WO2002068375A1 - Azeotropic distillation process - Google Patents

Azeotropic distillation process

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Publication number
WO2002068375A1
WO2002068375A1 PCT/JP2002/001372 JP0201372W WO02068375A1 WO 2002068375 A1 WO2002068375 A1 WO 2002068375A1 JP 0201372 W JP0201372 W JP 0201372W WO 02068375 A1 WO02068375 A1 WO 02068375A1
Authority
WO
WIPO (PCT)
Prior art keywords
carboxylic acid
aliphatic carboxylic
azeotropic distillation
acid ester
oil phase
Prior art date
Application number
PCT/JP2002/001372
Other languages
French (fr)
Japanese (ja)
Inventor
Motoki Numata
Takayuki Isogai
Original Assignee
Mitsubishi Chemical Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mitsubishi Chemical Corporation filed Critical Mitsubishi Chemical Corporation
Publication of WO2002068375A1 publication Critical patent/WO2002068375A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/42—Separation; Purification; Stabilisation; Use of additives
    • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
    • C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
    • C07C51/46—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation by azeotropic distillation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
    • B01D3/36—Azeotropic distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C67/00—Preparation of carboxylic acid esters
    • C07C67/48—Separation; Purification; Stabilisation; Use of additives
    • C07C67/52—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
    • C07C67/54—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation

Definitions

  • the present invention relates to an azeotropic distillation method.
  • the present invention is particularly effective when azeotropic distillation separates water from an aqueous feed stream containing an aliphatic carboxylic acid, such as acetic acid, to recover the aliphatic carboxylic acid.
  • the present invention relates to a method for producing an aromatic carboxylic acid by a liquid phase oxidation reaction in a solvent containing an aliphatic carboxylic acid, which method is suitable for recovering aliphatic sulfonic acid used as a solvent. Background technology>
  • the separation of distillation is improved by adding a substance (azeotropic agent or entrainer) that forms an azeotropic mixture with any of the component substances to a mixture that is difficult to separate by distillation. improves.
  • An industrial application of the azeotropic distillation method is to add acetic acid and water to a mixture of acetic acid and water by adding acetic acid n-propyl acetate or n-butyl acetate to form an azeotropic mixture with water and performing azeotropic distillation. There is a method of obtaining high-purity acetic acid from a water mixture.
  • One of the fields where the azeotropic distillation method can be applied is production of aromatic carboxylic acids. That is, the azeotropic distillation method can be applied in the process of recovering the solvent from the aromatic carboxylic acid production process.
  • an aromatic carboxylic acid such as terephthalic acid
  • a solvent containing an aliphatic carboxylic acid such as acetic acid.
  • a mixed vapor of aliphatic carboxylic acid and water is taken out from the reactor, and a feed stream containing a condensate of this vapor is distilled to separate water from the aliphatic carboxylic acid, and to remove the dehydrated aliphatic carboxylic acid.
  • An operation such as recirculating at least a part to the reaction raw material liquid adjusting tank is performed.
  • acetic acid which is widely used as the above solvent
  • rectification is usually used to separate water from the mixture of acetic acid and water, but azeotropic distillation may be more advantageous depending on installation and variable costs.
  • the main aspects of azeotropic distillation technology development can be broadly classified into separation, controllability, reduction of reflux ratio, and post-treatment of condensate from the azeotropic distillation column overhead.
  • the higher the reflux ratio the better the operational stability, and the lower the reflux ratio, the lower the operational stability.
  • the reflux ratio is below a certain limit value, the separability of the azeotropic distillation itself rapidly deteriorates.
  • This limit value is generally called the minimum reflux ratio, which is determined by the composition of the feed solution, the type of the entrainer, the position (height) of the feed solution to the azeotropic distillation column, the number of feed lines, It depends on the method of returning the reflux liquid and the method of returning the end trainer.
  • Japanese Patent Publication No. 62-41 219 discloses a method of reducing the oil phase component entrained in the water phase after separating the vapor condensate at the top of the azeotropic distillation column by liquid-liquid separation. Focusing on certain isobutyl acetate and an aliphatic carboxylic acid ester as an impurity, it has been proposed to strip the aqueous phase solution and collect them. However, this is intended to prevent loss due to entrainment of the oil phase component in the aqueous phase, and is not a technique for solving all the problems derived from the aliphatic carboxylic acid esters as impurities. The aliphatic carboxylic acid ester enters the distillation column along with the feed and accumulates in the oil phase. Tokiko Sho 62—
  • the method described in Japanese Patent No. 42119 is a technique for preventing a part of the aliphatic carboxylic acid ester of the accumulated impurities from being lost due to entrainment from the aqueous phase, and the aliphatic carboxylic acid contained in the oil phase.
  • the increase in the concentration of the aliphatic carboxylic acid ester deteriorates the separability between acetic acid and water in azeotropic distillation, and causes a loss of the active ingredient (acetic acid). Since then, various companies have proposed techniques for preventing the accumulation of impurities (aliphatic carboxylic esters) in the oil phase.
  • Korean Patent Publication No. 941-142292 discloses that the product obtained by condensing the vapor at the top of an azeotropic distillation column is subjected to liquid-liquid separation, and then the aliphatic aliphatic impurities entrained in the oil phase are removed.
  • a method for recovering a carboxylic acid ester by distillation has been proposed.
  • this method has a problem that a large amount of energy is required for separating the above-mentioned aliphatic carboxylic acid ester due to poor separability between the aliphatic carboxylic acid ester in the oil phase and the entrainer.
  • Japanese Patent Application Laid-Open No. 2000-72714 discloses that the vapor at the top of an azeotropic distillation column is fractionated and the fatty acid carboxylate ester of impurities in the remaining gas is absorbed and collected in acetic acid. A method has been proposed. However, in this method, since the entrainer component is entrained by the condensation, the aliphatic carboxylic acid ester alone cannot be taken out, resulting in loss of the effective component (entrainer component) and contamination of the product.
  • WO 98/45 239 proposes a method for recovering aliphatic carboxylic acid esters as impurities by distilling the vapor at the top of an azeotropic distillation column and distilling the remaining gas.
  • This technology also has an improvement in the amount of heat used, but it cannot isolate the aliphatic sulfonic acid ester, and is similar to the technology described in other patents in that it has a dedicated route for recovery. Problem. Further, in the publication, since the water concentration in the azeotropic composition is low, there is a problem that a large amount of an end trainer must be used to remove water by azeotropic distillation.
  • the amount of entrainer used in the azeotropic distillation depends on the azeotropic composition, but is generally at least 1 times, for example, 2 to 5 times the weight ratio to water. Therefore, in addition to the large amount of the entrainer itself, since the entrainer is usually used in circulation, it has a lower boiling point than acetic acid and is less soluble in water (for example, methyl-para-xylene acetate ) Accumulate on one side. Therefore, when the amount of impurities contained increases, the amount of the oil phase greatly increases. Therefore, the allowable range in which the aliphatic carboxylic acid ester, which is one of the impurities, can be contained is narrow.
  • the present invention has been made in view of the above circumstances, and has been made in consideration of the concentration of an aliphatic carboxylic acid ester as an impurity in an aqueous phase of a condensate obtained by condensing a distillate at the top of an azeotropic distillation column.
  • the starting point is a new idea obtained from the point of interest of the ratio with the entrainer concentration. It is known that the recovery of organic components from the aqueous phase is almost an essential operation, but the present invention has actively applied it and found a technique for suppressing an increase in aliphatic carboxylic acid esters as impurities. .
  • the present invention is based on this technology, and aims to provide an azeotropic distillation method that suppresses energy consumption and achieves excellent separation performance by introducing a simple process. .
  • the gist of the present invention resides in an azeotropic distillation method having at least the following steps (1) to (5).
  • Step (1) A solution to be distilled containing water, an aliphatic carboxylic acid and an aliphatic carboxylic acid ester is azeotropically distilled using an entrainer to obtain an aliphatic phenolic acid having reduced water content, A step of obtaining a water-enriched overhead distillate.
  • Step (2) a step of condensing the top distillate to obtain a gas and a condensate separated into two phases, an aqueous phase and an oil phase.
  • Step (3) a step of separating an aqueous phase and an oil phase of the condensate.
  • Step (4) A step of distilling a part or the whole of the aqueous phase obtained by the fractionation to obtain the overhead distillate containing the aliphatic carboxylic acid ester and having a reduced water content.
  • Step (5) The overhead distillate obtained in the step (4) is distilled together with a part or all of the oil phase collected in the step (3), and the aliphatic carboxylic acid obtained by the distillation is distilled. A step of collecting part or all of the ester outside the system.
  • FIG. 1 is a flowchart showing an example of a distillation process for carrying out the present invention.
  • 11 is an azeotropic distillation column
  • 13 is a liquid-liquid separation tank 1)
  • 2 is a stripping tower
  • 24 is an entrainer and a recovery column.
  • the “solution to be distilled” means a mixed solution containing a target substance to be purified and a substance whose concentration is to be reduced (hereinafter referred to as “reduced substance”).
  • Reduced substance means the third component added to perform azeotropic distillation.
  • the “azeotropic region” means a region where the concentration of the entrainer is at least 0.1% by weight in the entire composition existing as a liquid phase in the region.
  • the term “azeotropic distillation column” means a distillation column for distilling the above-mentioned solution to be distilled and the entrainer.
  • a solution to be distilled containing water, an aliphatic carboxylic acid and an aliphatic carboxylic acid ester is azeotropically distilled using an entrainer to obtain a water content as a target substance.
  • an aliphatic carboxylic acid having a reduced water content and a water-enriched overhead distillate is obtained.
  • the concentration of the entrain in the bottom liquid is 100 ppm or less.
  • the concentration of the aliphatic carboxylic acid in the condensate of the distillate at the top of the azeotropic distillation column is preferably not more than 1,000 p. It is recycled to the system of the liquid-phase oxidation reaction of substituted aromatic hydrocarbons.
  • the solution to be distilled in the present invention is a mixed solution containing the target substance and the reducing substance. Further, the entrainer to be added and the reducing substance form an azeotropic mixture, and the azeotropic temperature of the target substance is reduced. There is no particular limitation as long as it is lower than the boiling point. Further, it may contain a substance which does not substantially affect the azeotropic distillation.
  • the end trainer in the present invention is not particularly limited as long as the effect is exhibited. It does not need to be a single component, and may be a mixture of two or more components that form a heterogeneous azeotrope with the reducing substance, or may contain a part of a decomposition product of the component. You may.
  • the azeotropic distillation column in the present invention may be either a packed column or a tray column.
  • the supply position of the solution to be distilled is not particularly limited, it is usually the middle stage of the azeotropic distillation column, and the optimum position may be determined in consideration of the composition in the column in order to optimize the separation efficiency.
  • the operation of the azeotropic distillation column can be carried out under normal pressure, under pressure, or under reduced pressure, and the system may be a batch system or a continuous system. More preferably, it is carried out continuously under normal pressure.
  • the concentration of the above-mentioned aliphatic carboxylic acid ester in azeotropic distillation is arbitrary, but it is necessary to contain 3 to 50% by weight in the oil phase containing the entrainer to obtain a stable and high concentration of water from an aliphatic carboxylic acid such as acetic acid. From the viewpoint of separation.
  • the kind of the aliphatic carboxylic acid ester as an impurity contained in the solution to be distilled is not particularly limited, but usually, an ester of the aliphatic carboxylic acid of the target substance is mentioned, and specifically, for example, acetic acid Methyl.
  • the entrainer is selected in consideration of the type of the coexisting aliphatic carboxylic acid, but a known compound used for azeotropic distillation of a mixed solution containing the aliphatic carboxylic acid and water can be used.
  • esters such as butyl formate, n-propyl acetate, isobutyl acetate, n-butyl acetate, amyl acetate, n-butyl propionate, and isobutyl propionate, dichloromethyl ether, ethyl isoamyl ether, and linoleisoea Ethers such as mill ether and di-n-butylinoleether; halogenated hydrocarbons such as ethylene dichloride and chlorobenzene; ketones such as acetone chloride, dipropionoleketone, methylbutinoleketone and arinoleacetone; tonolenene and xylene Compounds that can form an
  • the solution to be distilled is a solvent used for the production of an aromatic carboxylic acid such as terephthalic acid, etc.
  • p in the solution to be distilled originates from the aromatic carboxylic acid production raw material.
  • Decomposition products of other substances such as xylene and methyl acetate may be contained.
  • composition of the aliphatic carboxylic acid and water in the solution to be distilled is arbitrary.
  • the present invention is applied to a mixed solution containing an aliphatic sulfonic acid and water having a water content in the range of 4 to 99% by weight, preferably in the range of 10 to 70% by weight / 0. You.
  • the solution to be distilled to which the method of the present invention is applied include those recovered in a process of producing an aromatic carboxylic acid in which a liquid-phase oxidizing and purifying an alkyl-substituted aromatic hydrocarbon in a solvent containing an aliphatic carboxylic acid.
  • a condensed and recovered product of a mixed vapor from a liquid-phase oxidation reactor of an alkyl-substituted aromatic hydrocarbon and a recovered product in which steam acetic acid in waste gas discharged from the reactor is absorbed by water.
  • the liquid and amount can be selected and used. These liquids may be mixed or treated independently.
  • a step (2) a step of condensing the overhead distillate to obtain a gas and a condensate separated into two phases, a water phase and an oil phase; Step (3): Separating each phase of the condensate separately.
  • a bottoms containing the target substance having a reduced concentration of the reduced substance is obtained from the bottom of the column, and the bottom is mainly composed of the reduced substance and the entrainer from the top of the column.
  • An azeotropic vapor (top distillate) is obtained.
  • the vapor obtained from the top is condensed to obtain a condensate and a gas.
  • This condensate is usually obtained as a two-phase liquid consisting of an aqueous phase mainly composed of the reducing substance and an oil phase mainly composed of the entrainer.
  • step (3) the two-phase condensate is separated into an aqueous phase and an oil phase.
  • fractionation means examples include liquid-liquid separation using a decanter or the like, but are not particularly limited as long as the purpose is achieved. In order to separate the two phases in this way, it is preferable to use an entrainer and a reducing substance that gives a heterogeneous azeotrope such that the aqueous phase and the oil phase constituting the condensate do not mix uniformly.
  • the amount of the aliphatic carboxylic acid ester recovered from the oil phase is calculated by subtracting the amount of the aliphatic carboxylic acid ester recovered from the aqueous phase by 2 It is preferable to set it to 0 times or less. This is, for example, “the flow rate of the oil phase per unit time X the concentration of the aliphatic carboxylic acid ester in the oil phase” and “the flow rate of the aqueous phase per unit time X the concentration of the aliphatic carboxylic acid ester in the aqueous phase” Is obtained.
  • the amount of the aliphatic carboxylic acid ester that can be recovered from the aqueous phase decreases, and the effect of the present invention may be reduced.
