U.S. patent application number 10/423389 was filed with the patent office on 2004-10-28 for method for heating a crude carboxylic acid slurry in a post oxidation zone by the addition of steam.
Invention is credited to de Boer, Martin, de Vreede, Marcel, Lin, Robert, Sluijmers, John, Woodruff, Thomas Earl.
Application Number | 20040215036 10/423389 |
Document ID | / |
Family ID | 33299111 |
Filed Date | 2004-10-28 |
United States Patent
Application |
20040215036 |
Kind Code |
A1 |
Lin, Robert ; et
al. |
October 28, 2004 |
Method for heating a crude carboxylic acid slurry in a post
oxidation zone by the addition of steam
Abstract
The present invention relates to a process for heating a
secondary oxidizer with steam. More specifically, the present
invention relates to a process for heating a secondary oxidizer
with steam in a process for the production of a crystallized
product. A process to produce a crystallized product comprises the
following steps (a) oxidizing in an primary oxidation zone an
aromatic feedstock to produce a crude carboxylic acid slurry; (b)
oxidizing said crude carboxylic acid slurry in a post oxidation
zone in the presence of steam to form a post oxidation product; (c)
purifying said post oxidation product to a decolorized post
oxidation product; and (d) crystallizing in a crystallization zone
said post oxidation product to form a crystallized product.
Inventors: |
Lin, Robert; (Kingsport,
TN) ; de Vreede, Marcel; (Kingsport, TN) ;
Sluijmers, John; (Barendrecht, NL) ; de Boer,
Martin; (Schoonhoven, NL) ; Woodruff, Thomas
Earl; (Kingsport, TN) |
Correspondence
Address: |
Steven A. Owen
Eastman Chemical Company
P.O. Box 511
Kingsport
TN
37662-5075
US
|
Family ID: |
33299111 |
Appl. No.: |
10/423389 |
Filed: |
April 25, 2003 |
Current U.S.
Class: |
562/485 |
Current CPC
Class: |
C07C 51/487 20130101;
C07C 51/487 20130101; C07C 63/26 20130101 |
Class at
Publication: |
562/485 |
International
Class: |
C07C 051/42 |
Claims
We claim:
1. A process to produce a post oxidation product comprising the
following steps: (a) oxidizing in a post oxidation zone a crude
carboxylic acid slurry in the presence of steam to form said post
oxidation product; wherein said post oxidation zone comprises at
least one post oxidation device; wherein said crude carboxylic acid
slurry comprises at least one carboxylic acid; (b) purifying said
post oxidation product to form a decolorized post oxidation product
having b* color of less than 4.5.
2. A process according to claim 1 where said decolorized post
oxidation product has a b* color less than 3.5.
3. A process according to claim 1 wherein said carboxylic acid is
selected from the group consisting of terephthalic acid,
isophthalic acid, naphthalene dicarboxylic acid, and mixtures
thereof.
4. A process according to claim 1 wherein said carboxylic acid is
terephthalic acid.
5. A process according to claim 4 wherein said steam is used to
heat said post oxidation zone to a temperature in a range from
about 180.degree. C. to about 280.degree. C.
6. A process according to claim 5 wherein said post oxidation zone
is operated at a pressure of about 10 barg to about 50 barg.
7. A process to produce a crystallized product said process
comprising the following steps: (a) oxidizing in a post oxidation
zone said crude carboxylic acid slurry in a post oxidation zone in
the presence of steam to form a post oxidation product and an
offgas stream; wherein said post oxidation zone comprises at least
one post oxidation device; (b) purifying said post oxidation
product before or after a crystallization zone to form a
decolorized post oxidation product having b* color of less than
4.5; and (c) crystallizing in said crystallization zone said post
oxidation product; wherein said crystallization zone comprises at
least one crystallizer.
8. A process according to claim 7 wherein said purified post
oxidation product has a b* color of less than 3.
9. A process according claim 7 wherein said carboxylic acid is
selected from the group consisting of terephthalic acid,
isophthalic acid, naphthalene dicarboxylic acid, and mixtures
thereof.
