WO2013077319A1

WO2013077319A1 - Method for removing impurities

Info

Publication number: WO2013077319A1
Application number: PCT/JP2012/080062
Authority: WO
Inventors: 雅志横田; 小林　由典
Original assignee: 住友化学株式会社
Priority date: 2011-11-25
Filing date: 2012-11-20
Publication date: 2013-05-30
Also published as: CN103946212A; CN103946212B; JP2013128919A

Abstract

The present invention pertains to a method for removing impurities, the method comprising: providing a first filled layer and a second filled layer that are filled with a filler material and supplying, through a gas supply unit that is located below the first filling layer, a mixed gas containing as an impurity either solid matter or a component capable of forming solid matter by polymerization; distilling in a distillation column and extracting a gas that contains a target matter from a first discharge line; extracting a liquid that contains the impurity from a second discharge line to the exterior of the distillation column; supplying at least some of the extracted liquid to the first filling layer from above as a circulated liquid; rinsing away the impurity captured in the first filling layer by using the circulated liquid as well as a reflux liquid from the top of the distillation column, to obtain a liquid that contains the impurity; and extracting the liquid that contains the impurity through the first discharge line. According to the present invention, it is possible to provide a method for removing impurities whereby solid matter or a component capable of forming solid matter by polymerization can be removed as an impurity from the interior of a distillation column when a target matter is being isolated by distillation in the distillation column.

Description

How to remove impurities

The present invention relates to a method for removing impurities when an object is separated by distillation.
This application claims priority based on Japanese Patent Application No. 2011-257557 for which it applied to Japan on November 25, 2011, and uses the content here.

When separating the target product from the mixed gas discharged from the reactor, such as when performing a gas phase reaction, supply the mixed gas to the distillation tower of the distillation device to adjust the temperature, and use the difference in boiling points. The separation method is applied. For example, a component having a boiling point higher than that of the target product is condensed by cooling and removed as a liquid from the lower part of the distillation column, and in some cases, the extracted liquid is returned to the distillation column and brought into contact with the mixed gas. Sometimes reused to promote condensation.

On the other hand, for example, when a fluidized bed type reactor is used, a mixed gas in which solid components such as the catalyst, reaction by-products, and components derived from the reaction by-products used in the reaction are discharged from the reactor. This solid content cannot be removed by condensation, adheres to and accumulates within the distillation apparatus, such as inside the distillation column or inside the piping connected to the distillation tower, and closes the distillation apparatus. It may end up. Therefore, a technique for suppressing the mixing of solid content into the distillation tower has been studied. For example, reaction conditions for suppressing by-products during reaction of reaction by-products may be studied.

However, mixing of solid content into the distillation tower cannot be completely suppressed. In addition, among the high boiling components having a particularly high boiling point, components capable of forming solids by polymerization (hereinafter sometimes referred to as “polymerizable components”) are in a gaseous state immediately after introduction into the distillation column. However, some of them adhere to the inside of the distillation apparatus to produce a polymer and solidify. Then, like the above solid content, the distillation apparatus may be blocked. Some of the above reaction by-products generate such polymerizable components.
As described above, the solid content and the polymerizable component in the mixed gas can block the distillation apparatus and hinder stable continuous operation of the distillation apparatus. Therefore, a technique for removing the solid content and polymerizable components mixed in the distillation column from the distillation column has been studied.

For example, in Patent Document 1, when an unsaturated nitrile is produced by an ammoxidation reaction of an organic compound, a mixed gas obtained by the reaction is brought into contact with a circulating liquid containing a reaction product, and a polymer, a catalyst, etc. It is disclosed that impurities are captured and removed with a circulating fluid.

Japanese Patent No. 3270479

However, Patent Document 1 does not disclose a specific configuration necessary for removing impurities with the circulating liquid, and an effective method for removing impurities such as a polymer and a catalyst from the inside of the distillation column is as follows. It is not substantially disclosed.

The present invention has been made in view of the above circumstances, and when separating an object from a mixed gas containing a solid content or a component capable of forming a solid content by polymerization by distillation in a distillation column, Alternatively, an object of the present invention is to provide an impurity removal method capable of removing a component capable of forming a solid content by polymerization as an impurity from the inside of a distillation column.

To solve the above problem,
The present invention relates to a method for removing impurities from the inside of a distillation column for distillation when a target product is separated by distillation from a solid gas or a mixed gas containing components that can form solids by polymerization as impurities. In the distillation column, one or more packed beds filled with a filler are provided in the height direction of the distillation column, and the lower portion of the packed bed has a lower portion than the packed bed. The mixed gas is supplied from the outside to perform distillation, and the gas containing the target product is extracted from above the uppermost packed bed in the distillation column and below the mixed gas supply unit. At least a part of the liquid extracted from the extraction site is supplied to the bottom packed bed as a circulating liquid from above, and the bottom packed with the circulating liquid and the reflux liquid from the upper part of the distillation column. The fault trapped in the layer Rinse things, the liquid containing the impurities, provides a method of removing impurities, characterized in that withdrawing from the site extraction of the lower.
In the impurity removal method of the present invention, it is preferable that the specific surface area of the filler in the lowermost packed bed is 70 to 300 m ² / m ³ .
In the impurity removal method of the present invention, the total flow rate of the circulating liquid and the reflux liquid in the plane perpendicular to the height direction of the distillation column of the bottom packed bed is 1.5 × 10 ^4. It is preferably ˜1.2 × 10 ⁵ kg / m ² / h.
In the impurity removal method of the present invention, it is preferable that the circulating liquid and the reflux liquid are filtered to remove solids, and then supplied to the bottom packed bed.
In the impurity removal method of the present invention, the mixed gas is preferably a gas after a gas phase reaction in which ε-caprolactam is generated from cyclohexanone oxime using a solid acid catalyst in the presence of a lower alcohol.

