DE1793100B2 - PROCESS FOR MANUFACTURING VINYL-SUBSTITUTED AROMATIC HYDROCARBONS - Google Patents

Description

if caused by the built-in heat exchanger. It is therefore with the procedure the prior art required to increase the inlet pressure.

According to the method of the present invention, it is possible to have a remarkably improved degree of conversion achievable in comparison with that of an adiabatic one-step reaction process. Furthermore, it is also possible to achieve an improved selectivity compared with the known one multi-stage adiabatic reaction processes using the same amount of feed Steam.

The method of the present invention is not particularly limited as to the number of stages of the reaction vessel used. A 2- to 4-S'ulen-Reaktü ·· is, however, for economic (:. Constitute preferred for the process of the present invention, the standard can be used for the dehydrogenation Dehydrierleaktion used..

When performing the \ experience of the present Invention, the proportion of aikylsubstituierteni aromatic hydrogen used in jeuer Reaction stage can be selected in a desired manner. If the same feed rate is used the amount of water vapor supplied should be greater in the later stages. For economic It would therefore usually be considered from a point of view recommended, the alk \! aromatic hydrocarbon to be initiated at such a rate that this decreases with each reaction stage.

The following examples describe some embodiments of the method according to the present invention.

example 1

Vaporous ethylbenzoi heated to 500 ° C. and steam superheated to 680 ° C. are mixed in a ratio of 5:15 kg / h. The reaction mixture obtained, the temperature of which is 600 ° C., is introduced into the first stage of the reactor, in which the ethylbenzene is brought into contact with a pelletized dehydrogenation catalyst at a liquid space velocity of 0.51. This catalyst is in the form of a fixed bed, or was made from 84% Fc ₁ O ₃ , 3% Cr ₀ O ₃ . 12 ⁰ O KOH and 1 ⁰ O NaOH produced.

Dehydration takes place, the ethylbenzene being converted to styrene with a degree of conversion of about 35% is convicted. The reaction mixture of the first stage of the reactor is then with 2 kg / h ethylbenzene, which is heated to 500 "C, and 20 kg / h steam, which is superheated to 750 C, mixed and in the second Stage the reactor at liquid space velocity. 0.52 initiated. The reaction mixture this second stage of the reactor is with 1 kg / h ethylbenzene (500 ° C) and 13 kg / h superheated steam (750 ° C) mixed and in the third stage of the reactor at a liquid space velocity of 0.73 initiated.

The total degree of conversion is 60%. Such a value is heretofore in a one-stage adiabatic reaction process never been achieved. The selectivity obtained by following the procedure of this example is 92.2%, which is greater than 90.1%. This latter value is in an adiabatic uieistlichen reaction processes obtainable if the same amount of supplied steam is used the same degree of conversion is used.

Example 2

Vaporized and superheated to 500 ^J C and heated to 650 C ethylbenzene steam are in a ratio of i, 4: mixed together 3.3 kg / h. The reaction mixture obtained, the temperature of which is 603 ^J C, is in the first stage of the

ίο Renktens initiated in which ethylbenzene is brought into contact with a fixed bed of a _{catalyst consisting of 93% Fe 0} O ₃ and a total of 7 ° O Cr ₀ O ₃ and KOH, at a liquid space velocity of 0.339. Dehydration takes place, with part of the ethylbenzene being converted into styrene. The reaction mixture of the first reactor stage is mixed with 1.04 kg-h of fresh ethylbenzene (500 "C) and 6.2 kg of superheated steam (850 Cj. This total mixture, which now has a temperature of 607" C, is now introduced into the second reactor stage The reaction mixture obtained therefrom is mixed with 1.04 kg of ethylbenzene (500 ° C.) and 8.5 kg-h of superheated steam (850 ° C.), and the total mixture, the temperature of which is now 615 ° C., becomes introduced into the third reactor stage, so that the liquid space velocity of the ethylbenzene is 0.318.

The total conversion is 60% and the selectivity is 91.9%. In contrast, the selectivity of the conventional adiabatic three-step reaction process using the same amount of added steam and at the same conversion wheel only 90.1%.

Comparison

Using the dehydrogenation apparatus described in the French patent 1 356 227 in the example was a starting mixture heated to 610 - C, containing 170 kg of ethylbenzene and 330 kg Water vapor, introduced into the apparatus. The same catalyst as used in Example 2 of the present was used Invention used. The starting mixture was used in the first reaction stage with a fixed bed catalyst passed, with 28 "/" of the ethylbenzene introduced in styrene in an endothermic reaction were convicted. After leaving the first reaction bed, the mixture had a temperature of 570 C. The reaction mixture obtained in the first reaction bed was withdrawn from the reactor and heated to 609 ° C by means of an indirect heat exchanger. The reheated mixture was in passed the second catalyst bed which contained the same catalyst as the first bed. In the second

j-, 5 reactor were 17% of the initially fed Converted ethylbenzene to styrene, and the temperature of the reaction mixture fell to 585 ° C. That The mixture withdrawn from the second reaction zone was in the empty space between the reaction beds with 126 kg of steam superheated to 660 ° C mixed. The gas mixture from the reaction mixture of the second reaction zone and that which has been blown in superheated steam then had a temperature of 607 ° C. This mixture was in passed the reaction zone with the third catalyst bed. The catalyst was the same as in that Lent introduced ethylbenzene converted into styrene, first two beds. 12% of the initial

