JP2004300139A - Device for purifying acrylic acid and method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the productivity in a purification process of an acrylic acid by preventing a polymer from attaching at the inside of a purification device in the purification of the acrylic acids. <P>SOLUTION: This device for distilling and purifying acrylic acids including acrylic acid and its esters is equipped with a distillation column 10 supplied with liquid containing the acrylic acids, taking out steam from the top of the column and taking out liquid from the bottom of the column, a condenser 20 connected with the top side of the distillation column 10, supplied with the steam taken out from the distillation column, condensing the steam, refluxing a part of the condensed liquid to the distillation column 10 and taking out the rest of the condensed liquid, and a reboiler 30 connected with the bottom side of the distillation column 10, supplied with the liquid in the distillation column 10, heating/boiling the supplied liquid and returning it to the distillation column 10. In a plurality of reboilers are installed in parallel to the distillation column 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an apparatus and a method for purifying acrylic acids, and in particular, in order to obtain a high-purity purified product from which impurities have been removed in the process of producing acrylic acid or acrylate ester as a raw material for producing various chemical products. The present invention is directed to a purification apparatus and a method for purifying acrylic acids using such a purification apparatus.

Acrylic acid and acrylic acid esters (hereinafter collectively referred to as acrylic acids) are widely used as raw materials for producing various chemical products.
In the industrial production of acrylic acids, the produced acrylic acids are purified in order to meet the intended use and required quality of the acrylic acids. In the production of acrylic acids, by-products such as maleic acid generated from propylene as a raw material and dimer acid generated in the production process may be contained as impurities, and a purification step for removing these impurities is required. Required.
A distillation technique is applied to the purification of acrylic acids. In the purification by distillation, for example, the acrylic acid is purified by evaporating a liquid containing the acrylic acid, and extracting and condensing a vapor containing a large amount of the acrylic acid and containing few impurities. In some cases, impurities may be obtained on the vapor side and the target substance may be obtained on the liquid side.

Various techniques have been proposed to increase the purification efficiency to produce high-quality acrylic acids and to improve the productivity.
In particular, since acrylic acid is an easily polymerizable substance, there is a problem that a polymer is generated in a purification device and adheres to an inner wall of the device or blocks a pipe. Many techniques for solving this problem have been proposed.
For example, there is a technique in which a plurality of condensers are installed in series with a distillation column to prevent a polymer from being generated and adhered in a device downstream of the condenser (see Patent Document 1). ).
For a reboiler that is connected to the distillation column and heats and re-boils and circulates the liquid in the distillation column, by installing a vapor dispersion device at the connection point to the distillation column, the drift of the vapor in the distillation column is reduced. There is a technique for suppressing the formation and adhesion of a polymer in a distillation column (see Patent Document 2).
JP 2001-131116 A JP-A-2000-254403

When a refiner is increased in size in order to improve the productivity of acrylic acids, the formation and adhesion of a polymer inside the apparatus become severe, and in severe cases, the polymer may block the internal piping of the apparatus. In order to remove the adhered polymer, it is necessary to frequently stop the operation of the apparatus, and the production efficiency is reduced.
In particular, in a reboiler having a structure in which a large number of thin pipes are arranged, the polymer adheres to the inner surface of the thin tube, so that the thin tube is likely to be clogged, and the heat exchange efficiency is greatly reduced even if no clogging occurs. As a result, the performance of the entire distillation apparatus is greatly reduced.
In the conventional techniques described in Patent Documents 1 and 2, the formation and adhesion of a polymer cannot be sufficiently prevented. In particular, in a large-scale refining apparatus, even when the apparatus is operated for a relatively short period of time, the performance is reduced due to the adhesion of the polymer, and it is necessary to stop the operation and perform the operation of removing the polymer.

  An object of the present invention is to solve the above-mentioned problems in the purification of acrylic acids, to prevent the adhesion of a polymer inside the purification device, and to improve the productivity in the purification step of acrylic acids.

The apparatus for purifying acrylic acid according to the present invention is an apparatus for distilling and purifying acrylic acid including acrylic acid and its ester, wherein a liquid containing the acrylic acid is supplied, vapor is taken out from the top of the tower, A distillation column from which a liquid is taken out from the bottom, connected to the top of the distillation column, the vapor taken out from the distillation column is supplied, the vapor is condensed, a part of the condensate is refluxed to the distillation column, A condenser for taking out the remaining condensate, and a reboiler connected to the bottom of the distillation column to supply the liquid in the distillation column, heating the supplied liquid to boil and returning it to the distillation column A plurality of the reboilers are installed in parallel with the distillation column.
The method for purifying acrylic acids according to the present invention is a method for distilling and purifying acrylic acids using the purifying apparatus according to the present invention, wherein the liquid in the distillation column is supplied to the plurality of reboilers. And returning the steam heated and boiled in the reboiler to the distillation column.

In the apparatus and method for purifying acrylic acid according to the present invention, the liquid contained in the distillation column is reboiled by a plurality of reboilers arranged in parallel with the distillation column to thereby form one reboiler. Compared to the case of performing the reboil treatment only with the vessel, it is possible to prevent the adhesion of the polymer inside the apparatus and the accompanying blockage without impairing the reboil processing capacity or the quality performance of the refining work. . By eliminating the drift of liquid or vapor in the distillation column, the internal temperature can be stabilized, and the distillation purification process can be stabilized and the efficiency can be improved.
As a result, it is possible to extend or omit the interval for inspection and cleaning work inside the apparatus, to continuously perform high-quality refining work over a long period of time, and to improve the production efficiency of acrylic acids or It can also contribute significantly to reducing production costs.

