Title of Invention

METHOD FOR RECOVERING ACRYLIC ACID

Abstract The invention discloses a method for recovering acrylic acid from a mixture containing 25 to 70 wt% of acrylic acid, 30 to 70 wt% of acrylic acid dimer and the residual quantity of impurities with high boiling point, which comprises the steps of: introducing the mixture into an acrylic acid recovering device comprising a thin film evaporator integrated with an acrylic acid dimer pyrolysis tank; and carrying out decomposition of acrylic acid dimer under reduced pressure ranging from 5 to 160 mmHg at a lower part of the acrylic acid recovering device, while recovering acrylic acid by distillation under reduced pressure ranging from 5 to 160 mmHg from a top of the acrylic acid recovering device. The invention is also for a apparatus for carrying out the above method.
Full Text Description
Technical Field
The present invention relates to a method for recovering acrylic acid. More par-
ticularly, the present invention relates to a method for recovering acrylic acid from a
mixture containing acrylic acid, acrylic acid dimer and impurities with high boiling
point, in a stable and efficient manner.
Background Art
The method according to the present invention can be applied after carrying out a
process wherein acrylic acid-containing gas obtained from the vapor phase oxidation
of propylene and/or acrolein in the presence of a catalyst is contacted with an
absorbing solvent to collect acrylic acid in a solution state, the solution is rectified to
recover crude acrylic acid, and the crude acrylic acid is purified in a separation tower
to remove impurities with high boiling point.
In general, because the crude acrylic acid obtained by the above-described
oxidation method contains impurities with high boiling point such as acrylic acid dimer
and maleic acid, it is not economically advisable to discard such impurities as waste
liquid due to the loss of acrylic acid. Acrylic acid has high polymerizability and poly-
merization of acrylic acid may occur during the above process. However, in addition to
such polymerization, oligomerization such as dimerization and trimerization of acrylic
acid may occur with ease. It is thought that such oligomerization results from serial
reactions. During the above purifying process based on distillation, acrylic acid dimer
is produced chiefly.
Production of acrylic acid dimer depends on temperatures and retention time. Ad-
ditionally, it is not possible to inhibit production of acrylic acid dimer completely by
adding a polymerization inhibitor. In conventional distillation processes, it is not
evitable that acrylic acid dimer is produced in an amount of 1-5 wt%. Even if the
impurities with high boiling point is removed by distillation, 5-50 wt% of acrylic acid
dimer may be concentrated at the bottom of the distillation column. Therefore, it is not
cost-efficient to discard the bottom liquid containing a high concentration of acrylic
acid dimer without any post-treatment.
To solve the above problems, methods for recovering acrylic acid by pyrolysis of
acrylic acid dimer into acrylic acid are suggested in Japanese Patent Publication Nos.
1970-19281B2, 1976-91208A, 1986-36501B2, 1999-12222A, etc.
The method disclosed in Japanese Patent Publication No. 1999-12222A uses an
acrylic acid recovering column having a distillation tower and thin fdm evaporator,
separated from a dimer pyrolysis unit. However, the method has a problem in that

polymerization of acrylic acid may occur at a duct connecting the recovering column
with the pyrolysis unit. Additionally, it is not cost-efficient that at least two equipments
should be added for the acrylic acid recovering column and the pyrolysis unit.
Further, according to the above method, the thin film evaporator is operated at
reduced pressure and the pyrolysis unit is operated at atmospheric pressure. In this
regard, the method uses a condenser in order to remove odors emitted from vapors
generated by acrylic acid, acrylic acid dimer and various kinds of impurities with high
boiling point. Therefore, when the system is operated for a long time, polymerization
of acrylic acid may occur at the part of the condenser to cause troubles in operation,
resulting in emission of bad odors toward the surroundings.