That is, the present invention relates to the following.
(1) A method of removing impurities from the inside of a distillation column that performs distillation when a target product is separated by distillation from a mixed gas containing solids or components capable of forming solids by polymerization as impurities. The distillation column is at least one layer provided in the height direction of the distillation column, a packed bed filled with a filler, a gas supply unit provided in a portion below the bottom packed bed, It has a first extraction site provided above the uppermost packed bed and a second extraction site provided below the gas supply unit, and is lower than the lower packed bed. Supplying the mixed gas from the outside to the inside of the distillation column to the lower site, performing distillation in the distillation column, from the first extraction site provided above the packed bed at the top, Gas containing the object Is extracted to the outside of the distillation column, the liquid containing the impurities is extracted to the outside of the distillation column from a second extraction site provided below the gas supply unit, and at least one of the extracted liquids Supplying the lower part of the packed bed as a circulating liquid from above, and washing the impurities trapped in the lower packed bed with the circulating liquid and the reflux liquid from the upper part of the distillation column. Obtaining a liquid containing the impurities, and extracting the liquid containing the impurities from the second extraction site to the outside of the distillation column,
(2) The method for removing impurities according to (1), wherein a specific surface area of the filler in the lowermost packed bed is 70 to 300 m ² / m ³ ,
(3) The total flow rate of the circulating liquid and the reflux liquid in an arbitrary plane perpendicular to the height direction of the distillation column in the lowermost packed bed is 1.5 × 10 ⁴ to 1.2. A method for removing impurities according to (1) or (2), which is × 10 ⁵ kg / m ² / h,
(4) The method further includes cooling and condensing a part of the gas containing the target product extracted from the first extraction site to form a liquid, and refluxing the liquid from the upper part of the distillation column. 1) a method for removing impurities according to any one of (3),
(5) The method according to any one of (1) to (4), further comprising: filtering the condensed liquid to remove solids before refluxing the liquid from the upper part of the distillation column. A method for removing the impurities described in the paragraph,
(6) Before supplying at least a part of the liquid extracted from the second extraction site as a circulating liquid to the lowermost packed bed from above, the liquid extracted from the second extraction site is filtered. (1) The method for removing impurities according to any one of (1) to (5), further comprising removing solids by filtration, and (7) the mixed gas is a solid in the presence of a lower alcohol. The method for removing impurities according to any one of (1) to (6), which is a gas obtained by a gas phase reaction in which ε-caprolactam is produced from cyclohexanone oxime using an acid catalyst.

ADVANTAGE OF THE INVENTION According to this invention, when separating a target object by distillation in a distillation column, the removal method of the impurity which can remove the solid content or the component which can form solid content by superposition | polymerization as an impurity from the inside of a distillation column is provided. it can.

It is the schematic for demonstrating the removal method of the impurity which concerns on 1st embodiment of this invention. It is the schematic for demonstrating the removal method of the impurity which concerns on 2nd embodiment of this invention. It is the schematic for demonstrating the removal method of the conventional impurity. It is the schematic for demonstrating the conventional removal method of other impurities. 6 is a graph showing LCV valve opening data in Examples 2 to 4.

In the method for removing impurities according to the present invention, distillation is performed when a target product is separated by distillation from a mixed gas containing solids or components capable of forming solids by polymerization (polymerizable components) as impurities. A method for removing the impurities from the inside of a column, wherein the distillation column comprises at least one packed bed filled with a filler provided in the height direction of the distillation column, and the packed bed at the bottom. A gas supply section installed at a lower position than the gas supply section, a first extraction section provided above the uppermost packed bed, and a second extraction section provided below the gas supply section. And supplying the mixed gas from the outside to the inside of the distillation column to the lower part of the packed bed at the bottom, performing distillation in the distillation column, and more than the packed bed at the top. Provided above Extracting the gas containing the target product from one extraction site to the outside of the distillation column, and extracting the impurities from the extraction site (the second extraction site) below the gas supply unit to the outside of the distillation column. Extracting the contained liquid, supplying at least a part of the extracted liquid to the bottom packed bed as a circulating liquid from above, the circulating liquid and the reflux liquid from the upper part of the distillation column, Washing off the impurities trapped in the bottom packed bed to obtain a liquid containing the impurities, and removing the liquid containing the impurities from the lower extraction site (second extraction site) to the distillation column. Including extraction outside.
Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic view for explaining an impurity removal method according to the first embodiment of the present invention.
The distillation apparatus 1 shown here includes a first packed bed 12 and a second packed bed 13 filled with a filler inside a distillation column 11 that performs distillation. The first packed bed 12 and the second packed bed 13 are spaced apart from each other in this order from below in the height direction of the distillation column 11.
The first packed bed 12 contributes to the separation of the target product from the mixed gas to be distilled and captures a solid content or a polymerizable component in the mixed gas. The second packed bed 13 mainly promotes separation of the target product from the mixed gas, and is configured to capture a solid content or a polymerizable component in the same manner as the first packed bed 12. May be.
In this specification, “filled with filler” means a direction perpendicular to the height direction of the distillation column (the direction of arrow Z in FIG. 1) (for example, when the distillation column is cylindrical). Indicates that the filler is spread in the radial direction).

