JP7456221B2 - Method for producing acrylic acid - Google Patents

Description

The present invention relates to a method for recovering acrylic acid from an aqueous acrylic acid solution using an extraction solvent.

Acrylic acid-containing gas obtained by the catalytic gas phase oxidation reaction of propane, propylene, or acrolein is cooled and absorbed by water or the like in a collection tower, and separated into an aqueous acrylic acid solution and residual gas. The aqueous acrylic acid solution is then separated into water, etc., and acrylic acid by extraction or distillation.
At the beginning of the development of this technology, an extraction method using a solvent with a large distribution coefficient of acrylic acid was widely used as a method for efficiently extracting acrylic acid from the acrylic acid aqueous solution obtained in the absorption column. The distribution coefficient here means the ratio of the concentration of acrylic acid in the extraction solvent to the concentration of acrylic acid in water in a liquid-liquid equilibrium state. For example, Patent Document 1 shows a method of extracting 99% or more of acrylic acid by using methyl isobutyl ketone as an extraction solvent in a weight ratio of 0.4 times (2 times) the weight of acrylic acid for a 20% acrylic acid aqueous solution.

As technology improves, the concentration of the acrylic acid aqueous solution obtained in the collection tower increases, and distillation methods that require less total heat for purification, specifically dehydration distillation using an azeotropic solvent, and acrylic acid aqueous solution Direct distillation, which involves distilling as-is, began to be used. For example, Patent Document 2 describes a method using toluene at a weight ratio of 2.6 times (4.7 times the weight of acrylic acid) as an azeotropic solvent for a 55% by weight aqueous acrylic acid solution; , about 80% by weight from the reactant gas
A method is shown in which an aqueous solution of acrylic acid is obtained and purified by distillation without a solvent.

Differently from these methods, a method of reducing the amount of heat required and unrecovered acrylic acid by using an extraction device with dynamic stirring ability and a high number of theoretical plates is also being considered. Patent Document 4 uses a reciprocating plate type countercurrent extraction device to extract a 59% by weight acrylic acid aqueous solution at a weight ratio of 2.3 times (
A method has been shown in which 98.1% of acrylic acid can be extracted even when the solvent contains 0.45% by weight of acrylic acid by using toluene (3.9 times the amount of acrylic acid) as an extraction solvent. There is. Patent Document 5 discloses that an Otto-Yoke vibrating tray extractor is used to extract 40 to 60% by weight.
By using a mixed solvent of isopropyl acetate and cyclohexane at a weight ratio of 1.9 times (3.2 to 4.8 times the weight of acrylic acid) to an aqueous solution of acrylic acid, a high volumetric efficiency of 99.7% can be achieved.
A method for extracting acrylic acid to a certain extent is shown. As a method of preventing flooding in the extraction tower and continuing stable operation, Patent Document 6 describes a method of measuring the differential pressure between the upper and lower sides of one or more stages of dispersion plates in a perforated plate extraction tower using a capillary differential pressure gauge. It is shown.

Special Publication No. 46-30493 Japanese Patent Application Publication No. 8-40974 Japanese Patent Application Publication No. 2013-107894 JP2009-242285A Japanese Patent Application Publication No. 2003-183221 JP 2008-173563 A

The method for separating acrylic acid and water from an acrylic acid aqueous solution is to separate water by distillation (
There are two common methods: a distillation method) and a method of extracting acrylic acid with a solvent (extraction method).
Compared to the distillation method, the extraction method allows for the separation of maleic acid and acrylic acid polymers, which are reaction by-products, along with water by extraction from acrylic acid by selecting an appropriate extraction solvent. This method has the advantage that fouling and clogging of equipment caused by these reaction by-products is alleviated or eliminated. However, it is required for economic reasons to minimize the scale of the extraction operation.

Since the heat required in the extraction method is roughly proportional to the amount of solvent used in the extraction, it is important to carry out the extraction using a smaller amount of solvent relative to the amount of acrylic acid in order to improve economic efficiency.
The "extraction method" described in Patent Document 1 uses a solvent with a large distribution coefficient of acrylic acid, and is an excellent method when the concentration of acrylic acid in the aqueous acrylic acid solution is low. However, since a large amount of water is extracted together with acrylic acid, a large amount of heat is required to separate a large amount of water from the extract. In addition, since the solvent with a large distribution coefficient has a high solubility in water, the water (
It is also necessary to recover the extraction solvent contained in the residual water (hereinafter sometimes referred to as "raffinate water").

