JP6824325B2 - Separation method for C8 aromatic mixture - Google Patents

Description

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

Ethylbenzene is a highly valued hydrocarbon compound that is widely used commercially. Ethylbenzene is mainly used in the production of styrene, which is an intermediate in polystyrene production. Ethylbenzene is commercially produced from the alkylation of benzene with ethylene. But,
The cost and competitive demand for ethylene and benzene are various Cs that already contain ethylbenzene.
8 Encouraged new efforts to recover ethylbenzene from aromatic feed streams. Such feed streams are generally produced as by-products from several petrochemical processes, and these feed streams are typically one with a boiling point close to that of ethylbenzene, as well as ethylbenzene, especially C8 aromatic isomers. Or more hydrocarbon compounds are included.

Methods for separating ethylbenzene from other near-boiling C8 aromatic compounds, especially xylene isomers, are known.

For example, US Pat. No. 3,917,734 discloses an adsorption separation process for separating ethylbenzene from a feed mixture containing ethylbenzene and at least one xylene isomer, which process adsorbs the feed mixture to crystalline aluminosilicate. It comprises a step of contacting with an agent to significantly remove ethylbenzene and selectively adsorbing the xylene isomer, followed by a step of recovering the purified ethylbenzene as a product. The separation efficiency of this process relies heavily on the adsorption capacity of the adsorbent, and therefore a complexed operation of the countercurrent moving floor system is preferred. Also, the impurity content in the feed stream needs to be carefully controlled to prevent interference with selective adsorption processes.

Of course, ethylbenzene can be separated from the xylene isomer by fractional distillation,
Fractionation is only possible in more complex and energy-intensive systems because their boiling points are so close to each other.

British Patent No. 1189592 discloses a process for separating C8 aromatic isomers using a single multifunction distillation column. This distillation is performed with at least 250, preferably 365 shelves and 100-25 to obtain commercially acceptable ethylbenzene purity.
This is done in a multi-stage tower with a reflux ratio of 0: 1.

Extractive distillation is a method of separating near-boiling compounds from each other by performing distillation in the presence of an added solvent or a so-called extractant. The presence of the extractant in the distillation system changes the specific volatility and thus can further increase the degree of separation of near-boiling compounds.

US Pat. No. 3,105,017 states that ethylbenzene from the xylene isomer in the presence of a compound containing a single benzene ring substituted with a chloro group at at least two positions on the ring under conditions that separate ethylbenzene-rich fractions. Is disclosed as a process for separating benzene by extraction distillation.

U.S. Pat. No. 3,917,734 British Patent No. 1198592 U.S. Pat. No. 3,105,017

The present invention relates to an alternative and improved method for the production of ethylbenzene by recovering ethylbenzene from the flow of hydrocarbon mixtures. The method comprises the step of distilling a mixture containing ethylbenzene and a C8 aromatic compound in a distillation column operating at quasi-atmospheric pressure in the presence of an extraction solvent.

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

Ethylbenzene is usually contained in a hydrocarbon stream predominantly containing a C8 hydrocarbon compound. The method according to the invention can effectively separate ethylbenzene from its near boiling point compounds, especially C8 aromatic compounds. In certain embodiments of the invention, at least one other C8 aromatic compound comprises a compound selected from p-xylene, m-xylene, o-xylene and mixtures thereof. The mixture is, in particular, both aromatic and non-aromatic types of C5-C1.
Other components in the range of 0 hydrocarbons may be further included. For example, the mixture may contain small amounts of benzene, toluene, styrene, and C5-C10 paraffin, olefins or naphthenes. The total 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, most preferably less than 5% by weight.

The solvent that can be used as the extraction solvent must be able to change the specific volatilization of the components in the system of interest. In addition, the solvent should have an appropriate boiling point difference from the components in the feed stream for convenient recovery and recirculation. An 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 as 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, benzenehexachlorolide,
It 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, quinolones,
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 acetophenone, 4-methoxyacetophenone, isophorone, 5-methyl-
2-hexanone, 2-heptanone, cyclohexanone, 2-octanone, 2-nonanone,
You can choose from 3-heptanone, diisobutylketone, 5-nonanonone, 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,
Contains Cl-containing compounds selected from 2,4-trichlorobenzene.