A gas supply unit 111 for supplying gas from the outside to the inside of the distillation column 11 is provided below the distillation column 11 below the first packed layer 12 which is the lowermost layer (lowermost) packed layer. It has been. Thus, the other packed bed filled with the filler is not provided inside the distillation column 11 below the gas supply unit 111 (on the column bottom side). That is, the packed bed 12 is provided above the gas supply unit 111.

Connected to the top of the distillation column 11 is a first discharge line 14 that is a first extraction site for extracting a gas containing the target substance to be separated, and a bottom for extracting a liquid. A second discharge line 15 which is a second extraction portion is connected.

The first discharge line 14 is provided with a cooler 140 in the middle, and a reflux line 141 is branched from the cooler 140 separately from the first discharge line. The cooler 140 of the reflux line 141 is branched. The end not connected to is connected above the second packed bed 13 which is the packed bed of the uppermost layer (uppermost part) in the distillation column 11. Examples of the cooler 140 include known ones such as a heat exchange type.

A circulation line 151 is branched from a middle portion of the second discharge line 15, and the end of the circulation line 151 not connected to the second discharge line 15 is the first packed bed in the distillation column 11. 12 above and below the second packed bed 13. That is, the circulation line 151 connects the space between the first packed bed 12 and the second packed bed 13 inside the distillation column 11 and the second discharge line 15.

The specific surface area of the filler in the first packed bed 12 is preferably 70 to 300 m ² / m ³ , more preferably 70 to 260 m ² / m ³ , and 70 to 160 m ² / m ³ . More preferably. By setting it as the said lower limit or more, the separation effect of the target object from mixed gas improves more, and the washing | cleaning effect of the capture | acquired solid content or polymeric component improves more by setting it as the said upper limit or less.

The specific surface area of the filler in the second packed bed 13 may be appropriately adjusted according to the purpose, but is preferably 70 to 270 m ² / m ³ , more preferably 90 to 260 m ² / m ^3. preferable. By setting the lower limit value or more, the effect of separating the target product from the mixed gas is further improved. By setting the lower limit value or less, the mixed gas that has passed through the first packed bed 12 has a solid content or a polymerizable component. Can be captured and washed out more effectively.

The height H ₁ of the first packed bed 12 is preferably 20 to 30% with respect to the height H ₀ of the distillation column 11. By setting it as the said lower limit or more, the capture | acquisition effect of the solid content or polymeric component in mixed gas improves more, By making it into the said upper limit or less, the target object can be isolate | separated more efficiently from mixed gas.

The height H ₂ of the second packed bed 13 is preferably 20 to 30% with respect to the height H ₀ of the distillation column 11. By setting it as the said lower limit or more, the separation effect of the target object from mixed gas improves more, and by setting it as the said upper limit or less, a target object can be isolate | separated more efficiently.

In the present invention, using a mixed gas containing a solid component or a polymerizable component as an impurity, distillation is performed in the distillation column 11, and when the target product in the mixed gas is separated, the inside of the distillation column 11 Remove impurities. Specifically, it is as follows.

First, the mixed gas is supplied from the gas supply unit 111 into the distillation column 11.
The mixed gas is not particularly limited as long as it contains a solid content or a polymerizable component as an impurity, and a preferable example is a gas after a gas phase reaction, which is transferred from a fluidized bed type reactor. Can be exemplified. Here, examples of the solid content include a catalyst; a polymer of a polymerizable component, or a reaction by-product such as a compound other than the polymer; or a component derived from the reaction by-product. Examples of the polymerizable component include reaction by-products generated during the reaction.
Suitable examples of the gas phase reaction include, but are not limited to, a reaction in which ε-caprolactam is produced from cyclohexanone oxime using a solid acid catalyst in the presence of a lower alcohol. Here, as the lower alcohol, methanol, ethanol, 1-propanol (n-propyl alcohol), 2-propanol (isopropyl alcohol), 1-butanol (n-butyl alcohol), 2-butanol (sec-butyl alcohol), 1 to 1 carbon atoms such as 2-methyl-1-propanol (isobutyl alcohol), 1-pentanol (n-pentyl alcohol), 1-hexanol (n-hexyl alcohol), 2,2,2-trifluoroethanol, etc. 6 alcohols can be exemplified. As the lower alcohol, methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol are preferable, and methanol and ethanol are more preferable.
Examples of the solid acid catalyst include a pentasil-type zeolite catalyst.

Then, by performing distillation, a gas containing the target product is extracted from the first discharge line 14 to the outside of the distillation column 11. At this time, solid components or polymerizable components (impurities) in the supplied mixed gas are captured by the first packed bed 12 and mixed in the distillation column 11 above the first packed bed 12. (Movement) is suppressed.