  • the amount is preferably 18 times or less, particularly 15 times or less. Is preferred.
  • the part is preferably recycled to the azeotropic distillation column.
  • the amount of entrainer recycled to the azeotropic distillation column is theoretically given by the amount of water to be discharged from the azeotropic distillation column and the composition of the azeotropic mixture.
  • the optimum amount of entrainer may be determined from the concentration of aliphatic carboxylic acid in the condensate of the effluent from the azeotropic distillation column and the concentration of entrainer in the bottoms.
  • a new trainer may be supplied to compensate for the lost trainer that has gone out of the system.
  • a part of the phase (aqueous phase) mainly containing the reducing substance is subjected to the step (4) described later.
  • the remaining aqueous phase may be returned to the azeotropic distillation column as a reflux liquid.
  • a part of the aqueous phase may be returned to the azeotropic distillation column as a reflux liquid.
  • water which is the main component of the phase (aqueous phase) mainly composed of the reducing substance, may be partially discarded after being reused in the process.
  • the method of returning water as a reflux liquid includes, for example, a method of returning to the top of the azeotropic distillation column and a method of returning to the middle stage of the column.
  • the amount of water reflux is usually set to about 0.1 to 3 depending on the ratio (return water amount / discharged water amount).
  • step (4) a part or all of the separated aqueous phase is distilled to obtain an overhead distillate containing the above-mentioned aliphatic sulfonic acid ester having a reduced water content.
  • the aqueous phase separated from the condensate of the distillate at the top of the azeotropic distillation tower (mainly water, which is a reducing substance) is sent to the distillation tower, and from the top of the distillation tower, A method for obtaining the above-mentioned aliphatic carboxylic acid having a reduced water content is exemplified. What is obtained from the bottom of the distillation column in this distillation is mainly water. Even if this water is discarded outside the system, a part of it is returned to the azeotropic distillation column as a reflux liquid.
  • the top distillate obtained in the step (4) is distilled together with part or all of the oil phase fractionated in the step (3), and the above-mentioned aliphatic product obtained by the distillation is distilled off. Carbo Part or all of the acid ester is recovered out of the system.
  • the distillation column in step (5) is for the purpose of recovering the entrainer.
  • the distillate at the top of step (4) and the oil phase of the condensate of the distillate at the top of the azeotropic distillation column collected in step (3) are collected. Feed part or all and distill.
  • This distillation separates the entrainer from the impurity aliphatic carboxylic acid ester.
  • the supply of the components to be distilled to step (5) was controlled so that at least 20% of the aliphatic carboxylic acid ester was derived from the overhead obtained in step (4). Is preferable in terms of energy efficiency.
  • the entrainer is collected from the bottom of the column, and part or all may be collected outside the system, or part or all may be returned to the azeotropic distillation column.
  • the aliphatic carboxylic acid ester which is an impurity, may be partially or entirely recovered outside the system.
  • the condensate of the azeotropic distillation column top distillate that is, the entrainer and the aliphatic A mixture of carboxylic acid ester
  • the gas obtained in step (2) may be supplied together with the oil phase.
  • the oil phase separated in the step (3) and the entrainer obtained in the step (5) are supplied to the azeotropic distillation column as described in JP-B-61-31091.
  • the azeotropic distillation column As described in JP-B-61-31091.
  • the effect of changing the operating conditions can be easily reflected, and the response can be speeded up.
  • water obtained in the step (2) or the step (4) as described in Japanese Patent Publication No. 10-504556, water is returned to the middle stage of the azeotropic distillation column as a reflux liquid to the column. It can also be used for a method of controlling the impurity concentration at the bottom of the column by controlling the amount.
  • the alkyl-substituted aromatic hydrocarbons accumulated in the entrainer may be separated directly from the entrainer, or may be azeotropic as described in JP-A-10-504556. It may be withdrawn from the middle stage of the distillation column. Further, the extracted product can be purified as described in WO 97/29068. Next, a method for producing an aromatic carboxylic acid of the present invention to which the azeotropic distillation method of the present invention is applied will be described.
  • the aromatic carboxylic acid as the target compound is any aromatic carboxylic acid, such as aromatic monocarboxylic acid, aromatic dicarboxylic acid, and aromatic tricarboxylic acid.
  • aromatic carboxylic acid such as aromatic monocarboxylic acid, aromatic dicarboxylic acid, and aromatic tricarboxylic acid.
  • aromatic monocarboxylic acid such as aromatic monocarboxylic acid, aromatic dicarboxylic acid, and aromatic tricarboxylic acid.
  • the corresponding alkyl-substituted aromatic hydrocarbon such as monoa / lequinolebenzene, dianolequinolebenzene, and trialkylbenzene is oxidized, preferably in a liquid phase.
  • the method of the present invention is preferably applied when the aromatic dicarboxylic acid, particularly the aromatic carboxylic acid is terephthalic acid.
  • P-xylene is used as the alkyl-substituted aromatic hydrocarbon as a raw material.
  • an aliphatic carboxylic acid When performing the oxidation reaction in a liquid phase, an aliphatic carboxylic acid is usually used as a solvent.
  • the aliphatic carboxylic acid which is a solvent for the liquid phase oxidation reaction for example, acetic acid is preferred, and the amount of the solvent is usually 2 to 6 times by weight based on the starting alkyl-substituted aromatic hydrocarbon.
  • the water concentration in the oxidation reaction system is usually 4 to 25% by weight, preferably 7 to 20% by weight.
  • a catalyst is usually used.
  • a transition metal compound such as manganese, cobalt, iron, chromium, and nickel is used.
  • a bromine compound may be used as the co-catalyst.
  • acetoaldehyde-methylethyl ketone or the like is used as a promoter for the cobalt catalyst.
  • oxidizing agent molecular oxygen or air is used, but usually air is used. Air having a high oxygen concentration by mixing oxygen gas, or air having a low oxygen concentration by mixing inert gas such as nitrogen gas, may be used.
  • the reaction temperature of the liquid phase oxidation may be appropriately selected, and is usually from 120 ° C to 220 ° C.
  • the reaction temperature is generally preferably 160 ° C. or less.
  • the pressure may be appropriately selected in the same manner.
  • acetic acid may be in a pressure range in which it can be in a gaseous state.
  • the heat of the oxidation reaction is mainly removed by flash evaporation of the aqueous acetic acid solvent. That is, the fraction (exhaust gas) from the oxidation reactor mainly contains evaporated acetic acid and water, and a small amount of low-boiling products and unreacted alkyl-substituted aromatic hydrocarbons among the by-products of the oxidation reaction. Contains. This vapor is cooled and condensed into a liquid by a condenser, and a part of the vapor is usually returned to the oxidation reactor as an oxidation reaction solvent.
  • Another part is sent to a dehydration tower for the purpose of removing water generated by the oxidation reaction, is subjected to the azeotropic distillation of the present invention, and the dehydrated acetic acid is sent again to the oxidation reactor as an oxidation reaction solvent.
  • the liquid-phase oxidation of alkyl-substituted aromatic hydrocarbons is usually performed in one reactor and, if necessary, in multiple reactors. If necessary, the reaction solution after the oxidation reaction is sent to one or two or more successively reduced pressure crystallizers, where it is cooled to the temperature corresponding to each pressure by the flash cooling action of the solvent to produce Most of the aromatic carboxylic acids crystallized as crystals, forming a slurry. The slurry is separated into a cake of aromatic rubonic acid crystals and an oxidation reaction mother liquor by any means of crystal separation, such as rotary vacuum filtration, centrifugation, or any other suitable separation method.
  • the cake of the aromatic carboxylic acid crystals is washed with acetic acid or water as required, and then the attached solvent is removed with a dryer. Further, if necessary, the slurry is re-slurried in a reaction mother liquor mainly composed of water, and is subjected to a hydrogenation step and then recrystallized to reduce impurities in the crystal and to be purified. Subsequently, after performing operations such as solid-liquid separation, washing, and drying, an aromatic carboxylic acid is obtained.
  • the azeotropic distillation method of the present invention and the method for producing aromatic carboxylic acid using the azeotropic distillation method will be described with reference to FIG. FIG.
  • 11 is an azeotropic distillation column.
  • the solution to be distilled containing water, aliphatic carboxylic acid (such as acetic acid) and aliphatic carboxylic acid ester of impurities is supplied from lines 40, 41, 42, etc.
  • the composition of the solutions is usually different from each other), and the end trainer
  • the mixture is supplied to an azeotropic distillation column 11 where azeotropic distillation is performed.
  • Heat is applied by heat exchanger 14 to add the heat required for distillation.
  • Heating oil or steam is used as a heating source.
  • a temperature higher than the normal pressure boiling point of acetic acid, specifically, 0.35 MPa steam is used.
  • the azeotropic mixture vapor containing the reducing substance whose concentration is to be reduced by azeotropic distillation and the entrainer (the distillate from the top of the azeotropic distillation column) is sent to the cooler 12 from the top of the azeotropic distillation column 11. It is condensed here.
  • the obtained condensate is separated into two phases in a liquid-liquid separation tank 13 and is separated therefrom.
  • An appropriate separation means may be selected depending on the properties of the azeotrope.
  • a part of the phase (aqueous phase) mainly composed of the reducing substance in the liquid-liquid separation tank 13 is sent to the stripping tower 21 through the line 17.
  • a part of the aqueous phase may be used as a reflux for water to the azeotropic distillation column 11 through the line 16.
  • the entrainer is circulated through line 15. Lines 15 and 16 are connected, if necessary, to the top or middle of the azeotropic distillation column 11.
  • the number of the lines 15 and 16 may be one or more, respectively.Furthermore, using a common line, the entrainer and the reducing substance are sent together to the azeotropic distillation column 11 It may be returned, or it may be returned by individual lines.
  • a liquid mainly containing a target substance for example, aliphatic carboxylic acid
  • a target substance for example, aliphatic carboxylic acid
  • the water and the aromatic carboxylic acid raw material mainly from line 22 in the middle stage of the tower are used.
  • a liquid comprising a substituted aromatic hydrocarbon is extracted.
  • organic components and in the method for producing an aromatic carboxylic acid of the present invention, mainly an aliphatic carboxylic acid ester as impurities are recovered, and reduced substances such as water separated by azeotropic distillation are collected in a line 1. It is recycled to the aromatic carboxylic acid production process through 8, where it is effectively used or discarded.
  • the organic components recovered in the stripping tower 21 are sent to an entrainer through a line 23 to an entrainer 24, where the entrainer and the aliphatic carboxylic acid ester of impurities are removed. Is separated into The entrainer is recovered from the bottom of the column and returned to the azeotropic distillation column 11 via lines 25 and 15.
  • the aliphatic carboxylic acid ester is recovered through line 26.
  • the aliphatic carboxylic acid ester may be stored as desired, or may be partially or wholly circulated in the oxidation reaction step for producing an aromatic carboxylic acid.
  • the entrainer and a mixture of the aliphatic carboxylic acid ester branched off at line 27 are directly introduced into the entrainer-one recovery tower 24. Although not shown, cooling is performed. It is also possible to introduce the gas generated in the vessel 12 into the entrainer-one recovery tower 24.
  • the amount of the aliphatic carboxylic acid ester recovered outside the system is indicated as the amount of the substance discharged from the line 26.
  • This effluent may contain impurities such as entrainers, water, aliphatic hydrocarbons, etc., and may be liquids, gases or mixtures thereof.
  • the amount of the aliphatic carboxylic acid ester introduced into the recovery step via the aqueous phase liquid of the condensed liquid phase at the top of the azeotropic distillation column 11 depends on the amount of the substance flowing through the line 17. Indicated as quantity.
  • the recovery ratio is at least 20%, preferably at least 30%, more preferably at least 40%, based on the total amount of the above-mentioned aliphatic carboxylic acid esters recovered outside the system, through the aqueous phase. Is preferable from the viewpoint of energy efficiency.
  • the above-mentioned aliphatic carboxylic acid ester can be accompanied, albeit very slightly, in the bottom liquid 25 of the entrainer recovery tower 24. Therefore, in the present invention, the above-mentioned recovery ratio is calculated based on the ratio of the amount of the aliphatic carboxylic acid ester via the aqueous phase to the amount of the aliphatic sulfonic acid ester introduced into the recovery step via the aqueous phase and the oil phase. .
  • the stream of the aliphatic carboxylic acid ester which has not passed through the aqueous phase is introduced into the entrainer-recovery column 24 through the line 27.
  • This flow may be a gas or a liquid or a mixture thereof, and the gas generated in the cooler 12 may be used in combination, as described in WO98 / 45239.
  • the concentration ratio of the aliphatic carboxylic acid ester of the impurity and the entrainer in the oil phase extracted from the liquid-liquid separation tank 13 is usually 1: 100 to 1: 2.
  • the recovery ratio is adjusted by adjusting the flow rate of the path indicated by the line 27 or the flow rate of the path indicated by the line 28.
  • the distribution of the aliphatic carboxylic acid ester as an impurity is calculated by: (total amount of the substance in the aqueous phase) / ( The greater the ratio indicated by (total amount of substances), the greater the effect of the method of the present invention. It can be obtained as, for example, (aqueous phase flow rate per unit time X concentration of the aliphatic carboxylic acid ester in the aqueous phase) Z (oil phase flow rate per unit time X concentration of the aliphatic carboxylic acid ester in the oil phase) Can be done.
  • the concentration of the above-mentioned aliphatic carboxylic acid ester in the oil phase is 1 to 50% by weight, but this concentration is determined by the amount of the above-mentioned aliphatic carboxylic acid ester to be recovered from the route shown in line 25. And the distribution ratio of the substance in the water and oil phases.
  • the amount of the aliphatic carboxylic acid ester as an impurity accompanying the oil phase is 20 times or less, preferably 17 times or less, more preferably the amount of the aliphatic carboxylic acid ester accompanying the water phase. Is preferably 15 times or less, or the water is refluxed.
  • the amount of entrainment here is determined by the product of the substance concentration and the flow rate of the liquid flowing through the route.
  • the recovery process is represented by two distillation columns, but it is also possible to connect the columns 21 and 24 and omit the reboiler of the column 24.
  • the present invention provides a greater effect in azeotropic distillation that requires separation and recovery of aliphatic carboxylic acid esters as impurities.
  • the aliphatic carboxylic acid concentration in the overhead liquid of the azeotropic distillation column is not more than 100 ppm and the can of the azeotropic distillation column
  • Example 1 Specific embodiments of the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.
  • Example 1
  • the p-xylene was withdrawn from the line 22 at the middle stage and recovered, and methyl acetate was recovered by distillation using an entrainer recovery column 24 having 13 theoretical plates. From the top of the azeotropic distillation column 11, water having an azeotropic composition and steam containing an entrainer were obtained, which was cooled and recovered in the liquid-liquid separation tank 13. The aqueous phase liquid of the two liquid phases separated in the liquid-liquid separation tank 13 is passed through the line 17 into the stripping tower 21 with eight theoretical plates, and after removal of organic components, the line 1 It is divided into 8 and 28. Line 18 was wastewater, and line 28 was reflux water to azeotropic distillation column 11.
