U.S. patent application number 09/286262 was filed with the patent office on 2002-01-03 for process of purifying and producing high purity aromatic polycarboxylic acids.
Invention is credited to LIN, TSONG-DAR VINCENT.
Application Number | 20020002304 09/286262 |
Document ID | / |
Family ID | 26807202 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020002304 |
Kind Code |
A1 |
LIN, TSONG-DAR VINCENT |
January 3, 2002 |
PROCESS OF PURIFYING AND PRODUCING HIGH PURITY AROMATIC
POLYCARBOXYLIC ACIDS
Abstract
The present invention provides a solvent extraction purification
method for aromatic polycarboxylic acids that meet or exceed
polymer-grade specification. The method includes dissolving a crude
aromatic polycarboxylic acid in a base compound; removing
impurities and excessive base compound; and removing residual base
compound while making purified product. The purification method
removes not only the impurities from the crude acid, but also the
residual base compound from finished product that otherwise will
contaminate the product. The salt in the cake is converted to
product by acid-substitution, thermal decomposition, or
electrolysis. The method uses base-extraction solvents to extract
base compound and impurities from the salt. The residual base
compound in the recovered product is then removed by leaching,
stripping, thermal agitating with electromagnetic waves, or
evaporation with thermal decomposition. The purification method
allows eliminating crystallizers for crystallization and equipment
for drying and pneumatically carrying. Finally, the purification
method is combined with the oxidation and solvent recovery in prior
art to use only one set of process steps, instead of two, to
produce aromatic polycarboxylic acids.
Inventors: |
LIN, TSONG-DAR VINCENT;
(HOUSTON, TX) |
Correspondence
Address: |
KEITH M, TACKETT
THOMASON, MOSER, & PATTERSON, LLP
3040 POST OAK BLVD.
SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
26807202 |
Appl. No.: |
09/286262 |
Filed: |
April 5, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60109648 |
Nov 24, 1998 |
|
|
|
Current U.S.
Class: |
562/485 ;
562/486 |
Current CPC
Class: |
C07C 51/42 20130101;
C07C 67/48 20130101; C07C 67/48 20130101; C07C 51/42 20130101; C07C
63/26 20130101; C07C 69/76 20130101 |
Class at
Publication: |
562/485 ;
562/486 |
International
Class: |
C07C 409/44; C07C
051/42 |
Claims
1. A method for making a purified organic acid, comprising:
dissolving a crude organic acid in a base compound; removing
impurities; and removing residual base compound while recovering
the purified organic acid.
2. The method as claimed in claim 1, wherein said crude organic
acid is dissolved by thermal agitating under electromagnetic
waves.
3. The method as claimed in claim 1, wherein said crude organic
acid is a crude aromatic polycarboxylic acid.
4. The method as claimed in claim 1, wherein said crude organic
acid is dissolved in the base compound and a dissolving
solvent.
5. The method as claimed in claim 1, wherein excessive base
compound is removed while removing the impurities.
6. A method for making a purified organic acid, comprising:
dissolving a salt formed by a crude organic acid and a base
compound; removing impurities and excessive base compound from the
salt of the crude organic acid using one or more processes selected
from a group consisting of pretreatment, crystallization by
cooling, crystallization by controlling composition with cooling,
crystallizing salt in the presence of a base-extraction solvent,
precipitating product in the presence of a base-extraction solvent,
crystallization with direct-extraction from salt, crystallization
with resalting, salt base-substitution, washing with a
base-extraction solvent, and leaching with a base-extraction
solvent; and removing residual base compound while recovering the
purified organic acid from the salt.
7. The method as claimed in claim 6, wherein said crude organic
acid is a crude aromatic polycarboxylic acid.
8. The method as claimed in claim 7, wherein said crude aromatic
polycarboxylic acid is a terephthalic acid or an isophthalic
acid.
9. The method as claimed in claim 7, wherein said crude aromatic
polycarboxylic acid is a 2,6-naphthalene dicarboxylic acid, a
2,7-naphthalene dicarboxylic acid, or a mixture of naphthalene
dicarboxylic acids.
10. The method as claimed in claim 6, wherein said salt is
dissolved by thermal agitating under electromagnetic waves.
11. The method as claimed in claim 6, wherein said base compound is
an oxygen containing base compound.
12. The method as claimed in claim 6, wherein said salt is
dissolved in the base compound and a dissolving solvent.
13. The method as claimed in claim 6, wherein said base compound is
morpholine and the salt is dissolved in water.
