RU2331623C1 - Method of obtaining vinylaromatic hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention pertains to the method of obtaining vinylaromatic hydrocarbons through dehydrogenation of corresponding alkylaromatic hydrocarbons in the presence of a catalyst and water vapour. The method involves cooling of the obtained reaction mixture, its condensation, division into hydrocarbon and water layers with separation of vinylaromatic hydrocarbon from the hydrocarbon layer, using the obtained water condensate for cooling the reaction mass through direct reaction, cleaning the water condensate using a steam-stripping column and filter, its evaporation and return to the dehydrogenation stage. It is characterised by cooling the reaction mixture, all the obtained water condensate is fed in, 0.5-20.0% of the mass of which is evaporated. The remaining part is taken for cleaning. Use of the given method allows attaining a more profound degree of purity of the water condensate, further returned to the dehydrogenation stage.

EFFECT: longer life service of the catalyst and the time between repairs of the device.

4 cl, 1 ex, 1 dwg, 1 tbl

Description

The present invention relates to a method for producing vinyl aromatic hydrocarbons by dehydrogenation of the corresponding alkyl aromatic hydrocarbons.

A known method of producing styrene by dehydrogenation of ethylbenzene in the presence of a catalyst and water vapor, in which the resulting reaction mass is cooled, then condensed and divided into hydrocarbon and water layers (Chemistry and technology of monomers for synthetic rubbers: Textbook for universities. / Kirpichnikov P.A., Liakumovich A.G., Pobedimsky D.G., Popova L.M. - L .: Chemistry, 1981, p. 152). The aqueous layer is returned to the stage of cooling the reaction mass in a foam apparatus, where they are directly contacted. In this case, the reaction mass is cooled to 118 ° C and cleaned of catalyst dust. Water condensate is then used to heat the starting ethylbenzene mixture.

One of the disadvantages of this method is the lack of reuse of water condensate at the dehydrogenation stage, which significantly reduces the efficiency of the process.

Closest to the proposed method is the catalytic conversion of hydrocarbons, for example, the production of styrene by dehydrogenation of ethylbenzene, in accordance with US patent No. 3 515 766 dated 06/02/1970. Dehydrogenation is carried out in the presence of a catalyst and water vapor, the resulting reaction mass is cooled, condensed and separated into water and hydrocarbon layers, followed by directing the hydrocarbon layer to separation. A small part of the water layer returns to the stage of cooling the reaction mass, where they interact directly, in which the water condensate completely evaporates and is removed together with the cooled reaction mass to condensate. The main amount of water condensate immediately after delamination is sent for cleaning first in a stripping column, and then on the filter. The condensed water thus purified is used to power the steam generator, steam boiler, superheater and is fed to the dehydrogenation step.

However, in this method, the purification of water condensate is insufficient, in particular, after the stripping column in the water condensate contains 0.01-0.08 mol%. hydrocarbons (more than 430 ppm). When this stream enters the steam generator, and especially in the superheater (in the high temperature zone), thermal cracking of hydrocarbons occurs by a radical mechanism with the formation of high-boiling compounds. Such compounds settle on the walls of the tubes of the steam generator and overheating furnace, impairing heat transfer, causing clogging, and as a result, premature production shutdown. In addition, getting into the dehydrogenation reactor, such high-boiling compounds settle on the catalyst, impairing its self-regeneration and ultimately leading to carbonization of the catalyst, premature shutdown of the production for regeneration or overloading of the catalyst. Process performance is reduced.

The problem solved by the present invention is to increase the efficiency of the process by increasing the service life of the catalyst and increasing the turnaround time of the installation. These effects are achieved due to a deeper purification of the water condensate obtained in the process and returned to the dehydrogenation stage.