On the other hand, since a part of the mixed gas is condensed inside the distillation column 11, the condensed liquid is extracted from the second discharge line 15 to the outside of the distillation column 11. Then, at least a part of the extracted liquid is separated, returned to the inside of the distillation column 11 through the circulation line 151, and supplied to the first packed bed 12 from above. In this way, the impurities trapped in the first packed bed 12 are washed away by the liquid (circulating liquid) passing through the first packed bed 12 from the upper side to the lower side. At this time, a part of the gas extracted from the first discharge line 14 is cooled by the cooler 140, or the gas is cooled above the first packed bed 12 inside the distillation column 11. Thus, inside the distillation column 11, a part of the gas is condensed above the first packed bed 12 to become a liquid and flow down. That is, as another aspect of the present invention, a part of the gas containing the target object extracted from the first extraction part (first discharge line 14) is cooled and condensed to form a liquid, Is preferably further refluxed from the top of the distillation column.
The cooling by the cooler 140 is performed by setting the temperature so that a gas having a boiling point higher than that of the object out of the gas including the object extracted from the first discharge line 14 is condensed to become a liquid. It is preferable to do.
The impurities trapped in the first packed bed 12 are also washed away by the liquid (reflux) supplied from the upper part of the distillation column by this reflux. At this time, the mixed gas supplied from the gas supply unit 111 is in gas-liquid contact with the circulating liquid and the reflux liquid. By washing away the impurities in this manner, the solid content in the mixed gas and the solid content captured by the first packed bed 12 move to the bottom of the distillation column 11. Similarly, the polymerizable component captured by the first packed bed 12 moves to the bottom of the column before becoming a polymer. Therefore, not only the impurities move to the bottom of the column, but also polymerization of the polymerizable component is suppressed, so that the total amount of solids in the distillation column 11 can be significantly reduced.

The washed liquid containing the impurities is extracted from the second discharge line 15 to the outside of the distillation column 11. A part of the extracted liquid is used for washing away the impurities trapped in the first packed bed 12 in the same manner. By the above process, the impurities are extracted from the second discharge line 15 to the outside of the distillation column 11 and are not returned to the inside of the distillation column 11 except for a part, so that the impurities are removed from the inside of the distillation column 11. To go.

The removal of the impurities suppresses the adhesion and accumulation of solids in each part of the distillation apparatus 1 including the distillation column 11, the first discharge line 14 and the second discharge line 15. Blockage in the interior of the is suppressed.

In the present invention, the flow rate of the liquid passing through the first packed bed 12, that is, the total flow rate of the circulating liquid and the reflux liquid is 1.5 × in the plane perpendicular to the height direction Z of the distillation column 11. It is preferably 10 ⁴ to 1.2 × 10 ⁵ kg / m ² / h. By setting the lower limit value or more, the effect of washing out the impurities in the first packed bed 12 is further improved. Moreover, by setting it as the said upper limit or less, while separating efficiency of a target object improves more, installation of the excessive pump for obtaining the said predetermined total flow rate is avoided. The flow rate of the circulating liquid can be adjusted, for example, by adjusting the amount of liquid separated from the second discharge line 15 to the circulating line 151. Further, the flow rate of the reflux liquid can be adjusted by adjusting the temperature of the distillation column 11 or the temperature of the cooler 140, for example.
The total flow rate is measured by a method such as measurement by a flow meter installed in a pipe through which each liquid flows.

The packing material for the distillation column according to the present invention is not particularly limited as long as it can capture impurities, and examples thereof include irregular packing such as cascade mini-ring, or regular packing. When distilling the gas after the gas phase reaction for producing ε-caprolactam from cyclohexanone oxime using a solid acid catalyst in the presence of a lower alcohol, the packing material is an irregular packing such as a cascade miniring, Or a regular packing etc. are mentioned. When the distillation column includes two or more packed beds, the packing materials may be the same or different.

FIG. 2 is a schematic view for explaining an impurity removal method according to the second embodiment of the present invention. 2 that are the same as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG. 1 and will not be described in detail. The same applies to the subsequent drawings.
The distillation apparatus 2 shown in FIG. 2 includes a first filtration unit 16 in the middle of the reflux line 141, and a second filtration unit 17 in the middle of the second discharge line 15. Except for these points, This is the same as the distillation apparatus 1 shown in FIG.

The method for removing impurities according to the second embodiment of the present invention further includes removing the solid content by filtering the condensed liquid before refluxing the reflux liquid from the upper part of the distillation column 11. Including.
That is, the first filtration unit 16 is arranged between the cooler 140 and the connection part of the reflux line 141 to the distillation column 11, and solids are mixed in the liquid condensed by the cooler 140. Even if this is done, it is possible to filter this off and allow the liquid not containing solids (reflux) to be refluxed to the distillation column 11. In this way, after removing the solid content, by supplying a reflux liquid to the second packed bed 13 and the first packed bed 12, the effect of washing away the impurities trapped in the first packed bed 12 is obtained. It can be improved further.

In addition, the method for removing impurities according to the second embodiment of the present invention is a method for supplying at least a part of the liquid extracted from the second extraction site to the lowermost packed bed as a circulating liquid from above. And further filtering the liquid extracted from the second extraction site to remove the solid content.
That is, the second filtration unit 17 is arranged in the second discharge line 15 between the connection part with the distillation column 11 and the branch part with the circulation line 151, and is extracted from the distillation column 11. It is possible to filter the solid content contained in the liquid and to circulate the liquid not containing the solid content (circulating liquid) in the distillation column 1. In this way, by removing the solid content and then supplying the circulating liquid to the first packed bed 12, the effect of washing out the impurities trapped in the first packed bed 12 can be further improved.

