WO2000044693A1 - Separation of aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof by extractive distillation - Google Patents

Separation of aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof by extractive distillation Download PDF

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Publication number
WO2000044693A1
WO2000044693A1 PCT/IB2000/000078 IB0000078W WO0044693A1 WO 2000044693 A1 WO2000044693 A1 WO 2000044693A1 IB 0000078 W IB0000078 W IB 0000078W WO 0044693 A1 WO0044693 A1 WO 0044693A1
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Prior art keywords
aromatic hydrocarbons
extractive distillation
mixture
liquid
separation
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PCT/IB2000/000078
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French (fr)
Inventor
Izak Nieuwoudt
Braam Van Dyk
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Izak Nieuwoudt
Braam Van Dyk
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Application filed by Izak Nieuwoudt, Braam Van Dyk filed Critical Izak Nieuwoudt
Priority to AU30701/00A priority Critical patent/AU3070100A/en
Publication of WO2000044693A1 publication Critical patent/WO2000044693A1/en
Priority to US09/671,333 priority patent/US6395141B1/en

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C7/00—Purification; Separation; Use of additives
    • C07C7/04—Purification; Separation; Use of additives by distillation
    • C07C7/05—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds
    • C07C7/08—Purification; Separation; Use of additives by distillation with the aid of auxiliary compounds by extractive distillation

Definitions

  • the present invention relates to the separation of aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof by extractive distillation.
  • Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome.
  • the extractive distillation solvent is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture.
  • extractive distillation is the method of separating close boiling compounds from each other 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 distillation solvent 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 require either fewer plates to effect the l same separation or make possible a greater degree of separation with the same number of plates.
  • the extractive distillation solvent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive distillation solvent is introduced a few plates from the top of the column to ensure that none of the extractive distillation solvent is carried over with the lowest boiling component.
  • a method of separation of aromatic hydrocarbons and non-aromatic hydrocarbons includes the step of distilling a mixture of aromatic hydrocarbons / non-aromatic hydrocarbons containing at least aromatic hydrocarbons and non- aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent selected from the group consisting of an ester of a dibasic acid and N-methyl-2-pyrrolidone.
  • the aromatic hydrocarbons / non-aromatic hydrocarbons mixture may contain only aromatic hydrocarbons and non-aromatic hydrocarbons.
  • the non-aromatic hydrocarbons may be C7-isomers.
  • the non-aromatic hydrocarbons may be C8-isomers.
  • the non-aromatic hydrocarbons may be a mixture of C7-isomers and C8-isomers.
  • the aromatic hydrocarbon may be toluene.
  • the ester of a dibasic acid may be dimethylmaleate.
  • the ester of a dibasic acid may be dimethylphtalate.
  • vapour-liquid equilibrium still 10 including a bulb flask 12 having a tube 14 leading to a condenser 16 and terminating in an outlet 18.
  • the outlet 18 has an electromagnetic closure mechanism 20.
  • a liquid phase sample conduit 22 leads into the flask 12.
  • a further liquid phase sample conduit 24 leads into the tube 14.
  • a first thermometer 26 is adapted to read the temperature of the liquid contained in the flask 12, and a second thermometer 28 is adapted to read the temperature of the vapour in the tube 14.
  • the flask 12 can be heated by a heating mantle 30.
  • the extractive distillation procedure is as follows:
  • a liquid mixture is prepared consisting of C7, C8-isomers (non-aromatic hydrocarbons), toluene (aromatic hydrocarbons) and an extractive distillation solvent.
  • the liquid is introduced into the bulb flask 12 via conduit 22.
  • the mixture in the bulb flask 12 is then heated by the heating mantle 30 and kept at boiling point. During boiling the mixture separates into a liquid phase remaining in the bulb flask 12 and a vapour phase in the tube 14. In the tube 14 the vapour phase is cooled by the condenser 16, whereafter it condenses and returns as liquid to the bulb flask 12.
  • the mixture is boiled and condensed for several hours, normally 5 to 6 hours. The process of evaporation and condensation is repeated until equilibrium is reached between the vapour and liquid phases. Thereafter, a liquid sample of the liquid phase in the bulb flask 12 is extracted through conduit 22 and a liquid sample of the condensed vapour phase in the tube 14 is extracted through conduit 24.
  • thermometer 26 The temperature of the liquid phase in the bulb flask 12 is continuously monitored by the thermometer 26, and the temperature of the vapour phase in the tube 14 is continuously monitored by the thermometer 28.
  • a C7, C8-isomers/toluene liquid mixture with a molar ratio of 0.96:1 has a relative volatility of 1.41.
  • the separation was effected by using a suitable ester of a dibasic acid as an extractive distillation solvent.
  • a C7, C8-isomers/toluene mixture with a molar ratio of 1.1:1 has a relative volatility of 1.38.
  • NMP N-methyl-2-pyrolidone
  • An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1:1.06 has a relative volatility of 1.38.
  • the separation was effected by using N-methyl-2-pyrrolidone as an extractive distillation solvent.
  • An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1 :1.16 has a relative volatility of 1.40.
  • the separation was effected by using a suitable ester of a dibasic acid such as dimethylmaleate as an extractive distillation solvent.
  • a suitable ester of a dibasic acid such as dimethylmaleate as an extractive distillation solvent.
  • a mixture of 2,2,4-trimethylpentane (22.9g), toluene (21.4g) and dimethylmaleate (226.5g) was charged into the flask 12 of the vapour- liquid equilibrium still 10 and the above procedure was applied.
  • the liquid and vapour phases were analysed.
  • the liquid and vapour molar fractions were determined to be as follows:
  • An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1 :1.16 has a relative volatility of 1.40.
  • the separation was effected by using a suitable ester of a dibasic acid such as dimethylphtalate as an extractive distillation solvent.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Analytical Chemistry (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture. The invention suggests a method of separation of aromatic hydrocarbons and non-aromatic hydrocarbons by distilling a mixture of aromatic hydrocarbons/non-aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent selected from the group consisting of an ester of a dibasic acid and N-methyl-2-pyrrolidone.

