RU2843182C1 - Method of producing vinyl aromatic hydrocarbons - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing vinyl aromatic hydrocarbons by dehydrogenation of corresponding alkyl aromatic hydrocarbons in the presence of a catalyst and steam. Method involves cooling the obtained reaction mass, its condensation, separation into hydrocarbon and water layers with extraction of the vinyl aromatic hydrocarbon from the hydrocarbon layer. Obtained water condensate is used to cool the reaction mass by means of their direct interaction in a heat and mass exchange apparatus. Disclosed method also involves purification of water condensate after a heat-mass exchange apparatus using a stripping column, its evaporation and return to the dehydrogenation step. At that, into the heat and mass exchanger below the input of the reaction mass and/or into the stripping column below the input of the water to be purified, live steam is supplied in amount of 0.5-30.0% of the weight of water in the reaction mass and 3.0-20.0% of the weight water in purified water condensate respectively.

EFFECT: high degree of purification of water condensate from hydrocarbons, which increases efficiency of the process of producing vinyl aromatic hydrocarbons.

5 cl, 1 dwg, 3 tbl, 3 ex

Description

The present invention relates to a method for producing vinyl aromatic hydrocarbons by dehydrogenating the corresponding alkyl aromatic hydrocarbons on a fixed catalyst bed in the presence of water vapor, followed by cooling and condensing the reaction mass, separating the condensate into hydrocarbon and water layers, purifying the aqueous condensate and returning it to the process. Purifying the aqueous condensate and returning it to the process is a pressing environmental and economic challenge.

A method is known for producing styrene by dehydrogenating ethylbenzene in the presence of a catalyst and water vapor, in which the resulting reaction mass is cooled, condensed, and separated into aqueous and hydrocarbon layers (US Patent 3,515,766 dated June 2, 1970). A small portion of the aqueous condensate is returned to the stage of cooling the reaction mass by their direct interaction, during which the aqueous condensate completely evaporates and is removed together with the cooled reaction mass for condensation. The main amount of aqueous condensate after stratification is sent for purification in a stripping column and filter. The aqueous condensate purified in this way is used to feed a steam generator, steam boiler, superheater furnace, and is fed to the dehydrogenation stage.

The disadvantage of this method is insufficient purification of water condensate. After the stripping column, the water condensate sent to the superheater furnace contains 0.01 - 0.08% mol of hydrocarbons (more than 430 ppm). In the superheater furnace, at high temperatures (usually more than 650 °C), hydrocarbons crack according to the radical mechanism with the formation of high-boiling compounds. Such compounds settle on the walls of the steam generator and superheater furnace tubes, impair heat exchange, cause blockages and reduce the overhaul life of critical equipment. Getting into the reactor with superheated steam, high-boiling compounds settle on the catalyst, impair its self-regeneration, lead to carbonization of the catalyst, reduce the process indicators, which ultimately ends in premature shutdown of production for regeneration or reloading of the catalyst.

The closest to the proposed method is the production of vinyl aromatic hydrocarbons by dehydrogenation of the corresponding alkyl aromatic hydrocarbons in the presence of a catalyst and water vapor, including cooling and condensation of the reaction mass, separation of the condensate into aqueous and hydrocarbon layers, and return of the aqueous layer to the stage of cooling the reaction mass by their direct interaction (Patent of the Russian Federation No. 2331623 of 25.04.2007). In this case, the entire obtained aqueous condensate, 0.5 - 20.0% by weight, is fed to cool the reaction mass, which is evaporated upon interaction with the reaction mass. The remaining portion 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 to the dehydrogenation stage. A stripping column with an additional supply of extractant below the water condensate inlet can be used to purify the aqueous condensate. Benzene, toluene or a mixture of benzene and toluene isolated from hydrocarbon condensate can be used as an extractant. The disadvantage of this method is the insufficient degree of purification of water condensate from hydrocarbons.

