DESCRIPTION】
【INVENTION TITLE】
PROCESS FOR CONTINUOUS RECOVERING (METH)ACRYLIC ACID
AND APPARATUS FOR THE PROCESS
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.
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 obtained in the (meth)acrylic
30 acid absorption tower, an azeotropic distillation method using a hydrophobic
2
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 reducing energy consumption
5 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. In addition, 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 decrease recovery efficiency of
(meth)acrylic acid.
15
【DETAILED DESCRIPTION OF THE INVENTION】
【Technical Problem】
It is an object of the present invention to provide a method for continuous
recovery of (meth)acrylic acid that may more effectively remove scum produced
20 in the continuous recovery process of (meth)acrylic acid, thus enabling stable
operation of the continuous process.
It is another object of the present invention to provide an apparatus that
can be used for the method for continuous recovery of (meth)acrylic acid.
25 【Technical Solution】
According to the present 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 through the upper outlet of the extraction
3
column, and obtain a raffinate solution that passes through the lower stationary
section of the extraction column through the lower outlet; and a distillation
process wherein a feed containing the (meth)acrylic acid extract solution is
distilled to obtain (meth)acrylic acid,
wherein the raffinate solution containing scum that 5 is accumulated at the
interface between an organic phase and an aqueous phase formed by phase
separation of the raffinate solution in the lower stationary section of the
extraction column is discharged through a side stream equipped at any one
point of the lower stationary section and filtered, and the filtrate is inflowed
10 through a side stream equipped at any other point of the lower stationary
section.
The extraction process may be conducted such that the interface
between an organic phase and an aqueous phase by phase separation of the
raffinate solution may be formed at a location of the side stream equipped at
15 any one point of the lower stationary section of the extraction column.
The discharging of the raffinate solution containing scum and the filtering
through the side streams of the extraction column may be conducted
continuously or discontinuously.
The outflow direction of the raffinate solution containing scum through
20 the side stream of the extraction column and the inflow direction of the filtrate
through the side stream of the extraction column may be opposite to each other.
The filtering may be conducted using a filter having pores with an
average diameter of 50 μm or less.
Besides the filtering through the side stream of the extraction column, a
25 step of filtering a raffinate solution obtained through the lower outlet of the
extraction column may be further conducted.
Meanwhile, according to the present invention, an apparatus for
continuous recovery of (meth)acrylic acid is provided, including:
a (meth)acrylic acid absorption tower (100) equipped with a mixed gas
30 inlet into which a mixed gas including (meth)acrylic acid, organic by-products,
4
and vapor, which is produced by a synthesis reaction of (meth)acrylic acid, is
fed, and a (meth)acrylic acid aqueous solution outlet from which a (meth)acrylic
acid aqueous solution obtained by contact of the mixed gas with an absorption
solvent including water is discharged;
a (meth)acrylic acid extraction column (5 200) equipped with a
(meth)acrylic acid aqueous solution inlet connected with the (meth)acrylic acid
aqueous solution outlet of the absorption tower (100) through an aqueous
solution transfer line (102), an extract outlet from which the (meth)acrylic acid
extract obtained by contact of the inflowed (meth)acrylic acid aqueous solution
10 with an extraction solvent is discharged, a lower stationary section in which a
raffinate solution obtained by contact of the (meth)acrylic aqueous solution with
an extraction solvent remains stationary, a raffinate outlet from which the
raffinate solution passing through the lower stationary section is discharged, a
scum outlet port where at least a part of the raffinate solution containing scum is
15 discharged through a side stream equipped at any one point of the lower
stationary section, and a filtrate inlet port formed such that a filtrate obtained
through filtering of the raffinate solution discharged from the scum outlet port is
inflowed through a side stream equipped at any other point of the lower
stationary section;
20 a side filtering system (220) equipped with a raffinate inlet connected
with the scum outlet port of the extraction column (200), into which the raffinate
containing scum is inflowed, a filter for filtering the inflowed raffinate solution, a
scum outlet from which the scum separated from the raffinate solution by
filtering is discharged, and a filtrate outlet connected such that the filtrate is fed
25 to the filtrate inlet port of the extraction column; and
a distillation column (300) equipped with 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 feed containing the inflowed extract solution is discharged.
30
5
【ADVANTAGEOUS EFFECTS】
The method of continuous recovery of (meth)acrylic acid according to the
present invention may effectively remove scum formed in the continuous
recovery process of (meth)acrylic acid, thus enabling more stable operation of
the 5 continuous process.
【BRIEF DESCRIPTION OF THE DRAWINGS】
FIGs. 1 to 5 respectively schematically show the method and apparatus
for continuous recovery of (meth)acrylic acid according to the embodiments of
10 the invention.

1: (meth)acrylic acid containing mixed gas
100: (meth)acrylic acid absorption tower
102: (meth)acrylic acid aqueous solution transfer line
15 150: acetic acid absorption tower
200: (meth)acrylic acid extraction column
201: filtrate transfer line
203: extract transfer line
220: side filtering system
20 221: scum outlet port
229: filtrate inlet port
250: lower filtering system
300: distillation column
350: phase separation tank
25 400: heavies separation tower
CAA: crude (meth)acrylic acid
HPAA: high purity (meth)acrylic acid
【DETAILED DESCRIPTION OF THE EMBODIMENTS】
30 Hereinafter, a method of continuous recovery of (meth)acrylic acid and a
6
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, and singular forms
used herein include plural forms, unless they have clearly opposite 5 meanings.
Further, the meaning of ‘comprising’ as used herein embodies a specific
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.
10 Unless otherwise described, terms used herein are defined as follows.
The term '(meth)acrylic acid’ generally refers to acrylic acid, methacrylic
acid, or a mixture thereof.