Description of Accompanying Drawings
FIGs. 1 and 2 are schematic views each showing a preferred embodiment of the
present invention, wherein reference letter A is a separation column for removing
impurities with high boiling point, B is an acrylic acid recovering device comprising a
thin film evaporator integrated with a pyrolysis tank, C is a acrylic acid recovery
column, and M is a motor.
Disclosure
Therefore, the present invention has been made in view of the above-mentioned
problems. It is an object of the present invention to provide a method and apparatus for
recovering acrylic acid by pyrolysis of acrylic acid dimer into acrylic acid. Particularly,
the present invention provides an economical method and apparatus for recovering
acrylic acid, which simplify a conventional multi-step process carried out under
reduced pressure alternately with atmospheric pressure, and improve the ratio of dimer
decomposition and recovering yield of acrylic acid.
We have found that it is possible to recover acrylic acid efficiently and eco-
nomically by using a novel apparatus comprising an acrylic acid distillation unit
integrated with an acrylic acid dimer decomposition unit, wherein the apparatus is
operated under reduced pressure. The present invention is based on this finding.
According to an aspect of the present invention, there is provided a method for
recovering acrylic acid from a mixture containing acrylic acid, acrylic acid dimer and
impurities with high boiling point, which comprises the steps of: introducing the
mixture into an acrylic acid recovering device comprising an acrylic distillation unit
integrated with an acrylic acid dimer pyrolysis tank; carrying out decomposition of
acrylic acid dimer under reduced pressure at the lower part of the acrylic acid
recovering device, while recovering acrylic acid by distillation from the top of the
acrylic acid recovering device; and optionally recycling a portion of the solution
obtained from the bottom of the acrylic acid recovering device to the upper part of the

device.
According to another aspect of the present invention, there is provided an apparatus
for recovering acrylic acid from a mixture containing acrylic acid, acrylic acid dimer
and impurities with high boiling point, which comprises: an acrylic acid recovering
device that comprises an acrylic acid distillation unit integrated with an acrylic acid
dimer pyrolysis tank and is operated under reduced pressure; a line for introducing the
mixture into the acrylic acid recovering device; and optionally, a line for recycling a
portion of the solution obtained from the bottom of the acrylic acid recovering device
to the upper part of the device, wherein decomposition of acrylic acid dimer is carried
out under reduced pressure at the lower part of the acrylic acid recovering device,
while acrylic acid is recovered by distillation from the top of the acrylic acid
recovering device.
Hereinafter, the present invention will be explained in more detail.
The method according to the present invention can be applied after carrying out a
process wherein acrylic acid-containing gas obtained from the vapor phase oxidation
of propylene and/or acrolein in the presence of a catalyst is contacted with an
absorbing solvent to collect acrylic acid in a solution state, the solution is rectified to
recover crude acrylic acid, and the crude acrylic acid is purified in a separation tower
to remove impurities with high boiling point.
Specifically, according to the present invention, acrylic acid-containing gas
obtained from the vapor phase oxidation of propylene and/or acrolein in the presence
of a catalyst is contacted with water to collect acrylic acid as aqueous solution, and the
aqueous "sortition is distilled with an azeotropic solvent to recover crude acrylic acid.
Next, the crude acrylic acid is purified at a column for separating out impurities with
high boiling point. Then, acrylic acid can be recovered from the mixture obtained from
the bottom liquid of the separation column with high efficiency,
FIG. 1 is a schematic view showing a preferred embodiment of the method
according to the present invention.
The method according to the present invention essentially comprises the following
steps:
(1) A mixture containing acrylic acid, acrylic acid dimer and impurities with high
boiling point (for example, a mixture obtained from the bottom of separation tower A
for separating impurities with high boiling point) is introduced into acrylic acid
recovering device B comprising an acrylic acid distillation unit integrated with a
pyrolysis tank according to the present invention.
Particularly, the integrated acrylic acid recovering device is set under such
conditions of temperature and pressure that acrylic acid having a relatively low boiling
point can be vaporized and acrylic acid dimer can be decomposed into acrylic acid