The "extraction method" described in Patent Document 4 uses a non-polar solvent, and the concentration of water incorporated into the extract is low, making it efficient in terms of water separation, and the concentration of the extraction solvent contained in the raffinate water is also low. However, since the partition coefficient of acrylic acid is small, a large amount of extraction solvent is required to obtain a sufficient extraction recovery rate of acrylic acid. It is necessary to increase the number of theoretical plates in an extraction device such as a column. In the case of nonpolar solvents, the small distribution coefficient of acrylic acid is particularly noticeable in regions where the concentration of acrylic acid in water is low, and many theoretical plates are required to reduce the amount of acrylic acid in raffinate water. Patent Document 4 states that by using an extraction column with dynamic stirring (dynamic extraction column), it is easier to obtain a high number of theoretical plates. As the diameter decreases and the sedimentation rate decreases, some water droplets cannot descend inside the column and tend to flow out from the top of the column together with the extraction solvent (hereinafter sometimes referred to as "flooding"). Therefore, more careful driving is required.

In the "extraction method" described in Patent Document 5, a mixed solvent of a non-polar solvent and a polar solvent is used as the extraction solvent,
A dynamic extraction column is used, and by increasing the mutual solubility of the aqueous phase and solvent phase, the necessary number of theoretical plates can be obtained even with relatively low stirring intensity, and flooding can be avoided, but reaction by-products The rate at which certain maleic acid and acrylic acid polymers are extracted into the solvent phase also increases.
There are problems such as increased contamination and clogging in the purification process after extraction, and the need to recover polar solvents because they dissolve in the raffinate water.

The method of measuring the differential pressure inside the extraction tower described in Patent Document 6 can detect the occurrence of flooding at an early stage, so it is considered effective in suppressing excessive design of the extraction tower, but it does not suppress the occurrence of flooding. do not have.

The present invention solves the above-mentioned conventional problems and enables stable and economical extraction of acrylic acid using a small amount of solvent in a method of extracting acrylic acid from an aqueous acrylic acid solution using an extraction device. An object of the present invention is to provide a method for producing acrylic acid, including a method.

The present inventor began studies to solve the above problems, and found that the higher the acrylic acid concentration in the extract liquid in a dynamic extraction device, the more likely flooding is to occur rapidly due to dynamic stirring, and the more likely flooding is to occur. In both cases, it was confirmed that the time required to separate the two liquids was significantly increased. We found that this is due to a decrease in the interfacial tension between the two liquids, and in other words, recognizing that it is difficult to essentially avoid the occurrence of flooding, we investigated an extraction method that allows a high number of theoretical plates while allowing the occurrence of flooding. As a result, we decided to use a static extraction device to extract acrylic acid from the aqueous solution with the highest concentration of acrylic acid, and to also use the static extraction device to separate fine water droplets, and to use a dynamic extraction column. By constantly monitoring the internal conditions, we discovered a method to efficiently extract and recover acrylic acid from an aqueous acrylic acid solution using a small amount of solvent.

The present invention has been achieved based on such knowledge, and its gist is as follows.

[ 1 ] An acrylic acid aqueous solution with an acrylic acid concentration of 60% by weight or more and a solvent phase A are supplied to the mixing section A of a static extraction device A that includes a mixing section A and a separation section A, and a mixed solution A is obtained. , the mixed liquid A
A method for producing acrylic acid comprising an extraction step of separating into an aqueous phase A and a solvent phase containing crude acrylic acid by the separation part A, and continuously recovering the solvent phase containing the crude acrylic acid,
The solvent phase A supplies the aqueous phase A and the extract to the mixing section B of a static extraction device B including a mixing section B and a separation section B to form a mixed solution B, and the mixed solution B is It is obtained by separating aqueous phase B by separation part B,
The extract is obtained by supplying the aqueous phase B and a liquid containing a solvent to a dynamic extraction tower, and extracting with the dynamic extraction tower,
The liquid containing the solvent includes a liquid obtained by separating crude acrylic acid from the solvent phase containing the crude acrylic acid,
The acrylic acid concentration in the extract is 15% by weight or more and 45% by weight or less,
The amount of solvent supplied in the extract to the mixture B of the static extraction device B is 2.5 times the amount of acrylic acid supplied in the acrylic acid aqueous solution to the mixing section A of the static extraction device A. less than twice the weight,
and a method for producing acrylic acid, wherein the solvent is a nonpolar solvent.
[ 2 ] The method for producing acrylic acid according to [ 1 ], wherein the water content of the extract is 10% by weight or less.
[ 3 ] The method for producing acrylic acid according to [1] or [ 2 ], wherein the mixing section of the static extraction device is a static mixer.

According to the present invention, it is possible to perform stable and economical extraction of acrylic acid from an aqueous acrylic acid solution using a small amount of solvent without causing flooding.

