[DESCRIPTION]
[INVENTION TITLE]
METHOD FOR CONTINUOUS RECOVERING (METH)ACRYLIC ACID
AND APPARATUS FOR THE METHOD
5
[TECHNICAL FIELD]
The present invention relates to a method of continuous recovery of
(meth)acrylic acid and an apparatus for the method.
10 [BACKGROUND OF ART]
(Meth)acrylic acid is generally prepared by gas phase oxidation of
propane, propylene, (meth)acrolein, and the like in the presence of a catalyst.
For example, propane, propylene, and the like are converted to (meth)acrylic
acid through (meth)acrolein by gas phase oxidation in the presence of an
15 appropriate catalyst in a reactor, and a reaction product mixed gas including
(meth)acrylic acid, non-reacted propane or propylene, (meth)acrolein, an inert
gas, carbon dioxide, water vapor, and various organic by-products (acetic acid,
heavies, and the like) is obtained in the back end of the reactor.
The (meth)acrylic acid-containing mixed gas contacts an absorption
20 solvent including water in a (meth)acrylic acid absorption tower, and is
recovered as a (meth)acrylic acid aqueous solution. Further, (meth)acrylic
acid-stripped insoluble gas is recycled for a synthesis reaction of (meth)acrylic
acid, and a part thereof is incinerated, converted into harmless gas, and
discharged. The (meth)acrylic acid aqueous solution is extracted, distilled, and
25 purified to obtain (meth)acrylic acid.
Meanwhile, various methods of controlling process conditions or a
process sequence and the like to improve the recovery efficiency of
(meth)acrylic acid have been suggested. Representatively, as a method for
separating water and acetic acid from the (meth)acrylic acid aqueous solution
30 obtained in the (meth)acrylic acid absorption tower, an azeotropic distillation
method using a hydrophobic solvent in a distillation column is known. Further,
a method of supplying a (meth)acrylic acid aqueous solution to an extraction
column to obtain a (meth)acrylic acid extract solution with reduced water
content and a raffinate solution thereof, and distilling the extract, thereby
5 reducing energy consumption amount, is known.
Meanwhile, in the (meth)acrylic acid aqueous solution obtained in the
(meth)acrylic acid absorption tower, in addition to (meth)acrylic acid, various
organic by-products such as maleic acid, terephthalic acid, aldehyde, and
(meth)acrylic acid polymer are included. Further, due to the properties of a
10 continuous process for recovering (meth)acrylic acid, scum is formed due to
poorly water-soluble materials in the organic by-products. The scum
contaminates a (meth)acrylic acid recovery apparatus, and is particularly
accumulated in an extraction column to lower recovery efficiency of
(meth)acrylic acid, rendering long-time operation of the continuous process
15 impossible.
Due to the properties of a continuous process, a possibility that solvents
used in a (meth)acrylic acid extraction process and a distillation process or the
organic by-products may be introduced into a (meth)acrylic acid absorption
process or a (meth)acrylic acid synthesis process may not be excluded.
20 Particularly, if the solvents or organic by-products are introduced into a
(meth)acrylic acid synthesis process, a reactor and catalyst may be
contaminated to lower reaction efficiency, and a serious stability problem may
be caused.
25 [DETAILED DESCRIPTION OF THE INVENTION]
[Technical Problem]
It is an object of the present invention to provide a method of continuous
recovery of (meth)acrylic acid that may more effectively remove scum produced
in the continuous recovery process of (meth)acrylic acid, thus enabling stable
30 operation of the continuous process.
3
It is another object of the present invention to provide an apparatus that
can be used for the method of continuous recovery of (meth)acrylic acid.
[Technical Solution]
5 According to the present invention, provided is a method of continuous
recovery of (meth)acrylic acid including
an extraction process wherein a (meth)acrylic acid aqueous solution is
contacted with an extraction solvent in an extraction column to obtain a
(meth)acrylic acid extract solution and a raffinate solution, and a distilling
10 process wherein feed containing the (meth)acrylic acid extract is distilled to
obtain (meth)acrylic acid,
wherein the raffinate solution produced in the extraction process remains
stationary inside the extraction column and is then discharged, and the mass
flow of the raffinate solution is controlled such that the amount of raffinate
15 solution discharged from the extraction column is larger than the amount of
raffinate solution produced by extraction, and the raffinate solution discharged
from the extraction column is filtered to remove scum included in the raffinate
solution.
Herein, the filtering of the raffinate solution may be conducted using a
20 filter having pores with an average diameter of 50 on or less.
The extraction solvent may be a hydrophobic solvent having a boiling
point of 10 to 120 C .
Meanwhile, according to the present invention, the method of continuous
recovery of (meth)acrylic acid may include: an absorption process wherein a
25 mixed gas including (meth)acrylic acid, organic by-products, and vapor, which is
produced by a synthesis reaction of (meth)acrylic acid, is contacted with water
to obtain a (meth)acrylic acid aqueous solution; an extraction process wherein
the (meth)acrylic acid aqueous solution obtained through the absorption
process is contacted with an extraction solvent in an extraction column to obtain
30 a (meth)acrylic acid extract solution and a raffinate solution; and a distillation
process wherein a feed including the (meth)acrylic acid extract obtained through
the extraction process is distilled to obtain (meth)acrylic acid.
Further, according to the present invention, the method of continuous
recovery of (meth)acrylic acid may include: an absorption process wherein a
5 mixed gas including (meth)acrylic acid, organic by-products, and vapor, which is
produced by a synthesis reaction of (meth)acrylic acid, is contacted with water
to obtain a (meth)acrylic acid aqueous solution; an extraction process wherein a
part of the (meth)acrylic acid aqueous solution obtained through the absorption
process is contacted with an extraction solvent in an extraction column to obtain
10 a (meth)acrylic acid extract solution and a raffinate solution; and a distillation
process wherein a feed including the remainder of the (meth)acrylic acid
aqueous solution obtained through the absorption process and the (meth)acrylic
acid extract solution obtained through the extraction process is distilled to obtain
(meth)acrylic acid.
15 The filtrate from which scum has been removed through filtering of the
raffinate solution may be separated into an aqueous phase and an organic
phase by phase separation, the aqueous phase may be fed to the absorption
process, and the organic phase may be fed to the distillation process.
The filtrate from which scum has been removed through filtering of the
20 raffinate solution may be separated into an aqueous phase and an organic
phase by phase separation, the aqueous phase may be fed to the absorption
process, a part of the organic phase may be fed to the distillation process, and
the remainder of the organic phase is fed to the extraction process.
Meanwhile, according to the present invention, provided is an apparatus
25 for continuous recovery of (meth)acrylic acid, including:
a (meth)acrylic acid absorption tower (100) equipped with a mixed gas
inlet to which a mixed gas including (meth)acrylic acid, organic by-products, and
vapor, which is produced by a synthesis reaction of (meth)acrylic acid, is fed,
and an aqueous solution outlet from which a (meth)acrylic acid aqueous
30 solution obtained by contact of the mixed gas with water is discharged;
a (meth)acrylic acid extraction column (200) equipped with an aqueous
solution inlet connected with the aqueous solution outlet of the absorption tower
(100) through an aqueous solution transfer line (102), an extract outlet from
which (meth)acrylic acid extract solution obtained by contact of the introduced
5 (meth)acrylic acid aqueous solution with an extraction solvent is discharged,
and a raffinate outlet where the raffinate solution remains stationary and is then
discharged;
a distillation column (300) equipped with an extract inlet connected with
the extract outlet of the extraction column (200) through an extract transfer line
10 (203), and a (meth)acrylic acid outlet from which (meth)acrylic acid obtained by
distillation of the introduced extract solution is discharged; and
a filtering system (250) equipped with a raffinate inlet connected with the
raffinate outlet of the extraction column (200), a filter for filtering the introduced
raffinate solution, a scum outlet from which scum separated from the raffinate
15 solution by the filtering is discharged, and a filtrate outlet from which the filtrate
is discharged, wherein the extraction column (200) is operated while controlling
the mass flow of the raffinate solution such that the amount of raffinate solution
discharged from the extraction column is larger than the amount of raffinate
solution produced by extraction.
20 According to the present invention, the distillation column (300) is
equipped with an aqueous solution inlet connected with the aqueous solution
outlet of the absorption tower (100) through an aqueous solution transfer line
(103), an extract inlet connected with the extract outlet of the extraction column
(200) through an extract transfer line (203), and a (meth)acrylic acid outlet from
25 which (meth)acrylic acid obtained by distillation of a mixture of the introduced
aqueous solution and extract solution is discharged, wherein the apparatus may
be operated such that a part of the (meth)acrylic acid aqueous solution
discharged from the absorption tower(100) is fed to the extraction column (200),
and the remainder of the (meth)acrylic acid aqueous solution is fed to the
30 distillation column (300).