Further, the term '(meth)acrylic acid-containing mixed gas' generally
refers to a mixed gas that may be produced when (meth)acrylic acid is prepared
15 by gas phase oxidation. As a non-limiting example, the (meth)acrylic
acid-containing 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 (‘raw material compound’) in
the presence of a catalyst, wherein the (meth)acrylic acid-containing mixed gas
20 may include (meth)acrylic acid, non-reacted raw material compounds,
(meth)acrolein, an inert gas, carbon monoxide, carbon dioxide, water vapor,
and various organic by-products (acetic acid, heavies, and the like), and the like.
Herein, a poorly water-soluble floating material formed by the organic
by-products is referred to as ‘scum’.
25 The term '(meth)acrylic acid aqueous solution' refers to an aqueous
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’ in an extraction process refers to a liquid mixture
30 containing a solute to be extracted, and it may be a mixture of a solute that is
7
soluble in an extraction solvent and 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 5 of a significant
amount of solutes forms a raffinate 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
10 the upper stage of the extraction column. Further, extraction is progressed by
the contact of materials fed to the extraction column, to obtain a light phase and
a heavy phase of new compositions.
The light phase of a new composition obtained through the extraction
process is obtained through the upper outlet of the extraction column, and the
15 heavy phase of a new composition is obtained through the lower outlet of the
extraction column. In general, the heavy phase of the new composition
obtained through the 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
20 extraction column. Herein, the section of the extraction column in which the
heavy phase remains stationary is 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
25 (meth)acrylic acid aqueous solution that is in a relatively heavy phase is fed to
the upper stage of the extraction column, and the extraction solvent that is in a
relatively light phase is fed to the lower stage of the extraction column. Further,
extraction is progressed by the contact thereof, an extract solution in which a
significant amount of (meth)acrylic acid is dissolved and a raffinate solution that
30 is deprived of a significant amount of (meth)acrylic acid are obtained. Herein,
8
the extract solution that is in a relatively light phase is obtained 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 5 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 extraction
column. The section of the extraction column in which the raffinate solution
remains stationary is referred to as ‘lower stationary section’ (or ‘stationary
10 section of raffinate solution’). Further, in the raffinate solution, an organic
phase and an aqueous phase exist together, and the raffinate solution may be
separated into an organic phase and an aqueous phase and form an interface
in the lower stationary section according to process conditions.
With regard to filtering in the extraction process, among the main stream
15 of the extraction column (namely, upper discharge flow or lower discharge flow
of the extraction column), a filtering method for the lower discharge flow is
referred to as ‘lower filtering’, and the means for conducting the lower filtering is
referred to as ‘lower filtering system’. Further, besides the main stream of the
extraction column, a filtering method for side stream discharge flow is referred
20 to as ‘side filtering’, and the means for conducting the side filtering is referred to
as ‘side filtering system’.
Hereinafter, referring to the attached drawings, specific embodiments of
the invention will be explained in detail so that one of ordinary knowledge in the
25 art may easily practice it. However, the present invention may be embodied in
various forms, and is not limited to the examples.
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
30 by poorly water-soluble substances included in the organic by-products. Due
9
to the characteristic of a continuous process, scum contaminates the inside of
various apparatuses, thus making stable process operation impossible, and
lowers the 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, 5 an extraction
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
10 that the lower filtering can remove only a part of scum included in the raffinate
solution, and thus, as the operation time elapses, scum is accumulated inside
the extraction column. Namely, scum is accumulated in 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 in the
15 stationary section) while forming a layer, and as the operation time elapses, the
thickness of accumulated scum increases from the interface respectively toward
the direction of the organic phase and the direction of the aqueous phase.
However, the previously suggested lower filtering selectively recovers
and filters only the aqueous phase formed in the stationary section of the lower
20 part 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 lower
filtering, scum accumulated close to the aqueous phase can be removed, but
scum accumulated close to the organic phase cannot be removed and remains.
Thus, as the operation time elapses, scum is accumulated toward the direction
25 of the organic phase, and finally, shutdown of the extraction column becomes
inevitable.
Thus, the inventors confirmed during repeated studies for ameliorating
these problems that if scum that is accumulated at the interface between an
organic phase and an aqueous phase formed by separation of the raffinate
30 solution in the lower stationary section of the extraction column is discharged
10
through a side stream equipped at any one point of the lower stationary section
of the extraction column and filtered, and the filtrate is inflowed again into the
lower stationary section of the extraction column (side filtering method), scum
accumulated close to the organic phase as well as scum accumulated close to
the aqueous phase at the interface may be 5 effectively removed.
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:
10 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 through the upper outlet of the extraction
column, and obtain a raffinate solution that passes through the lower stationary
section of the extraction column through the lower outlet; and a distillation
15 process wherein a feed containing the (meth)acrylic acid extract solution is
distilled to obtain (meth)acrylic acid,
wherein the raffinate solution containing scum that is accumulated at the
interface between an organic phase and an aqueous phase formed by phase
separation of the raffinate solution in the lower stationary section of the
20 extraction column is discharged through a side stream equipped at any one
point of the lower stationary section and filtered, and the filtrate is inflowed
through a side stream equipped at any other point of the lower stationary
section.
Basically, the method of continuous recovery of (meth)acrylic acid
25 according to the present invention includes an extraction process of a
(meth)acrylic acid aqueous solution and a distillation process, and particularly,
scum accumulated in the lower stationary section in the extraction process may
be more effectively removed by side filtering.