monomer.
The present invention is characterized in that acrylic acid is vaporized and acrylic
acid dimer is pyrolyzed under reduced pressure, for example a pressure of between 5
and 160 mmHg, preferably of between 10 and 150 mmHg. Particularly, vaporization of
acrylic acid and pyrolysis of acrylic acid dimer are accomplished under substantially
the same pressure. With regard to the expression of 'substantially the same pressure', it
means that the pressure is same excluding a pressure difference generated by a grav-
itational difference resulting from the height in the acrylic acid recovering device
according to the present invention.
(2) The acrylic acid contained in the stream from the bottom of the distillation
column and the acrylic acid obtained by pyrolysis of acrylic acid dimer as described
hereinafter are vaporized and then recovered from the top of the acrylic acid
recovering device.
The acrylic acid obtained from the top of the acrylic acid recovering device
contains a significantly reduced amount of impurities such as acrylic acid dimer and
maleic acid. Preferably, it contains 0-2 wt% of maleic acid and 0-0.1 wt% of acrylic
acid dimer.
Kind of built-in distillation unit in the acrylic acid recovering device according to
the present invention is not particularly limited. However, it is preferable to use a thin
film evaporator for the purpose of more efficient operation, because such thin film
evaporators cause high-viscosity acrylic acid to be coated on the wall surface thereof,
thereby carrying out vaporization of acrylic acid sufficiently at the wall surface heated
to 60-150 °C.
Meanwhile, acrylic acid recovered from the acrylic acid recovering device may be
recycled to the preceding purification unit.
(3) Materials having a relatively high boiling point, such as acrylic acid dimer,
flow down along the wall surface of the acrylic acid recovering device toward the
pyrolysis tank disposed at the downstream of the acrylic acid recovering device. Then,
the materials are retained in the pyrolysis tank for a certain time to perform pyrolysis
of acrylic acid dimer.
Preferably, the bottom temperature of the integrated acrylic acid recovering device
according to the present invention, i.e., the bottom temperature of the lower pyrolysis
tank ranges from 100 °C to 160 °C , more preferably from 130 °C to 135 °C ,
considering a pressure difference between the top and the bottom under reduced
pressure. If the bottom temperature is too high, precipitation caused by maleic acid
may be generated, resulting in a troublesome occlusion in terms of long-term
operation.
Although the retention time at the bottom of the acrylic acid recovering device

varies depending on the temperature where pyrolysis of acrylic acid dimer is
performed, it is generally known that a retention time of between 20 and 50 hours is
desirable. However, according to the present invention, it was found that pyrolysis
under reduced pressure conditions needs a shorter retention time. It is possible to
perform pyrolysis of acrylic acid dimer in a time of between 10 and 30 hours, which is
shorter than the above-mentioned conventional retention time. It is generally known
that pyrolysis carried out in a relatively short time may result in undesired de-
composition, polymerization, etc. However, because pyrolysis is performed under
reduced pressure according to the present invention, contrary to conventional pyrolysis
performed under atmospheric pressure, pyrolyzed acrylic acid is easily vaporized
under reduced pressure at a sufficiently high temperature at the bottom of the acrylic
acid recovering device, resulting in being recovered at the top of the acrylic acid
recovering device.
(4) Meanwhile, waste liquid is discharged from the bottom of the acrylic acid
recovering device. The waste liquid comprises impurities containing a significantly
reduced amount of acrylic acid dimer due to the above pyrolysis step.
Optionally, the waste liquid obtained from the bottom of the acrylic acid
recovering device may be recycled to the top of the device and the remaining liquid
may be discarded.
In the pyrolysis tank disposed at the lower part of the acrylic acid recovering
device according to the present invention, acrylic acid dimer is pyrolyzed, thereby
forming acrylic acid. However, it is preferable that at least a part of the waste liquid is
recycled to the evaporator disposed at the upper part of the device in order to recover
acrylic acid with an increased yield and to control the retention time. In order to
recover acrylic acid more efficiently from the bottom liquid of the acrylic acid
recovering device, recycle ratio to the thin film evaporator disposed at the upper part
may be increased. However, it is preferable that the recycled ratio is 200-800 wt%
based on the weight of the mixture containing acrylic acid, acrylic acid dimer and
impurities with high boiling point, wherein the mixture is obtained from the bottom of
the separation tower for removing impurities with high boiling point and then is
supplied to the acrylic acid recovering device.
(5) In order to reduce concentration of acrylic acid dimer and impurities with high
boiling point contained in the stream recovered from the top of the acrylic acid
recovering device (B) and then recycled to the separation tower, the present invention
can add a tray distillation column C whose theoretical plate number is 1-5 to the top of
the acrylic acid recovering device, as shown in FIG. 2. By doing so, it is possible to
increase the purity of acrylic acid at the top of the recovering device, and thus to
ensure the operational stability of the separation column for removing impurities with

