JP2532042B2 - Organic acid recovery method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering a useful organic acid from an aqueous organic acid solution. More specifically, the present invention relates to a method for recovering an organic acid that efficiently recovers an organic acid from an aqueous solution of an organic acid that is generated in large quantities in the cellulose industry, fermentation industry, chemical industry, and the like.

[Problems to be Solved by Conventional Techniques and Inventions] Generally, in order to recover an organic acid from an aqueous solution of an organic acid, a method of extracting the organic acid with an organic solvent and dehydrating and desolventizing the extract by distillation is adopted. Has been done. In this method, when an organic solvent having a boiling point lower than that of the organic acid is used, the organic acid aqueous solution is extracted with the organic solvent, the extract is led to a distillation column, and water and the organic solvent are distilled off from the top of the column. , The organic acid is recovered from the bottom of the tower. More specifically, as shown in FIG. 5, first, the organic acid aqueous solution (51) is extracted with the organic solvent (52) in the extraction tower (53), and the organic acid contained in the extract is distilled. Collect in a tower. On the other hand, the organic solvent contained in the raffinate (54) is recovered by a solvent recovery distillation column (not shown). When the organic acid aqueous solution (51) contains a high boiling point component, the extraction liquid (55) is supplied to the evaporator (57) by the pump (56) to evaporate the extraction liquid (55) to remove the high boiling point component, It is also supplied to the distillation column (58). In this distillation column (58), a fraction (59) containing water and an organic solvent (52) distilled from the top of the column is condensed in a condenser (60) while partially refluxing it, and then a tank (61). The high purity organic acid (62) is recovered from the bottom of the distillation column (58). When using an organic solvent having a boiling point higher than that of the organic acid, the organic acid aqueous solution is extracted with an organic solvent, and the extract is introduced into a distillation column to distill off water from the top of the column,
The organic acid and the solvent are withdrawn from the bottom of the column, the liquid at the bottom of the column is further introduced into a distillation column, and the organic acid is distilled off from the top of the column to recover a pure organic acid. In any of the above methods for recovering the organic acid, it is necessary to evaporate and distill off the water having a large latent heat of vaporization dissolved in the extract in the distillation column, which consumes a lot of energy. Therefore, when selecting the extraction solvent, it is necessary to select an organic solvent having a large partition coefficient for the organic acid and a large selectivity which is a value obtained by multiplying the partition coefficient for the organic acid by the partition coefficient for water. However, a solvent having a large partition coefficient for organic acids generally has a large partition coefficient for water as well. For example, when the organic acid aqueous solution is an acetic acid aqueous solution, a solvent having a large partition coefficient for acetic acid, for example, a solvent such as ethyl acetate, ethyl propionate, methyl ethyl ketone, methyl propyl ketone, and diethyl ketone has a large partition coefficient for water. When an aqueous solution of acetic acid is extracted with the solvent described above, the concentration of water inevitably greatly increases as the concentration of acetic acid in the extract increases. That is, acetic acid-water-solvent 3 shown in FIG.
As is clear from the liquid-liquid equilibrium diagram of the component system, an acetic acid aqueous solution consisting of 28% by weight of acetic acid and 72% by weight of water was used as the organic acid aqueous solution, and ethyl acetate ( (Indicated by EA in the figure) is 1.1 parts by weight, the composition of the extract in equilibrium with the raffinate (indicated by Ext ₁ in the figure) is 18% by weight acetic acid and 17% by weight water.
When the amount of ethyl acetate used is 0.63 parts by weight, the composition of the extract (shown as Ext ₂ in the figure) is 24.9% by weight of acetic acid and 2% of water.
It becomes 4.5% by weight, and not only the acetic acid concentration in the extract but also the water concentration increases significantly. Thus, the concentration of acetic acid increases when extracted with a small amount of organic solvent, but there is a drawback that the cost of recovering the organic acid increases due to an increase in the amount of water that is extracted along with it.