According to one embodiment of the invention, the method of continuous
30 recovery of (meth)acrylic acid includes: an absorption process wherein a mixed
11
gas including (meth)acrylic acid, organic by-products, and vapor, which is
produced by a synthesis reaction of (meth)acrylic acid, is contacted with an
absorption solvent including 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 5 extraction solvent
in an extraction column to obtain a (meth)acrylic acid extract solution through
the upper outlet of the extraction column and a raffinate solution through the
lower outlet of the extraction column; and a distillation process wherein a feed
including the (meth)acrylic acid extract obtained through the extraction process
10 is distilled to obtain (meth)acrylic acid. The method of continuous recovery of
(meth)acrylic acid according to the 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: the absorption process
15 for obtaining 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 a (meth)acrylic acid extract solution through the upper outlet of
the extraction column and a raffinate solution through the lower outlet of the
20 extraction column; and a distillation process wherein a feed containing 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. The method of
continuous recovery of (meth)acrylic acid according to the embodiment may be
25 conducted using the apparatus shown in FIG. 2.
According to another embodiment of the invention, the method of
continuous recovery of (meth)acrylic acid may further include a step of filtering
the raffinate solution obtained from the lower outlet of the extraction column in
each embodiment according to FIG. 1 or FIG. 2, as shown in FIG. 4 and FIG. 5.
30 Hereinafter, referring to FIG. 1 and FIG. 2, each process that can be
12
included in the embodiments of the invention will be explained.
(Absorption process)
An absorption process is a process for obtaining a (meth)acrylic acid
aqueous solution, and it may be conducted by contacting 5 a (meth)acrylic
acid-containing mixed gas obtained through the synthesis reaction of
(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
10 from the group consisting of propane, propylene, butane, isobutylene, and
(meth)acrolein in the presence of a gas phase catalyst. Herein, the gas phase
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
15 example, catalysts suggested in Korean Registered Patent No. 0349602 and
No. 037818, and the like may be used. In the (meth)acrylic acid-containing
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, an inert gas, carbon dioxide, vapor, and various
20 organic by-products (acetic acid, light ends, heavies, and the like) may be
included.
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), so as to contact it with an absorption
25 solvent including water.
Herein, the kind of the (meth)acrylic acid absorption tower (100) may be
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.
30 Inside the packed tower, filler such as a Raschig ring, a pall ring, a saddle,
13
gauze, structured packing, and the like may be applied.
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
5 (100).
The absorption solvent may include water such as tap water, deionized
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 the absorption solvent, a trace
10 amount of organic by-products introduced from other processes (for example,
acetic acid) may be included. However, considering the absorption efficiency
of (meth)acrylic acid, it is preferable that organic by-products are 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).
15 According to the embodiment of the invention, a raffinate solution
obtained in a (meth)acrylic acid extraction column (200) may be recycled to the
absorption tower (100) and used as an absorption solvent. Herein, it may be
advantageous in terms of improvement in process efficiency that the raffinate
solution is fed to the upper part of the absorption tower (100).
20 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
of 50 to 100 ℃ or 50 to 80 ℃, considering condensation conditions and
moisture content according to saturated water vapor pressure, and the like.
Meanwhile, through the absorption process, a (meth)acrylic acid
25 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 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%, or 50 to 80 wt% of (meth)acrylic acid may be included in the
30 (meth)acrylic acid aqueous solution.
14
The obtained (meth)acrylic acid aqueous solution, as shown in FIG. 1,
may be fed to the (meth)acrylic acid extraction column (200) through an
aqueous 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 5 column (300)
through aqueous solution transfer lines (102 and 103).
As shown in FIG. 1, if an extraction process is introduced between a
(meth)acrylic acid absorption process and a distillation process, most
absorption solvent included in the (meth)acrylic acid aqueous solution may be
10 removed in the extraction process, thus lowering the treatment load of the
distillation process, and reducing energy consumption.
As shown in FIG. 2, if an extraction process is introduced between a
(meth)acrylic acid absorption process and a distillation process, and
simultaneously a (meth)acrylic acid aqueous solution is divided and fed to the
15 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. 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,
20 energy efficiency improvement effect, and the like. According to one
embodiment, it may be favorable for manifestation of the above-explained effect
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).
25 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
process of 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
30 invention, a process of contacting the non-condensable gas with an absorption
15
solvent to recover acetic acid included in the non-condensable gas may be
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) 5 for absorbing acetic
acid may be fed to the upper part of the acetic acid absorption tower (150), and
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
10 absorption tower(100) and used as an absorption solvent, and acetic
acid-stripped non-condensable gas may be recycled to the synthesis process of
(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
15 bar, and at the internal temperature of 50 to 100 ℃ or 50 to 80 ℃. 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.
20 (Extraction process)
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 thereof is conducted.
Herein, the (meth)acrylic acid aqueous solution may be prepared by the
25 above-explained absorption process.
The extraction process may be conducted in a (meth)acrylic acid
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
30 and a raffinate solution that is deprived of a significant amount of (meth)acrylic
16
acid, respectively. Herein, the extraction solution that is in a relatively light
phase is obtained through the upper outlet of the extraction column (200), and
the raffinate solution that is in 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 5 thereof remains
stationary in the stationary section of the lower part of the extraction column,
and a part thereof 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
10 energy consumption compared to distillation), most water included in the
(meth)acrylic acid aqueous solution may be removed. Thereby, the treatment
load of the subsequent distillation process may be lowered, thus improving
energy efficiency of the total process. Furthermore, by lowering the treatment
load of the distillation process, polymerization of (meth)acrylic acid that may be
15 generated during distillation may be minimized, to secure more improved
recovery efficiency of (meth)acrylic acid.
Meanwhile, in the extraction process, at the lower stationary section of
the extraction column (200), a certain amount of a raffinate solution remains
stationary and exists while being phase separated into an organic phase and an
20 aqueous phase. Further, as the production amount of a raffinate solution by
the extraction and the discharged amount of a raffinate solution through the
lower outlet are maintained substantially the same, the amount of a raffinate
solution that remains stationary at the lower part of the extraction column (200)
and the interface between the organic phase and the aqueous phase are
25 maintained at a constant level.