The temperature of the reaction mixture fell to 5 ^{° C} > 2 ° C. After leaving the third catalyst, the reaction mixture was then mixed with 630 kg of steam superheated to 660 ° C. in an intermediate zone. The temperature of the reaction mixture was then 604 ° C. This mixture was passed into the fourth catalyst bed.

where X ° o of the initially supplied Athylbirim.k were transferred in Sivrol and the temperature aut 594 'C expired The total degree of conversion d.-, , "^ Led ethylbenzene in styrene was o.v, with "a selectivity of 82 -... The yield at Styrene from ethylbenzene is accordingly 65 «,, · S2" i. = - 53.3 ° / ...

Claims (1)

Claim: Process for the preparation of vinyl-substituted aromatic hydrocarbons by catalytic Dehydrogenation of alkyl-substituted aromatic hydrocarbons in several in Series of interconnected reaction zones. with superheated steam as a heat transfer medium is added to the reaction mixture before each reaction zone, marked thereby e ~ t that fresh alkyl-substituted aromatic hydrocarbons are gradually added to each reaction zone are fed to the reaction mixture. The present invention relates to an improved process for the preparation of vinyl substituted ones aromatic hydrocarbons by catalytic dehydrogenation of alkyl-substituted aromatic Hydrocarbons. The present invention is based on the object of a new deliydria experienced to linden, according to the vinylsub-stitiiierte aromatic hydrocarbons from the corresponding alkyl-substituted aromatic hydrocarbons with an improved degree of conversion and greater selectivity compared to the known Process can be produced. The terms "conversion rate" and "selectivity ■ ···. as they are within the meaning of the present invention can be used by the following equations To be defined: Degree of conversion (' ») - selectivity Moles of alkyl aromatic hydrocarbon consumed. Moles of alkyl aromatic hydrocarbon fed in Moles of manufactured vinyl aromatic! COMBINED HYDROGEN Moles of used alkvlaromatici coal a ^ stofl I DO . It is known that a vinyl-substituted aromatic c " Hydrocarbon can be produced by steaming the alkyl-substituted aromatic hydrocarbon with superheated steam mixed and this mixture is then passed into a dehydrogenation reaction zone, which is with a dehydrogenation catalyst is filled. The dehydrogenation reaction of alkyl aromatic hydrocarbons however, it is strongly endothermic. Therefore it is difficult to achieve a conversion rate of more than 40'Vu at this To achieve reaction, in view of the temperature drop. That's why you already have a adiabaiisdies carried out many stage reaction processes, the superheated steam during the dehydrogenation reaction in each stage of the reaction system is blown in to maintain the reaction temperature. It is still isothermal Reaction method has been used in which the reaction system is supplied from the outside of the reaction vessel heat of reaction is supplied. However, these prior art methods suffer inevitable due to various disadvantages. In the isothermal reaction process using of a heat exchanger type reactor, the selectivity obtained is low because of an unexpectedly high reaction pressure, the results from the shape of the catalyst layer formed in thin elongated tubes. At the is adiabatic reaction process including intermittent addition of superheated steam the selectivity achieved in the initial stage, in which the highest degree of conversion is achieved, is remarkable lower compared to the selectivity of the one-step adiabatic reaction process which the same amount of steam is used as the molar ratio of steam to alkyl aromatic Hydrocarbon in the interior is small. The subject of the present invention is a method for the division of vinyl-substituted aromatic Carbons hydrogen by catalytic dehydrogenation of alkyl-substituted aromatic oils, Hydrogen in several in series with one another: connected reaction zones, whereby overheated! Steam is fed as a heat transfer medium to the reaction mixture before each reaction zone, which thereby it is characterized that fresh alkyl substituents have aromatic hydrocarbons gradually in each Reaction zone are fed to the reaction mixture. As demonstrated by the following examples according to this method, an overall yield can be obtained of over 55% can be achieved. According to the known method in which only water vapor is fed stepwise to each reactor zone. on the other hand, when ethylbenzene is converted into styrene, a yield of only et ν a 50% is obtained (German Auslegeschrift 1 169 918). When carrying out such a process on an industrial scale such a lower yield is a considerable technical disadvantage. From the French patent 1 356 227 it is known for converting ethylbenzene into styrene, the gradual introduction of steam into each reaction zone and indirect heating of the reaction mixture after leaving each catalyst layer. According to the following However, given the results of the comparison test, an overall yield is optimal of 53.3% (degree of conversion 65%; selectivity 82%) obtained, with more reaction stages or catalyst beds must be used than according to the process of the invention. Furthermore is the indirect heating between the catalyst beds associated with the disadvantage that an additional heat exchanger is required in the reactor, thereby complicating the construction of this reactor, there is poor thermal efficiency and an increased pressure drop in the reactor, also