The problem solved by the present invention is to increase the degree of purification of aqueous condensate from hydrocarbons, which will ensure an increase in the efficiency of the process for obtaining vinyl aromatic hydrocarbons due to:

- increasing the service life and efficiency of the dehydrogenation catalyst used as a result of an additional (compared to the prototype) reduction in the content of heavy hydrocarbons formed in the superheater furnace from hydrocarbons supplied with the evaporated water condensate for superheating,

- increasing the efficiency of superheating furnaces due to the reduction of heavy hydrocarbon deposits on the heat transfer surface (on the coils).

A method is proposed for producing vinyl aromatic hydrocarbons by dehydrogenating corresponding alkyl aromatic hydrocarbons in the presence of a catalyst and water vapor, comprising cooling and condensing the reaction mass, separating the condensate into hydrocarbon and aqueous layers, followed by isolating the vinyl aromatic hydrocarbon from the hydrocarbon layer, using the aqueous condensate to cool the reaction mass by their direct interaction in a heat and mass exchange apparatus, purifying the aqueous condensate using a stripping column, evaporating it and returning it to the dehydrogenation stage. In this case, sharp water vapor is fed into the heat and mass exchange apparatus below the input of the obtained reaction mass and/or into the stripping column below the input of the purified aqueous condensate, respectively, in an amount of 0.5-30.0% of the mass of water in the reaction mass and 3.0-20.0% of the mass of water in the purified aqueous condensate.

The process of dehydrogenation of alkyl aromatic hydrocarbons can be carried out at pressures below atmospheric pressure.

Purification of water condensate in a stripping column can be carried out at a pressure below atmospheric.

An extractant can be fed into the stripping column below the inlet of the purified water condensate or below the inlet of the purified water condensate and above the inlet of the live steam.

Benzene and/or toluene can be used as an extractant for the stripping column.

The introduction of live steam into the heat and mass exchange apparatus at the stage of cooling the reaction mass is carried out below the introduction of the reaction mass. In this case, in the case of feeding live steam above the liquid level, additional stripping of hydrocarbons from the water condensate occurs in the mass exchange devices; in the case of feeding live water steam below the liquid level, directly into the water condensate, additional stripping of hydrocarbons from the water condensate occurs, sent for further purification.

The amount of sharp water vapor supplied to the heat and mass exchange apparatus is 0.5 - 30.0% of the mass of water in the reaction mass. When sharp water vapor is supplied less than 0.5%, the effect is insignificant, and when more than 30.0% is supplied, the load on the condensation apparatus increases significantly, the amount of condensate sent to the phase separator increases, as a result, the time the condensate spends in the phase separator is reduced and the phase separation is worsened.

Part of the live steam supplied to the heat and mass exchange apparatus is condensed and removed with the water condensate supplied for purification in the stripping column. Due to the live steam condensate, the concentration of hydrocarbons in the water condensate is reduced and effective further purification of the water condensate in the stripping column is ensured.

The supply of live steam for heating the stripping column is carried out below the inlet of the purified water condensate, and in the case of additional supply of the extractant, carried out below the inlet of the purified condensate, the supply of live steam is carried out below the inlet of the extractant. This method ensures effective heat transfer from the heat carrier (water vapor) to the heating of the water condensate to ensure stripping of hydrocarbons. In addition, live water vapor is condensed and removed from the column with purified water condensate, further reducing the hydrocarbon content in it. The amount of live water vapor supplied to the stripping column is 3.0 - 20% of the mass of water in the purified condensate and depends on the parameters of live water vapor (temperature, pressure) and the heat balance of the stripping column - the amount of condensate returned as phlegm. When supplying sharp water vapor of less than 3% of the mass of water in the purified condensate, the efficiency of hydrocarbon stripping decreases, and when supplying sharp water vapor of more than 20% of the mass of water in the purified condensate, the energy consumption of the column increases significantly.