Therefore, as an extraction solvent, an organic solvent such as air,
The organic acid is extracted in a state where the solubility in water is reduced using another solvent having a low solubility in water, for example, a mixed solvent in which benzene is combined. For example, as shown in FIG. 6, a mixed solvent of 75% by weight of ethyl acetate and 25% by weight of benzene (shown as EA / Bz = 75/25 in the figure) as an extraction solvent is added to 1 part by weight of an aqueous acetic acid solution. When used as 1.45 parts by weight, the composition of the extract that is in equilibrium with the extraction phase (shown as Ext ₃ in the figure)
Is 16% by weight of acetic acid and 6% by weight of water, and the water concentration in the extract can be reduced as compared with the case where the ethyl acetate (EA) alone solvent is used. However, in this method, even though the organic solvent has a large partition coefficient for the organic acid, it is used as a mixed solvent having a reduced partition coefficient for the organic acid, so that the extraction efficiency of the organic acid is high. There was a problem of deterioration.

On the other hand, as a method for recovering alcohol from an azeotropic mixture such as water-alcohol, the azeotropic mixture is separated by pervaporation, and the separated two liquids are respectively fed to a distillation column to be separated by distillation, and the desired components are continuously extracted. Method (Japanese Patent Publication No. 59-40048) or a water-ethanol azeotrope mixture is separated by pervaporation, and the ethanol vapor having a high water content discharged to the secondary side is condensed to a distillation column. A method (Japanese Patent Publication No. 60-42210) of returning and continuously obtaining anhydrous ethanol from the primary side has been proposed.
The pervaporation process disclosed in these prior arts supplies a liquid to be treated such as an azeotrope to the high pressure side of the polymer membrane on the high pressure side, and selectively supplies it as a vapor to the low pressure side of the secondary side. It is a method of transmitting the light through. This membrane separation method has an advantage that desired components can be separated and collected by a simple method from an azeotropic mixture, a mixture having a small boiling point difference, a liquid mixture having similar molecular sizes, and the like.

However, when the alcohol is purified using the pervaporation process described above, the alcohol
%, 5% water 5% azeotropic composition alcohol concentration 99.5 ~
Since it is necessary to concentrate to about 99.9%, it is necessary to set the operating pressure on the depressurization side to 10 torr or less, and there is a problem that the condensing temperature becomes below the zero point and the permeated liquid freezes, and workability is not sufficient. Further, in selecting a polymer membrane, it is necessary to use a separation membrane having high water selective permeability in order to enhance the water separation efficiency.

It is an object of the present invention to provide a method for recovering an organic acid which has a low recovery energy and is excellent in workability even if the organic acid aqueous solution has a high water concentration.

Another object of the present invention is to use an organic solvent having a high partition coefficient for water as well as an organic acid,
An object of the present invention is to provide a method for recovering an organic acid, which can efficiently recover the organic acid even when the amount of the organic solvent used is small, and which has excellent recovery efficiency.

Still another object of the present invention is to provide a method for recovering an organic acid which does not particularly require a separation membrane having high water selective permeability and which can be used as a separation membrane having a wide water selective permeability. .

[Structure of the Invention] The present inventors have completed the present invention as a result of intensive research to solve the above problems.

That is, the present invention is a method for recovering an organic acid from an organic acid aqueous solution, wherein the organic acid aqueous solution is extracted with an organic solvent in the extraction unit, and the extract is separated by a separation unit equipped with a water-selective permeable separation membrane. The organic acid recovery method of supplying a fraction that has passed through the separation section to the extraction section, and supplying a fraction that does not pass through the separation section to the dehydration desolvation section to continuously recover the organic acid, Is the solution.

The method for recovering an organic acid according to the present invention will be described with reference to the accompanying drawings, taking a case where an organic solvent having a boiling point lower than that of the organic acid is used as an example. In addition, in order to help understanding, the same elements will be described with the same reference numerals.