A method is proposed for producing vinyl aromatic hydrocarbons by dehydrogenation of the corresponding alkyl aromatic hydrocarbons in the presence of a catalyst and water vapor, which includes cooling the reaction mixture, its subsequent condensation, separation into hydrocarbon and water layers with the release of vinyl aromatic hydrocarbon from the hydrocarbon layer and returning the water layer to the stage of cooling the reaction mass by direct interactions. At the same time, for the cooling of the reaction mass, all the resulting aqueous condensate, 0.5-20.0% by weight, is fed. which when interacting with the reaction mass is evaporated. The remaining part of the aqueous condensate after interaction with the reaction mass is removed for purification, which is carried out using a stripping column and a filter, then for evaporation and the dehydrogenation stage.

The process can be carried out at a pressure below atmospheric.

For the purification of water condensate, a stripping column can be used with an additional supply of extractant below the input of the purified water condensate.

As the extractant, benzene, toluene or a mixture of benzene and toluene separated from hydrocarbon condensate can be used.

The amount of evaporated water condensate is controlled, for example, by the pressure in the heat-mass transfer apparatus, where the reaction mass and water condensate interact, and / or the temperature of the supplied reaction mass, and / or the temperature of the water condensate.

Cooling of the reaction mass immediately after the dehydrogenation reactor can be carried out by heating the initial alkylaromatic hydrocarbon before feeding it to dehydrogenation and / or by generating steam in the riboiler.

Water condensate can be cleaned first in a stripping column, then on a filter, or first on a filter, and then in a stripping column.

The differences of the proposed method from the prototype are:

- direction to the stage of cooling the reaction mass of all the obtained water condensate;

- evaporation in the interaction with the cooled reaction mass of 0.5-20.0% wt. condensate supplied;

- direction for cleaning the remaining water condensate after its interaction with the cooled reaction mass;

- use for cleaning stripping columns with an additional supply of extractant below the input of the purified water condensate.

In the proposed method, when the reaction mass and water condensate interact, partial evaporation of the latter occurs, in which more than 85% of the hydrocarbons contained in the water condensate are evaporated. The load on the next stages of purification of water condensate is significantly reduced. As a result, it becomes possible to reduce the amount of hydrocarbons in the aqueous condensate returned to dehydrogenation by almost 100 times. More than 20% wt. it is not practical to evaporate the water condensate, since on the one hand the quality of the water condensate remains practically unchanged, and on the other hand, the cost of condensing the reaction mixture with an additional amount of evaporated water condensate increases significantly. With evaporation of less than 0.5% wt. water condensate is insufficient stripping hydrocarbons.

When using a stripping column at the stage of purification of water condensate with an extractant supply below the water condensate inlet, a part of the column between the inlet of the extractant and the inlet of water condensate additionally works as an extractor. Fine purification of water condensate is carried out, its quality is improved.

Benzene, toluene or mixtures thereof are preferably used as extractants, as they have good extraction ability with respect to vinyl aromatic and high boiling hydrocarbons.

As an example of the implementation of the proposed method for the production of vinyl aromatic hydrocarbons, the drawing shows a schematic process diagram of the production of styrene by dehydrogenation of ethylbenzene.