It is a schematic diagram showing the extraction process of the acrylic acid aqueous solution of this invention. It is another schematic diagram showing the extraction process of the acrylic acid aqueous solution of the present invention. FIG. 3 is a schematic diagram showing the configuration of the dynamic extraction tower in FIGS. 1 and 2. FIG. FIG. 3 is a schematic diagram showing the static extraction device, separation device, and incidental equipment in FIGS. 1 and 2. FIG. It is a liquid-liquid equilibrium diagram of water-acrylic acid-toluene. It is a correlation diagram of acrylic acid concentration, density, and viscosity. FIG. 1 is a correlation diagram of acrylic acid concentration, interfacial tension, and separation time of two liquid phases. It is a correlation diagram between acrylic acid concentration and partition coefficient. FIG. 2 is a correlation diagram between the amplitude number of a dynamic extraction column and the bed height per theoretical plate (HETP). FIG. 1 is a correlation diagram of the extraction recovery rate and the extraction concentration with respect to the acrylic acid concentration and the amount of extraction solvent. FIG. 3 is a diagram for calculating the extraction recovery rate of acrylic acid from an acrylic acid aqueous solution using acrylic acid-containing toluene. FIG. 12 is a diagram showing various physical property values at each stage when the extraction in FIG. 11 was performed using 12 theoretical stages.

Hereinafter, the present invention will be explained in detail with reference to the drawings, but the present invention is not limited to the following explanation at all, and can be implemented with various modifications within the scope of the gist of the present invention.

FIG. 1 is a schematic diagram showing the extraction process of an aqueous acrylic acid solution according to the present invention.
The acrylic acid-containing gas produced by the above process becomes an aqueous acrylic acid solution in a collection tower (not shown) and is supplied to a static mixer A, which is a mixing section of a static extraction apparatus including a mixing section and a separation section, via a pipe 11. In addition to the aqueous acrylic acid solution, an extract 21 obtained from the top of a dynamic extraction tower C is supplied to the static mixer A via a pipe 12. The aqueous acrylic acid solution has an acrylic acid concentration of 60% by weight or more, preferably 65% by weight or more, and more preferably 70% by weight or more. When the acrylic acid concentration is less than 60% by weight, the amount of solvent required for extraction and recovery of crude acrylic acid (for example, ≧95%) increases relative to the amount of crude acrylic acid recovered,
There is a possibility that the solvent separation step of separating the crude acrylic acid and the solvent from the solvent phase containing the crude acrylic acid recovered from the decanter D becomes excessively large. The higher the acrylic acid concentration of the aqueous acrylic acid solution, the better. However, taking into consideration the heat quantity and equipment required in the absorption tower, the acrylic acid concentration is preferably 85% by weight or less, and more preferably 80% by weight or less. Since it is easy to mix the high-concentration aqueous acrylic acid solution and the extract, the mixing section is not limited to a high-performance static mixer,
A structure that generates a vortex in the flow path can be used, such as an orifice plate, a piping with a different diameter, a butterfly valve, etc. In terms of efficiency, precision, and versatility, a high-performance static mixer in which packing is regularly arranged in the flow path is preferred, and in terms of reducing equipment costs and avoiding clogging, an orifice-type static mixer that is inserted into the flange connection part of the piping is more preferred.

In the static mixer A, crude acrylic acid is continuously extracted from the acrylic acid aqueous solution to form a mixed liquid, and the mixed liquid is sent to a decanter D (two-liquid separation tank), which is a separation section, via a pipe 13. . In the decanter D, the mixed liquid is separated into an aqueous phase and a solvent phase containing crude acrylic acid. Incidentally, in order to accelerate the separation of the mixed liquid, it is preferable to provide a device such as a coalescer or a centrifugal separator between the static mixer A and the decanter D, for example. By introducing this device, even if fine water droplets of the acrylic acid aqueous solution are generated in the mixed liquid by mixing by the static mixer A, it is possible to promote the coalescence of the water droplets and accelerate liquid-liquid separation. As a countermeasure against clogging of the coalescer, it is preferable to provide a filter for solid matter removal on the upstream side of the coalescer, or to arrange a plurality of coalescers in parallel and use them by switching. Both the oil droplets in the aqueous phase and the water droplets in the solvent phase separated in the decanter D are preferably less than 1% by weight, more preferably less than 0.5% by weight. The separation section includes a vertical or horizontal tank without a partition plate inside, a tank with a vertical partition plate for overflow of the solvent phase, and a vertical partition plate and lower connecting pipe for separating the aqueous phase. From the viewpoint of minimizing the influence of flow rate fluctuations on the next process, an overflow type decanter having one or more partition plates for the solvent phase is preferred.
The separated solvent phase containing crude acrylic acid is recovered via piping 15, and the recovered solvent phase containing crude acrylic acid is separated into crude acrylic acid and a solvent by a solvent separation column (not shown) or the like.
By installing the decanter D at a sufficiently high position, it is also possible to omit the liquid pump from the piping 15 to the next process. The separated crude acrylic acid is supplied to further purification steps such as distillation and crystallization to purify acrylic acid.

