JP2019142929A - Separation method for c8 aromatic mixture - Google Patents

Abstract

An improved process for recovering ethylbenzene from a hydrocarbon mixture.
A method for distilling ethylbenzene from a mixture containing ethylbenzene and at least one other C ₈ aromatic compound, comprising 1,2,4-trichlorobenzene, nitrobenzene, benzonitrile, isophorone, methyl salicylate The distillation column is operated at subatmospheric pressure in the presence of an extraction solvent such as benzaldehyde, sulolane, N-methyl-2-pyrrolidone, N-formylmorpholine, and the like. Feature method.
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Description

The present invention relates to a process for the separation by extraction distillation of ethylbenzene from a mixture comprising ethylbenzene and at least one other C8 aromatic compound.

Ethylbenzene is a valuable hydrocarbon compound that is widely used commercially. Ethylbenzene is mainly used for the production of styrene, an intermediate for the production of polystyrene. Ethylbenzene is produced commercially from the alkylation of benzene with ethylene. But,
The cost and competitive demand for ethylene and benzene is due to the various Cs already containing ethylbenzene.
Urged new efforts to recover ethylbenzene from eight aromatic feed streams. Such feed streams are generally produced as by-product streams from several petrochemical processes, and these feed streams are usually one having a boiling point close to that of ethylbenzene, as well as ethylbenzene, particularly the C8 aromatic isomer. Or more hydrocarbon compounds.

Methods for separating ethylbenzene from other near-boiling C8 aromatics, particularly xylene isomers, are known.

For example, US Pat. No. 3,917,734 discloses an adsorptive separation process for separating ethylbenzene from a feed mixture comprising ethylbenzene and at least one xylene isomer, the process comprising adsorbing the feed mixture to a crystalline aluminosilicate adsorption. A step of contacting the agent and selectively adsorbing xylene isomers by largely removing ethylbenzene, and then recovering purified ethylbenzene as a product. The separation efficiency of this process relies heavily on the adsorption capacity of the adsorbent, and therefore a complex operation of a countercurrent moving bed system is preferred. Also, the impurity content in the feed stream needs to be carefully controlled to prevent interference with the selective adsorption process.

Of course, ethylbenzene can be separated from the xylene isomers by fractional distillation,
Since their boiling points are very close to each other, fractional distillation is only realized in more complex and energy intensive systems.

British Patent 1 198592 discloses a process for separating C8 aromatic isomers using a single multifunctional distillation column. This distillation is performed with at least 250, preferably 365 plates and 100-25 to obtain commercially acceptable ethylbenzene purity.
It is carried out in a multistage column having a reflux ratio of 0: 1.

Extractive distillation is a method in which near-boiling compounds are separated from each other by performing distillation in the presence of an added solvent or a so-called extractant. When the extractant is present in the distillation system, the relative volatility changes, thus further increasing the resolution of near-boiling compounds.

U.S. Pat. No. 3,1050,017 describes an ethylbenzene from xylene isomer in the presence of a compound containing a single benzene ring substituted with chloro groups at least two positions on the ring under conditions that separate ethylbenzene-enriched fractions. A process is disclosed for separating by extraction distillation.

U.S. Pat. No. 3,917,734 British Patent No. 1198592 U.S. Pat. No. 3,1050,017

The present invention relates to an alternative and improved process for the production of ethylbenzene by recovering ethylbenzene from a hydrocarbon mixture stream. The method includes distilling a mixture comprising ethylbenzene and a C8 aromatic compound in a distillation column operating at sub-atmospheric pressure in the presence of an extraction solvent.

The present invention relates to ethylbenzene and C8 in a distillation column operating at sub-atmospheric pressure in the presence of an extraction solvent.
The present invention relates to an extractive distillation method for separating ethylbenzene, which comprises a step of distilling a mixture containing an aromatic compound.

Ethylbenzene is usually contained in a hydrocarbon stream mainly containing C8 hydrocarbon compounds. The process according to the invention can effectively separate ethylbenzene from its near-boiling compounds, in particular C8 aromatics. In certain embodiments of the present invention, the at least one other C8 aromatic compound comprises a compound selected from p-xylene, m-xylene, o-xylene, and mixtures thereof. Mixtures are especially C5-C1 of both aromatic and non-aromatic types.
Other components in the 0 hydrocarbon range may also be included. For example, the mixture may contain small amounts of benzene, toluene, styrene, and C5-C10 paraffins, olefins or naphthenes. The sum of these other components in the mixture is preferably less than 20% by weight, more preferably less than 15% by weight, even more preferably less than 10% by weight and most preferably less than 5% by weight.

