(DESCRIPTION1
[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 used for the continuous recovery method.
[BACKGROUND OF ART1
(Meth)acrylic acid is generally prepared by gas phase oxidation of
lo 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
appropriate catalyst in a reactor, and a reaction product mixed gas including
(meth)acrylic acid, non-reacted propane or propylene, (meth)acrolein, inert gas,
15 carbon dioxide, water vapor, and various organic by-products (acetic acid, high
boiling point by-products, and the like) is obtained in the back end of the
reactor.
The (meth)acrylic acid-containing mixed gas contacts an absorption
solvent such as process water and the like in a (meth)acrylic acid absorption
20 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 distilled and
purified while passing through a water separation tower and the like, to obtain
25 (meth)acrylic acid.
Meanwhile, in order to improve the recovery efficiency of (meth)acrylic
acid, various methods of controlling process conditions or process sequence
and the like have been suggested. Among them, as a method for separating
water and acetic acid from the (meth)acrylic acid aqueous solution obtained in
30 the (meth)acrylic acid absorption tower, an azeotropic distillation method is
+%
known, wherein acetic acid, the main by-product of a (meth)acrylic acid process,
is recovered from the upper part of the water separation tower together with
water using a hydrophobic azeotropic solvent in the water separation tower, and
(meth)acrylic acid is recovered from the lower part of the water separation
5 tower.
Particularly, the inventors suggested a method of recycling acetic
acid-containing waste water that is recovered from the upper part of the water
separation tower to the (meth)acrylic acid absorption tower and reusing it, in
Korean Laid-Open Patent No. 2009-0041 355.
10 The method of distilling a (meth)acrylic acid aqueous solution using a
hydrophobic azeotropic solvent in the water separation tower may reduce the
amount of waste water and simultaneously effectively prevent introduction of
organic substances, and simplify a subsequent purification step.
However, the above method and previously disclosed recovery methods
15 of (meth)acrylic acid have problems in that a very large amount of energy is
consumed in the process of distilling a (meth)acrylic acid aqueous solution, and
normal operation cannot be conducted due to the production of polymers by
polymerization of (meth)acrylic acid, and thus operation stability is lowered.
[DETAILED DESCRIPTION OF THE INVENTION1
20 [Technical Problem]
It is an object of the invention to provide a method of continuous recovery
of (meth)acrylic acid that may largely reduce energy consumption and yet
exhibit improved operation stability.
It is another object of the invention to provide an apparatus for
25 continuous recovery of (meth)acrylic acid.
[Technical Solution]
According to one embodiment of the invention, a method of continuous
recovery of (meth)acrylic acid is provided, including:
contacting a mixed gas including (meth)acrylic acid, organic by-products,
30 and vapor, which is produced by a synthesis reaction of (meth)acrylic acid, with
-23
water in a (meth)acrylic acid absorption tower (100) to obtain a (meth)acrylic
acid aqueous solution;
dividing and feeding the (meth)acrylic acid aqueous solution to a
(meth)acrylic acid extraction tower (200) and a water separation tower (300);
5 obtaining a (meth)acrylic acid extract with reduced water content from
the (meth)acrylic acid aqueous solution that is fed to the (meth)acrylic acid
extraction tower (200), and feeding it to a water separation tower (300); and
distilling the (meth)acrylic acid aqueous solution and the (meth)acrylic
acid extract that are fed to the water separation tower (300) to obtain
lo (meth)acrylic acid.
The step of dividing and feeding the (meth)acrylic acid aqueous solution
to a (meth)acrylic acid extraction tower (200) and a water separation tower
(300) may be conducted in such a way that 5-70 wt% of the obtained
(meth)acrylic acid aqueous solution is fed to the (meth)acrylic acid extraction
15 tower(200), and the remainder is fed to the water separation tower(300).
The synthesis reaction of (meth)acrylic acid may be conducted by an
oxidation reaction of at least one compound selected from the group consisting
of propane, propylene, butane, isobutylene, t-butylene, and (meth)acrolein in
the presence of a gas phase catalyst.
20 Meanwhile, the internal temperature of the (meth)acrylic acid absorption
tower (100) may be maintained at 50 to 100 "C.
The step of obtaining the (meth)acrylic acid aqueous solution may be
conducted in such a way that a (meth)acrylic acid-containing aqueous solution
is discharged to the lower part of the (meth)acrylic acid absorption tower (loo),
25 and (meth)acrylic acid-stripped non-condensable gas is discharged to the upper
part of the (meth)acrylic acid absorption tower (100). In this case, the method
for continuous recovery of (meth)acrylic acid according to the present invention
may further include contacting the non-condensable gas with water to recover
acetic acid that is included in the non-condensable gas.
In the water fed to the (meth)acrylic acid absorption tower(100), organic
++I
by-products may be included at a concentration of 3 to 20 wt%.
In the (meth)acrylic acid aqueous solution obtained in the (meth)acrylic
acid absorption tower (loo), (meth)acrylic acid may be included at a
concentration of 40 to 90 wt%.
5 The (meth)acrylic acid extract may be obtained by contacting the
(meth)acrylic acid aqueous solution that is fed to the (meth)acrylic acid
extraction tower (200) with a hydrophobic extraction solvent to remove water
included in the aqueous solution.
The (meth)acrylic acid extract may be obtained from the upper part of the
lo (meth)acrylic acid extraction tower (200) and fed to the water separation tower
(300), and at least a part of the lower discharged liquid of the (meth)acrylic acid
extraction tower (200) may be fed to the upper end of the (meth)acrylic acid
absorption tower (100) and used as an absorption solvent of (meth)acrylic acid.
In the lower discharged liquid of the (meth)acrylic acid extraction tower (200),
15 (meth)acrylic acid may be included at a concentration of 5 wt% or less. The
upper end of the (meth)acrylic acid absorption tower (100) to which at least a
part of the lower discharged liquid of the (meth)acrylic acid absorption tower
(200) is fed may be at least one point corresponding to a height of 70 % or more
from the lowest part of the absorption tower.
20 The distillation in the water separation tower (300) may be conducted in
the presence of a hydrophobic azeotropic solvent. Herein, the hydrophobic
azeotropic solvent may include the same compound as the hydrophobic
extraction solvent in the (meth)acrylic acid extraction tower (200).
By distillation in the water separation tower (300), discharged liquid
25 including (meth)acrylic acid may be recovered from the lower part of the water
separation tower (300), and discharged liquid including a hydrophobic
azeotropic solvent, water, and acetic acid may be recovered from the upper part
of the water separation tower (300).
At this time, the upper discharged liquid of the water separation tower
30 (300) may be separated into an organic layer including the hydrophobic
azeotropic solvent and an aqueous layer including acetic acid, at least a part of
the organic layer may be fed to the upper end of the wakr separation tower
(300) as an azeotropic solvent, and at least a part of the aqueous layer may be
fed to the upper end of the (meth)acrylic acid absorption tower (100) as an
5 absorption solvent.
According to another embodiment of the invention, an apparatus for
continuous recovery of (meth)acrylic acid is provided, including:
a (meth)acrylic acid absorption tower (100) for contacting a mixed gas
including organic by-products, vapor, and (meth)acrylic acid, which is produced
lo by a synthesis reaction of (meth)acrylic acid, with water, to obtain a
(meth)acrylic acid aqueous solution;
(meth)acrylic acid aqueous solution transfer lines (102 andl03) that are
respectively connected from the (meth)acrylic acid absorption tower (100) to a
(meth)acrylic acid extraction tower (200) and a water separation tower (300), to
15 which the (meth)acrylic acid aqueous solution is divided and fed;
a (meth)acrylic acid extraction tower (200) for obtaining (meth)acrylic
acid extract with reduced water content from the (meth)acrylic acid aqueous
solution that is fed through the (meth)acrylic acid aqueous solution transfer line
(1 02), and feeding it to a water separation tower (300);
20 a (meth)acrylic acid extract transfer line (203) that is connected from the
(meth)acrylic acid extraction tower (200) to a water separation tower (300), to
which the (meth)acrylic acid extract is fed; and
a water separation tower (300) for distilling a (meth)acrylic acid aqueous
solution fed through the (meth)acrylic acid aqueous solution transfer line(l03),
25 and (meth)acrylic acid extract fed through the (meth)acrylic acid extract transfer
line (203), to obtain (meth)acrylic acid.
