US 4,292,142 AGrant
Separation of Ethylbenzene From Para- And Meta-Xylenes by Extractive Distillation
Issue Date:1981-09-29
•18 Claims
Abstract
Ethylbenzene and para-xylene and/or meta-xylene are difficult to separate by distillation because they boil only 2.3 C..degree. and 3.1 C..degree. apart. Ethylbenzene can be readily separated from the xylenes by using extractive distillation in which the extractive distillation agent is a mixture of oxygen-containing organic compounds boiling higher than the xylenes. The mixture typically includes phthalic anhydride and maleic anhydride with or without a solvent.
Metadata
Assignee
- International Synthetic Rubber Co., Ltd.
Inventor
- Lloyd Berg
Application Information
Application Number:US 2241757
Filing Date:1981-01-12
Priority Date:1981-01-12
Art Unit:177
Classifications
IPC:
F01D 340
Field of Search:
585203805;807;80850;51;57;61
Patent Drawings
This patent does not have any drawings.
Description
Field of the Invention
This invention relates to a method for separating ethylbenzene from the xylenes using mixtures of two or more compounds as extractive agents in extractive distillation.
Description of the Prior Art
Extractive distillation is the method of separating close boiling compounds by carrying out the distillation in a multiplate rectification column in the presence of an added liquid or liquid mixture, said liquid(s) having a boiling point higher than the compounds being separated. The extractive agent is introduced near the top of the column and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the rectification column alters the relative volatility of the close boiling compounds in a direction to make the separation on each plate greater and thus required either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The extractive agent should boil higher than any of the close boiling liquids being separated and not form minimum boiling azeotropes with them. Usually the extractive agent is introduced a few plates from the top of the column to insure that none of the extractive agent is carried over with the lowest boiling component. This usually requires that the extractive agent boil twenty Centigrade degrees or more higher than the lowest boiling component.
At the bottom of a continuous column, the less volatile components of the close boiling mixture and the extractive agent are continuously removed from the column. The usual methods of separation of these two components are the use of another rectification column, cooling and phase separation, or solvent extraction.
The separation of ethylbenzene from p-xylene and/or m-xylene by extractive distillation has been reported. Amir, U.S. Pat. No. 3,105,017 describes the use of single compounds to effect this separation and he prefers 1,2,4-trichlorobenzene. This compound increases the relative volatility from 1.06 to 1.116. Nixon, U.S. Pat. Nos. 2,532,031 and 2,638,441 reported that antimony trichloride gave a relative volatility of 1.15. Anstey, Brit. Pat. No. 1,257,024-5 used phosphazines to effect this separation. Berg & Kober, AIChE Journ., 26,862 (September 1980) and Berg, U.S. Pat. Appl. Ser. No. 929,929, Aug. 1, 1978 reported on the use of mixtures of polychloro compounds to effect this separation. They prefer mixtures of pentachlorophenol, 2,3,4,6-tetrachlorophenol, 1,2,4-trichlorobenzene, 1,2,3-trichlorobenzene, benzene hexachloride, 2,4-dichlorotoluene, 1,2,4,5-tetrachlorobenzene and polychlorobenzenes, some of these mixtures raising the apparent relative volatility to as high as 1.27.
The advantage of using extractive distillation in this separation can be seen from Table I below. To separate ethylbenzene from p-xylene in 99% purity by conventional rectification requires a minimum of 157 theoretical plates at total reflux, thus somewhat more at a finite reflux ratio. With an extractive distillation agent such as 1,2,4-trichlorobenzene, the relative volatility goes to 1.11 and only 87 plates are now required. The best extractive distillation agents that I have discovered push the relative volatility up to about 1.2 and Table I shows that they will reduce the plate requirement to 50 plates
Extractive distillation typically requires the addition of an equal amount to twice as much extractive agent as close boiling compounds on each plate in the rectification column. The extractive distillation agent should be heated to about the same temperature as the plate into which it is introduced. Thus extractive distillation imposes an additional heat requirement on the column as well as somewhat larger diameter plates for the same production output. To be economically attractive, the extractive distillation system must save more in the reduction of the number of theoretical plates and the size of the column than it adds in the cost of larger plates and additional heat requirement. This will vary depending on the difficulty of the separation and the cost of heat. I found that in the separation of ethylbenzene from p-xylene and/or m-xylene, the extractive agent should increase the relative volatility to about 1.2 to make the process economically attractive under the equipment and heat costs in effect at the time of my investigation.