Hereinafter, an apparatus and a method for purifying acrylic acids according to the present invention will be described in detail, but the scope of the present invention is not limited to these descriptions, and the scope of the present invention is impaired except for the following examples. Changes can be made as appropriate within a range that does not exist.
(Purification of acrylic acids)
In the present invention, acrylic acid is a concept including acrylic acid and acrylic acid ester. Specifically, examples of the acrylate include methyl ester, ethyl ester, isopropyl ester, n-butyl ester, 2-ethylhexyl ester, 2-hydroxyethyl ester, hydroxypropyl ester, and dialkylaminoethyl ester.

As a basic production technique for these acrylic acids, ordinary production techniques for acrylic acids can be applied. Raw materials, reaction conditions, and the like may be set by combining ordinary acrylic acid production techniques in accordance with the purpose of use and required quality of acrylic acids.
The acrylic acid produced by the reaction contains unreacted raw materials, additives added during the reaction, and impurities such as by-products accompanying the reaction. According to the purpose of use and required quality, in order to remove undesired impurities and obtain high-purity acrylic acid, a purification step using a stripping tower, an azeotropic dehydration tower, a light-boiling substance separation tower, a high-boiling substance separation tower, etc. Done.
What should be removed in the purification process include water, a solvent for collecting the reaction gas, high boiling inert hydrophobic organic liquids (such as diphenyl ether and diphenyl), and maleic acid, dimer acid, acetic acid, formaldehyde, acrolein, and propione, which are impurities. Includes acids, acetone, furfural, benzaldehyde, protoanemonin and the like. Usually, the content of impurities is preferably 0.01 to 10% by weight. The purity of the acrylic acid obtained by the purification step is preferably 99.0 to 99.99% by weight.

A device equipped with a distillation column, a condenser and a reboiler is used as a device for purifying acrylic acids.
(Distillation tower)
A liquid containing acrylic acid is supplied, and functions to take out a vapor or liquid containing the target acrylic acid.
Basically, a device similar to a distillation column used in a normal distillation device can be used.
As a general distillation column, a tray column and a packed column are known. A tray column is preferred from the viewpoint of preventing the formation of a polymer in the distillation column. Of the tray towers, those using a non-weir sheep tray are preferred.

The temperature in the distillation column for purifying acrylic acids is preferably set to 120 ° C. or lower, more preferably 100 ° C. or lower. If the temperature in the tower is too high, a polymer is generated, which causes an increase in pressure loss and blockage of piping. The temperature in the column can be adjusted by heating conditions using a reboiler or a heating device provided in the distillation column. It is desirable that the temperature in the column is as small as possible and stable. Specifically, it is preferable that the fluctuation range of the temperature measured at the same position in the distillation column be within 0 to 10 ° C. In particular, in the case of an azeotropic dehydration tower, the composition change in the tower is drastic, and the temperature fluctuation width at the same position tends to be large.
Although the shape and size of the distillation column vary depending on the internal structure, the treatment method, the amount of acrylic acid to be treated, and the like, the outer shape of the distillation column is generally preferably cylindrical. When the outer shape of the distillation column is cylindrical, the outer diameter of the distillation column can be set to preferably 0.5 to 6 m, more preferably 2 to 6 m. The height of the distillation column is preferably 2 to 40 m. Capacity of the distillation column is preferably set to 0.5~1000m ^3.

The distillation column is provided with a pipe for introducing acrylic acid, which is a distillation raw material, and a pipe for circulating a liquid with a reboiler or a condenser. A portion between the distillation tower and the reboiler is connected by a liquid take-out pipe for taking out the liquid from the distillation tower and supplying the liquid to the reboiler, and a vapor return pipe returning the vapor from the reboiler to the distillation tower. . A delivery pipe for delivering the liquid to the outside is connected to the liquid extraction pipe. The distillation column and the condenser are connected by a vapor extraction pipe for extracting vapor from the distillation tower and supplying it to the condenser, and a liquid return pipe for returning the condensed liquid condensed in the condenser to the distillation tower. A purified product take-out tube for taking out a purified product is connected to the liquid return tube.
Each pipe is generally connected in a direction perpendicular to the outer peripheral surface of the distillation column, but may be connected in a direction inclined to the outer peripheral surface of the distillation column. For example, in addition to connecting to the outer peripheral side surface of the distillation column toward the center axis of the distillation column, the connection may be performed in a direction slightly deviated from the central axis. In addition to the horizontal direction or the vertical direction, the connection can also be performed in an oblique vertical direction.

By adjusting the connection position and direction of the pipe to the distillation column, the flow of liquid and vapor flowing into and out of the pipe and the distillation column can be changed, and the flow in the distillation column can be equalized and drift can be prevented. it can.
A pump, valves such as a pressure regulating valve, a flow regulating valve, a check valve, a safety valve, a drain valve, a flow meter, a thermometer, and the like can be installed in each pipe as necessary.
A measuring instrument and a sensor for detecting the temperature and pressure in the distillation column are also installed in the distillation column. A pressurizing device or a depressurizing device for adjusting the pressure in the distillation column can be incorporated.
The flow rate of unpurified acrylic acid supplied to the distillation column can be preferably set to 0.5 to 100 m ³ / h.

A polymerization inhibitor can be supplied to the distillation column for the purpose of preventing polymerization of acrylic acids. As the polymerization inhibitor, hydroquinone monomethyl ether (methquinone), manganese acetate, copper dibutyldithiocarbamate, an N-oxyl compound, hydroquinone, phenothiazine and other known polymerization inhibitors can be used. These polymerization inhibitors may be mixed with acrylic acid, an azeotropic solvent, water, or the like, and supplied from the top of the distillation column or from inside the column. Blowing a molecular oxygen-containing gas such as air or oxygen from the bottom of the tower or the lower part of the reboiler is also effective for preventing polymerization.
(Reboiler)
The liquid connected to the bottom of the distillation column and supplied to the distillation column is supplied, and the supplied liquid is heated, boiled and returned to the distillation column.