[ADVANTAGEOUS EFFECTS]
The continuous recovery method of (meth)acrylic acid according to the
present invention may maintain a recovery rate of (meth)acrylic acid equivalent
30 to that of the previous recovery method, and yet may significantly reduce
-5-.G
energy consumption, and may minimize polymerization of (meth)acrylic acid in
the recovery process; thus providing more improved operation stability.
Specifically, the continuous recovery method of (meth)acrylic acid
according to the present invention introduces a (meth)acrylic acid extraction
5 tower (200) before a water separation tower (300) for distilling a (meth)acrylic
acid aqueous solution to recover (meth)acrylic acid, thereby largely reducing an
energy consumption amount in the water separation tower (300), thus improving
energy efficiency of the total process.
Furthermore, the method according to the present invention divides and
lo feeds the (meth)acrylic acid aqueous solution obtained from the (meth)acrylic
acid absorption tower (100) to the (meth)acrylic acid extraction tower (200) and
the water separation tower (300), thereby reducing the capacities of the
(meth)acrylic acid extraction tower and the water separation tower, thus
lowering facility load, and simultaneously maintaining treatment capacity of the
15 (meth)acrylic acid aqueous solution fed from the (meth)acrylic acid absorption
tower equivalent to that of the previous method, thus exhibiting high energy
efficiency and improved productivity.
Further, since the method of the present invention may effectively divide
treatment of the (meth)acrylic acid aqueous solution in the (meth)acrylic acid
20 extraction tower (200) and the water separation tower (300), a load in the water
separation tower (300) may be reduced, and thus temperature near the feed
inlet of the water separation tower (300) may be maintained low, thus
minimizing polymerization of (meth)acrylic acid during distillation to provide
more improved operation stability.
25 [BRIEF DESCRIPTION OF THE DRAWING]
Fig. 1 is a flowchart schematically showing the continuous recovery
method of (meth)acrylic acid according to one embodiment of the invention.
[DETAILED DESCRIPTION OF THE EMBODIMENTS]
Hereinafter, the method of continuous recovery of (meth)acrylic acid and
30 the recovery apparatus according to specific embodiments of the invention will
a7
be explained.
Unless otherwise described, terms used herein are defined as follows.
First, '(meth)acrylic acid' generally refers to acrylic acid andlor
methacrylic acid.
5 Second, '(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. That is, according to one embodiment of the invention, 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
l o 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 may include (meth)acrylic acid, non-reacted raw
material compounds, (meth)acrolein, inert gas, carbon monoxide, carbon
dioxide, water vapor, and various organic by-products (acetic acid, high boiling
15 point by-products, and the like), and the like.
As used herein, 'low boiling point by-products' (light ends) or 'high boiling
point by-products' (heavies) are kinds of by-products that can be produced in
the process of preparation and recovery of (meth)acrylic acid, and generally
refer to compounds having smaller or larger molecular weight than (meth)acrylic
20 acid.
The term '(meth)acrylic acid aqueous solution' refers to an aqueous
solution in which (meth)acrylic acid is dissolved, and for example, the
(meth)acrylic acid aqueous solution may be obtained by contacting the
(meth)acrylic acid-containing mixed gas with water.
2 5 The term '(meth)acrylic acid extract' refers to an aqueous solution having
a relatively higher concentration of (meth)acrylic acid than the (meth)acrylic acid
aqueous solution, and for example, the meth)acrylic acid extract may be
obtained by lowering the content of water included in the (meth)acrylic acid
aqueous solution in a (meth)acrylic acid extraction tower (200).
Meanwhile, the technical terms used herein are only to mention specific
+g
embodiments, and are not intended to limit the invention.
Singular forms used herein include plural forms, unless they have clearly
opposite meanings.
The meaning of 'comprising' as used herein embodies specific property,
5 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.
Hereinafter, referring to the attached drawings, specific embodiments of
the invention will be explained in detail so that one of ordinary knowledge in the
lo art may easily practice it. However, the present invention may be embodied in
various forms, and is not limited to the examples.
The inventors confirmed during studies on the continuous recovery
method of (meth)acrylic acid that the previously disclosed recovery method of
15 (meth)acrylic acid through azeotropic distillation has problems in that a very
large amount of energy is consumed in a water separation tower (or distillation
tower) for distilling a (meth)acrylic acid aqueous solution, and operation stability
is lowered due to the production of a polymer by polymerization of (meth)acrylic
acid.
20 Therefore, the inventors confirmed during repeated studies for improving
these problems that if a (meth)acrylic acid extraction tower (200) is introduced
before a water separation tower (300) for distilling a (meth)acrylic acid aqueous
solution that is obtained in a (meth)acrylic acid absorption tower (loo), and
particularly, if the (meth)acrylic acid aqueous solution obtained in the
25 (meth)acrylic acid absorption tower (100) is divided and fed to the (meth)acrylic
acid extraction tower (200) and the water separation tower (300), as shown in
Fig. 1, energy efficiency of the total process may be improved. Furthermore,
the inventors confirmed that the process of Fig. 1 may effectively divide the load
of the water separation tower (300), thus minimizing a polymerization reaction
30 of (meth)acrylic acid in a distillation process, to provide more improved
-8-9
operation stability.
Thus, according to one embodiment of the invention, a method of
continuous recovery of (meth)acrylic acid is provided, including:
contacting a mixed gas including (meth)acrylic acid, organic by-products,
5 and vapor, which is produced by a synthesis reaction of (meth)acrylic acid, with
water in a (meth)acrylic acid absorption tower (100) to obtain a (meth)acrylic
acid aqueous solution;
dividing and feeding the (meth)acrylic acid aqueous solution to a
(meth)acrylic acid extraction tower (200) and a water separation tower (300);
10 obtaining a (meth)acrylic acid extract with reduced water content from
the (meth)acrylic acid aqueous solution that is fed to the (meth)acrylic acid
extraction tower(200), and feeding it to a water separation tower (300); and
distilling the (meth)acrylic acid aqueous solution and the (meth)acrylic
acid extract that are fed to the water separation tower (300) to obtain
15 (meth)acrylic acid.
Hereinafter, referring to Fig. 1, each step of the continuous recovery
method of (meth)acrylic acid according to the present invention will be
explained.
20 First, the method of continuous recovery of (meth)acrylic acid according
to the present invention includes a step of obtaining a (meth)acrylic acid
aqueous solution.
Since the (meth)acrylic acid aqueous solution may be obtained by a
common method in the technical field to which the invention pertains, the
25 method is not specifically limited. However, according to the present invention,
this step may be conducted by contacting a mixed gas including (meth)acrylic
acid, organic by-products, and vapor, which is produced by a synthesis reaction
of (meth)acrylic acid, with an absorption solvent in a (meth)acrylic acid
absorption tower (100) to obtain a (meth)acrylic acid aqueous solution.
Herein, the synthesis reaction of the (meth)acrylic acid may be
-4 \o
conducted by an oxidation reaction of at least one compound selected from the
group consisting of propane, propylene, butane, isobutylene, t-butylene, and
(meth)acrolein in the presence of a gas phase catalyst.
The gas phase oxidation reaction may be progressed in a gas phase
5 oxidation reactor of a common structure and under common reaction conditions.
As the catalyst of the gas phase oxidation reaction, common catalysts may be
used, and preferably, catalysts described in Korean Registered Patent No.
0349602 and No. 037818, and the like may be used. However, the gas phase
oxidation reaction is not limited to the above examples in the present invention.
10 In the (meth)acrylic acid-containing mixed gas produced by the gas
phase oxidation reaction, unreacted raw material compounds, intermediate
(meth)acrolein, other inert gasses, carbon dioxide, vapor, and various organic
by-products (acetic acid, low boiling point by-products, high boiling point
by-products, and the like), and the like may be included, in addition to the end
15 product (meth)acrylic acid.
According to the present invention, the (meth)acrylic acid-containing
mixed gas (1) may be fed to the (meth)acrylic acid absorption tower (100) and
contact with absorption solvent water, and thereby be obtained in the form of an
aqueous solution in which (meth)acrylic acid is dissolved.
20 The (meth)acrylic acid absorption tower (100) may be in the form of a
packed column including fillers such as raschig rings, pall rings, a saddles,
gauze, a structured packing, and the like, or a common multistage column, so
as to improve contact efficiency of the (meth)acrylic acid-containing mixed
gas(1) with an absorption solvent.