  • the amount of reflux water was determined so that the water reflux ratio defined by Wr / Ww became a desired value.
  • the amount (Ww) of the discharged aqueous phase liquid is 17.3 parts by weight per unit time
  • the amount of the reflux water (Wr) is 11 parts by weight
  • the water reflux ratio is 0.64. It was carried out in.
  • the organic components recovered in the stripping tower 21 are transferred to the entrainer-collection tower 24 through the line 23.
  • the entrainer was subjected to liquid-liquid separation in a liquid-liquid separation tank 13 and then circulated through a line 15 to an azeotropic distillation column 11.
  • Example 1 except that the amount of methyl acetate introduced into the recovery step via the aqueous phase condensate was reduced to 15% of the amount of methyl acetate recovered outside the system. Distillation was performed in the same manner as in Example 1.
  • the amount of heat used in the entrainer recovery tower 24 was 2.0 Gca1r.
  • azeotropic distillation can be operated with reduced energy without using a complicated distillation process. Therefore, the method of the present invention has a great effect on variable costs or environmental protection, and has a high stability due to its simplicity, and has an effect of reducing the outflow of active ingredients.

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Abstract

A process of azeotropic distillation which comprises the following steps (1) to (5): step (1): a step of azeotropically distilling a solution to be distilled containing water, an aliphatic carboxylic acid and an aliphatic carboxylate using an entrainer to give an aliphatic carboxylic acid having a reduced water content and an overhead fraction having a concentrated water content, step (2): a step of condensing the overhead fraction to give a gas and a liquid condensate being separated into a water phase and an oil phase, step (3): a step of withdrawing the water phase and the oil phase of the condensate separately, step (4): a step of distilling a part or all of the water phase thus withdrawn to give an overhead fraction containing the above aliphatic carboxylate and having a reduced water content, and step (5): a step of distilling the overhead fraction in step (4) together with a part or all of the oil phase in step (3) to give a fraction containing the above aliphatic carboxylate and recovering a part or all of the aliphatic carboxylate fraction to the outside of the azeotropic distillation system.

Description

明 細 書 共沸蒸留方法 <技術分野 >  Description Azeotropic distillation method <Technical field>
本発明は共沸蒸留方法に関する。本発明は共沸蒸留により、脂肪族カルボン酸、 たとえば酢酸を含有する水性供給流から、 水を分離して脂肪族カルボン酸を回収 する場合に特に効果を奏する。 本発明は脂肪族カルボン酸を含む溶媒中での液相 酸化反応により芳香族カルボン酸を製造する方法において、 溶媒として用いられ る脂肪族力ルポン酸の回収に適した方法に関する。 ぐ背景技術 >  The present invention relates to an azeotropic distillation method. The present invention is particularly effective when azeotropic distillation separates water from an aqueous feed stream containing an aliphatic carboxylic acid, such as acetic acid, to recover the aliphatic carboxylic acid. The present invention relates to a method for producing an aromatic carboxylic acid by a liquid phase oxidation reaction in a solvent containing an aliphatic carboxylic acid, which method is suitable for recovering aliphatic sulfonic acid used as a solvent. Background technology>
共沸蒸留方法においては、 蒸留分離が困難な混合物に、 成分物質のいずれかと 共沸混合物を形成するような物質 （共沸剤またはェントレーナー） を添加するこ とにより、 蒸留の分離性が向上する。 共沸蒸留方法の工業的適用例として、 酢酸 と水の混合液に、 水と共沸混合物を形成する酢酸 n—プロピルまたは酢酸 n—ブ チルを添加して共沸蒸留することによって、 酢酸と水の混合液から純度の高い酢 酸を得る方法等がある。  In the azeotropic distillation method, the separation of distillation is improved by adding a substance (azeotropic agent or entrainer) that forms an azeotropic mixture with any of the component substances to a mixture that is difficult to separate by distillation. improves. An industrial application of the azeotropic distillation method is to add acetic acid and water to a mixture of acetic acid and water by adding acetic acid n-propyl acetate or n-butyl acetate to form an azeotropic mixture with water and performing azeotropic distillation. There is a method of obtaining high-purity acetic acid from a water mixture.
共沸蒸留方法の適用が考えられる分野の一つとして、 芳香族カルボン酸の製造 'がある。 即ち芳香族カルボン酸製造プロセスからの溶媒の回収過程において共沸 蒸留方法の適用が可能である。  One of the fields where the azeotropic distillation method can be applied is production of aromatic carboxylic acids. That is, the azeotropic distillation method can be applied in the process of recovering the solvent from the aromatic carboxylic acid production process.
テレフタル酸等の芳香族カルボン酸の製造は、 一般に、 酢酸等の脂肪族カルボ ン酸を含む溶媒中で実施される。 しかし該製造工程中で水が生成するので、 反応 系中に水が蓄積するのを防ぐ必要がある。 このため、 反応器より脂肪族カルボン 酸と水の混合蒸気を取り出し、 この蒸気の凝縮液を含む供給流を蒸留して水を脂 肪族カルボン酸から分離し、 脱水された脂肪族カルボン酸の少なくとも一部を反 応原料液調整槽へ再循環する等の操作が行なわれる。  The production of an aromatic carboxylic acid such as terephthalic acid is generally carried out in a solvent containing an aliphatic carboxylic acid such as acetic acid. However, since water is generated during the production process, it is necessary to prevent water from accumulating in the reaction system. For this reason, a mixed vapor of aliphatic carboxylic acid and water is taken out from the reactor, and a feed stream containing a condensate of this vapor is distilled to separate water from the aliphatic carboxylic acid, and to remove the dehydrated aliphatic carboxylic acid. An operation such as recirculating at least a part to the reaction raw material liquid adjusting tank is performed.
脂肪族カルボン酸の内、 上記溶媒として広く使用されている酢酸について注目 すると、 通常、 酢酸と水との混合物からの水の分離には精留が用いられるが、 設 備費及び変動費次第では共沸蒸留の方が有利となる。 Of aliphatic carboxylic acids, focus on acetic acid, which is widely used as the above solvent Then, rectification is usually used to separate water from the mixture of acetic acid and water, but azeotropic distillation may be more advantageous depending on installation and variable costs.
共沸蒸留の技術開発の主要な観点は、 分離性、 制御性、 還流比低減、 共沸蒸留 塔塔頂留出物の凝縮液の後処理に大別される。 一般に、 還流比が大きければ運転 安定性が良く、還流比を小さくするにつれて運転安定性は次第に悪くなる。更に、 還流比がある限界値以下となると、 共沸蒸留自体の分離性が急激に悪化する。 こ の限界値は一般に最小還流比と呼ばれ、 その値は、 供給液組成、 ェントレー^ ~一 の種類、 共沸蒸留塔への供給液の供給位置 （高さ）、 給液ラインの数、還流液を戻 す方法、 ェントレーナーを戻す方法等によって異なる。  The main aspects of azeotropic distillation technology development can be broadly classified into separation, controllability, reduction of reflux ratio, and post-treatment of condensate from the azeotropic distillation column overhead. In general, the higher the reflux ratio, the better the operational stability, and the lower the reflux ratio, the lower the operational stability. Furthermore, when the reflux ratio is below a certain limit value, the separability of the azeotropic distillation itself rapidly deteriorates. This limit value is generally called the minimum reflux ratio, which is determined by the composition of the feed solution, the type of the entrainer, the position (height) of the feed solution to the azeotropic distillation column, the number of feed lines, It depends on the method of returning the reflux liquid and the method of returning the end trainer.
非常に高い還流比で運転を行えば、 制御性及び分離性を満足させることは容易 である力 このような運転はエネルギーを大量に消費し経済的に不利であるので、 実際には還流比を最小還流比に極力近づけてエネルギー消費を可能な限り低減し た運転が行われている。  If the operation is performed at a very high reflux ratio, it is easy to satisfy controllability and separability. Power such as this consumes a large amount of energy and is economically disadvantageous. Operation is performed with energy consumption as low as possible by approaching the minimum reflux ratio as much as possible.
酢酸と水との分離のための共沸蒸留方法は、 特公昭 62— 4121 9号、 韓国 特許公開 94— 14292号、 特開 2000 72714号、 W098Z45 2 An azeotropic distillation method for separating acetic acid and water is disclosed in JP-B-62-41219, Korean Patent Publication No. 94-14292, JP-A-2000-72714, W098Z452.
39号等の各公報にも開示されている。 It is also disclosed in each gazette such as No. 39.
特公昭 62-41 21 9号公報には、 共沸蒸留塔塔頂蒸気凝縮物を液液分離し た後に、 水相側に同伴される油相成分を低減させる方法として、 特に油相成分で ある酢酸ィソブチルと不純物の脂肪族カルボン酸エステルとに着目し、 水相液を ス トリツビングしてこれらを回収することが提案されている。 しかし、 これは水 相への油相成分の同伴による損失対策を目的としたものであり、 不純物の脂肪族 カルボン酸エステルに由来する問題を全て解決する技術ではない。 上記脂肪族力 ルボン酸エステルは給液に同伴して蒸留塔に入り油相に蓄積する。 特公昭 62— Japanese Patent Publication No. 62-41 219 discloses a method of reducing the oil phase component entrained in the water phase after separating the vapor condensate at the top of the azeotropic distillation column by liquid-liquid separation. Focusing on certain isobutyl acetate and an aliphatic carboxylic acid ester as an impurity, it has been proposed to strip the aqueous phase solution and collect them. However, this is intended to prevent loss due to entrainment of the oil phase component in the aqueous phase, and is not a technique for solving all the problems derived from the aliphatic carboxylic acid esters as impurities. The aliphatic carboxylic acid ester enters the distillation column along with the feed and accumulates in the oil phase. Tokiko Sho 62—
4121 9号公報記載の方法は、 この蓄積した不純物の脂肪族カルボン酸エステ ルの一部が水相から同伴して損失となることを防ぐ技術であり、 油相中に上記脂 肪族カルボン酸エステルが蓄積し、濃度が上昇していく問題には言及していない。 上記脂肪族カルボン酸エステルの濃度の上昇は共沸蒸留における酢酸と水との分 離性を悪化させ、 有効成分 （酢酸） の損失を生じさせる。 その後も各社から、 油相への不純物 （脂肪族カルボン酸エステル） の蓄積を防 止するための技術が提案されている。 The method described in Japanese Patent No. 42119 is a technique for preventing a part of the aliphatic carboxylic acid ester of the accumulated impurities from being lost due to entrainment from the aqueous phase, and the aliphatic carboxylic acid contained in the oil phase. No mention is made of the problem of ester accumulation and increasing concentrations. The increase in the concentration of the aliphatic carboxylic acid ester deteriorates the separability between acetic acid and water in azeotropic distillation, and causes a loss of the active ingredient (acetic acid). Since then, various companies have proposed techniques for preventing the accumulation of impurities (aliphatic carboxylic esters) in the oil phase.
例えば韓国特許公開 9 4一 1 4 2 9 2号公報には、 共沸蒸留塔塔頂蒸気を凝縮 して得られたものを液液分離した後に、 油相側に同伴される不純物の脂肪族カル ボン酸エステルを蒸留回収する方法が提案されている。 しかし、 この方法は油相 中の上記脂肪族カルボン酸エステルとェントレーナ一との分離性が悪いために上 記脂肪族カルボン酸エステルの分離に大量のエネルギーを要するという問題があ る。  For example, Korean Patent Publication No. 941-142292 discloses that the product obtained by condensing the vapor at the top of an azeotropic distillation column is subjected to liquid-liquid separation, and then the aliphatic aliphatic impurities entrained in the oil phase are removed. A method for recovering a carboxylic acid ester by distillation has been proposed. However, this method has a problem that a large amount of energy is required for separating the above-mentioned aliphatic carboxylic acid ester due to poor separability between the aliphatic carboxylic acid ester in the oil phase and the entrainer.
また、 特開 2 0 0 0— 7 2 7 1 4号公報には共沸蒸留塔の塔頂蒸気を分縮し、 残留するガス中の不純物の脂肪酸カルボン酸エステルを酢酸に吸収して回収する 方法が提案されている。 しかし、 この方法では分縮でェントレーナー成分を同伴 するため、 上記脂肪族カルボン酸エステルのみを取り出すことは出来ず、 有効成 分 （ェントレーナー成分） の損失や製品の汚染を招く。  Japanese Patent Application Laid-Open No. 2000-72714 discloses that the vapor at the top of an azeotropic distillation column is fractionated and the fatty acid carboxylate ester of impurities in the remaining gas is absorbed and collected in acetic acid. A method has been proposed. However, in this method, since the entrainer component is entrained by the condensation, the aliphatic carboxylic acid ester alone cannot be taken out, resulting in loss of the effective component (entrainer component) and contamination of the product.
WO 9 8 / 4 5 2 3 9号公報には共沸蒸留塔の塔頂蒸気を分縮し残留するガス を蒸留して不純物の脂肪族カルボン酸エステルを回収する方法が提案されている。 この技術も使用熱量の点で改善が見られるが、 上記脂肪族力ルポン酸エステルを 単離することは出来ず、 回収のための専用の経路を設ける点では他の特許に記載 の技術と同様な問題がある。 さらに同公報では共沸組成における水濃度が低いた め、 共沸蒸留により水を除くためにはェントレーナ一を大量に用いなければなら ないという問題もある。 共沸蒸留で使用するェントレーナ一の量は共沸組成によ つて決まるが、一般的には水に対する重量比で 1倍以上、例えば 2〜 5倍である。 従って、 ェントレーナ そのものが大量であることに加え、 通常、 ェントレーナ 一は循環させて使用する為、 酢酸より沸点が低く水に溶けにくいもの （例えばテ レフタル酸の製造に於いては酢酸メチルゃパラキシレン） はェントレー ^ ~一側に 蓄積する。 よってその含有不純物量が増えると油相量が大幅に増大する。 そのた め不純物の一種である脂肪族カルボン酸エステルを含有できる許容幅は狭い。 上記の通り、 不純物の脂肪族カルボン酸エステルの回収については、 蒸留系の 入りと出とをバランスさせる、 分離回収のためのエネルギー使用量を下げる、 高 純度で回収する、 簡単な設備で変動損失を回避すると言った課題全てに対応して いることが好ましい。 そのため、 これまでに不純物である脂肪族カルボン酸エス テル回収専用の設備が提案されてきた。 WO 98/45 239 proposes a method for recovering aliphatic carboxylic acid esters as impurities by distilling the vapor at the top of an azeotropic distillation column and distilling the remaining gas. This technology also has an improvement in the amount of heat used, but it cannot isolate the aliphatic sulfonic acid ester, and is similar to the technology described in other patents in that it has a dedicated route for recovery. Problem. Further, in the publication, since the water concentration in the azeotropic composition is low, there is a problem that a large amount of an end trainer must be used to remove water by azeotropic distillation. The amount of entrainer used in the azeotropic distillation depends on the azeotropic composition, but is generally at least 1 times, for example, 2 to 5 times the weight ratio to water. Therefore, in addition to the large amount of the entrainer itself, since the entrainer is usually used in circulation, it has a lower boiling point than acetic acid and is less soluble in water (for example, methyl-para-xylene acetate ) Accumulate on one side. Therefore, when the amount of impurities contained increases, the amount of the oil phase greatly increases. Therefore, the allowable range in which the aliphatic carboxylic acid ester, which is one of the impurities, can be contained is narrow. As mentioned above, regarding the recovery of aliphatic carboxylic acid esters as impurities, balance the entry and exit of the distillation system, reduce the amount of energy used for separation and recovery, and increase It is preferable to address all the issues of recovering with purity and avoiding fluctuation loss with simple equipment. For this reason, facilities dedicated to the recovery of aliphatic carboxylic acid esters, which are impurities, have been proposed.