Basically, a device similar to a reboiler used in a normal distillation device can be used.
Known types of reboilers include a multi-tube type, a spiral type, and a plate type. Either form can be used. In order to prevent the formation and adhesion of the polymer inside the reboiler, a multi-tube type is preferable. Among the multi-tube type, those having a vertical type in-tube evaporation structure are preferable.
The reboiler includes a thin tube through which the supply liquid flows, and a body portion that houses the thin tube and through which the heat medium flows, and performs heat exchange between the supply liquid and the heat medium through the thin tube wall. .
The size and capacity of the reboiler are set in accordance with the capacity required for the acrylic acid purification treatment. In the present invention, since a plurality of reboilers are used, the overall capacity of the plurality of reboilers may be set so as to satisfy the processing performance required for the entire purification apparatus.

The inner diameter of the narrow tube of the reboiler can be preferably set to 10 to 50 mm. More preferably, it is 15 to 35 mm. The capillary length is preferably 1 to 7 m, more preferably 2 to 6 m. The number of thin tubes incorporated in the reboiler is preferably 10 to 3000. The diameter of the body can be preferably set to 0.2 to 4 m. It is more preferably 2 m or less. If the diameter of the body designed based on the reboil processing capacity becomes large, the reboiler is divided into multiple units to prevent the body diameter of each reboiler from becoming too large. Prevention of polymerization in the boiler can be favorably achieved.
As the heat medium introduced into the reboiler, water vapor, a phenyl ether-based heat medium as an organic solvent, or the like is used. The temperature of the heating medium is preferably from 80 to 250 ° C. The pressure of the steam can be set to preferably 0.6 MPaG or less, more preferably 0.4 MPaG or less.

The reboiler is provided with a supply port to which the processing liquid is supplied and a return port for sending out the reboiled vapor, the supply port is connected to a liquid extraction pipe of the distillation column, and the return port is connected to the distillation column. Connected to steam return pipe.
The flow rate of the processing liquid is preferably set to 1 to 3000 m ³ / h. Circulation of the processing liquid or steam between the reboiler and the distillation column can be performed both by forced circulation by a pump or the like and by natural circulation by the weight of the processing liquid or the rising power of the steam. Usually, it is preferable to use natural circulation that can reduce the operating energy.
A plurality of reboilers are installed in parallel for one distillation column. Parallel means that the same treatment liquid is divided and sent to a plurality of reboilers, and reboiled in each of the reboilers. This is a technical concept that is opposed to the serial arrangement of a plurality of reboilers in which the same processing liquid is processed in one reboiler, and the processed liquid is sent to another reboiler for further processing.

Although multiple reboilers may have different methods, dimensions, shapes, processing capacities, etc., it is usually effective to combine reboilers with the same specifications, because efficient processing is possible. Manufacturing and maintenance are easy and practical. The same specification means devices having the same basic shape and dimensions. Devices having the same basic specification and symmetrical structure are also included in the substantially same specification.
The reboiler is disposed on the bottom side of the distillation column in order to treat the liquid collected on the bottom side in the distillation column. Equally or symmetrically arranging multiple reboilers around the distillation column enables the efficient use of multiple reboilers and maintenance of the reboilers. Easy. Specifically, since the distillation column extends in the vertical direction, a plurality of reboilers are arranged at positions that are point-symmetric with respect to the center of the distillation column in a horizontal direction orthogonal to the center axis of the distillation column. it can. In the case of two reboilers, each reboiler can be arranged at an equidistant position on the extension of the diameter of the distillation column.

It is also preferable that the arrangement of the liquid extraction pipe and the vapor return pipe connecting the plurality of reboilers and the distillation column be equal or symmetric about the distillation column.
Specifically, the steam return pipes are separately provided for each of the plurality of reboilers, and the connection position of each steam return pipe to the distillation column is preferably at a height difference of 0 to 1 m, and the distillation is performed in the horizontal direction. The included angle can be set preferably at 20 to 180 ° with respect to the center of the tower. It is more preferably at least 60 °, further preferably at least 100 °. The included angle means an angle between two adjacent vapor return pipes that is sandwiched by a virtual line extending from the connection position to the center of the distillation column. The wider the included angle, the more evenly the reboiled steam can be fed into the distillation column from a plurality of directions, and the more uneven flow of the processing liquid or vapor can be prevented in the distillation column. When the number of reboilers is two, the maximum possible included angle is preferably 180 °. As the number of reboilers installed increases, the maximum included angle decreases. The smaller the difference in the height of the connection position is, the more effective it is to prevent the treatment liquid or vapor from drifting inside the distillation column.

If the liquid take-out pipe for supplying the processing liquid from the distillation column to the reboiler is attached to the distillation column, if the processing liquid can be taken out from the distillation tower uniformly, the processing liquid stays in the distillation tower. And uneven temperature can be prevented. Specifically, as in the case of the steam return pipe, it is effective to reduce the difference in height position, widen the included angle, and install the pipe at a uniform or symmetrical position on the outer periphery of the distillation column.
The liquid discharge pipe can be set to have a branched structure in which one end is connected to the center of the bottom of the distillation column, and the other end is branched in a plurality of directions and connected to each reboiler. In addition, a plurality of reboilers can be connected to the bottom of the distillation column by separate liquid extraction tubes. In any case, it is desirable that the length, bend, connection height position, and the like of each pipe be the same, so that there is no difference in liquid passage pressure loss from the tower bottom to each reboiler. With such a structure, the removal of the processing liquid from the distillation column can be prevented from being biased to a specific reboiler.