The 1st filtration part 16 and the 2nd filtration part 17 will not be specifically limited if solid content can be filtered, Well-known filter filtration apparatuses, such as a strainer, can be illustrated.
What is necessary is just to adjust suitably the filtration capability of the 1st filtration part 16 and the 2nd filtration part 17 according to the kind of mixed gas of distillation object, respectively. The first filtration unit 16 and the second filtration unit 17 may be the same or different from each other.

In FIG. 2, although the 2nd filtration part 17 has shown the example arrange | positioned in the 2nd discharge line 15 between the connection part with the distillation column 11, and the branch part of the circulation line 151, The distillation apparatus according to the present invention is not limited to this. For example, in the circulation line 151, the distillation apparatus may be disposed between the connection part with the distillation column 11 and the branch part from the second discharge line 15. Well (not shown), in this case, the same effect as described above can be obtained.

1 and 2 show a distillation apparatus provided with two layers of a first packed bed 12 and a second packed bed 13 as packed beds, but the distillation apparatus used in the present invention is not limited to these, and packing is performed. It is sufficient that at least one layer is provided. The number of packed layers is preferably one or more and three or less, more preferably one or more and two or less.

In the case of distillation apparatus having further seen a packed bed, for example, the height of the packed bed, the height H ₁ of the first filling layer 12, the high H ₂ of the second filling layer 13 It is preferable to be equal to or greater than the total value. And the other end of the circulation line branched from the 2nd discharge line and the other end of the recirculation | reflux line 141 branched from the cooler 140 should just be connected above the packed bed. By using such a distillation apparatus, impurities can be separated by the same method as in the case of using the distillation apparatus shown in FIGS.

On the other hand, in the case of a distillation apparatus having three or more packed beds, for example, in the distillation apparatus shown in FIGS. 1 and 2, the second inside the distillation column 11 and above the second packed bed 13, the second One or more packed layers may be disposed apart from the packed layer 13, and these one or more packed layers may be disposed apart from each other. These filling layers above the second filling layer 13 may be the same as the second filling layer 13, for example. By using such a distillation apparatus, impurities can be separated by the same method as in the case of using the distillation apparatus shown in FIGS.

However, the distillation apparatus according to the present invention has a packed bed as shown in FIGS. 1 and 2 in consideration of the separation effect of the target product, the removal effect of the solid content and the polymerizable component, the handleability, or the cost. Those having two layers are particularly preferred.

1 and 2 show an example in which the first discharge line 14 is connected to the top of the distillation column 11 and the second discharge line 15 is connected to the bottom of the distillation column 11. The distillation apparatus according to the invention is not limited to this, and the first discharge line 14 is connected to the upper side of the second packed bed 13, and the second discharge line 15 is connected to the lower side of the gas supply unit 111. Just do it. That is, in the distillation column 11, the gas containing the target product is extracted from the first extraction site located above the uppermost packed bed, and from the second extraction site located below the gas supply unit 111. The liquid containing impurities may be extracted.

According to the present invention, when the target product is separated by distillation in the distillation column, even if the mixed gas supplied to the inside of the distillation column contains solids or polymerizable components as impurities, These impurities can be effectively removed from the inside. Therefore, solid content adhesion and accumulation are suppressed in the distillation apparatus such as each part in the distillation column and the piping connected to the distillation tower, and the clogging of the distillation apparatus is suppressed. And the distillation apparatus can be stably operated for a long period of time.

Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples.

[Example 1]
In the presence of a lower alcohol, a target gas ε-caprolactam is obtained using a mixed gas obtained by a reaction for producing ε-caprolactam from cyclohexanone oxime using a solid acid catalyst in a distillation apparatus shown in FIG. During the separation, impurities were removed. Specifically, it is as follows.

The reaction was carried out using methanol as the lower alcohol and a pentasil-type zeolite catalyst as the solid acid catalyst. The obtained mixed gas contains methanol at an average temperature of 379 ° C., about 60% by mass of methanol, about 6% by mass of inert gas containing water, and about 34% by mass of ε-caprolactam containing reaction byproducts. It was.
In the distillation apparatus 2, those having a specific surface area of 257 m ² / m ³ (cascade mini ring 1 P) are used as the fillers of the first packed bed 12 and the second packed bed 13, respectively. The height H ₁ and the height H ₂ of the second packed bed 13 were 22% with respect to the height H ₀ of the distillation column 11, respectively.
The mixed gas is supplied to the inside of the distillation column 11 set at a pressure of 97.3 kPa (730 Torr) and a temperature of 200 to 220 ° C., and with respect to ε-caprolactam containing a reaction by-product in the supplied mixed gas, An amount of liquid corresponding to about 14% by mass is extracted from the second discharge line 15 connected to the bottom of the column with a liquid level control valve (hereinafter referred to as LCV), and the remaining portion of the mixed gas has an average temperature of 178 The amount condensed at 0 ° C. was withdrawn from the first discharge line 14 connected to the top of the column while being refluxed inside the distillation column 11. The total flow rate of the circulating liquid and the reflux liquid in the radial direction of the first packed bed 12 was 2.4 × 10 ⁴ kg / m ² / h. As the circulating liquid, a liquid obtained by filtering the solid content through a strainer provided as the second filtration unit 17 in the second discharge line 15 was extracted into the circulation line 151 and used.

