CS200154B2 - Method of separing styrene from mixture of aromatic,unsaturated and naphthenic hydrocarbons - Google Patents

Abstract

1437470 Separation of vinyl aromatics from mixtures by extractive distillation SNAMPROGETTI SpA 23 Nov 1973 [29 Nov 1972] 54626/73 Heading C5E Vinyl aromatic hydrocarbons are separated from hydrocarbon mixtures comprising other aromatic hydrocarbons by extractive distillation using a solvent mixture comprising 1-30% by weight of water, and one or more polar solvents boiling above 150‹ C. and selected from aldomorpholines (e.g. N-formyl morpholine), ketomorpholines, sulpholane N-methyl pyrrolidone. A feed 1, e.g. a C 8 or C 6-8 cut produced from the steam cracking of naphtha, is extractively distilled at 9 using a solvent mixture 2 to produce an overhead 3, which is separated into a water stream 17 and a hydrocarbon stream 16, and an extract 4 comprising styrene, o-xylene and solvent mixture. The extract 4 is extractively distilled in a second column 10 to provide an overhead 6 which is enriched in oxylene and which is recycled to the column 9 and a bottoms 7. the bottoms 7 is stripped at 12 to provide a solvent stream 14 and an overhead which is separated into a styrene product 8, e.g. containing 99À8% styrene and an aqueous stream 18.

Description

The present invention relates to a process for separating high purity vinyl aromatic hydrocarbons from mixtures containing said hydrocarbon. More particularly, the invention relates to a process for separating high purity vinyl aromatic hydrocarbons from hydrocarbon mixtures, said hydrocarbon-containing hydrocarbons, by extractive distillation in the presence of suitable water-containing solvents.

Numerous methods have been developed for separating styrene from a hydrocarbon mixture. Current processes are based on extractive distillation of hydrocarbon mixtures in the presence of suitable solvents. It should be pointed out that the temperature must be kept very low in these processes in order to prevent styrene polymerization due to heat. In the special case of styrene, it is necessary to operate at temperatures below 110 ° C. At this temperature, the initial polymerization rate, expressed as% per hour; less or maximum 1%.

Since the solvents of the highest selectivity boil at high temperature, it is necessary to operate at a very high vacuum to maintain these solvents at a distillation temperature of less than 110 ° C, resulting in unacceptably high costs.

It has now surprisingly been found that the addition of water to high-boiling polar solvents or solvent mixtures from the group consisting of aldo- and ketomorpholines, in particular N-formylmorpholine and N-methylpyrrolidone, to a water content of 1 to 30% by weight of the mixture, and preferably from 5 to 20% by weight does not significantly reduce the solvent strength. Using such aqueous solvents, it is thus possible to maintain temperatures below 110 ° C in the extractive distillation columns and greatly reduce the necessary use of vacuum, without this process being burdened with appreciable disadvantages.

It is further known that the addition of water · to said solvents · or solvent mixtures · allows to increase the selectivity of the solvent itself. The effect of water on reducing the working pressure of the extractive distillation columns is given in Table 1, which shows the values for anhydrous solvents and for solvents with different water contents in relation to the working pressures, at the column bottom temperature of 100 ° C.

The amount of xylenes present is constant and equal to 10% by weight.

AND

Table 1

T (° C) Pressure (kPa)

N-methylpyrrolidone (anhydrous) 4-10% xylenes 100 ALIGN! 11.7 N-methylpyrrolidone (+ 5% H2O) + 10% xylenes 100 ALIGN! 31.0 N-methylpyrrolidone (+ 10% H2O) 4- 10% xxlen 100 ALIGN! 54.6 N-methylpyrrolidone (+ 20% H2O) 4- 10% x-im 100 ALIGN! 74.7 N-formylmorpholine (anhydrous) 4- Ю% 'x ^ en 100 ALIGN! 6.7 N-formylmorpholine (4-5% H2O) + 10% xylenes 100 ALIGN! 3δ, 7 N-formylmorpholine (4- 20% H2O) 4- Ю '/ о' У ^ У1п ^ П1 100 ALIGN! 93.4

Thus, the present invention relates to a process for separating styrene from a mixture of aromatic, saturated and naphthenic hydrocarbons, styrene containing, by extractive distillation in the presence of one or more high boiling polar solvents, characterized in that the solvent is selected from aldomorpholines and ketomorpholines. (are) in a mixture with water in the range of from 1 to 30% by weight, preferably from 5 to 20% by weight.