When sharp water vapor is supplied simultaneously to the heat and mass exchange apparatus and to the stripping column, the efficiency of water condensate purification increases and a synergistic effect occurs.

In the proposed method, due to the increased efficiency of purification of water condensate, it becomes possible to direct additional condensate containing water and/or aromatic hydrocarbons to the phase separator, for example, from a collector of atmospheric precipitation, wash water during cleaning of equipment, during emptying of equipment, condensate containing water and/or aromatic hydrocarbons from other productions, for example, from the production of ethylbenzene, from other sources of water and/or hydrocarbon condensate.

Collection of contaminated condensate from various sources in a phase separator with subsequent purification of the total water condensate in a heat and mass exchange apparatus, on a filter and in a stripping column increases the environmental safety of the process.

The proposed method can be used to obtain styrene by dehydrogenation of ethylbenzene, alpha-methylstyrene by dehydrogenation of isopropylbenzene, vinyltoluene by dehydrogenation of ethyltoluene, and divinylbenzene by dehydrogenation of diethylbenzene.

The basic process flow diagram of the proposed method for obtaining vinyl aromatic hydrocarbons is shown in the drawing Fig. 1 (using the example of obtaining styrene by dehydrogenating ethylbenzene with the supply of acute water vapor to the heat and mass exchange apparatus and to the stripping column).

Ethylbenzene and water vapor enter the ethylbenzene dehydrogenation section I, which includes a reactor and a superheater furnace. The reaction mass leaving the reactor, which is a mixture of hydrocarbons (mainly styrene, unreacted ethylbenzene and some benzene, toluene and light gases - hydrogen, carbon dioxide, methane, ethane, 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 is usually maintained at a level above 120 °C (mainly 150 - 200 °C). From the recuperator II, the reaction mass is directed to the heat and mass exchange apparatus III (stream 1), where additionally, sharp water vapor (stream 2) is fed below the input of the reaction mass. From the heat and mass transfer apparatus, the mixture of the reaction mass and water vapor is sent to condensation section IV (stream 3), where condensation and separation of the condensate mixture in the phase separator into water and hydrocarbon layers by decantation occur. Uncondensed light gases, mainly hydrogen, carbon dioxide, methane, ethane, ethylene are compressed, sent to capture entrained aromatic hydrocarbons and then (stream 4) can be sent to the separation of hydrogen, carbon dioxide or used as fuel in the superheater furnace. After decantation, the hydrocarbon layer is sent by a pump to the separation and purification of styrene in the rectification section V (stream 5), and the water layer contaminated with hydrocarbons is sent by a pump to the heat and mass transfer apparatus III (stream 6). In the heat and mass exchange apparatus, direct contact of the reaction mass, aqueous condensate and sharp water vapor takes place, wherein the reaction stream is cooled to a temperature of 70-110°C (depending on the process pressure), and the aqueous condensate is heated to a temperature of 60-98°C. In this case, the main part of the hydrocarbons is stripped from the aqueous condensate and the reaction mass is washed from catalyst dust, polymers and high-boiling hydrocarbons. During condensation of the purified reaction mass, the probability of clogging of the condensers is reduced, and during further processing of the hydrocarbon condensate - the boilers and mass-exchange devices of the columns. The aqueous condensate freed from the main part of the hydrocarbons with some content of catalyst dust, polymers and high-boiling hydrocarbons is fed by a pump to a special filter VI (stream 7), where catalyst dust, polymers and high-boiling hydrocarbons are extracted from the aqueous condensate. Then the aqueous condensate is fed for final fine cleaning to stripping column VII (stream 8). Sharp water vapor (stream 9) is fed into the lower part of the stripping column. In stripping column VII, preferably at a pressure below atmospheric, fine purification of the water condensate occurs to a quality suitable for reuse by evaporation in recuperator II and then in the superheater furnace. From the bottom of stripping column VII, purified water condensate (stream 10) is partially fed by a pump into recuperator II, from where it is fed in the gas phase into dehydrogenation section I, and the remaining portion of purified water condensate is fed into the water circulation system.