06
Herein, the filter of the filtering system (250) has pores with an average
diameter of 50 Lim or less.
The apparatus for continuous recovery of (meth)acrylic acid according to
the present invention may include a phase separation tank (350) equipped with
5 a filtrate inlet connected with the filtrate outlet of the filtering system (250)
through a filtrate transfer line (235), and an aqueous phase outlet and an
organic phase outlet from which an aqueous phase and an organic phase
obtained by phase separation of the filtrate are respectively discharged, wherein
the apparatus may be operated such that the aqueous phase is fed to the
10 absorption tower (100), and the organic phase is fed to the distillation column
(300).
In the apparatus for continuous recovery of (meth)acrylic acid according
to the present invention, the filtrate outlet of the filtering system (250) may be
connected with the upper part of the absorption tower (100) through a filtrate
15 transfer line.
[ADVANTAGEOUS EFFECTS]
The method of continuous recovery of (meth)acrylic acid according to the
present invention may effectively remove scum formed in the continuous
20 recovery process of (meth)acrylic acid, and simultaneously recover
(meth)acrylic acid with excellent efficiency, thus enabling more stable operation
of the continuous process.
[BRIEF DESCRIPTION OF THE DRAWINGS]
25 FIGS. 1 to 3 respectively schematically show the method and apparatus
for continuous recovery of (meth)acrylic acid according to the embodiments of
the invention.

1: (meth)acrylic acid containing mixed gas
30 100: (meth)acrylic acid absorption tower
102: (meth)acrylic acid aqueous solution transfer line
150: acetic acid absorption tower
200: (meth)acrylic acid extraction column
203: extract transfer line
5 250: filtering system
253, 201: filtrate transfer line
300: distillation column
350: phase separation tank
400: high boiling point by-product separation tower
CAA: crude (meth)acrylic acid
HPAA: high purity (meth)acrylic acid
[DETAILED DESCRIPTION OF THE EMBODIMENTS]
Hereinafter, a method of continuous recovery of (meth)acrylic acid and a
15 recovery apparatus according to the embodiments of the invention will be
explained.
First, the technical terms used herein are only to mention specific
embodiments, and are not intended to limit the invention. Further, singular
forms used herein include plural forms, unless they have clearly opposite
20 meanings. In addition, the meaning of 'comprising' as used herein embodies
specific a property, area, integer, step, operation, element, or component, and it
does not exclude the addition of other specific properties, areas, integers, steps,
operations, elements, or components.
Unless otherwise described, terms used herein are defined as follows.
25 The term '(meth)acrylic acid' generally refers to acrylic acid, methacrylic
acid, or a mixture thereof.
The term '(meth)acrylic acid-containing mixed gas' generally refers to a
mixed gas that may be produced when (meth)acrylic acid is prepared by gas
phase oxidation. As a non-limiting example, the (meth)acrylic acid-containing
30 mixed gas may be obtained by gas phase oxidation of at least one compound
selected from the group consisting of propane, propylene, butane, i-butylene,
t-butylene, and (meth)acrolein craw material compound') in the presence of a
catalyst, wherein the (meth)acrylic acid-containing mixed gas may include
(meth)acrylic acid, non-reacted raw material compounds, (meth)acrolein, an
5 inert gas, carbon monoxide, carbon dioxide, water vapor, and various organic
by-products (acetic acid, heavies, and the like), and the like. Further, poorly
water-soluble floating material formed by the organic by-products is referred to
as 'scum'.
The term '(meth)acrylic acid aqueous solution' refers to an aqueous
10 solution containing (meth)acrylic acid, and for example, it may be obtained by
contacting the (meth)acrylic acid-containing mixed gas with an absorption
solvent containing water.
The term 'feed' refers to a liquid mixture containing solute to be extracted,
and it may be a mixture of a solute that is soluble in an extraction solvent and
15 an inert material that is not soluble in an extraction solvent. Herein, if the
extraction solvent is added to the feed, the solute is dissolved in the extraction
solvent from the feed by mass transfer. Thereby, the extraction solvent in
which a significant amount of solutes is dissolved forms an extract solution, and
the feed that is deprived of a significant amount of solutes forms a raffinate
20 solution,
Meanwhile, in liquid-liquid extraction using agitated columns such as a
Karr-type column and a Scheibel-type column, a relatively light phase is fed to
the lower stage of the extraction column, and a relatively heavy phase is fed to
the upper stage of the extraction column. Extraction is progressed by the
25 contact of materials fed to the extraction column, to obtain a light phase and a
heavy phase of new compositions. The light phase of the new composition
obtained through the extraction process is obtained through the upper outlet of
the extraction column, and the heavy phase of the new composition is obtained
through the lower outlet of the extraction column.
30 In general, the heavy phase of the new composition obtained through the
Oct
extraction process, before being discharged to the lower outlet of the extraction
column, remains stationary at the lower part of the extraction column, and a part
thereof is discharged to the lower outlet of the extraction column. Herein, the
section of the extraction column in which the heavy phase remains stationary is
5 referred to as 'lower stationary section' (or 'stationary section of heavy phase').
For example, in the process of extracting (meth)acrylic acid included in a
(meth)acrylic acid aqueous solution using an extraction solvent, the
(meth)acrylic acid aqueous solution that is a relatively heavy phase is fed to the
upper stage of the extraction column, and the extraction solvent that is a
10 relatively light phase is fed to the lower stage of the extraction column. Further,
extraction is progressed by the contact thereof, and an extract solution in which
a significant amount of (meth)acrylic acid is dissolved and a raffinate solution
that is deprived of a significant amount of (meth)acrylic acid are obtained.
Herein, the extract solution that is in a relatively light phase is obtained
15 through the upper outlet of the extraction column, and the raffinate solution that
is in a relatively heavy phase is obtained through the lower outlet of the
extraction column. The raffinate solution, before being discharged to the lower
outlet of the extraction column, remains stationary at the lower section of the
extraction column, and a part thereof is discharged to the lower outlet of the
20 extraction column. The section of the extraction column in which the raffinate
solution remains stationary is referred to as 'lower stationary section' (or
'stationary section of raffinate solution'), and, in the raffinate solution, an organic
phase and an aqueous phase exist together, while the raffinate solution may be
separated into an organic phase and an aqueous phase and form an interface
25 at the lower stationary section according to process conditions.
Hereinafter, referring to the attached drawings, specific embodiments of
the invention will be explained in detail so that one of ordinary knowledge in the
art may easily practice it. However, the present invention may be embodied in
30 various forms, and is not limited to the examples.
010
In general, in the synthesis process of (meth)acrylic acid, various organic
by-products are produced together with (meth)acrylic acid, and scum is formed
by poorly water-soluble substances included in the organic by-products. Due
5 to the characteristic of a continuous process, scum contaminates the inside of
various apparatuses, thus making stable process operation impossible, and
lowers recovery rate of (meth)acrylic acid.
In this regard, the inventors have suggested a method of continuous
recovery of (meth)acrylic acid including an absorption process, an extraction
10 process, and a distillation process, wherein the lower discharged material
(raffinate solution) of the extraction column is filtered to remove scum, and the
filtrate is used as an absorption solvent of the absorption process.
However, according to the study results of the inventors, it was confirmed
that the previously suggested method can remove only a part of scum included
15 in the raffinate solution, and thus, as the operation time elapses, scum is
accumulated inside of the extraction column. Namely, scum is accumulated at
the stationary section of a raffinate solution of the lower part of the extraction
column (particularly, at the interface of the organic phase and the aqueous
phase formed at the stationary section) while forming a layer, and as the
20 operation time elapses, the thickness of accumulated scum increases from the
interface respectively in the direction of the organic phase and the direction of
the aqueous phase.
However, the previously suggested method selectively recovers and
filters only the aqueous phase formed at the stationary section of the lower part
25 of the extraction column, so as to use the filtrate as an absorption solvent of the
absorption process of (meth)acrylic acid. Thus, according to the previously
suggested method, among the scum accumulated at the interface, scum
accumulated close to the aqueous phase can be removed, but scum
accumulated close to the organic phase cannot be removed and remains.
30 Thus, as the operation time elapses, scum is accumulated, and finally,
•
shutdown of the extraction column becomes inevitable.