As for the vapor return pipe, similarly to the liquid extraction pipe, it is desirable to set the pipe installation conditions so that the gas passage pressure loss from each reboiler to the distillation column is equal. From the viewpoint of preventing polymerization in the piping, it is desirable to make the piping as short as possible. It is preferred to connect directly from the reboiler to the distillation column with the shortest distance. By providing the steam return pipe separately for each reboiler, gas dispersion in the distillation column can be improved.
〔Condenser〕
It is connected to the top of the distillation column, is supplied with vapor taken out of the distillation column, condenses the supplied vapor, returns a part of the condensed liquid to the distillation column, and has a function of taking out the remaining liquid.

Basically, a device similar to a condenser used in an ordinary distillation device can be used. Since both the reboiler and the condenser have a common point of performing a heat exchange function, the same conditions as those of the reboiler can be adopted for the type, structure, dimensions, and the like of the condenser.
As the condenser, a multi-tube type, in particular, a vertical type condensing structure in a pipe is preferably used.
For one distillation column, only one condenser may be provided, or a plurality of condensers may be provided as in the reboiler described above. Also in this case, it is desirable to arrange the distillation column in parallel, and the same arrangement conditions as those of the above-described reboiler can be adopted.
The heat medium of the condenser is a low-temperature heat medium or a cooling medium for cooling the steam sent from the distillation column. As the heat medium, the same material as that of a normal condenser can be used. Specifically, water and an aqueous solution of ethylene glycol are preferably exemplified. As the heat medium, a heat medium material having a low melting point and a low viscosity is preferable. The ethylene glycol aqueous solution preferably has an ethylene glycol concentration of 10 to 50% by weight. The temperature of the heating medium is preferably set to 0 to 50C.

The size and capacity of the condenser are set in accordance with the capacity required for the purification treatment of acrylic acids. When a plurality of condensers are used, the total capacity of the plurality of condensers may be set so as to satisfy the processing performance required for the entire purification apparatus.
When a plurality of condensers are used, the specifications of the thin tube, the body and the like can be set in the same range as the reboiler. In the case of one condenser, the capacity becomes larger. In particular, it is preferable that the diameter of the trunk is set to be 3 m or less. If the diameter of the body is too large, it is better to use a plurality of condensers.
The condenser is connected to a vapor extraction pipe through which steam is sent from the distillation tower, and a liquid return pipe that sends back the condensed liquid to the distillation tower. When using a plurality of condensers, each condenser and the distillation column may be connected by a separate vapor extraction pipe or a liquid return pipe, or a plurality of vapor extraction pipes connected to the plurality of condensers. Alternatively, the liquid return pipes may be merged on the way and connected to the distillation column.

When the connection position of the vapor extraction tube and the liquid return tube to the distillation column is divided into a plurality, it is preferable to reduce the difference in height position or set a wide included angle as in the case of the reboiler. .
The flow rate of steam supplied from the distillation column to the condenser can be preferably set to 1 to 100 ton / h. As the circulation of the vapor or the condensed liquid between the condenser and the distillation column, either forced circulation or natural circulation can be adopted.
A part of the condensate sent out from the condenser is refluxed to the distillation column, and the rest can be taken out as purified acrylic acid. It can also be sent to a subsequent acrylic acid processing unit.

(Purification method)
Except for using the refining apparatus of the present invention, basically, a technique common to a method for distilling and refining ordinary acrylic acids can be applied.
Since a plurality of reboilers are provided, when the liquid to be reboiled is supplied from the distillation column to the reboiler, the reboiler is divided and supplied to the plurality of reboilers. At this time, it is preferable to equally supply to a plurality of reboilers. As a result, the formation and adhesion of the polymer in the distillation column and each reboiler can be prevented, and efficient reboil treatment can be performed. In particular, it is possible to prevent the steam returned from the return pipe of the reboiler to the distillation column from causing drift in the distillation column, and the distillation treatment in the distillation column is performed favorably. The processing capacity of multiple reboilers is evenly exhibited, the overall processing capacity is increased, and efficient reboil processing can be performed.

If a plurality of reboilers have the same specifications and are arranged evenly or symmetrically in parallel with respect to the distillation column, it is easy to evenly supply the processing liquid.
[Structure of purification device]
The purifying apparatus shown in FIGS. 1 and 2 is provided with two reboilers and two condensers in parallel for one distillation column.
As shown in FIG. 1, the distillation column 10 has a column structure having a vertically long cylindrical tank. In the middle of the distillation column 10 in the height direction, a treatment liquid introduction pipe 12 is connected. The upper part of the distillation column 10 is connected to a vapor extraction pipe 22 for taking out the vapor generated in the distillation column 10. At the center of the bottom of the distillation column 10, a bottom liquid take-out pipe 32 for taking out the processing liquid is connected.

The bottom liquid outlet pipe 32 is branched in three directions. One of them is a delivery pipe 16 for sending the liquid to the outside. The remaining two directions extend symmetrically with respect to the distillation column 10 and are each connected to another reboiler 30.
<Reboiler>
The reboiler 30 has a function as a heat exchanger for heating and boiling the liquid taken out of the distillation column 10. As the reboiler 30, a multi-tube vertical in-tube evaporation structure having a substantially cylindrical shape as a whole is used. The liquid is supplied from the lower end side of the reboiler 30, and the boiling liquid, that is, steam is sent out from the upper end side.