high boiling point, to which the above-recovered acrylic acid is recycled.
The mixture to be introduced to the acrylic acid recovering device according to the
present invention, which contains acrylic acid, acrylic acid dimer and impurities with
high boiling point, comprises at least 10 wt% of acrylic acid dimer. Preferably, the
present invention may be applied to a mixture containing 5-10 wt% of maleic acid in
addition to acrylic acid, i.e., an acrylic acid-containing mixture purified through
azeotropic distillation. For example, a mixture containing 25-70 wt% of acrylic acid,
30-70 wt% of acrylic acid dimer, 5-20 wt% of a polymerization inhibitor
(hydroquinone, phenothiazine, copper dibutyldithiocarbamatc, etc.) and other
impurities with high boiling point can be treated according to the present invention.
Mode for Invention
Reference will now be made in detail to the preferred embodiments of the present
invention. It is to be understood that the present invention is not limited to the
following examples.
Example 1
Acrylic acid-containing gas obtained by partial oxidation of propylene was
subjected to a processing comprising an absorption, azeotropic separation and pu-
rification steps to provide the mixture containing acrylic acid, acrylic acid dimmer and
impurities with high boiling point. The acrylic acid-containing mixture was introduced
to an acrylic acid recovering device equipped with a thin film evaporator having an
electric heating area of 3.5 m2 at a flow rate of 250 kg per hour. The wall surface of the
acrylic acid recovering device was maintained at a temperature of 150 ° C and operated
under a pressure of 75 mmHg. Acrylic acid was recovered from the top of the device at
a rate of 175 kg per hour. The pyrolysis tank disposed at the lower part of the device
was operated at a temperature of 135 ° C and pyrolysis was performed in a retention
time of 18 hours. Additionally, the bottom liquid was recycled to the top of the device
at a flow rate of 870 kg per hour. The recycled liquid is about 350 wt% based on the
weight of the acrylic acid-containing mixture that contains acrylic acid dimer,
introduced to the acrylic acid recovering device. The remaining liquid was discarded to
treat as waste oil. The composition of acrylic acid, acrylic acid dimer and other
impurities with high boiling point in each stream is as follows.


After operation for 4 months under the above conditions, the device could be
operated in a stable manner without a significant change in concentration of acrylic
acid or acrylic acid dimmer in the waste liquid. Further, there was no trouble caused by
polymerization or the like.
Example 2
Example 1 was repeated, except that a tray distillation column whose theoretical
plate number is 5 was added to the top of the recovering device as shown in FIG. 2 and
that acrylic acid-containing mixture was introduced to the distillation column, in order
to reduce the concentration of acrylic acid dimer and impurities with high boiling point
in the stream recovered from the top of the acrylic acid recovering device according to
the present invention and then recycled to the preceding purification stage for
removing impurities with high boiling point. The wall temperature of the thin film
evaporator was controlled so that the bottom temperature of the distillation column is
90 ° C, and the distillation column was operated at a reflux ratio of 0.7. As a result, the
composition of the stream recycled to the preceding separation column was 99.8 wt%
of acrylic acid, 0.06 wt% of dimer and the balance amount of impurities.
Industrial Applicability
As can be seen from the foregoing, according to the method of the present
invention, decomposition of acrylic acid dimer is carried out efficiently by using an
integrated system of distillation unit and pyrolysis tank, which can be operated under
reduced pressure simultaneously. Therefore, it is possible to reduce the concentration
of acrylic acid discharged as waste liquid and to increase the yield of acrylic acid,
while maintaining the temperature of the pyrolysis tank at a reduced temperature, so
that the method can be cost-efficient. In brief, according to the present invention, it is
possible to recover acrylic acid efficiently by carrying out pyrolysis of acrylic acid
dimer. Additionally, it is possible to operate the apparatus for carrying out the method
for a long time in a stable manner.

