CS233540B1 - Process for the production of ethylbenzene with reduced monochlorobenzene content - Google Patents

Abstract

The invention relates to the production of ethylbenzene by alkylation of benzene with ethylene in the presence of a liquid aluminum chloride complex as a catalyst, in which a reduced content of monochlorobenzene in the finished product is achieved by reducing the chlorine in the recycled diethylbenzene fraction during its separation from heavy residues to a content of less than 100 ppm by mass. The distillation separation of the diethylbenzene fraction from heavier distillation residues takes place at a reflux flow greater than 0.1.

Description

The invention relates to a process for the production of ethylbenzene by alkylation of benzene with ethylene from the presence of an aluminum chloride complex as a catalyst, wherein the content of chlorine-containing compounds bound to the aromatic nucleus is reduced by distillation of the recirculated diethylbenzene fraction. Thus, the flow of these diethylbenzene fraction compounds into the alkylation reactors of ethylbenzene production is limited and the monochlorobenzene content of the pure ethylbenzene produced is reduced.

Ethylbenzene is one of the most important aromatic hydrocarbons in industry. A significant portion of the benzene production from the coke-chemical or petrochemical industries is subjected to alkylation with ethylene to form ethylbenzene. Ethylbenzene is then a raw material for the production of styrene, which is one of the basic monomers for the production of plastics and synthetic rubber.

The alkylation of benzene with ethylene can be carried out in the gas phase on a fixed catalyst, the active ingredient of which is, for example, phosphoric acid or boron trifluoride. However, the bulk of ethylbenzene production is still produced worldwide by alkylation of benzene with ethylene on Friedel-Crafts catalysts. This catalyst, used in the alkylation of benzene with ethylene, is a viscous liquid with a density higher than that of aromatic hydrocarbons.

It is a complex compound formed by the reaction of aluminum chloride, aromatic hydrocarbons and some cocatalysts, which may be ethyl chloride, hydrogen chloride, water and others.

Alkylation of benzene with ethylene in the liquid phase, catalyzed by an aluminum chloride complex, is usually carried out in a column bubbled reactor. In addition to the basic addition of ethylene to benzene from the formation of ethylbenzene, a number of side and subsequent reactions take place in the reactor, in particular to produce the above-alkylated benzene derivatives, i.e., diethylbenzenes and triethylbenzenes. In order to suppress the formation of the above alkylated derivatives, the reaction usually results in an excess of benzene, which also makes it possible to work with virtually complete conversion of ethylene.

A typical alkylation product has the following composition:

Benzene toluene ethylbenzene cumene diethylbenzenes triethylbenzenes and others

44.4 wt. 0.9 wt.

39.8 wt. 0.1 wt.

13.0 wt. 1.8 wt.

The alkylation product ee in the de-distillation column system is divided into the following fractions:

- unreacted benzene circulated back to the alkylation reactors

- pure ethylbenzene (product of production)

- the diethylbenzene fraction returned to the alkylation reactors in the conversion into ethylbenzene by reaction with benzene

- distillation residues.

In addition to the aforementioned main, side and subsequent reactions, chlorinated hydrocarbons are formed to a small extent during the production of ethylbenzene by the alkylation of benzene with a catalysed aluminum chloride complex. The formation of monochlorobenzene, which has a boiling point close to ethylbenzene, is very harmful in terms of the quality of the resulting product:

ethylbenzene monochlorobenz en

136.3 ° C at atmospheric pressure

131.7 ° C at atmospheric pressure

It has been shown that monochlorobenzene is practically the only carrier of the chlorine content of the pure ethylbenzene produced in the normal production mode. The chlorine content of the product is strictly limited, since it adversely affects the function of the subsequent processing of ethylbenzene to styrene. The stringent requirements for the chlorine content of ethylbenzene are still increasing, often the highest chlorine content of 3 ppm, corresponding to 9 ppm of monochlorobenzene, is required.

Monochlorobenzene is a compound that has chlorine bound to an aromatic ring. In addition to the alkylation reactions, the electrophilic substitution of hydrogen with chlorine on the benzene nucleus probably also occurs during the preparation of the catalytic complex, where conditions are favorable in view of the assumed trace elemental chlorine content. Chlorine edged on the aromatic nucleus and then transferred to the alkali product. If present in the form of monochlorobenzene, it penetrates into the ethylbenzene produced and degrades its quality.

By suitable modifications of the distillation mode of the unreacted benzene it is possible to achieve a partial separation of monochlorobenzene from ethylbenzene and its transition into the unreacted benzene stream and with it back to the alkylation reactors. Upon re-passage through the alkylation reactor along with the circulated benzene, the monochlorobenzene is alkylated to, for example, ethylchlorobenzene and a high normal boiling point (180 ° C), which leaves the system together with the higher boilers.