Surprisingly, it has been found that reducing the operating pressure of the distillation column to quasi-atmospheric levels according to the present invention can significantly improve the efficiency of ethylbenzene separation. In particular,
Surprisingly, it was found that operating the distillation column at quasi-atmospheric pressure could achieve high separation efficiency of ethylbenzene from a mixture containing ethylbenzene and at least one other C8 aromatic compound. However, a vacuum pressure that is too low can result in extremely high steam flow rates and thus reduced column filling or stage efficiency. In one embodiment, the quasi-atmospheric pressure is 10
~ 900mbar, preferably 50 ~ 500mbar, more preferably 100 ~ 300m
It is 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 top to bottom of the column. The distillation column operates at the 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 to 200 ° C., and even more preferably 70 to 180 ° C.

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

Preferably, the method of the invention can be operated in a hydrated environment. To create a hydrated environment, water and / or steam is preferably zero based on the overall flow of the 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 specific volatilization of ethylbenzene and its near boiling components to be separated by introduction into a 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-propanol, 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 containing ethylbenzene and at least one other C8 aromatic compound.

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

The method of the present invention can further include the step of extracting the bottom stream from the bottom of the distillation column. This bottom stream is preferably ethylbenzene lean and mainly contains an extraction solvent and a C8 aromatic compound heavier than ethylbenzene. It is preferable to run the bottom stream through a subsequence separation unit to recover the extraction solvent and generate a C8 aromatic product from this stream. The recovered extraction solvent is then recirculated to the distillation column. In certain embodiments where the C8 aromatic compound contains a significant portion of p-xylene when optimized operating conditions are applied, the C8 aromatic product can contain less than 20% by weight ethylbenzene. It can be further utilized as a mixed xylene isomer grade.

The present invention is, for example, as it is possible to reduce the reflux ratio, for increasing the efficiency of the separation, ethylbenzene and, for distillation separation of ethylbenzene from a mixture comprising at least one other C ₈ aromatics Regarding the use of quasi-atmospheric pressure in a distillation column in the above method.

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

Example 1
Using the simulation software "Aspen HYSYS®",
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 supply of 15000 kg / h.
A computer simulation was performed simulating the supply to an extraction distillation column having 30 stages. The various extraction solvents shown in Table 1 were introduced into the extraction distillation column at stage 7, i.e., above the introduction point of the feed stream in stage 74. As a comparative example, a simulation was carried out when no solvent was introduced. The operating temperature was simulated in the range of 75 ° C to 175 ° C along the tower. The pressures in the column were simulated to be 200 mbar and 1000 mbar, respectively (see Table 1 below). The weight ratio of solvent to feed stream was fixed at 5: 1. The simulation model also included the feature that the ethylbenzene-rich stream was extracted at the top of the column and the ethylbenzene lean stream was extracted at the bottom of the column. Part of the ethylbenzene-rich stream from the top of the column has a reflux ratio of 8, as reflux.
Simulated to be returned to the tower at 5.

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

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]
And ethylbenzene, comprising the step of distilling a method for distillative separation of ethylbenzene from a mixture comprising at least one other C ₈ aromatics, the presence of the extraction solvent, the mixture in the distillation column, said distillation column A method characterized by being operated at quasi-atmospheric pressure.
[2]
The method according to the above [1], wherein the extraction solvent has a boiling point of more than 150 ° C.
[3]
The method according to the above [1] or [2], wherein the extraction solvent contains a Cl-containing compound, an S-containing compound, an N-containing compound, an O-containing compound, and an organic compound selected from a mixture thereof.
[4]
The Cl-containing compounds are 2,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzene, benzenehexachlorolide, 2 , 3,4,6-tetrachlorophenol, 1,2,3-trichloropropane, the method according to the above [3].
[5]
The method according to [3] or [4] above, wherein the S-containing compound is selected from dimethyl sulfoxide, sulfolane, methyl sulfolane and a mixture thereof.
[6]
From the above [3], 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 according to any one of [5].
[7]
The O-containing compound is methyl salicylate, methylbenzoate, n-methyl-2-pyrrolidone, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, benzaldehyde, phenol, tetrahydrofurfuryl alcohol, Diethylmaleate, ethylacetoacetate, 4-methoxyacetophenone, isophorone, 5-methyl-2-hexanone, 2-heptanone, cyclohexanone, 2-octanone, 2-nonanone, 3-heptanone, diisobutylketone, 5-nonanone, benzyl alcohol And the method according to any one of the above [3] to [6], which is selected from a mixture thereof.
[8]
The method according to any one of the above [1] to [7], wherein the quasi-atmospheric pressure is in the range of 10 to 900 mbar.
[9]
The method according to [8] above, wherein the quasi-atmospheric pressure is in the range of 50 to 600 mbar.
[10]
The method according to any one of the above [1] to [9], wherein the distillation column is operated at a temperature in the range of 50 to 250 ° C.
[11]
Any one of the above [1] to [10], wherein the mass ratio of the extraction solvent to the mixture containing ethylbenzene and the at least one other C8 aromatic compound is in the range of 1: 1 to 10: 1. The method described in the section.
[12]
The item according to any one of [1] to [11] above, wherein the at least one other C8 aromatic compound comprises 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 the above [1] to [12], wherein the method comprises 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 overall 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 (10)