25 According to thk present invention, the (meth)acrylic acid-containing
mixed gas (1) may be fed to the lower part of the (meth)acrylic acid absorption
tower (loo), and an absorption solvent for absorbing (meth)acrylic acid included
in the mixed gas (1) is fed to the upper part of the (meth)acrylic acid absorption
tower (1 00).
The absorption solvent of the (meth)acrylic acid may be water such as
4% \ tap water, deionized water, and the like, and the absorption solvent may include
cycle process water that is introduced from a different process. Thus, the
absorption solvent may include a trace amount of organic by-products (for
example, acetic acid) introduced from a different process, and according to one
5 embodiment of the invention, in the absorption solvent fed to the (meth)acrylic
acid absorption tower(100), organic by-products may be included at a
concentration of 3 to 20 wt%.
That is, considering absorption efficiency of (meth)acrylic acid in the
(meth)acrylic acid absorption tower(100), it is preferable that the absorption
lo solvent (particularly, cycle process water) fed to the (meth)acrylic acid
absorption tower(100) includes 20 wt% or less of organic by-products.
Meanwhile, the (meth)acrylic acid absorption tower (100) may be
operated at the internal pressure of 1 to 1.5 bar, preferably 1 to 1.3 bar,
considering the condensation condition of (meth)acrylic acid and moisture
15 content condition according to saturated water vapor pressure, and the like; and
the internal temperature of the (meth)acrylic acid absorption tower(l00) may be
controlled to 50 to 100 "C, preferably 50 to 80 "C .
Through the above process, a (meth)acrylic acid aqueous solution is
discharged to the lower part of the (meth)acrylic acid absorption tower (loo),
20 and (meth)acrylic acid-stripped non-condensable gas may be discharged to the
upper part of the (meth)acrylic acid absorption tower (100).
Herein, it is advantageous in terms of improvement in process efficiency
that the (meth)acrylic acid aqueous solution that is discharged to the lower part
of the (meth)acrylic acid absorption tower (100) includes (meth)acrylic acid at a
25 concentration of 40 to 90 wt%, preferably 50 to 90 wt%, and more preferably 50
to 80 wt%.
Meanwhile, at least a part of the non-condensable gas that is discharged
to the upper part of the (meth)acrylic acid absorption tower (100) may be fed to
a step of recovering organic by-products (particularly acetic acid) included in the
30 non-condensable gas, and the remainder may be fed to a waste gas incinerator.
4-t IL
That is, according to one embodiment of the invention, a step of contacting
non-condensable gas that is discharged to the upper part of the (meth)acrylic
acid absorption tower (100) with absorption solvent water to recover acetic acid
included in the non-condensable gas may be further conducted.
5 According to the present invention, the step of contacting
non-condensable gas with an absorption solvent may be conducted in an acetic
acid absorption tower (150). Further, for an effective acetic acid absorption
process, the acetic acid absorption tower (150) may be operated at a pressure
of 1 to 1.5 bar, and preferably 1 to 1.3 bar, and the internal temperature of the
lo acetic acid absorption tower(l50) may be controlled to 50 to 100 "C, and
preferably 50 to 80 "C. Further, specific operation conditions of the acetic acid
absorption tower (150) may follow Korean Laid-Open Patent No. 2009-0041 355
of the applicant.
Herein, an absorption solvent for absorbing particularly acetic acid
15 among the organic by-products included in the non-condensable gas 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 (1 50).
As the acetic acid absorption solvent, the same kind as the
20 above-explained (meth)acrylic acid absorption solvent may be used, and
preferably, the acetic acid-containing aqueous solution that is discharged from
the acetic acid absorption tower (150) may be fed to the (meth)acrylic acid
absorption tower (100) and used as an absorption solvent. Further, acetic
acid-stripped gas is discharged to the upper part of the acetic acid absorption
25 tower (150), and may be recycled to the above-explained (meth)acrylic acid
synthesis reaction step and reused.
Meanwhile, the method of continuous recovery of (meth)acrylic acid
includes a step of dividing and feeding the (meth)acrylic acid aqueous solution
30 that is discharged from the (meth)acrylic acid absorption tower (100) to the
A-2 I3
(meth)acrylic acid extraction tower (200) the a water separation tower (300).
According to the present invention, as shown in Fig. 1, the (meth)acrylic
acid absorption tower (100) is connected simultaneously to the (meth)acrylic
acid extraction tower (200) and the water separation tower (300) through
5 (meth)acrylic acid aqueous solution transfer lines (102 and 103), respectively,
and the (meth)acrylic acid extraction tower (200) is connected to the water
separation tower (300) through a (meth)acrylic acid extract transfer line (203).
The (meth)acrylic acid extraction tower (200) is an apparatus for
removing water that has been used as an absorption solvent in the step of
lo obtaining a (meth)acrylic acid aqueous solution and recovering an extract with a
higher concentration of (meth)acrylic acid therefrom.
Further, the water separation tower (300) is an apparatus for
azeotropically distilling the (meth)acrylic acid aqueous solution fed from the
(meth)acrylic acid absorption tower (100) and the (meth)acrylic acid extract fed
15 from the (meth)acrylic acid extraction tower (200), to recover (meth)acrylic acid
therefrom. The (meth)acrylic acid extraction tower (200) and the water
separation tower (300) will be explained later.
As explained above, in the previously disclosed recovery method of
(meth)acrylic acid through azeotropic distillation, the whole (meth)acrylic acid
20 aqueous solution obtained from the (meth)acrylic acid absorption tower(100) is
fed to a water separation tower(300) and distilled.
To the contrary, the method of continuous recovery of (meth)acrylic acid
according to the present invention introduces a (meth)acrylic acid extraction
tower (200) before the water separation tower (300), thereby largely reducing
25 treatment load of the (meth)acrylic acid aqueous solution in the water
separation tower (300) and energy consumption amount.
Furthermore, the method of the present invention divides and supplies
the (meth)acrylic acid aqueous solution obtained from the (meth)acrylic acid
absorption tower (100) to the (meth)acrylic acid extraction tower (200) and the
30 water separation tower (300), thereby reducing total facility load, and
*'9
simultaneously minimizing a polymerization reaction of (meth)acrylic acid in the
water separation tower(300), thus providing more improved operation stability.
According to the present invention, the ratio of dividing and feeding the
(meth)acrylic acid obtained from the (meth)acrylic acid absorption tower (1 00) to
5 the (meth)acrylic acid extraction tower (200) and the water separation tower
(300) may be determined considering a capacity ratio of the (meth)acrylic acid
extraction tower (200) and the water separation tower (300), treatment capacity,
energy efficiency improvement effect of the total process, and the like.
Taking the above conditions into consideration, it is advantageous for
lo 5-70 wt%, more preferably 20-50 wt%, of the (meth)acrylic acid aqueous
solution obtained from the (meth)acrylic acid absorption tower(100) to be fed to
the (meth)acrylic acid extraction tower (200), and the remainder may be fed to
the water separation tower (300).
In other words, the content ratio (wt%) of the (meth)acrylic acid aqueous
15 solution divided and fed from the (meth)acrylic acid absorption tower (100) to
the (meth)acrylic acid extraction tower (200) and the water separation tower
(300) may be 5:95, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55,
50:50, 55:45, 60:40, 65:35, 70:30, or the like, preferably 20:80 to 70:30, more
preferably 30:70 to 60:40, and most preferably 40:60 to 50:50. However, the
20 present invention is not limited to the above exemplified ratios, and the ratio
may be variously controlled within the above range, considering the purpose
and the effect of the present invention.
According to the present invention, as the amount of the (meth)acrylic
acid aqueous solution fed to the (meth)acrylic acid extraction tower (200)
25 becomes larger, the effect of dividing treatment with the water separation tower
(300) may be improved, and thus energy efficiency of the total process may be
improved.
However, if excessive (meth)acrylic acid aqueous solution is fed to the
extraction tower (200), an extraction tower (200) having larger capacity may be
30 required, the operation conditions of the water separation tower (300) at the
J-4- I5
back end may become inferior, thus increasing loss of (meth)acrylic acid to
lower process efficiency, and thus it is advantageous for the feed ratio of the
(meth)acrylic acid aqueous solution to be controlled within the above-explained
range.