However, as the operation of the extraction column is continued, scum is
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 on the
30 interface between the organic phase and the aqueous phase formed in the
17
stationary section of the lower part of the extraction column, and as the
operation time elapses, 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 5 lower the recovery
rate of (meth)acrylic acid, it is preferable to remove scum for stable process
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
10 part of the extraction column (200), and using the filtrate as an absorption
solvent of an absorption process. However, according to the previously
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
15 and remains inside the extraction column. Thus, in the case of the previously
suggested method, as the operation time elapses, scum is accumulated inside
the extraction column, and finally, shutdown of the extraction column becomes
inevitable.
However, the method of continuous recovery of (meth)acrylic acid
20 according to one embodiment of the invention uses side filtering, wherein a
raffinate solution containing scum accumulated at the interface between an
organic phase and an aqueous phase formed in the lower stationary section of
the extraction column (200) is discharged through a side stream equipped at
any one point of the lower stationary section and filtered, and the filtrate is
25 inflowed again through a side stream equipped at any other point of the lower
stationary section.
Namely, as shown in FIG. 1 or FIG. 2, the side filtering is a method of
discharging the raffinate solution containing scum accumulated at the interface
between an organic phase and an aqueous phase using a pump through a side
30 stream equipped at any one point of the lower stationary section of the
18
extraction column (200), filtering it through a side filtering system (220) to
remove scum from the raffinate solution, and then introducing the filtrate again
into the lower stationary section of the extraction column through a side stream
equipped at any other point of the lower stationary section. Thereby, the side
filtering may more effectively remove even scum accumulated 5 close to the
organic phase at the interface, which was difficult to remove by the previous
lower filtering.
The side filtering is a method of recovering a part of the raffinate solution
that remains stationary at the lower part of the extraction column (200)
10 (particularly, a certain amount of the raffinate solution including the interface
between the organic phase and the aqueous phase) through a side stream
equipped at the lower stationary section of the extraction column (200). Thus,
it is advantageous that the interface between the organic phase and the
aqueous phase formed by phase separation of the raffinate solution is
15 maintained at a constant level, so as to conduct the side filtering with higher
efficiency. Preferably, the extraction process may be conducted such that the
interface between the organic phase and the aqueous phase by phase
separation may be formed at a location of the side stream equipped at any one
point of the lower stationary section of the extraction column. Herein, the
20 location at which the interface is formed may be controlled through the
production amount of the raffinate solution by extraction and the discharge
amount of the raffinate solution through the lower outlet of the extraction column
(200).
Further, the discharging of the raffinate solution containing scum and the
25 filtering through the side streams of the extraction column may be conducted
continuously or discontinuously. Namely, the side filtering may be
continuously conducted over the whole extraction process, or it may be
discontinuously conducted according to the amount of scum accumulated at the
interface.
30 Meanwhile, since scum has high viscosity and adheres together, if the
19
discharge mass flow through the side stream of the extraction column (200) is
low, scum may not be smoothly discharged. In this regard, according to the
study result of the inventors, the discharge efficiency of scum through the side
stream of the extraction column (200) may vary according to the location of a
port connecting the extraction column (200) and the side filtering 5 system (220).
Namely, scum removal efficiency may vary according to the outflow direction of
the raffinate solution containing scum through the side stream of the extraction
column (200) and the inflow direction of the filtrate through the side stream of
the extraction column (200).
10 According to one embodiment, as shown in FIG. 3 (a), in case the
outflow direction of scum (Filter In) through the side stream of the extraction
column (200) and the inflow direction (Filter Out) of the filtrate into the extraction
column (200) are identical, scum may be accumulated around a filtrate inlet port
(229) by a fluid mechanical principle, and scum discharge efficiency through a
15 scum outlet port (221) may relatively decrease. To the contrary, as shown in
FIG. 3 (b), in case the outflow direction of scum (Filter In) through the side
stream of the extraction column (200) and the inflow direction (Filter Out) of the
filtrate into the extraction column (200) are opposite to each other, scum may be
discharged more smoothly due to the flow of filtrate through the filtrate inlet port
20 (229).
That is to say, compared to the case wherein the scum outlet port (221)
and the filtrate inlet port (229) of the extraction column (200) make an angle of
180° as shown in the right drawing of FIG. 3 (a), the case wherein the angle is
less than 180°, less than 135°, or less than 90°, or less than 45°, or 0° as
25 shown in the right drawing of FIG. 3 (b) may be favorable for smooth discharge
of scum.
Herein, considering that an organic phase and an aqueous phase may
be included in the discharged substance through the scum outlet port (221) and
the introduced substance through the filtrate inlet port (229), and for smooth
30 phase separation of the organic phase and the aqueous phase in the lower
20
stationary section of the extraction column, it is advantageous that the filtrate
inlet port (229) is located at a higher position than the scum outlet port (221) at
the lower stationary section of the extraction column.
Meanwhile, the side filtering may be conducted using a filter that can
sufficiently remove scum from the raffinate solution discharged 5 through the side
stream of the extraction column (200), and the method or the construction of the
filter are not specifically limited. However, according to one embodiment, the
side filtering may be conducted using a filter having pores with an average
diameter of 50 μm or less, or 0.1 to 30 μm, or 0.5 to 20 μm, or 0.5 to 10 μm.
10 Namely, for sufficient removal of scum, it is advantageous that the filter used for
the side filtering has pores with an average diameter of 50 μm or less.
However, considering filtering efficiency, process flow, and the like, it is
advantageous that the filter has pores with an average diameter of 0.1 μm or
more.
15 Further, it is preferable that the filter used for the side filtering is made of
a material that is resistant to an extraction solvent and (meth)acrylic acid, and
for example, it may be made of cotton, a metal such as SUS (steel use
stainless), and the like.