本発明は、 係る事情に鑑みてなされたものであって、 共沸蒸留塔塔頂留出物を 凝縮して得られる凝縮液の水相中にある不純物の脂肪族カルボン酸エステルの濃 度とェントレーナー濃度との比という着目点から得られた、 新たな発想を出発点 としている。 この水相からの有機成分回収がほぼ必須の操作であることは公知で あるが、 本発明はそれを積極的に応用し、 不純物の脂肪族カルボン酸エステルの 増加を抑えるための技術を見出した。 そして本発明は、 この技術から構築された ものであり、 簡単なプロセスを導入することによって、 エネルギー使用量を低く 抑え、且つ優れた分離性能を奏する共沸蒸留方法を提供しようとする発明である。  The present invention has been made in view of the above circumstances, and has been made in consideration of the concentration of an aliphatic carboxylic acid ester as an impurity in an aqueous phase of a condensate obtained by condensing a distillate at the top of an azeotropic distillation column. The starting point is a new idea obtained from the point of interest of the ratio with the entrainer concentration. It is known that the recovery of organic components from the aqueous phase is almost an essential operation, but the present invention has actively applied it and found a technique for suppressing an increase in aliphatic carboxylic acid esters as impurities. . The present invention is based on this technology, and aims to provide an azeotropic distillation method that suppresses energy consumption and achieves excellent separation performance by introducing a simple process. .
<発明の開示 > <Disclosure of Invention>
本発明は共沸蒸留の操作における、 共沸蒸留塔内に存在するェントレーナ一中 に蓄積する不純物の脂肪族カルボン酸エステルの回収に関する。 本発明者らは共 沸蒸留塔塔頂留出物の凝縮液の水相における上記脂肪族カルボン酸エステル濃度 とェントレーナ一濃度との比が油相中に比べて高いことに着目し、 水相から上記 脂肪族カルボン酸エステルを回収することで、 従来着目されてきた経路から回収 する方法に比べて簡易かつ低いエネルギーで上記脂肪族カルボン酸エステルを回 収できることを見出した。 本発明はこれらの知見に基づいて成し遂げられたもの である。  The present invention relates to the recovery of an aliphatic carboxylic acid ester of impurities that accumulate in an entrainer present in an azeotropic distillation column in an azeotropic distillation operation. The present inventors have focused on the fact that the ratio of the aliphatic carboxylic acid ester concentration to the entrainer concentration in the aqueous phase of the condensate of the azeotropic distillation column overhead is higher than that in the oil phase. It has been found that, by recovering the above-mentioned aliphatic carboxylic acid ester, it is possible to recover the above-mentioned aliphatic carboxylic acid ester easily and with low energy as compared with the method of recovering from the conventionally focused route. The present invention has been accomplished based on these findings.
即ち本発明の要旨は、 少なくとも以下の工程 （1 ) 〜 （5 ) を有する共沸蒸留 方法に存する。  That is, the gist of the present invention resides in an azeotropic distillation method having at least the following steps (1) to (5).
工程（1 )： 水、脂肪族カルボン酸及び脂肪族カルボン酸エステルを含む蒸留対 象溶液を、 ェントレーナーを用いて共沸蒸留して、 含水量の低減された脂肪族力 ノレボン酸と、 水分の濃縮された塔頂留出物を得る工程。 Step (1): A solution to be distilled containing water, an aliphatic carboxylic acid and an aliphatic carboxylic acid ester is azeotropically distilled using an entrainer to obtain an aliphatic phenolic acid having reduced water content, A step of obtaining a water-enriched overhead distillate.
工程 （2 )： 該塔頂留出物を凝縮させて、 ガスと、水相及び油相の 2相に分れた 凝縮液とを得る工程。 工程 （3 ) ： 該凝縮液の水相及ぴ油相を分取する工程。 Step (2): a step of condensing the top distillate to obtain a gas and a condensate separated into two phases, an aqueous phase and an oil phase. Step (3): a step of separating an aqueous phase and an oil phase of the condensate.
工程（4 )： 該分取で得られた水相の一部または全部を蒸留して、上記脂肪族力 ルボン酸エステルを含み、 含水量の低減された塔頂留出物を得る工程。 Step (4): A step of distilling a part or the whole of the aqueous phase obtained by the fractionation to obtain the overhead distillate containing the aliphatic carboxylic acid ester and having a reduced water content.
工程 （5 ) ： 工程 （4 ) にて得られた塔頂留出物を、 工程 （3 ) で分取した油相 の一部又は全部と共に蒸留し、 該蒸留によって得られる上記脂肪族カルボン酸ェ ステルの一部又は全部を系外へ回収する工程。 ぐ図面の簡単な説明 > Step (5): The overhead distillate obtained in the step (4) is distilled together with a part or all of the oil phase collected in the step (3), and the aliphatic carboxylic acid obtained by the distillation is distilled. A step of collecting part or all of the ester outside the system. Brief description of the drawing>
図 1は、 本発明を実施するための蒸留プロセスの一例を示す流れ図である。 なお、 図中の符号、 1 1は共沸蒸留塔、 1 3は液液分離槽 一）、 2 はストリッビング塔、 2 4はェントレーナ一回収塔である。  FIG. 1 is a flowchart showing an example of a distillation process for carrying out the present invention. In the figures, 11 is an azeotropic distillation column, 13 is a liquid-liquid separation tank 1), 2 is a stripping tower, and 24 is an entrainer and a recovery column.
<発明を実施するための最良の形態〉 <Best mode for carrying out the invention>
以下、 本発明の実施の形態について詳細に説明する。  Hereinafter, embodiments of the present invention will be described in detail.
本明細書において、 「蒸留対象溶液」 とは、精製したい目的物質と濃度を低減さ せたい物質 （以下「低減物質」 とレ、う） とを含む混合溶液を意味する。 「ェントレ ーナ一」 とは共沸蒸留を行うために加える第三成分を意味する。また、「共沸領域」 とは、 その領域内で液相として存在する組成全体の中でェントレーナ一の濃度が 少なくとも 0 . 1重量％である領域を意味する。 「共沸蒸留塔」 とは、上記の蒸留 対象溶液及びェントレーナ一を蒸留する蒸留塔を意味する。  In the present specification, the “solution to be distilled” means a mixed solution containing a target substance to be purified and a substance whose concentration is to be reduced (hereinafter referred to as “reduced substance”). "Entrena" means the third component added to perform azeotropic distillation. The “azeotropic region” means a region where the concentration of the entrainer is at least 0.1% by weight in the entire composition existing as a liquid phase in the region. The term “azeotropic distillation column” means a distillation column for distilling the above-mentioned solution to be distilled and the entrainer.
[工程 （1 ) の説明] [Explanation of step (1)]
本発明に於いてはまず工程 （1 ) として、 水、 脂肪族カルボン酸及び脂肪族力 ルボン酸エステルを含む蒸留対象溶液を、ェントレーナ一を用いて共沸蒸留して、 目的物質である含水量の低減された脂肪族カルボン酸と、 水分の濃縮された塔頂 留出物を得る工程を有する。  In the present invention, first, as a step (1), a solution to be distilled containing water, an aliphatic carboxylic acid and an aliphatic carboxylic acid ester is azeotropically distilled using an entrainer to obtain a water content as a target substance. To obtain an aliphatic carboxylic acid having a reduced water content and a water-enriched overhead distillate.
共沸蒸留により脂肪族カルボン酸及び水を含有する混合物中の水の濃度を低減 させるために、 通常、 塔底から水の量の低減された脂肪族カルボン酸を含む缶出 液を得、 塔頂から主に水とェントレーナ一とを含む共沸混合物の蒸気を得るよう に蒸留を行う。 この際、 脂肪族カルボン酸を再使用する等の目的のためには、 缶 出液中におけるェントレー ·^ "一の濃度は 1 0 0 p p m以下であることが好ましく、 また、 経済性の要請等から、 共沸蒸留塔塔頂留出物の凝縮液中における脂肪族力 ルボン酸の濃度は 1 , 0 0 0 p 以下であることが好ましい。 缶出液は原料調 製液として一部、 アルキル置換芳香族炭化水素の液相酸化反応の系にリサイクル される。 In order to reduce the concentration of water in a mixture containing aliphatic carboxylic acid and water by azeotropic distillation, a bottom containing an aliphatic carboxylic acid having a reduced amount of water is usually discharged from the bottom of the column. A liquid is obtained, and distillation is performed so as to obtain a vapor of an azeotropic mixture mainly containing water and an entrainer from the top of the column. At this time, for the purpose of reusing the aliphatic carboxylic acid, etc., it is preferable that the concentration of the entrain in the bottom liquid is 100 ppm or less, From the above, the concentration of the aliphatic carboxylic acid in the condensate of the distillate at the top of the azeotropic distillation column is preferably not more than 1,000 p. It is recycled to the system of the liquid-phase oxidation reaction of substituted aromatic hydrocarbons.
次いで蒸留対象溶液及びェントレー^ "一について説明する。  Next, the solution to be distilled and the entrainer will be described.
本発明における蒸留対象溶液は、 目的物質と低減物質とを含む混合溶液であつ て、 更に、 添加するェントレーナーと該低減物質とが共沸混合物を生成し、 かつ その共沸温度が目的物質の沸点よりも低いものであれば、 特に制限はない。 また 更に、 本共沸蒸留に本質的に影響を与えないような物質を含んでいてもよい。 本発明におけるェントレーナ一は、 その効果を発現する限り特に制限はない。 また、 単一成分である必要はなく、 低減物質と不均一共沸混合物を形成する 2種 類以上の成分の混合物であつてもよいし、 また該成分の分解物の一部が含有され ていてもよい。  The solution to be distilled in the present invention is a mixed solution containing the target substance and the reducing substance. Further, the entrainer to be added and the reducing substance form an azeotropic mixture, and the azeotropic temperature of the target substance is reduced. There is no particular limitation as long as it is lower than the boiling point. Further, it may contain a substance which does not substantially affect the azeotropic distillation. The end trainer in the present invention is not particularly limited as long as the effect is exhibited. It does not need to be a single component, and may be a mixture of two or more components that form a heterogeneous azeotrope with the reducing substance, or may contain a part of a decomposition product of the component. You may.
本発明における共沸蒸留塔は、 充填塔または棚段塔のいずれであってもよい。 蒸留対象溶液の供給位置は特に制限されないが、通常、共沸蒸留塔の中段であり、 分離効率の最適化のために塔内組成を勘案して最適位置を決めればよい。 該共沸 蒸留塔の運転は常圧下、加圧下、あるいは減圧下のいずれの条件下でも実施でき、 その方式は回分式でも連続式でもよい。 より好ましくは、 常圧下に連続式に実施 される。  The azeotropic distillation column in the present invention may be either a packed column or a tray column. Although the supply position of the solution to be distilled is not particularly limited, it is usually the middle stage of the azeotropic distillation column, and the optimum position may be determined in consideration of the composition in the column in order to optimize the separation efficiency. The operation of the azeotropic distillation column can be carried out under normal pressure, under pressure, or under reduced pressure, and the system may be a batch system or a continuous system. More preferably, it is carried out continuously under normal pressure.
共沸蒸留における上記脂肪族カルボン酸エステル濃度は任意であるが、 ェント レーナ一を含む油相中に 3〜 5 0重量％含有することが酢酸等の脂肪族カルボン 酸から水を安定かつ高い濃度で分離する点から好ましい。  The concentration of the above-mentioned aliphatic carboxylic acid ester in azeotropic distillation is arbitrary, but it is necessary to contain 3 to 50% by weight in the oil phase containing the entrainer to obtain a stable and high concentration of water from an aliphatic carboxylic acid such as acetic acid. From the viewpoint of separation.
本発明において、 精製したい目的物質は脂肪族カルボン酸であり、 通常、 炭素 数 2〜6の飽和または不飽和の脂肪族カルボン酸である。 好ましくは炭素数 2〜 4の飽和脂肪族カルボン酸である酢酸、 プロピオン酸、 酪酸等が挙げられる。 濃 度を低減させたい低減物質は水である。 In the present invention, the target substance to be purified is an aliphatic carboxylic acid, usually a saturated or unsaturated aliphatic carboxylic acid having 2 to 6 carbon atoms. Preferable examples include acetic acid, propionic acid, and butyric acid, which are saturated aliphatic carboxylic acids having 2 to 4 carbon atoms. Dark The reducing substance to be reduced in degree is water.
また本発明において蒸留対象溶液中に含有される不純物の脂肪族カルボン酸ェ ステルの種類は特に限定されないが、 通常、 上記目的物質の脂肪族カルボン酸の エステルが挙げられ、 具体的には例えば酢酸メチルが挙げられる。  Further, in the present invention, the kind of the aliphatic carboxylic acid ester as an impurity contained in the solution to be distilled is not particularly limited, but usually, an ester of the aliphatic carboxylic acid of the target substance is mentioned, and specifically, for example, acetic acid Methyl.