FIG. 1 is a process diagram showing a flow using pervaporation, in which an organic acid aqueous solution (1) is subjected to extraction treatment in an extraction tower (3) by an organic solvent (2) having a large partition coefficient with respect to the organic acid, The organic acid and water in the organic acid aqueous solution (1) are transferred to the organic solvent (2) according to their partition coefficient. At this time, as the organic solvent (2), since the water in the extract (5) can be removed by the separation membrane (8) having the selective water permeability of the separation part (7), the partition coefficient for water can be reduced. Regardless of this, an organic solvent having a large partition coefficient for the organic acid can be used. Therefore, even if the amount of the organic solvent used is small, the organic acid can be efficiently extracted, the amount of the organic solvent can be saved, and the recovery cost of the organic acid can be reduced. Furthermore, since the amount charged to the extraction tower and dehydration desolvation tower can be reduced,
The extraction tower and dehydration desolvation tower can be downsized. This means that if the present invention is applied to existing equipment, the capacity of organic acid recovery equipment is greatly increased.

As the organic solvent (2) for extracting the organic acid aqueous solution (1), a solvent having a large partition coefficient with respect to the organic acid in the organic acid aqueous solution is used in order to enhance extraction efficiency. Examples of such an organic solvent include methyl ethyl ketone,
Ketones such as diethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and 4-methyl-3-penten-2-one; butanol, isobutanol, tert-amyl alcohol and 3-
Alcohols such as pentanol; ethers such as dipropyl ether, isopropyl ether, ethyl isopropyl ether, ethyl isobutyl ether, methyl isoamyl ether, allyl ether and allyl ethyl ether; butyl formate, isobutyl formate, propyl acetate, isopropyl acetate, acetic acid Esters such as butyl, acetic acid-sec-butyl, acetic acid-tert-butyl, vinyl acetate, methyl propionate, ethyl propionate and methyl butanoate are exemplified. At least one organic solvent is used. In addition, in order to efficiently separate and collect the organic acid in the fraction (13) in the dehydration desolvation section (15), among the organic solvents, a solvent having a boiling point difference of 20 ° C. or more from the organic acid is preferable. For example, when the organic acid is acetic acid, methyl isopropyl ketone, ethyl acetate, isopropyl acetate, methyl propionate and the like are preferable.

As the extraction column (3), an extraction column of a commonly used type, for example, a mixer-settler type extraction column, a perforated plate column, a packed column, a baffle column and the like can be used. The organic solvent contained in the raffinate (4) is recovered in a distillation column (not shown).

On the other hand, since the extract (5) contains a large amount of water together with the organic acid, the extract (5) is supplied to the separation part (7) provided with the cylindrical separation membrane (8) having selective water permeability by the pump (6). , A fraction (11) that has passed through the separation part (7) and a fraction (13) that has not passed through the separation part (7). In this example, a cylindrical separation membrane is used as the separation membrane (8).

The separation part (7) selectively permeates the water in the extract (5) through the water-selective separation membrane (8) to separate the water-rich fraction (11) and the separation membrane. It does not have to pass through (8) and is separated into a fraction (13) having a high content of an organic acid and an organic solvent, but in order to efficiently separate the extract (5), Liquid / gas separation is preferably carried out by pervaporation. In this pervaporation, since the separation membrane (8) has a water selective permeability, the water content in the extract (5) supplied to the primary side (9) of the separation section (7) is mainly water. Is a separation membrane (8)
Is selectively permeated as vapor and flows out from the secondary side (10) which is the permeation side of the separation section (7). On the other hand, mainly the organic acid and the organic solvent (2) in the extract (5) do not pass through the separation membrane (8) and flow out from the primary side (9) of the separation section (7). By using pervaporation, even if the water concentration of the extract (5) is high, the water can be efficiently separated, and the energy consumption can be significantly reduced as compared with the conventional distillation method.