When distillation and removal of impurities were performed under the above conditions, the amount of liquid withdrawn from the second discharge line 15 and the valve opening of the LCV were stabilized over about 30 days, and the solid content in the distillation apparatus 2 was stable. It was confirmed that occlusion was suppressed. Thus, the distillation apparatus 2 could be stably operated continuously.

[Comparative Example 1]
Using the mixed gas obtained by the reaction for producing ε-caprolactam from cyclohexanone oxime using a solid acid catalyst in the presence of a lower alcohol, the target product ε-caprolactam was obtained using the distillation apparatus shown in FIG. At the time of separation, impurities were removed by a conventional method. Specifically, it is as follows.

The distillation apparatus 8 shown in FIG. 3 is different from the distillation apparatus 2 shown in FIG. 2 in that the other end of the circulation line 151 is replaced with a space between the first packed bed 12 and the second packed bed 13 inside the distillation column 11. The gas supply unit 111 is connected to a supply line for supplying a mixed gas connected to the upstream side of the gas supply unit 111. That is, in the distillation apparatus 8, the circulation line 158 is connected to the supply line 18 so that the mixed gas before being supplied into the distillation column 11 and the circulating liquid come into gas-liquid contact and the mixed gas is cooled. ing. Except for this point, the distillation apparatus 8 is the same as the distillation apparatus 2 shown in FIG.

The reaction was carried out using methanol as the lower alcohol and a pentasil-type zeolite catalyst as the solid acid catalyst. The obtained mixed gas contains methanol at an average temperature of 390 ° C., about 61% by mass of methanol, about 4% by mass of inert gas containing water, and about 35% by mass of ε-caprolactam containing reaction byproducts. It was.
The mixed gas is supplied to the inside of the distillation column 11 set at a pressure of 97.3 kPa (730 Torr) and a temperature of 200 to 220 ° C., and with respect to ε-caprolactam containing a reaction by-product in the supplied mixed gas, An amount of liquid corresponding to about 7% by mass is extracted by LCV from the second discharge line 15 connected to the bottom of the column, and the remaining portion of the mixed gas is condensed at an average temperature of 184 ° C. Was extracted from the first discharge line 14 connected to the top of the column. Then, a circulating fluid having a flow rate of 2 × 10 ⁴ kg / m ² / h in terms of the flow rate of the passing liquid in the radial direction of the first packed bed 12 was supplied to the supply line 18. As the circulating liquid, a liquid obtained by filtering the solid content through a strainer provided as the second filtration unit 17 in the second discharge line 15 was extracted into the circulation line 158 and used.

When distillation and removal of impurities were performed for about 30 days under the above conditions, the strainer provided as the second filtration unit 17 was frequently clogged, the amount of liquid withdrawn from the second discharge line 15, and the LCV It was suggested that the valve opening became unstable, and solid content was adhered and blocked inside the distillation apparatus 8. This is because the solid content as impurities is insufficiently removed, and the polymerizable component is not washed away, but adheres to various places inside the distillation column 11 and polymerizes to increase the amount of the polymer. This is presumably because the total amount has increased significantly.

[Comparative Example 2]
Using the mixed gas obtained by the reaction for producing ε-caprolactam from cyclohexanone oxime using a solid acid catalyst in the presence of a lower alcohol, the target ε-caprolactam was obtained using the distillation apparatus shown in FIG. At the time of separation, impurities were removed by a conventional method. Specifically, it is as follows.

The distillation apparatus 9 shown in FIG. 4 is different from the distillation apparatus 8 shown in FIG. 3 in that the second cooler 150 (hereinafter referred to as the second cooler 150 in order to distinguish the first discharge line 14 in the middle of the supply line 18). And the circulation line 158 is connected to the supply line 18 on the distillation column 11 side (downstream side) with respect to the second cooler 150. It is composed. That is, in the distillation apparatus 9, the circulation line 158 is connected to the supply line 18 so that the cooled mixed gas before being supplied into the distillation column 11 and the circulating liquid come into contact with each other and the mixed gas is further cooled. It is connected. The second cooler 150 is the same as the first cooler 140. Except for these points, the distillation apparatus 9 is the same as the distillation apparatus 8 shown in FIG.

The reaction was carried out using methanol as the lower alcohol and a pentasil-type zeolite catalyst as the solid acid catalyst. The obtained mixed gas contains methanol at an average temperature of 387 ° C., about 61% by mass of methanol, about 3% by mass of inert gas containing water, and about 36% by mass of ε-caprolactam containing reaction byproducts. It was.
The mixed gas was cooled to an average of 320 ° C. with an indirect heat exchange type second cooler 150 using a high-temperature gas of 160 ° C., and further brought into contact with a circulating liquid described later. Next, the cooled mixed gas is supplied to the inside of the distillation column 11 set to a pressure of 97.3 kPa (730 Torr) and a temperature of 200 to 220 ° C., and ε-caprolactam containing reaction by-products in the supplied mixed gas is supplied. On the other hand, an amount of liquid corresponding to about 7% by mass is extracted by LCV from the second discharge line 15 connected to the bottom of the column, and the remaining amount of the mixed gas is condensed at an average temperature of 185 ° C. While refluxing inside the distillation column 11, it was extracted from the first discharge line 14 connected to the top of the column. Then, a circulating fluid having a flow rate of 2 × 10 ⁴ kg / m ² / h in terms of the flow rate of the passing liquid in the radial direction of the first packed bed 12 was supplied to the supply line 18. As the circulating liquid, the liquid obtained by filtering the solid content through the strainer provided as the second filtration unit 17 in the second discharge line 15 is extracted and used in the circulation line 158, and this circulating liquid is cooled by the cooler 150. In contact with the mixed gas.