While this invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be understood
that the invention is not limited to the disclosed embodiment and the drawings. On the
contrary, it is intended to cover various modifications and variations within the spirit
and scope of the appended claims.

WE CLAIM:
1. A method for recovering acrylic acid from a mixture containing 25 to 70
wt% of acrylic acid, 30 to 70 wt% of acrylic acid dimer and the residual quantity of
impurities with high boiling point, which comprises the steps of:
introducing the mixture into an acrylic acid recovering device comprising a
thin film evaporator integrated with an acrylic acid dimer pyrolysis tank; and
carrying out decomposition of acrylic acid dimer under reduced pressure
ranging from 5 to 160 mmHg at a lower part of the acrylic acid recovering device,
while recovering acrylic acid by distillation under reduced pressure ranging from 5 to
160 mmHg from a top of the acrylic acid recovering device.
2. The method as claimed in claim 1, which optionally comprises a step of
recycling a portion of the solution obtained from the bottom of the acrylic acid
recovering device to the acrylic acid recovering device.
3. The method as claimed in claim 1, wherein the acrylic acid recovering
device is operated under reduced pressure ranging from 10 to 150 mmHg.
4. The method as claimed in claim 1, wherein the acrylic acid recovered from
the acrylic acid recovering device is recycled to a purification unit preceding the
recovering device.
5. The method as claimed in claim 1, wherein the acrylic acid recovering
device is operated at a bottom temperature of between 100° C. and 160° C.
6. The method as claimed in claim 1, wherein retention time at the bottom of
the acrylic acid recovering device is 10 to 30 hours.
7. The method as claimed in claim 2, wherein the recycle flow from the
bottom of the acrylic acid recovering device to the top thereof is 2 to 8 times of the
weight of the mixture containing acrylic acid, acrylic acid dimer and impurities with
high boiling point, me mixture being obtained from the preceding purification step

and supplied to the acrylic acid recovering device.
8. The method as claimed in claim 1, wherein the mixture containing acrylic
acid, acrylic acid dimer and impurities with high boiling point, introduced to the
acrylic acid recovering device is obtained from a process comprising: a vapor phase
partial oxidation step of propylene, acrolein, or the mixture of propylene and
acrolein; absorption step; azeotropic distillation step; and a rectification step of
impurities.
9. An apparatus for carrying out the method of recovering acrylic acid from a
mixture, as claimed in any one of the preceding claims, which comprises :
an acrylic acid recovering device that comprises an acrylic acid distillation
unit integrated with an acrylic acid dimer pyrolysis tank and is operated under
reduced pressure; and
a line for introducing the mixture into the acrylic acid recovering device,
wherein decomposition of acrylic acid dimer is carried out under reduced pressure at
a lower part of the acrylic acid recovering device, while acrylic acid is recovered by
distillation under reduced pressure from a top of the acrylic acid recovering device.
10. The apparatus as claimed in claim 9, which optionally comprises a line for
recycling a portion of the solution obtained from the bottom of the acrylic acid
recovering device to the acrylic acid recovering device.
11. The method as claimed in claim 1, wherein the acrylic acid obtained from
the top of the acrylic acid recovering device contains 0-2 wt % of malic acid and 0-
0.1 wt % of acrylic acid dimer.


The invention discloses a method for recovering acrylic acid from a mixture
containing 25 to 70 wt% of acrylic acid, 30 to 70 wt% of acrylic acid dimer and the
residual quantity of impurities with high boiling point, which comprises the steps of:
introducing the mixture into an acrylic acid recovering device comprising a thin film
evaporator integrated with an acrylic acid dimer pyrolysis tank; and carrying out
decomposition of acrylic acid dimer under reduced pressure ranging from 5 to 160
mmHg at a lower part of the acrylic acid recovering device, while recovering acrylic
acid by distillation under reduced pressure ranging from 5 to 160 mmHg from a top
of the acrylic acid recovering device.
The invention is also for a apparatus for carrying out the above method.