Since the fraction (11) that has passed through the separation membrane (8) is recycled to the extraction section (3), the separation membrane (8) having water selective permeability does not necessarily have high water selective permeability. There is no need, and any solvent can be used as long as it has solvent resistance to the organic solvent (2). Examples of the separation membrane having selective water permeability include polyethylene, polypropylene, polybutadiene, polybutene, and poly-4-.
Methyl pentene-1, polyacrylonitrile, polystyrene, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyvinyl acetate, polyacrylic acid, polymethacrylic acid, polyacrylic acid ester, polymethacrylic acid ester, polyether, polycarbonate, Polyesters, polyamides, polyimides, polysulfones, polyphenylene oxides, polydimethylsiloxanes, cellulosic polymers, their copolymers, graft copolymers, mixtures, and even amination and sulfonation of these polymer substances Examples thereof include a film made of a product subjected to a polymer reaction. The water-selective separation membrane may be a porous membrane formed by a micro phase separation method, a stretching method, a charge track etching method, or the like, or may be a non-porous membrane.

The membrane structure of the separation membrane is either a composite consisting of two or more of the above separation membranes, an asymmetric body consisting of a surface skin layer having a selective permeation function and a porous layer supporting the surface skin layer, and a uniform body. However, it is preferably a complex or an asymmetric body. The membrane module of the separation part may be, for example, a flat membrane module, a hollow fiber module, a spiral module, a cylindrical module, or the like. The thickness of the active part of the separation membrane can be appropriately set according to the material of the separation membrane within a range that does not impair the durability and the separation speed, but it is possible to efficiently extract water from the extract (5) having a high water concentration. Since it can be separated as desired, it may be thinner than the conventionally used polymer membrane. The thickness of the active part of the separation membrane is usually 0.01 to 10
μm, preferably 1 μm or less. The thickness of the active part is 0.
If it is less than 01 μm, the durability of the active part may be problematic, and if it exceeds 10 μm, the pressure loss becomes large and the separation speed decreases.

The temperature of the separation part (7) can be appropriately set according to the desired permeation rate, permeation amount, heat resistance of the separation membrane (8), etc., but is usually 40 to 120 ° C, preferably 50 to 120 ° C. 100
° C. If the temperature is below 40 ° C, the permeation rate will be low,
When the temperature exceeds 120 ° C, the shape retention of the separation membrane (8) deteriorates. The operating pressure of the separation part (7) is determined by the water concentration and temperature on the primary side. The pressure (10) on the secondary side is set lower than the partial pressure of water on the primary side (9).

As described above, in the case of alcohol purification, not only the operating pressure in the separation section needs to be set to 10 torr or less, but also the condensation temperature becomes lower than the zero point, and the permeated liquid freezes. On the other hand, in the method of the present invention, since the final water concentration is kept at several%, for example, about 1 to 10%, the extraction liquid (5) having a high water concentration can be used at a high speed and in recovering the organic acid. It can be permeated with sufficient selectivity. Further, since the distillate (13) is distilled in the dehydration desolvation tower (15), the water concentration of the distillate (13) that does not pass through the separation section (7) may be set to about several%. Therefore, the operating pressure of the separating part (7) can be set higher than the conventional operating pressure, the condensation temperature does not have to be lowered so much, and the workability is excellent. In addition, since the water can be efficiently separated from the extract (5) by using the thin separation membrane (8), the organic acid recovery efficiency is excellent and the organic acid recovery energy is small.

In pervaporation of the extract (5), the composition of the extract (5) affects the permeation rate and separation selectivity. Especially, the permeation rate and the amount of liquid permeation are greatly influenced by the water concentration in the extract (5). Therefore, it is preferable to operate under optimum conditions corresponding to the water concentration in the extract (5) in consideration of the equipment cost and the like. At this time, as the extract liquid (5) to be subjected to pervaporation, the extract liquids (5) having different water concentrations within the range of the water concentration of the extract liquid (5) and the water concentration of the target recovery liquid are used, You may operate on the optimal conditions according to the water concentration of each extract (5).