ェントレーナ一は、共存する脂肪族カルボン酸の種類を勘案して選択されるが、 脂肪族カルボン酸と水とを含む混合溶液の共沸蒸留に用いられる公知の化合物を 用いることができる。 例えば、 ギ酸ブチル、 酢酸 n—プロピル、 酢酸イソブチル、 酢酸 n—プチル、 酢酸ァミル、 プロピオン酸 n—プチル、 プロピオン酸イソプチ ルなどのエステル類、 ジクロルメチルエーテル、 ェチルイソアミルエーテル、 了 リノレイソァミルエーテル、 ジー n—プチノレエーテルなどのエーテル類、 二塩化工 チレン、 クロルベンゼンなどのハロゲン化炭化水素類、 塩化アセトン、 ジプロピ ノレケトン、 メチルプチノレケトン、 ァリノレアセトンなどのケトン類、 トノレエン、 キ シレン、 ェチルベンゼンなどの芳香族炭化水素のように、 水と共沸混合物を作る ことのできる化合物が通常使用される。 これらのェントレー^ "一のうちではエス テル類を使用するのが好ましい。 中でも、 酢酸 n—プロピルまたは酢酸 n—ブチ ルの使用が好適である。  The entrainer is selected in consideration of the type of the coexisting aliphatic carboxylic acid, but a known compound used for azeotropic distillation of a mixed solution containing the aliphatic carboxylic acid and water can be used. For example, esters such as butyl formate, n-propyl acetate, isobutyl acetate, n-butyl acetate, amyl acetate, n-butyl propionate, and isobutyl propionate, dichloromethyl ether, ethyl isoamyl ether, and linoleisoea Ethers such as mill ether and di-n-butylinoleether; halogenated hydrocarbons such as ethylene dichloride and chlorobenzene; ketones such as acetone chloride, dipropionoleketone, methylbutinoleketone and arinoleacetone; tonolenene and xylene Compounds that can form an azeotrope with water, such as aromatic hydrocarbons such as ethylbenzene, are commonly used. It is preferable to use esters among these entrains. Among them, n-propyl acetate or n-butyl acetate is preferable.
尚、 本発明に於いては、 蒸留対象溶液がテレフタル酸等の芳香族カルボン酸の 製造に用いられた溶媒である場合などは、 蒸留対象溶液中に該芳香族カルボン酸 製造原料に由来する p—キシレンや酢酸メチル等の他の物質ゃェントレーナ一の 分解物が含まれていてもよい。  In the present invention, when the solution to be distilled is a solvent used for the production of an aromatic carboxylic acid such as terephthalic acid, etc., p in the solution to be distilled originates from the aromatic carboxylic acid production raw material. —Decomposition products of other substances such as xylene and methyl acetate may be contained.
蒸留対象溶液中の脂肪族カルボン酸及び水の組成は任意である。 通常、 水の含 有率が 4から 9 9重量％の範囲、 好ましくは 1 0から 7 0重量 °/0の範囲にある脂 肪族力ルポン酸および水を含む混合溶液に本発明が適用される。 The composition of the aliphatic carboxylic acid and water in the solution to be distilled is arbitrary. Generally, the present invention is applied to a mixed solution containing an aliphatic sulfonic acid and water having a water content in the range of 4 to 99% by weight, preferably in the range of 10 to 70% by weight / 0. You.
本発明方法を適用する具体的な蒸留対象溶液として、 脂肪族カルボン酸を含む 溶媒中でアルキル置換芳香族炭化水素を液相酸化し精製する芳香族カルボン酸の 製造工程において回収されたものが挙げられる。 例えばアルキル置換芳香族炭化 水素の液相酸化反応器からの混合蒸気の凝縮回収物や、 同反応器から出た廃ガス 中の蒸気酢酸を水で吸収した回収物などが挙げられる。 また回収された反応母液 の少なくとも一部を蒸発させて凝縮した回収物や、 芳香族カルボン酸と反応母液 とを固液分離し回収した反応母液または該工程で洗浄に使用したものの回収物等 が挙げられ、 これらから任意の液と量がを選択し、 用いることが出来る。 これら の液は混合されても、 独立に処理されてもよい。 Specific examples of the solution to be distilled to which the method of the present invention is applied include those recovered in a process of producing an aromatic carboxylic acid in which a liquid-phase oxidizing and purifying an alkyl-substituted aromatic hydrocarbon in a solvent containing an aliphatic carboxylic acid. Can be For example, there are a condensed and recovered product of a mixed vapor from a liquid-phase oxidation reactor of an alkyl-substituted aromatic hydrocarbon, and a recovered product in which steam acetic acid in waste gas discharged from the reactor is absorbed by water. The recovered mother liquor And a reaction mother liquor obtained by solid-liquid separation of an aromatic carboxylic acid and a reaction mother liquor or a reaction mother liquor used for washing in this step. The liquid and amount can be selected and used. These liquids may be mixed or treated independently.
[工程 （2 )、 ( 3 ) の説明] [Description of Steps (2) and (3)]
本発明では工程 （1 ) に続いて、 工程 （2 ) ：塔頂留出物を凝縮させて、 ガスと、 水相及ぴ油相の 2相に分れた凝縮液とを得る工程、及び工程（3 )：凝縮液の各相 を別個に分取する工程を有する。  In the present invention, following the step (1), a step (2): a step of condensing the overhead distillate to obtain a gas and a condensate separated into two phases, a water phase and an oil phase; Step (3): Separating each phase of the condensate separately.
本発明では工程 （1 ) の共沸蒸留によって、 塔底からは低減物質の濃度の低減 された目的物質を含む缶出液が得られ、 塔頂からは主に低減物質とェントレーナ 一とより成る共沸混合物の蒸気 （塔頂留出物） が得られる。 工程 （2 ) としては、 塔頂から得られた蒸気を凝縮し、 凝縮液とガスを得る。 この凝縮液は通常、 低減 物質を主とする水相と、 ェントレーナ一を主とする油相との二相の液として得ら れる。 ついで工程 （3 ) として、 この二相の凝縮液を水相、 油相に分取する。 該 分取手段としてはデカンター等での液液分離等が挙げられるが、 目的が達せられ れば特に限定されない。 この様に二相を分取出来るように、 凝縮液を構成する水 相と油相が均一に混じり合わないような、 不均一共沸混合物を与える低減物質と ェントレーナ一とを用いることが好ましい。  In the present invention, by the azeotropic distillation in the step (1), a bottoms containing the target substance having a reduced concentration of the reduced substance is obtained from the bottom of the column, and the bottom is mainly composed of the reduced substance and the entrainer from the top of the column. An azeotropic vapor (top distillate) is obtained. In the step (2), the vapor obtained from the top is condensed to obtain a condensate and a gas. This condensate is usually obtained as a two-phase liquid consisting of an aqueous phase mainly composed of the reducing substance and an oil phase mainly composed of the entrainer. Next, in step (3), the two-phase condensate is separated into an aqueous phase and an oil phase. Examples of the fractionation means include liquid-liquid separation using a decanter or the like, but are not particularly limited as long as the purpose is achieved. In order to separate the two phases in this way, it is preferable to use an entrainer and a reducing substance that gives a heterogeneous azeotrope such that the aqueous phase and the oil phase constituting the condensate do not mix uniformly.
工程 （2 ) で得られた凝縮液の水相及ぴ油相においては、 油相より回収される 上記脂肪族カルボン酸エステル量を、 水相より回収される上記脂肪族カルボン酸 エステル量の 2 0倍以下とすることが好ましい。 これは例えば、「単位時間当たり の油相流量 X油相中の上記脂肪族カルボン酸エステルの濃度」 と 「単位時間当た りの水相流量 X水相中の上記脂肪族カルボン酸エステルの濃度」 によって得られ る。 上記値が 2 0倍を超えると、 水相から回収できる脂肪族カルボン酸エステル の量が少なくなり、本発明の効果が薄くなる場合があるので、中でも 1 8倍以下、 特に 1 5倍以下とするのが好ましい。  In the aqueous phase and the oil phase of the condensate obtained in step (2), the amount of the aliphatic carboxylic acid ester recovered from the oil phase is calculated by subtracting the amount of the aliphatic carboxylic acid ester recovered from the aqueous phase by 2 It is preferable to set it to 0 times or less. This is, for example, “the flow rate of the oil phase per unit time X the concentration of the aliphatic carboxylic acid ester in the oil phase” and “the flow rate of the aqueous phase per unit time X the concentration of the aliphatic carboxylic acid ester in the aqueous phase” Is obtained. If the above value exceeds 20 times, the amount of the aliphatic carboxylic acid ester that can be recovered from the aqueous phase decreases, and the effect of the present invention may be reduced.Therefore, the amount is preferably 18 times or less, particularly 15 times or less. Is preferred.
分取された 2相のうち、 ェントレーナーを主とする相 （油相） の少なくとも一 部は共沸蒸留塔へリサイクルされるのが好ましい。 ェントレーナ一を戻す方法に は、 塔頂に全量戻す方法と、 一部分割して塔中段に戻す方法とがある。 共沸蒸留 塔へリサイクルされるェントレーナ一の量は共沸蒸留塔より排出すべき水の量と 共沸混合物組成より理論値が与えられる。 実際には共沸蒸留塔塔頂留出物の凝縮 液中の脂肪族カルボン酸濃度および缶出液中のェントレーナ一濃度より最適なェ ントレーナー量を求めればよい。 尚、 系外へ出て失ったェントレーナー分を補う ために、 ェントレーナーを新たに供給してもよい。 At least one of the two phases (oil phase) mainly consisting of the entrainer The part is preferably recycled to the azeotropic distillation column. There are two ways to return the entrainer: returning the entire amount to the top of the tower, or returning the entrainer to the middle of the tower. The amount of entrainer recycled to the azeotropic distillation column is theoretically given by the amount of water to be discharged from the azeotropic distillation column and the composition of the azeotropic mixture. In practice, the optimum amount of entrainer may be determined from the concentration of aliphatic carboxylic acid in the condensate of the effluent from the azeotropic distillation column and the concentration of entrainer in the bottoms. In addition, a new trainer may be supplied to compensate for the lost trainer that has gone out of the system.
一方、 低減物質を主とする相 （水相） は、 少なくともその一部は後述する工程 ( 4 ) に供される。 残余分の水相については還流液として共沸蒸留塔へ戻されて もよい。 なお水相の全てを工程 （4 ) に共した後、 その一部を還流液として共沸 蒸留塔へ戻してもよい。 また、 低減物質を主とする相 （水相） の主成分である水 はプロセス内で再利用された後、 その一部が廃棄されてもよい。 水を還流液とし て戻す方法には、 例えば、 共沸蒸留塔塔頂に戻す方法と塔中段に戻す方法とがあ る。 水の還流量はその比 （還流水量/排出水量） により通常 0 . 1から 3程度に 設定される。  On the other hand, at least a part of the phase (aqueous phase) mainly containing the reducing substance is subjected to the step (4) described later. The remaining aqueous phase may be returned to the azeotropic distillation column as a reflux liquid. After all of the aqueous phase is subjected to step (4), a part of the aqueous phase may be returned to the azeotropic distillation column as a reflux liquid. In addition, water, which is the main component of the phase (aqueous phase) mainly composed of the reducing substance, may be partially discarded after being reused in the process. The method of returning water as a reflux liquid includes, for example, a method of returning to the top of the azeotropic distillation column and a method of returning to the middle stage of the column. The amount of water reflux is usually set to about 0.1 to 3 depending on the ratio (return water amount / discharged water amount).
[工程 （4 ) の説明] [Explanation of step (4)]
工程 （4 ) では分取した水相の一部または全部を蒸留して、 含水量の低減され た上記脂肪族力ルポン酸ェステルを含む塔頂留出物を得る。  In step (4), a part or all of the separated aqueous phase is distilled to obtain an overhead distillate containing the above-mentioned aliphatic sulfonic acid ester having a reduced water content.
具体的には例えば、 共沸蒸留塔塔頂留出物の凝縮液から分取された （低減物質 である水を主成分とする） .水相を蒸留塔に送り、 この蒸留塔塔頂より含水量の低 減された上記脂肪族カルボン酸を得る方法が挙げられる。 この蒸留にて蒸留塔の 塔底より得られるものは主として水である。 この水は系外へ廃棄しても、 また一 部を共沸蒸留塔へ還流液として戻  Specifically, for example, the aqueous phase separated from the condensate of the distillate at the top of the azeotropic distillation tower (mainly water, which is a reducing substance) is sent to the distillation tower, and from the top of the distillation tower, A method for obtaining the above-mentioned aliphatic carboxylic acid having a reduced water content is exemplified. What is obtained from the bottom of the distillation column in this distillation is mainly water. Even if this water is discarded outside the system, a part of it is returned to the azeotropic distillation column as a reflux liquid.
[工程 （5 ) の説明] [Explanation of step (5)]
工程 （5 ) では、 工程 （4 ) にて得られた塔頂留出物を、 工程 （3 ) で分取し た油相の一部又は全部と共に蒸留し、 該蒸留によって得られる上記脂肪族カルボ ン酸エステルの一部又は全部を系外へ回収する。 In the step (5), the top distillate obtained in the step (4) is distilled together with part or all of the oil phase fractionated in the step (3), and the above-mentioned aliphatic product obtained by the distillation is distilled off. Carbo Part or all of the acid ester is recovered out of the system.
工程（5) における蒸留塔は、ェントレーナーの回収を目的としたものである。 工程 （5) における蒸留塔へは、 工程 （4) の塔頂留出物と、 工程 （3) にて分 取された共沸蒸留塔塔頂留出物の凝縮液のうちの油相の一部又は全部とを供給し、 蒸留する。 この蒸留によって、 ェントレーナーと、 不純物の脂肪族カルボン酸ェ ステルとを分離する。 尚、 本工程において脂肪族カルボン酸エステルのうち、 2 0%以上が、 工程 （4) にて得られた塔頂物に由来する様に、 工程 （5) への被 蒸留成分の供給をコントロールするのが、 エネルギー効率の点で好ましい。  The distillation column in step (5) is for the purpose of recovering the entrainer. In the distillation column in step (5), the distillate at the top of step (4) and the oil phase of the condensate of the distillate at the top of the azeotropic distillation column collected in step (3) are collected. Feed part or all and distill. This distillation separates the entrainer from the impurity aliphatic carboxylic acid ester. In this step, the supply of the components to be distilled to step (5) was controlled so that at least 20% of the aliphatic carboxylic acid ester was derived from the overhead obtained in step (4). Is preferable in terms of energy efficiency.
ェントレーナーは塔底より回収され、 一部又は全部を系外へ回収するか、 一部 又は全部を共沸蒸留塔へ戻してもよい。 また不純物である上記脂肪族カルボン酸 エステルは一部又は全部を系外へ回収すればよい。  The entrainer is collected from the bottom of the column, and part or all may be collected outside the system, or part or all may be returned to the azeotropic distillation column. The aliphatic carboxylic acid ester, which is an impurity, may be partially or entirely recovered outside the system.
また工程 （5) における蒸留塔には、 分取した油相の一部又は全部以外の油相 成分として、 共沸蒸留塔塔頂留出物の凝縮液 （つまりェントレーナー及び上記脂 肪族カルボン酸エステルの混合物） や、 工程 （2) で得られたガスを、 油相と併 せて供給してもよい。  In the distillation column in the step (5), the condensate of the azeotropic distillation column top distillate (that is, the entrainer and the aliphatic A mixture of carboxylic acid ester) and the gas obtained in step (2) may be supplied together with the oil phase.