14. The method as claimed in claim 6, wherein said base compound is
trimethylamine, triethylamine, or triethanolamine, and the salt is
dissolved in water or an alcohol.
15. The method as claimed in claim 6, wherein said base compound is
an amide compound.
16. The method as claimed in claim 15, wherein said amide compound
is N-methyl-pyrrolidone.
17. The method as claimed in claim 6, wherein said base compound is
an amide compound and the salt is dissolved in a dissolving
solvent.
18. The method as claimed in claim 6, wherein said impurities are
removed with the base-extraction solvent, and the base-extraction
solvent comprises water, methanol, ethanol, alkylene glycol,
acetone, tetrahydrofuran, or tetrahydropyran.
19. The method as claimed in claim 6, wherein recovering the
purified organic acid from the salt is by adding an
acid-substitution solvent in the presence of a base-extraction
solvent.
20. The method as claimed in claim 6, wherein recovering the
purified organic acid from the salt is by thermal decomposition
using electromagnetic waves.
21. The method as claimed in claim 6, wherein the residual base
compound is removed from the purified organic acid by one or more
processes selected from a groups consisting of leaching, stripping,
thermal agitating with electromagnetic waves, and evaporation with
thermal decomposition.
22. A method for making a purified organic acid, comprising:
dissolving a salt formed by a crude organic acid and a base
compound; and removing impurities from the salt using one or more
processes selected from a group consisting of crystallization with
direct-extraction from salt, crystallizing salt in the presence of
a base-extraction solvent, precipitating product in the presence of
a base-extraction solvent, crystallization with resalting using a
base-extraction solvent, salt base-subsstitutioon, and leaching
with a base-extraction solvent.
23. The method as claimed in claim 22, wherein said crude organic
acid is a crude aromatic polycarboxylic acid.
24. The method as claimed in claim 22, wherein said salt is
dissolved by thermal agitating under electromagnetic waves.
25. The method as claimed in claim 22, wherein said salt is
dissolved in a dissolving solvent.
26. The method as claimed in claim 22, wherein said base compound
is an oxygen containing base compound.
27. The method as claimed in claim 22, further including recovering
the purified organic acid from the salt by acid-substitution,
thermal decomposition, or electrolysis.
28. The method as claimed in claim 27, further including removing
the residual base compound while recovering the purified organic
acid from the salt using one or more processes selected from a
group consisting of leaching, stripping, thermal agitating with
electromagnetic waves, and evaporation with thermal
decomposition.
29. A method for preparing a purified solution consisting of an
aromatic polycarboxylic acid find a monomer to make polyester,
comprising: mixing an aromatic polycarboxylic acid containing
residual solvents with a monomer; and removing the residual solvent
by increasing temperature to between 50.degree. C.-350.degree.
C.
30. The method as claimed in claim 29, wherein said monomer is an
alkylene glycol.
31. The method as claimed in claim 29, wherein said removing the
residual solvent is conducted under electromagnetic waves.
32. A method for producing a purified aromatic polycarboxylic acid,
comprising the steps of: preparing a crude aromatic polycarboxylic
acid by oxidizing alkyl groups on a aromatic compound with
molecular oxygen in the presence of catalysts and a solvent;
dissolving a salt formed by the crude aromatic polycarboxylic acid
and a base compound; removing impurities from the salt of the crude
aromatic polycarboxylic acid; removing residual base compound while
recovering said purified aromatic polycarboxylic acid from the
salt; and recovering solvents and catalysts.
33. The method as claimed in claim 32, wherein said salt is
dissolved in said base compound and a dissolving solvent.
34. The method as claimed in claim 32, wherein the crude aromatic
polycarboxylic acid is prepared by flashing and evaporation.
35. A method for making a purified organic acid, comprising:
dissolving a crude organic acid containing impurities in a base
compound by thermal agitating under electromagnetic waves; and
removing the impurities.
36. The method as claimed in claim 35, wherein the crude organic
acid is dissolved in the base compound and a dissolving
solvent.
37. The method as claimed in claim 35, further comprising
recovering the purified organic acid.
38. The method as claimed in claim 36, wherein residual base
compound is removed while recovering the purified organic acid.
Description
FIELD OF THE INVENTION
[0001] This invention relates to aromatic polycarboxylic acids,
especially to an improved process of purifying and producing
aromatic polycarboxylic acids in high purity.
BACKGROUND OF THE INVENTION
[0002] Aromatic polycarboxylic acids have been produced through the
oxidation of the corresponding alkyl group with molecular oxygen.