Documents:

02914-kolnp-2006 abstract.pdf

02914-kolnp-2006 assignment.pdf

02914-kolnp-2006 claims.pdf

02914-kolnp-2006 correspondence others.pdf

02914-kolnp-2006 darwings.pdf

02914-kolnp-2006 description(complete).pdf

02914-kolnp-2006 form-1.pdf

02914-kolnp-2006 form-3.pdf

02914-kolnp-2006 form-5.pdf

02914-kolnp-2006 international publication.pdf

02914-kolnp-2006 international search authority report.pdf

02914-kolnp-2006 pct form.pdf

02914-kolnp-2006 priority document.pdf

02914-kolnp-2006-assignment-1.1.pdf

02914-kolnp-2006-correspondence others-1.1.pdf

2914-kolnp-2006-abstract.pdf

2914-kolnp-2006-amanded claims.pdf

2914-kolnp-2006-assignment.pdf

2914-kolnp-2006-correspondence.pdf

2914-kolnp-2006-description (complete).pdf

2914-kolnp-2006-drawings.pdf

2914-KOLNP-2006-ENGLISH TRANSLATION.pdf

2914-kolnp-2006-examination report.pdf

2914-kolnp-2006-form 1.pdf

2914-KOLNP-2006-FORM 13.pdf

2914-kolnp-2006-form 18.1.pdf

2914-kolnp-2006-form 18.pdf

2914-kolnp-2006-form 2.pdf

2914-kolnp-2006-form 3.1.pdf

2914-kolnp-2006-form 3.pdf

2914-kolnp-2006-form 5.pdf

2914-KOLNP-2006-FORM-27.pdf

2914-kolnp-2006-gpa.pdf

2914-kolnp-2006-granted-abstract.pdf

2914-kolnp-2006-granted-claims.pdf

2914-kolnp-2006-granted-description (complete).pdf

2914-kolnp-2006-granted-drawings.pdf

2914-kolnp-2006-granted-form 1.pdf

2914-kolnp-2006-granted-form 2.pdf

2914-kolnp-2006-granted-specification.pdf

2914-kolnp-2006-others.pdf

2914-KOLNP-2006-PETITION UNDER RULE 137-1.1.pdf

2914-KOLNP-2006-PETITION UNDER RULE 137.pdf

2914-KOLNP-2006-REPLY TO EXAMINATION REPORT-1.1.pdf

2914-kolnp-2006-reply to examination report.pdf

abstract-02914-kolnp-2006.jpg


Patent Number 249634
Indian Patent Application Number 2914/KOLNP/2006
PG Journal Number 44/2011
Publication Date 04-Nov-2011
Grant Date 31-Oct-2011
Date of Filing 10-Oct-2006
Name of Patentee LG CHEM, LTD.
Applicant Address 20, YOIDO-DONG, YOUNGDUNGPO-GU, SEOUL 150-721, REPUBLIC OF KOREA
Inventors:
# Inventor's Name Inventor's Address
1 KANG SEONG-PIL 107-1103, HYANGCHON APARTMENT, DUNSAN2-DONG, SEO-GU, DAEJEON 302-122, REPUBLIC OF KOREA
2 HA KYOUNG-SU 109-502 CHOWON APARTMENT, MANNYUN-DONG, SEO-GU, DAEJEON 305-751, REPUBLIC OF KOREA
3 KO JUN-SEOK 128-86 HAENGDANG-DONG, SEONGDONG-GU, SEOUL 133-070, REPUBLIC OF KOREA
4 WOO BOO-GON 8-401, LG CHEMICAL APT., DORYONG-DONG, YUSEONG-GU, DAEJEON 305-340, REPUBLIC OF KOREA
5 KIM YOUNG-BAE 3-206 LG SATAIK 29, ANSAN-DONG, YEOSU-SI, JEOLLANAM-DO 555-050, REPUBLIC OF KOREA
6 CHOI SEOK-HWAN 6-104, LG CHEMICAL APARTMENT DORYONG-DONG, YUSEONG-GU, DAEJEON 305-340, REPUBLIC OF KOREA
PCT International Classification Number C07C 51/44
PCT International Application Number PCT/KR2005/001199
PCT International Filing date 2005-04-26
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10-2004-0029872 2004-04-29 Republic of Korea