Example 1 (with the supply of sharp water vapor to the stripping column).

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

30,207 kg/hour of ethylbenzene and 57,513 kg/hour of water vapor are fed into the dehydrogenation reactor. A mixture of hydrocarbons and water vapor in the amount of 87,720 kg/hour exits the reactor. 5,100 kg/hour of sharp water vapor (8.9% of the mass of the purified water condensate) is fed into the stripping column.

The process conditions and flow compositions are given in Table 1.

Example 2 (with the supply of acute water vapor to the heat and mass transfer apparatus).

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

30,207 kg/hour of ethylbenzene and 57,513 kg/hour of water vapor are fed into the dehydrogenation reactor. A mixture of hydrocarbons and water vapor in the amount of 87,720 kg/hour exits the reactor.

Sharp water vapor in the amount of 2866 kg/h (5% of the amount of water in the reaction mass) is fed into the heat and mass exchange apparatus below the upper edge of the reaction mass input pipeline, below the level of the water condensate (directly into the water condensate).

The process conditions and flow compositions are given in Table 2.

Example 3 (with the supply of acute water vapor to the heat and mass exchange apparatus and the stripping column).

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

30,207 kg/hour of ethylbenzene and 57,513 kg/hour of water vapor are fed into the dehydrogenation reactor. A mixture of hydrocarbons and water vapor in the amount of 87,720 kg/hour exits the reactor.

Sharp water vapor in the amount of 2866 kg/h (5% of the amount of water in the reaction mass) is fed into the heat and mass exchange apparatus below the upper edge of the reaction mass input pipeline, below the water condensate level (directly into the water condensate). Sharp water vapor in the amount of 5100 kg/h (8.48% of the mass of the purified water condensate) is fed into the stripping column.

The process conditions and flow compositions are given in Table 3.

As can be seen from the examples given, using the proposed method ensures:

- efficient purification of water condensate from aromatic hydrocarbons, catalyst dust and high-boiling hydrocarbons; purified water condensate can be used to generate water vapor and/or in the water circulation system without the risk of contamination of the surfaces of the devices and the risk of environmental pollution

- efficient cleaning of the reaction mass from catalyst dust and high-boiling hydrocarbons (including resin), which increases the service life and efficiency of heat and mass exchange devices during the processing of hydrocarbon condensate.

Claims (5)

1. A method for producing vinyl aromatic hydrocarbons by dehydrogenating corresponding alkyl aromatic hydrocarbons in the presence of a catalyst and water vapor, comprising cooling the resulting reaction mass, condensing it, separating it into hydrocarbon and aqueous layers with the isolation of the vinyl aromatic hydrocarbon from the hydrocarbon layer, using the resulting aqueous condensate to cool the reaction mass by their direct interaction in a heat and mass exchange apparatus, purifying the aqueous condensate after the heat and mass exchange apparatus using a stripping column, evaporating it and returning it to the dehydrogenation stage, characterized in that sharp water vapor is fed into the heat and mass exchange apparatus below the feed of the reaction mass and/or into the stripping column below the feed of the purified aqueous condensate, respectively, in an amount of 0.5-30.0% of the weight of the water in the reaction mass and 3.0-20.0% of the weight of the water in the purified aqueous condensate. 2. The method according to paragraph 1, characterized in that the dehydrogenation of alkyl aromatic hydrocarbons is carried out at a pressure below atmospheric. 3. The method according to paragraph 1, characterized in that the purification of water condensate in the stripping column is carried out at a pressure below atmospheric. 4. The method according to paragraph 1, characterized in that an extractant is fed into the stripping column below the inlet of the purified water condensate and above the inlet of the sharp water vapor. 5. The method according to item 4, characterized in that benzene and/or toluene are used as an extractant for the stripping column.

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