Examples of such acids are pure terephthalic acid (PTA),
isophthalic acid (IPA), trimellitic acid (TMA), 2,6-naphthalene
dicarboxylic acid (2,6 NDA), 2,7-naphthalene dicarboxylic acid
(2,7-NDA), and others. Since PTA is the most typical process, it
will be used for illustrations in the invention. However, the
purification and production methods of the instant invention are
applicable for all aromatic polycarboxylic acids.
[0003] A predominant process for making PTA consists of the
following steps to prepare crude terephthalic acid (CTA).
[0004] 1) Oxidization: The reaction of p-xylene (PX) with air is
carried out in a liquid phase at 150-230 .degree. C. and 150-425
psia using cobalt-manganese-bromine as catalysts and acetic acid as
solvent.
[0005] 2) Crystallization: The effluent from the reactor is
crystallized through 3 to 5 large crystallizers at a reduced
pressure and temperature to precipitate terephthalic acid from
mother liquor.
[0006] 3) Filtration: The crude acid is then separated from mother
liquor by centrifuigation/filtration. The mother liquor, with or
without treatment, is recycled to the oxidation step.
[0007] 4) Drying: The crude acid is dried by blowing inert gas, and
the acetic acid carried by inert gas is then recovered by a
scrubber. The dried crude terephthalic acid is pneumatically
carried to a silo or storage bin that requires large nitrogen flow
or an air separation plant for some PTA plants.
[0008] 5) Solvents and catalysts recovery: Solvent and catalysts
are recovered by various processes.
[0009] CTA containing about 0.5% impurities is then purified by a
hydrogenation process to produce polymer-grade PTA containing about
25 PPM of 4-carboxybenzaldehyde (4 CBA), 150 PPM of p-toluic acid,
and about 0-50 PPM of benzoic acid. Similar to CTA, the purified
PTA from hydrogenation unit goes through another set of process
steps: crystallization; filtration; and drying as described above.
Thus, to remove impurities from reactor effluent at about 0.5% to a
purified product at about 0.025%, the predominate process uses the
following expensive steps:
[0010] 1) Requiring two sets of process steps for crystallization,
centrifugation/filtration, drying, and pneumatically carrying
equipment.
[0011] 2) Using expensive purification process by chemical
reaction. Disregarding the higher capital cost of hydrogenation
unit, high production cost is required because of operating under
high temperature and pressure by using expensive noble metals as
catalyst.
[0012] 3) Requiring long resident time for crystallization. CTA
takes about 3-5, and PTA takes about 5, large crystallizers to
recover product from mother liquor. In addition, due to highly
corrosive bromine-acetic acid environment, some crystallizers may
require using expensive corrosive-resistant material, such as
titanium-lined equipment.
[0013] 4) Requiring drying and pneumatically carrying to make
finished product.
[0014] 5) Meeting polymer-grade specification, but product still
containing about 0.01% of impurities.
[0015] PTA in high purity is required to be suitable for making
polyester fibers, films, and molding resin. Terephthalic acid is
difficult to be purified due to its low solubility in most
solvents, high boiling temperature, and similarities in physical
and chemical properties with impurities present.
[0016] An alternative is to remove impurities by solvent
extraction. The solvent extraction approach is attractive because
of lower costs. It can be the traced back to 1953 (U.S. Pat. No.
2,664,440), or even earlier. In early stage, solvents suggested are
unstable, reactive with the product, toxic, or unable to purify CTA
to desired level. Thereafter, Iwane (U.S. Pat. No. 5,344,969) and
Hirowatari (U.S. Pat. No. 5,565,609) disclosed methods that use
more stable solvents. The following summarizes these methods.
[0017] 1) Dissolving crude acid: The aromatic polycarboxylic acid
forms salt with many base compounds, and the salt is soluble in a
dissolving solvent such as water or alcohol at elevated
temperature.
[0018] 2) Removing impurities: Some impurities can be easily
separated by solution pretreatment, such as activated carbon for
colorants. The impurities having close properties with the acid are
separated in mother liquor by crystallizing with cooling for at
least 30.degree. C.
[0019] 3) Recovering product: Hirowatari thermally decomposes the
solution from pretreatment by heating or contacting steam with a
concentrated solution in the presence of alkylene glycol. Iwane
precipitates and washes the salt that is then converted to a
purified product by thermally decomposing or by adding an
acid-substitution solvent to substitute the product acid in the
salt. Iwane also recovers product by directly adding an
acid-substitution solvent to the solution.