The extract liquid is obtained from the top of the dynamic extraction column C by supplying the aqueous phase and a liquid containing a solvent to the dynamic extraction column C, and extracting with the dynamic phase extraction column C. The aqueous phase is separated and discharged by a decanter D, and is supplied to the upper part of the dynamic extraction column C via a pipe 14. A filter can be installed in the feed line to the dynamic extraction column C to remove solids contained in the aqueous phase. By installing the decanter D at a sufficiently high position, it is possible to omit the liquid pump from the piping 14 to the dynamic extraction tower C, but if solid content is removed using a filter or the like, pressurization is necessary. Since this is necessary, it is preferable to send the liquid using a pump. The liquid containing the solvent is separated by a decanter D,
Containing the liquid obtained by separating crude acrylic acid from the solvent phase containing recovered crude acrylic acid, pipe 1
7 and is fed to the lower part of the dynamic extraction column C. In order to increase the extraction rate of crude acrylic acid from the aqueous phase 22 in the dynamic extraction column C, the concentration of acrylic acid in the solvent-containing liquid 23 is preferably 1% by weight or less, more preferably 0.5% by weight or less. , more preferably 0.3% by weight or less. The concentration of acrylic acid in the extract 21 obtained from the top of the dynamic extraction column C is 20% by weight or more and 45% by weight or less. The lower limit is preferably 25% by weight, more preferably 30% by weight. If the acrylic acid concentration is too low, sufficient acrylic acid may not be recovered in the solvent phase containing crude acrylic acid in the static extraction device (static mixer A and decanter D (two-liquid separation tank)). The upper limit of the acrylic acid concentration is preferably 40% by weight. If the acrylic acid concentration is too high, flooding will easily occur in the upper part of the dynamic extraction column C, and the stirring intensity will need to be reduced to continue operation, which may reduce the extraction efficiency of the dynamic extraction column C. There is. Raffinate water 24 is discharged from the bottom of the dynamic extraction column C via a pipe 16.

The amount of solvent supplied in the extract to the static mixer A is 2.5 times or less by weight, preferably 2.2 times the amount of acrylic acid in the acrylic acid aqueous solution supplied to the static mixer A. It is not more than twice the weight, more preferably not more than 2.0 times the weight. If the amount of solvent supplied is too large, the solvent separation step for separating the crude acrylic acid and the solvent from the solvent phase containing the crude acrylic acid recovered from the decanter D may become excessive.

Note that the solvent used in the production method of the present invention is a nonpolar solvent. Nonpolar solvents include saturated or unsaturated aliphatic hydrocarbons and aromatic hydrocarbons having 6 to 8 carbon atoms, and from the viewpoint of ease of distillation separation from acrylic acid, hexane, cyclohexane, hexene, heptene, Toluene and xylene are preferred, hexene and toluene are more preferred, and toluene is even more preferred.

Further, the content of water in the extract 21 is preferably 10% by weight or less, more preferably 5% by weight or less, still more preferably 3% by weight or less. Further, the lower limit of the water content is preferably 0.3% by weight, more preferably 0.5% by weight, and even more preferably 1.0% by weight. Note that the water content here refers to the water contained in the water dispersed as water droplets without including water dissolved in the extract. If the water content is too high, flooding in the upper part of the dynamic extraction column C may occur excessively. If the water content is too low, the stirring power of the dynamic extraction column C will be small, and the equipment performance of the extraction column will not be fully utilized. Extraction recovery rate may be poor. The water content in the extract 21 can be adjusted by adjusting the stirring power of the dynamic extraction tower.

FIG. 2 is another schematic diagram showing the extraction process of the acrylic acid aqueous solution of the present invention. The acrylic acid-containing gas produced in the reactor (not shown) becomes an acrylic acid aqueous solution in the collection tower (not shown), and passes through piping 11 to the mixing section of the static extraction device, which includes a mixing section and a separation section. The static mixer A1 is supplied to the static mixer A1. In addition to the acrylic acid aqueous solution, a solvent phase separated from the aqueous phase B in a decanter D2 is supplied to the static mixer A1 via a pipe 20. The acrylic acid concentration of the acrylic acid aqueous solution is 60% by weight or more, preferably 65% by weight or more, and more preferably 70% by weight or more. When the acrylic acid concentration is less than 60% by weight, the amount of solvent required for extracting and recovering crude acrylic acid (for example, ≧95%) increases relative to the amount of crude acrylic acid recovered, and the crude acrylic acid recovered from the decanter D1 increases. The solvent separation step for separating the crude acrylic acid and the solvent from the acid-containing solvent phase may become excessive. The higher the acrylic acid concentration of the acrylic acid aqueous solution is, the more preferable it is, but when considering the amount of heat and equipment required for the collection tower, the acrylic acid concentration is preferably 85% by weight or less, more preferably 80% by weight or less. . still,
Examples of the mixing part of the static extraction device include a static mixer, an orifice plate, piping of different diameters, a butterfly valve, etc., but a static mixer is preferable from the viewpoints of efficiency, precision, and versatility.