One end of a bottom liquid outlet pipe 32 of the distillation column 10 is connected to a lower end of the reboiler 30. Another end of the bottom liquid outlet pipe 32 is connected to a position where the central axis C of the distillation column 10 penetrates the bottom, extends downward from the connection position of the distillation column 10, and branches right and left. The left and right reboilers 30 are connected. The delivery pipe 16 is connected to a branch position of the tower bottom liquid discharge pipe 32.
A steam return pipe 34 is connected to the upper end of the reboiler 30, and the other end of the steam return pipe 34 is connected to the outer peripheral side surface of the distillation column 10. The reboiler 30 is provided with heating medium tubes 36, 36 for circulating a heating medium.
In the left and right reboilers 30, reboilers 30, 30 having exactly the same specifications are arranged symmetrically. That is, they are arranged in parallel at the same height, separated from the distillation column 10 by the same distance. In the planar shape shown in FIG. 2, a pair of left and right reboilers 30 are arranged symmetrically in the diameter direction with respect to the center axis C of the distillation column 10. A vapor return pipe 34 connected to the upper end of the reboiler 30 extends in the radial direction of the distillation column 10 toward the central axis C, and is connected to a symmetrical position on the outer peripheral surface of the distillation column 10. The position at which the pair of reboilers 30 or the vapor return pipes 34 are attached to the distillation tower 10 is at an included angle θ = 180 ° with respect to the central axis C.

<Condenser>
Two condensers 20, 20 are arranged in parallel on the side of the top of the distillation column 10.
Similarly to the reboiler 30, the condenser 20 has a multi-tube vertical condensing structure in a substantially cylindrical shape as a whole. Steam is supplied from the upper end side of the condenser 20, and the condensate is sent out from the lower end side. The upper end of each condenser 20 is connected to a vapor extraction pipe 22 connected to the distillation column 10. The vapor extraction pipe 22 is branched into two at the connection side with the condenser 20, but is joined on the way and connected to the outer peripheral side surface of the distillation column 10. A condensate return pipe 24 is connected to the lower end of the condenser 20, and the liquid return pipe 24 joins and is connected to the outer peripheral side surface of the distillation column 10. The liquid return pipe 24 is separated from the connection path to the distillation column 10 downstream of the junction position, and is connected to the condensed liquid extraction pipe 14 for taking out the purified liquid. The condenser 20 is also provided with heating medium tubes 26, 26 through which a cooling medium circulates.

As shown in FIG. 2, the planar arrangement of the condensers 20 is such that the condensers 20 are arranged at positions laterally symmetrical with respect to a diameter line passing through the central axis C of the distillation column 10 on the side of the distillation column 10. ing. The steam extraction pipes 22 are similarly arranged line-symmetrically. After the left and right steam extraction pipes 22 have joined, they are connected to the distillation column 10 along the axis of symmetry. Although not shown, the liquid return pipe 24 of the condensed liquid may have the same arrangement structure as the vapor extraction pipe 22.
(Purification step)
An unpurified liquid of acrylic acid produced in another step or another apparatus is supplied to the distillation column 10 from the introduction pipe 12.

The unpurified liquid accumulated in the distillation column 10 is refluxed between the bottom liquid outlet pipe 32, the pair of reboilers 30, and the vapor return pipe 34. In the reboiler 30, the heating medium is supplied to the heating medium pipe 36, whereby the refluxing liquid is heated and boiled and sent back to the distillation column 10.
In the distillation column 10, the vapor of the unpurified liquid rises. The acrylic acid contained in the unpurified liquid rises to the upper part of the distillation column 10 due to the difference in the properties of the components contained in the unpurified liquid, but the impurities can only rise halfway and fall. The vapor that has risen to the upper portion of the distillation column 10 has a high purity of acrylic acid and a low content of impurities.
In the upper part of the distillation column 10, the steam sent out to the steam extraction pipe 22 is condensed in the condenser 20 and sent out to the liquid return pipe 24. The condensate sent to the liquid return pipe 24 is acrylic acid purified to high purity, and a part of the condensate is taken out from the condensate discharge pipe 14 to be a product.

The remaining condensate is returned to the distillation column 10, moves to the bottom of the distillation column 10, and returns to the processing liquid collected at the bottom.
By continuously performing the reboil treatment of the treatment liquid in the distillation column 10 in the reboiler 30 and the recovery of the purified acrylic acid in the condenser 20, the unpurified acrylic acid supplied from the introduction pipe 12 is removed. And can be continuously purified and recovered.
In such a purification treatment, acrylic acid may be polymerized in the distillation column 10, the reboiler 30, the condenser 20, and the pipes 22, 24, 32, and 34 connecting them. The polymerization of acrylic acids is likely to occur at a location where a liquid containing acrylic acids or a liquid in which vapor is condensed stays. If a flow that is deviated from the flow of the liquid or vapor is generated, the polymer easily adheres to the inner wall of the apparatus in a portion where the flow is stagnated. For example, in the reboiler 30 or the condenser 20 in which a large number of small tubes are arranged, if the flow is blocked in some of the small tubes, the polymer adheres to the inner wall of the small tubes and becomes difficult to flow, or the small tubes are blocked. Things also happen. If the flow of the liquid or vapor is deviated inside the distillation column 10, the polymer adheres to the inner wall of the distillation column 10 or an installation member inside the column at a place where the flow is likely to be stagnated, and the distillation operation is hindered.

  However, in the above embodiment, the liquid in the distillation column 10 is equally supplied to the two reboilers 30 arranged in parallel in a symmetrical structure with respect to the distillation column 10 to perform the reboil treatment. I have. Compared to using one large-capacity, large-sized reboiler 30 having the same reboiling ability, formation and adhesion of a polymer inside the reboiler 30 are less likely to occur. This is because the larger the capacity and the size of the reboiler 30, the more likely the difference is in the flow rate and the flow rate of the liquid among the many thin tubes. For example, it is inevitable that a difference in flow occurs between the central portion and the outer peripheral portion of the reboiler 30. The heating effect of the heating medium may be different between the center side and the outer peripheral side. If two relatively small reboilers 30 are made to perform the same processing capacity as one large reboiler 30, the dispersion and deviation of the liquid flow inside each reboiler 30 are reduced. In addition, the possibility of formation and adhesion of a polymer is reduced.

