PROCESS FOR THE ENHANCED SEPARATION OF ETHYLBENZENE

Abstract

A process for the distillative separation of ethylbenzene from a mixture comprising ethylbenzene and at least one other C8 aromatic compound, comprising introducing a feed stream comprising said mixture into a first distillation column, introducing a first stream comprising a heavy solvent above the feed stream into the first distillation column, introducing an aqueous stream below the feed stream into the first distillation column.

Claims

1. A process for the distillative separation of ethylbenzene from a mixture comprising ethylbenzene and at least one other C.sub.8 aromatic compound selected from the group consisting of p-xylene, m-xylene, o-xylene, and mixtures thereof, the process 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 below the feed stream into the first distillation column.

2. The process according to claim 1, wherein the heavy solvent comprises at least one Cl, S, N or O-containing compounds, or mixtures thereof.

3. The process according to claim 2, wherein the Cl-containing compound is selected from the group consisting of 2,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzene, polychlorobenzenes, benzene hexachloride, 2,3,4,6-tetrachlorophenol, 1,2,3-trichloropropane, and mixtures thereof.

4. The process according to claim 2, wherein the S-containing compound is selected from the group consisting of dimethylsulfoxide, sulfolane, methyl sulfolane, and mixtures thereof.

5. The process according to claim 2, wherein the N-containing compound is selected from the group consisting of N-formylmorpholine, aniline, 2-pyrrolidinone, quinoline, n-methyl-2-pyrrolidone, n-methylaniline, benzonitrile, nitrobenzene, and mixtures thereof.

6. The process according to claim 2, wherein the O-containing compound is selected from the group consisting of methyl salicylate, methylbenzoate, n-methyl-2-pyrrolidone, 1,2-propanediol (propylene glycol), 1,2-butanediol, 1,3-butanediol, benzaldehyde, phenol, tetrahydrofurfuryl alcohol, diethyl maleate, ethyl acetoacetate, 4-methoxy acetophenone, isophorone, 5-methyl-2-hexanone, 2-heptanone, cyclohexanone, 2-octanone, 2-nonanone, 3-heptanone, diisobutyl ketone, 5-nonanone, benzyl alcohol, and mixtures thereof.

7. The process according to claim 1, wherein the aqueous stream includes steam.

8. The process according to claim 1, wherein the aqueous stream comprises water and at least one light solvent selected from Cl, S, N or O-containing compound and mixtures thereof.

9. The process according to claim 1, wherein the Cl-containing light solvent compound is selected from the group consisting of chloroform, carbon tetrachloride, and mixtures thereof.

10. The process according to claim 1, wherein the N-containing light solvent compound includes dimethylamine, diethylamine, acetonitrile, and mixtures thereof.

11. The process according to claim 1, wherein the O-containing light solvent compound is selected from the group consisting of 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.

12. (canceled)

13. The process according to claim 1, wherein the mass feed of the aqueous stream is from 0.5 to 25 wt % based on a mass feed of the heavy solvent.

14. The process according to claim 1, wherein the mass feed ratio of heavy solvent to the feed is from 1:1 to 10:1.

15. The process according to claim 1, further comprising: d) withdrawing a second stream enriched in ethylbenzene from the first distillation column

16. (canceled)

17. The process according to claim 1 wherein the heavy solvent is selected from one or more aromatic solvents.

18. The process according to claim 3, wherein the Cl-containing compound is selected from the group consisting of 1,2,4-trichlorobenzene, 1,2,3-trichlorobenzene, and mixtures thereof.

19. A process for the distillative separation of ethylbenzene from a mixture comprising ethylbenzene and at least one other Cg aromatic compound, the process 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; and c) introducing an aqueous stream below the feed stream into the first distillation column, the aqueous stream having a mass feed from 5 wt % to 25 wt % based on a mass feed of the heavy solvent.

20. The method of claim 19 wherein the mass feed of the aqueous stream is from 5 wt % to 10 wt % based on the mass feed of the heavy solvent.

Description

[0060] The present invention will be further illustrated by an example described below, and by reference to the following FIGURE:

[0061] FIG. 1 shows a typical process flow scheme in accordance with one embodiment of the present invention.

EXTRACTIVE DISTILLATION PROCESS SCHEME

[0062] An exemplary process flow scheme for simulating the process according to one embodiment of this invention will be explained hereinunder by reference to FIG. 1.

[0063] Three streams are introduced into an extractive distillation column 10, which is also referred to as first distillation column. The internal of the first distillation column can be variously chosen to get a desired efficiency, for example the distillation column may be filled with a number of packed beds or trays.

[0064] A feed stream 11 comprising a mixture comprising ethylbenzene and at least one other C8 aromatic compound is introduced into the column 10 via a conduit, for instance in a middle portion of the column. The temperature of the mixture may be adjusted as needed, for instance using a heat exchanger. Simultaneously, a first stream 12 comprising a heavy solvent and an aqueous stream 13 comprising 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 instance in an upper portion of the column 10, whereas the aqueous stream 13 is simultaneously introduced below the feed stream 11, for instance in a lower portion of the column 10.