The solvent that can be used as the extraction solvent must be capable of changing the relative volatility of the components in the system of interest. In addition, the solvent should have an appropriate boiling point difference with the components in the feed stream in order to be conveniently recovered and recycled. The extraction solvent suitable for the present invention is:
It has a boiling point above 150 ° C, preferably 151-290 ° C. Many organic compounds are considered extraction solvents of the present invention, and in one embodiment, the extraction solvent is an organic compound selected from Cl-containing compounds, S-containing compounds, N-containing compounds, O-containing compounds and mixtures thereof. Including.

Cl-containing compounds are 2,4-dichlorobenzene, 1,2,4-trichlorobenzene, 1
, 2,4,5-tetrachlorobenzene, polychlorobenzene, benzene hexachloride,
Can be selected from 2,3,4,6-tetrachlorophenol, 1,2,3-trichloropropane and mixtures thereof, preferably 1,2,3-trichlorobenzene and 1,2,4-trichlorobenzene .

The S-containing compound can be selected from dimethyl sulfoxide, sulfolane, methyl sulfolane, and mixtures thereof.

N-containing compounds include N-formylmorpholine, aniline, 2-pyrrolidinone, quinolone,
It can be selected from N-methyl-2-pyrrolidone, N-methylaniline, benzonitrile, nitrobenzene and mixtures thereof.

O-containing compounds include methyl salicylate, methyl benzoate, N-methyl-2-pyrrolidone, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol,
Benzaldehyde, phenol, tetrahydrofurfuryl alcohol, diethyl maleate, ethyl acetoacetate, 4-methoxyacetophenone, isophorone, 5-methyl-
2-hexanone, 2-heptanone, cyclohexanone, 2-octanone, 2-nonanone,
It can be selected from 3-heptanone, diisobutyl ketone, 5-nonanone, benzyl alcohol and mixtures thereof.

The extraction solvent preferably contains a Cl-containing compound. More preferably, the extraction solvent is 1,
2,3-trichlorobenzene and 1,2,4-trichlorobenzene, most preferably 1,
A Cl-containing compound selected from 2,4-trichlorobenzene.

Surprisingly, it has been found that reducing the operating pressure of the distillation column to sub-atmospheric levels according to the present invention can significantly improve the efficiency of ethylbenzene separation. In particular,
Surprisingly, it has been found that operating a distillation column at sub-atmospheric pressure can achieve a high separation efficiency of ethylbenzene from a mixture comprising ethylbenzene and at least one other C8 aromatic compound. However, a vacuum pressure that is too low can result in a very high vapor flow rate and thus reduce the column packing or stage efficiency. In some embodiments, the subatmospheric pressure is 10
~ 900mbar, preferably 50-500mbar, more preferably 100-300m
The range of bar.

The more volatile fraction, in this case ethylbenzene, is distilled above the column and the less volatile fraction is distilled below the column, leading to the desired separation from the top of the column. The distillation column operates at a temperature distributed to the bottom. In a preferred embodiment, the distillation column is 50
It is operated at a temperature in the range of ~ 250 ° C, preferably 60-200 ° C, and even more preferably 70-180 ° C.

In the distillation column, the mass ratio of the extraction solvent to the mixture comprising ethylbenzene and at least one other C8 aromatic compound is preferably 1: 1 to 10: 1, preferably 2: 1 to 1.
8: 1, most preferably in the range 3: 1 to 7: 1.

Preferably, the method of the present invention can be operated in a hydrating environment. To create a hydrating environment, water and / or steam is preferably added based on the total flow of extraction solvent used.
, 1-25% by weight can be added to the distillation column.

In certain embodiments, additional solvents may be used to further alter the relative volatility of ethylbenzene and its near-boiling components to be separated by introduction into the distillation column. The additional solvent can be selected from Cl-containing, S-containing, N-containing and O-containing compounds or mixtures thereof. Preferably, the additional solvent is chloroform, carbon tetrachloride, dimethylamine, diethylamine, acetonitrile, acetaldehyde, 1-propanal, methyl isopropyl ketone, 3-methyl-2-pentanone, 3,3-dimethyl-2-butanone, It is selected from the group consisting of 2-pentanone, 2-methylpropanal, 1-butanal, cyclopentanone, acetone, ethanol and mixtures thereof. Usually, the additional solvent is introduced into the distillation column simultaneously with a mixture comprising ethylbenzene and at least one other C8 aromatic compound.