In the static mixer A1, crude acrylic acid is continuously extracted from the acrylic acid aqueous solution to form a mixed liquid A, and the mixed liquid A is sent to a decanter D1 (two-liquid separation tank), which is a separation section, through a pipe 13. be done. In the decanter D1, the mixed liquid A is separated into an aqueous phase A and a solvent phase containing crude acrylic acid. In order to accelerate the separation of the liquid mixture A, it is preferable to provide a device such as a coalescer or a centrifugal separator between the static mixer A1 and the decanter D1.
By introducing this equipment, even if fine water droplets of the acrylic acid aqueous solution are generated in the mixed liquid A due to mixing by the static mixer A1, it is possible to promote the coalescence of the water droplets and accelerate liquid-liquid separation. . As a countermeasure against clogging of the coalescer, it is preferable to provide a filter for solid matter removal on the upstream side of the coalescer, or to arrange a plurality of coalescers in parallel and use them by switching. Both the oil droplets in the aqueous phase A separated in the decanter D1 and the water droplets in the solvent phase containing crude acrylic acid are 1
Preferably it is less than 0.5% by weight, more preferably less than 0.5% by weight. In addition, as a separation part,
A vertical or horizontal tank without a partition plate inside, a tank with a vertical partition plate for overflow of the solvent phase containing crude acrylic acid, and a vertical partition plate and lower connecting pipe to separate the aqueous phase A. However, an overflow type decanter having one or more partition plates for the solvent phase is preferred from the viewpoint of minimizing the influence of flow rate fluctuations on the next process.

The separated solvent phase containing crude acrylic acid is recovered via piping 15, and the recovered solvent phase containing crude acrylic acid is separated into crude acrylic acid and a solvent by a solvent separation column (not shown) or the like.
The separated crude acrylic acid is supplied to further purification steps such as distillation and crystallization to purify acrylic acid.

The solvent phase is obtained by supplying the aqueous phase A and the extract separated by the decanter D1 to a static mixer A2 to obtain a mixed solution B, and supplying the mixed solution B to a decanter D2.
It was obtained by separating it from the aqueous phase B.

The extraction liquid is supplied to a dynamic extraction column C1 by supplying the aqueous phase B and a liquid containing a solvent to the dynamic extraction column C1.
and is supplied to a static mixer A2 via a pipe 12.
The aqueous phase B is separated and discharged by the decanter D2, and is supplied to the upper part of the dynamic extraction column C1 via a pipe 19. In order to remove solids contained in the aqueous phase B, a filter can be provided in the supply line to the dynamic extraction column C1. The solvent-containing liquid includes a liquid obtained by separating the crude acrylic acid from the solvent phase containing the crude acrylic acid separated and recovered by the decanter D1, and is supplied to the lower part of the dynamic extraction column C1 via a pipe 17. In order to increase the extraction rate of the crude acrylic acid from the aqueous phase B in the dynamic extraction column C1, the concentration of acrylic acid in the solvent-containing liquid is preferably 1% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.3% by weight or less.
% by weight or less.

The concentration of acrylic acid in the extract 21 is 15% by weight or more and 45% by weight or less. The lower limit is preferably 20% by weight, more preferably 25% by weight. If the acrylic acid concentration is too low, two static extractors in series (static mixers A1, A2 and decanters D1, D2)
In this case, there is a possibility that sufficient acrylic acid cannot be recovered in the solvent phase containing crude acrylic acid. The upper limit of the acrylic acid concentration is preferably 40% by weight. If the acrylic acid concentration is too high, flooding will easily occur in the upper part of the dynamic extraction column C1, and the stirring intensity will need to be reduced to continue operation, which may reduce the extraction efficiency of the dynamic extraction column C. There is.
The amount of solvent supplied in the extract to the static mixer A2 is
The amount of acrylic acid supplied in the aqueous acrylic acid solution is 2.5 times or less, preferably 2.2 times or less, and more preferably 2.0 times or less by weight. If the amount of solvent supplied is too large, the solvent separation step for separating the crude acrylic acid and the solvent from the solvent phase containing the crude acrylic acid recovered from the decanter D1 may become excessive.