10. A process according to claim 7 wherein said carboxylic acid is
terephthalic acid.
11. A process according to claim 10 wherein said steam is used to
heat the post oxidation zone to a temperature in a range from about
180.degree. C. to about 280.degree. C.
12. A process according to claim 11 wherein said post oxidation
zone is operated at a pressure of about 10 barg to about 50
barg.
13. The process according to claim 10 wherein said crystallizer is
operated at a temperature between about 140.degree. C. and
190.degree. C.
14. A process to produce a post oxidation product comprising
oxidizing in a post oxidation zone a crude carboxylic acid slurry
in the presence of steam to form said post oxidation product;
wherein said crude carboxylic acid slurry comprises terephthalic
acid; wherein said post oxidation zone comprises at least one post
oxidation device; wherein said post oxidation product has a b*
color of less than about 4.5.
15. A process according to claim 14 wherein said steam is used to
heat the post oxidation zone to a temperature in a range from about
180.degree. C. to about 280.degree. C.
16. A process according to claim 15 wherein said post oxidation
zone is operated at a pressure of about 10 barg to about 50
barg.
17. A process to produce crystallized product said process
comprising the following steps: (a) oxidizing said crude carboxylic
acid slurry in a post oxidation zone in the presence of steam to
form a post oxidation product; wherein said post oxidation zone
comprises at least one post oxidation device; wherein the pressure
of said post oxidation zone is between about 10 barg to about 50
barg; and (b) crystallizing in a crystallization zone said post
oxidation product to form a crystallized product; wherein said
crystallization zone comprises at least one crystallizer; wherein
said crystallizer is operated at a temperature between about
140.degree. C. and 190.degree. C.; and wherein said crystallized
product has a b* color of less than 4.5.
18. A process according to claim 17 where said crystallized product
has a b* color of less than 3.
Description
FIELD OF INVENTION
[0001] The present invention relates to a process for heating
carboxylic acid slurry in a post oxidation zone by the addition of
steam. More specifically, the present invention relates to a
process for heating a terephthalic acid slurry in a post oxidation
zone by the addition of steam in a process for the production of a
crystallized product.
BACKGROUND OF THE INVENTION
[0002] Terephthalic acid (TPA) is commercially produced by
oxidation of paraxylene in the presence of a catalyst, such as, for
example, Co, Mn, Br and a solvent. Terephthalic acid used in the
production of polyester fibers, films, and resins must be further
treated to remove impurities present due to the initial oxidation
of paraxylene. Typical commercial processes remove impurities by
isolating a crude terephthalic acid solid, dissolving the solid in
water at high temperatures and pressures, hydrogenating the
resultant solution, cooling and crystallizing the terephthalic acid
product out of solution, and separating the solid terephthalic
product from the liquid as discussed in U. S. Pat. No. 3,584,039,
herein incorporated by reference. Colored impurities from the
benzil, anthraquinone, and fluorenone families are hydrogenated to
colorless products and leave the process with the terephthalic acid
solid product and wastewater streams.
[0003] Still other methods of obtaining a terephthalic acid product
suitable as starting material for the production of polyesters do
not involve a hydrogenation step. A method of producing a
terephthalic acid product suitable for polyester production is to
completely or nearly completely react paraxylene in a multiple
stage oxidation process. In this invention, a unique and novel
process is provided wherein a crude terephthaic slurry produced by
the oxidation of an aromatic feedstock, typically p-xylene, is
further oxidized in a multiple step process wherein heat is
provided to a post oxidation zone by steam addition. The addition
of steam to an oxidation zone subsequent to the primary oxidation
zone results in a higher quality terephthalic acid product compared
to conventional techniques.
SUMMARY OF THE INVENTION
[0004] This invention provides a process to produce a crystallized
product from a crude carboxylic acid slurry by injecting steam in a
post oxidation zone subsequent to the primary oxidation zone.