Further, due to the characteristic of a continuous process, a possibility
that solvents used in the (meth)acrylic acid extraction process and distillation
process or the organic by-products may be introduced in the (meth)acrylic acid
5 absorption process or (meth)acrylic acid synthesis process cannot be
eliminated. If the solvents or organic by-products are introduced in the
absorption process or (meth)acrylic acid synthesis process, an absorption tower,
a reactor, a reaction catalyst, and the like may be contaminated, recovery rate
of (meth)acrylic acid may decrease, and a serious safety problem may be
10 caused.
Thus, during the repeated studies of the inventors for ameliorating the
problems, it was confirmed that if an extraction column is controlled such that
an interface between an organic phase and an aqueous phase is not formed at
the stationary section of a raffinate solution of the lower part of the extraction
15 column (namely, among the organic phase and the aqueous phase, only a
relatively light phase exists at the stationary section of a raffinate solution),
accumulation of scum inside of the extraction column may be fundamentally
blocked. Particularly, the blocking of accumulation of scum inside of the
extraction column may be achieved by controlling the mass flow of the raffinate
20 solution such that the amount of raffinate solution discharged from the
extraction column ('discharged amount of raffinate solution') is larger than the
amount of raffinate solution produced by extraction (`production amount of
raffinate solution').
25 I. A method of continuous recovery of (meth)acrylic acid
According to one embodiment of the invention, a method of continuous
recovery of (meth)acrylic acid is provided, including
an extraction process wherein a (meth)acrylic acid aqueous solution is
contacted with an extraction solvent in an extraction column to obtain a
30 (meth)acrylic acid extract solution and a raffinate solution, and a distilling
process wherein a feed containing the (meth)acrylic acid extract solution is
distilled to obtain (meth)acrylic acid, wherein the raffinate solution produced in
the extraction process remains stationary inside the extraction column and then
is discharged, mass flow of the raffinate solution is controlled such that the
5 amount of raffinate solution discharged from the extraction column is larger than
the amount of raffinate solution produced by extraction, and the raffinate
solution discharged from the extraction column is filtered to remove scum
included in the raffinate solution.
Basically, the method of continuous recovery of (meth)acrylic acid
10 includes an extraction process of a (meth)acrylic acid aqueous solution and a
distillation process. Particularly, the method of continuous recovery of
(meth)acrylic acid may block accumulation of scum inside the extraction column,
by controlling the mass flow of the raffinate solution such that the amount of
raffinate solution discharged from the extraction column is larger than the
15 amount of raffinate solution produced by extraction in the extraction process.
Specifically, at a steady state where stable operation is conducted, a
raffinate solution that remains stationary at the stationary section of the lower
part of the extraction column exists while an aqueous phase and an organic
phase form an interface by phase separation. However, by controlling the
20 mass flow of the raffinate solution such that the interface between the aqueous
phase and the organic phase may not exist at the stationary section of the lower
part of the extraction column, accumulation of scum inside the extraction
column may be fundamentally blocked. Furthermore, by filtering the raffinate
solution discharged to the lower part of the extraction column, most scum
25 included in the raffinate solution may be more effectively removed, thus
enabling more stable operation of the continuous process.
According to one embodiment of the invention, the method of continuous
recovery of (meth)acrylic acid includes: an absorption process wherein a mixed
gas including (meth)acrylic acid, organic by-products, and vapor, which is
30 produced by a synthesis reaction of (meth)acrylic acid, is contacted with water
-013
to obtain a (meth)acrylic acid aqueous solution; an extraction process wherein
the (meth)acrylic acid aqueous solution obtained through the absorption
process is contacted with an extraction solvent in an extraction column to obtain
the (meth)acrylic acid extract solution and the raffinate solution; and a
5 distillation process wherein a feed including the (meth)acrylic acid extract
obtained through the extraction process is distilled to obtain (meth)acrylic acid.
The method of continuous recovery of (meth)acrylic acid according to the first
embodiment may be conducted using the apparatus shown in FIG. 1.
According to another embodiment of the invention, the method of
continuous recovery of (meth)acrylic acid may include: an absorption process
wherein a mixed gas including (meth)acrylic acid, organic by-products, and
vapor, which is produced by a synthesis reaction of (meth)acrylic acid, is
contacted with water to obtain a (meth)acrylic acid aqueous solution; an
extraction process wherein a part of the (meth)acrylic acid aqueous solution
15 obtained through the absorption process is contacted with an extraction solvent
in an extraction column to obtain a (meth)acrylic acid extract solution and a
raffinate solution; and a distillation process wherein a feed including the
remainder of the (meth)acrylic acid aqueous solution obtained through the
absorption process and the (meth)acrylic acid extract solution obtained through
20 the extraction process is distilled to obtain (meth)acrylic acid. The method of
continuous recovery of (meth)acrylic acid according to the second embodiment
may be conducted using the apparatus shown in FIG. 2.
Hereinafter, referring to FIG. 1 and FIG. 2, each process that can be
included in the embodiments of the invention will be explained.
25
(Absorption process)
An absorption process is a process for obtaining a (meth)acrylic acid
aqueous solution, and it may be conducted by contacting the (meth)acrylic
acid-containing mixed gas obtained through the synthesis reaction of
30 (meth)acrylic acid with an absorption solvent including water.
As a non-limiting example, the synthesis reaction of (meth)acrylic acid
may be conducted by the oxidation reaction of at least one compound selected
from the group consisting of propane, propylene, butane, isobutylene, and
(meth)acrolein in the presence of a gas phase catalyst. Herein, the gas phase
5 oxidation reaction may be progressed using a gas phase oxidation reactor of a
common structure and under common reaction conditions. As the catalyst for
the gas phase oxidation reaction, common catalysts may be used, and for
example, catalysts suggested in Korean Registered Patent No. 0349602 and
No. 037818, and the like may be used. In the (meth)acrylic acid-containing
10 mixed gas produced by the gas phase oxidation reaction, in addition to the
desired product (meth)acrylic acid, non-reacted raw material compounds,
intermediate (meth)acrolein, inert gas, carbon dioxide, vapor, and various
organic by-products (acetic acid, light ends, heavies, and the like) may be
included.
15 Further, referring to FIG. 1, the (meth)acrylic acid aqueous solution may
be obtained by feeding a (meth)acrylic acid-containing mixed gas (1) to a
(meth)acrylic acid absorption tower (100), to contact it with an absorption
solvent including water.
Herein, the kind of the (meth)acrylic acid absorption tower (100) may be
20 determined considering contact efficiency of the mixed gas (1) with the
absorption solvent, and the like. As non-limiting examples, the (meth)acrylic
acid absorption tower (100) may be a packed tower or a multistage tray tower.
Inside the packed tower, a filler such as a Raschig ring, a pall ring, a saddle,
gauze, structured packing, and the like may be applied.
25 Further, considering the efficiency of the absorption process, the mixed
gas (1) may be fed to the lower part of the absorption tower (100), and the
solvent including water may be fed to the upper part of the absorption tower
(100).
The absorption solvent may include water such as tap water, deionized
30 water, and the like, and it may include recycled process water introduced from
other processes (for example, an aqueous phase recycled from an extraction
process and/or a distillation process). In addition, in the absorption solvent, a
trace amount of organic by-products introduced from other processes (for
example, acetic acid) may be included. However, considering the absorption
5 efficiency of (meth)acrylic acid, it is preferable that organic by-products may be
included in the content of 15 wt% or less in the absorption solvent fed to the
absorption tower (100) (particularly, in the recycled process water).
The (meth)acrylic acid absorption tower (100) may be operated at an
internal pressure of 1 to 1.5 bar or 1 to 1.3 bar, and at an internal temperature
10 of 50 to 100 t or 50 to 80 °C , considering condensation conditions and
moisture content according to saturated water vapor pressure, and the like.
Meanwhile, in the absorption process, a (meth)acrylic acid aqueous
solution is discharged to the lower part of the (meth)acrylic acid absorption
tower (100), and (meth)acrylic acid-stripped non-condensable gas is discharged
15 to the upper part thereof. Herein, it may be favorable in terms of the efficiency
of the total process that 40 wt% or more, or 40 to 90 wt%, or 50 to 90 wt% of
(meth)acrylic acid may be included in the (meth)acrylic acid aqueous solution.
The obtained (meth)acrylic acid aqueous solution, as shown in FIG. 1,
may be fed to a (meth)acrylic acid extraction column (200) through an aqueous
20 solution transfer line (102). Further, the obtained (meth)acrylic acid aqueous
solution, as shown in FIG. 2, may be divided and fed to the (meth)acrylic acid
extraction column (200) and a distillation column (300) through aqueous
solution transfer lines (102 and 103).