When distillation and removal of impurities were performed for about 30 days under the above conditions, as in the case of Comparative Example 1, the strainer provided as the second filtration unit 17 was frequently clogged, and the second discharge line 15 Both the amount of liquid extracted from the liquid and the valve opening of the LCV became unstable, suggesting that solid content adhered and clogged inside the distillation apparatus 9.

[Example 2]
In the presence of a lower alcohol, a target gas ε-caprolactam is obtained using a mixed gas obtained by a reaction for producing ε-caprolactam from cyclohexanone oxime using a solid acid catalyst in a distillation apparatus shown in FIG. During the separation, impurities were removed. Specifically, it is as follows.
The reaction was carried out using methanol as the lower alcohol and a pentasil-type zeolite catalyst as the solid acid catalyst. The obtained mixed gas contains methanol at an average temperature of 376 ° C., about 61% by mass of methanol, about 8% by mass of inert gas containing water, and about 31% by mass of ε-caprolactam containing reaction byproducts. It was.
In the distillation apparatus 2, the first packing layer 12 has a specific surface area of 90 m ² / m ³ (“Melgrid 90X” manufactured by Sulzer) and the second packing layer 13 has a specific surface area. 125 m ² / m ³ ("Merapack 125X" manufactured by Sulzer) is used, the height H ₁ of the first packed bed 12 is set to 25% with respect to the height H ₀ of the distillation column 11, and the second The height H ₂ of the packed bed 13 was 20% with respect to the height H ₀ of the distillation column 11.
The mixed gas is supplied to the inside of the distillation column 11 set to a pressure of 96.1 kPa (721 Torr) and a temperature of 200 to 220 ° C., and with respect to ε-caprolactam containing a reaction by-product in the supplied mixed gas, An amount of liquid corresponding to about 8% by mass is extracted by LCV from the second discharge line 15 connected to the bottom of the column, and the remaining amount of the mixed gas is condensed at an average temperature of 185 ° C. Was extracted from the first discharge line 14 connected to the top of the column. The total flow rate of the circulating liquid and the reflux liquid in the radial direction of the first packed bed 12 was 2.9 × 10 ⁴ kg / m ² / h. As the circulating liquid, a liquid obtained by filtering the solid content through a strainer provided as the second filtration unit 17 in the second discharge line 15 was extracted into the circulation line 151 and used.

As a result, the amount of liquid withdrawn from the second discharge line 15 and the valve opening of the LCV are stabilized for 120 days or more, solid matter is hardly observed inside the distillation apparatus 2, and the blockage is not observed. It was confirmed that it was suppressed. The LCV valve opening data at this time is shown in FIG. In FIG. 5, the horizontal axis indicates the number of operating days of the distillation apparatus 2, and the vertical axis indicates the difference between the LCV valve opening degree at an arbitrary time after the start of operation of the distillation apparatus 2 and the LCV valve opening degree on the first operation day. ([LCV valve opening at an arbitrary time after the start of operation] − [LCV valve opening on the first day of operation]). Thus, the distillation apparatus 2 could be stably operated continuously.

[Example 3]
In the presence of a lower alcohol, a target gas ε-caprolactam is obtained using a mixed gas obtained by a reaction for producing ε-caprolactam from cyclohexanone oxime using a solid acid catalyst, using the distillation apparatus shown in FIG. During the separation, impurities were removed. Specifically, it is as follows.
The reaction was carried out using methanol as the lower alcohol and a pentasil-type zeolite catalyst as the solid acid catalyst. The obtained mixed gas contains methanol at an average temperature of 378 ° C., about 60% by mass of methanol, about 9% by mass of inert gas containing water, and about 31% by mass of ε-caprolactam containing reaction byproducts. It was.
In the distillation apparatus 1, as the fillers of the first packed bed 12 and the second packed bed 13, those having a specific surface area of 90 m ² / m ³ (“Melgrid 90X” manufactured by Sulzer) are used. the height _{H 1} of the filling layer 12 was 25% relative to the height _{H 0} of the distillation column 11, and 20% the height of _{H 2} second fill layer 13 relative to the height _{H 0} of the distillation column 11 did.
The mixed gas is supplied to the inside of the distillation column 11 set to a pressure of 92.0 kPa (690 Torr) and a temperature of 200 to 220 ° C., and with respect to ε-caprolactam containing a reaction by-product in the supplied mixed gas, An amount of liquid corresponding to about 9% by mass is extracted by LCV from the second discharge line 15 connected to the bottom of the column, and the remaining amount of the mixed gas is condensed at an average temperature of 184 ° C. Was extracted from the first discharge line 14 connected to the top of the column. The total flow rate of the circulating liquid and the reflux liquid in the radial direction of the first packed bed 12 is 3.1 × 10 ⁴ kg / m ² / h. As the circulating liquid, the liquid extracted from the second discharge line 15 is used. Extracted into the circulation line 151 and used.

As a result, the amount of liquid withdrawn from the second discharge line 15 and the valve opening of the LCV are stabilized for 150 days or more, and almost no solid content is observed inside the distillation apparatus 2, resulting in blockage. It was confirmed that it was suppressed. The LCV valve opening data at this time is shown in FIG. Thus, the distillation apparatus 2 could be stably operated continuously.

