JP2019151644A - Process for enhanced separation of ethylbenzene - Google Patents

Abstract

To provide a process for enhanced distilled separation of ethylbenzene from a mixture comprising ethylbenzene and at least one other C8 aromatic compound which allows ethylbenzene to be obtained with high purity and achieves a high separation efficiency.SOLUTION: A process comprises the steps of: introducing a feed stream 11 comprising a mixture comprising ethylbenzene and at least one other C8 aromatic compound into a first distillation column 10; introducing a first stream 12 comprising a heavy solvent above the feed stream into the first distillation column; and introducing an aqueous stream 13 below the feed stream into the first distillation column.SELECTED DRAWING: Figure 1

Description

The present invention relates to a process for the distillation separation of ethylbenzene from a mixture comprising ethylbenzene and at least one other C ₈ 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 can be obtained from an alkylation reaction between benzene and ethylene. An alternative method for producing ethylbenzene is to recover ethylbenzene from a hydrocarbon mixture containing ethylbenzene, which is generally produced as a by-product stream from several petrochemical processes. Hydrocarbon mixtures containing ethylbenzene are usually ethylbenzene, in particular C8.
Also included are one or more hydrocarbon compounds having a boiling point close to that of the aromatic isomer.

The separation of near-boiling compounds usually requires a more sophisticated process than conventional distillation. Extractive distillation is one of the techniques developed for this purpose. Extractive distillation has been applied in industrial processes. And it is becoming an increasingly important separation method in the petrochemical industry. The main feature of extractive distillation is that a high boiling point solvent is usually added as an extractant to the mixture of components to be separated to increase the relative volatility of the target component.

Specific volatility is a measure of the difference between the vapor pressure of the more volatile components and the vapor pressure of the less volatile components in the liquid mixture. Specific volatility indicates the degree of separability of two components in a mixture. In addition to changing the specific volatility, it should also be possible for the extractant to be easily separable from the distillation product, i.e. it is desirable that the boiling point difference between the extractant and the components to be separated is large. Extractants play an important role in the design of extractive distillation. Therefore, the selection of a suitable extractant is extremely important for an effective and economical design.

Attempts have been made to separate ethylbenzene from hydrocarbon mixtures. British Patent 11985
No. 92 describes a process for separating C8 aromatic isomers using a single multifunctional distillation column. This distillation is carried out in a multistage column having at least 250, preferably 365 plates and a reflux ratio of 100: 1 to 250: 1, in order to obtain a highly pure ethylbenzene product. Large distillation columns are known to be expensive to build and consume large amounts of energy during operation.

U.S. Pat. No. 3,1050,017 describes a C8 aromatic hydrocarbon 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 method for separating the mixture by distilling the mixture is described. However, this method does not increase the separation efficiency.

U.S. Pat. No. 4,299,668 describes the use of p-xylene and / or m-
A method for separating ethylbenzene from xylene is described. Pentachlorophenol occurs as a white crystalline solid at room temperature with a high melting point and is therefore US Pat.
The 299668 process requires additional steps and energy to dissolve it in a suitable solvent before using pentachlorophenol as an extractant. Furthermore, pentachlorophenol from acute ingestion and inhalation exposure is extremely toxic to humans.

U.S. Pat. No. 5,425,855 discloses the use of 5-methyl-2-hexanone as an extractant in distillation. This agent has been shown to improve the relative volatility of ethylbenzene relative to p-xylene and to allow separation of ethylbenzene from p-xylene by rectification.

However, ethylbenzene, at least one other C ₈ aromatics, such as o- xylene, p- xylene, m- xylene or improved process for the distillation separation of ethylbenzene from a mixture comprising these mixtures There is still a need.

British Patent No. 1198592 U.S. Pat. No. 3,1050,017 US Pat. No. 4,299,668 US Pat. No. 5,425,855

Therefore, an object of the present invention makes it possible to obtain ethylbenzene in high purity, high to realize separation efficiency, ethylbenzene and, improved distillation of ethylbenzene from a mixture comprising at least one other C ₈ aromatics Is to provide a way for.

Another object of the present invention is to increase the relative volatility between ethylbenzene and xylene in a distillation fractionation process.