Similarly, by performing the same processing capacity with two relatively small condensers 20 as compared with one large condenser 20, the condenser 20 has a vapor or condensate inside the condenser 20. Proper liquid flow reduces the likelihood of polymer deposits.
Since the connection position of the steam return pipe 34 from the two reboilers 30 to the distillation column 10 is symmetrically arranged with respect to the distillation column 10, the flow of the steam returned to the distillation column 10 is 10 are uniform in the plane direction, and local flow bias is less likely to occur. Thereby, the formation and adhesion of the polymer inside the distillation column 10 can be prevented. The distillation action in the distillation column 10 is also uniform as a whole, and an efficient distillation action can be achieved.

[Another example of device structure]
The embodiment shown in FIGS. 3 and 4 has the same basic apparatus configuration as the above embodiment, but differs in the pipe connection structure between the condenser 20 and the distillation column 10.
As shown in FIG. 3, the two condensers 20, 20 are connected to the distillation column 10 by independent piping paths. A vapor extraction pipe 22 for supplying vapor from the distillation column 10 to the condenser 20 and a liquid return pipe 24 for returning a condensed liquid from the condenser 20 to the distillation column 10 are provided for each condenser 20. The liquid delivery pipe 14 is connected to the middle of each liquid return pipe 24. Although not shown in the drawing, the two liquid delivery pipes 14 may be joined to continue to the next step.

  As shown in FIG. 4, in the planar structure, two condensers 20, 20 are arranged at symmetric positions with the diameter of the distillation column 10 as a symmetric axis. The vapor extraction pipe 22 and the liquid return pipe 24 of each condenser 20 extend from the radial direction of the distillation column 10 to the center C, are connected to the distillation column 10, and form an included angle θ with each other. In the figure, the included angle θ is set to a narrow angle of about 60 ° for display together with the reboiler 30, but a wider included angle θ can be taken. For example, the same included angle θ as that of the reboiler 30 can be set to 180 °.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
The result of specifically constructing the purifying apparatus of the present invention and purifying acrylic acid is shown.
[Example 1]
Basically, a purifying apparatus having the structure shown in FIGS.
<Distillation tower>
Tower diameter 4m, non-sheep sheep tray 50-stage equipment, material SUS316.
<Condenser>
A vertical multi-tube condenser was used. The two condensers were arranged at an included angle θ = 180 ° in FIG.

Thin tube: outer diameter 38.1 mm, tube wall thickness 2.11 mm, length 3048 mm.
The number is 1160 and the material is SUS316.
Body: outer diameter 1800 mm.
<Reboiler>
A vertical multi-tube reboiler was used. Two reboilers were installed in the arrangement shown in FIG.
Thin tube: outer diameter 38.1 mm, tube wall thickness 2.11 mm, length 4000 mm.
The number is 894 and the material is SUS316.
Body: 1600 mm outside diameter.

Angle between two reboilers: θ = 180 °.
<Purification work>
Unpurified acrylic acid-containing liquid (containing 96.5% by weight of acrylic acid, 1.9% by weight of acrylic acid dimer, 0.4% by weight of maleic acid, and 200% by weight of phenothiazine) was introduced into distillation column 10 through inlet tube 12. , 18.7 m ³ / h.
Distillation was carried out under the processing conditions of a top pressure of the distillation column 10 of 3.3 kPa and a reflux ratio of 1.5, and a vapor containing 99.9% by weight of acrylic acid and 40% by weight of maleic acid was passed through a vapor extraction pipe 22 at the top of the column. Got. The purity of acrylic acid is higher than that of the unpurified liquid, and most of impurities such as acrylic acid dimer are removed.

The obtained steam was supplied to a pair of condensers 20 and 20 from steam extraction pipes 22 having a diameter of 1800 mm, respectively, and was condensed from 56 ° C to 40 ° C. Cooling water of 30 ° C. was passed through the heat medium pipe 26 of the condenser 20. Part of the condensate sent to the liquid return pipe 24 was returned to the distillation column 10, and the rest was taken out to the condensate discharge pipe 14.
On the bottom side of the distillation column 10, the bottom liquid was sent from the bottom liquid outlet pipe 32 having a diameter of 1100 mm to the pair of reboilers 30, 30 by natural circulation. Part of the bottom liquid was withdrawn from the delivery pipe 16. In the reboiler 30, the liquid was evaporated and returned to the distillation column 10 from a vapor return pipe 34 having a diameter of 1250 mm. 0.6 MPaG saturated steam was supplied to the heating medium tube 36 of the reboiler 30. 20 Nm ³ / h of molecular oxygen gas was supplied from the lower part of the reboiler 30. The molecular oxygen gas performs a polymerization preventing function.

Under the above operating conditions, the purifier was operated for one month. After the operation was completed, the inside of the device was inspected. In any of the distillation column 10, the condenser 20, and the reboiler 30, almost no polymer was found inside.
[Comparative Example 1]
In the purification device of Example 1, the condenser 20 and the reboiler 30 were changed as follows.
<Condenser>
Only one vertical multi-tube condenser was installed.
Thin tube: outer diameter 38.1 mm, tube wall thickness 2.11 mm, length 3048 mm.

The number is 2,320 and the material is SUS316.
Body: 2500 mm outside diameter.
Compared to the condenser of the first embodiment, the number of thin tubes per unit is larger and the diameter of the body is larger. The condensing capacity is equivalent to the sum of the two condensers in the first embodiment.
<Reboiler>
Only one vertical multi-tube reboiler was installed.
Thin tube: outer diameter 38.1 mm, tube wall thickness 2.11 mm, length 4000 mm.
The number is 1788 and the material is SUS316.