Besides the side filtering, the method of continuous recovery of
20 (meth)acrylic acid may further include a step of filtering the raffinate solution
obtained through the lower outlet of the extraction column (200) in each
embodiment according to FIG. 1 and FIG. 2 (lower filtering), as shown in FIG. 4
and FIG. 5.
As the above-explained side filtering is used, scum may not substantially
25 exist in the raffinate solution obtained through the lower outlet of the extraction
column (200). However, in order to more completely remove scum that can be
included, if necessary, the lower filtering may be further conducted. Herein,
the description ‘not substantially exist’ means that the amount of scum included
in the raffinate solution obtained through the lower outlet of the extraction
30 column (200) is 5 wt% or less, or 3 wt% or less, or 1 wt% or less, or 0.1 wt% or
21
less, and in which the influence of scum on the stability of process operation is
insignificant.
The lower filtering may be conducted using a filter that can sufficiently
remove scum included in the raffinate solution discharged from the extraction
column (200), and the filtering method and the construction 5 of the filter are not
specifically limited. However, according to one embodiment, the lower part
filtering may be conducted using a filter having pores with an average diameter
of 10 ㎛ or less, or 0.1 to 10 ㎛, or 0.5 to 10 ㎛. Further, since the extraction
solvent does not substantially exist in the raffinate solution obtained through the
10 lower outlet of the extraction column (200), it is preferable that a filter used for
the lower part filtering may be made of material having resistance to
(meth)acrylic acid and the like, and as a non-limiting example, the filter may be
made of a polymer, cotton, or a metal such as SUS (steel use stainless).
The filtrate obtained through the lower filtering may be recycled to the
15 absorption process and used as an absorption solvent of (meth)acrylic acid.
The side filtering system (220) and the lower filtering system (250) may
respectively include at least one filter fulfilling the above requirements, and
preferably, they may have a construction including two or more filters having
pores with different average diameters connected in series.
20 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 that (meth)acrylic acid. According to one
25 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 ℃ or less, or 10 to 120 ℃, or 50 to 120 ℃.
Specifically, the extraction solvent may be at least one selected from the
group consisting of benzene, toluene, xylene, n-heptane, cycloheptane,
30 cycloheptene, 1-heptene, ethyl-benzene, methyl-cyclohexane, n-butyl acetate,
22
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.
Further, the feed amount of the extraction solvent may 5 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
10 (meth)acrylic acid aqueous solution and the extraction solvent fed to the
extraction column(200) is maintained 1:1 or more. If the weight ratio exceeds
1:2, although extraction efficiency may be good, loss of (meth)acrylic acid at the
distillation column (300) of the subsequent process may increase, and reflux of
an azeotropic solvent for blocking it may excessively increase, which is not
15 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 ℃.
As the extraction column (200), common extraction columns of a
20 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.
25 Through the extraction process, a (meth)acrylic acid extract solution is
discharged to the upper part of the extraction column (200), and the discharged
extract solution is fed to the 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 may be filtered
30 through a lower filtering system (250) as necessary, and then recycled to the
23
(meth)acrylic acid absorption tower (100) through a transfer line (201).
Herein, in the extract solution, in addition to a 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 5 wt% of an extraction
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 included in the
(meth)acrylic acid aqueous solution (for example, 85 wt% or more of water
included in the aqueous solution) may be recovered as a raffinate solution
10 through the extraction process.
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,
15 thus securing operation stability and improving recovery efficiency of
(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
20 (meth)acrylic acid may be included in the raffinate solution, thus minimizing the
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
25 extract solution is distilled to obtain (meth)acrylic acid is conducted.
According to one embodiment of the invention, the feed may be a
(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.
30 According to another embodiment, the feed may be a mixture of the
24
(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 a distillation column (300) through the (meth)acrylic acid
aqueous solution transfer line (103) and the (meth)acrylic 5 acid extract solution
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
10 stages from the uppermost stage of the distillation column (300).
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.
15 Herein, in order to effectively separate (meth)acrylic acid included in the
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
20 azeotropic solvent that may form an azeotrope with water and acetic acid, and
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 ℃ or less, or 10 to 120 ℃, or 50 to
120 ℃).
25 Specifically, the hydrophobic azeotropic solvent may be at least one
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,
30 4-methyl-1-heptene, 2-ethyl-1-hexene, ethylcyclopentane, 2-methyl-1-hexene,
25
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 kind 5 of solvents are
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 a
phase separation tank (350) may be fed to the (meth)acrylic acid extraction
column (200) and reused as an extraction solvent.
10 Through the distillation process, among the feed, components other than
(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
15 to the phase separation tank (350) and reused after a predetermined treatment.
Herein, the phase separation tank (350) is an apparatus for separating
immiscible liquids by gravity or centrifugal force and the like, wherein a relatively
light liquid (for example, an organic phase) may be recovered from the upper
part of the phase separation tank (350) and a relatively heavy liquid (for
20 example, an aqueous phase) may be recovered from the lower part of the
phase 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).
25 Further, the filtrate obtained through filtering of the raffinate solution in the
above-explained extraction process may be fed to the phase separation tank
(350) through a 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
30 used as an azeotropic solvent, and if necessary, at least a part of the organic
26
phase may be fed to the extraction column (200) and used as an extraction
solvent.
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 5 as waste water. In
the aqueous phase, acetic acid 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%,
10 or 2 to 40 wt%, or 3 to 30 wt%.
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
15 such polymerization of (meth)acrylic acid, common polymerization inhibitors
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 a polymer of (meth)acrylic acid,
polymerization inhibitors, and the like may be included. Thus, if necessary, a
20 step of feeding the lower discharged solution of the distillation column (300) to a
heavies separation tower (400) and separating heavies included in the lower
discharged solution may be further conducted. 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).