[0065] The heavy solvent will preferentially form a higher boiling point mixture with the at least one other C8 aromatic compound and be distilled down the first distillation column 10, whereas the lighter boiling ethylbenzene which has less affinity with the heavy solvent will be distilled up the column.

[0066] From the top or upper part of the first column a second stream 14 comprising ethylbenzene, water and optionally light solvent, is withdrawn. This second stream can be introduced into a phase separator 20, wherein the ethylbenzene is separated from water. A stream comprising the separated ethylbenzene, which is also referred to as ethylbenzene rich stream, part of which may then be recycled into the first distillation column as reflux 21 or simply passed to storage 22. The separated water can also be further used, or recycled into the first distillation column 10 as aqueous stream 23 as shown in FIG. 1.

[0067] From the bottom of the first column 10 a third stream 15 comprising heavy solvent and the at least one other C8 aromatic compound is withdrawn. This third stream 15 may also comprise small and less amounts of ethylbenzene. The third stream can be introduced into a solvent recovery column 30, which is also referred to as second distillation column. Therein, the at least one other C8 aromatic compound is separated from the heavy solvent. From the bottom of the solvent recovery column 30, heavy solvent is withdrawn which can be recycled into the first distillation column 10 as first stream 32.

[0068] From the top of the solvent recovery column 30, a stream 31 comprising the at least one other C8 aromatic compound and probably minor amounts of ethylbenzene is withdrawn. This stream is also referred to as ethylbenzene lean stream.

[0069] Additional equipment such as heat exchanger, pump or compressor may be added to any appropriate location of the process system in order to properly adjust condition of the process. Suitable dimension and configuration of all equipment in the process can be modified by those having ordinary skills in the art to match with the exact composition of the feed stream, the extractive agent and specific operating conditions employed.

[0070] Embodiments of the present invention are further described in the following example.

Example 1

[0071] A computer simulation has been performed using the simulation software “Aspen HYSYS®”, simulating that a feed stream containing 14.66 wt % ethylbenzene, 20.21 wt % p-xylene, 43.35 wt % m-xylene and 21.78 wt % o-xylene was fed at a feed rate of 133 g/min to an extractive distillation column having 18 stages. Various solvents as shown in Table 1 were introduced to the extractive distillation column at stage 2, i.e. a location above the point of introduction of the feed stream at stage 10. As a comparative example, a simulation has been run where no solvent is introduced. The operating temperatures were simulated along the column within the range of 75° C. to 175° C. The pressure in the column was simulated to be 200 mbar and 1000 mbar, respectively (see Table 1 below). The weight ratio of the solvent to the feed stream was fixed at 5:1. The simulation model further included the features that an ethylbenzene-rich stream was withdrawn at the top of the column and an ethylbenzene-lean stream was withdrawn at the bottom of the column. A portion of the ethylbenzene-rich stream from the top of the column was simulated to be returned to the column as reflux at a reflux ratio of 10.

[0072] To demonstrate the effect of addition of water to the column, it has been simulated that water is introduced above (“water above”) and below (“water below”) the feed stream, respectively, at a rate of 36 g/min. For comparison, it has also been simulated that no water is introduced into the column. The results are shown in the following Table 1 below.

[0073] It can be seen in Table 1 that the introduction of water into the system improves the separation efficiency of the process at an operating pressure of 200 mbar and 1000 mbar, respectively, and for all solvents employed. It has been found that a higher ethylbenzene content was obtained in the overhead stream withdrawn from the top of the column (“EB concentration in overhead”). In particular, a higher efficiency was found when the water was introduced at a location below the introduction point of the feed stream according to the present invention (“water below”).

[0074] In table 1 below, TCB is 1,2,4-trichlorobenzene, and NMP is n-methyl-2-pyrrolidone.

TABLE-US-00001 TABLE 1 EB conc. in EB conc. in EB conc. in EB conc. in EB conc. in EB conc. in Solvent with overhead overhead overhead overhead overhead overhead 5 wt % water wt % wt % wt % wt % wt % wt % WATER OPTIONS NO WATER WATER NO WATER WATER WATER ABOVE BELOW WATER ABOVE BELOW TOP PRESSURE [mbar] 200 200 200 1000 1000 1000 NO SOLVENT 24.80 25.35 25.86 22.78 23.53 24.04 TCB 30.50 31.82 37.83 27.40 28.49 32.35 NITROBENZENE 56.01 56.26 56.53 54.25 54.51 54.96 ISOPHORONE 38.32 38.86 39.82 34.90 35.30 36.35 METHYL-SALICYLATE 44.85 46.28 50.00 27.39 28.49 32.34 BENZALDEHYDE 30.60 31.93 32.46 27.78 28.49 29.92 SULFOLANE 26.99 27.49 28.94 25.35 25.79 26.94 NMP 37.47 38.58 41.04 33.12 34.62 36.85