The solvent used in the production method of the present invention is a non-polar solvent. Examples of the non-polar solvent include saturated or unsaturated aliphatic hydrocarbons and aromatic hydrocarbons having 6 to 8 carbon atoms. From the viewpoint of ease of separation by distillation from acrylic acid, hexane, cyclohexane, hexene, heptene, toluene, and xylene are preferred, hexene and toluene are more preferred, and toluene is even more preferred.
Furthermore, the content of water in the extract is preferably 10% by weight or less, more preferably 5% by weight or less.
The lower limit of the water content is 0.3% by weight or less, and more preferably 3% by weight or less.
It is preferable that the content of water is 0.5% by weight, more preferably 1.0% by weight. The water content here means the water contained in the extract dispersed as water droplets, not including the water dissolved in the extract. If the water content is too high,
There is a possibility that flooding occurs excessively at the top of the dynamic extraction tower. If the water content is too low, the stirring power of the dynamic extraction tower is small, and the performance of the extraction tower is not fully exerted, that is, the extraction recovery rate of acrylic acid may be inferior to that in the case where the stirring power is increased to increase the number of theoretical plates. The water content in the extract can be adjusted by adjusting the stirring power of the dynamic extraction tower.

FIG. 3 is a schematic diagram showing the configuration of the dynamic extraction column in FIGS. 1 and 2. The figure on the left shows a structure in which many perforated plates connected by rods are vibrated up and down.
-Glitsch). Since the movement of both the continuous phase and the dispersed phase is limited to the vertical direction, there is no difference in stirring strength in the radial direction, and this is one of the extraction towers that processes the largest amount of liquid per cross-sectional area of the tower. Due to the unique specification of moving the perforated plate up and down, there are many restrictions associated with increasing the size, and efficiency also decreases. The figure on the right shows a multi-stage mixer-settler consisting of a large number of stirring blades attached to a central rotating shaft and baffles placed above and below the blades.
This is an extraction column for high theory plates such as ibel(R) and Koch-Glitsch. When increasing the size, there are fewer problems with mechanical strength and accuracy as with KARR (R), but as the column diameter increases, the horizontal movement distance of the fluid increases, resulting in a decrease in efficiency. In other words, in these dynamic extraction towers, a reduction in the amount of processed fluid is expected, in addition to a reduction in equipment costs due to a reduction in the diameter of the extraction tower, as well as higher separation.

In the dynamic extraction column C, the droplets of the dispersed phase are struck by perforated plates and stirring blades to become finer, increasing their surface area and promoting mass transfer between the two liquid phases. If too much, the movement of the dispersed phase becomes slow and flooding occurs. As the concentration of acrylic acid in the liquid increases, the interfacial tension between the two liquid phases decreases, and the droplets of the dispersed phase tend to become finer. Therefore, flooding occurs more easily in the upper part of the dynamic extraction column C. In the upper part of the dynamic extraction column C, by widening the installation interval of perforated plates and stirring blades, increasing the porosity of the perforated plate, or reducing the area of the stirring blades, the upper part of the dynamic extraction tower C can be improved. If the interfacial tension at is about 1/10 or more than the interfacial tension at the lower part of the dynamic extraction column C, it is possible that the likelihood of flooding occurring at the upper part of the dynamic extraction column C can be alleviated. However, when the amount of the liquid 23 containing the solvent used for extraction is less than 2.5 times the amount of acrylic acid, these alone become insufficient, and it is necessary to significantly reduce the amplitude speed of the perforated plate and the rotation speed of the stirring blade. Efforts to alleviate flooding may cause a decline in the performance of the dynamic extraction column C, resulting in an increase in the size of the required equipment even though the amount of extraction solvent has been reduced. Furthermore, in a region where the interfacial tension is 0.001 N/m or less, white turbidity occurs due to fine droplets, and once this white turbidity occurs, it takes several tens of minutes to several hours to eliminate it, so dynamic extraction tower C It becomes necessary to provide a liquid holding part, which is an excessively large amount of incidental equipment, on the upper part of the tank.

Unlike the conventional problem-solving method of avoiding conditions that cause flooding, the present invention makes maximum use of the capacity of the current dynamic extraction column C, and the Acrylic acid is extracted from the aqueous phase 22 with a liquid 23 containing a solvent supplied to the lower part, and is discharged from the top of the dynamic extraction column C as an extract 21. % or more of an acrylic acid aqueous solution using a mixing device and then separated into an aqueous phase and a solvent phase, it becomes possible to extract acrylic acid stably and economically using a small amount of solvent. In other words, by extracting and separating acrylic acid from the portion where the acrylic acid concentration increases independently of the dynamic extraction column C, the acrylic acid concentration in the top liquid of the dynamic extraction column C is reduced, and the dynamic This reduces the ratio of interfacial tension between the upper and lower parts of the extraction column, and prevents the water droplets flowing out from the top of the dynamic extraction column and the impurities contained therein from going to the downstream process.