Embodiments of the present invention can further include removing a top stream rich in ethylbenzene from the top of the distillation column relative to the mixture entering the distillation column. This ethylbenzene rich stream can be sent directly to downstream processes that require ethylbenzene as a feedstock. In a more specific case, the ethylbenzene-rich stream may be subjected to another treatment, such as another purification, before entering any downstream industrial process that requires more purified ethylbenzene. In a preferred embodiment, at least a portion of the top stream enriched in ethylbenzene is condensed and returned to the distillation column as reflux. The concentration of ethylbenzene in the top stream can vary widely according to the operating conditions used.

The method of the present invention may further comprise the step of removing the bottom stream from the bottom of the distillation column. This bottom stream is preferably ethylbenzene lean and contains mainly the extraction solvent and the C8 aromatic compound heavier than ethylbenzene. The bottom stream is preferably subjected to a subsequence separation unit to recover the extraction solvent and produce a C8 aromatic product from this stream. The recovered extraction solvent is then recycled to the distillation column. In certain embodiments where the C8 aromatic compound includes a significant portion of p-xylene when optimized operating conditions are applied, the C8 aromatic product can include less than 20 wt% ethylbenzene. And can be further utilized as a mixed xylene isomer grade.

The present invention also provides for the distillation separation of ethylbenzene from a mixture comprising ethylbenzene and at least one other C ₈ aromatic compound to increase the efficiency of the separation, for example to reduce the reflux ratio. The use of sub-atmospheric pressure in the distillation column in the process of.

Embodiments of the invention will be further described in the following examples, without limiting the invention described in the claims.

Example 1
Using simulation software “Aspen HYSYS (registered trademark)”
A feed stream containing 64,93 wt% ethylbenzene, 7.9 wt% p-xylene, 18,14 wt% m-xylene and 9,02 wt% o-xylene is 1 at a feed rate of 15000 kg / h.
A computer simulation was performed to simulate feeding to an extractive distillation column having 30 stages. Various extraction solvents shown in Table 1 were introduced into the extractive distillation column at stage 7, ie above the feed stream introduction point in stage 74. As a comparative example, a simulation was conducted when no solvent was introduced. The operating temperature was simulated in the range of 75 ° C to 175 ° C along the tower. The pressure in the tower was simulated to be 200 mbar and 1000 mbar, respectively (see Table 1 below). The solvent weight ratio to the feed stream was fixed at 5: 1. The simulation model further included the feature that an ethylbenzene-rich stream was withdrawn at the top of the tower and an ethylbenzene-lean stream was withdrawn at the bottom of the tower. A portion of the ethylbenzene rich stream from the top of the column is refluxed with a reflux ratio of 8,
5 was simulated to be returned to the tower.

In Table 1 it can be seen that the pressure in the distillation column has been reduced from 1000 mbar to 200 mbar, ie to sub-atmospheric pressure, the process separation efficiency has been improved. In particular, when the pressure in the column is lowered, the concentration of ethylbenzene in the column top stream is significantly increased even when no solvent is used.

In Table 1 below, TCB is 1,2,4-trichlorobenzene and NMP is N-methyl-2.
-Pyrrolidone, NFM is N-formylmorpholine.