In the process of the invention, the solvent is preferably N-methylpyrrolidone.

The process according to the invention can be carried out according to the following scheme, which, without limiting the nature of the invention, comprises the following steps: (see drawing):

1) Feeding a hydrocarbon mixture containing styrene (obtained by steam cracking of naphtha) into the intermediate zone of the first extractive distillation column to which a mixture of water and solvent is fed at the head of the column.

2) Extraction from the head of the first extractive distillation column stream. % of hydrocarbons containing substantially the majority of the xylenes together with saturated and olefinic hydrocarbons, ethylbenzene and water.

3) Leaving the bottom of the first column of the extractive distillation of a stream composed mainly of styrene, o-xylene and an extraction solvent.

4) Feeding the stream from 3) to a second extractive distillation column where a solvent / water mixture is fed to the head.

5) Extracting from the top of the second column the extractive distillation of a stream comprising water, styrene and o-xylene, wherein said stream is recycled to the first extractive distillation column near the original packing.

6) Extraction from the bottom of the second column by extractive distillation of a stream containing styrene, solvent and water.

(7) Feeding the stream from (6) to a strlpper for recovery as a overhead product, after separation of water, styrene and as solvent product, which is recycled to the extractive distillation column near its peak.

The following examples serve to illustrate the process of the invention in more detail without limiting its nature. .

P said dl

In this example, the device of the figure was used.

A stream of 1100 kg / h of batch Ce having the following composition was fed to column 9:

Ce saturated and olefinic hydrocarbons 3.5 kg / h

O-xylene 17.0 kg / h

- m-xylene 43.1 kg / h p-xylene 43.1 kg / h ethylbenzene 8.6 kg / h styrene 27.8 kg / h

The reaction conditions were as follows:

Upper pressure · = 118.7 kPa reflux ratio == 5 number · floors = 10 lower temperature = 100 ° C

Extraction solvent consisting of N- was passed through column 2 to the top of column 9. - Formyl morpholine containing 5% H 2 O at a rate 15 times higher. Than filling 1.

Water and an organic raffinate stream of the following composition were collected as a product from the column head:

Ce saturated and olefinic

3.5 kg / h 16.15 kg / h 43.10 kg / h 43.10 kg / h

1.60 kg / h 0.30 kg / h

The stream was fed to separators (decanter) 11 to separate from the organic hydrogen hydrocarbon O-xylene m-xylene p-xylene ethylbenzene styrene 16 water 17, which was reused at a suitable point in the cycle.

A solvent / hydrocarbon fraction stream of the following composition was withdrawn (line 4) from the bottom of column 9:

styrene o-xylene

38.28 kg / h

6.8 Okg / h

This last stream was fed to an extractive distillation column 10 operating under the following conditions:

Upper pressure reflux ratio number of floors bottom temperature = 21.4 kPa = 2.5 = 60 = 100 ° C

To the head of the column. 10, an extraction solvent consisting of N-formylmorpholine with 5% HaO was fed through line 5 at a rate of 1.5 times the load.

The product 'water' and the stream 'of organic raffinate having the following composition were taken from the head (via line 6):

Styrene 1 ≥ 0.78 kg / h

O-xylene .......... 6 6.60kh / h

This last stream was fed back into the column. 9 at the same height as the primary cartridge 1.

A stream 7 consisting of a solvent and a hydrocarbon fraction having the following composition was withdrawn from the bottom of the column 10:

styrene 27.50 kg / h

O-xylene 0.05 kg / h

Stream 7 was fed to a stripper. 12 'to the separation. of hydrocarbons from the solvent. The solvent was removed from the bottom of the column via line 14 and reused in the cycle, after mixing at 15 with water, recovered at different stages of the cycles 17 and 16 to maintain a constant solvent concentration.

A portion of the water (17 and 16) recovered from the separators (decanters) was passed to the bottom of the extractive distillation column 9 and 10 or. to other cycle points depending on need.