25 Herein, the heavies separation process and the 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.
30 Further, in addition to the above-explained steps, processes that can be
27
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, 5 as shown in FIGs. 1
to 3, 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
10 vapor, which is produced by a synthesis reaction of (meth)acrylic acid, is fed,
and a (meth)acrylic acid 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 a
(meth)acrylic acid aqueous solution inlet connected with the (meth)acrylic acid
15 aqueous solution outlet of the absorption tower (100) through an aqueous
solution transfer line (102), an extract outlet from which the (meth)acrylic acid
extract obtained by contact of the inflowed (meth)acrylic acid aqueous solution
with an extraction solvent is discharged, a lower stationary section in which a
raffinate solution obtained by contact of the (meth)acrylic aqueous solution with
20 an extraction solvent remains stationary, a raffinate outlet from which the
raffinate solution passing through the lower stationary section is discharged, a
scum outlet port where at least a part of the raffinate solution containing scum is
discharged through a side stream equipped at any one point of the lower
stationary section, and a filtrate inlet port formed such that a filtrate obtained
25 through filtering of the raffinate solution discharged from the scum outlet port is
inflowed through a side stream equipped at any other point of the lower
stationary section;
a side filtering system (220) equipped with a raffinate inlet connected
with the scum outlet port of the extraction column (200), into which the raffinate
30 containing scum is inflowed, a filter for filtering the inflowed raffinate solution, a
28
scum outlet from which the scum separated from the raffinate solution by
filtering is discharged, and a filtrate outlet connected such that the filtrate is fed
to the filtrate inlet port of the extraction column; and
a distillation column (300) equipped with an extract inlet connected with
the extract outlet of the extraction column (200) through an extract 5 transfer line
(203), and a (meth)acrylic acid outlet from which (meth)acrylic acid obtained by
distillation of a feed containing the inflowed extract solution is discharged.
According to yet another embodiment, as shown in FIGS. 2 and 3, the
distillation column (300) is equipped with a (meth)acrylic acid aqueous solution
10 inlet connected with the (meth)acrylic acid 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 which
(meth)acrylic acid obtained by distillation of the inflowed (meth)acrylic acid
15 aqueous solution and a feed containing an extract solution is discharged; and
the apparatus is operated such that a part of the (meth)acrylic acid
aqueous solution discharged from the absorption tower (100) is fed to the
(meth)acrylic acid aqueous solution inlet of the extraction column (200) through
the aqueous solution transfer line (102), and the remainder of the (meth)acrylic
20 acid aqueous solution discharged from the absorption tower (100) is fed to the
(meth)acrylic acid aqueous solution inlet of the distillation column (300) through
the aqueous solution transfer line (103).
The apparatus for continuous recovery of (meth)acrylic acid according to
25 the above embodiments may be operated according to the above-explained
method for continuous recovery of (meth)acrylic acid.
Particularly, it is preferable that the scum outlet port and the filtrate inlet
port of the extraction column (200) are formed such that the outflow direction of
the raffinate solution and the inflow direction of the filtrate through the side
30 streams are opposite to each other. Namely, compared to the case wherein
29
the scum outlet port (221) and the filtrate inlet port (229) of the extraction
column (200) make an angle of 180° as shown in the right drawing of FIG. 3 (a),
the case wherein the angle is less than 180°, less than 135°, or less than 90°,
or less than 45°, or 0° as shown in the right drawing of FIG. 3 (b) may be
favorable for smooth 5 discharge of scum.
Herein, considering that an organic phase and an aqueous phase may
be included in the discharged substance through the scum outlet port (221) and
the introduced substance through the filtrate inlet port (229), and for smooth
phase separation of the organic phase and the aqueous phase in the lower
10 stationary section of the extraction column, it is advantageous that the filtrate
inlet port (229) is located at a higher position than the scum outlet port (221) at
the lower stationary section of the extraction column.
Further, it is preferable that the side filtering system (220) is equipped
with a filter having pores with an average diameter of 50 μm or less, or 0.1 to 30
15 μm, or 0.5 to 20 μm, or 0.5 to 10 μm, so as to sufficiently remove scum from the
raffinate solution discharged through the side stream of the extraction column
(200). It is also preferable that the filter of the side filtering system (220) is
made of a material that is resistant to an extraction solvent and (meth)acrylic
acid, and for example, it may be made of cotton, a metal such as SUS (steel
20 use stainless), and the like.
Meanwhile, as shown in FIG. 4 and FIG. 5, the apparatus of each
embodiment according to FIG. 1 and FIG. 2 may be further equipped with a
lower filtering system equipped with a raffinate inlet connected with the raffinate
outlet of the extraction column (200), into which the raffinate solution is inflowed,
25 a filter for filtering the inflowed raffinate solution, and a filtrate outlet from which
a filtrate obtained by filtering is discharged. It is preferable that the lower
filtering system (250) is equipped with a filter having pores with an average
diameter of 10 μm or less, or 0.1 to 10 μm, or 0.5 to 10 μm.
In addition, since extraction solvents do not substantially exist in the
30 raffinate solution obtained through the lower outlet of the extraction column
30
(200), it is preferable that the filter of the lower filtering system (250) is made of
a material that is resistant to (meth)acrylic acid, and for example, it may be
made of polymer such as polypropylene, cotton, a metal such SUS (steel use
stainless), and the like.
Meanwhile, the (meth)acrylic acid absorption tower(5 100) may be a
packed tower or a multistage tray tower for improving contact efficiency of the
(meth)acrylic acid-containing mixed gas (1) with an absorption solvent. 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.
10 As the (meth)acrylic acid extraction column (200), common 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
15 column, and the like.