Furthermore, it is an object of the present invention to be simple and cost-effective to implement, avoiding or at least reducing the use of harmful substances as much as possible.

The present invention, the above object is, and ethylbenzene, on the surprising finding that achieved by extractive distillation method aqueous stream below the feed stream comprising a mixture of at least one other C ₈ aromatics is introduced Is based.

The present invention is therefore a process for the distillation separation of ethylbenzene from a mixture comprising ethylbenzene and at least one other C ₈ aromatic compound, comprising:
a) introducing a feed stream comprising said mixture into a first distillation column;
b) introducing a first stream comprising a heavy solvent above the feed stream into the first distillation column;
c) introducing an aqueous stream into the first distillation column below the feed stream.

Of course, while carrying out the method of the invention, steps a) to c) are performed simultaneously for at least most of the time.

In the method of the present invention, a mixture of ethylbenzene and at least one other C ₈ aromatics, it is introduced into the first distillation column of step a) as the feed stream. The ethylbenzene content of the mixture may vary over a wide range. However, very low ethylbenzene content can make the process less economically attractive.

In one embodiment, the mixture is 5 to 99% by weight ethylbenzene, preferably 1
It contains 0-95 wt% ethylbenzene, more preferably 10-85 wt% ethylbenzene.

  The feed stream can be introduced, for example, in the middle part of the first distillation column.

Feed stream contains ethylbenzene and at least one other C ₈ aromatics.

At least one other C ₈ aromatics, preferably, p- xylene, are selected from m- xylene, o- xylene and mixtures thereof.

Preferably, the entire feed to the column enters as one feed stream into the column, i.e. as the feed stream of step a).

The first stream being introduced into the first distillation column contains or preferably consists of a heavy solvent. The term “heavy solvent” also applies to a mixture of compounds that are considered heavy solvent (s) and then represents the whole of such compounds.

The term “heavy solvent” as used herein generally refers to a solvent having a boiling point higher than that of at least one other C ₈ aromatic compound. The heavy solvent preferably has a boiling point in excess of 150 ° C, more preferably in the range of 151-290 ° C.

  The first stream is introduced into the first distillation column above the feed stream in step b).

For example, if the feed stream is introduced into the middle part of the first distillation column, the first stream is introduced at the top of the column.

The heavy solvent preferably comprises or consists of at least one Cl, S, N or O containing compound or a mixture thereof.

The Cl-containing compound is preferably 2,4-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzene, benzenehexachloride, 2,3,4,6- Selected from tetrachlorophenol, 1,2,3-trichloropropane and mixtures thereof, more preferably selected from 1,2,4-trichlorobenzene and 1,2,3-trichlorobenzene.

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

The N-containing compound is preferably selected from N-formylmorpholine, aniline, 2-pyrrolidinone, quinoline, n-methyl-2-pyrrolidone, n-methylaniline, benzonitrile, nitrobenzene and mixtures thereof.

The O-containing compound is preferably methyl salicylate, methyl benzoate, n-methyl-2-pyrrolidone, 1,2-propanediol (propylene glycol), 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, Selected from 5-nonanone, benzyl alcohol and mixtures thereof.

  The aqueous stream is introduced below the feed stream into the first distillation column in step c).

For example, if the feed stream is introduced into the middle part of the first distillation column, the aqueous stream is introduced at the bottom of the column.

The aqueous stream preferably contains water and / or steam, or consists of water and / or steam, more preferably contains water or consists of water.

The amount of aqueous stream introduced into the distillation column in step c) is preferably such that the mass feed of the aqueous stream is from 0.5 to 25% by weight, more preferably based on the mass feed of heavy solvent to the distillation column. The amount is 1 to 20% by weight, even more preferably 2 to 15% by weight, and most preferably 4 to 10% by weight.

In an embodiment of the invention, the aqueous stream comprises or consists of water and at least one light solvent selected from Cl, S, N or O containing compounds and mixtures thereof.

The term “light solvent” as used herein generally refers to a solvent having a boiling point lower than that of at least one other C ₈ aromatic compound and lower than that of ethylbenzene. The term “light solvent” also applies to a mixture of compounds considered as light solvent (s), and then represents the whole of such compounds.