[0020] Both Iwane and Hirowatari use amine compound consisting of
nitrogen as the only hetero atom, such as aliphatic, alicyclic,
aromatic, or heterocyclic amines. Iwane uses an alcohol as the
dissolving solvent for the purification of crude NDA from
oxidation. Hirowatari uses water as the dissolving solvent to
recover aromatic dicarboxylic acids from hydrolyzed polyester
resins. In his approach, no purified salt is prepared because its
impurities consist of only additives and colorants that can be
simply removed by activated carbon. Thus, this method is suitable
for purifying hydrolyzed resins containing already highly purified
PTA with colorants or additives that are easy to be separated, but
not for the crude aromatic dicarboxylic acids from oxidation
containing impurities that are difficult to be separated.
[0021] For thermal decomposition, Iwane adds heat to the salt that
may be dispersed in a paraffin, alkylbenzene, alkylnaphthalene, or
alkylbiphenyl, and does not use steam for heating. The chosen
solvents have high boiling temperature that will be presented in
the finished product as another contaminant. Hirowatari heats the
pretreated aqueous solution while refluxing to decompose the amine
salt, or concentrates the solution by distillation before
contacting with steam to decompose and remove the amine compound.
Alkylene glycol is used to raise reflux temperature. The refluxing
increases the content of base compound in the finished product, and
the distillation has to evaporate more than 50% of water that
requires significant energy.
[0022] Iwane claims improving 2,6-NDA purity from 97.2% to about
99.8%, and Hirowatari recovers a hydrolyzed resin to a 99.9% PTA.
Iwane applies his method to crude NDA from reactor effluent at a
purity level lower than CTA that is purified to a level only close
to CTA. Although both approaches improves product purity, they are
still off from the specification of polymer-grade PTA
(>99.98%).
[0023] The other approach is Lee (U.S. Pat. No.5,767,311) that uses
N-methyl pyrrolidone (NMP) to dissolve CTA between 140-190.degree.
C. without using a dissolving solvent. The solution is cooled to
5-50.degree. C. for crystallization. Filtering and washing the
precipitate make a PTA meeting polymer-grade specification without
using means to recover product from salt. However, experiments
using this method indicate that unconverted salts contaminate the
finished product. The contamination may be from the failure to
recognize the existence of salt formed by NMP and PTA in the
process. Lee identifies the precipitation from solution as PTA, but
it is actually a salt. The salt is converted to product during
washing by some of his washing solvents, such as methanol. However,
significant salts are unconverted because only washing is
insufficient to convert all salts to product. The dissolution
process and solvent recovery of the method are expensive. Compared
with amine compound or morpholine, NMP is about 2-3 times more
expensive and requires 3-5 times more to dissolve the crude acid.
It also costs more to heat and recover the high boiling solvent. In
addition, Lee incorrectly asserts that CTA can be dissolved in a
nonaqueous morpholine solution. Its solubility is negligible
disregarding solution temperature unless water is presented. Even
if morpholine were able to dissolve CTA, the finished product is
not a PTA but a salt, because methanol cannot convert morpholine
salt to PTA. The difference in NMP and morpholine salts will be
further discussed and taken advantaged by the present invention.
The present invention uses new crystallization process and washing
solvent to improve product quality of this method.
[0024] Disregarding the advantages there is no known commercial
application of purification by solvent extraction. A major problem
is from the fact that the residual base compound remaining in the
finished product becomes a contaminant itself. All proposed organic
base compounds contain nitrogen that causes color and other
problems in making polyesters, and no prior art discusses the
problem and teaches how to remove the base compound from the
finished product.
[0025] Crystals always contain residual solvent by inclusion during
crystallization. Using the known methods, it may contain more than
0.1% of residual base compound that is close to the impurity level
of CTA. To be suitable for making polyesters, the residual base
compound has to be removed to a few parts per million that is close
to the impurity level of PTA. Therefore, the previously known prior
art of solvent extraction removes impurities in the crude acid, but
introduces residual base compound as contaminant in the product
that makes it unsuitable for making polyesters.
[0026] The known methods do not attempt to remove residual base
compound from the finished product. Iwane teaches using acid
solvent, Hirowatari teaches using water to wash base compound from
the filter finished product cake, and Lee teaches using NMP,
p-xylene, acetone, methyl ethyl ketone, or methanol to wash the
filter cake. An experiment using 100:1 ratio of water to wash and
leach the cake for about 10 hours, produces a purified product
still contains significant amount of base compound. This indicates
that the base compound is difficult to be removed once it is
included in product crystalline. This problem is either unknown for
having not been addressed in open literatures, or known by those
highly skilled in the art, but remained to be unsolved.