As shown in FIG. 1, if an extraction process is introduced between a
25 (meth)acrylic acid absorption process and a distillation process, most
absorption solvent included in the (meth)acrylic acid aqueous solution may be
removed in the extraction process, thus lowering a treatment load of the
distillation process, and reducing energy consumption.
As shown in FIG. 2, if an extraction process is introduced between a
30 (meth)acrylic acid absorption process and a distillation process, and
simultaneously, a (meth)acrylic acid aqueous solution is divided and fed to the
extraction process and the distillation process, the distillation process may be
operated under more relaxed operation conditions than the process as shown in
FIG. 1.
5 Herein, the ratio of the (meth)acrylic acid aqueous solution divided and
fed to the extraction column (200) and the distillation column (300) may be
determined considering capacity of each column, treatment performance,
energy efficiency improvement effect, and the like. According to one
embodiment, it may be favorable for manifestation of the above explained effect
10 that 5 to 70 wt%, or 10 to 60 wt%, or 10 to 50 wt% of the (meth)acrylic acid
aqueous solution may be fed to the extraction column (200), and the remainder
may be fed to the distillation column (300).
Meanwhile, at least a part of the non-condensable gas discharged to the
upper part of the (meth)acrylic acid absorption tower(100) may be fed to a
15 process for recovering organic by-products (particularly, acetic acid) included in
the non-condensable gas, and the remainder may be fed to a waste gas
incinerator and discarded. Namely, according to one embodiment of the
invention, a process of contacting the non-condensable gas with an absorption
solvent to recover acetic acid included in the non-condensable gas may be
20 progressed.
The process of contacting the non-condensable gas with an absorption
solvent may be conducted in an acetic acid absorption tower (150). As a
non-limiting example, an absorption solvent (process water) for absorbing acetic
acid may be fed to the upper part of the acetic acid absorption tower (150), and
25 an aqueous solution containing acetic acid may be discharged to the lower part
of the acetic acid absorption tower (150). Further, the acetic acid-containing
aqueous solution may be fed to the upper part of the (meth)acrylic acid
absorption tower (100) and used as an absorption solvent, and acetic
acid-stripped non-condensable gas may be recycled to the synthesis process of
30 (meth)acrylic acid and reused.
Herein, for effective absorption of acetic acid, the acetic acid absorption
tower (150) may be operated at the internal pressure of 1 to 1.5 bar or 1 to 1.3
bar, and at the internal temperature of 50 to 100 C or 50 to 80 t In addition,
specific operation conditions of the acetic acid absorption tower (150) may
follow the disclosure of Korean Laid-Open Patent Publication No.
2009-0041355.
(Extraction process)
Meanwhile, an extraction process wherein a (meth)acrylic acid aqueous
10 solution is contacted with an extraction solvent in an extraction column to obtain
the (meth)acrylic acid extract solution and the raffinate solution is conducted.
Herein, the (meth)acrylic acid aqueous solution may be prepared by the
above-explained absorption process.
The extraction process may be conducted in a (meth)acrylic acid
15 extraction column (200). The (meth)acrylic acid aqueous solution fed to the
extraction column (200) contacts an extraction solvent, and is discharged as an
extract solution in which a significant amount of (meth)acrylic acid is dissolved
and a raffinate solution that is deprived of a significant amount of (meth)acrylic
acid, respectively. Herein, the extraction solution that is a relatively light phase
20 is obtained through the upper outlet of the extraction column (200), and the
raffinate solution that is a relatively heavy phase is obtained through the lower
outlet of the extraction column. Before the raffinate solution is discharged from
the extraction column (200), a certain amount thereof remains stationary at the
stationary section of the lower part of the extraction column, and a part thereof
25 is discharged to the lower outlet of the extraction column.
As such, by contacting the (meth)acrylic acid aqueous solution with an
extraction solvent in an extraction column (200) (namely, extraction with small
energy consumption compared to distillation), most water included in the
(meth)acrylic acid aqueous solution may be removed. Thereby, the treatment
30 load of the subsequent distillation process may be lowered, thus improving
4r1E
energy efficiency of the total process. Furthermore, by lowering the treatment
load of the distillation process, polymerization of (meth)acrylic acid that may be
generated during distillation may be minimized, to secure more improved
recovery efficiency of (meth)acrylic acid.
5 Meanwhile, in the case of a general extraction process, at the lower part
of the extraction column, a certain amount of a raffinate solution remains
stationary and exists while being phase separated into an organic phase and an
aqueous phase. Further, as the production amount of a raffinate solution by
the extraction and the discharged amount of a raffinate solution through the
10 lower outlet are maintained substantially the same, the amount of raffinate
solution that remains stationary at the lower part of the extraction column and
the interface between the organic phase and the aqueous phase are maintained
at a constant level.
However, as the operation of the extraction column is continued, scum is
15 accumulated at the interface between the organic phase and the aqueous
phase due to the raffinate solution that remains stationary at the lower part of
the extraction column. The scum is accumulated while forming a layer at the
interface between the organic phase and the aqueous phase formed at the
stationary section of the lower part of the extraction column, and as the
20 operation progresses, the thickness of accumulated scum increases from the
interface respectively toward the organic phase direction and the aqueous
phase direction. However, since the scum contaminates various apparatuses,
and particularly is accumulated at the extraction column to lower the recovery
rate of (meth)acrylic acid, it is preferable to remove the scum for stable process
25 operation.
With regard to removal of the scum, the inventors have suggested a
method of removing scum by filtering a raffinate solution discharged to the lower
part of the extraction column (200), and using the filtrate as an absorption
solvent of an absorption process. However, according to the previously
30 suggested method, among the scum accumulated at the interface between the
organic phase and the aqueous phase, the scum close to the aqueous phase
may be removed, but the scum close to the organic phase may not be removed
and remains inside the extraction column. Thus, in the case of the previously
suggested method, as the operation time elapses, scum is accumulated inside
5 the extraction column, and finally, shut-down of the extraction column becomes
inevitable.
However, in the method of continuous recovery of (meth)acrylic acid
according to one embodiment, by controlling such that an interface between an
organic phase and an aqueous phase may not be formed at the stationary
10 section of a raffinate solution of the lower part of the extraction column (200)
(namely, only a relatively light phase among the organic phase and the aqueous
phase may exist at the stationary section of a raffinate solution), accumulation
of scum inside the extraction column (200) may be fundamentally blocked.
Particularly, the blocking of the accumulation of scum inside the extraction
15 column (200) may be achieved by controlling the mass flow of a raffinate
solution such that the amount of a raffinate solution discharged from the
extraction column (discharged amount of a raffinate solution) is larger than the
amount of a raffinate solution produced by extraction (production amount of a
raffinate solution).
20 In addition, the method of continuous recovery of (meth)acrylic acid
according to one embodiment may effectively remove scum included in the
raffinate solution by filtering the raffinate solution discharged to the lower part of
the extraction column (200), thus enabling more stable operation of the
continuous process.
25 According to the embodiment of the invention, the production amount of
a raffinate solution and the discharged amount of a raffinate solution in the
extraction process may be controlled such that an interface between an organic
phase and an aqueous phase may not be formed at the stationary section of a
raffinate solution of the lower part of the extraction column (200), and only a
30 relatively light phase may exist. Namely, at the stationary section of a raffinate
solution of the lower part of the extraction column (200), the organic phase due
to the phase separation of the raffinate solution is formed above the aqueous
phase. Thus, the mass flow of the raffinate solution may be controlled such
that the aqueous phase at the stationary section of a raffinate solution may be
5 completely discharged, or a part of the organic phase may be discharged
together with the aqueous solution.
Further, by additionally introducing the extraction solvent in the amount
included in the raffinate solution discharged to the lower part of the extraction
column (200), the weight ratio of the (meth)acrylic acid aqueous solution and
10 the extraction solvent fed to the extraction column may be maintained at a
constant level, thus maintaining stable extraction efficiency.
In addition, filtering of the raffinate solution may be conducted using a
filter that can sufficiently remove scum included in the raffinate solution
discharged from the extraction column (200). Thus, the filtering method of the
15 raffinate solution and a filter used for the filtering are not specifically limited.
However, in order to obtain a substantial effect through filtering of the
raffinate solution, it is preferable that 80 wt% or more, or 90 wt% or more of
scum included in the raffinate solution may be removed by filtering. For this,
filtering of the raffinate solution may be conducted using a filter having pores
20 with an average diameter of 50 gm or less, or 0.1 to 30 gm, or 0.5 to 20 on, or
0.5 to 10 UM. Namely, for sufficient removal of scum included in the raffinate
solution, it is advantageous that a filter used for filtering may have pores with an
average diameter of 50 gm or less. However, considering filtering efficiency,
process flow, and the like, it is advantageous that the filter may have pores with
25 an average diameter of 0.1 jim or more.