尚、 工程 （3) にて分取された油相や工程 （5) にて得られたェントレーナー については、 特公昭 61-3109 1号公報に記載のように、 共沸蒸留塔へのェ ントレーナ一の循環流を分割して一方は共沸蒸留塔塔頂に、 他方は塔中段に戻す ことで、 運転条件を変更した効果が反映され易く し、 応答を速めた方法を用いて もよレ、。 更に、 工程 （2) や工程 （4) にて得られる水については、 特表平 10 - 504556号公報に記載のように、 共沸蒸留塔への還流液として水を塔中段 へ戻し、 その量の操作で塔底における不純物濃度の制御を行うという方法にも用 いることができる。  The oil phase separated in the step (3) and the entrainer obtained in the step (5) are supplied to the azeotropic distillation column as described in JP-B-61-31091. By splitting the circulating flow of the entrainer and returning one to the top of the azeotropic distillation column and the other to the middle of the column, the effect of changing the operating conditions can be easily reflected, and the response can be speeded up. Yeah. Further, as for the water obtained in the step (2) or the step (4), as described in Japanese Patent Publication No. 10-504556, water is returned to the middle stage of the azeotropic distillation column as a reflux liquid to the column. It can also be used for a method of controlling the impurity concentration at the bottom of the column by controlling the amount.
また、 ェントレーナ一中に蓄積するアルキル置換芳香族炭化水素を回収するた めに、 これらをェントレーナ一から直接分離してもよいし、 特表平 10— 504 556号公報に記載のように共沸蒸留塔の中段から抜き出してもよい。 さらにそ の抜き出したものを WO 97/29068号公報に記載のように精製することも 可能である。 次に、 本発明の共沸蒸留方法が適用された、 本発明の芳香族カルボン酸の製造 方法について説明する。 In order to recover the alkyl-substituted aromatic hydrocarbons accumulated in the entrainer, they may be separated directly from the entrainer, or may be azeotropic as described in JP-A-10-504556. It may be withdrawn from the middle stage of the distillation column. Further, the extracted product can be purified as described in WO 97/29068. Next, a method for producing an aromatic carboxylic acid of the present invention to which the azeotropic distillation method of the present invention is applied will be described.
まず芳香族カルボン酸の製造方法自体について説明する。  First, the method for producing an aromatic carboxylic acid will be described.
目的化合物である芳香族カルボン酸は、 任意の芳香族カルボン酸を示し、 例え ば芳香族モノカルボン酸、 芳香族ジカルボン酸、 芳香族トリカルボン酸等が挙げ られる。 これらが例えば芳香族環としてベンゼン環を有する際には、 これらに応 するモノア/レキノレベンゼン、 ジァノレキノレベンゼン、 トリアルキルベンゼン等のァ ルキル置換芳香族炭化水素を酸化、 好ましくは液相酸化することによって製造さ れる。 中でも本発明の方法は、 芳香族ジカルボン酸、 特に芳香族カルボン酸がテ レフタル酸である場合に適用するのが好ましく、 この場合、 原料となるアルキル 置換芳香族炭化水素としては P—キシレンが挙げられる。  The aromatic carboxylic acid as the target compound is any aromatic carboxylic acid, such as aromatic monocarboxylic acid, aromatic dicarboxylic acid, and aromatic tricarboxylic acid. When these have, for example, a benzene ring as an aromatic ring, the corresponding alkyl-substituted aromatic hydrocarbon such as monoa / lequinolebenzene, dianolequinolebenzene, and trialkylbenzene is oxidized, preferably in a liquid phase. Manufactured by oxidation. In particular, the method of the present invention is preferably applied when the aromatic dicarboxylic acid, particularly the aromatic carboxylic acid is terephthalic acid. In this case, P-xylene is used as the alkyl-substituted aromatic hydrocarbon as a raw material. Can be
酸化反応を液相中にて行う際には、 通常、 溶媒として脂肪族カルボン酸を用い る。 液相酸化反応の溶媒である脂肪族カルボン酸としては、 例えば酢酸が好まし く、 該溶媒の使用量は、 通常、 原料アルキル置換芳香族炭化水素に対して 2〜 6 重量倍である。 また、 酸化反応系内の水分濃度は、 通常 4〜2 5重量％、 好まし くは 7〜 2 0重量％である。  When performing the oxidation reaction in a liquid phase, an aliphatic carboxylic acid is usually used as a solvent. As the aliphatic carboxylic acid which is a solvent for the liquid phase oxidation reaction, for example, acetic acid is preferred, and the amount of the solvent is usually 2 to 6 times by weight based on the starting alkyl-substituted aromatic hydrocarbon. The water concentration in the oxidation reaction system is usually 4 to 25% by weight, preferably 7 to 20% by weight.
アルキル置換芳香族炭化水素を液相酸化して芳香族カルボン酸を製造する酸化 反応においては、 通常、 触媒を使用する。 この触媒としては例えばマンガン、 コ バルト、 鉄、 クロム、 ニッケル等の遷移金属化合物が用いられる。 また、 助触媒 として臭素化合物を用いてもよい。 臭素化合物触媒を用いない場合には、 コバル ト触媒に対する促進剤としてァセトアルデヒドゃメチルェチルケトン等が使用さ れる。  In an oxidation reaction for producing an aromatic carboxylic acid by subjecting an alkyl-substituted aromatic hydrocarbon to liquid phase oxidation, a catalyst is usually used. As the catalyst, for example, a transition metal compound such as manganese, cobalt, iron, chromium, and nickel is used. Further, a bromine compound may be used as the co-catalyst. When a bromine compound catalyst is not used, acetoaldehyde-methylethyl ketone or the like is used as a promoter for the cobalt catalyst.
酸化剤には分子状酸素や空気が使用されるが、 通常は空気が使用される。 酸素 ガスを混じて酸素濃度を高めた空気、 逆に窒素ガス等の不活性ガスを混じて酸素 濃度を低くした空気を用いてもよい。  As the oxidizing agent, molecular oxygen or air is used, but usually air is used. Air having a high oxygen concentration by mixing oxygen gas, or air having a low oxygen concentration by mixing inert gas such as nitrogen gas, may be used.
液相酸化の反応温度は適宜選択すればよいが、 通常 1 2 0 °Cから 2 2 0 °Cであ る。 例えば臭素化合物触媒を使わない酸化方法においては、 一般に反応温度は 1 6 0 °C以下であることが好ましい。 圧力も同様に適宜選択すればよく、 溶媒 （例 えば酢酸） が気体状態となりうる圧力範囲であればよい。 The reaction temperature of the liquid phase oxidation may be appropriately selected, and is usually from 120 ° C to 220 ° C. For example, in an oxidation method that does not use a bromine compound catalyst, the reaction temperature is generally preferably 160 ° C. or less. The pressure may be appropriately selected in the same manner. For example, acetic acid) may be in a pressure range in which it can be in a gaseous state.
酸化反応熱は主として含水酢酸溶媒のフラッシュ蒸発によって除去される。 即 ち、 酸化反応器からの留分 （排ガス） は、 蒸発した酢酸及び水を主として含み、 その他に酸化反応副生物のうちの低沸点生成物や未反応アルキル置換芳香族炭化 水素等をわずかに含んでいる。 この蒸気はコンデンサーによって冷却され凝縮さ れて液体となり、 通常はその一部が再び酸化反応溶媒として酸化反応器内に還流 される。 また他の一部は酸化反応によって生成した水を除く目的で脱水塔へ送ら れ、 本発明の共沸蒸留に供され、 脱水された酢酸は再び酸化反応溶媒として酸化 反応器内へ送られる。  The heat of the oxidation reaction is mainly removed by flash evaporation of the aqueous acetic acid solvent. That is, the fraction (exhaust gas) from the oxidation reactor mainly contains evaporated acetic acid and water, and a small amount of low-boiling products and unreacted alkyl-substituted aromatic hydrocarbons among the by-products of the oxidation reaction. Contains. This vapor is cooled and condensed into a liquid by a condenser, and a part of the vapor is usually returned to the oxidation reactor as an oxidation reaction solvent. Another part is sent to a dehydration tower for the purpose of removing water generated by the oxidation reaction, is subjected to the azeotropic distillation of the present invention, and the dehydrated acetic acid is sent again to the oxidation reactor as an oxidation reaction solvent.
アルキル置換芳香族炭化水素の液相酸化は通常 1基、 必要に応じて複数の反応 器で行われる。 酸化反応を終えた反応液は必要であれば 1基または連続した 2基 以上の順次降圧された晶析器に送られ、 それぞれの圧力に対応する温度まで溶媒 のフラッシュ冷却作用で冷却され、 生成した芳香族カルボン酸の大部分が結晶と して晶析し、 スラリーとなる。 スラリーは任意の結晶分離手段、 例えばロータリ 一バキュームフィルタ一法、 遠心分離法、 あるいは他の適当な分離法で芳香族力 ルボン酸結晶のケーキと酸化反応母液とに分離される。 芳香族カルボン酸結晶の ケーキは、 必要に応じて酢酸あるいは水で洗浄された後、 ドライヤーで付着溶媒 を除去される。 さらに必要に応じて、 主に水から成る反応母液中に再スラリー化 され、 水添工程を経てから再結晶することで結晶中の不純物を低減し、 精製され る。 次いで固液分離、 洗浄、 乾燥等の操作を経た後に芳香族カルボン酸が得られ る。 次に図 1を用いて、 本発明の共沸蒸留方法、 およびこれを用いる芳香族カルボ ン酸の製造方法について説明する。 図 1は本発明方法を適用するための蒸留プロ セスの一例を示す流れ図である。 1 1は共沸蒸留塔である。 水、 （酢酸等の）脂肪 族カルボン酸及び不純物の脂肪族カルボン酸エステルを含む蒸留対象溶液はライ ン 4 0、 4 1、 4 2等から （複数の供給ラインから供給する場合、 各蒸留対象溶 液の組成は通常、相互に異なる）、 またェントレーナーはライン 1 5力ゝら、それぞ れ共沸蒸留塔 1 1に供給されて、 共沸蒸留が行なわれる。 The liquid-phase oxidation of alkyl-substituted aromatic hydrocarbons is usually performed in one reactor and, if necessary, in multiple reactors. If necessary, the reaction solution after the oxidation reaction is sent to one or two or more successively reduced pressure crystallizers, where it is cooled to the temperature corresponding to each pressure by the flash cooling action of the solvent to produce Most of the aromatic carboxylic acids crystallized as crystals, forming a slurry. The slurry is separated into a cake of aromatic rubonic acid crystals and an oxidation reaction mother liquor by any means of crystal separation, such as rotary vacuum filtration, centrifugation, or any other suitable separation method. The cake of the aromatic carboxylic acid crystals is washed with acetic acid or water as required, and then the attached solvent is removed with a dryer. Further, if necessary, the slurry is re-slurried in a reaction mother liquor mainly composed of water, and is subjected to a hydrogenation step and then recrystallized to reduce impurities in the crystal and to be purified. Subsequently, after performing operations such as solid-liquid separation, washing, and drying, an aromatic carboxylic acid is obtained. Next, the azeotropic distillation method of the present invention and the method for producing aromatic carboxylic acid using the azeotropic distillation method will be described with reference to FIG. FIG. 1 is a flowchart showing an example of a distillation process for applying the method of the present invention. 11 is an azeotropic distillation column. The solution to be distilled containing water, aliphatic carboxylic acid (such as acetic acid) and aliphatic carboxylic acid ester of impurities is supplied from lines 40, 41, 42, etc. The composition of the solutions is usually different from each other), and the end trainer The mixture is supplied to an azeotropic distillation column 11 where azeotropic distillation is performed.
蒸留に必要な熱を加えるために、 熱交換機 1 4によって加熱する。 加熱源とし て加熱油や加熱蒸気を用いる。 ここでは酢酸の常圧沸点より温度の高い、 具体的 には 0.35 MPa蒸気を用いる例を示している。  Heat is applied by heat exchanger 14 to add the heat required for distillation. Heating oil or steam is used as a heating source. Here, an example is shown in which a temperature higher than the normal pressure boiling point of acetic acid, specifically, 0.35 MPa steam is used.
共沸蒸留によって濃度を低減させたい低減物質およびェントレーナ一を含む共 沸混合物蒸気 （共沸蒸留塔塔頂留出物） は、 共沸蒸留塔 1 1の塔頂より冷却器 1 2に送られ、 ここで凝縮される。 得られた凝縮液は液液分離槽 1 3で 2相に分離 され、 ここから分取される。 分離手段は共沸混合物の性質により適切なものを選 択すればよい。  The azeotropic mixture vapor containing the reducing substance whose concentration is to be reduced by azeotropic distillation and the entrainer (the distillate from the top of the azeotropic distillation column) is sent to the cooler 12 from the top of the azeotropic distillation column 11. It is condensed here. The obtained condensate is separated into two phases in a liquid-liquid separation tank 13 and is separated therefrom. An appropriate separation means may be selected depending on the properties of the azeotrope.
図 1においては、 液液分離槽 1 3において低減物質を主成分とする相 （水相） の一部はライン 1 7を通ってストリッビング塔 2 1に送られる。 また水相の一部 はライン 1 6を通して共沸蒸留塔 1 1への水還流としてもよい。 ェントレー^ "一 はライン 1 5を通って循環される。 ライン 1 5およびライン 1 6は必要により共 沸蒸留塔 1 1の塔頂または塔中段に接続される。 この共沸蒸留塔 1 1へのライン 1 5および 1 6の本数はそれぞれ 1本または複数本のいずれであってもよい。 更 には共通のラインを使用して、 ェントレーナ一及び低減物質を一緒に共沸蒸留塔 1 1へ戻してもよいし、 個別のラインによって戻してもよい。  In FIG. 1, a part of the phase (aqueous phase) mainly composed of the reducing substance in the liquid-liquid separation tank 13 is sent to the stripping tower 21 through the line 17. A part of the aqueous phase may be used as a reflux for water to the azeotropic distillation column 11 through the line 16. The entrainer is circulated through line 15. Lines 15 and 16 are connected, if necessary, to the top or middle of the azeotropic distillation column 11. To this azeotropic distillation column 11 The number of the lines 15 and 16 may be one or more, respectively.Furthermore, using a common line, the entrainer and the reducing substance are sent together to the azeotropic distillation column 11 It may be returned, or it may be returned by individual lines.
共沸蒸留塔 1 1の塔底よりライン 1 9を通って水含量の低減された目的物質 (例えば脂肪族カルボン酸）を主成分とする液が取り出される。また目的物質が、 本発明の芳香族カルボン酸の製造方法に用いられた脂肪族カルボン酸である際に は、 塔の中段のライン 2 2より主に水及び芳香族カルボン酸の原料であるアルキ ル置換芳香族炭化水素からなる液が抜き出される。  From the bottom of the azeotropic distillation column 11, a liquid mainly containing a target substance (for example, aliphatic carboxylic acid) having a reduced water content is taken out through a line 19. When the target substance is the aliphatic carboxylic acid used in the method for producing an aromatic carboxylic acid of the present invention, the water and the aromatic carboxylic acid raw material mainly from line 22 in the middle stage of the tower are used. A liquid comprising a substituted aromatic hydrocarbon is extracted.