[0005] In a first embodiment of this invention, a process to
produce a post oxidation product is provided comprising
[0006] (a) oxidizing in a post oxidation zone a crude carboxylic
acid slurry in the presence of steam to form the post oxidation
product; wherein the post oxidation zone comprises at least one
post oxidation device; wherein thecrude carboxylic acid slurry
comprises at least one carboxylic acid;
[0007] (b) purifying the post oxidation product to form a
decolorized post oxidation product having b* color of less than
4.5.
[0008] In another embodiment of this invention, a process to
produce a crystallized product is provided. The process comprising
the following steps:
[0009] (a) oxidizing in a post oxidation zone thecrude carboxylic
acid slurry in a post oxidation zone in the presence of steam to
form a post oxidation product and an offgas stream; wherein the
post oxidation zone comprises at least one post oxidation
device;
[0010] (b) purifying the post oxidation product before or after the
crystallization zone to form a decolorized post oxidation product
having b* color of less than 4.5; and
[0011] (c) crystallizing in a crystallization zone the post
oxidation product; wherein the crystallization zone comprises at
least one crystallizer.
[0012] In another embodiment of this invention, a process to
produce a crystallized product is provided. The process comprises
oxidizing in a post oxidation zone a crude carboxylic acid slurry
in the presence of steam to form the post oxidation product;
wherein the crude carboxylic acid slurry comprises terephthalic
acid; wherein the post oxidation zone comprises at least one post
oxidation device; wherein the post oxidation product has a b* color
of less than about 4.5.
[0013] In another embodiment of this invention, a process to
produce a crystallized product is provided. The process comprises
the following steps:
[0014] (a) oxidizing the crude carboxylic acid slurry in a post
oxidation zone in the presence of steam to form a post oxidation
product; wherein the post oxidation zone comprises at least one
post oxidation device; wherein the pressure of the post oxidation
zone is between about 10 barg to about 50 barg; and
[0015] (b) crystallizing in a crystallization zone the post
oxidation product to form a crystallized product; wherein the
crystallization zone comprises at least one crystallizer; wherein
the crystallizer is operated at a temperature between about
140.degree. C. and 190.degree. C.; and wherein the crystallized
product has a b* color of less than 4.5.
[0016] These objects, and other objects, will become more apparent
to others with ordinary skill in the art after reading this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic of a process for heating a crude
carboxylic acid slurry in a post oxidation zone by the addition of
steam to produce a post oxidation product.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The present invention provides a process to produce a post
oxidation product comprising oxidizing a crude carboxylic acid
slurry in the presence of steam to form the post oxidation product
120 and a offgas stream 80.
[0019] In a first embodiment of this invention, a process to
produce a post oxidation product 120 is provided. The process
comprises oxidizing in a post oxidation zone 90 a crude carboxylic
acid slurry 30 in the presence of steam 100 to form the post
oxidation product 120 and an offgas stream 80; wherein the post
oxidation zone 90- comprises at least one post oxidation device;
wherein the carboxylic acid slurry comprises at least one
carboxylic acid; and wherein the post oxidation product 120 has a
b* color of less than 4.5.
[0020] This oxidizing step and the post oxidation zone are
described subsequently in this disclosure.
[0021] In another embodiment of the invention, a process to produce
a crystallized product 180 is provided as shown in FIG. 1. The
process comprises the following steps.
[0022] Step (a) comprises oxidizing the crude carboxylic acid
slurry 30 in a post oxidation zone 90 in the presence of steam 100
to form a post oxidation product 120. Generally, the crude
carboxylic acid slurry 30 is produced by oxidizing in a primary
oxidation zone 20 an aromatic feed stock 10. The primary oxidation
zone 20 comprises at least one oxidation reactor, and the crude
carboxylic acid slurry 30 comprises at least one carboxylic
acid.
[0023] The oxidizing in the primary oxidation zone 20 is completed
under reaction conditions, which produces a crude carboxylic acid
slurry 30 from an aromatic feedstock 10. Typically, the crude
carboxylic acid slurry 30 comprises at least one carboxylic acid.
Generally, the carboxylic acid is terephthalic acid.