Further, although most raffinate solution discharged to the lower part of
the extraction column (200) is in an aqueous phase, since an organic phase
may be partly included, it is preferable that a filter used for filtering may be
made of material having resistance to the extraction solvent, (meth)acrylic acid,
30 and the like. As a non-limiting example, the filter may be made of cotton or a
metal such as SUS (steel use stainless).
A filtering system (250) used for filtering of the raffinate solution may
include at least one filter fulfilling the above requirement. Preferably, the
filtering system (250) may have a structure wherein two or more filters having
5 different average diameters are connected in series.
Most of the filtrate obtained through filtering of the raffinate solution may
be in an aqueous phase, and an organic phase may be partly included. In
case most of the filtrate is an aqueous solution, the filtrate may be fed as an
absorption solvent of the above explained absorption process through a filtrate
10 transfer line (201), as shown in FIG. 3. However, in case an organic phase
unsuitable for use as an absorption solvent is included in the filtrate, it is
preferable that the filtrate may be fed to a separate phase separation tank (350)
through a filtrate transfer line (253) as shown in FIG. 1 or FIG. 2.
The aqueous phase obtained in the phase separation tank (350) may be
15 fed to the absorption process as an absorption solvent, and the organic phase
obtained in the phase separation tank (350) may be fed to the distillation
process as an azeotropic solvent. Further, a part of the organic phase
obtained in the phase separation tank (350) may be fed as an azeotropic
solvent of the distillation process, and the remainder of the organic phase may
20 be fed as an extraction solvent of the extraction process. However, in case an
organic phase is divided and fed to the absorption process and the extraction
process, it is a prerequisite that the same kind of solvent is used as the
azeotropic solvent of the absorption process and the extraction solvent of the
extraction process.
25 Meanwhile, it is preferable that the extraction solvent fed to the extraction
column (200) may have solubility and hydrophobicity to (meth)acrylic acid.
Further, considering the kind of solvent and the properties required in the
subsequent distillation process, it is preferable that the extraction solvent may
have a lower boiling point than (meth)acrylic acid. According to one
30 embodiment of the invention, it is advantageous for process operation that the
extraction solvent may be a hydrophobic solvent having a boiling point of
120 °C or less, or 10 to 120 t , or 50 to 120 °C.
Specifically, the extraction solvent may be at least one selected from the
group consisting of benzene, toluene, xylene, n-heptane, cycloheptane,
5
cycloheptene, 1-heptene, ethyl-benzene, methyl-cyclohexane, n-butyl acetate,
isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methyl
isobutyl ketone, 2-methyl-1-heptene, 6-methyl-1-heptene, 4-methyl-1-heptene,
2-ethyl-1-hexene, ethylcyclopentane, 2-methyl-1-hexene, 2,3-dimethylpentane,
5-methyl-1-hexene, and isopropyl-butyl-ether.
10
The feed amount of the extraction solvent may be controlled such that
the weight ratio of the (meth)acrylic acid aqueous solution and the extraction
solvent fed to the extraction column (200) may be 1:1 to 1:2, or 1:1.0 to 1:1.8, or
1:1.1 to 1:1.5, or 1:1.1 to 1:1.3. Namely, in order to secure appropriate
extraction efficiency, it is preferable that the weight ratio of the (meth)acrylic acid
15
aqueous solution and the extraction solvent fed to the extraction column (200) is
maintained at 1:1 or more. Further, if the weight ratio exceeds 1:2, although
extraction efficiency may be improved, loss of (meth)acrylic acid at a distillation
column (300) of the subsequent process may increase, and reflux of an
azeotropic solvent for blocking it may excessively increase, which is not
20 preferable.
According to one embodiment of the invention, it is favorable for securing
extraction efficiency that the temperature of the (meth)acrylic acid aqueous
solution fed to the extraction column (200) may be 10 to 70 °C .
As the extraction column (200), common extraction columns of a
25 liquid-liquid contact type may be used without specific limitations. As
non-limiting examples, the extraction column (200) may be a Karr-type
reciprocating plate column, a rotary-disk contactor, a Scheibel column, a Kuhni
column, a spray extraction tower, a packed extraction tower, a pulsed packed
column, and the like.
30 Through the extraction process, a (meth)acrylic acid extract solution is
W.:2 3
discharged to the upper part of the extraction column (200), and the discharged
extract solution is fed to a distillation column (300) through a transfer line (203).
Further, a raffinate solution is discharged to the lower part of the extraction
column (200), and the discharged raffinate solution is filtered through a filtering
5 system (250) as explained above.
Herein, in the extract solution, in addition to the desired compound
(meth)acrylic acid, an extraction solvent, water, and organic by-products may be
included, As non-limiting examples, at a steady state where stable operation is
conducted, 30 to 40 wt% of (meth)acrylic acid, 55 to 65 wt% of an extraction
10 solvent, 1 to 5 wt% of water, and a remaining amount of organic by-products
may be included in the extract solution. Namely, most water (for example, 85
wt% or more of water included in the aqueous solution) included in the
(meth)acrylic acid aqueous solution may be recovered as a raffinate solution
through the extraction process.
15
As most water is recovered from the extraction column (200), the
distillation load of the distillation column (300) may be reduced to lower energy
consumption. Further, since distillation conditions may be relaxed,
polymerization of (meth)acrylic acid may be minimized in the distillation process,
thus securing operation stability and improving recovery efficiency of
20 (meth)acrylic acid.
In the raffinate solution discharged from the extraction column(200),
non-extracted (meth)acrylic acid may be included. However, according to one
embodiment of the invention, 5 wt% or less, or 0.5 to 5 wt%, or 1 to 3 wt% of
(meth)acrylic acid may be included in the raffinate solution, thus minimizing the
25 loss of (meth)acrylic acid in the absorption process and extraction process,
(Distillation process)
A distillation process wherein a feed including the (meth)acrylic acid
extract solution is distilled to obtain (meth)acrylic acid is conducted.
30 According to one embodiment of the invention, the feed may be a
.rat
(meth)acrylic acid extract solution fed from the above-explained extraction
process. In this case, the feed is fed to the distillation column (300) through
the (meth)acrylic acid extract solution transfer line (203), as shown in FIG. 1.
Further, according to another embodiment, the feed may be a mixture of
5 the (meth)acrylic acid aqueous solution fed from the above-explained
absorption process and the (meth)acrylic acid extract solution fed from the
above-explained extraction process. In this case, the feed may be
simultaneously fed to the distillation column (300) through the (meth)acrylic acid
aqueous solution transfer line (103) and the (meth)acrylic acid extract solution
10 transfer line (203), as shown in FIG. 2.
Herein, for effective distillation, it is advantageous that a feed point to
which the feed is supplied may be a central part of the distillation column (300),
and preferably, it may be any one point corresponding to 40 to 60 % of total
stages from the uppermost stage of the distillation column (300).
15
As the feed supplied to the distillation column (300) contacts an
azeotropic solvent introduced into the upper part of the distillation column (300),
and is heated to an optimum temperature, distillation by evaporation and
condensation is achieved.
Herein, in order to effectively separate (meth)acrylic acid included in the
20 feed from the remaining components (for example, water, acetic acid, extraction
solvents, and the like), the distillation is preferably conducted by azeotropic
distillation.
A solvent used for the azeotropic distillation is preferably a hydrophobic
azeotropic solvent that may form an azeotrope with water and acetic acid, and
25 may not form an azeotrope with (meth)acrylic acid. Further, the hydrophobic
azeotropic solvent preferably has a lower boiling point than (meth)acrylic acid
(for example, a boiling point of 120 °C or less, or 10 to 120 C, or 50 to
120 °C).
Specifically, the hydrophobic azeotropic solvent may be at least one
30 selected from the group consisting of benzene, toluene, xylene, n-heptane,
cycloheptane, cycloheptene, 1-heptene, ethyl-benzene, methyl-cyclohexane,
n-butyl acetate, isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl
acetate, methyl isobutyl ketone, 2-methyl-1-heptene, 6-methyl-1-heptene,
4-methyl-1-heptene, 2-ethyl-1-hexene, ethylcyclopentane, 2-methyl-l-hexene,
5 2,3-dimethylpentane, 5-methyl-1-hexene, and isopropyl-butyl-ether,
Particularly, in case the extraction process is introduced as in FIG. 1 and
FIG. 2, considering production efficiency according to a continuous process, it is
preferable that the hydrophobic azeotropic solvent is identical to the extraction
solvent of the extraction process. As such, if the same kinds of solvents are
10 used in the extraction process and the distillation process, at least a part of the
solvent that is distilled in the distillation column (300) and recovered through the
phase separation tank (350) may be fed to the (meth)acrylic acid extraction
column (200) and reused as an extraction solvent.