The distillation column (300) may be a packed column including fillers
inside or a multistage column, preferably a sieve tray column or a dual flow tray
column, and the like.
In addition, the acetic acid absorption tower (150), (meth)acrylic acid
20 aqueous solution transfer line (102), extract transfer line (203), phase
separation tank (350), heavies separation tower (400), and the like may have
constructions common in the technical field to which the invention pertains.
Hereinafter, preferable examples are presented to aid in understanding
25 of the invention. However, these examples are only to illustrate the invention,
and the scope of the invention is not limited thereto.
Comparative Example
A Scheibel type of extraction column with an extraction part of a total of
30 72 stages, a column inner diameter of 32 inches, and a column height of 545
31
inches was prepared. Into the feed inlet of the extraction column, an acrylic
acid aqueous solution (acrylic acid concentration of about 65.5 wt%, acetic acid
concentration of about 2.25 wt%) was fed, and into the extraction solvent inlet of
the extraction column, toluene (acrylic acid concentration of about 0.18 wt%)
was fed. Herein, the weight ratio of the acrylic acid 5 aqueous solution to
toluene fed to the extraction column was fixed to about 1:1.3.
At the lower part of the extraction part from which a raffinate solution was
discharged, a lower filter system including a metal mesh filter having pores with
an average diameter of about 20 μm and a metal mesh filter having pores with
10 an average diameter of about 1 μm connected in series was installed, and using
the same, scum included in the raffinate solution discharged to the lower part
was removed.
Herein, the input of the acrylic acid aqueous solution was controlled to
5.3 ton/h, and the input of toluene was controlled to about 6.89 ton/h. Further,
15 the discharge mass flow of the raffinate solution was maintained at about 1.55
ton/h so that the 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, and the discharge
mass flow of the extract solution was about 10.64 ton/h.
20 Under a 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.
As the result, at the beginning of operation, the concentration of acrylic
25 acid in the raffinate solution consisting of an aqueous phase was about 1.65
wt%, and the concentration of toluene was about 820 ppm. However, after
about 24 h of operation, the concentration of acrylic acid in the raffinate solution
increased to about 4.2 wt%, and the concentration of toluene increased to about
6.5 wt%. This is because the amount of scum accumulated at the interface
30 between the organic phase and the aqueous phase increases (the thickness of
32
a scum layer increases), and the organic phase and the aqueous phase exist
together in the form of emulsion in the scum and are discharged together to the
lower part of the extraction column.
Herein, although the raffinate solution discharged from the lower part of
the extraction column passed through the lower filtering 5 system connected to
the extraction column to remove scum, the concentration of acrylic acid was
high, and due to a high concentration of toluene, the raffinate solution could not
be fed as an absorption water of the acrylic acid absorption process.
Further, as the operation of the extraction column continued, scum was
10 accumulated toward the organic phase (namely, to the internal direction of the
extraction column) at the interface between the organic phase and the aqueous
phase of the lower stationary section of the extraction column. Due to the
accumulation of scum, the extraction column was contaminated, extraction
efficiency gradually decreased, and finally, the operation of the extraction
15 column was stopped.
Example
At the lower stage of an extraction column from which a raffinate solution
is discharged, a lower filtering system equipped with a metal mesh filter having
20 pores with an average diameter of about 1 μm was installed. Further, a side
filtering system equipped with a metal mesh filter having pores with an average
diameter of about 20 μm was installed so as to be connected with the side
stream of the extraction column, as shown in FIG. 3 (b).
As such, except that the above lower filtering system and side filtering
25 system were installed, the extraction process was progressed by the same
method as the comparative example. Herein, the mass flow of the raffinate
solution passing through the side filtering system was controlled to about 1.5 to
5 ton/h.
As the result, at the beginning of the operation, the concentration of
30 acrylic acid in the raffinate solution consisting of an aqueous phase was about
33
1.64 wt%, and the concentration of toluene was about 620 ppm. Further, even
after the operation time elapsed, the concentrations of acrylic acid and toluene
in the raffinate solution were maintained at the initial values.
The differential pressure of the side filtering system increased as the
operation time of the extraction column elapsed, and after 5 about 2 days to 3
days of operation, maximum differential pressure limit was reached, and after
removing scum by backwashing, the side filtering system was reused. Further,
the differential pressure of the lower filtering system increased very slowly, and
after about 8 to 10 days of operation, maximum differential pressure limit was
10 reached, and after removing scum by backwashing, the lower filtering system
was reused.
As explained, by using the side filtering system, accumulation of scum
inside the extraction column could be prevented, and the extraction process
could be operated for more than 3 months without contamination of the
15 extraction column and a decrease in extraction efficiency due to scum.

【CLAIMS】
【Claim 1】
A method of continuous recovery of (meth)acrylic acid, comprising:
an extraction process wherein a (meth)acrylic acid aqueous solution is
contacted with an extraction solvent in an extraction 5 column to obtain a
(meth)acrylic acid extract solution through an upper outlet of the extraction
column, and obtain a raffinate solution passing through a lower stationary
section of the extraction column through the lower outlet; and a distillation
process wherein a feed containing the (meth)acrylic acid extract solution is
10 distilled to obtain (meth)acrylic acid,
wherein the raffinate solution containing scum that is accumulated at an
interface between an organic phase and an aqueous phase formed by phase
separation of the raffinate solution in the lower stationary section of the
extraction column is discharged through a side stream equipped at any one
15 point of the lower stationary section and filtered, and a filtrate is inflowed
through a side stream equipped at any other point of the lower stationary
section.
【Claim 2】
20 The method according to claim 1, wherein the extraction process is
conducted such that the interface between an organic phase and an aqueous
phase by phase separation of the raffinate solution is formed at a location of the
side stream equipped at any one point of the lower stationary section of the
extraction column.