If the operation is performed with the upper part of the dynamic extraction tower C flooded, the water contained in the aqueous phase 22 supplied to the upper part of the dynamic extraction tower C cannot reach the bottom of the tower and overflows into the tower, causing the dynamic extraction to fail. There is a possibility that Tower C will be shut down. Stopping the operation of the dynamic extraction column C affects the upstream oxidation reaction process and the downstream separation and purification process, resulting in large economic losses, so it is essential to avoid it. Flooding is likely to occur in the upper part of dynamic extraction tower C, where the concentration of acrylic acid is high, and as flooding progresses, the proportion of the acrylic acid aqueous solution dispersed in the continuous phase increases. The liquid density at the top increases. Therefore, by providing a plurality of nozzles on the side surface of the dynamic extraction column C and continuously measuring the differential pressure therebetween, it is possible to indirectly monitor the status of the dynamic extraction column C. Since the density change is small in the entire dynamic extraction column C, the measurement range of differential pressure is limited to the dynamic extraction column C.
It is preferable to limit the extraction to the upper part of the dynamic extraction column C rather than the whole, and the length in the vertical direction is preferably 5 m or less. Moreover, it is preferable that it is 0.5 m or more. If it is shorter than 0.5 m, it may not be possible to determine whether it is a differential pressure or a fluctuation in the measured value when the fluctuation of the pressure measurement value is large, and there is also a possibility that there is sufficient space for ancillary equipment such as flanges and nozzles. It may not be possible to secure sufficient space.

If an increase in the differential pressure over time is confirmed, that is, if it is considered that flooding is progressing, it is necessary to reduce the load on the dynamic extraction column C. For example, one countermeasure is to reduce the flow rate of the aqueous phase 22 and solvent-containing liquid 23 to be supplied, but in order to suppress the impact on upstream and downstream processes, it is also possible to In order to suppress changes in the concentration of acrylic acid in the extract 21, a method of lowering the amplitude and rotation speed of the dynamic extraction column C is simple and reliable, and is therefore preferable.
On the other hand, if the differential pressure is not confirmed to increase over time, it may be due to a reduction in the load on the solvent separation process by reducing the extraction solvent, an increase in the amplitude of the perforated plate of the dynamic extraction column C, or an increase in the rotation speed of the stirring blade. It is possible to try to improve the extraction recovery rate as appropriate.

[Three liquid equilibrium]
Using a glass container with a jacket-type double structure and a nozzle that allows sampling of the internal liquid from the upper and lower sides of the side, toluene, water, and acrylic acid are mixed in a weight ratio of approximately 7:
3: Add to the container in the range of 0.01 to 15, stir the internal liquid with a magnetic stirrer, and
．． The mixture was allowed to stand for 5 to 2 hours. Next, the aqueous phase and toluene phase were sampled from a nozzle on the side of the glass container, and analyzed using gas chromatography and a Karl Fischer moisture meter. After sampling, the two liquid phases in the container were separated, and the density and viscosity were measured using a float densitometer and a vibration viscometer, respectively. FIG. 5 is based on a function of the concentration correlation of the three components so as to reproduce the analysis results in the entire concentration range. NRTL and U commonly used to calculate liquid-liquid equilibrium composition.
Activity calculation models such as NIUQAC have poor reproducibility, especially in the dilute concentration range of acrylic acid, and are therefore not used. FIG. 6 shows a correlation diagram of density and viscosity versus acrylic acid concentration in the toluene phase. FIG. 8 shows the distribution coefficient versus acrylic acid concentration in the toluene phase. It can be confirmed that the distribution coefficient rapidly decreases as the acrylic acid concentration decreases.

[Separation time and interfacial tension]
Add toluene, water, and acrylic acid to a 100 ml sample bottle so that the aqueous phase and toluene phase are approximately 30 ml each, cover with a lid, shake by hand for 1 minute, and let stand to determine the time required for separation of the two liquids. was measured. The separation time was defined as the time required for the interface position to rise to 95% of the interface height (distance from the bottom of the bottle to the interface) before shaking by hand. In systems where the acrylic acid concentration in the toluene phase exceeds 35% by weight, the toluene phase remains cloudy even after the separation time.
Although the mixture was allowed to stand for twice the separation time, the cloudiness of the toluene phase did not disappear. Although they cannot be seen as droplets with the naked eye, it is thought that fine water droplets with a diameter of about 1 to 50 μm, which can scatter visible light, were dispersed.
Toluene, water, and acrylic acid were added to a beaker so that the height of the toluene phase was 6 cm or more, and the interfacial tension was measured by the ring method.
Figure 7 shows the relationship of separation time and interfacial tension to acrylic acid concentration in the toluene phase. In any of the above analyses, the liquid composition was calculated from the relationship between the composition of the charged liquid and the concentrations of the three components. It was confirmed that as the concentration of acrylic acid increases, the time required to separate the two liquids increases significantly, and that the separation time has a high correlation with the interfacial tension of the two liquids.