[0027] The prior art of solvent extraction purification methods
either specifically or implicitly suggest replacing hydrogenation
unit and uses CTA as feed except Lee. Lee incorrectly asserts that
high percentage of CTA can be directly recovered from filtering
reactor effluent without using crystallization or other means.
Because most CTA remain in the mother liquor of reactor effluent,
and it requires long residence time to precipitate CTA. Therefore,
the predominated process uses 3-5 large crystallizers to recover
CTA. The instant invention suggests using flashing and evaporation
to reduce residence time.
[0028] Because the purification method itself needs another set of
process steps for crystallization, filtration, drying, and
pneumatically carrying, the prior art also requires two sets of
process steps to produce PTA. Thus, using the known methods of
solvent extraction for producing aromatic polycarboxylic acids
suffers the following disadvantages:
[0029] 1) Introducing base compound that contaminates the finished
product.
[0030] 2) Requiring two sets of process steps for crystallization,
centrifugation/filtration, drying, and pneumatically carrying
equipment.
[0031] 3) Significant detectable impurities remaining in the
purified product.
[0032] 4) Requiring long resident time for crystallization, and
thus, several large crystallizers.
[0033] 5) Requiring drying and pneumatically carrying to make
finished product.
[0034] Accordingly, several objects of the present invention
are:
[0035] 1) To provide a solvent extraction purification method to
remove impurities from the crude acid to meet or exceed the
specification of polymer-grade aromatic polycarboxylic acids.
[0036] 2) To remove the base compound from purified product so that
it will be suitable for making polyester fibers, films, molding
resin, or other applications.
[0037] 3) To provide a process for producing polymer-grade aromatic
polycarboxylic acids that requires only one set of process steps to
substantially reduce capital and production costs.
[0038] 4) To reduce the number of crystallizers required for
crystallization, or eliminate them.
[0039] 5) To produce aromatic polycarboxylic acids that may be used
directly for making polyesters without requiring drying and
pneumatically carrying steps.
[0040] Further objects and advantages will become apparent from the
disclosed solvent extraction method that unexpectedly and
surprisingly removes impurities to undetectable level by the
current standard HPLC measurement.
SUMMARY OF THE INVENTION
[0041] The present invention provides a solvent extraction
purification method for aromatic polycarboxylic acids that meet or
exceed polymer-grade specification. The method includes dissolving
a crude aromatic polycarboxylic acid in a base compound; removing
impurities and excessive base compound; and removing residual base
compound while making purified product. The purification method
removes not only the impurities from the crude acid, but also the
residual base compound from finished product that otherwise will
contaminate the product. The salt in the cake is converted to
product by acid-substitution, thermal decomposition, or
electrolysis. The method uses base-extraction solvents to extract
base compound and impurities from the salt. The residual base
compound in the recovered product is then removed by leaching,
stripping, thermal agitating with electromagnetic waves, or
evaporation with thermal decomposition. The purification method
allows eliminating crystallizers for crystallization and equipment
for drying and pneumatically carrying. Finally, the purification
method is combined with the oxidation and solvent recovery in prior
art to use only one set of process steps, instead of two, to
produce aromatic polycarboxylic acids, and capital and production
costs are substantially reduced.
DETAILED DESCRIPTION OF THE INVENTION
[0042] The present invention provides a solvent extraction
purification method for aromatic polycarboxylic acids that meet or
exceed polymer-grade specification. The method applies to any
polycarboxylic acid such as PTA, IPA, TMA, 2,6-NDA, 2,7-NDA, and
others. It includes dissolving a crude aromatic polycarboxylic acid
in a base compound; removing impurities and excessive base
compound; and removing residual base compound while making purified
product. The preferred base compound contains both oxygen and
nitrogen as hetero atom, such as morpholine or NMP. Additional base
compounds are discussed in more detail below. The salt in the cake
is then converted to product by acid-substitution solvent, thermal
decomposition, or electrolysis.
[0043] In addition to removing impurities from crude acids, the
method uses base-extraction solvents to extract base compound and
impurities from the salt and recovered product. The residual base
compound in the recovered product is removed by leaching,
stripping, thermal agitating with electromagnetic waves, or
evaporation with thermal decomposition. The residual base compound
is not an impurity but a contaminant introduced by the purification
process. The method allows eliminating crystallizers for
crystallization and equipment for drying and pneumatically carrying
to reduce costs. Finally, the purification method is combined with
the oxidation and solvent recovery in prior art to use only one set
of process steps, instead of two, to produce aromatic
polycarboxylic acids.