Another consideration in the selection of the extractive distillation agent is its recovery from the bottoms product. The usual method is by rectification in another column. In order to keep the cost of this operation to a minimum, an appreciable boiling point difference between the compound being separated and the extractive agent is desirable. I recommend twenty Centigrade degrees or more difference.
Ethylbenzene is the major precursor to most processes for producing styrene. Styrene is used principally in plastics manufacture. In the preparation of high polymers, extreme purity is absolutely necessary. It is the presence of impurities that stops chain growth and prevents polymerization to the desired molecular weight. To make high purity styrene, it is necessary to use high purity ethylbenzene. Ethylbenzene is frequently found admixed with its isomers, the xylenes. Since ethylbenzene boils 2.3 C. degrees from p-xylene and 3.1 C. degrees from m-xylene, separation of ethylbenzene from these xylenes by conventional rectification to produce high purity ethylbenzene is almost impossible. One of the major sources of ethylbenzene is the C.sub.8 fraction of hydroformed naphthenic petroleum and here the xylenes will be present with the ethylbenzene.
Objective of the Invention
The object of this invention is to provide a process or method of extractive distillation that will enhance the apparent relative volatility of ethylbenzene and the xylenes in their separation in a rectification column. It is a particular object of this invention to identify suitable mixtures of oxygenated organic compounds which will increase the apparent relative volatility of ethylbenzene to p-xylene and/or m-xylene to about 1.2. It is a further object of this invention to identify oxygenated organic compounds which, in addition to the above constraints, are stable, can be separated from the xylenes by rectification with relatively few theoretical plates and can be recycled to the extractive distillation column and reused with little decomposition.
Summary of the Invention
The objects of this invention are provided by a process for separating ethylbenzene from p-xylene and/or m-xylene using a mixture of phthalic anhydride and maleic anhydride with or without an oxygen containing organic compound as a solvent, as the agent in extractive distillation.
Detailed Elaboration of the Invention
I have discovered that a mixture of approximately equal parts of phthalic anhydride and maleic anhydride when used as the agent in extractive distillation to separate ethylbenzene from p-xylene and/or m-xylene, will give a relative volatility of 1.21 when the amount of agent is between one and two parts per part of ethylbenzene-xylene mixture. When phthalic anhydride is used alone the relative volatility is 1.17, when maleic anhydride is used alone, the relative volatility is 1.13. Thus the mixture is considerably more effective than either the phthalic anhydride or the maleic anhydride when used alone.
Phthalic anhydride, maleic anhydride and phthalic anhydridemaleic anhydride mixtures melt so high that they freeze in the presence of ethylbenzene relatively close to the boiling point of ethylbenzene which is 136.15.degree. C. at 760 mm.Hg. While this does not preclude the use of the phthalic anhydride-maleic anhydride mixture, there is an advantage in the ease of operation to adding a third component to the phthalic anhydride-maleic anhydride mixture to lower the freezing point.
Table II is a list of organic compounds which when added to phthalic anhydride-maleic anhydride mixtures in the amount of 15-25%, lower the relative volatility to less than 1.20. Table III is a list of those organic compounds which when added to the phthalic anhydride-maleic anhydride mixture in the amount of 15-25%, retain or increase the 1.20 relative volatility.
I have discovered several combinations of organic compounds which do not fit the categories phthalic anhydride-maleic anhydride-solvent and they are listed in Table IV.
The question might be asked, are three or four components really necessary or would one or two of them serve as well. The answer to this question is presented in Table V. It lists the relative volatility of a number of the three component systems and the relative volatility of each binary combination as well as the relative volatility of the solvent. Note that the relative volatility of phthalic anhydride is 1.17, of maleic anhydride,1.13. The relative volatility of the phthalic anhydride-maleic anhydride mixture is 1.22. In every case in Table V the ratios of the solvent to the ethylbenzene-xylene mixture is 1 and 1.5, of the binary combinations 1/2:1/2 and 3/4:3/4 per part of ethylbenzene-xylene and the phthalic anhydride-maleic anhydride-solvent is 0.4:0.4:0.2 and 0.6:0.6:0.3 per part of ethylbenzene-xylene. To evaluate the data shown in Table V, consider the first solvent, o-toluic acid. The mixture phthalic anhydride-maleic anhydride-o-toluic acid has a relative volatility of 1.20. Phthalic anhydride-o-toluic acid is 1.10 and 1.12, maleic anhydride-o-toluic acid is 1.11 and 1.12 and o-toluic acid alone is 1.17 and 1.11. Thus the three component mixture is considerably more effective than any of its components used singularly or in binary combinations. Table V shows this comparison for several of the solvents that are part of this invention.