ストリツビング塔 2 1では有機成分、 （本発明の芳香族カルボン酸の製造方法 においては主として、 不純物の脂肪族カルボン酸エステル） を回収し、 共沸蒸留 により分離された水などの低減物質はライン 1 8を通して芳香族カルボン酸製造 プロセスに循環され、 そこにおいて有効利用されるかまたは廃棄される。 ストリ ッビング塔 2 1で回収された有機成分はライン 2 3を通ってェントレー^ "一回収 塔 2 4へ送られ、 ここでェントレーナ一と不純物の脂肪族カルボン酸エステルと に分離される。 ェントレーナーは塔底より回収され、 ライン 2 5及び 1 5を通つ て共沸蒸留塔 1 1へ戻される。 上記脂肪族カルボン酸エステルはライン 2 6を通 つて回収される。 この脂肪族カルボン酸エステルは、 所望に応じて貯蔵しても、 また芳香族カルボン酸を製造する酸化反応工程に一部又は全部を循環させてもよ い。 また、 このェントレー "一回収塔 2 4にはライン 2 7で分岐させたェントレ ーナー及ぴ上記脂肪族カルボン酸エステルの混合物の少なくとも一部が直接導入 される。 また図示してはいないが、 冷却器 1 2にて発生したガスをェントレーナ 一回収塔 2 4に導入することも可能である。 In the stripping tower 21, organic components and (in the method for producing an aromatic carboxylic acid of the present invention, mainly an aliphatic carboxylic acid ester as impurities) are recovered, and reduced substances such as water separated by azeotropic distillation are collected in a line 1. It is recycled to the aromatic carboxylic acid production process through 8, where it is effectively used or discarded. The organic components recovered in the stripping tower 21 are sent to an entrainer through a line 23 to an entrainer 24, where the entrainer and the aliphatic carboxylic acid ester of impurities are removed. Is separated into The entrainer is recovered from the bottom of the column and returned to the azeotropic distillation column 11 via lines 25 and 15. The aliphatic carboxylic acid ester is recovered through line 26. The aliphatic carboxylic acid ester may be stored as desired, or may be partially or wholly circulated in the oxidation reaction step for producing an aromatic carboxylic acid. In addition, the entrainer and a mixture of the aliphatic carboxylic acid ester branched off at line 27 are directly introduced into the entrainer-one recovery tower 24. Although not shown, cooling is performed. It is also possible to introduce the gas generated in the vessel 12 into the entrainer-one recovery tower 24.
本発明に従って不純物の脂肪族カルボン酸エステルを回収する方法について図 1に従って具体的に説明する。  A method for recovering an aliphatic carboxylic acid ester as an impurity according to the present invention will be specifically described with reference to FIG.
系外に回収される上記脂肪族カルボン酸エステルの量、 つまり工程 （5 ) にて 得られるその量は、 ライン 2 6より排出される当該物質の量として示される。 こ の排出流にはェントレーナ一や水、 脂肪族炭化水素等の不純物が含まれていても よく、 液、 ガスまたはその混合物である。 共沸蒸留塔 1 1の塔頂留出物凝縮液相 の水相液を経由して回収工程に導入される上記脂肪族カルボン酸エステルの量は、 ライン 1 7を経由して流れる当該物質の量として示される。 系外に回収される上 記脂肪族カルボン酸エステルの総量に対し、 回収比率は 2 0 %以上、 好ましくは 3 0 %以上、 より好ましくは 4 0 %以上が、 水相を経由して回収工程に導入する のがエネルギー効率の点から好ましい。  The amount of the aliphatic carboxylic acid ester recovered outside the system, that is, the amount obtained in the step (5) is indicated as the amount of the substance discharged from the line 26. This effluent may contain impurities such as entrainers, water, aliphatic hydrocarbons, etc., and may be liquids, gases or mixtures thereof. The amount of the aliphatic carboxylic acid ester introduced into the recovery step via the aqueous phase liquid of the condensed liquid phase at the top of the azeotropic distillation column 11 depends on the amount of the substance flowing through the line 17. Indicated as quantity. The recovery ratio is at least 20%, preferably at least 30%, more preferably at least 40%, based on the total amount of the above-mentioned aliphatic carboxylic acid esters recovered outside the system, through the aqueous phase. Is preferable from the viewpoint of energy efficiency.
なお、 ェントレーナー回収工程において、 ェントレーナー回収塔 2 4の缶出液 2 5に、 極僅かではあるが上記脂肪族カルボン酸エステルが同伴しうる。 そこで 本発明では、 水相経由及び油相経由で回収工程に導入される脂肪族力ルポン酸ェ ステルの量における、 水相経由の脂肪族カルボン酸エステル量の割合をもって上 記回収比率を算出する。  In the entrainer recovery step, the above-mentioned aliphatic carboxylic acid ester can be accompanied, albeit very slightly, in the bottom liquid 25 of the entrainer recovery tower 24. Therefore, in the present invention, the above-mentioned recovery ratio is calculated based on the ratio of the amount of the aliphatic carboxylic acid ester via the aqueous phase to the amount of the aliphatic sulfonic acid ester introduced into the recovery step via the aqueous phase and the oil phase. .
水相を経ない上記脂肪族カルボン酸エステルの流れは、 ライン 2 7を通ってェ ントレーナ一回収塔 2 4に導入される。 この流れはガスもしくは液もしくはその 混合物のいずれでもよく、 WO 9 8 / 4 5 2 3 9号公報に記載されているように、 冷却器 1 2にて発生したガスの併用も可能である。 尚、 液液分離槽 1 3から抜き出される油相中における不純物の脂肪族カルボン 酸エステルとェントレー^ "一との濃度比は、 通常 1 ： 1 0 0〜1 ： 2であり、 該 油相のみから上記脂肪族カルボン酸エステルを回収するのは不利である。 一方、 水相における濃度を見ると、 この比は通常 1 : 1〜1 5 ： 1であり、 上記脂肪族 カルボン酸エステルの回収に有利である。 従って、 水相からの上記脂肪族カルボ ン酸エステルの回収比率が下がるほど回収工程での負荷が上がることとなり、 当 該回収比率が低すぎると、 エネルギー使用量の増大が顕著となる。 従って、 より 好ましくは、 該回収比率が 2 0 %以上である。 該回収比率の調節は、 ライン 2 7 に示される経路の流量やライン 2 8に示される経路の流量調節によって行なうこ とができる。 なお、 ライン 2 8に示される経路による調節の場合、 水還流量の総 量は変わらないように調節されることが好ましい。 また、 ストリツビング塔 2 1 から排出される水を液液分離槽 1 3に再循環させて該回収比率を上げることも可 能である。 The stream of the aliphatic carboxylic acid ester which has not passed through the aqueous phase is introduced into the entrainer-recovery column 24 through the line 27. This flow may be a gas or a liquid or a mixture thereof, and the gas generated in the cooler 12 may be used in combination, as described in WO98 / 45239. The concentration ratio of the aliphatic carboxylic acid ester of the impurity and the entrainer in the oil phase extracted from the liquid-liquid separation tank 13 is usually 1: 100 to 1: 2. However, it is disadvantageous to recover the above-mentioned aliphatic carboxylic acid ester only from the aqueous phase, but when looking at the concentration in the aqueous phase, this ratio is usually 1 : 1 to 15: 1, and the above-mentioned aliphatic carboxylic acid ester is recovered. Accordingly, the lower the recovery ratio of the aliphatic carboxylic acid ester from the aqueous phase, the higher the load in the recovery step, and if the recovery ratio is too low, the energy consumption will increase significantly. Therefore, more preferably, the recovery ratio is 20% or more.The recovery ratio is adjusted by adjusting the flow rate of the path indicated by the line 27 or the flow rate of the path indicated by the line 28. You can do In the case of adjustment by the route indicated by the line 28, it is preferable to adjust the total amount of water reflux so as not to change, and the water discharged from the stripping tower 21 is returned to the liquid-liquid separation tank 13. It is also possible to increase the recovery ratio by circulating.
なお本発明では、 例えば液液分離槽 1 3で液液分離した際の、 不純物である脂 肪族カルボン酸エステルの分配は、 （水相中の当該物質合計量） / (油相中の当該 物質合計量） で示される比率が大きいほど、 本発明方法の効果が大きい。 それは 例えば （単位時間当たりの水相流量 X水相中の上記脂肪族カルボン酸エステルの 濃度） Z (単位時間当たりの油相流量 X油相中の上記脂肪族カルボン酸エステル の濃度） で得ることが出来る。  In the present invention, for example, when liquid-liquid separation is performed in the liquid-liquid separation tank 13, the distribution of the aliphatic carboxylic acid ester as an impurity is calculated by: (total amount of the substance in the aqueous phase) / ( The greater the ratio indicated by (total amount of substances), the greater the effect of the method of the present invention. It can be obtained as, for example, (aqueous phase flow rate per unit time X concentration of the aliphatic carboxylic acid ester in the aqueous phase) Z (oil phase flow rate per unit time X concentration of the aliphatic carboxylic acid ester in the oil phase) Can be done.
通常、 油相中の上記脂肪族カルボン酸エステルの濃度は 1〜5 0重量％である が、 この濃度は、 ライン 2 5に示される経路から回収しょうとする上記脂肪族力 ルボン酸エステルの量及び、 水相と油相それぞれへの当該物質の分配比率に依存 する。  Usually, the concentration of the above-mentioned aliphatic carboxylic acid ester in the oil phase is 1 to 50% by weight, but this concentration is determined by the amount of the above-mentioned aliphatic carboxylic acid ester to be recovered from the route shown in line 25. And the distribution ratio of the substance in the water and oil phases.
当該物質の水相からの回収量が同じ条件でェントレーナ一の種類を変更する場 合には、 油相への分配比率が高いェントレーナーであるほど、 油相中の上記脂肪 族カルボン酸エステルの絶対量が増加する。 これは油相に同伴する該物質の量が 多くなること、 すなわちェントレーナ一を含む油相総量の増加を意味しており、 設備的およびエネルギー的なデメリットを生ずる。特に、エネルギーに関しては、 ェントレーナ一を塔頂より全量回収するため、 使用熱量が増加することとなる。 ただし、 ライン 1 6のような水還流を実施するプロセスでは、 ライン 1 7からの 当該物質の流出量を維持しながらも、ライン 1 6の水還流量を減らすことにより、 ェントレー > "一増加分の熱量増加を低減させることができる。 WO 9 8 / 4 5 2 3 9号公報には油相に同伴する不純物の脂肪族カルボン酸エステルが多く、 水還 流を実施していない例が示されている。 If the type of entrainer is changed under the same conditions for the amount of the substance recovered from the aqueous phase, the higher the ratio of the entrainer to the oil phase, the higher the aliphatic carboxylic acid ester in the oil phase The absolute amount of This means that the amount of the substance entrained in the oil phase is increased, that is, the total amount of the oil phase including the entrainer is increased, resulting in disadvantages in terms of equipment and energy. In particular, regarding energy, Since the entire entrainer is recovered from the top of the tower, the amount of heat used will increase. However, in a process that implements water recirculation, such as line 16, the amount of the substance that flows out of line 17 is maintained while reducing the amount of water recirculation on line 16, thereby making the WO98 / 452339 discloses an example in which an aliphatic carboxylic acid ester which is an impurity accompanying the oil phase is large and water reflux is not carried out. ing.
従って、本発明は、油相に同伴する不純物の脂肪族カルボン酸エステルの量が、 水相に同伴する上記脂肪族カルボン酸エステルの量の 2 0倍以下、 好ましくは 1 7倍以下、 より好ましくは 1 5倍以下での実施、 又は水還流を実施していること が好ましい。 なお、 ここでの同伴量は該物質濃度と経路を流通する液流量の積に よって決まる。  Accordingly, in the present invention, the amount of the aliphatic carboxylic acid ester as an impurity accompanying the oil phase is 20 times or less, preferably 17 times or less, more preferably the amount of the aliphatic carboxylic acid ester accompanying the water phase. Is preferably 15 times or less, or the water is refluxed. The amount of entrainment here is determined by the product of the substance concentration and the flow rate of the liquid flowing through the route.
なお、 図 1においては回収工程を 2つの蒸留塔で表記しているが、 塔 2 1と 2 4を連結し、 塔 2 4のリボイラーを省略した工程とすることも可能である。  In addition, in FIG. 1, the recovery process is represented by two distillation columns, but it is also possible to connect the columns 21 and 24 and omit the reboiler of the column 24.
本発明は、 不純物の脂肪族カルボン酸エステルの分離回収を必要とする共沸蒸 留において、 より大きな効果をもたらす。 上記した本発明の適用例の更に好まし い一態様として、 共沸蒸留塔の塔頂液中に於ける脂肪族カルボン酸濃度が 1， 0 O O p p m以下、 かつ、 該共沸蒸留塔の缶出液中におけるェントレーナー濃度が 1 0 0 p m以下、 ェントレーナ一中の不純物の脂肪族カルボン酸エステルの濃 度が 2 5 %以下となるように共沸蒸留塔の運転条件を制御する方法が挙げられる。  INDUSTRIAL APPLICABILITY The present invention provides a greater effect in azeotropic distillation that requires separation and recovery of aliphatic carboxylic acid esters as impurities. As a more preferred embodiment of the above-mentioned application example of the present invention, the aliphatic carboxylic acid concentration in the overhead liquid of the azeotropic distillation column is not more than 100 ppm and the can of the azeotropic distillation column A method of controlling the operating conditions of the azeotropic distillation column so that the concentration of the entrainer in the discharged liquid is 100 pm or less and the concentration of the aliphatic carboxylic acid ester of the impurity in the entrainer is 25% or less. No.