[0044] The crystal of aromatic polycarboxylic acid purified by
solvent extraction typically contains base compound and other
solvents through the mechanism of adsorption on crystal surfaces;
entrapment in cracks, crevices, and agglomerates; and inclusion of
pockets of liquid. The base compound in the crystal does not
present as liquid but as solid salt formed with the product
crystalline or acid-substitution solvent. Washing or thermal
decomposition may remove some of the adsorbed or the entrapped but
not the included solid that is shielded by the product crystalline
with subliming temperature around 300-425.degree. C. This makes the
removal of residual base compound from product crystalline
extremely difficult.
[0045] Prior art prevents oxidizing the base compound by conducting
under an inert atmosphere to avoid deteriorating the product color
that hides the existence of base compound. The standard HPLC
analysis technique used to measure impurities cannot detect
non-aromatic base compounds; color measurement of purified product
cannot detect the base compound either, unless the compound is
intentionally oxidized to show its existence. A simple technique to
detect the presence of residual base compound is to burn the
finished product in air to non-white color at high temperature for
a long period of time. The degree of the presence of residual base
compound can then be detected by comparing the degree of whiteness
with the PTA purified by hydrogenation, or using existing technique
of color measurement.
[0046] In a purified salt, the base compound not bonded to the
carboxylic acid functional group is excessive base compound.
Removing the excessive base compound in the salt cannot avoid the
recovered product contacting base compound because the compound is
also a constituent of salt. Thus, additional process is required to
remove the residual base compound included inside the recovered
product crystalline, and it is difficult and unobvious.
[0047] The instant invention finds base-extraction solvents that
extract both base compounds and impurities from the purified salt
and recovered product. A suitable base-extraction solvent is any
non-nitrogen-containing compound having low solubility for a
targeted crystalline or having capability to convert salt to
product acid; high solubility for the base compound and impurities;
and easy to be separated, or not required to be separated, from the
finished product. The solvent may contain hydroxyl, carbonyl,
ether, ketone, ester, or other functional group.
[0048] Unless it is specifically specified, the solvent extraction
method is conducted in a range of temperature from the freezing
temperature to the highest boiling temperature of the solution at a
predetermined pressure, and preferably from the chilled water
temperature to the highest boiling temperature. The operation
pressure is not particularly limited; it may vary from 0 to 100,
and preferably from 0.001 to 5, atmosphere absolute.
[0049] The purification method for removing impurities and residual
base compounds comprises the following process steps.
DISSOLVING CRUDE ACID
[0050] A crude aromatic polycarboxylic acid is dissolved in a base
compound by forming a salt. If the salt can be dissolved in a
dissolving solvent, then it will be used to enhance solubility and
reduce dissolution cost. Otherwise, no dissolving solvent is used.
This also includes the rare case that a crude acid is dissolved in
a base compound without forming a salt.
[0051] The crude aromatic polycarboxylic acid can be from any
source containing any kind of impurity. It can be from oxidation
reactor, intermediate production streams, such as in the production
of dimethyl terephthalate (DMT) or dimethyl-2,6-naphthalene
dicarboxylate (NDC), hydrolyzed polyester, or others. The base
compound includes oxygen containing base compound and non-oxygen
containing base compound. The oxygen containing base compound
includes any compound having oxygen and nitrogen as hetero atoms,
such as morpholine compounds, amide compounds, inorganic bases, and
others. The non-oxygen containing base compound comprises amine
compound and ammonia. The base compound includes aliphatic,
alicyclic, aromatic, and heterocyclic compounds. The amount of base
compound used is 0.5-100 mole per mole of carboxylic functional
group in the aromatic polycarboxylic acid, preferably 1-2 mole per
mole of carboxylic functional group in the crude aromatic
polycarboxylic acid. The dissolving solvent comprises water,
alcohol, ether, ketone, and ester. The amount of dissolving solvent
may vary from 0-100, preferably 1-10, mole per mole of carboxylic
functional group in the crude aromatic polycarboxylic acid.