[0024] Therefore, when terephthalic acid is utilized, the crude
carboxylic acid slurry 30 would be referred to as crude
terephthalic acid slurry. However, suitable carboxylic acids
include, but are not limited to, terephthalic acid, isophthalic
acid, naphthalene dicarboxylic acid, and mixtures thereof. Crude
terephthalic acid slurry is conventionally synthesized via the
liquid phase oxidation of paraxylene in the presence of metal
oxidation catalyst. Suitable catalysts include, but are not limited
to, cobalt, manganese and bromide compounds, which are soluble in
the selected solvent. Suitable solvents include, but are not
limited to, aliphatic mono-carboxylic acids, preferably containing
2 to 6 carbon atoms, or benzoic acid and mixtures thereof and
mixtures of these compounds with water. Preferably, the solvent is
acetic acid mixed with water in a ratio of about 5:1 to about 25:1,
preferably between about 10:1 and about 15:1. However, it should be
appreciated that other suitable solvents, such as those disclosed
herein, may also be utilized. Patents disclosing the production of
terephthalic acid, such as U.S. Pat. Nos. 4,158,738 and 3,996,271,
are hereby incorporated by reference.
[0025] In cases where the carboxylic acid is terephthalic acid, the
primary oxidation zone 20 has a water concentration less than about
10 wt %, preferably the water concentration is less than about 8 wt
%, and most preferably the water concentration is less than about 6
wt %.
[0026] The post oxidation zone 90 comprises at least one post
oxidation device. The crude carboxylic acid slurry 30 is fed to the
post oxidation zone 90. The post oxidation zone 90 comprises at
least one post oxidation device. The term post oxidation means that
the oxidation occurs after the primary oxidation zone 20 discussed
previously. For example, the post oxidation zone 90 can comprise
post oxidation devices in series.
[0027] When the carboxylic acid is terephthalic acid, the crude
carboxylic acid slurry 30 in the post oxidation device is heated
with steam 100 to between about 180.degree. C. and about
280.degree. C., preferably between about 190.degree. C. and about
240.degree. C., and most preferably between 195.degree. C. to
215.degree. C. and further oxidized with air or a source of
molecular oxygen fed by line 115 to produce a post oxidation
product 120. The temperature is the internal temperature of the
post oxidation device. When the post oxidation zone comprises more
than one post oxidation device, the temperature can vary within the
specified range for each post oxidation device. The steam 100 can
be fed in the post oxidation zone 90 by any means known in the art.
For example, a connection can be made for the steam 100 to be
directly fed to the acetic acid vapor line. So the steam could be
injected into the digester through the sparge ring. In addition to
using steam, the post oxidation zone 90 can be heated with acetic
acid vapor.
[0028] Additional air or molecular oxygen may be fed to the post
oxidation zone 90 in an amount necessary to oxidize a substantial
portion of the partially oxidized products and
4-carboxybenzaldehyde (4-CBA) in the crude carboxylic acid slurry
30 to the corresponding carboxylic acid. Generally, at least 70% by
weight of the 4-CBA is converted to terephthalic acid in the post
oxidation zone 90. Preferably at least 80% by weight of the 4-CBA
is converted to terephthalic acid in the post oxidation zone 90.
4-carboxybenzaldehyde and p-toluic acid in high enough
concentrations in the terephthalic acid product can be particularly
detrimental to polymerization processes as they act as a chain
terminator during the condensation reaction between terephthalic
acid and ethylene glycol in the production of PET and can be
detrimental to the performance of terephthalic acid hydrogenation
processes. Typical terephthalic acid product contains on a weight
basis less than 500 parts per million (ppm) 4-carboxybenzaldehyde
and less than 250 ppm p-toluic acid. Preferably, the post oxidation
zone is operated at a temperature and pressure sufficient that the
b* color of the post oxidation product 120 ranges from about 0.5 to
about 4.5.
[0029] Step (b) comprises purifying the post oxidation product
before or after a crystallization zone to form a decolorized post
oxidation product having b* color of less than 4.5.