In Table 1 below, TCB is 1,2,4-trichlorobenzene, NMP is N-methyl-2-pyrrolidone, and NFM is N-formylmorpholine.
The present invention includes the following aspects.
[1]
A method for distilling and separating ethylbenzene from a mixture comprising ethylbenzene and at least one other C ₈ aromatic compound, comprising the step of distilling the mixture in a distillation column in the presence of an extraction solvent, Is operated at sub-atmospheric pressure.
[2]
The method according to [1] above, wherein the extraction solvent has a boiling point exceeding 150 ° C.
[3]
The method according to [1] or [2] above, wherein the extraction solvent comprises an organic compound selected from a Cl-containing compound, an S-containing compound, an N-containing compound, an O-containing compound, and a mixture thereof.
[4]
The Cl-containing compound is 2,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzene, benzenehexachloride, 2 , 3,4,6-tetrachlorophenol, 1,2,3-trichloropropane, The method according to [3] above.
[5]
The method according to [3] or [4] above, wherein the S-containing compound is selected from dimethyl sulfoxide, sulfolane, methyl sulfolane, and mixtures thereof.
[6]
From [3] above, wherein the N-containing compound is selected from N-formylmorpholine, aniline, 2-pyrrolidinone, quinolone, n-methyl-2-pyrrolidone, n-methylaniline, benzonitrile, nitrobenzene and mixtures thereof. [5] The method according to any one of [5].
[7]
The O-containing compound is methyl salicylate, methyl benzoate, n-methyl-2-pyrrolidone, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, benzaldehyde, phenol, tetrahydrofurfuryl alcohol, Diethyl maleate, ethyl acetoacetate, 4-methoxyacetophenone, isophorone, 5-methyl-2-hexanone, 2-heptanone, cyclohexanone, 2-octanone, 2-nonanone, 3-heptanone, diisobutyl ketone, 5-nonanone, benzyl alcohol And the method according to any one of [3] to [6] above, which is selected from these and mixtures thereof.
[8]
The method according to any one of [1] to [7], wherein the sub-atmospheric pressure is in the range of 10 to 900 mbar.
[9]
The method according to [8] above, wherein the sub-atmospheric pressure is in the range of 50 to 600 mbar.
[10]
The method according to any one of [1] to [9], wherein the distillation column is operated at a temperature in the range of 50 to 250 ° C.
[11]
Any one of [1] to [10] above, wherein a mass ratio of the extraction solvent to the mixture containing ethylbenzene and the at least one other C8 aromatic compound is in a range of 1: 1 to 10: 1. The method according to item.
[12]
[13] The above [1] to [11], wherein the at least one other C8 aromatic compound includes a compound selected from p-xylene, m-xylene, o-xylene, or a mixture thereof. the method of.
[13]
The method according to any one of [1] to [12], wherein the method includes a step of adding water and / or steam to the distillation column.
[14]
The method according to [13] above, wherein the water and / or steam is added in an amount of 0.1 to 25% by weight based on the total flow of the extraction solvent used.
[15]
Ethylbenzene, in a method for the distillative separation of ethylbenzene from a mixture comprising at least one other C ₈ aromatics, for increasing the efficiency of the separation, the use of sub-atmospheric pressure in the distillation column.

Claims (15)

A method for distilling and separating ethylbenzene from a mixture comprising ethylbenzene and at least one other C ₈ aromatic compound, comprising the step of distilling the mixture in a distillation column in the presence of an extraction solvent, Is operated at sub-atmospheric pressure.   The method of claim 1, wherein the extraction solvent has a boiling point greater than 150 ° C. The method according to claim 1 or 2, wherein the extraction solvent comprises an organic compound selected from a Cl-containing compound, an S-containing compound, an N-containing compound, an O-containing compound, and a mixture thereof. The Cl-containing compound is 2,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzene, benzenehexachloride, 2 , 3,4,6-tetrachlorophenol, 1,
4. A process according to claim 3, wherein the process is selected from 2,3-trichloropropane. The method according to claim 3 or 4, wherein the S-containing compound is selected from dimethyl sulfoxide, sulfolane, methyl sulfolane and mixtures thereof. 6. The N-containing compound is selected from N-formylmorpholine, aniline, 2-pyrrolidinone, quinolone, n-methyl-2-pyrrolidone, n-methylaniline, benzonitrile, nitrobenzene and mixtures thereof. The method as described in any one of. The O-containing compound is methyl salicylate, methyl benzoate, n-methyl-2-pyrrolidone, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, benzaldehyde, phenol, tetrahydrofurfuryl alcohol, Diethyl maleate, ethyl acetoacetate, 4-methoxyacetophenone, isophorone, 5-methyl-2-hexanone, 2-heptanone, cyclohexanone, 2-octanone, 2-nonanone, 3-heptanone, diisobutyl ketone, 5-nonanone, benzyl alcohol 7. A process according to any one of claims 3 to 6 selected from and mixtures thereof. The method according to claim 1, wherein the subatmospheric pressure is in the range of 10 to 900 mbar.   The method according to claim 8, wherein the subatmospheric pressure is in the range of 50 to 600 mbar. The process according to any one of the preceding claims, wherein the distillation column is operated at a temperature in the range of 50-250 ° C. 11. A mass ratio of the extraction solvent to the mixture comprising ethylbenzene and the at least one other C8 aromatic compound is in the range of 1: 1 to 10: 1. the method of. 12. A method according to any one of the preceding claims, wherein the at least one other C8 aromatic compound comprises a compound selected from p-xylene, m-xylene, o-xylene or mixtures thereof. 13. A method according to any one of claims 1 to 12, wherein the method comprises adding water and / or steam to the distillation column. Based on the total flow of the extraction solvent used, the water and / or steam is 0,1 to
14. A method according to claim 13 added in an amount of 25% by weight. Ethylbenzene, in a method for the distillative separation of ethylbenzene from a mixture comprising at least one other C ₈ aromatics, for increasing the efficiency of the separation, the use of sub-atmospheric pressure in the distillation column.