[Dynamic extraction tower]
A continuous extraction test was conducted using a glass curl column (R) with an inner diameter of 3 cm. Open area rate 50%
Using PTFE perforated plates, the plate spacing is 50 to 100 mm, the layer height is 1.8 to 3 m, and the amplitude is ±25 m.
m, amplitude number 100-500/min, cylinder speed 10-55 m/hr, concentration 35-6
Extraction was performed using toluene containing 0.5% by weight of acrylic acid with respect to a 5% by weight of acrylic acid aqueous solution. The compositions of the extract and raffinate water were analyzed by gas chromatography, and the number of theoretical plates was calculated based on a three-component concentration correlation equation.
Figure 9 summarizes the analysis results when the acrylic acid concentration in the extract is 32 to 35% by weight and the plate spacing is 50 mm. It was confirmed that it does not depend on the amplitude (time) and is inversely proportional to the number of amplitudes (dotted line in FIG. 9). Also, only the plate spacing is 10
The analysis result when changing to 0 mm was an average of 2.2 times in terms of HETP.
Figure 10 summarizes the relationship between the cylinder velocity and the amplitude number at which the flooding limit was observed.
○ indicates that the acrylic acid concentration in the extract is approximately 16% by weight, △ indicates approximately 26% by weight, ◇ indicates 3
3% by weight. Furthermore, by widening the plate spacing to 100 mm, the amplitude number at the flooding limit of 33% by weight acrylic acid and 26% by weight acrylic acid (cylinder speed 50 m/h) increased to about 300/min.

[Calculation]
Figure 11 shows that acrylic acid aqueous solutions with various acrylic acid concentrations were extracted using toluene containing 0.5% by weight of acrylic acid in an extraction column with a sufficiently large number of theoretical plates (15 plates). This is a calculation of the recovery rate when It can be confirmed that unless the concentration of the acrylic acid aqueous solution is sufficiently high, a high extraction recovery rate and a reduction in the amount of extraction solvent cannot be achieved.
Figure 12 shows the amount of acrylic acid in toluene in each stage when extraction was performed using 12 theoretical plates using 1.8 times by weight of toluene containing 0.5% by weight of acrylic acid for a 70% by weight aqueous acrylic acid solution. The maximum values of acid concentration, acrylic acid extraction recovery rate, in-column liquid flow rate, and interfacial tension are each set to 1.
The recovery rate is 99.1%, assuming that the acrylic acid aqueous solution is supplied to the first stage and toluene is supplied to the 12th stage. It can be confirmed that for all items, the first stage is most likely to cause flooding.

11-20 Piping 21 Extract 22 Aqueous phase 23 Liquid containing solvent 24 Raffinate water A, A1, A2 Static mixer B Coalescer C, C1 Extraction tower D, D1, D2 Decanter L-11, L-12 Level gauge P -11~P-17 Pump V-11, V-12 Valve

Claims (3)

An acrylic acid aqueous solution having an acrylic acid concentration of 60% by weight or more and a solvent phase A are supplied to the mixing section A of a static extraction device A including a mixing section A and a separation section A to form a mixed solution A. A method for producing acrylic acid, comprising an extraction step of separating liquid A into an aqueous phase A and a solvent phase containing crude acrylic acid by the separation section A, and continuously recovering the solvent phase containing the crude acrylic acid,
The solvent phase A supplies the aqueous phase A and the extract to the mixing section B of a static extraction device B including a mixing section B and a separation section B to form a mixed solution B, and the mixed solution B is It is obtained by separating aqueous phase B by separation part B,
The extract is obtained by supplying the aqueous phase B and a liquid containing a solvent to a dynamic extraction tower, and extracting with the dynamic extraction tower,
The liquid containing the solvent includes a liquid obtained by separating crude acrylic acid from the solvent phase containing the crude acrylic acid,
The acrylic acid concentration in the extract is 15% by weight or more and 45% by weight or less,
The amount of solvent supplied in the extract to the mixing section B of the static extraction device B is 2. 5 times the weight or less,
and a method for producing acrylic acid, wherein the solvent is a nonpolar solvent. The method for producing acrylic acid according to claim 1, wherein the water content in the extract is 10% by weight or less. The method for producing acrylic acid according to claim 1 or 2 , wherein the mixing section of the static extraction device is a static mixer.

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