[0052] The prior art uses conventional heating to dissolve the
crude acid by transferring energy from solvent molecules to the
salt ions to overcome the attraction force. In addition of using
the conventional heating, the invention may dissolve the crude acid
by thermal agitation under electromagnetic waves. Thermally
agitating an ionized solution under electromagnetic waves differs
from the conventional or microwaves heating. The wave provides
thermal agitation to both solvent molecules and salt ions. However,
the ions receive far more energy so that the ions heat up the
molecules instead of the reverse way of the other heating. Thus, it
has distinct characteristics, such as solubility, solvent
evaporation, and crystallization. For instance, it has different
solubility because the salt ions receive more energy to dissolve
but may also be thermally decomposed back to acid; better
crystallization efficiency because higher vapor evaporation and
less solvent for crystallization; and different precipitation
mechanism because high energy ions may be used to thermally
decompose a portion of salts to product acid. The main advantage is
its significant saving in dissolution energy and time. Less
dissolution time reduces solvent degradation or reaction with
impurities.
[0053] Iwane and Hirowatari use non-oxygen containing amine
compound, and Lee uses pyrrolidone compound, an alicyclic amide
compound having characteristics of carbonyl and amine functional
groups. The other preferred oxygen containing base compound is
morpholine compound having characteristics of ether and amine
functional groups. The oxygen containing organic base compound has
significant different characteristics from the non-oxygen
containing base compound in basicity, dielectric constant, dipole
moment, or hygroscopic with the dissolving solvent. The present
invention takes the advantage of the characteristics to remove base
compound and impurities from the purified product.
[0054] The oxygen containing salt is called basic salts, and the
non-oxygen containing salt is called normal salts. Most normal
salts are soluble in many solvents such as water and alcohol. The
salt containing ether group that will be called ether basic salt is
soluble in water, but many are insoluble in other solvents, such as
alcohol. The salt containing carbonyl group, will be called
carbonyl basic salt, is insoluble in most solvents including water
and alcohol. The solvent having low solubility for salt or capable
to convert salt back to acid, but still having high solubility for
impurities and base compound, is used as a base-extraction solvent
to purify the salt or product. The present invention discovers that
carbonyl basic salts are weakly bonded. Therefore, it is easier to
recover the salt to product and remove its base compound from the
product, but it is more difficult and expensive to form the salt.
The reverse is true for ether basic salts. Thus, the base compound
removes the impurities from the crude acid, and the base-extraction
solvent removes base compound and impurities from the purified salt
and finished product.
[0055] More specifically, the aromatic polycarboxylic acids are
those having one or more condensed rings, wherein two or more
carboxylic acid groups may be at any positions of the aromatic ring
or rings, and any hydrogen may be substituted by any other
functional groups. Examples of one-ring aromatic dicarboxylic acids
include, but are not necessarily limited to terephthalic acid,
isophthalic acid, orthophthalic acid, trimellitic acid,
hemimellitic acid, trimesic acid, pyromellitic acid, and mellitic
acid. Examples of two-ring aromatic polycarboxylic acids include,
but are not necessarily limited to 2,6-naphthalene dicarboxylic
acid, 2,7-naphthalene dicarboxylic acid, 1,7-naphthalene
dicarboxylic acid, 1,8-naphthalene dicarboxylic acid,
2,3,6-naphthalene tricarboxylic acid, 1,4,5,8-naphthalene
tetracarboxylic acid, and 2,3,6,7-naphthalene tetracarboxylic acid.
Examples of three-condensing ring aromatic polycarboxylic acids
include, but are not necessarily limited to 2,6-anthracene
dicarboxylic acid, 2,7-anthracene dicarboxylic acid, 2,8-anthracene
dicarboxylic acid, 2,9-anthracene dicarboxylic acid, 1,9-anthracene
dicarboxylic acid, 2,3,6-anthracene tricarboxylic acid,
1,4,5,8-anthracene tetracarboxylic acid, and 2,3,6,7-anthracene
tetracarboxylic acid. The aromatic polycarboxylic acid also
includes a mixture of aromatic polycarboxylic acids, for instance,
2,6-naphthalene dicarboxylic acid and 2,7-naphthalene dicarboxylic
acid, in any proportion.
[0056] For base compound, the nitrogen atom in a base compound may
have three or five valences. The base compound includes all
combinations of hetero-atom and carbon-atom at different positions
of the compound, and their saturated and unsaturated compounds with
one or more hydrogen atoms that may be substituted by an alkyl,
aryl, or acyl group, or the ammonium salts derived from such
compounds. If a base compound is in solid or gaseous state under
normal condition, then its aqueous solution may be used. A base
compound can be a mixture in any proportion. Inorganic bases may be
sodium hydroxide, potassium hydroxide, etc.