The hydrocarbons recovered as the overhead product and separated from the water at 13 were passed through line 6 for routine rectification for further purification. ^of

The purity of the styrene obtained was about 99.6 why.

P. k i 1 and d '2

In this . The apparatus of FIG. 1 was also used.

A column 1 was fed with the following composition, based on 100 kg / h:

C6 hydrocarbons 51.06 kg / h

C7 Hydrocarbons 27.40 kg / h

C5 saturated a. Olefinic hydrocarbons, m-xylene, p-xylene 11,37 kgeh styrene 6,30 'kg / h

O-xylene 3.85 kg / h

The working conditions were as follows:

Total pressure · at the top of the column = 16.7 kPa reflux ratio = 5 number of levels · - = δ0 foot temperature, column = 100 ° c

An extraction solvent was passed to the top of column 9 via line 2, the solvent being N-formylmorpholine containing 5% H 2 O and a feed rate of 30 times higher than the feed rate 1.

H 2 O and a hydrocarbon raffinate stream having the following composition were removed from the column head (line 3):

Contains 51.08 kg / h

C7 Hydrocarbons 27.40 kg / h

C 6 - saturated and olefinic hydrocarbons,. m-xylene, p-xylene 11.36 kgeh

O-xylene 3.83 kg / h styrene 0.06 kg / li

This stream was fed to a separator (decanters) 14 to separate water 17 from the organic raffinate 16, wherein said water was reused at a suitable point in the cycle.

From the bottom of column 9 was. a stream consisting of a solvent 'and a hydrocarbon' fraction of the following composition is discharged (via line 4):

O-xylene = 2.35 kg / h styrene = 10.02 kg / h

The last stream was fed to the column. extractive distillation 10 operating at. the following conditions:

Column head pressure 21.4 kPa reflux ratio 1.6 number of plates · 66 column bottom temperature 100 ° C

Extraction solvent, composed of N-for? mylmorpholine with 5% water, fed at 1.5 times the feed rate, was fed to column 10 through line 5.

As product from the top of the column (line 6) was removed. water and organic raffinate stream having the following composition: _x

O-xylene styrene

2.31 kg / h

3.76 kg / h

This stream was fed back to the column 9 at the same height as the primary packing 1.

A stream 7 consisting of a solvent and a hydrocarbon fraction of the following composition was withdrawn from the bottom of the column 10:

O-xylene 0.01 kgh styrene 6.24 kg / h

Stream 7 was passed to stripper 12 to separate the hydrocarbons contained in the stream from the solvent. The solvent was drained from the heel through line 14 and reused in a cycle, after mixing at 15 with water, recovered from different process stages (streams 17 and 18) to maintain its constant concentration in the solvent. If necessary, some of the water from streams 17 and 18 was fed to the foot zones of the extractive distillation columns 9 and 10 or to other points of the cycle.

The hydrocarbons recovered in the form of the overhead product and separated from the water at 13 were passed through line 8 for routine rectification for further purification.

The purity of the styrene obtained was about 99.8 why.

Example 3

In this example, the device according to the drawing was used.

Claims (3)

Method for separating styrene from a mixture of aromatic, saturated and naphthenic hydrocarbons, styrene-containing, extractive by distillation in the presence of one or more high-boiling polar solvents, characterized in that the high-boiling polar solvent belongs to the group formed by aldomorpholines and ketomorpholines, A batch of Ca corresponding to the batch used in Example 1 was fed. The solvent used was N-methylpyrrolidone with 5% H 2 O, its rate was 15 times higher than the feed rate; the working conditions of column 9 were as follows: Column head pressure 18.7 kPa reflux ratio 5 number of trays80 column bottom temperature 100 ° C The operating conditions of column 10 were as follows: Column head pressure 21.4 kPa reflux ratio 2.5 number of trays60 column bottom temperature 100 The extracted styrene showed a purity of ca. 99.8%. All remaining conditions omitted in this example were similar to those in Examples -1 and 2. YNALEZU by mylmorpholine, and is in admixture with water in an amount of 1 to 30% by weight. 2. The process according to claim 1, wherein the amount of water in the solvent is 5 to 20% by weight. 3. The process of claim 1 wherein the solvent is N-methylpyrrolidone. л, - '