The latent heat of the liquid component that passes through the separation membrane (8) is given by the heat exchanger, and the smaller the temperature difference between the inlet and outlet of the membrane module, the more evaporation energy can be given.
Therefore, the extract (5) between the heat exchanger and the membrane module
It is advantageous to increase the circulation amount of. At this time, the circulation amount is limited by the pressure loss of the membrane module and the like, so that there is an optimum value.

The gaseous fraction (11) that has passed through the separation section (7) is condensed in the condenser (12). The condensed fraction (11) contains a large amount of water, an organic acid and an organic solvent, and thus is supplied to the extraction column (3). Since the fraction (11) that has passed through the separation membrane (8) is recycled to the extraction column (3), a separation membrane having high water selective permeability is not particularly required as described above,
A relatively wide range of separation membranes can be used. The fraction (11) is usually the separation part (7) of the extraction column (3).
The fraction (11) that has passed through is recycled to a position showing the same composition.

On the other hand, the fraction (13) that does not pass through the separation section (7) is
It is supplied to the dehydration desolvation tower (15) by a pump (14).
In the dehydration desolvation tower (15), a part of the organic solvent and water present in the fraction (13) are refluxed and distilled off from the top of the dehydration desolvation tower (15) by a distillation operation. With
The distilled fraction (16) is condensed in the condenser (17) and stored in the tank (18). In this tank (18), the lower layer water (19) and the upper layer organic solvent (20) are separated, so that the lower layer water (19) is discharged and the upper layer organic solvent (20) is discharged.
Is recycled to the organic solvent (2). The organic acid (21) in the organic acid aqueous solution (1) is recovered from the bottom of the dehydration desolvation column (15).

The separation membrane (8) may have a relatively high permeability to an organic solvent that is an extraction solvent. In such a case, the fraction (11) that has permeated the separation membrane (8) is separated into two. You may perform liquid separation. At that time, a decanter is provided, and the lower layer liquid is
The extraction column (3) is recycled to a position having substantially the same composition as the lower layer liquid, and the upper layer liquid is recycled to the extraction column (3) or directly supplied to the dehydration desolvation column (15), or a separation membrane. It may be combined with the fraction (13) which does not permeate (8).

When the high boiling point component is contained in the fraction (13) which does not pass through the separation part (7), the fraction (13) which does not pass through the separation part (7) is evaporated as shown in FIG. It is preferable to supply the vapor of the fraction (13), which is supplied to the vessel (30) and evaporated in the evaporator (30), to the dehydration desolvation column (15). When an evaporator (30) is installed, high boiling point components are dehydrated and desolvated (1
Since it can be suppressed from being supplied to the organic acid solution (5), the highly pure organic acid (21) can be efficiently recovered even if the high boiling point component is contained in the organic acid aqueous solution (1). The high boiling point component is recovered from the bottom of the evaporator (30).

As shown in FIG. 2, since the separation unit (7) supplies evaporation energy, the fraction (13) that does not pass through the separation unit (7) circulates around the separation unit (7) and is heated. Bowl (3
Heated in 1).

Furthermore, as shown in FIG. 3, the evaporator may be provided between the extraction column (3) and the separation section (7). In this case, a recovery process of the organic acid by the vapor infiltration method is constituted. The vapor permeation method is a gas / gas separation method in which the liquid to be treated is supplied in the vapor state to the primary side, which is the high-pressure side of the separation membrane, and is selectively permeated to the secondary side, which is the low-pressure side, as vapor. is there. FIG. 3 is a process diagram showing a flow using the vapor infiltration method. In this vapor infiltration method, the extract liquid (5) extracted in the extraction tower (3) in the same manner as described above is evaporated in the evaporator (30) and supplied in the vapor state to the separation section (7) to remove gas / gas.
Separate the gas. The vapor of the extract liquid supplied to the separation part (7) is a fraction (11) that permeates the separation membrane (8), that is, a fraction containing a large amount of water vapor and a fraction (13) that does not permeate the separation membrane (8). ), Ie, a fraction rich in organic acids and organic solvents. Further, as in the case of the pervaporation, the fraction (11) that has passed through the separation membrane (8) is recycled to the extraction column (3), and the fraction (13) that does not pass through the separation membrane (8) is dehydrated desolventized. Supplied to the tower (15). According to this vapor permeation method, even if the high boiling point component is contained in the organic acid aqueous solution (1), not only the high boiling point component can be removed by the evaporator (30) but also the extraction liquid (5) is converted into a vapor state. Since it is supplied to the separation part (7), the permeation rate can be increased and the organic acid can be efficiently recovered. The operating conditions of the separation part (7) by the vapor permeation method can be appropriately set according to the composition of the extraction liquid (5) and its vapor pressure, etc., but normally the temperature of the separation part (7) is The temperature is not lower than the boiling point of the extract, preferably higher than the boiling point, and the pressure on the secondary side is 10 to 1000 torr.