25
【Claim 3】
The method according to claim 1, wherein discharging of the raffinate
solution containing scum and filtering through the side streams of the extraction
column are conducted continuously or discontinuously.
30
35
【Claim 4】
The method according to claim 1, wherein the outflow direction of the
raffinate solution containing scum through the side stream of the extraction
column and the inflow direction of the filtrate through the side stream of the
extraction column are 5 opposite to each other.
【Claim 5】
The method according to claim 1, wherein the filtering is conducted using
a filter having pores with an average diameter of 50 μm or less.
10
【Claim 6】
The method according to claim 1, wherein the method comprises:
an absorption process wherein a mixed gas including (meth)acrylic acid,
organic by-products, and water vapor, which is produced by a synthesis
15 reaction of (meth)acrylic acid, is contacted with an absorption solvent including
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 a (meth)acrylic acid extract solution through
20 the upper outlet of the extraction column, and obtain a raffinate solution passing
through the lower stationary section of the extraction column through the lower
outlet; and
a distillation process wherein a feed containing the (meth)acrylic acid
extract solution obtained through the extraction process is distilled to obtain
25 (meth)acrylic acid.
【Claim 7】
The method according to claim 6, wherein the method comprises:
an absorption process wherein a mixed gas including (meth)acrylic acid,
30 organic by-products, and water vapor, which is produced by a synthesis
36
reaction of (meth)acrylic acid, is contacted with an absorption solvent including
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 a (meth)acrylic 5 acid extract solution
through the upper outlet of the extraction column, and obtain a raffinate solution
passing through the lower stationary section of the extraction column through
the lower outlet; and
a distillation process wherein a feed containing the remainder of the
10 (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.
【Claim 8】
15 The method according to claim 6, further comprising a step of filtering the
raffinate solution obtained through the lower outlet of the extraction column.
【Claim 9】
The method according to claim 8, wherein the filtering of the raffinate
20 solution obtained through the lower outlet of the extraction column is conducted
using a filter having pores with an average diameter of 10 μm or less.
【Claim 10】
The method according to claim 8, wherein the filtrate obtained through
25 the filtering is recycled to the absorption process and used as the absorption
solvent.
【Claim 11】
An apparatus for continuous recovery of (meth)acrylic acid, comprising:
30 a (meth)acrylic acid absorption tower equipped with a mixed gas inlet
37
into 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 a (meth)acrylic acid aqueous solution outlet from which an aqueous
solution obtained by contact of the mixed gas with an absorption solvent
including 5 water is discharged;
a (meth)acrylic acid extraction column equipped with a (meth)acrylic acid
aqueous solution inlet connected with the (meth)acrylic acid aqueous solution
outlet of the absorption tower through an aqueous solution transfer line, an
extract outlet from which the (meth)acrylic acid extract solution obtained by
10 contact of the inflowed (meth)acrylic acid aqueous solution with an extraction
solvent is discharged, a lower stationary section in which a raffinate solution
obtained by contact of the (meth)acrylic aqueous solution with an extraction
solvent remains stationary, a raffinate outlet from which the raffinate solution
passing through the lower stationary section is discharged, a scum outlet port
15 where at least a part of the raffinate solution containing scum is discharged
through a side stream equipped at any one point of the lower stationary section,
and a filtrate inlet port formed such that a filtrate obtained through filtering of the
raffinate solution discharged from the scum outlet port is inflowed through a side
stream equipped at any other point of the lower stationary section;
20 a side filtering system equipped with a raffinate inlet connected with the
scum outlet port of the extraction column, into which the raffinate containing
scum is inflowed, a filter for filtering the inflowed raffinate solution, a scum outlet
from which the scum separated from the raffinate solution by filtering is
discharged, and a filtrate outlet connected such that the filtrate is fed to the
25 filtrate inlet port of the extraction column; and
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
a feed containing the inflowed extract solution is discharged.
30
38
【Claim 12】
The apparatus for continuous recovery of (meth)acrylic acid according to
claim 11, wherein the distillation column is equipped with a (meth)acrylic acid
aqueous solution inlet connected with the (meth)acrylic acid aqueous solution
outlet of the absorption tower through an aqueous solution 5 transfer line, 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 inflowed (meth)acrylic acid aqueous solution
and the feed containing the extract solution is discharged; and
10 the apparatus is operated such that a part of the (meth)acrylic acid
aqueous solution discharged from the absorption tower is fed to the
(meth)acrylic acid aqueous solution inlet of the extraction column through the
aqueous solution transfer line, and the remainder of the (meth)acrylic acid
aqueous solution discharged from the absorption tower is fed to the
15 (meth)acrylic acid aqueous solution inlet of the distillation column through the
aqueous solution transfer line.
【Claim 13】
The apparatus for continuous recovery of (meth)acrylic acid according to
20 claim 11, wherein the scum outlet port and the filtrate inlet port of the extraction
column are formed such that the outflow direction of the raffinate solution and
the inflow direction of the filtrate through side streams are opposite to each
other.
25 【Claim 14】
The apparatus for continuous recovery of (meth)acrylic acid according to
claim 11, wherein the filter of the side filtering system has pores with an
average diameter of 50 μm or less.
39
【Claim 15】
The apparatus for continuous recovery of (meth)acrylic acid according to
claim 11, further comprising a lower filtering system equipped with a raffinate
inlet connected with the raffinate outlet of the extraction column, into which the
raffinate solution is inflowed, a filter for filtering the inflowed 5 raffinate solution,
and a filtrate outlet from which a filtrate obtained by filtering is discharged.
【Claim 16】
The apparatus for continuous recovery of (meth)acrylic acid according to
10 claim 15, wherein the filter of the lower filtering system has pores with an
average diameter of 10 μm or less.