5 Further, as the amount of the (meth)acrylic acid aqueous solution fed to
the water separation tower(300) becomes larger, the amount of water that
should be removed by azeotropic distillation in the water separation tower(300)
may be increased, thus lowering the effect of reducing energy consumption,
such that it is advantageous for the feed ratio of the (meth)acrylic acid aqueous
l o solution to be controlled within the above-explained range.
The (meth)acrylic acid aqueous solution may be divided and fed from the
(meth)acrylic acid absorption tower(100) through the (meth)acrylic acid aqueous
solution transfer lines (1 02 and 103) respectively connected to the (meth)acrylic
acid extraction tower (200) and the water separation tower (300). The
15 (meth)acrylic acid aqueous solution may be divided and fed at the
above-explained ratio by common means installed in the transfer lines (1 02 and
103).
Meanwhile, the method of continuous recovery of (meth)acrylic acid
20 according to the present invention includes a step of obtaining a (meth)acrylic
acid extract with reduced water content from the (meth)acrylic acid aqueous
solution that is fed to the (meth)acrylic acid extraction tower (200), and feeding
it to the water separation tower (300) (hereinafter referred to as an 'extraction
process').
2 5 According to the present invention, the (meth)acrylic acid extraction
tower (200) receives a part of the (meth)acrylic acid aqueous solution obtained
from the (meth)acrylic acid absorption tower (loo), removes most of water
included in the (meth)acrylic acid aqueous solution without using a significant
amount of energy, and feeds it to the water separation tower (300), thereby
30 reducing energy used for azeotropic distillation in the water separation tower
45 16
(300) as described below.
Herein, the (meth)acrylic acid extract may be obtained by contacting the
(meth)acrylic acid aqueous solution that is fed to the (meth)acrylic acid
extraction tower (200) with a hydrophobic extraction solvent to remove water
5 included in the aqueous solution. That is, it is preferable in terms of
improvement in energy efficiency of the total process for the extraction in the
(meth)acrylic acid extraction tower(200) to use a liquid-liquid contact method.
The hydrophobic extraction solvent may be a hydrocarbon solvent that
forms an azeotrope with water and organic by-products (acetic acid and the
lo like), and that does not form an azeotrope with (meth)acrylic acid but can
sufficiently extract it. Further, it may have a boiling point of 10 to 120 "C so as
to improve extraction process efficiency.
According to the present invention, the hydrophobic extraction solvent
satisfying the above properties may be at least one solvent selected from the
15 group consisting of benzene, toluene, xylene, n-heptane, cycloheptane,
cycloheptene, I -heptene, ethyl-benzene, methyl-cyclohexane, n-butyl acetate,
isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methyl
isobutyl ketone, 2-methyl-I -heptene, 6-methyl-I -heptene, 4-methyl-I -heptene,
2-ethyl-I -hexenel ethylcyclopentane, 2-methyl-I -hexenel 2,3-dimethylpentane,
20 5-methyl-I -hexene, and isopropyl-butyl-ether.
Meanwhile, it is advantageous in terms of improvement in process
efficiency for the temperature of the (meth)acrylic acid aqueous solution to be
10 to 70 "C in the extraction process, and for the weight ratio of the
hydrophobic extraction solvent to the (meth)acrylic acid aqueous solution to be
25 1.1 to 1.5, preferably 1:1.2 to 1.2.5.
Further, for the extraction process, a common extraction apparatus
according to a liquid-liquid contact method may be used. Non-limiting
examples of the extraction apparatus may include a Karr reciprocating plate
column, a rotary-disk contactor, a Scheibel column, a Kuhni column, a spray
30 extraction tower, a packed extraction tower, a pulsed packed column, a
17
mixer-settler, a centrifugal counter current extractor, and the like.
By this method, (meth)acrylic acid extract from which most water
included in the (meth)acrylic acid aqueous solution has been removed may be
obtained, and preferably, (meth)acrylic acid extract is discharged to the upper
5 part of the (meth)acrylic acid extraction tower (200), and the discharged extract
is fed to the water separation tower (300) through the (meth)acrylic acid extract
transfer line (203).
In addition, at least a part of the lower discharged liquid of the
(meth)acrylic acid extraction tower (200) may be fed to the upper end of the
lo (meth)acrylic acid absorption tower (100) and used as a part of the
(meth)acrylic acid absorption solvent, and a part of the lower discharged liquid
may be treated as waste water.
It is also preferable in terms of improvement in the efficiency of the
absorption process for the upper end of the (meth)acrylic acid absorption tower
15 (100) to which the lower discharged liquid of the extraction tower (200) is
recycled to be at least one point corresponding to the height of 70 % or more
from the lowest part of the absorption tower (100). In addition, it is preferable
that (meth)acrylic acid is not included in the lower discharged liquid of the
(meth)acrylic acid extraction tower (200), but it may be included a little, and the
20 amount may be preferably 5 wt% or less.
Meanwhile, the method of continuous recovery of (meth)acrylic acid
according to the present invention includes a step of distilling the (meth)acrylic
acid aqueous solution and the (meth)acrylic acid extract that are fed to the
25 water separation tower (300) to obtain (meth)acrylic acid (hereinafter referred to
as a 'distillation process').
The distillation process is a process for azeotropically distilling the
(meth)acrylic acid aqueous solution that is fed from the (meth)acrylic acid
absorption tower (1 00) to the water separation tower (300) and the (meth)acrylic
30 acid extract that is fed from the (meth)acrylic acid extraction tower (200) to the
* 18
water separation tower (300), thereby removing water and organic by-products
and separating and obtaining (meth)acrylic acid.
The (meth)acrylic acid aqueous solution and the (meth)acrylic acid
extract are fed to the water separation tower (300) respectively through
5 separate transfer lines (103 and 203), wherein the location of the water
separation tower (300) to which each solution is fed may be the same or
different, but it is advantageous in terms of improvement in the process
efficiency for the solutions to be fed to the same location.
Meanwhile, according to the present invention, it is advantageous for the
lo distillation in the water separation tower (300) to be conducted in the presence
of a hydrophobic azeotropic solvent, because it may simultaneously recover
water and organic by-products (acetic acid and the like).
The hydrophobic azeotropic solvent is a hydrophobic solvent that can
form an azeotrope with water and acetic acid, and that does not form an
15 azeotrope with (meth)acrylic acid, and hydrocarbon solvents satisfying the
above properties may be used without specific limitations. Further, the
hydrophobic azeotropic solvent may have a lower boiling point than
(meth)acrylic acid, and preferably, it may have a boiling point of 10 to 120 "C.
The hydrophobic azeotropic solvents satisfying the above properties may
20 include at least one selected from the group consisting of benzene, toluene,
xylene, n-heptane, cycloheptane, cycloheptene, I-heptene, ethyl-benzene,
methyl-cyclohexane, n-butyl acetate, isobutyl acetate, isobutyl acrylate, n-propyl
acetate, isopropyl acetate, methyl isobutyl ketone, 2-methyl-I-heptene,
6-methyl-I -heptene, 4-methyl-I -heptene, 2-ethyl-I -hexenel ethylcyclopentane,
25 2-methyl-I -hexene, 2,3-dimethylpentane, 5-methyl-I -hexene, and
isopropyl-butyl-ether.
The hydrophobic azeotropic solvent may be identical to or different from
the hydrophobic extraction solvent that is applied for the (meth)acrylic acid
extraction tower(200). However, considering the production efficiency
30 according to the continuous process, the hydrophobic azeotropic solvent
*)'=I
preferably includes the same compounds as the hydrophobic extraction solvent.
As such, if the same compound is used as the azeotropic solvent and the
extraction solvent, at least a part of the azeotropic solvent that is distilled in the
water separation tower (300) and recovered may be fed to the lower part of the
5 (meth)acrylic acid extraction tower (200) and used as a part of the extraction
solvent.
Meanwhile, the water separation tower (300) may be equipped with a
packed column or multistage column including the above-explained filler,
preferably a sieve tray column or a dual flow tray column, therein.
10 If the hydrophobic azeotropic Solvent is introduced into the upper part of
the water separation tower (300), the azeotrope of (meth)acrylic acid and the
absorption solvent (for example, water) may be broken. Thus, water and
acetic acid in the (meth)acrylic acid aqueous solution directly fed from the
(meth)acrylic acid absorption tower (100); a part of water, acetic acid, and
15 hydrophobic extraction solvent that are not removed in the (meth)acrylic acid
extraction tower (200); and the hydrophobic azeotropic solvent used for
azeotropic distillation may form an azeotrope and be recovered from the upper
part of the water separation tower (300). Further, discharged liquid containing
(meth)acrylic acid may be recovered from the lower part of the water separation
20 tower (300).