Description

Separation of aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof by extractive distillation.
FIELD OF INVENTION
The present invention relates to the separation of aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof by extractive distillation.
BACKGROUND TO INVENTION
Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture.
As an example, the separation of C7, C8-isomers (non-aromatic hydrocarbons) and toluene (aromatic hydrocarbons) is complicated due to low relative volatilities or the existence of an azeotrope. Aniline or phenol have been proposed in the literature as extractive distillation solvents to produce C7, C8-isomers as distillate.
As has been stated in US Patent 5,800,681 (Berg) extractive distillation is the method of separating close boiling compounds from each other 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 distillation solvent 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 require either fewer plates to effect the l same separation or make possible a greater degree of separation with the same number of plates. The extractive distillation solvent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive distillation solvent is introduced a few plates from the top of the column to ensure that none of the extractive distillation solvent is carried over with the lowest boiling component.
It is an object of this invention to suggest at least one further extractive distillation solvent for the separation of aromatic hydrocarbons and non- aromatic hydrocarbons from mixtures thereof.
SUMMARY OF INVENTION
According to the invention, a method of separation of aromatic hydrocarbons and non-aromatic hydrocarbons includes the step of distilling a mixture of aromatic hydrocarbons / non-aromatic hydrocarbons containing at least aromatic hydrocarbons and non- aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent selected from the group consisting of an ester of a dibasic acid and N-methyl-2-pyrrolidone.
The aromatic hydrocarbons / non-aromatic hydrocarbons mixture may contain only aromatic hydrocarbons and non-aromatic hydrocarbons.
The non-aromatic hydrocarbons may be C7-isomers.
The non-aromatic hydrocarbons may be C8-isomers.
The non-aromatic hydrocarbons may be a mixture of C7-isomers and C8-isomers.
The aromatic hydrocarbon may be toluene.
The ester of a dibasic acid may be dimethylmaleate.
The ester of a dibasic acid may be dimethylphtalate. BRIEF DESCRIPTION OF DRAWING
The invention will now be described by way of example with reference to the accompanying schematic drawing.
In the drawing there is shown a schematic view of an experimental apparatus for testing an extractive distillation solvent for separating aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof in accordance with the invention.
DETAILED DESCRIPTION OF DRAWING AND EXPERIMENTS
In the drawing there is shown a vapour-liquid equilibrium still 10 including a bulb flask 12 having a tube 14 leading to a condenser 16 and terminating in an outlet 18. The outlet 18 has an electromagnetic closure mechanism 20.
A liquid phase sample conduit 22 leads into the flask 12.
A further liquid phase sample conduit 24 leads into the tube 14.
A first thermometer 26 is adapted to read the temperature of the liquid contained in the flask 12, and a second thermometer 28 is adapted to read the temperature of the vapour in the tube 14.
The flask 12 can be heated by a heating mantle 30.
The extractive distillation procedure is as follows:
A liquid mixture is prepared consisting of C7, C8-isomers (non-aromatic hydrocarbons), toluene (aromatic hydrocarbons) and an extractive distillation solvent. The liquid is introduced into the bulb flask 12 via conduit 22.
The mixture in the bulb flask 12 is then heated by the heating mantle 30 and kept at boiling point. During boiling the mixture separates into a liquid phase remaining in the bulb flask 12 and a vapour phase in the tube 14. In the tube 14 the vapour phase is cooled by the condenser 16, whereafter it condenses and returns as liquid to the bulb flask 12.