We have now found a process for producing ethylbenzene with a reduced monochlorobenzene content corresponding to a total chlorine concentration of less than 4 ppm by weight, alkylation of benzene with ethylene at 90 to 120 ° C, an absolute pressure of 0.10 to 0.20 MPa and a molar ratio of benzene to ethylene 8 to 3.5 in the presence of a catalyst which is a liquid aluminum chloride complex in which the alkylation reaction product undergoes a distillation separation into circulated unreacted benzene, produced ethylbenzene, circulating diethylbenzene fraction, and heavy distillation residues in which alkylated derivatives also leave the system. monochlorobenzene or hydrocarbon derivatives 8 by a plurality of bonded chlorine atoms, characterized in that the alkylation reaction recirculates the diethylbenzene fraction with a chlorine content of up to 100 ppm, separated from the heavy distillation residues in a distillation stage corresponding to at least one theoretical palate at t lower than atmospheric varnish. Preferably, the diethylbenzene fraction is separated in a distillation step of 3 to 8 theoretical plates.

In order to save raw materials, i.e. benzene and ethylene, in the production of ethylbenzene, it is advantageous to carry out the separation of the diethylbenzene fraction from the heavier distillation residues in a distillation stage, e.g. a column, operating with a reflux ratio greater than 0.1.

The reflux ratio is understood as the ratio between the flow rate of the distilled liquid returned to the distillation stage and the flow rate of the distillate, i.e. the diethylbenzene fraction.

Improved separation of the diethylbenzene fraction has a further beneficial effect on the activity and lifetime of the alkylation catalyst and, as a result, results in savings of aluminum chloride.

It has been found that alkylation of monochlorobenzene in alkylation reactors in the presence of an aluminum chloride catalyst complex is reversible. Monochlorobenzene reacts with ethylene for example by the following reactions:

monochlorobenzene + ethylene-> 1-ethyl-4-monochlorobenzene

1-ethyl-4-monochlorobenzene + ethylene-> 1,3-diethyl-4-monochlorobenzene and the like.

Alkylated monochlorobenzenes have high boiling points and leave for distillation residues during the distillation treatment of alkylation products. If, however, they are recirculated in greater concentration together with the diethylbenzene fraction back to alkylation reactors in which the benzene concentration is high, they are converted back to monochlorobenzene, for example by the following reactions:

1,3-diethyl-4-monochlorobenzene + benzene-> 1-ethyl-4-monochlorobenzene + ethylbenzene

1-ethyl-4-monochlorobenzene + benzene-> monochlorobenzene + ethylbenzene

The reverse conversion of alkylated chlorobenzenes to basic monochlorobenzene increases the concentration of this compound in the electrolytic products, makes it difficult to separate during distillation, and deteriorates the quality of the ethylbenzene produced in terms of chlorine content. A longer possible mechanism for the formation of monochlorobenzene from higher boiling chlorinated derivatives is the migration of chlorine, which leads to the conversion of hydrocarbons having two or more chlorine atoms attached to the aromatic ring to monochlorobenzene.

In addition to the experimental results, the preferred formation of monochlorobenzene from the alkylated chlorinated aromatic compounds was confirmed by calculation of chemical equilibria.

The calculation was performed at 100 ° C for the liquid phase system, the input mixture composition and thermodynamic equilibrium composition composition are given in Table 1.

Table 1

Ethyl group migration balance (% mol)

Component Input mixture Equilibrium mixture benzene 56.44 53.61 1,3-diethylbenzene 5,530 3,530 ethylbenzene 34.97 40.44 1,4-diethylbenzene 2,766 2,300 1,3,5-triethylbenzene 0,274 5 0,105 8 parechloroethylbenzene 0,006 6 0,457 7. 10 ³ ortochloroethylbenzene 0.000 0 0,711 0. 10 ~ ⁴ 1,3-diethyl-4-chlorobenzene 0,005 5 0,547 3. ³ “ ³ monochlorobenzene 0.000 0 0,011 57

The table shows that in thermodynamic equilibrium, 95.6% of the chlorine contained in the incoming parachloroethylbenzene and 1,3-diethyl-4-chlorobenzene will be converted to monochlorobenzene, which was not present in the feed mixture.

Similarly, at 100 ° C, the thermodynamic equilibria for the migration of the chlorine atom between aromatic nuclei were calculated from the preferred formation of monochlorobenzene. The results are shown in Table 2.