The light solvent is preferably less than 135 ° C, more preferably less than 130 ° C, even more preferably less than 125 ° C, even more preferably less than 120 ° C, most preferably 11
Has a boiling point of less than 0 ° C.

The Cl-containing compound is preferably selected from chloroform, carbon tetrachloride and mixtures thereof.

The N-containing compound is preferably selected from dimethylamine, diethylamine, acetonitrile and mixtures thereof.

The O-containing compound is preferably acetaldehyde, 1-propanal, methyl isopropyl ketone, 3-methyl-2-pentanone, 3,3-dimethyl-2-butanone, 2-pentanone, 2-methylpropanal, 1-butanal , Cyclopentanone, acetone, ethanol and mixtures thereof.

The method of the present invention, ethylbenzene and at least one other C ₈ aromatics, such as o- xylene, are not limited to the separation of ethylbenzene from p- xylene and m- xylene or mixture containing a mixture thereof.

In certain embodiments of the methods of the invention, ethylbenzene and at least one other C
_The mixture comprising ₈ aromatic compounds further comprises at least one non-aromatic compound and / or at least one other aromatic compound.

The at least one non-aromatic compound can be a paraffin, olefin, naphthalene or other aliphatic hydrocarbon. Preferably, the at least one non-aromatic compound is a C7-C11 non-aromatic compound such as isopropylcyclopentane, 2,4,4-trimethylhexane, 2,2-dimethylheptane, cis-1,2-dimethylcyclohexane, 1,1,4-trimethylcyclohexane, 2,3,4-trimethylhexane, 1,3
, 4-trimethylcyclohexane, 2,3-dimethylheptane, 3,5-dimethylheptane, 3,4-dimethylheptane, 2-methyloctane, 3-methyloctane, 1-ethyl-4-methylcyclohexane, ethylcyclohexane, trans 2-nonene, isobutylcyclopentane, 3-ethyl-4-methyl-3-hexene, n-nonane, cis-1
-Selected from methyl-3-ethylcyclohexane, cyclooctane, isopropylhexane and mixtures thereof.

The at least one other aromatic compound can be benzene, toluene, styrene or a mixture thereof.

Also, in certain embodiments, a mixture comprising ethylbenzene and at least one other C8 aromatic compound enters the first distillation column to prepare a feed stream that is more suitable for the process of the present invention. You may pass a pre-processing process before. The pretreatment step may include, for example, separation of a heavy hydrocarbon compound having 9 or more carbon atoms.

The first distillation column is preferably from 100 mbar to 1100 mbar, more preferably 1
It is operated at a pressure of 40 mbar to 900 mbar, even more preferably 180 to 700 mbar, most preferably 200 to 500 mbar.

The temperature in the first distillation column is preferably 50 ° C to 250 ° C, more preferably 60 ° C to 2 ° C.
It is 00 degreeC, More preferably, it is 70 degreeC-180 degreeC.

The amount of heavy solvent introduced into the distillation column in step b) should be large enough to improve the relative volatility of ethylbenzene relative to at least one other C8 aromatic.

The amount of heavy solvent stream introduced into the distillation column in step b) is preferably the mass feed ratio of heavy solvent to feed, i.e. the total amount of heavy solvent stream relative to the total mass of feed stream introduced into the first distillation column. Mass ratio is 1: 1 to 10: 1, more preferably 2: 1
An amount such that it is ˜8: 1, even more preferably 3: 1 to 7: 1.

In a preferred embodiment, the process according to the invention comprises a step d) in which a second stream enriched in ethylbenzene is taken from the first distillation column, usually from the top or the top of the column. The recovery of ethylbenzene, defined as the ratio of ethylbenzene in the second stream to ethylbenzene in the feed stream, is preferably greater than 1, more preferably greater than 1,5, more preferably greater than 2, even more preferably Is greater than 2, 5 and even more preferably 3
Larger, most preferably greater than 3,5. Usually this ratio is not greater than 50.

The second stream or overhead stream may further comprise water and a light solvent. In such a case, the process according to the invention preferably further comprises a step f) of separating ethylbenzene from the water and light solvent present in the second stream of step d). This can be done, for example, by phase separation in a decanter and / or distillation separation in another distillation column after the overhead stream has been removed.