[0030] The purifying of the post oxidation product can be
accomplished by any means known in the art. For example colored
impurities from the benzil, anthroquinone, and fluorenone families
can be hydrogenated to colorless products. In addition any amount
of process steps can be between the post oxidation zone and the
purifying of the post oxidation product and the isolation or
recovery of the post oxidation product if desired.
[0031] The b* color of the post oxidation product in conduit 180 is
between about 0.5 to about 4.5. Preferably, the b* color of the
decolorized post oxidation product in conduit 120 is between 0.5 to
2.0. Most preferably, the b* color in the decolorized post
oxidation product in conduit 120 is between 0.5 to 1.5. The b*
color is one of the three-color attributes measured on a
spectroscopic reflectance-based instrument. The color can be
measured by any device known in the art. A Hunter Ultrascan XE
instrument is typically the measuring device. Positive readings
signify the degree of yellow (or absorbance of blue), while
negative readings signify the degree of blue (or absorbance of
yellow).
[0032] Offgas from the post oxidation zone is withdrawn via line 80
and fed to a recovery system where the solvent is removed from the
offgas. The solvent comprising volatile organic compounds (VOCs).
The VOCs and any hazardous pollutants may be incinerated.
[0033] Step (c) comprises crystallizing the post oxidation product
120 in the crystallization zone 160 to form a crystallized product
180; wherein the crystallized product 180 has a b* color of less
than 4.5.
[0034] Generally, the crystallization zone 160 comprises at least
one crystallizer. Vapor product from the crystallization zone 160
is withdrawn via line 130, condensed in a condenser zone 170, which
comprises at least one condenser and returned to the
crystallization zone 160. Optionally, the liquid in conduit 140 or
vapor 130 in the condenser zone 170 can be recycled, or it can be
withdrawn or sent to an energy recovery device. In addition, the
liquid crystallization offgas 150 from the condenser zone 170 is
removed via line 150 and can be routed to a recovery system where
the solvent is removed and crystallization offgas 150 comprising
VOCs and pollutants are burned.
[0035] When the carboxylic acid is terephthalic acid, the post
oxidation product 120 from the post oxidation zone 90 is withdrawn
via line 120 and fed to a crystallization zone 160 comprising at
least one crystallizer where it is cooled to a temperature between
about 110.degree. C. and about 190.degree. C. to form a
crystallized product 180, preferably to a temperature between about
140.degree. C. to about 180.degree. C., most preferably 150.degree.
C. to 170.degree. C. Preferably, the b* color of the crystallized
product in conduit 180 is between about 0.5 to about 4.5. More
preferably, the b* color of the crystallized product in conduit 135
is between 0.5 to 2.0. Most preferably, the b* color in the
crystallized product in conduit 135 is between 0.5 to 1.5
[0036] The crystallized product 180 from the crystallization zone
160 is withdrawn via line 180. Typically, the crystallized product
180 is then fed directly to a vessel and cooled to form a cooled
crystallized product. When the carboxylic acid is terephthalic
acid, the cooled crystallized product is cooled in a vessel to
typically a temperature of approximately 90.degree. C. or less than
before being introduced into a process for recovering the
carboxylic acid as a dry powder or wet cake.
EXAMPLES
[0037] The invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
Example 1
[0038] In a plant trial, steam was used in the heating of a post
oxidation device. The temperature of the post oxidation device was
operating at about 195.degree. C. to about 215.degree. C. The
airflow was set at a ratio of about 3.8 kg air/ton crude carboxylic
acid slurry. The steam flow to the post oxidation device was
between about 6.5 to about 8.2 metric tons/hour. An overall
reduction in energy of 0.3 GJ/ton for producing terephthalic acid
was observed. This represents a 5% reduction in energy versus
operating without the use of steam to the post oxidation device.
The acid burn and decomposition in the post oxidation device
decreased due to the injection of steam into the post oxidation
device. The acid loss (acetic acid/ton post oxidation product)
dropped about 10%. Therefore, both reduction in energy consumption
and acid burn were observed through the use of steam to heat the
post oxidation device.
* * * * *