Table 2

Equilibrium migration of chlorine atoms (% mol)

Component

Input mixture

Equilibrium mixture

benzene \ 56.44 I 53.59 ethylbenzene 34.97 40.44 1,3-diethylbenzene 5,530 3,533 1,4-diethylbenzene 2,766 2,301 1,3,5-triethylbenzene 0,274 5 0,105 9 perechloroethylbenzene 0.000 0 0,802 3. 10 “ ortochloroethylbenzene 0.000 0 0,124 6. 10 “ 1,3-diethyl-4-chlorobenzene 0.000 0 0,960 1. 10 ^! 1-ethyl-2,4-dichlorobenzene 0.010 6 0,146 5. 10 “' monochlorobenzene 0.000 0 0.020 26

Even in this case, the 1-ethyl-2,4-dichlorobenzene initially present disappeared virtually completely in the state of thermodynamic equilibrium and 95.6% of the total chlorine present was converted to monochlorobenzene.

Example 1

Two similar operating regimes of the operational benzene elution with ethylene on a liquid catalyst complex based on aluminum chloride were compared. Both modes can be characterized by the following basic data:

- aromatic cores and ethyl groups in the feedstocks 2,5: 1

- pressure in the scrubber (steam space) 0.13 MPa

The only difference between the two regimens was the different chlorine content of the recirculated diethylbenzene fraction returned to the alkylene reactors. This different chlorine content, i.e., alkylated chlorobenzenes, was controlled by a distillation regime for separating the diethylbenzene fraction from boiling residues. The mode designated B corresponds to the production method according to the invention. The chlorine content of the recycled diethylbenzene fraction, the crude product of the alkylation, and the pure ethylbenzene produced, determined in the course of the work of the two Wickbold Oxygen Combustion Modes, is shown in the following table.

Table

Chlorine content in the streams, ppm wt.

Mode A

Mode B diethylbenzene fraction crude alkylation product pure ethylbenzene (product)

180

6.5

3.2

The diethylbenzene fraction was separated from the heavy residues in both cases in a single-stage evaporator at an absolute pressure of 8.0 kPa. In the case of mode A, the temperature of the bottom of the evaporator was kept at 140 ° C, in the case of mode B the temperature was 95 ° C.

Example 2

Two methods of distillation of the residue after distillation of unreacted benzene 8 produced by ethylbenzene from the alkylation product were compared.

The distillation residue had the following composition:

ethylbenzene 20 kg isopropylbenzene 5 kg n-propylbenzene 60 kg o-diethylbenzene 60 kg p-diethylbenzene 210 kg m-diethylbenzene 420 kg triethylbenzenes 225 kg total 1000 kg

This distillation residue contained 110 ppm of chlorine.

In the first process, a diethylbenzene fraction of the following composition was distilled off from this distillation residue in a vacuum, single-stage evaporator:

ethylbenzene 20 May kg isopropylbenzene 5 kg n-propylbenzene 60 kg o-diethylbenzene 45 kg m-Diethylbenzene 320 kg p-diethylbenzene 160 kg triethylbenzene 143 kg total 753 kg

The diethylbenzene fraction thus obtained contained 180 ppm by weight. chlorine.

In the second method, a distillation column having a total of 6 theoretical stages was used to distill off the diethylbenzene fraction, operating at a reflux ratio of R = 0.8 at a head pressure of 7 kPa. The distilled diethylbenzene fraction had the following composition:

ethylbenzene. 20 May kg isopropylbenzene 5 kg n-propylbenzene 60 kg o-diethylbenzene 55 kg m-Diethylbenzene 395 kg p-diethylbenzene 204 kg triethylbenzenes 14 kg total 753 kg

The fraction contained 60 ppm by weight. chlorine.

Claims (2)

SUBJECT OF THE INVENTION Process for producing ethylbenzene having a reduced monochlorobenzene content corresponding to a total chlorine concentration of less than 4 ppm by weight, of alkyl benzene by ethylene at a temperature of 90 ° C to 120 ° C, absolute pressure 0.10 MPa to 0.20 MPa and a molar ratio of benzene to ethylene of 1.8 to 3.5, in the presence of a catalyst, which is a liquid aluminum chloride complex, in which the reaction product of alkylation subjected to a distillation separation into circulated unreacted benzene, produced ethylbenzene, circulating! diethylbenzene fraction and heavy distillation residues leaving the system! also alkylated derivatives _e monochloro benzene or hydrocarbon derivatives with vétel number of bound chlorine atoms, characterized in that the reaction is recirculated elltyleční dietylbenzenová fraction having a chlorine content to 100 ppm, separated from the heavy destilečnlch residues in the distillation step, corresponding to at least 4 to one theoretical peter at a pressure lower than atmospheric. 2. A process according to claim 1, wherein the diethylbenzene fraction is separated from the diethylbenzene fraction 1 mined distillation residues in the distillation stage with an efficiency of 3 to 8 theoretical backbones 1 operating with a reflux ratio of 0.2 to 1.2.