Body: outer diameter 2250 mm.
Compared to the reboiler of Example 1, the number of thin tubes per unit is larger, and the diameter of the body is larger. The reboil processing capacity is equivalent to the sum of the two reboilers in Example 1.
<Purification work>
The operation was performed under the same conditions as in Example 1. From the top of the distillation column 10, steam containing 99.9% by weight of acrylic acid and 180% by weight of maleic acid was obtained. The purified product itself is not so different from Example 1.
However, 21 days after the operation, the operation was stopped because the pressure loss in the distillation column 10 increased. When the insides of the distillation column 10, the condenser 20 and the reboiler 30 were inspected, 55 kg of polymer was accumulated on a tray installed inside the distillation column 10. 2 kg was accumulated in the upper tube sheet inside the condenser 20. In the reboiler 30, 57 thin tubes were blocked by the polymer.

[Example 2]
A purifying apparatus having the structure shown in FIGS. 1 and 2 was used. Basically, the specifications common to the first embodiment are adopted, but the structure of the condenser is different. Only different specification items will be described.
<Condenser>
Basically, it is common to the first embodiment. The different specification items are as follows.
Capillary tube: length 6096 mm, number 2948
Body: outer diameter 2800 mm.
As a connection structure between the two condensers and the distillation column 10, as shown in FIG. 2, a vapor extraction pipe 22 and a liquid return pipe 24 having a branched structure were used.

<Purification work>
An unpurified aqueous solution of acrylic acid (67.5% by weight of acrylic acid, 2.2% by weight of acetic acid, 28.6% by weight of water, and the remainder including maleic acid, acetaldehyde, acrolein, and 200 ppm by weight of hydroquinone) The liquid was supplied from the inlet pipe 12 to the 23rd stage of the distillation column 10 at 23.0 m ³ / h.
The azeotropic distillation was performed at a top pressure of the distillation column 10 of 18.7 kPa. The top liquid taken out from the vapor discharge pipe 22 at the top and condensed by the condenser 20 was separated into two phases, and the toluene phase as the azeotropic agent was all refluxed to the distillation column 10. The aqueous phase was distilled off as wastewater. The reflux amount was 60 m ³ / h. To the reflux liquid, 150 ppm by weight of phenothiazine as a polymerization inhibitor was added.

As a result, a purified product comprising 96.2% by weight of acrylic acid and 300% by weight of acetic acid was obtained as a bottom liquid.
The steam extraction pipe 22 into which steam was introduced from the distillation column 10 to the condenser 20 had a diameter of 1800 mm on the distillation column 10 side and a diameter of 1300 mm at a branch portion connected to the two condensers 20, 20. It was cooled from 46 ° C. to 37 ° C. in the condenser 20 to condense. Cooling water at 30 ° C. was passed through the heat medium pipe 26 of the condenser 20.
The bottom liquid outlet pipe 32 from the distillation tower 10 to the reboiler 30 had a diameter of 1300 mm. The steam boiled from the liquid in the reboiler 30 returned to the distillation column 10 from a steam return pipe 34 having a diameter of 1250 mm. The circulation of the liquid or vapor between the reboiler 30 and the distillation column 10 was performed by natural circulation. 0.6 MPaG saturated steam was supplied to the heating medium tube 36 of the reboiler 30. 100 Nm ³ / h of molecular oxygen gas was supplied from the lower part of each reboiler 30.

The operation was continued for one month under the above conditions. The internal temperature of the distillation column 10 was stable. For example, the 29 stage temperature was in the range of 93-97 ° C. After the operation was completed, the inside of each apparatus was inspected. As a result, no adhesion of the polymer was observed inside any of the distillation column 10, the condenser 20, the reboiler 30, and each pipe.
[Comparative Example 2]
The following device specifications and working conditions were changed based on Example 2.
Although the distillation column 10 and the condenser 20 and the arrangement structure thereof are common to those in Example 2, only one reboiler having the following specifications was used.

<Reboiler>
Basically, it is common to the second embodiment. The different specification items are as follows.
Capillary tube: 4000 mm long, 1788 pieces.
Body: outer diameter 2250 mm.
The processing capacity of the reboiler is equivalent to the sum of the two reboilers in Example 2.
<Purification work>
Distillation was performed under the same working conditions as in Example 2. A purified product consisting of 96.0% by weight of acrylic acid and 600% by weight of acetic acid was obtained as a bottom liquid. The temperature in the distillation column 10 fluctuated considerably. For example, the 29th stage temperature fluctuated in the range of 83-96 ° C. At the time of operation for 12 hours, the operation was stopped because the pressure loss in the tower increased. When the insides of the distillation column 10, the condenser 20 and the reboiler 30 were inspected, 130 kg of a polymer was found on the tray of the distillation column 10. In the reboiler 30, 92 thin tubes were blocked by the adhesion of the polymer.

[Example 3]
3 and 4, but only one condenser 20 was installed. Basically, specifications common to the first embodiment are adopted, and only different specification items are shown below.
<Distillation tower>
The structure was the same as that of Example 1, and the tower diameter was changed to 2 m.
<Condenser>
Basically, it is common to the first embodiment. The different specification items are as follows.
Thin tube: length 4000 mm, number 492, material SUS304.

Body: 1900 mm outside diameter.
<Reboiler>
Basically, it is common to the first embodiment. The different specification items are as follows.
Thin tube: length 4000 mm, number 170, material SUS304.
Body: 700 mm outside diameter.
Angle between two reboilers: θ = 180 °.
<Purification work>
An unpurified acrylate solution (containing 78.0% by weight of butyl acrylate, 18.6% by weight of butyl alcohol, 2.9% by weight of water and 80 ppm by weight of phenothiazine) was added at a flow rate of 8.0 m ³ / h. The mixture was supplied to 16 columns of the distillation column 10. An azeotropic distillation was performed at a top pressure of 33 kPa and a reflux ratio of 3. As the bottom liquid, a purified product consisting of 99.9% by weight of butyl acrylate and 50% by weight of butyl alcohol was obtained.