Through the distillation process, among the feed, components other than
15 (meth)acrylic acid are discharged to the upper part of the distillation column
(300) together with the azeotropic solvent, and (meth)acrylic acid is discharged
to the lower part of the distillation column (300).
The upper discharged solution of the distillation column (300) may be fed
to the phase separation tank (350) and reused after a predetermined treatment.
20 Herein, the phase separation tank (350) is an apparatus for separating
immiscible liquids by gravity or centrifugal force and the like, wherein relatively
light liquid (for example, an organic phase) may be recovered from the upper
part of the phase separation tank (350), and relatively heavy liquid (for example,
an aqueous phase) may be recovered from the lower part of the phase
25 separation tank (350).
For example, the upper discharged solution of the distillation column
(300) may be separated into an organic phase including an azeotropic solvent
and an aqueous phase including water in the phase separation tank (350).
Further, the filtrate obtained through filtering of the raffinate solution in the
30 above-explained extraction process may be fed to the phase separation tank
aor
(350) through the filtrate transfer line (253) and phase separated together with
the upper discharged solution of the distillation column (300). The separated
organic phase may be fed to the upper part of the distillation column (300) and
used as an azeotropic solvent. Further, if necessary, at least a part of the
5 organic phase may be fed to the extraction column (200) and used as an
extraction solvent. In addition, at least a part of the aqueous phase separated
in the phase separation tank (350) may be fed to the (meth)acrylic acid
absorption tower (100) and used as an absorption solvent, and a part thereof
may be treated as waste water. Further, in the aqueous phase, acetic acid
10 may be partly included, and the concentration of acetic acid included in the
aqueous phase may vary according to the kind of azeotropic solvents and reflux
ratio and the like. As non-limiting examples, the concentration of acetic acid
included in the aqueous phase may be 1 to 50 wt%, or 2 to 40 wt%, or 3 to 30
wt%.
15 Meanwhile, while the (meth)acrylic acid aqueous solution passes through
the (meth)acrylic acid absorption tower (100), extraction column (200),
distillation column (300), and the like, at least a part of (meth)acrylic acid
included in the aqueous solution may form dimers or oligomers. To minimize
such polymerization of (meth)acrylic acid, common polymerization inhibitors
20 may be added to the distillation column (300).
In the lower discharged solution of the distillation column (300), in
addition to (meth)acrylic acid, heavies such as polymers of (meth)acrylic acid,
polymerization inhibitors, and the like may be included. Thus, if necessary, a
step of feeding the lower discharged solution of the distillation column (300) to a
25 high boiling point by-product separation tower (400) and separating heavies
included in the lower discharged solution may be further conducted. Further,
crude (meth)acrylic acid (CAA) recovered through the process may be passed
through an additional crystallization process and obtained as high purity
(meth)acrylic acid (HPAA). Herein, the heavies separation process and the
30 crystallization process and the like may be conducted under common conditions,
and the process conditions are not specifically limited.
Meanwhile, in the method of continuous recovery of (meth)acrylic acid,
each above-explained step may be conducted organically and continuously.
Further, in addition to the above explained steps, processes that can be
5 commonly conducted before or after or simultaneously with each step may be
further included.
II. An apparatus for continuous recovery of (meth)acrylic acid
According to another embodiment of the invention, as shown in FIG_ 1,
10 an apparatus for continuous recovery of (meth)acrylic acid is provided,
including:
a (meth)acrylic acid absorption tower (100) equipped with a mixed gas
inlet to which a mixed gas including (meth)acrylic acid, organic by-products, and
vapor, which is produced by a synthesis reaction of (meth)acrylic acid, is fed,
15 and an aqueous solution outlet from which a (meth)acrylic acid aqueous
solution obtained by contact of the mixed gas with water is discharged;
a (meth)acrylic acid extraction column (200) equipped with an aqueous
solution inlet connected with the aqueous solution outlet of the absorption tower
(100) through an aqueous solution transfer line (102), an extract outlet from
20 which the (meth)acrylic acid extract obtained by contact of the introduced
(meth)acrylic acid aqueous solution with an extraction solvent is discharged,
and a raffinate outlet where the raffinate solution remains stationary and then is
discharged;
a distillation column (300) equipped with an extract inlet connected with
25 the extract outlet of the extraction column (200) through an extract transfer line
(203), and a (meth)acrylic acid outlet from which (meth)acrylic acid obtained by
distillation of the introduced extract solution is discharged; and
a filtering system (250) equipped with a raffinate inlet connected with the
raffinate outlet of the extraction column (200), a filter for filtering the introduced
30 raffinate solution, a scum outlet from which scum separated from the raffinate
solution by the filtering is discharged, and a filtrate outlet from which the filtrate
is discharged,
wherein the extraction column (200) is operated while controlling the
mass flow of the raffinate solution such that the amount of raffinate solution
5 discharged from the extraction column is larger than the amount of raffinate
solution produced by extraction.
According to yet another embodiment, as shown in FIG. 2, the distillation
column (300) is equipped with an aqueous solution inlet connected with the
aqueous solution outlet of the absorption tower (100) through an aqueous
10 solution transfer line (103), an extract inlet connected with the extract outlet of
the extraction column (200) through an extract transfer line (203), and a
(meth)acrylic acid outlet from which (meth)acrylic acid obtained by distillation of
a mixture of the introduced aqueous solution and extract is discharged, and the
apparatus may be operated such that a part of the (meth)acrylic acid aqueous
15 solution discharged from the absorption tower (100) is fed to the extraction
column (200), while the remainder of the (meth)acrylic acid aqueous solution is
fed to the distillation column (300).
In the apparatus according to the above embodiments, the (meth)acrylic
acid absorption tower (100) may be a packed tower or a multistage tray tower
20 for improving contact efficiency of the (meth)acrylic acid-containing mixed gas
(1) with an absorption solvent including water. Inside of the packed tower,
fillers such as a Raschig ring, a pall ring, a saddle, gauze, structured packing,
and the like may be applied.
Further, as the (meth)acrylic acid extraction column (200), common
25 extraction columns of a liquid-liquid contact type may be used without specific
limitation. As non-limiting examples, the extraction column may be a Karr-type
reciprocating plate column, a rotary-disk contactor), a Scheibel column, a Kuhni
column, a spray extraction column, a packed extraction tower, a pulsed packed
column, and the like.
30 Particularly, the filter of the filtering system (250) preferably has
performance for sufficiently removing scum included in the raffinate solution
discharged from the extraction column (200). Specifically, the filter may have
pores with an average diameter of 50 gm or less, or 0.1 to 30 um, or 0.5 to 20
um, or 0.5 to 10 gm. Further, the filter is preferably made of a material having
5 resistance to the extraction solvent and (meth)acrylic acid and the like, and as
non-limiting examples, it may be made of cotton or a metal such as SUS (steel
use stainless). In addition, the filtering system (250) used for filtering of the
raffinate solution may include at least one filter fulfilling the above requirements.
Preferably, the filtering system (250) may have a structure wherein two or more
10 filters having pores with different average diameters are connected in series.
Meanwhile, the apparatus according to the above embodiments may
include a phase separation tank (350) equipped with a filtrate inlet connected
with the filtrate outlet of the filtering system (250) through a filtrate transfer line
(253), and an aqueous phase outlet and an organic phase outlet from which an
15 aqueous phase and an organic phase obtained by phase separation of the
filtrate are respectively discharged. Herein, the apparatus may be operated
such that the aqueous phase discharged from the phase separation tank (350)
is fed to the absorption tower (100) and the organic phase is fed to the
distillation column (300). Further, if necessary, the apparatus may be operated
20 such that a part of the organic phase may be fed to the distillation column (300),
and the remainder of the organic phase may be fed to the extraction column
(200).
When most filtrate obtained in the filtering system (250) is in an aqueous
phase, the filtrate outlet of the filtering system (250) may be connected to the
25 upper part of the absorption tower (100) through a filtrate transfer line (201).
Further, the distillation column (300) may be a packed column including
fillers inside or a multistage column, and preferably a sieve tray column, a dual
flow tray column, and the like.