The mixture is boiled and condensed for several hours, normally 5 to 6 hours. The process of evaporation and condensation is repeated until equilibrium is reached between the vapour and liquid phases. Thereafter, a liquid sample of the liquid phase in the bulb flask 12 is extracted through conduit 22 and a liquid sample of the condensed vapour phase in the tube 14 is extracted through conduit 24.
The temperature of the liquid phase in the bulb flask 12 is continuously monitored by the thermometer 26, and the temperature of the vapour phase in the tube 14 is continuously monitored by the thermometer 28.
Experiment 1
A C7, C8-isomers/toluene liquid mixture with a molar ratio of 0.96:1 has a relative volatility of 1.41.
The separation was effected by using a suitable ester of a dibasic acid as an extractive distillation solvent.
A mixture of C7, C8-isomers (19.1g), toluene (18.4g) and Dimethylphtalate (266.2g) was charged into the flask 12 of the vapour- liquid equilibrium still 10 and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: Table 1 :
Figure imgf000007_0001
This translates to a relative volatility of 6.89 for the system C7, 08- isomers/toluene in the ternary system shown above, the C7, C8-isomers being the distillate.
Experiment 2
A C7, C8-isomers/toluene mixture with a molar ratio of 1.1:1 has a relative volatility of 1.38.
The separation was effected by using N-methyl-2-pyrolidone (NMP) as an extractive distillation solvent.
A mixture of C7, C8-isomers (30.2g), toluene (25.2g) and NMP (208.8g) was charged into the flask 12 of the vapour-liquid equilibrium still 10 and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows:
Table 2:
Figure imgf000007_0002
This translates to a relative volatility of 6.36 for the system 07, C8- isomer/toluene in the ternary system shown above, the 07, C8-isomers being the distillate.
Experiment 3
An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1:1.06 has a relative volatility of 1.38.
The separation was effected by using N-methyl-2-pyrrolidone as an extractive distillation solvent.
A mixture of 2,2,4-trimethylpentane (19.3g), toluene (16.5g) and NMP (130.4g) was charged into the flask 12 of the vapour-liquid equilibrium still 10 and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows:
Table 3:
Figure imgf000008_0001
This translates to a relative volatility of 4.04 for the system 2,2,4- trimethylpentane/toluene in the ternary system shown above, the 2,2,4- trimethylpentane being the distillate.
Experiment 4
An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1 :1.16 has a relative volatility of 1.40.
The separation was effected by using a suitable ester of a dibasic acid such as dimethylmaleate as an extractive distillation solvent. A mixture of 2,2,4-trimethylpentane (22.9g), toluene (21.4g) and dimethylmaleate (226.5g) was charged into the flask 12 of the vapour- liquid equilibrium still 10 and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows:
Table 4:
Figure imgf000009_0001
This translates to a relative volatility of 3.91 for the system 2,2,4- trimethylpentane/toluene in the ternary system shown above, the 2,2,4- trimethylpentane being the distillate.
Experiment 5
An 2,2,4-trimethylpentane/toluene mixture with a molar ratio of 1 :1.16 has a relative volatility of 1.40.
The separation was effected by using a suitable ester of a dibasic acid such as dimethylphtalate as an extractive distillation solvent.
A mixture of 2,2,4-trimethylpentane (18.9g), toluene (14.9g) and dimethylphtalate (246.8g) was charged into the flask 12 of the vapour- liquid equilibrium still 10 and the above procedure was applied. The liquid and vapour phases were analysed. The liquid and vapour molar fractions were determined to be as follows: Table 5:
Figure imgf000010_0001
This translates to a relative volatility of 3.15 for the system 2,2,4- trimethylpentane/toluene in the ternary system shown above, the 2,2,4- trimethylpentane being the distillate.