The vapor outlet pipe 22 from the distillation column 10 to the condenser 20 had a diameter of 550 mm. In the condenser 20, the steam was cooled from 83 ° C. to 40 ° C. and condensed. Cooling water of 30 ° C. was passed through the heat medium pipe 26 of the condenser 20.
The bottom liquid outlet pipe 32 from the distillation tower 10 to the reboiler 30 had a diameter of 450 mm. The steam return pipe 34 had a diameter of 550 mm. Circulation of the liquid or vapor between the distillation column 10 and the reboiler 30 was performed by natural circulation. A part of the circulating liquid was drawn out to the delivery pipe 16. 0.6 MPaG saturated steam was supplied to the heat medium pipe 36 of each reboiler 30, and air 4 Nm ³ / h was supplied from the lower part of the reboiler 30.

It was operated for one month under the above conditions. The internal temperature of the distillation column 10 was stable. For example, the 35 stage temperature was in the range of 102-104 ° C. When the inside of the apparatus was inspected after the end of the operation, almost no polymer was found inside any of the distillation column 10, the condenser 20, and the reboiler 30.
[Comparative Example 3]
The following device specifications and working conditions were changed based on Example 3.
The arrangement of the distillation column 10 and the condenser 20 and their arrangement are the same as those of the third embodiment, but only one reboiler having the following specifications was used.

<Reboiler>
Basically, it is common to the third embodiment. The different specification items are as follows.
Thin tubes: 340 tubes.
Body: 950 mm outside diameter.
The processing capacity of the reboiler is equivalent to the sum of the two reboilers in Example 3.
<Purification work>
Distillation was performed under the same working conditions as in Example 3. As the bottom liquid, a purified product consisting of 99.9% by weight of butyl acrylate and 200% by weight of butyl alcohol was obtained.

The temperature in the distillation column 10 fluctuated considerably. For example, the 35 stage temperature varied in the range of 99-104 ° C. When the inside of the apparatus was inspected after one month of operation, 6 kg of a polymer was found on the tray of the distillation column 10. In the reboiler 30, five thin tubes were blocked by the adhesion of the polymer.
[Evaluation]
(1) In each of the examples, there were no problems such as adhesion of the polymer and clogging of the internal piping, and the temperature in the distillation column was stable. The purification work of acrylic acids was successfully achieved.
(2) In each comparative example in which one reboiler achieves the same processing capacity as that of the example, the acrylic acid can be purified itself, but the polymer adheres to the inside of the apparatus early after the start of operation, The piping is clogged.

It can be inferred that the fluctuation in the internal temperature of the distillation column is large, and the flow of the liquid or vapor in the distillation column is biased or unstable. As a result, the work of purifying acrylic acids was also unstable.
(3) Good results were obtained in Examples 1 and 2 in which acrylic acid was purified and Example 3 in which acrylic acid ester was purified. It can be seen that the present invention is effective for any substance contained in acrylic acids.
In the first and second embodiments, not only a plurality of reboilers but also a plurality of condensers are used. In the third embodiment, one condenser is provided. In each case, good performance is exhibited. Therefore, it is necessary to use a plurality of reboilers, but it can be seen that the present invention can be practiced with only one condenser. In the case of the third embodiment using a small apparatus with a smaller processing amount than the first and second embodiments, it can be estimated that the purpose can be sufficiently achieved even with one condenser.

FIG. 1 is an overall structural diagram of a purification apparatus showing an embodiment of the present invention. FIG. 2 is a plan view showing an arrangement structure of each device of the purification apparatus of FIG. Overall structure diagram of a purification device showing another embodiment FIG. 3 is a plan view showing an arrangement structure of each device of the purification device in FIG. 3.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 Distillation tower 12 Injection pipe 14 Condensate removal pipe 16 Delivery pipe 20 Condenser 22 Vapor removal pipe 24 Liquid return pipe 26 Heat medium pipe 30 Reboiler 32 Liquid removal pipe 34 Steam return pipe 36 Heat medium pipe θ

Claims (4)

An apparatus for purifying acrylic acid including acrylic acid and its ester by distillation,
A liquid containing the acrylic acid is supplied, a vapor is taken out from the top of the column, and a distillation column from which a liquid is taken out from the bottom,
A condenser connected to the top of the distillation column, supplied with steam taken out of the distillation column, condensing the steam, refluxing part of the condensate to the distillation column, and taking out the remaining condensate,
A reboiler is connected to the bottom of the distillation column, the liquid in the distillation column is supplied, and the supplied liquid is heated and boiled and returned to the distillation column.
An apparatus for purifying acrylic acids, wherein a plurality of the reboilers are provided in parallel with the distillation column. The acrylic acid purifier according to claim 1, wherein a plurality of the condensers are arranged in parallel with the distillation column. The distillation column has a cylindrical shape with an outer diameter of 2 to 6 m,
The plurality of reboilers are arranged symmetrically with respect to the center of the distillation column in the horizontal direction,
The distillation column and the reboiler take out a liquid from the distillation column and supply a liquid to each reboiler, and a vapor return pipe that returns vapor from each reboiler to the distillation column. The acrylic acid purifying apparatus according to claim 1 or 2, wherein the acrylic acid is purified. A method for purifying acrylic acids by distillation using the purifying apparatus according to any one of claims 1 to 3,
A method for purifying acrylic acid, comprising a step of supplying a liquid in the distillation column to the plurality of reboilers and returning the steam heated and boiled by the reboiler to the distillation column.

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