The Usefulness of the Invention
The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables I, III and V. When ethylbenzene is separated from p-xylene by rectification in 99% purity, 157 theoretical plates are required at total reflux, somewhat more under a finite reflux ratio. Table III and V show that a mixture of phthalic anhydride, maleic anhydride and 2-octanone change the relative volatility to 1.20. From Table I it is apparent that now only 50 theoretical plates will be required to effect the separation of ethylbenzene from p-xylene in 99% purity.
Working Examples
Example 1
A mixture comprising 50 grams of ethylbenzene and 50 grams of p-xylene was charged to an Othmer vapor-liquid equilibrium still and refluxed for six hours. Samples of the vapor and liquid were removed and analysed by gas chromatography. The vapor contained 51.0% ethylbenzene and 49.0% p-xylene, the liquid 49.5% ethylbenzene and 50.5% p-xylene. This indicates a relative volatility of ethylbenzene to p-xylene of 1.06. This has been confirmed by numerous other investigators.
Example 2
A mixture comprising 50 grams of ethylbenzene and 50 grams of m-xylene was charged to the Othmer vapor-liquid equilibrium still and refluxed for six hours. Samples of the vapor and liquid were removed and analysed. The vapor contained 51.2% ethylbenzene and 48.8% m-xylene, the liquid 49.3% ethylbenzene and 50.7% m-xylene. This indicates a relative volatility of ethylbenzene to m-xylene of 1.08. This too is the value reported in the literature.
Example 3
A mixture comprising 25 grams ethylbenzene, 25 grams p-xylene, 20 grams phthalic anhydride, 20 grams maleic anhydride and 10 grams isobornyl acetate was charged to the vapor-liquid equilibrium still and refluxed for twelve hours. Analyses indicated a vapor composition of 53.0% ethylbenzene 47.0% p-xylene and a liquid composition of 47.2% ethylbenzene 52.8% p-xylene. This indicates a relative volatility of 1.25.
Example 4
A mixture comprising 25 grams ethylbenzene, 25 grams m-xylene, 20 grams phthalic anhydride, 20 grams maleic anhydride and 10 grams isobornyl acetate was refluxed for eleven hours in the vapor-liquid equilibrium still. Analyses showed a vapor composition of 54.1% ethylbenzene, 45.9% m-xylene and a liquid composition of 49.0% ethylbenzene and 51.0% m-xylene indicating a relative volatility of 1.22.
Example 5
The ratios shown in Examples 3 and 4 were changed to 20 grams ethylbenzene, 20 grams p-xylene or m-xylene, 25 grams phthalic anhydride, 25 grams maleic anhydride, 10 grams isobornyl acetate and refluxed in the vapor-liquid equilibrium still for twelve hours. The relative volatility for ethylbenzene-p-xylene was 1.22, for ethylbenzene-m-xylene 1.18.
Example 6
The ratios of ethylbenzene to p-xylene or m-xylene in Examples 3, 4 and 5 were changed to 45 grams ethylbenzene, 5 grams p-xylene; 40 grams ethylbenzene, 10 grams p-xylene; 40 grams ethylbenzene, 10 grams m-xylene; 10 grams ethylbenzene, 40 grams p-xylene and 10 grams ethylbenzene, 40 grams m-xylene, the solvent quantity being the same. The relative volatility of these mixtures was as follows:
Every combination of successful extractive distillation agents listed in Table III was investigated under the conditions listed in Examples 3,4,5 and 6. In order to be listed in Table III, their relative volatilities must average 1.20 or higher.