Ethylbenzene I and dehydrated water are fed to the ethylbenzene I dehydrogenation reactor. The reaction mixture, which is a mixture of hydrocarbons (mainly styrene, unreacted ethylbenzene and a certain amount of benzene, toluene and light gases - hydrogen, CO ₂ , methane, ethylene) and water vapor with a temperature of 530-600 ° C, enters the recuperator II. The temperature of the reaction stream at the outlet of the recuperator (for example, riboiler) is maintained at a level not lower than 150 ° C (usually not lower than 190 ° C) when the process is carried out at a pressure close to atmospheric and not lower than 120 ° C (usually not lower than 150 ° C) when carrying out the process at a pressure below atmospheric. From the recuperator II, the reaction mass is sent to the heat and mass transfer apparatus III (stream 1), from there to the condensation unit IV (stream 2), where the reaction mass is condensed and separated into water and hydrocarbon layers by decantation. Uncondensed light gases, mainly hydrogen, CO ₂ , methane, ethylene, are compressed, sent to trapped aromatic hydrocarbons (stream 3) and used as fuel in a superheater. After decanting, the hydrocarbon layer is sent to the styrene V isolation and purification unit (stream 4), and the aqueous layer contaminated with hydrocarbons is sent to the heat and mass transfer apparatus III (stream 5). There, the reaction stream is cooled to a temperature of 100-110 ° C during the process at a pressure close to atmospheric, and to a temperature of 70-90 ° C during the process at a pressure below atmospheric. Water condensate is heated to a temperature of 60-98 ° C. Due to the fact that the interaction of the flows occurs by direct mixing, there is no problem with a decrease in heat transfer. In this case, as already noted, the stripping of the main part of C ₆ -C ₈ hydrocarbons from water condensate occurs. At the same time, the reaction mass is washed away from catalyst dust, polymers and high boiling hydrocarbons, which creates favorable conditions for the condensation of the reaction mass - there is no clogging of the condensers, and the likelihood of clogging of distillation columns when separating hydrocarbon condensate free of the above impurities is reduced. The water condensate freed from C ₆ -C ₈ hydrocarbons with a certain content of catalyst dust, polymers and high boiling hydrocarbons enters special filter VI (stream 6), where catalyst dust, polymers and high boiling hydrocarbons are extracted from the water condensate. Next, the water condensate enters the final purification in stripper column VII (stream 7). Since water condensate leaves the heat-mass transfer apparatus hot, the heat load on the stripping column is reduced. In stripper column VII, fine condensate is refined to a quality suitable for reuse by evaporation in riboiler II and then in a superheater.

Example

The process of obtaining styrene by dehydrogenation of ethylbenzene in accordance with the scheme shown in the drawing.

30,200 kg / h of ethylbenzene and 57,400 kg / h of water vapor are fed to the dehydrogenation reactor I. A mixture of hydrocarbons and water vapor in the amount of 87,600 kg / h leaves the reactor.

The process conditions and composition of the flows are shown in the table.

Material balance of the process as exemplified Stream composition Number, parameters and composition of flows, kg / h Stream number one 2 3 four 5 6 7 8 Light gases * 790 790 790 Aromatic hydrocarbons ** 29641 29731 24 29612 95 5 5 0.2 High boiling hydrocarbons *** and catalyst dust 47 16 16 31 Water 57122 66433 8 29th 66396 57085 57085 57085 Total 87600 91970 822 24657 66491 57121 57090 57,085.2 Temperature ° C 250 69.2 5 37.5 39.5 69.3 69.0 80 Pressure, MPa 0,037 0,034 0,025 0,025 0.42 0.6 0.57 0.04 * - hydrogen, methane, ethylene, CO ₂ ** - aromatic hydrocarbons C ₆ -C ₈ (benzene, toluene, ethylbenzene, styrene, xylenes, a-methylstyrene) *** - hydrocarbons> C ₉ , polymers

In the above example (drawing, table) ~ 14% wt. water condensate [(66396-57085) × 100%: 66396], while 94.7% wt. hydrocarbons from the aqueous layer [(95-5) × 100% / 95].

The hydrocarbon content in the purified aqueous condensate (stream 8) is 0.2: 57085.2 = 3.5 × 10 ^-6 (3.5 ppm)

Claims (4)

1. A method of producing vinyl aromatic hydrocarbons by dehydrogenation of the corresponding alkyl aromatic hydrocarbons in the presence of a catalyst and water vapor, which includes cooling the resulting reaction mass, condensing it, separating it into hydrocarbon and water layers, releasing vinyl aromatic hydrocarbon from the hydrocarbon layer, using the resulting water condensate to cool the reaction mass by direct interaction, the purification of water condensate using a stripper and a filter, and man and return to the dehydrogenation stage, characterized in that the cooling of the reaction mass is fed all the resulting aqueous condensate 0,5-20,0 wt.% of which was evaporated, and to send the remainder of the purification. 2. The method according to claim 1, characterized in that the process is carried out at a pressure below atmospheric. 3. The method according to claim 1, characterized in that the purification of the water condensate in the stripping column is carried out with an additional supply of extractant below the input of the purified water condensate. 4. The method according to claim 3, characterized in that benzene, toluene or a mixture of benzene and toluene separated from hydrocarbon condensate are used as extractant for the stripping column.