A plurality of separating parts may be arranged in parallel. In this case, in order to increase the throughput of the extraction liquid, the extraction liquid is supplied to a plurality of separation units arranged in parallel, and the fractions that have passed through the respective separation units are combined and recycled to the extraction tower and separated. The fractions that do not pass through the parts may be combined and supplied to the dehydration desolvation column.

Fractions that do not pass through the separation unit are sequentially supplied to subsequent separation units, and finally fractions that do not pass through the separation unit are supplied to the dehydration desolvation tower, and fractions that have passed through each separation unit are extracted into the extraction column. May be recycled to. More specifically, as shown in FIG. 4, in this example, a flat sheet membrane type module using a flat sheet membrane separation membrane is used as a separation portion. The extraction liquid (5) is composed of a plurality of separation units (7a) (7b) (7c) arranged in parallel.
It is supplied to the primary side (9a) of the first separation part (7a) provided with the separation membrane (8a). The fraction (11a) that does not permeate the separation membrane (8a) of the first separation part (7a) is partially heated by the heater (41) and recycled to the extract (5), and then follows. It is supplied to the primary side (9b) of the second separation section (7b). In addition, the separation membrane (8b) of the second separation section (7b)
The fraction (11b) that does not permeate through is part of the fraction (11b) heated by the heater (42) is recycled to the second separation section (7b) and the third separation section (7c). Is supplied to the primary side (9c). The fraction (11c) that does not pass through the separation membrane (8c) of the third separation section (7c) is partially heated by the heater (43) in the same manner as above, and the third separation section (7c) is heated. ) And supplied to the dehydration desolvation tower. on the other hand,
Separation membranes (8a) (8b) (8) of each separation part (7a) (7b) (7c)
c) and the secondary side (1) of each separation part (7a) (7b) (7c)
Fractions (9a) (9b) discharged from 0a) (10b) (10c)
(9c) are combined with each other and recycled to the extraction tower. According to such a process, the separation efficiency of the extract (5) can be improved, and the heat exchanger gives latent heat of the liquid component passing through the separation membranes (8a) (8b) (8c) in the circulation line. Therefore, there is an advantage that the temperature difference between the inlet and the outlet of the membrane module can be reduced and the heat transfer coefficient of the heat exchanger can be increased.

In each of the above examples, an organic solvent having a boiling point lower than that of the organic acid is used, but an organic solvent having a boiling point higher than that of the organic acid may be used. In this case, the organic acid is recovered from the top of the dehydration desolvation tower (15), and the organic solvent is recovered from the bottom of the dehydration desolvation tower (15),
The collected organic solvent may be recycled to the extraction tower (3).

The method for recovering an organic acid of the present invention can be applied to various organic acids such as formic acid, butyric acid, acetic acid, propionic acid, acrylic acid and methacrylic acid.

[Effects of the Invention] As described above, according to the method for recovering an organic acid of the present invention,
The water in the fraction that does not pass through the separation unit can be efficiently removed by the separation unit, and the water can be removed by the dehydration desolvation unit, so that the recovery energy can be reduced even if the water concentration of the extract is high, and the work can be performed. It has excellent properties. In addition, as long as it is an organic solvent that has a high partition coefficient for organic acids, even an organic solvent that has a high partition coefficient for water can be used, and an organic acid can be efficiently recovered with a small amount of organic solvent. It has excellent recovery efficiency. Furthermore, since the fraction that has passed through the separation section is supplied to the extraction column, a separation membrane having a high water selective permeability is not particularly required, and a separation membrane having a wide range of water selective permeability can be used as the separation membrane.