Example 7
A column consisting of two twenty-plate sections of one-inch diameter glass perforated plates equipped with a vacuum jacket was employed. The column was fitted with a Corad constant reflux ratio distilling head. Between the Corad head and the top of the column, a feed line from a constant flow pump was introduced. The stillpot was equipped with a sampling tube. The column was calibrated with a test mixture of ethylbenzene and p-xylene, which mixture possesses a relative volatility of 1.06. At a constant reflux ratio of 10 to 1, this column calibrated twelve theoretical plates. Then a run was made with a charge of approximately 20% ethylbenzene, 80% p-xylene in the stillpot. The column was operated at total reflux for about an hour, then switched to 10 to 1 reflux ratio and the pump started at a rate to deliver about one part of extractive agent to one part of ethylbenzene-p-xylene mixture being boiled up. The extractive agent in this example was 40% phthalic anhydride, 40% maleic anhydride and 20% isobornyl acetate. The following data was obtained:
It will be noted that after two hours, equilibrium has been achieved and the relative volatility remains essentially constant at about 1.21. Without extractive distillation agents, it would have been 1.06.
I have shown that the proper combination of one or more compounds with phthalic anhydride and/or maleic anhydride will yield separations of ethylbenzene from p-xylene or m-xylene better than what is obtainable from any of these compounds individually.
Claims
The nature of the present invention having been described and illustrated, what I wish to claim as new and useful and secure by Letters Patent is:
1. A method for the separation of ethylbenzene from p-xylene and/or m-xylene which comprises distilling a mixture of ethylbenzene and p-xylene and/or m-xylene in the presence of an effective amount of an extractive agent comprising a mixture of phthalic anhydride and maleic anhydride.
2. The process of claim 1 in which the extractive distillation agent comprises a mixture of phthalic anhydride, maleic anhydride and one of the following; Acetonylacetone, Acetphenone, Acetyl salicylic acid, Adiponitrile, p-tertiary Amyl phenol, Anisole, Azelaic acid, Benzaldehyde, Benzoic acid, Benzonitrile, Benzophenone, Benzyl acetate, Benzyl alcohol, Butoxypropanol, Butyl benzyl phthalate, o-secondary Butyl phenol, 2-tertiary Butyl phenol, 3-tertiary Butyl phenol, 4-tertiary Butyl phenol, 1,3-Butylene glycol, beta-Butyrolactone, Carbitol acetate, Citronellyl acetate, m-Cresol o-Cresol, Cuminaldehyde, Cyanoacetic acid, Decanoic acid, Dibenzofuran, 2,6-di-tertiary Butyl-p-cresol, Dibutyl ether, 2,5-di-tertiary Butyl hydroquinone, 2,6-di-tertiary Butyl phenol, Diethyl maleate, Diethyl malonate, Diethyl phenyl malonate, Diethyl phthalate, Diethyl succinate, Diethylene glycol butyl ether acetate, Diethylene glycol dimethyl ether, Diethylene glycol methyl ether, Dihydroterpinyl acetate, Diisobutyl ketone, Dimethyl formamide, 3,5-Dimethyl phenol, Dimethyl succinate, Dimethyl sulfone, Dimethyl sulfoxide, Ethyl acetoacetate, 2-Ethyl butyric acid, 2-Ethylhexanol, Ethyl hexyl acetate, Ethyl phenyl acetate, Ethyl salicylate, p-Ethyl phenol, Ethylene glycol butyl ether, Ethylene glycol ethyl ether acetate, Ethylene glycol mono stearate, Fenchyl alcohol, 9-Fluorenone, 1,6-Hexanediol, Hexahydrophthalic acid anhydride, Hexyl acetate, Hexylene glycol, Hexylene glycol diacetate, Hydro bis phenol A, Isoborneol, Isobornyl acetate, Isobornyl methyl ether, Isooctanol, Isophorone, Isopropyl myristate, Linalyl acetate, Menthyl acetate, Methyl benzoate, 4-Methyl benzophenone-2-carboxylic acid, Methyl hexanoate, Myristic acid, m-Nitroacetophenone, p-Nitroacetophenone, m-Nitrobenzaldehyde, m-Nitrobenzoic acid, 5-Nitroisophthalic acid diethyl ester, p-Nitrophenol, p-Nitrophenylacetic acid, p-Nitrotoluene, Nonanic acid, 2-Octanone, Phenethyl alcohol, Phenol, Phenyl acetate, Phenyl acetic acid, 2-Phenylphenol, 3-Phenyl-1-propanol, Propionic anhydride, Propoxypropanol, Propyl-p-hydroxybenzoate, Sebacic acid,, Succinic anhydride, Succinimide, Sulfolane, Sulfolene, Tetrahydrofurfuryl alcohol, 2,2',4,4'-Tetrahydroxybenzophenone, p-Tolualdehyde, Tributylphosphate, Triethylene glycol diacetate, o-Toluic acid.