The upper discharged liquid of the water separation tower (300) may be
fed to a phase separator (350) and subjected to predetermined treatment and
then reused. The phase separator (350) is an apparatus for separating liquid
phases that are not mixed with each other using gravity or centrifugal force, and
25 the like, and a relatively light liquid may be recovered from the upper part of the
phase separator (350), while a relatively heavy liquid may be recovered from
the lower part of the phase separator (350).
In the present invention, for example, in case water is used as an
absorption solvent of (meth)acrylic acid, the upper discharged liquid that is fed
30 to the phase separator (350) may be separated into an organic layer containing
49 Z b
a hydrophobic azeotropic solvent and an aqueous layer containing water.
At least a part of the organic layer that is separated in the phase
separator (350) may be fed to the upper end of the water separation tower (300)
and used as an azeotropic solvent, and the remainder of the organic layer may
5 be fed to the (meth)acrylic acid extraction tower (200) and used as an extraction
solvent, as necessary. At least a part of the aqueous layer that is separated in
the phase separator (350) may be fed to the upper end of the (meth)acrylic acid
absorption tower (100) and used as an absorption solvent, and a part thereof
may be treated as waste water.
10 Acetic acid may be included in the water layer, and the concentration of
acetic acid included in the aqueous layer may be varied according to the kind of
azeotropic solvents and reflux ratio of the column installed in the water
separation tower, and the like. According to the present invention, the
concentration of acetic acid included in the aqueous layer of the upper
15 discharged liquid may be 1 to 50 wt%, preferably 2 to 40 wt%, more preferably
3 to 30 wt%.
Meanwhile, discharged liquid containing (meth)acrylic acid is recovered
from the lower part of the water separation tower (300), which is crude
(meth)acetic acid, and may be fed to an additional purification process as
20 necessary.
Water, acetic acid, and the azeotropic solvent may be included in the
lower discharged liquid of the water separation tower (300), and preferably, the
water, the acetic acid, and the azeotropic solvent may be included respectively
in an amount of less than 0.1 wt%, so that the lower discharged liquid may be
25 used as crude (meth)acrylic acid.
While the (meth)acrylic acid aqueous solution passes through the
(meth)acrylic acid absorption tower (loo), the (meth)acrylic acid extraction
tower (200), the water separation tower (300), and the like, at least a part of
(meth)acrylic acid included in the aqueous solution may be polymerized to
30 produce a polymer such as a dimer or oligomer and the like. In order to
20 21
minimize the polymerization of (meth)acrylic acid, a polymerization inhibitor may
be added to the water separation tower (300), and commonly used
polymerization inhibitors may be used without specific limitations.
5 Meanwhile, in the lower discharged liquid of the water separation tower
(300), high boiling point by-products such as a (meth)acrylic acid polymer, a
polymerization inhibitor, and the like may be included in addition to (meth)acrylic
acid. Thus, as necessary, a step of feeding the lower discharged liquid of the
water separation tower (300) to a high boiling point by-product separation tower
lo (400) to separate high boiling point by-products included in the lower
discharged liquid may be further conducted.
The high boiling point by-product separation tower (400) may have a
common structure, it may be operated under common reaction conditions, and
the construction and reaction conditions of the separation tower are not
15 specifically limited. High boiling point by-products included in the lower
discharged liquid of the water separation tower (300) may be recovered from
the lower part of the high boiling point by-product separation tower (400), and
crude (meth)acrylic acid (CAA) free of high boiling point by-products may be
recovered from the upper part of the high boiling point by-product separation
20 tower (400).
The crude (meth)acrylic acid (CAA) may be obtained as high purity
(meth)acrylic acid (HPAA) through an additional crystallization process.
Each step that can be included in the method of recovery of (meth)acrylic
acid according to the present invention may be conducted continuously, and
25 besides the above-explained steps, any steps commonly conducted in the
technical field to which the invention pertains may be further conducted before
or after each step.
For example, a process of feeding the (meth)acrylic acid aqueous
solution obtained in the (meth)acrylic acid absorption tower (1 00) to a separate
30 stripping tower, before dividing and feeding it to the (meth)acrylic acid extraction
*22
tower (200) and the water separation tower (300) so as to remove low boiling
point by-products (acrolein, propionaldehyde, acetaldehyde, formaldehyde,
isopropyl acetate, and the like) dissolved in the (meth)acrylic acid aqueous
solution may be further conducted.
5
Meanwhile, according to another embodiment of the invention, an
apparatus for continuous recovery of (meth)acrylic acid is provided, including:
a (meth)acrylic acid absorption tower (100) for contacting mixed gas
including organic by-products, vapor, and (meth)acrylic acid, which is produced
lo by a synthesis reaction of (meth)acrylic acid, with water, to obtain a
(meth)acrylic acid aqueous solution;
(meth)acrylic acid aqueous solution transfer lines (1 02 and1 03) that are
connected from the (meth)acrylic acid absorption tower (100) to the
(meth)acrylic acid extraction tower (200) and the water separation tower (300)
15 respectively, to which the (meth)acrylic acid aqueous solution is divided and
fed;
a (meth)acrylic acid extraction tower (200) for obtaining (meth)acrylic
acid extract with reduced water content from the (meth)acrylic acid aqueous
solution that is fed through the (meth)acrylic acid aqueous solution transfer line
20 (1 02), and feeding it to a water separation tower (300);
a (meth)acrylic acid extract transfer line (203) that is connected from the
(meth)acrylic acid extraction tower (200) to the water separation tower (300), to
which the (meth)acrylic acid extract is fed; and
the water separation tower (300) for distilling the (meth)acrylic acid
25 aqueous solution fed through the (meth)acrylic acid aqueous solution transfer
line (103) and the (meth)acrylic acid extract fed through the (meth)acrylic acid
extract transfer line (203) to obtain (meth)acrylic acid.
Specifically, in the apparatus according to the present invention, the
(meth)acrylic acid absorption tower (100) is connected simultaneously to the
30 (meth)acrylic acid extraction tower (200) and the water separation tower (300)
23 23
through each (meth)acrylic acid aqueous solution transfer line (102 andl03),
and the (meth)acrylic acid extraction tower (200) is connected to the water
separation tower (300) through a (meth)acrylic acid extract transfer line (203).
According to the present invention, the (meth)acrylic acid absorption
5 tower (100) may be in the form of a packed column or a multistage column
including fillers such as raschig rings, pall rings, a saddles, a gauze, a structure
packing, and the like therein, so as to improve contact efficiency of the
(meth)acrylic acid-containing mixed gas (1) with an absorption solvent water.
As the (meth)acrylic acid extraction tower (200), a common extractor
lo according to a liquid-liquid contact method may be used, and non-limiting
examples thereof may include a Karr 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, a mixer-settler, a centrifugal
counter current extractor, and the like.
15 The water separation tower (300) may be equipped with a pack column
or a multistage column including the above-explained fillers, preferably a sieve
tray column or a dual flow tray column, therein.
In addition, the acetic acid absorption tower (150), the (meth)acrylic acid
aqueous solution transfer lines (102 and 103), the (meth)acrylic acid extract
20 transfer line (203), the phase separator (350), the high boiling point by-product
separation tower (400), and the like, which are shown in Fig. 1, may have
constructions common in the technical field to which the invention pertains, and
the action and effect in each process are as explained above.
Hereinafter, preferable examples are presented to aid in understanding
of the invention. However, these examples are only to illustrate the invention,
and the invention is not limited thereto.
Example 1
In order to verify the effects of energy reduction and improvement in
30 operation stability of the water separation tower (300) resulting from the dividing
23 24
and feeding of the (meth)acrylic acid aqueous solution obtained in the
(meth)acrylic acid absorption tower (100) to the (meth)acrylic acid extraction
tower (200) and the water separation tower (300), a continuous recovery
apparatus having the construction as shown in Fig. 1 was prepared, and the
5 following process was continuously conducted.
I. (Meth)acrylic acid absorption tower - preparation of an acrylic
acid aqueous solution
The reaction gas obtained by oxidation of propylene was introduced into
a (meth)acrylic acid absorption tower (100) to obtain an acrylic acid aqueous
lo solution (composition: about 68 wt% of acrylic acid, about 2 wt% of acetic acid,
and about 30 wt% of water) from the lower part of the (meth)acrylic acid
absorption tower (100) using water as a (meth)acrylic acid absorption solvent.