[Example 4]
In the presence of a lower alcohol, a target gas ε-caprolactam is obtained using a mixed gas obtained by a reaction for producing ε-caprolactam from cyclohexanone oxime using a solid acid catalyst in a distillation apparatus shown in FIG. During the separation, impurities were removed. Specifically, it is as follows.
The reaction was carried out using methanol as the lower alcohol and a pentasil-type zeolite catalyst as the solid acid catalyst. The obtained mixed gas contains methanol at an average temperature of 375 ° C., about 60% by mass of methanol, about 5% by mass of inert gas containing water, and about 35% by mass of ε-caprolactam containing reaction byproducts. It was.
In the distillation apparatus 2, those having a specific surface area of 257 m ² / m ³ are used as fillers for the first packed bed 12 and the second packed bed 13, respectively, and the height H ₁ of the first packed bed 12 is distilled. and 22% of the height _{H 0} of the tower 11, the height _{H 2} of the second fill layer 13 was 22% relative to the height _{H 0} of the distillation column 11.
The mixed gas is supplied to the inside of the distillation column 11 set at a pressure of 97.3 kPa (730 Torr) and a temperature of 200 to 220 ° C., and with respect to ε-caprolactam containing a reaction by-product in the supplied mixed gas, An amount of liquid corresponding to about 16% by mass is extracted by LCV from the second discharge line 15 connected to the bottom of the column, and the remaining amount of the mixed gas is condensed at an average temperature of 174 ° C. Was extracted from the first discharge line 14 connected to the top of the column. The total flow rate of the circulating liquid and the reflux liquid in the radial direction of the first packed bed 12 is 2.6 × 10 ⁴ kg / m ² / h. As the circulating liquid, the second filtration is performed in the second discharge line 15. A liquid obtained by filtering the solid content through a strainer provided as the section 17 was extracted into the circulation line 151 and used.

As a result, almost 80% of solid matter was not observed inside the distillation apparatus 2 over 80 days, and it was confirmed that the blockage was suppressed. During this time, a slight amount of solid matter adhered to the first packed bed 12 or the second packed bed 13 and collapsed, and the accompanying increase in the valve opening of the LCV occurred several times, but this hindered continuous operation of the distillation apparatus 2. There was no. The LCV valve opening data at this time is shown in FIG.

The present invention can be used in all purification processes in which a target product is separated from a mixed gas by distillation.

DESCRIPTION OF SYMBOLS 1, 2 ... Distillation apparatus, 11 ... Distillation tower, 111 ... Gas supply part, 12 ... 1st packed bed, 13 ... 2nd packed bed, 14 ... 1st Discharge line, 141 ... reflux line, 15 ... second discharge line, 151 ... circulation line, 16 ... first filtration part, 17 ... second filtration part, Z · ..Height direction of distillation tower

Claims

A method of removing impurities from the inside of a distillation column that performs distillation when a target product is separated by distillation from a mixed gas containing solids or components capable of forming solids by polymerization as impurities,
The distillation column is a packed bed filled with at least one layer provided in the height direction of the distillation column,
A gas supply unit provided in a lower part of the lowermost packed bed,
A first extraction site provided above the uppermost packed bed, and a second extraction site provided below the gas supply unit,
Supplying the mixed gas from the outside to the inside of the distillation column to a portion below the packed bed at the bottom;
Performing distillation in the distillation column, and extracting the gas containing the target product from the first extraction site provided above the packed bed at the top, to the outside of the distillation column;
Extracting the liquid containing the impurities from the second extraction site provided below the gas supply unit to the outside of the distillation column;
At least a part of the extracted liquid is supplied to the bottom packed bed as a circulating liquid from above, and trapped in the bottom packed bed by the circulating liquid and a reflux liquid from the upper part of the distillation column. Washing away the impurities, to obtain a liquid containing the impurities;
A method for removing the impurity, comprising extracting the liquid containing the impurity from the second extraction site to the outside of the distillation column.
The method for removing impurities according to claim 1, wherein a specific surface area of the filler in the lowermost packed bed is 70 to 300 m 2 / m 3 .
The total flow rate of the circulating liquid and the reflux liquid in an arbitrary plane perpendicular to the height direction of the distillation column of the lowermost packed bed is 1.5 × 10 4 to 1.2 × 10 5. The method for removing impurities according to claim 1, wherein the impurity is kg / m 2 / h.
The method further comprises cooling a part of the gas containing the target substance extracted from the first extraction site to condense into a liquid, and refluxing the liquid from the upper part of the distillation column. 4. A method for removing the impurity according to any one of 3 above.
The impurity according to any one of claims 1 to 4, further comprising filtering the condensed liquid to remove solids before refluxing the liquid from the top of the distillation column. How to remove.
Before supplying at least a part of the liquid extracted from the second extraction site to the bottom packed bed as a circulating liquid from above, the liquid extracted from the second extraction site is filtered. The method for removing impurities according to any one of claims 1 to 5, further comprising removing solids.
The mixed gas according to any one of claims 1 to 6, wherein the mixed gas is a gas obtained by a gas phase reaction in which ε-caprolactam is generated from cyclohexanone oxime using a solid acid catalyst in the presence of a lower alcohol. A method for removing impurities.