In addition, the acetic acid absorption tower (150), (meth)acrylic acid
30 aqueous solution transfer line (102), extract solution transfer line (203), phase
separation tank (350), high boiling point separation tower (400), and the like
may have constructions common in the technical field to which the invention
pertains.
5 Hereinafter, preferable examples are presented to aid in understanding
of the invention. However, these examples are only to illustrate the invention,
and the scope of the invention is not limited thereto.
Comparative Example 1
10 A Karr-type extraction column with an extraction part of a total of 52
stages and a total height of about 3 m was prepared. In the extraction column,
the inner diameter of the column corresponding to the 1st stage to the 6th stage
(namely, the upper 6 stages including the uppermost stage) was controlled to
about 45 mm, and the inner diameter of the column corresponding to the
15 remaining 7th stage to 50th stage was controlled to about 22 mm. Among the
porous plates positioned at each stage of the extraction column and repeatedly
moving up and down, the aperture ratios of the porous plates positioned at the
1st stage to the 6th stage were controlled to about 50 %, and the aperture ratio of
the porous plates positioned at the 7th stage to the 50th stage were controlled to
20 about 28.3 %.
To the feed inlet of the extraction column, an acrylic acid aqueous
solution (acrylic acid concentration: about 65.5 wt%, acetic acid concentration:
about 2.25 wt%) was fed, and toluene was fed to the extraction solvent inlet of
the extraction column. Herein, the weight ratio of the acrylic acid aqueous
25 solution to toluene fed to the extraction column was fixed to about 1:1.3.
At the lower stage of the extraction column from which the raffinate
solution is discharged, a filtering system equipped with a cartridge type of filter
having pores with an average diameter of about 10 /fin was installed, and scum
included in the raffinate solution discharged to the lower part of the extraction
30 column was removed using the same.
Under maximum mechanical reciprocating speed of the porous plate
(namely, maximum rpm immediately before generating flooding) enabling
realization of a maximum acrylic acid extraction rate in the extraction column,
the acrylic acid concentration in the raffinate solution was analyzed.
5 Herein, the input of the acrylic acid aqueous solution was controlled to
91.3 g/min, and the input of toluene was controlled to 115.8 g/min. Further, the
discharge mass flow of the raffinate solution was controlled such that the
interface of an organic phase and an aqueous phase formed by the raffinate
solution that remains stationary at the lower part of the extraction column may
10 be maintained at a constant level.
At the beginning of the operation, the mass flow of the raffinate solution
was maintained at about 25.0 g/min and the interface was maintained at a
constant level, but due to interface management failure during continued
operation, the raffinate solution was discharged at about 30.6 g/min, which
15 corresponds to about a 20 % increase. Herein, in the raffinate solution in
which an organic phase and an aqueous phase exist together in the emulsion
form, acrylic acid concentration was about 1.17 wt%, and toluene concentration
was about 13.6 wt%. The raffinate solution was inappropriate for use as an
absorption solvent of the absorption process due to a high toluene
20 concentration.
Comparative Example 2
To the feed inlet of an extraction column identical to that of Comparative
Example 1, an acrylic acid aqueous solution (acrylic acid concentration: about
25 65.5 wt%, acetic acid concentration: about 2.25 wt%) was fed, and toluene was
fed to the extraction solvent inlet of the extraction column. Herein, the weight
ratio of the acrylic acid aqueous solution to toluene that were fed to the
extraction column was fixed to about 1:1.3.
At the lower stage of the extraction column from which the raffinate
30 solution is discharged, a filtering system equipped with a cartridge type of filter
having pores with an average diameter of about 10 um was installed, and scum
included in the raffinate solution discharged to the lower part of the extraction
column was removed using the same.
Herein, the input of the acrylic acid aqueous solution was controlled to
5 91.3 g/min, and the input of toluene was controlled to 118.1 g/min. Further, the
discharge mass flow of the raffinate solution was maintained at about 25.0
g/min so that an interface between an organic phase and an aqueous phase
formed by the raffinate solution that remains stationary at the lower part of the
extraction column may be maintained at a constant level, wherein the discharge
10 mass flow of the extract solution was about 184.4 g/min.
Under maximum mechanical reciprocating speed of the porous plate
(namely, maximum rpm immediately before generating flooding) enabling
realization of a maximum acrylic acid extraction rate in the extraction column,
acrylic acid concentration in the raffinate solution was analyzed.
15 As the result, at the beginning of the operation, in a raffinate solution
consisting of an aqueous phase, acrylic acid concentration was about 1.45 wt%,
and toluene concentration was 720 ppm. Further, the mass flow of acrylic acid
leaving as a raffinate solution was calculated as about 0.362 g/min.
However, at the stationary section of a raffinate solution of the lower part
20 of the extraction column, scum was continuously accumulated at the interface
between an organic phase and an aqueous phase due to phase separation of
the raffinate solution. Further, as the operation of the extraction column was
continued, scum was continuously accumulated toward the organic phase
(namely, internal direction of the extraction column) at the interface between the
25 organic phase and the aqueous phase at the stationary section of a raffinate
solution of the lower part of the extraction column. Due to the accumulation of
scum, the extraction column was contaminated, extraction efficiency gradually
decreased, and finally, operation of the extraction column was stopped.
30 Example 1
ae. 3_3
A Karr type of extraction column with an extraction part of a total of 52
stages and a total height of about 3 m was prepared. In the extraction column,
the inner diameter of the column corresponding to the 1st stage to the 6th stage
(namely, the upper 6 stages including the uppermost stage) was controlled to
5 about 45 mm, and the inner diameter of the column corresponding to the
remaining 7th stage to 50th stage was controlled to about 22 mm. Among the
porous plates positioned at each stage of the extraction column and repeatedly
moving up and down, the aperture ratios of the porous plates positioned at the
1st stage to the 6th stage were controlled to about 50 °A), and the aperture ratio of
10 the porous plates positioned at the 7th stage to the 50th stage were controlled to
about 28.3 %.
To the feed inlet of the extraction column, an acrylic acid aqueous
solution (acrylic acid concentration: about 65.5 wt%, acetic acid concentration:
about 2.25 wt%) was fed, and toluene was fed to the extraction solvent inlet of
15 the extraction column. Herein, the weight ratio of the acrylic acid aqueous
solution to toluene that were fed to the extraction column was fixed to about
1:1.3.
At the lower stage of the extraction column from which the raffinate
solution is discharged, a filtering system equipped with a cartridge type of filter
20 having pores with an average diameter of about 10 gm was installed, and scum
included in the raffinate solution discharged to the lower part of the extraction
column was removed using the same.
Herein, the input of the acrylic acid aqueous solution was controlled to
91.3 g/min, and the input of toluene was controlled to 115.8 g/min. Further, the
25 mass flow of the raffinate solution was maintained at about 30.6 g/min so that
an interface between an organic phase and an aqueous phase may not exist by
the raffinate solution that remains stationary at the lower part of the extraction
column.
The raffinate solution obtained through the lower outlet of the extraction
30 column was passed through the filtering system to remove scum. In the filtrate
in which an organic phase and an aqueous phase exist together in the emulsion
form, acrylic acid concentration was about 1.17 wt%, and toluene concentration
was about 13.6 wt%.
Further, the filtrate was fed to a phase separation tank, and
5 phase-separated into an organic phase and an aqueous phase together with
distillate of a distillation column. Herein, in the aqueous phase obtained from
the separation tank, about 0.72 wt% of acrylic acid and about 730 ppm of
toluene were included. Namely, it was confirmed that in the aqueous phase
obtained in the phase separation tank, most toluene was removed compared to
io
the raffinate solution obtained in the extraction column of Comparative Example
1, and acrylic acid was partly removed, and thus the aqueous phase was
sufficient for use as an absorption solvent of an acrylic acid absorption process.
Example 2
15
A Karr type of extraction column with an extraction part of a total of 52
stages and a total height of about 3 m was prepared. In the extraction column,
the inner diameter of the column corresponding to the 1st stage to the 6th stage
(namely, the upper 6 stages including the uppermost stage) was controlled to
about 45 mm, and the inner diameter of the column corresponding to the
20 remaining 7th stage to 50th stage was controlled to about 22 mm. Among the
porous plates positioned at each stage of the extraction column and repeatedly
moving up and down, the aperture ratios of the porous plates positioned at the
1st stage to the 6th stage were controlled to about 50 %, and the aperture ratio of
the porous plates positioned at the 7th stage to the 50th stage were controlled to
25 about 28.3 %.
To the feed inlet of the extraction column, an acrylic acid aqueous
solution (acrylic acid concentration: about 65.5 wt%, acetic acid concentration:
about 2.25 wt%) was fed, and toluene was fed to the extraction solvent inlet of
the extraction column. Herein, the weight ratio of the acrylic acid aqueous
30 solution to toluene that were fed to the extraction column was fixed to about
• MS • I .•M •
1:1.3.