The acrylic acid aqueous solution was divided and fed to a (meth)acrylic
acid extraction tower (200) and a water separation tower (300) at the weight
15 ratio of 35:65.
II. (Meth)acrylic acid extraction tower - removal of water from the
acrylic acid aqueous solution
As a (meth)acrylic acid extraction tower (200), a Karr type liquid-liquid
reciprocating extractor having an inner diameter of 22 mm and a total of 56
20 stages was used. 35 wt% of the acrylic acid aqueous solution discharged to
the lower part of the (meth)acrylic acid absorption tower was introduced through
a first stage, the uppermost stage of the extraction tower (ZOO), at a flow rate of
about 91.09 glmin. A part of reflux flow containing toluene obtained as an
organic layer in the upper discharged liquid of the water separation tower (300)
25 described below was used as an extraction solvent, and the extraction solvent
was introduced through a 56th stage, the lowest stage of the extraction tower
(ZOO), at a flow rate of about 11 8.73 glmin.
After stable operation was conducted, at a steady state, an acrylic acid
extract (composition: about 64.8 wt% of toluene, about 32.9 wt% of acrylic acid,
30 about 1.6 wt% of water, and about 0.6 wt% of acetic acid) was obtained from
44-25
the upper part of the extraction tower (200), and water (composition: about 95.1
wt% of water, about 1.8 wt% of acrylic acid, and about 3.1 wt% of acetic acid)
was discharged to the lower part of the extraction tower (200). As the result of
operation of the (meth)acrylic acid extraction tower (200), the removal rate of
5 water from the acrylic acid aqueous solution fed from the (meth)acrylic acid
absorption tower (100) was measured to be about 89.7 %, and the removal rate
of acetic acid was measured to be about 65.6 %. Further, the acrylic acid
extract discharged to the upper part of the extraction tower (200) was fed to the
water separation tower (300).
10 Ill. Water separation tower - azeotropic distillation
As the water separation tower (300), a dual flow tray pilot column having
an inner diameter of 30 mm and a total of 28 stages was used, and the
operation pressure was maintained at 11 0 torr.
To the water separation tower (300), 65 wt% of the acrylic acid aqueous
15 solution that is discharged to the lower part of the (meth)acrylic acid absorption
tower (100) and the acrylic acid extract that is discharged to the upper part of
the (meth)acrylic acid extraction tower (200) were fed. At this time, the acrylic
acid aqueous solution was introduced into the 14'~s tage from the upper part of
the water separation tower (300) at a flow rate of about 6.08 glmin, and the
20 acrylic acid extract was introduced into the 14'~st age from the upper part of the
water separation tower (300) at a flow rate of about 6.55 glmin. A part of the
toluene reflux flow that is separated from a phase separator (350) was
introduced to the first stage, the uppermost stage of the water separation tower
(300), at a flow rate of about 7.66 glmin as an azeotropic solvent.
2 5 Heat was fed through a reboiler at the lower stage of the water
separation tower (300) so that the temperature of the 16'~ stage of the water
separation tower (300) became about 86 "C or more, and the temperature of
the 12nd stage may not exceed about 58 "C. After stable operation was
conducted for about 10 hours at a steady state, a distillate was discharged to
30 the upper part of the water separation tower (300) at a flow rate of 14.01 glmin,
* 2g
and an acrylic acid flow of 6.29 glmin was obtained from the lower part of the
water separation tower (300). Herein, at a steady state, the temperature of the
upper part of the water separation tower (300) was maintained at about 40.1 "C,
and the temperature of the lower part was maintained at about 96.9 "C.
5 As the result of the operation of the water separation tower (300), the
removal rate of water and acetic acid included in the acrylic acid extract and the
acrylic acid aqueous solution fed to the water separation tower was about 99 %
or more, acrylic acid flow wherein most water and acetic acid were removed
could be obtained from the lower part of the water separation tower (300), and
lo acrylic acid that was lost to the upper part of the water separation tower (300)
was about 0.22 wt%.
The water separation tower (300) could be operated stably without
producing a polymer in the tower even after 10 days of long term operation.
The following Table 1 shows the flow rate and the concentration of each
15 flow at a steady state operation of the water separation tower (300).
The treatment amount of the acrylic acid aqueous solution through the
(meth)acrylic acid absorption tower (IOO), (meth)acrylic acid extraction tower
20 (200), and water separation tower (300) was about 9.4 g per minute, the
[Table 1 I
-
Lower
flow of
water
separation
tower
6.29
0.00
99.95
0.03
0.00
0.03
Mass Flow
(glmin)
Acrylic
acid
aqueous
solution
6.08
0.00
67.99
2.00
29.22
0.02
Composition
(wt%)
Toluene
Acrylic
acid
Acetic
acid
Water
Heavies
Acrylic
acid
extract
flow
6.55
64.88
32.90
0.66
1.55
0.02
Reflux
flow of
azeotropic
solvent
7.66
99.74
0.10
0.16
0.00
0.00
Upper
flow of
water
separation
tower
14.01
84.58
0.22
1.22
13.98
0.00
production amount of acrylic acid was about 6.3 g per minute, and total
recovery rate of acrylic acid was about 99.6 %. As a result of calculating
energy consumption amount using an ASPEN PLUS process simulator program
(AspenTech Inc.), it was confirmed that 22.7 cal was consumed per 1 g of the
5 obtained acrylic acid.
Example 2
An acrylic acid aqueous solution was obtained from the (meth)acrylic
acid absorption tower (100) by the same method as Example 1.
10 The obtained acrylic acid aqueous solution was fed to the (meth)acrylic
acid extraction tower (200) and the water separation tower (300) in the amount
of each 50 wt%. Herein, the acrylic acid aqueous solution discharged from the
(meth)acrylic acid absorption tower (1 00) and the acrylic acid extract discharged
from the (meth)acrylic acid extraction tower (200) were introduced into the 14'~
15 stage from the upper part of the water separation tower (300), respectively at a
flow rate of about 5.75 glmin and about 11.5 glmin.
The toluene reflux flow of the upper part of the water separation
tower(300) was introduced into the first stage that is the uppermost stage at a
flow rate of 4.4 glmin. Heat was fed through a reboiler at the lower part of the
20 water separation tower (300) so that the temperature of the 16'~s tage became
about 81 "C or more, and the temperature of the 12nd stage may not exceed
about 49 "C.
After stable operation was conducted for about 10 hours, at a steady
state, distillate was discharged to the upper part of the water separation tower
25 (300) at a flow rate of about 14.0 glmin, and acrylic acid flow of about 7.65
glmin was obtained from the lower part of the water separation tower(300).
Herein, at a steady state, the temperature of the upper part of the water
separation tower (300) was maintained at about 40.4 "C, and the temperature
of the lower part was maintained at about 96.2 "C.
As a result of operation of the water separation tower (300), the removal
4720
rate of water and acetic acid included in the acrylic acid extract and the acrylic
acid aqueous solution fed to the water separation tower was about 98 % or
more, acrylic acid flow wherein most of water and acetic acid were removed
could be obtained from the lower part of the water separation tower, and acrylic
5 acid lost to the upper part of the water separation tower was about 0.50 wt%.
The water separation tower (300) could be operated stably without
producing a polymer in the tower even after 10 days of long term operation.
The following Table 2 shows the flow rate and the concentration of each
flow at steady stage operation of the water separation tower (300).
10
[Table 21
The treatment amount of the acrylic acid aqueous solution through the
(meth)acrylic acid absorption tower (loo), (meth)acrylic acid extraction tower
(200), and water separation tower (300) was about 11.5 g per minute, the
15 production amount of acrylic acid was about 7.65 g per minute, and total
recovery rate of acrylic acid was about 99.1 %. As a result of calculating
energy consumption amount using an ASPEN PLUS process simulator program
(AspenTech Inc.), it was confirmed that 18.7 cal was consumed per 1 g of the
obtained acrylic acid.