[Examples] Hereinafter, the present invention will be described in more detail based on Examples.

Comparative Example 1 The apparatus shown in FIG. 5 was used as the organic acid recovery apparatus. As the extraction column, a 20 m high extraction column equipped with a 40 mmφ glass ring and plate was used to extract 28% by weight acetic acid aqueous solution with a mixed solvent of ethyl acetate / benzene = 75% by weight / 25% by weight. did. At this time, in order to reduce the concentration of acetic acid in the raffinate to 0.1% by weight or less, 1.45 parts by weight of the mixed solvent was required for 1 part by weight of the 28% by weight acetic acid aqueous solution. Also, evaporate the extract with an evaporator,
99.9% from the bottom of the tower by performing dehydration and desolvation by supplying to a glass Oldershaw tower with a vacuum jacket of stages.
Acetic acid was recovered with a concentration and yield of not less than wt%. Table 1 shows data such as the required steam usage rate by this method.

Comparative Example 2 A 28 wt% aqueous acetic acid solution was extracted in the same manner as in Comparative Example 1 except that ethyl acetate was used instead of the mixed solvent of Comparative Example 1.
At that time, 0.63 parts by weight of ethyl acetate was necessary for 1 part by weight of a 28% by weight acetic acid aqueous solution in order to reduce the concentration of acetic acid in the raffinate to 0.1% by weight or less. The extract was evaporated in an evaporator, supplied to the distillation column of Comparative Example 1, and dehydrated and desolvated to recover acetic acid from the bottom of the column at a concentration of 99.9% by weight or more and a yield. Table 1 shows data such as the required steam usage rate by this method.

From the results shown in Table 1, the use of the organic solvent of Comparative Example 2 can reduce the amount of the organic solvent used in the extraction column rather than the mixed solvent of Comparative Example 1, but the energy consumption in the dehydration desolvation column Will increase.

Example 1 The apparatus shown in FIG. 2 was used as an organic acid recovery apparatus. A 28% by weight aqueous acetic acid solution was extracted with ethyl acetate using the extraction column of Comparative Example 1. At that time, at a position 5 m from the top of the extraction column, a liquid expected to have the composition of the fraction permeated through the separation membrane (80% by weight of water, 8.5% by weight of acetic acid and 11.5% of ethyl acetate) was used.
Wt%) was fed at a rate of 30% of the feed rate of 28% by weight aqueous acetic acid. At this time, adjust the acetic acid concentration of the raffinate to 0.
In order to reduce the amount to 1% by weight or less, 0.9 part by weight of ethyl acetate was required for 1 part by weight of 28% by weight aqueous acetic acid solution.

Prior to permeation through the separation membrane, the permeation rate of the membrane and the selectivity of the membrane were investigated using a flat membrane composed of polyacrylic acid composite membrane. That is, a mixture of acetic acid, water and ethyl acetate is kept at a constant temperature in a constant temperature bath, and is circulated and supplied to the primary side of the separation membrane by a pump while the secondary side of the separation membrane is depressurized at 50 torr. The gas permeated through the separation membrane was cooled by a condenser, and the fraction permeated through the separation membrane was recovered. In this pervaporation, since the water content in the fraction that does not permeate through the separation membrane is high, a much higher permeation rate can be obtained as compared with the pervaporation operation carried out in a water-alcohol system, and the process of the present invention. The water permeated with sufficient selectivity to allow The results are shown in Table 2.

Based on the above results, when the extract was pervaporated, the composition of the fraction that did not permeate through the separation membrane was estimated, and the fraction having this composition was supplied to the distillation column of Comparative Example 1 to obtain a column. Acetic acid was recovered from the bottom in a concentration and yield of over 99.9%. Table 2 shows data such as the required steam usage rate by this method.

