DE1075602B - Process for the catalytic hydrogenation of benzene - Google Patents

Description

Process for the Catalytic Hydrogenation of Benzene The invention relates to a process for the catalytic hydrogenation of benzene to cyclohexane.

As is known, this hydrogenation is carried out with suitable elyrogenation catalysts, mostly with a nickel catalyst, carried out in the vapor phase or can be worked in the liquid phase.

The production of e-catalysts suitable for this hydrogenation is z. B. in German Patent 969,471. During execution the hydrogenation of benzene in the liquid phase must be under sufficiently high pressure worked to keep the reaction mixture liquid, one having the advantage has that the considerable heat of reaction is easily dissipated by means of the liquid can be, which helps to maintain the catalyst activity. A such a liquid phase process is disclosed in U.S. Patent 2,373,501 - the release of the heat of reaction being distributed over two stages and the first stage, in which the starting product is not yet with larger quantities of the forming cyclohexane is diluted, is run through quickly so that the Temperature does not rise too much. In the second stage it is diluted with cyclohexane Benzene hydrogenated further at lower temperatures.

In a way that is simpler per se, according to the German patent specification 827 361 carried out the hydrogenation of benzene in the gas phase, with high pressures superfluous, so that expensive printing systems are not required. With this one Process in which the heat of reaction is dissipated by the gases or vapors you regenerate the catalyst regularly in order to lead to high yields To secure catalyst activity.

It has now been found that the catalytic hydrogenation of benzene .both the advantages of working in the liquid phase as those of working can be achieved in the gas phase when the hydrogenation is carried out in the presence of cyclohexanol is carried out..

Because of the high boiling point, the hydrogenation can be carried out in the presence of Cvclohexanol can easily be carried out so that the benzene hydrogenates in the vapor phase is, while the cyclohexanol remains partially liquid, so that the heat dissipation means the liquid can take place. Both benzene and cyclohexane can also be used keep liquid in a printing system, with the advantage that right from the start the benzene is in a dilute form, so that an overly vigorous initial reaction avoided, which makes it easier to control the temperature.

If you want to work entirely in the vapor phase, you have too the advantage of easy temperature control. However, it is preferred to work in such a way that that the catalyst is always in contact with liquid cyclohexanol during the reaction is held.

Especially when with powdery, z. B. - the so-called - Raney catalysts, is being worked; one has the advantage that -man the catalyst in the form of a Pass the suspension in the cyclohexane continuously through the reaction system - can.

Carrying out this hydrogenation in the presence of cyclohexanol has the further advantage that the cyclohexanol is treated with hydrogen at the same time thereby reducing the impurities present in the cyclohexanol.

The hydrogenation of benzene to cyclohexane takes place at temperatures from 150 to 2500 C almost quantitative. At lower temperatures, below 1500 C, the hydrogenation proceeds slowly; hence these lower temperatures offer little interest. Higher temperatures, above 2500 C, are avoided preferably because of the possibility of decomposition and formation of undesirable by-products. You can keep the pressure relatively low, namely below 100 at, a pressure of 20, 30 or 50 atm is preferably used. Working in the Vapor phase can be at atmospheric pressure or at a low pressure of 2 to 10 at.

The hydrogenation gas does not have to be pure hydrogen, it can also contain inert gases, such as nitrogen.

The inventive method offers the advantage that impure cyclohexanol can be applied in the hydrogenation of benzene, whereupon from the reaction products Cyclohexane and pure cyclohexanol can be excreted. There is no need therefore to clean the cyclohexanol separately. This is especially important when these are processes in which cyclohexanol is used as the starting product will, e.g. B. in the production of cyclohexanone, with already low levels in the cyclohexanol existing amounts of impurities affect the hydrogenation in a very unfavorable sense. But especially if you get the cyclohexanol by oxidation of cyclohexane, for example with air, is to render it harmless for its further processing into cyclohexanone of the impurities necessary, which is possible in a simple manner according to the invention is.

The amount of cyclohexanol to be used can be varied significantly. It is preferred to use amounts of 0.1 to 1 mole of cyclohexanol per mole of benzene on, either with a solid porous catalyst, or with Raney nickel, the catalyst in the form of a suspension in cyclohexanol through continuously the reaction chamber can be passed, works. The usual amount can be used Catalyst are used, namely, based on the benzene, 0.1 to 10 percent by weight Catalyst.

To maintain the liquid phase, it is preferable to turn no smaller amounts containing less than 0.1 mole of cyclohexanol per mole of benzene.

Cyclohexanol can be added in various ways. The benzene and the cyclohexanol can be taken together in vapor form or as a liquid or be introduced individually into the hydrogenation space. A catalyst is used in powder form, which is passed continuously through the hydrogenation chamber, the Catalyst in the form of a suspension in benzene or in that of a suspension in cyclohexanol or suspended in a mixture of benzene and cyclohexanol in the hydrogenation space be initiated.

The vapors present in the reaction mixture are after consummated Hydrogenation condenses, and then the liquid products can be used in the usual way Way to be separated into fractions by distillation, one in addition to cyclohexane purified cyclohexanol is obtained.

Example 1 The hydrogenation of benzene is carried out in a reaction space carried out, which is composed of ten vertical tubes each with a length 5 m and a diameter of 7.5 cm in series connection. The pipes are for Regulating the temperature equipped with a jacket, by means of which one can control the temperature holds in the pipes at 1800 C. The pressure is kept at 32 at.

30 kg of benzene and 20 kg of cyclohexanol are used per hour as well 1 kg of Raney catalyst, which is suspended in the cyclohexanol, into the reaction space initiated. Furthermore, a hydrogenation gas is introduced into the reaction space, which consists of 85 percent by volume hydrogen and 15 percent by volume nitrogen, namely in an amount of 3.65 moles of hydrogen per mole of benzene. The settling of the catalyst particles the suspension is prevented by some of the gases in the reaction space returns.

The cyclohexanol that is used is obtained by oxidation of cyclohexane with air and subsequent separation of the crude cyclohexanol the cyclohexanolw and cyclohexanone-containing reaction product obtained. This cyclohexanol contains about 1 percent by weight of impurities that are difficult to remove by distillation, which prevent the dehydrogenation of cyclohexanol to cyclohexanone.

The reaction product emerging from the reaction space is cooled and then, after filtration, the liquid product to a distillation device fed to the separation of cyclohexane and cyclohexanol. Per hour are 32 kg of cyclohexane and 20 kg of pure cyclohexanol, which is the theoretically achievable Quantities correspond approximately.

The cyclohexanol obtained can be converted into cyclohexanone without difficulty are processed.

Example 2 Under otherwise the same conditions as in the example 1 is in the hydrogenation device described in this example benzene at a Hydrogenated at a temperature of 1850 ° C., 40 kg of benzene per hour in the reaction chamber are introduced and also 10 kg of impure cyclohexanol, the origin of which is the same is as in the example in which - lkg Raney nickel is suspended.

42 kg of cyclohexane and 10 kg of pure cyclohexanol are produced per hour separated from the reaction products.

PATENT CLAIM 1. Process for the catalytic hydrogenation of benzene, characterized in that the hydrogenation is carried out in the presence of cyclohexanol will.

Claims (1)

2. The method according to claim 1, characterized in -that as a catalyst a nickel catalyst suspended in cyclohexanol is used. Considered publications: German Patent Specifications No. 827361, 969471; U.S. Patent No. 2373 501.