20
Mass Flow
(glm in)
Acrylic
acid
extract
flow
11.50
Acrylic
acid
aqueous
solution
5.75
Reflux
flow of
azeotropic
solvent
4.40
Composition
(wt%)
99.74
0.10
0.16
0.00
0.00
Upper
flow of
water
separation
tower
14.00
----
Toluene
Acrylic
acid
Acetic
acid
Water
Heavies
Lower
flow of
water
separation
tower
7.65
84.07
0.50
1.40
14.03
0.00
0.00
99.92
0.05
0.00
0.04
0.00
67.99
2.00
29.99
0.02
64.88
32.90
0.66
1.55
0.02
Comparative Example 1: Azeotropic distillation bv feeding the total
amount of an acrylic acid aqueous solution to a water separation tower
An acrylic acid aqueous solution was obtained from the (meth)acrylic
acid absorption tower (100) by the same method as Example 1.
5 The total amount of the obtained acrylic acid aqueous solution was fed to
the water separation tower (300). Herein, the acrylic acid aqueous solution
discharged from the (meth)acrylic acid absorption tower (100) was introduced
into the 14'~s tage from the upper part of the water separation tower (300) at a
flow rate of about 6.5 glmin.
10 The toluene reflux flow of the upper part of the water separation tower
(300) was introduced into the first stage that is the uppermost stage at a flow
rate of 11.95 glmin. Heat was fed through a reboiler at the lower part of the
water separation tower (300) so that the temperature of the 16'~ stage became
about 88 "C or more, and the temperature of the 12nd stage may not exceed
15 about 65 "C.
After stable operation was conducted for about 10 hours, at a steady
state, distillate was discharged to the upper part of the water separation tower
(300) at a flow rate of about 14.14 glmin, and acrylic acid flow of about 4.31
glmin was obtained from the lower part of the water separation tower (300).
20 Herein, at a steady state, the temperature of the upper part of the water
separation tower(300) was maintained at about 40.4 "C, and the temperature of
the lower part was maintained at about 97.1 "C.
As a result of operation of the water separation tower (300), the removal
rate of water and acetic acid included in the acrylic acid extract and the acrylic
25 acid aqueous solution fed to the water separation tower was about 99 % or
more, acrylic acid flow wherein most of water and acetic acid were removed
could be obtained from the lower part of the water separation tower, and acrylic
acid lost to the upper part of the water separation tower was about 0.13 wt%.
When the water separation tower (300) was operated for 5 days,
30 production of polymer was observed at the stages around the feed stage in the
=30
tower, and after operated for 10 days, normal operation could not be conducted
any longer due to the production of polymer in the tower.
The following Table 3 shows the flow rate and the concentration of each
flow at steady stage operation of the water separation tower (300).
5
(Table 31
The treatment amount of the acrylic acid aqueous solution through the
(meth)acrylic acid absorption tower (100) and water separation tower (300) was
about 6.5 g per minute, production amount of acrylic acid was about 4.31 g per
lo minute, and total recovery rate of acrylic acid was about 99.8 %. As a result of
calculating energy consumption amount using an ASPEN PLUS process
simulator program (AspenTech Inc.), it was confirmed that 30.32 cal was
consumed per 1 g of the obtained acrylic acid.
15 Comparative Example 2: Sequentiallv passing through lacnrlic acid
absorption tower - extraction tower - water separation tower1
An acrylic acid aqueous solution was obtained from the (meth)acrylic
acid absorption tower (100) by the same method as Example 1. The total
amount of the obtained acrylic acid aqueous solution was fed to the
20 (meth)acrylic acid extraction tower (200), and the acrylic acid extract discharged
from the (meth)acrylic acid extraction tower (200) was fed to the water
=3Lower flow
of water
separation
tower
4.31
0.00
99.96
0.02
0.00
0.02
Upper flow
of water
separation
tower
14.14
84.90
0.13
1.01
13.96
0.00
Reflux flow
of
azeotropic
solvent
11.95
99.74
0.10
0.16
0.00
0.00
Acrylic
acid
aqueous
solution
6.50
0.00
67.99
2.00
29.99
0.02
Mass Flow
(glmin)
Composition
(wt%)
Toluene
acid
Acetic
acid
Water
Heavies
separation tower (300).
Herein, feed to the water separation tower (300) was only the acrylic acid
extract, and the acrylic acid extract was introduced into the 14'~s tage from the
upper part of the water separation tower (300) at a flow rate of about 8.3 glmin.
5 The toluene reflux flow of the upper part of the water separation tower
(300) was introduced into the first stage that is the uppermost stage at a flow
rate of about 8.4 glmin as a solvent. This corresponds to a reflux ratio (that is,
the ratio of the flow rate of reflux liquid to discharged liquid) of about 1.5.
Heat was supplied through a reboiler at the lower part of the water
lo separation tower (300) so that the temperature of the 16'~s tage became about
88 "C or more, and the temperature of the 12nd stage may not exceed about
65 "C.
After stable operation was conducted for about 10 hours, at a steady
state, distillate was discharged to the upper part of the water separation tower
15 (300) at a flow rate of about 14.10 glmin, and acrylic acid flow of about 2.65
glmin was obtained from the lower part of the water separation tower(300).
Herein, at a steady state, the temperature of the upper part of the water
separation tower(300) was maintained at about 41.2 "C , and the temperature of
the lower part was maintained at about 96.5 "C.
20 As the result of operation of the water separation tower (300), the
removal rate of water and acetic acid included in the acrylic acid extract and the
acrylic acid aqueous solution supplied to the water separation tower was about
99 % or more, acrylic acid flow wherein most of water and acetic acid were
removed could be obtained from the lower part of the water separation tower,
25 and acrylic acid lost to the upper part of the water separation tower was about
1.07 wt%.
The water separation tower (300) could be operated stably without
producing a polymer in the tower even after 10 days of long term operation.
The following Table 4 shows the flow rate and the concentration of each
30 flow at steady stage operation of the water separation tower (300).
*3L
[Table 41
The treatment amount of the acrylic acid aqueous solution through this
process was about 4.15 g per minute, production amount of acrylic acid was
5 about 2.65 g per minute, and total recovery rate of acrylic acid was about
94.8 %. As a result of calculating energy consumption amount using an
ASPEN PLUS process simulator program (AspenTech Inc.), it was confirmed
that 54.25 cal were consumed per 1 g of the obtained acrylic acid.
10 Discussion
As can be seen from the operation results of Examples 1-2 and
Lower flow
of water
separation
tower
2.65
0.00
99.92
0.02
0.00
0.06
Comparative Examples 1-2, according to the method of Example I, there was
Upper flow
of water
separation
tower
14.10
92.03
1.07
1.24
5.66
0.00
a 7.6 cal decrease per 1 g of the recovered acrylic acid compared to the method
Reflux flow
of
azeotropic
solvent
8.40
99.74
0.10
0.16
0.00
0.00
of Comparative Example 1, which corresponds to energy reduction of about
Acrylic
acid
aqueous
solution
8.30
64.87
32.90
0.66
1.55
0.02
Mass Flow
(glmin)
15 25.1 %. Further, according to the method of Example 2, there was a decrease
Composition
(wt%)
of about 11.62 cal per 1 g of the recovered acrylic acid compared to
Toluene
acid
Acetic
acid
Water
Heavies
Comparative Example 1, which corresponds to energy reduction of about
38.3 %.
According to the method of Example 1, there was a decrease of about
20 31.52 cal per 1 g of the recovered acrylic acid compared to Comparative
Example 2, which corresponds to energy reduction of 58.1 %. Further,
according to the method of Example 2, there was a decrease of about 35.54 cal
per 1 g of the recovered acrylic acid compared to Comparative Example 2,
which corresponds to energy reduction of about 65.5 %.
As such, it is confirmed that the method of continuous recovery of
5 (meth)acrylic acid according to the present invention may maintain a recovery
rate of (meth)acrylic acid equivalent to the previous recovery method using a
single water separation tower (the method of the comparative example), and yet
may largely reduce energy consumption amount.
Moreover, if a distillation apparatus having equivalent capacity is used
lo and equivalent amounts of azeotropic solvents and operation energy are
introduced, the method according to the present invention may further increase
treatment capacity of a (meth)acrylic acid aqueous solution, and recover
(meth)acrylic acid with high energy efficiency. Furthermore, the method
according to the present invention may maintain a low temperature around a
15 feed stage of a water separation tower which has a relatively high possibility to
produce a polymer of (meth)acrylic acid, and thus is effective for preventing
production of a polymer, thereby providing more improved operation stability.