Example 2 The extraction column used in Example 1 was reduced to 12 m, and 3 m from the top of the column.
To the lower position, a liquid consisting of 80% by weight of water, 8.5% by weight of acetic acid and 11.5% by weight of ethyl acetate was supplied at a rate of 30% of the supply rate of the above 28% by weight acetic acid aqueous solution, and the extraction operation was performed with ethyl acetate. I did. At this time, change the acetic acid concentration of the raffinate
In order to achieve 0.1% by weight or less, 1.1 parts by weight of ethyl acetate was needed for 1 part by weight of 28% by weight acetic acid aqueous solution. Based on the composition of this extract, the composition of the fraction that does not permeate the separation membrane when pervaporating was estimated in the same manner as in Example 1, and the distillation was performed in the same manner as in Example 1 to give 99.9. Acetic acid was recovered with a concentration and yield of not less than%. Table 2 shows data such as the required steam usage rate by this method.

As is clear from Table 2, in the methods of Examples 1 and 2, the amount of the organic solvent supplied to the extraction column can be smaller than that in Comparative Example 1. Therefore, it was found that the extraction column can be downsized, the amount of the distillate supplied to the distillation column can be reduced, and the distillation column can be downsized. Furthermore, it was found that the methods of Examples 1 and 2 markedly reduced the steam usage rate and required less energy to recover than the methods of Comparative Examples 1 and 2.

Examples 3 to 5 A flat membrane made of a polyacrylic acid composite membrane was used as the separation membrane. A mixture of acetic acid, water and ethyl acetate is kept at a constant temperature in a constant temperature bath and is circulated and supplied to the primary side of the separation membrane by a pump, and the secondary side of the separation membrane is supplied to 50%.
Pervaporation was performed under a reduced pressure of torr, the gas that permeated the separation membrane was cooled by a condenser, and the fraction that permeated the separation membrane was collected.

As a result, the water concentration in the mixed solution used for pervaporation is high, so that a higher flux can be obtained and the process of the present invention is enabled as compared with the pervaporation operation performed in a water-alcohol system. Water permeated with sufficient selectivity for. The results are shown in Table 3.

[Brief description of drawings]

FIG. 1 is a process diagram showing a flow of the present invention using pervaporation, FIG. 2 is a process diagram showing another flow of the present invention, and FIG. 3 shows a flow of the present invention using a vapor permeation method. Fig. 4 is a process diagram showing another flow of the present invention, Fig. 5 is a process diagram showing a conventional method for recovering an organic acid, and Fig. 6 is a liquid-liquid equilibrium diagram of acetic acid-water-solvent. is there. (1) ... Aqueous organic acid solution, (2) ... Organic solvent, (3)
…… Extraction tower, (5) …… Extraction liquid, (7) (7a) (7b)
(7c) …… Separation section, (8) (8a) (8b) (8c) …… Separation membrane, (11) (11a) (11b) (11c) …… Distillate passed through the separation section, (13) (13a) (13b) (13c) …… Fraction that does not pass through the separation section, (15) …… dehydration desolvation tower, (21) …… organic acid, (30) …… evaporator

Claims (3)

(57) [Claims] 1. A method for recovering an organic acid from an organic acid aqueous solution, wherein the organic acid aqueous solution is extracted with an organic solvent in an extraction section,
The extract is separated by a separation unit equipped with a water-selective permeable separation membrane, the fraction that has passed through the separation unit is supplied to the extraction unit, and the fraction that does not pass through the separation unit is supplied to the dehydration desolvation unit. A method for recovering an organic acid, characterized in that the organic acid is continuously recovered. 2. The method for recovering an organic acid according to claim 1, wherein the extract is separated by pervaporation in the separation section. 3. The method for recovering an organic acid according to claim 1, wherein the extract is evaporated in the evaporator and then separated in the separator by a vapor permeation method.