3. The process of claim 1 in which the extractive distillation agent comprises a mixture of phthalic anhydride and benzoic acid.
4. The process of claim 1 in which the extractive distillation agent comprises a mixture of phthalic anhydride, benzoic acid and one of the following; Diisononyl phthalate, Diethylene glycol ethyl ether acetate, Methyl salicylate, Diisobutyl ketone, Diisononyl phthalate, Diisobutyl phthalate, Diethyl maleate, Methyl hexanoate, Isobutyl isobutyrate, Dimethylsulfoxide, Dimethylformamide, n-Octanol, n-Decanol, Ethyl acetoacetate, 4-Nitrophenol, 4-tertiary Butyl phenol, Dimethylsulfone, 4-tertiary Butyl catechol, 2-Phenylphenol.
5. The process of claim 1 in which the extractive distillation agent comprises a mixture of phthalic anhydride, salicylic acid and one of the following; Diisobutyl phthalate, Methyl hexanoate, Ethylene glycol phenyl ether, and the pair Dimethylsulfoxide, Methyl hexanoate.
6. The process of claim 1 in which the extractive distillation agent comprises a mixture of benzoic acid, maleic anhydride and one of the following; Diethyl maleate, Methyl hexanoate, Acetophenone, Triethylene glycol diacetate, Diethylene glycol hexyl ether, Dimethyl phthalate, Dibutyl phthalate, Diisononyl adipate, Tributyl phosphate, n-Octanol, 1,6-Hexanediol, 4-secondary Butyl phenol, p-Ethylbenzaldehyde.
7. The process of claim 1 in which the extractive distillation agent comprises a mixture of benzoic acid, maleic anhydride, phthalic anhydride and one of the following; Glycerol triacetate, Diethyl maleate, Phenyl acetate, Ethylene glycol diacetate, Dimethyl adipate, Ethylene glycol methyl ether acetate, Diethylene glycol diethyl ether, Tributyl phosphate, Tricresyl phosphate, Catechol, Ethyl acetoacetate, Phenol, o-Cresol, 2,6-Dibutyl phenol, Diisobutyl ketone, Tetrahydrofurfuryl alcohol.
8. The process of claim 1 in which the extractive distillation agent comprises a mixture of maleic anhydride and one of the following pairs; m-Nitrobenzoic acid & Butoxypropanol, 4-tertiary Butyl catechol & Nonanic acid, 2-Phenylphenol & Isobornyl acetate, p-Nitrophenol & Myristic acid.
9. The process of claim 1 in which the extractive distillation agent comprises a mixture of phthalic anhydride and one of the following; Levulinic acid, m-Nitrobenzoic acid, Acetonylacetone.
10. The process of claim 1 in which the extractive distillation agent comprises a mixture of phthalic anhydride and one of the following pairs; Acetylsalicylic acid & Isophorone, Azelaic acid & Isophorone, o-Toluic acid & Phenol.
11. The process of claim 1 in which the extractive distillation agent comprises a mixture of hexahydrophthalic anhydride, maleic anhydride and one of the following; Butoxypropanol, n-Octanol.
12. The process of claim 1 in which the extractive distillation agent comprises a mixture of maleic anhydride, azelaic acid and one of the following; Ethylphenyl acetate, Phenylacetic acid.
13. The process of claim 1 in which the extractive distillation agent comprises a mixture of Phthalic anhydride, Benzoic acid, Dimethylsulfoxide and Methyl hexanoate.
14. The process of claim 1 in which the extractive distillation agent comprises a mixture of Phthalic anhydride, Succinic acid, Ethylene glycol diacetate and Carbitol acetate.
15. The process of claim 1 in which the extractive distillation agent comprises a mixture of Benzoic acid, Succinic anhydride and Diethyl maleate.
16. The process of claim 1 in which the extractive distillation agent comprises a mixture of Phthalic anhydride, Methyl p-hydroxybenzoate and Diethyl oxalate.
17. The process of claim 1 in which the extractive distillation agent comprises a mixture of Benzoic acid, Salicylic acid and Tributyl phosphate.
18. The process of claim 1 in which the extractive distillation agent comprises a mixture of Maleic anhydride and m-Nitroacetophenone.
Patent Citations (2)
| Patent | Date | Inventor | Cited By |
|---|---|---|---|
| US2431655 | 1947-11-01 | Amos et al. | |
| US2945902 | 1960-07-01 | Romans |