 200 to 250 ⁰ C and in the vicinity of the Gas outlet temperatures in the range from 100 to 150 ⁰ C, each measured in the catalyst bed, sets. Le A 15 655 -12- 509883/0 952