<実施例 > <Example>
以下、 本発明の具体的態様を実施例により更に詳細に説明するが、 本発明は、 その要旨を越えない限り、 下記の実施例によって限定されるものではない。 実施例 1  Hereinafter, specific embodiments of the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded. Example 1
蒸留対象溶液として酢酸及び酢酸メチルを含有する水混合物を、 ェントレーナ 一として酢酸 n—プチルを使用し、 図 1に示す蒸留プロセスによって連続的に蒸 留処理を実施した。 蒸留対象溶液は、 p—キシレンの液相酸化によつてテレフタル酸を製造するプ ロセスの各工程から回収されたものであって、 その単位時間当たりの総供給量は 酢酸 1 1 6 . 9重量部、 水 2 5， 5重量部、 酢酸メチル 1 . 3重量部からなる混 合物であるが、 それらを 3つの異なる組成のフィードとして理論段数 2 1段の共 沸蒸留塔 1 1の 7段、 1 6段、 2 1段にそれぞれ供給した。 共沸蒸留塔の塔底よ り缶出液として濃縮酢酸を単位時間当たり 1 2 8 . 2重量部で抜き出した。 缶出 液中の酢酸ブチル濃度は 2 5 0 p p m以下とした。 Using a water mixture containing acetic acid and methyl acetate as a solution to be distilled, and n-butyl acetate as an entrainer, continuous distillation was carried out by the distillation process shown in FIG. The solution to be distilled was recovered from each step of the process for producing terephthalic acid by liquid-phase oxidation of p-xylene, and the total supply per unit time was acetic acid, 16.9 wt. Of water, 25,5 parts by weight of water, and 1.3 parts by weight of methyl acetate. , 16 stages and 21 stages, respectively. Concentrated acetic acid was withdrawn from the bottom of the azeotropic distillation column as a bottoms at 18.28.2 parts by weight per unit time. The butyl acetate concentration in the bottoms was set at 250 ppm or less.
p—キシレンはライン 2 2より中段抜き出しして回収し、 酢酸メチルは理論段 数 1 3段のェントレーナー回収塔 2 4により蒸留回収した。 共沸蒸留塔 1 1の塔 頂からは共沸組成の水及びェントレーナ一を含む蒸気が得られ、 これを冷却して 液液分離槽 1 3に回収した。 液液分離槽 1 3で分離した 2液相のうち水相液は、 ライン 1 7を通って全量が理論段数 8段のストリッビング塔 2 1へ導入され、 有 機成分を除去した後にライン 1 8と 2 8とに分けられる。 ライン 1 8は廃水、 ラ イン 2 8は共沸蒸留塔 1 1への還流水とした。 廃水の量 （Ww) と還流水として 戻される量 （W r ) とから、 W r /Wwで定義される水還流比が所望の値となる ように還流水量を決めた。 本実施例においては、 排出される水相液の量 （Ww) が単位時間当たり 1 7 . 3重量部、還流水 （W r ) が 1 1重量部で水還流比が 0 . 6 4の条件で実施した。 ストリッビング塔 2 1で回収された有機成分はライン 2 3を通ってェントレーナ一回収塔 2 4へ移される。 ェントレーナ一は液液分離槽 1 3で液液分離した後、 ライン 1 5から共沸蒸留塔 1 1へ循環供給した。 ェント レーナ一の損失分はライン 3 0より補給した。 また、 酢酸メチル回収のために所 望に応じてェントレーナ一をェントレーナ一回収塔 2 4の 8段目に導入するライ ン 2 7を設けた。 このライン 2 7を流れるェントレーナー量を調整して、 系外へ 回収される酢酸メチルの量と塔頂凝縮液の水相液を経由して回収工程に導入され る酢酸のメチルの量との比を設定した。 具体的には、 系外へ回収される酢酸メチ ルの量はライン 2 6を通る酢酸メチルの量、 塔頂凝縮液の水相液を経由して回収 工程に導入される酢酸メチルの量はライン 1 7を通る酢酸メチルの量として計算 した。 系外へ回収される酢酸メチ^^の量に対して、 塔頂凝縮液の水相液を経由して回 収工程に導入される酢酸メチルの量が 2 4 %、 ライン 2 6からの回収酢酸メチル 中の酢酸 n—ブチルの濃度が 0 . 9 0 %で、 ェントレーナー回収塔 2 4の使用熱 . . 3 G c a 1 / h rであった。 実施例 2 The p-xylene was withdrawn from the line 22 at the middle stage and recovered, and methyl acetate was recovered by distillation using an entrainer recovery column 24 having 13 theoretical plates. From the top of the azeotropic distillation column 11, water having an azeotropic composition and steam containing an entrainer were obtained, which was cooled and recovered in the liquid-liquid separation tank 13. The aqueous phase liquid of the two liquid phases separated in the liquid-liquid separation tank 13 is passed through the line 17 into the stripping tower 21 with eight theoretical plates, and after removal of organic components, the line 1 It is divided into 8 and 28. Line 18 was wastewater, and line 28 was reflux water to azeotropic distillation column 11. Based on the amount of wastewater (Ww) and the amount returned as reflux water (Wr), the amount of reflux water was determined so that the water reflux ratio defined by Wr / Ww became a desired value. In the present embodiment, the amount (Ww) of the discharged aqueous phase liquid is 17.3 parts by weight per unit time, the amount of the reflux water (Wr) is 11 parts by weight, and the water reflux ratio is 0.64. It was carried out in. The organic components recovered in the stripping tower 21 are transferred to the entrainer-collection tower 24 through the line 23. The entrainer was subjected to liquid-liquid separation in a liquid-liquid separation tank 13 and then circulated through a line 15 to an azeotropic distillation column 11. The loss of the Ent Rainer was replenished from line 30. In addition, a line 27 was installed for the purpose of collecting methyl acetate by introducing an entrainer to the eighth stage of the entrainer recovery tower 24 as desired. The amount of entrainer flowing through this line 27 was adjusted to determine the amount of methyl acetate recovered outside the system and the amount of methyl acetate introduced into the recovery process via the aqueous phase condensate at the top. Was set. Specifically, the amount of methyl acetate recovered outside the system is the amount of methyl acetate passing through line 26, and the amount of methyl acetate introduced into the recovery process via the aqueous phase condensate at the top is Calculated as the amount of methyl acetate passing through line 17. 24% of the amount of methyl acetate introduced into the recovery process via the aqueous phase condensate at the top of the column compared to the amount of methyl acetate recovered outside the system, recovered from line 26 The concentration of n-butyl acetate in methyl acetate was 0.90%, and the heat used in the entrainer recovery tower 24 was 3 Gca1 / hr. Example 2
実施例 1において、 系外へ回収される酢酸メチルの量に対して塔頂凝縮液の水 相液を経由して回収工程に導入される酢酸メチルの量を 1 5 %に下げた以外は、 実施例 1と同様に蒸留処理を実施した。 ェントレーナー回収塔 2 4での使用熱量 は 2 . 0 G c a 1 rであった。  In Example 1, except that the amount of methyl acetate introduced into the recovery step via the aqueous phase condensate was reduced to 15% of the amount of methyl acetate recovered outside the system. Distillation was performed in the same manner as in Example 1. The amount of heat used in the entrainer recovery tower 24 was 2.0 Gca1r.
このように、 油相から直接酢酸メチルを回収する比率が増えると、 使用熱量が 増大することが確認された。 本発明を詳細にまた特定の実施態様を参照して説明したが、 本発明の精神と範 囲を逸脱することなく様々な変更や修正を加えることができることは当業者にと つて明らかである。  Thus, it was confirmed that when the ratio of recovering methyl acetate directly from the oil phase increased, the amount of heat used increased. Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
本出願は、 2001年 2月 27日出願の日本特許出願 （特願 2001— 051553)、 に基 づくものであり、 その内容はここに参照として取り込まれる。  This application is based on Japanese Patent Application (No. 2001-051553) filed on Feb. 27, 2001, the contents of which are incorporated herein by reference.
<産業上の利用可能性 > <Industrial applicability>
本発明により、 複雑な蒸留プロセスを用いることなく、 低減されたエネルギー で共沸蒸留を運転することができる。 従って、 本発明の方法は、 変動費上または 環境保護上大きな効果をもたらし、 さらにはその単純さの故に安定性が高く、 有 効成分の流出を低減する効果を有する。  According to the present invention, azeotropic distillation can be operated with reduced energy without using a complicated distillation process. Therefore, the method of the present invention has a great effect on variable costs or environmental protection, and has a high stability due to its simplicity, and has an effect of reducing the outflow of active ingredients.

Claims

請 求 の 範 囲 The scope of the claims
1. 少なくとも以下の工程 （1) 〜 （5) を有する共沸蒸留方法。 1. An azeotropic distillation method having at least the following steps (1) to (5).
工程（1)： 水、脂肪族カルボン酸及び脂肪族カルボン酸エステルを含む蒸留対 象溶液を、 ェントレーナーを用いて共沸蒸留して、 含水量の低減された脂肪族力 ルボン酸と、 水分の濃縮された塔頂留出物を得る工程。 Step (1): A solution to be distilled containing water, an aliphatic carboxylic acid and an aliphatic carboxylic acid ester is azeotropically distilled using an entrainer to obtain an aliphatic carboxylic acid having a reduced water content; A step of obtaining a water-enriched overhead distillate.
工程 （ 2)： 該塔頂留出物を凝縮させて、 ガスと、 水相及び油相の 2相に分れた 凝縮液とを得る工程。 Step (2): a step of condensing the top distillate to obtain a gas and a condensate separated into two phases, an aqueous phase and an oil phase.
工程 （3) ： 該凝縮液の水相及び油相を分取する工程。 Step (3): a step of separating an aqueous phase and an oil phase of the condensate.
工程（4)： 該分取で得られた水相の一部または全部を蒸留して、上記脂肪族力 ルボン酸エステルを含み、 含水量の低減された塔頂留出物を得る工程。 Step (4): a step of distilling a part or the whole of the aqueous phase obtained by the fractionation to obtain the overhead distillate containing the aliphatic carboxylic acid ester and having a reduced water content.
工程 （5) ： 工程 （4) にて得られた塔頂留出物を、 工程 （3) で分取した油相 の一部又は全部と共に蒸留し、 該蒸留によって得られる上記脂肪族カルボン酸ェ ステルの一部又は全部を系外へ回収する工程。 Step (5): The overhead distillate obtained in the step (4) is distilled together with a part or all of the oil phase collected in the step (3), and the aliphatic carboxylic acid obtained by the distillation is distilled. A step of collecting part or all of the ester outside the system.
2. 共沸蒸留における油相中の上記脂肪族カルボン酸エステル濃度が、 3 〜 50重量％であることを特徴とする請求の範囲第 1項に記載の共沸蒸留方法。 2. The azeotropic distillation method according to claim 1, wherein the concentration of the aliphatic carboxylic acid ester in the oil phase in the azeotropic distillation is 3 to 50% by weight.
3. 工程 （3) で分取した油相の少なくとも一部を共沸蒸留塔に戻すこと を特徴とする請求の範囲第 1項または第 2項に記載の共沸蒸留方法。 3. The azeotropic distillation method according to claim 1, wherein at least a part of the oil phase fractionated in step (3) is returned to an azeotropic distillation column.
4. 工程 （5) にて得られる脂肪族カルボン酸エステルの 20%以上が、 工程 （4) にて得られた塔頂留出物に由来することを特徴とする請求の範囲第 1 項乃至第 3項のいずれか 1項に記載の共沸蒸留方法。 4. The method according to claim 1, wherein at least 20% of the aliphatic carboxylic acid ester obtained in the step (5) is derived from the overhead product obtained in the step (4). 4. The azeotropic distillation method according to any one of paragraphs 3 to 7.
5. 工程 （5) にて得られる脂肪族カルボン酸エステルのうち、 分取した 油相の一部または全部に由来するものが 80%以下であることを特徴とする請求 の範囲第 1項乃至第 4項のいずれか 1項に記載の共沸蒸留方法。 5. The aliphatic carboxylic acid ester obtained in the step (5), wherein a portion derived from a part or the whole of the separated oil phase is 80% or less, wherein the aliphatic carboxylic acid ester is 80% or less. 7. The azeotropic distillation method according to any one of the items 4 to 4.
6 . 工程 （5 ) にて得られる脂肪族カルボン酸エステルの一部を共沸蒸留 塔に戻すことを特徴とする請求の範囲第 1項乃至第 5項のいずれか 1項に記載の 共沸蒸留方法。 6. The azeotrope according to any one of claims 1 to 5, wherein a part of the aliphatic carboxylic acid ester obtained in the step (5) is returned to the azeotropic distillation column. Distillation method.
7 . 工程 （3 ) で分取した水相の少なくとも一部を還流液として共沸蒸留 塔に戻すことを特徴とする請求の範囲第 1項乃至第 6項のいずれかに 1項記載の 共沸蒸留方法。 7. The method according to any one of claims 1 to 6, wherein at least a part of the aqueous phase collected in the step (3) is returned to the azeotropic distillation column as a reflux liquid. Boiling distillation method.
8 . 工程（5 ) において、工程（4 ) にて得られた塔頂留出物を、工程（3 ) で分取された油相の一部又は全部及び工程 （2 ) で得られたガスと共に蒸留する ことを特徴とする請求の範囲第 1項乃至第 7項のいずれか 1項に記載の共沸蒸留 方法。 8. In the step (5), the top distillate obtained in the step (4) is partially or entirely separated from the oil phase obtained in the step (3) and the gas obtained in the step (2). The azeotropic distillation method according to any one of claims 1 to 7, wherein the azeotropic distillation is performed together with the distillation.
9 . 工程 （2 ) で得られた凝縮液の油相から回収される上記脂肪族カルボ ン酸ェステルの量を、 該凝縮液の水相から回収される上記脂肪族カルボン酸ェス テルの量の 2 0倍以下とすることを特徴とする請求の範囲第 1項乃至第 8項のい ずれか 1項に記載の共沸蒸留方法。 9. The amount of the aliphatic carboxylic acid ester recovered from the oil phase of the condensate obtained in the step (2) is determined by the amount of the aliphatic carboxylic acid ester recovered from the aqueous phase of the condensate. 9. The azeotropic distillation method according to any one of claims 1 to 8, wherein the method is 20 times or less of the azeotropic distillation method.
1 0 . 脂肪族カルボン酸溶媒中でアルキル置換芳香族炭化水素を酸化して 芳香族カルボン酸を製造する方法において、 酸化反応で得られる水と脂肪族カル ボン酸を主として含む留分を蒸留対象溶液として請求の範囲第 1項乃至第 9項の いずれか 1項に記載の共沸蒸留方法を行なうことを特徴とする芳香族カルボン酸 の製造方法。 10. A method for producing an aromatic carboxylic acid by oxidizing an alkyl-substituted aromatic hydrocarbon in an aliphatic carboxylic acid solvent, wherein a fraction mainly containing water and aliphatic carboxylic acid obtained by the oxidation reaction is subjected to distillation. 10. A method for producing an aromatic carboxylic acid, comprising performing the azeotropic distillation method according to any one of claims 1 to 9 as a solution.
1 1 . 工程 （5 ) で回収された脂肪族カルボン酸エステルの少なくとも一 部を、 アルキル置換芳香族炭化水素を酸化して芳香族カルボン酸を製造する工程 のいずれかにリサイクルすることを特徴とする請求の範囲第 1 0項に記載の芳香 族力ルポン酸の製造方法。 11. The method is characterized in that at least a part of the aliphatic carboxylic acid ester recovered in the step (5) is recycled to any of the steps for producing an aromatic carboxylic acid by oxidizing an alkyl-substituted aromatic hydrocarbon. 12. The method for producing an aromatic ruponic acid according to claim 10.
PCT/JP2002/001372 2001-02-27 2002-02-18 Azeotropic distillation process WO2002068375A1 (en)

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