And ethylbenzene, a method for distillative separation of ethylbenzene from a mixture comprising at least one other C ₈ aromatics,
Water and / or steam with chloroform, carbon tetrachloride, dimethylamine, diethylamine, acetonitrile, acetaldehyde, 1-propanol, methyl isopropyl ketone, 3-methyl-2-pentanone, 3,3-dimethyl-2-butanone, 2 -The step of adding a solvent to the distillation column containing one or more selected from the group consisting of pentanone, 2-methylpropanol, 1-butanal, cyclopentanone, acetone, ethanol and mixtures thereof, and above 150 ° C. Including the step of distilling the mixture in the distillation column in the presence of an extraction solvent having a boiling point.
The mass ratio of the extraction solvent to the mixture is 3: 1 to 7: 1.
A method characterized in that the distillation column is operated at a temperature in the range of 70 to 180 ° C. at a quasi-atmospheric pressure in the range of 50 to 500 mbar. The method according to claim 1, wherein the extraction solvent contains a Cl-containing compound, an S-containing compound, an N-containing compound, an O-containing compound, and an organic compound selected from a mixture thereof. The Cl-containing compounds are 2,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzene, benzenehexachlorolide, 2 , 3, 4,6-Tetrachlorophenol, 1,2,3-trichloropropane and mixtures thereof, according to claim 2. The method according to claim 2 or 3, wherein the S-containing compound is selected from dimethyl sulfoxide, sulfolane, methyl sulfolane and mixtures thereof. The N-containing compound is selected from N-formylmorpholine, aniline, 2-pyrrolidinone, quinolone, n-methyl-2-pyrrolidone, n-methylaniline, benzonitrile, nitrobenzene and mixtures thereof, claims 2-4. The method according to any one of the above. The O-containing compound is methyl salicylate, methylbenzoate, n-methyl-2-pyrrolidone, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, benzaldehyde, phenol, tetrahydrofurfuryl alcohol, Diethylmalate, ethylacetoacetate, 4-methoxyacetophenone, isophorone, 5-methyl-2-hexanone, 2-heptanone, cyclohexanone, 2-octanone, 2-nonanone, 3-heptanone, diisobutylketone, 5-nonanone, benzyl alcohol The method according to any one of claims 2 to 5, which is selected from the mixture thereof. The method according to any one of claims 1 to 6, wherein the quasi-atmospheric pressure is in the range of 100 to 300 mbar. Wherein the at least one other C ₈ aromatics, p- xylene, m- xylene, is selected from o- xylene or a mixture thereof containing compounds The method according to any one of claims 1 7 .. The method of any one of claims 1-8, wherein the water and / or steam is added in an amount of 0.1 to 25% by weight based on the overall flow of the extraction solvent used. The extraction compounds are 2,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzene, benzenehexachlorolide, 2, Cl-containing compounds selected from 3,4,6-tetrachlorophenol and 1,2,3-trichloropropane, S-containing compounds, N-containing compounds, O-containing compounds, and organic compounds selected from mixtures thereof. The method according to any one of claims 1 to 9, which includes.