In a further preferred embodiment, the process according to the invention comprises a step in which a third stream rich in at least one other C8 aromatic compound and further comprising a heavy solvent is taken from the column, usually from the bottom or the bottom of the column. e).

In one embodiment of the method of the present invention, a second distillation column is used. This second column is also called a solvent recovery column. In this embodiment, the method preferably comprises treating the pre-removed third stream of step e) in a second distillation column to separate at least one other C8 aromatic from the heavy solvent. Step g).

For efficiency reasons, the stream can be recovered and recycled in the process of the present invention. For example, the stream taken from the separation unit of step e) and / or the second distillation column of step g) can be recycled into the first distillation column. Preferably, water and / or heavy solvent and / or light solvent are recycled to the first distillation column.

The term “reflux ratio” as used herein is defined as the ratio of reflux to distillate stream. Preferably, in the first distillation column of the process of the invention, 1-30, more preferably 2
A reflux ratio of 25, more preferably 4-20, most preferably 5-15 is applied.

The invention also increases the efficiency of separation in the distillation separation of ethylbenzene from an aqueous stream introduced below a feed stream comprising a mixture of ethylbenzene and at least one other C ₈ aromatic compound. For use.

The invention is further illustrated by the example described below and by reference to the following figures.

2 illustrates an exemplary process flow scheme according to one embodiment of the present invention.

Extractive Distillation Process Scheme An exemplary process flow scheme for simulating a method according to one embodiment of the present invention is described below with reference to FIG.

The three streams are introduced into the extractive distillation column 10, also called the first distillation column. The interior of the first distillation column can be variously selected to obtain the desired efficiency, for example the distillation column may be filled with several packed beds or trays.

A feed stream 11 comprising a mixture comprising ethylbenzene and at least one other C8 aromatic is introduced via a conduit into the column 10, for example in the middle part of the column. The temperature of the mixture may be adjusted as necessary, for example using a heat exchanger. At the same time, a first stream 12 containing a heavy solvent and an aqueous stream 13 containing water are introduced into the first distillation column 10 via two respective conduits. The first stream 12 is introduced above the feed stream 11, for example at the top of the tower 10, while the aqueous stream 13 is simultaneously introduced below the feed stream 11, for example at the bottom of the tower 10.

The heavy solvent preferentially produces a higher boiling mixture with at least one other C8 aromatic compound and is distilled below the first distillation column 10, while having a low affinity with the heavy solvent, Lighter boiling ethylbenzene is distilled above the column.

A second stream 14 containing ethylbenzene, water, and optionally a light solvent is removed from the top or top of the first column. This second stream can be introduced into the phase separator 20, where the ethylbenzene is separated from the water. The stream containing the separated ethylbenzene, also referred to as the ethylbenzene rich stream, may then be recirculated as a reflux 21 into the first distillation column or simply transferred to the storage 22. . The separated water can be further used or an aqueous stream 23 in the first distillation column 10 as shown in FIG.
Can also be recycled.

A third stream 15 comprising a heavy solvent and at least one other C8 aromatic compound is withdrawn from the bottom of the first column 10. This third stream 15 may contain a small amount and even a small amount of ethylbenzene. The third stream can be introduced into a solvent recovery tower 30, also called a second distillation tower. There, at least one other C8 aromatic compound is separated from the heavy solvent. A heavy solvent is removed from the bottom of the solvent recovery tower 30 and can be recycled as a first stream 32 into the first distillation tower 10.

From the top of the solvent recovery column 30, a stream 31 containing at least one other C8 aromatic compound and possibly a small amount of ethylbenzene is removed. This flow is also called ethylbenzene lean flow.

Additional equipment, such as heat exchangers, pumps, or compressors, may be added at any suitable location in the process system to properly adjust the process conditions. The appropriate dimensions and configuration of all equipment in the process can be varied by those skilled in the art to suit the exact composition of the feed stream, the extractant and the specific operating conditions used.

  Embodiments of the invention are further described in the following examples.