Claims

PATENT CLAIMS
1. A method of separation of aromatic hydrocarbons and non- aromatic hydrocarbons, which includes the step of distilling a mixture of aromatic hydrocarbons / non-aromatic hydrocarbons containing at least aromatic hydrocarbons and non-aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent selected from the group consisting of an ester of a dibasic acid and N-methyl-2- pyrrolidone.
2. A method as claimed in claim 1 , in which the aromatic hydrocarbons / non-aromatic hydrocarbons mixture contains only aromatic hydrocarbons and non-aromatic hydrocarbons.
3. A method as claimed in claim 1 or claim 2, in which the non- aromatic hydrocarbons are C7-isomers.
4. A method as claimed in claim 1 or claim 2, in which the non- aromatic hydrocarbons are C8-isomers.
5. A method as claimed in claim 1 or claim 2, in which the non- aromatic hydrocarbons are a mixture of C7-isomers and C8- isomers.
6. A method as claimed in claim 1 or claim 2, in which the aromatic hydrocarbon is toluene.
7. A method as claimed in any one of the preceding claims, in which the ester of a dibasic acid is dimethylmaleate.
8. A method as claimed in any one of claims 1 to 6, in which the ester of a dibasic acid is dimethylphtalate.
PCT/IB2000/000078 1999-01-28 2000-01-26 Separation of aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof by extractive distillation WO2000044693A1 (en)

Priority Applications (2)

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AU30701/00A AU3070100A (en) 1999-01-28 2000-01-26 Separation of aromatic hydrocarbons and non-aromatic hydrocarbons from mixtures thereof by extractive distillation
US09/671,333 US6395141B1 (en) 1999-01-28 2000-09-28 Separation of components from aromatic hydrocarbon mixtures thereof by extractive distillation

Applications Claiming Priority (4)

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ZA99/0654 1999-01-28
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4514262A (en) * 1982-08-02 1985-04-30 Lloyd Berg Separation of benzene from non-aromatic hydrocarbons by extractive distillation
US5145562A (en) * 1991-07-01 1992-09-08 Phillips Petroleum Company Extractive distillation of mixtures containing aromatic and olefinic hydrocarbons

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4514262A (en) * 1982-08-02 1985-04-30 Lloyd Berg Separation of benzene from non-aromatic hydrocarbons by extractive distillation
US5145562A (en) * 1991-07-01 1992-09-08 Phillips Petroleum Company Extractive distillation of mixtures containing aromatic and olefinic hydrocarbons

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