At the lower stage of the extraction column from which the raffinate
solution is discharged, a filtering system equipped with a cartridge type of filter
having pores with an average diameter of about 10 gm was installed, and scum
5 included in the raffinate solution discharged to the lower part of the extraction
column was removed using the same.
Herein, the input of the acrylic acid aqueous solution was controlled to
91.2 g/min, and the input of toluene was controlled to 123.6 g/min, Further, the
mass flow of the raffinate solution was maintained at about 30.6 g/min so that
10 an interface between an organic phase and an aqueous phase may not exist by
the raffinate solution that remains stationary at the lower part of the extraction
column, wherein the mass flow of an extract solution was 184.2 g/min.
The raffinate solution obtained through the, lower outlet of the extraction
column was passed through the filtering system to remove scum, and the filtrate
15 was fed to a phase separation tank and separated into an organic phase and an
aqueous phase. Herein, in the aqueous phase separated from the filtrate,
about 1.34 wt% of acrylic acid and about 750 ppm of toluene were included,
and in the organic phase separated from the filtrate, about 0.1 wt% of acrylic
acid was included. Further, total mass flow of acrylic acid in the filtrate was
20 calculated as about 0.359 g/min.
This result shows that extraction efficiency of an equivalent level to the
initial extraction efficiency of the extraction column according to Comparative
Example 2 is maintained. Further, as the apparatus was operated so that an
interface between an organic phase and an aqueous phase may not exist at the
25 stationary section of a raffinate solution of the lower part of the extraction
column, the concentration of acrylic acid included in the raffinate solution did not
increase even after operation for 7 or more days, enabling stable operation
without accumulation of scum inside of the extraction column. Further, if
differential pressure of the filtering system reaches a limit pressure, a filter is
30 replaced or washed and reused, thereby enabling more stable long time
operation of the extraction column.

We Claim:
[Claim 1]
A method of continuous recovery of (meth)acrylic acid, comprising
5 an extraction process wherein a (meth)acrylic acid aqueous solution is
contacted with an extraction solvent in an extraction column to obtain a
(meth)acrylic acid extract solution and a raffinate solution, and a distilling
process wherein a feed containing the (meth)acrylic acid extract is distilled to
obtain (meth)acrylic acid,
10 wherein the raffinate solution produced in the extraction process remains
stationary inside the extraction column and then is discharged, and a mass flow
of the raffinate solution is controlled such that an amount of raffinate solution
discharged from the extraction column is larger than an amount of raffinate
solution produced by extraction, and the raffinate solution discharged from the
is extraction column is filtered to remove scum included in the raffinate solution.
[Claim 2]
The method according to claim 1, wherein the filtering of the raffinate
solution is conducted using a filter having pores with an average diameter of 50
20 UM or less.
[Claim 3]
The method according to claim 1, wherein the extraction solvent is a
hydrophobic solvent having a boiling point of 10 to 120 t
25
[Claim 4]
The method according to claim 1, wherein the method comprises:
an absorption process wherein a mixed gas comprising (meth)acrylic
acid, organic by-products, and vapor, which is produced by a synthesis reaction
30 of (meth)acrylic acid, is contacted with water to obtain a (meth)acrylic acid
3""
aqueous solution;
an extraction process wherein the (meth)acrylic acid aqueous solution
obtained through the absorption process is contacted with an extraction solvent
in an extraction column to obtain a (meth)acrylic acid extract solution and a
5 raffinate solution; and
a distillation process wherein a feed including the (meth)acrylic acid
extract obtained through the extraction process is distilled to obtain
(meth)acrylic acid.
10 [Claim 5]
The method according to claim 4, wherein the method comprises:
an absorption process wherein a mixed gas comprising (meth)acrylic
acid, organic by-products, and vapor, which is produced by a synthesis reaction
of (meth)acrylic acid, is contacted with water to obtain a (meth)acrylic acid
is aqueous solution;
an extraction process wherein a part of the (meth)acrylic acid aqueous
solution obtained through the absorption process is contacted with an extraction
solvent in an extraction column to obtain a (meth)acrylic acid extract solution
and a raffinate solution thereof; and
20 a distillation process wherein a feed including the remainder of the
(meth)acrylic acid aqueous solution obtained through the absorption process
and the (meth)acrylic acid extract obtained through the extraction process is
distilled to obtain (meth)acrylic acid.
25 [Claim 6]
The method according to claim 4, wherein a filtrate from which scum has
been removed through filtering of the raffinate solution is separated into an
aqueous phase and an organic phase by phase separation, and
the aqueous phase is fed to the absorption process and the organic
30 phase is fed to the distillation process.
4e-31
[Claim 7]
The method according to claim 4, wherein a filtrate from which scum has
been removed through filtering of the raffinate solution is separated into an
5 aqueous phase and an organic phase by phase separation, and
the aqueous phase is fed to the absorption process, a part of the organic
phase is fed to the distillation process, and the remainder of the organic phase
is fed to the extraction process.
10 [Claim 8]
The method for continuous recovery of (meth)acrylic acid according to
claim 4, wherein the synthesis reaction of (meth)acrylic acid is an oxidation
reaction of at least one compound selected from the group consisting of
propane, propylene, butane, isobutylene, and (meth)acrolein in the presence of
15 a gas phase catalyst.
[Claim 9]
An apparatus for continuous recovery of (meth)acrylic acid, comprising:
a (meth)acrylic acid absorption tower equipped with a mixed gas inlet to
20 which a mixed gas including (meth)acrylic acid, organic by-products, and vapor,
which is produced by a synthesis reaction of (meth)acrylic acid, is fed, and an
aqueous solution outlet from which a (meth)acrylic acid aqueous solution
obtained by contact of the mixed gas with water is discharged;
a (meth)acrylic acid extraction column equipped with an aqueous
25 solution inlet connected with the aqueous solution outlet of the absorption tower
through an aqueous solution transfer line, an extract outlet from which the
(meth)acrylic acid extract obtained by contact of the introduced (meth)acrylic
acid aqueous solution with an extraction solvent is discharged, and a raffinate
outlet where the raffinate solution remains stationary and then is discharged;
30 a distillation column equipped with an extract inlet connected with the
extract outlet of the extraction column through an extract transfer line, and a
(meth)acrylic acid outlet from which (meth)acrylic acid obtained by distillation of
the introduced extract solution is discharged; and
a filtering system equipped with a raffinate inlet connected with the
5 raffinate outlet of the extraction column, a filter for filtering the introduced
raffinate solution, a scum outlet from which scum separated from the raffinate
solution by filtering is discharged, and a filtrate outlet from which the filtrate is
discharged,
wherein the apparatus is operated while controlling the mass flow of the
to raffinate solution such that the amount of raffinate solution discharged from the
extraction column is larger than the amount of raffinate solution produced by
extraction.
(Claim 101
15 The apparatus for continuous recovery of (meth)acrylic acid according to
claim 9, wherein the distillation column is equipped with an aqueous solution
inlet connected with the aqueous solution outlet of the absorption tower through
an aqueous solution transfer line, an extract inlet connected with the extract
outlet of the extraction column through an extract transfer line, and a
20 (meth)acrylic acid outlet from which (meth)acrylic acid obtained by distillation of
a mixture of the introduced aqueous solution and extract is discharged, and
the apparatus is operated such that a part of the (meth)acrylic acid
aqueous solution discharged from the absorption tower is fed to the extraction
column, and the remainder of the (meth)acrylic acid aqueous solution is fed to
25 the distillation column.
(Claim 111
The apparatus for continuous recovery of (meth)acrylic acid according to
claim 9, wherein the filter of the filtering system has pores with an average
30 diameter of 50 gm or less.
[Claim 12]
The apparatus for continuous recovery of (meth)acrylic acid according to
claim 9, wherein the apparatus comprises a phase separation tank equipped
5 with a filtrate inlet connected with the filtrate outlet of the filtering system
through a filtrate transfer line, and an aqueous phase outlet and an organic
phase outlet from which an aqueous phase and an organic phase obtained by
phase separation of the filtrate are respectively discharged, and
the apparatus is operated such that the aqueous phase is fed to the
10 absorption tower and the organic phase is fed to the distillation column.
[Claim 13]
The apparatus for continuous recovery of (meth)acrylic acid according to
claim 9, wherein the filtrate outlet of the filtering system is connected with the
15
upper part of the absorption tower through a filtrate transfer line.