[DESCRIPTION OF REFERENCE NUMERALS AND SIGNS]
1: (meth)acrylic acid containing mixed gas
20 100: (meth)acrylic acid absorption tower
102, 103: (meth)acrylic acid aqueous solution transfer lines
150: acetic acid absorption tower
200: (meth)acrylic acid extraction tower
203: (meth)acrylic acid extract transfer line
2 5 300: water separation tower
350: phase separator
400: high boiling point by-product separation tower
[CLAIMS]
[Claim 1 I
A method of continuous recovery of (meth)acrylic acid, comprising:
contacting a mixed gas comprising (meth)acrylic acid, organic
5 by-products, and vapor, which is produced by a synthesis reaction of
(meth)acrylic acid, with water in a (meth)acrylic acid absorption tower (100) to
obtain a (meth)acrylic acid aqueous solution;
dividing and feeding the (meth)acrylic acid aqueous solution to a
(meth)acrylic acid extraction tower(200) and a water separation tower(300);
10 obtaining a (meth)acrylic acid extract with reduced water content from
the (meth)acrylic acid aqueous solution that is fed to the (meth)acrylic acid
extraction tower (200), and feeding it to a water separation tower (300); and
distilling the (meth)acrylic acid aqueous solution and the (meth)acrylic
acid extract that are fed to the water separation tower (300) to obtain
15 (meth)acrylic acid.
(Claim 21
The method for continuous recovery of (meth)acrylic acid according to
claim 1, wherein 5-70 wt% of the (meth)acrylic acid aqueous solution obtained
20 in the (meth)acrylic acid absorption tower (100) is fed to the (meth)acrylic acid
extraction tower (200), and the remainder is fed to the water separation tower
(300).
[Claim 31
2 5 The method for continuous recovery of (meth)acrylic acid according to
claim 1, 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, t-butylene, and (meth)acrolein in the
presence of a gas phase catalyst.
3 0
*35
[Claim 41
The method for continuous recovery of (meth)acrylic acid according to
claim 1, wherein the internal temperature of the (meth)acrylic acid absorption
tower (1 00) is maintained at 50 to 100 "C.
5
[Claim 51
The method for continuous recovery of (meth)acrylic acid according to
claim 1, wherein in the step of obtaining the (meth)acrylic acid aqueous solution,
a (meth)acrylic acid aqueous solution is discharged to the lower part of the
lo (meth)acrylic acid absorption tower (loo), and (meth)acrylic acid-stripped
non-condensable gas is discharged to the upper part of the (meth)acrylic acid
absorption tower (1 00).
[Claim 61
15 The method for continuous recovery of (meth)acrylic acid according to
claim 5, further comprising contacting the non-condensable gas with water to
recover acetic acid that is included in the non-condensable gas.
[Claim 71
20 The method for continuous recovery of (meth)acrylic acid according to
claim 1, wherein the water fed to the (meth)acrylic acid absorption tower(100)
includes organic by-products at a concentration of 3 to 20 wt%.
[Claim 81
2 5 The method for continuous recovery of (meth)acrylic acid according to
claim 1, wherein the (meth)acrylic acid aqueous solution obtained in the
(meth)acrylic acid absorption tower (100) includes (meth)acrylic acid at a
concentration of 40 to 90 wt%.
30 [Claim 91
The method for continuous recovery of (meth)acrylic acid according to
claim 1, wherein the (meth)acrylic acid extract is obtained by contacting the
(meth)acrylic acid aqueous solution that is fed to the (meth)acrylic acid
extraction tower (200) with a hydrophobic extraction solvent to remove water
5 included in the aqueous solution.
[Claim 101
The method for continuous recovery of (meth)acrylic acid according to
claim 9, wherein the hydrophobic extraction solvent is at least one selected from
lo 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-I -heptene, 6-methyl-1-heptene, 4-methyl-I -heptene,
2-ethyl-I-hexene, ethylcyclopentane, 2-methyl-I-hexene, 2,3-dimethylpentane,
15 5-methyl-1 -hexene, and isopropyl-butyl-ether.
[Claim 11 I
The method for continuous recovery of (meth)acrylic acid according to
claim 9, wherein the (meth)acrylic acid extract is obtained from the upper part of
20 the (meth)acrylic acid extraction tower (200) and fed to the water separation
tower (300), and
at least a part of the lower discharged liquid of the (meth)acrylic acid
extraction tower (200) is fed to the upper end of the (meth)acrylic acid
absorption tower (1 00) and used as an absorption solvent of (meth)acrylic acid.
2 5
[Claim 121
The method for continuous recovery of (meth)acrylic acid according to
claim 11, wherein the lower discharged liquid of the (meth)acrylic acid extraction
tower (200) includes (meth)acrylic acid at a concentration of 5 wt% or less.
[Claim 131
The method for continuous recovery of (meth)acrylic acid according to
claim 1 1, wherein the upper end of the (meth)acrylic acid absorption tower (1 00)
to which at least a part of the lower discharged liquid of the (meth)acrylic acid
5 absorption tower (200) is fed is at least one point corresponding to a height of
70 % or more from the lowest part of the absorption tower.
[Claim 141
The method for continuous recovery of (meth)acrylic acid according to
lo claim 1, wherein the distillation in the water separation tower (300) is conducted
in the presence of a hydrophobic azeotropic solvent.
[Claim 151
The method for continuous recovery of (meth)acrylic acid according to
15 claim 14, wherein the hydrophobic azeotropic solvent is at least one selected
from the group consisting of benzene, toluene, xylene, n-heptane, cycloheptane,
cycloheptene, I-heptene, ethyl-benzene, methyl-cyclohexane, n-butyl acetate,
isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methyl
isobutyl ketone, 2-methyl-I -heptene, 6-methyl-I-heptene, 4-methyl-I -heptene,
20 2-ethyl-I-hexene, ethylcyclopentane, 2-methyl-I-hexene, 2,3-dimethylpentane,
5-methyl-I -hexenel and isopropyl-butyl-ether.
[Claim 161
The method for continuous recovery of (meth)acrylic acid according to
25 claim 15, wherein the hydrophobic azeotropic solvent includes the same
compound as the hydrophobic extraction solvent in the (meth)acrylic acid
extraction tower (200).
[Claim 171
The method for continuous recovery of (meth)acrylic acid according to
H39
claim 14, wherein discharged liquid including (meth)acrylic acid is recovered
from the lower part of the water separation tower (300), and discharged liquid
including a hydrophobic azeotropic solvent, water, and acetic acid is recovered
from the upper part of the water separation tower (300), by distillation in the
5 water separation tower (300).
[Claim 181
The method for continuous recovery of (meth)acrylic acid according to
claim 17, wherein the upper discharged liquid of the water separation tower
l o (300) is separated into an organic layer including the hydrophobic azeotropic
solvent and an aqueous layer including acetic acid, at least a part of the organic
layer is fed to the upper end of the water separation tower (300) as an
azeotropic solvent, and at least a part of the aqueous layer is fed to the upper
end of the (meth)acrylic acid absorption tower (1 00) as an absorption solvent.
15
[Claim 191
An apparatus for continuous recovery of (meth)acrylic acid, comprising:
a (meth)acrylic acid absorption tower (100) for contacting a mixed gas
including organic by-products, vapor, and (meth)acrylic acid, which is produced
20 by a synthesis reaction of (meth)acrylic acid, with water, to obtain a
(meth)acrylic acid aqueous solution;
(meth)acrylic acid aqueous solution transfer lines (1 02 and1 03) that are
respectively connected from the (meth)acrylic acid absorption tower (100) to a
(meth)acrylic acid extraction tower (200) and a water separation tower (300), to
25 which the (meth)acrylic acid aqueous solution is divided and fed;
the (meth)acrylic acid extraction tower (200) for obtaining (meth)acrylic
acid extract with reduced water content from the (meth)acrylic acid aqueous
solution that is fed through the (meth)acrylic acid aqueous solution transfer line
(102), and feeding it to the water separation tower (300);
a (meth)acrylic acid extract transfer line (203) that is connected from the
* 3 q
(meth)acrylic acid extraction tower (200) to the water separation tower (300), to
which the (meth)acrylic acid extract is fed; and
the water separation tower (300) for distilling a (meth)acrylic acid
aqueous solution fed through the (meth)acrylic acid aqueous solution transfer
5 line (103), and (meth)acrylic acid extract fed through the (meth)acrylic acid
extract transfer line (203), to obtain (meth)acrylic acid.