Example 1
Using simulation software “Aspen HYSYS (registered trademark)”
14,66 wt% ethylbenzene, 20,21 wt% p-xylene, 43,35 wt% m
A computer simulation was performed to simulate a feed stream comprising xylene and 21,78 wt% o-xylene being fed to an extractive distillation column having 18 stages at a feed rate of 133 g / min. The various solvents shown in Table 1 were introduced into the extractive distillation column at stage 2, ie above the feed stream introduction point in stage 10. 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 was simulated as being returned to the column as reflux at a reflux ratio of 10. To show the effect of adding water to the tower, above the feed stream (
Simulating the introduction of water at a feed rate of 36 g / min respectively in the “upper water”) and lower (“lower water”). For comparison, it was also simulated that no water was introduced into the tower. The results are shown in Table 1 below. In Table 1, the introduction of water into the system is the operating pressure 20
It can be seen that at 0 mbar and 1000 mbar respectively, the separation efficiency of the process is improved for all solvents used. In the tower top stream taken from the top of the tower,
It became clear that higher ethylbenzene content was obtained ("EB concentration at the top")
. In particular, higher efficiency was seen when water was introduced at a position below the point of introduction of the feed stream according to the present invention ("downward water").

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

Claims (16)

A process for distilling off ethylbenzene from a mixture comprising ethylbenzene and at least one other C ₈ aromatic compound, comprising:
a) introducing a feed stream comprising said mixture into a first distillation column;
b) introducing into the first distillation column a first stream comprising a heavy solvent above the feed stream;
c) introducing an aqueous stream into the first distillation column below the feed stream. The method of claim 1, wherein the heavy solvent comprises at least one Cl, S, N or O-containing compound and mixtures thereof. The Cl-containing compound is 2,4-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzene, benzenehexachloride, 2,3,4,6-tetrachloro. 3. Process according to claim 2, selected from phenol, 1,2,3-trichloropropane and mixtures thereof, preferably 1,2,4-trichlorobenzene and 1,2,3-trichlorobenzene. 4. A process according to claim 2 or 3, wherein the S-containing compound is selected from dimethyl sulfoxide, sulfolane, methyl sulfolane and mixtures thereof. 5. The N-containing compound is selected from N-formylmorpholine, aniline, 2-pyrrolidinone, quinoline, 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 (propylene glycol), 1,2-butanediol, 1,3-butanediol, benzaldehyde, phenol, tetrahydro Furfuryl alcohol, diethyl maleate, ethyl acetoacetate, 4-methoxyacetophenone, isophorone, 5-methyl-2-hexanone, 2-heptanone, cyclohexanone, 2
6. The method according to any one of claims 2 to 5, selected from: -octanone, 2-nonanone, 3-heptanone, diisobutyl ketone, 5-nonanone, benzyl alcohol and mixtures thereof.   7. A method according to any one of claims 1 to 6, wherein the aqueous stream is water and / or steam. 8. A method according to any one of the preceding claims, wherein the aqueous stream comprises water and at least one light solvent selected from Cl, S, N or O containing compounds and mixtures thereof. 9. The method of claim 8, wherein the Cl-containing light solvent compound is selected from chloroform, carbon tetrachloride, and mixtures thereof. The method according to claim 8 or 9, wherein the N-containing light solvent compound is dimethylamine, diethylamine, acetonitrile, or a mixture thereof. The O-containing light solvent compound is acetaldehyde, 1-propanal, methyl isopropyl ketone, 3-methyl-2-pentanone, 3,3-dimethyl-2-butanone,
11. A process according to any one of claims 8 to 10 selected from 2-pentanone, 2-methylpropanal, 1-butanal, cyclopentanone, acetone, ethanol and mixtures thereof. Wherein the at least one other C ₈ aromatics, p- xylene, m- xylene, is selected from o- xylene and mixtures thereof, The method according to any one of claims 1 to 11. The mass feed of the aqueous stream is 0.5-25 based on the mass feed of the heavy solvent.
13. The method according to any one of claims 1 to 12, wherein the method is% by weight. The mass supply ratio of heavy solvent to said supply is from 1: 1 to 10: 1.
14. The method according to any one of 13 to 13. 15. A method according to any one of claims 1 to 14, comprising
d) removing a second stream enriched in ethylbenzene from the first distillation column. And ethylbenzene, the aqueous stream is introduced below the feed stream comprising a mixture of at least one other C ₈ aromatics, in the distillation separation of ethylbenzene from the mixture, used to increase the efficiency of the separation.