[0057] The morpholine compounds comprise morpholine,
N-methylmorpholine, N-ethylmorpholine, N-propylmorpholine,
N-isopropylmorpholine, N-methylmorpholine oxide,
N-phenylmorpholine, 4-morpholinepropionitrile,
1-morpholine-1-cyclohexene, or others. The other base compound
containing ether group includes mono-heterocyclic compound
containing 3 to 8 atoms having nitrogen and oxygen in the ring, and
it comprises oxazocines, oxazepines, oxazines, oxazoles,
isoxazoles, oxadiazetes, oxazirines, etc.
[0058] The amide compounds include aliphatic amide, such as
dimethylformamide, dimethylacetamide, ethanamide, acetamide, and
others. An alicyclic amide includes pyrrolidone,
N-methyl-pyrrolidone, N-ethyl-pyrrolidone, N-alkyl-2-pyrrolidone,
N-mercaptoalkyl-2-pyrrolidone- , N-mercaptoethyl-2-pyrrolidone,
N-alkyl-2-thiopyrrolidone, N-methyl-2-thiopyrrolidone,
N-hydroxyalkyl-2-pyrrolidone, and N-hydroxyethyl-2-pyrrolidone,
lactam, etc. An aromatic amide includes phenylacetamide, phenylene
terephthalamide, etc.
[0059] The aliphatic amine comprises methylamine, dimethylamine,
trimethylamine, ethylamine, diethylamine, triethylamine,
n-propyamine, di-n-propylamine, tri-n-propylamine, isopropylamine,
diisopropylamine, triisopropylamine, ethylenediamine,
N-methylethyleneamine, N,N-dimethylethylenediamine,
N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine,
N,N,N',N'-tetramethylethylenediamine, 1,2-diaminopropane,
1,3-diaminopropane, monoethanolamine, diethanolamine,
triethanolamine, dimethylacetamide, dimethylformamide, etc. The
alicyclic amine comprises methylcyclohexylamine,
N-methylcyclohexylamine, N,N-dimethylcyclohexylamine,
ethylcyclohexylamine, N-ethylcyclohexylamine,
N,N-diethylcyclohexylamine, isopropylcyclohexylamine,
N-isopropylcyclohexylamine, N,N-diisopropylcyclohexylamine,
ethylene imine, propylene imine, etc. The aromatic amine comprises
N,N-dimethylaniline, N,N-diethylaniline, N,N-dibutylaniline,
N,N-dimethyltoluidine, N,N-diethyltoluidine, etc. The heterocyclic
amines includes pyridine, piperidine, N-methylpiperidine,
N-methylpyrrolidine, etc.
[0060] The preferred base compound is morpholine,
N-methyl-pyrrolidone, trimethylamine, triethyalamine, or
triethanolamine.
[0061] The alcohol includes aliphatic monohydric alcohol such as
methanol, ethanol, n-propanol, isopropanol, n-butyl alcohol,
isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-amyl
alcohol, isoamyl alcohol, sec-amyl alcohol, tert-amly alcohol,
neopentyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol,
nonyl alcohol, and decyl alcohol; alicyclic monohydric alcohol such
as cyclopentyl alcohol and cyclohexyl alcohol; aliphatic
straight-chain diols such as ethylene glycol, diethylene glycol,
propylene glycol, butanediol, and pentanediol; alicyclic diols such
as 1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,2-cyclohexanediol,
1,3-cyclohexanediol, 1,4-cyclohexanediol; and aliphatic polyols
such as glycerol and pentaerythritol. Aliphatic monohydric alcohol
having 3 or less carbon atoms and diols having 4 or less carbon
atoms, are preferred. An alcohol can be a mixture of these in any
proportion. The preferred alcohol is methanol, ethanol, or alkylene
glycol.
[0062] Ether includes dimethyl ether, diamyl ether, diethyl ether,
isopropyl ether, n-butyl ether, n-hexyl ether, chlorodimethyl
ether, phenyl methyl ether, dibenzyl ether, ethylene oxide,
dioxane, trioxane, furan, tetrahydrofuran, methyl-tetrahydrofuran,
tetrahydropyran, methyl-tetrahydropyran, and others. Ketone
includes acetone, methyl ethyl ketone, methyl n-propyl ketone,
methyl n-butyl ketone, methyl amyl ketone, methyl acetone, 2-methyl
cyclopentanone, cyclopentanone, cyclohexanone, cyclohexanol, and
others. Ester includes ethylene glycol methyl ether, diethylene
glycol methyl ether, ethylene glycol ethyl ether, diethylene glycol
ethyl ether, ethylene glycol butyl ether, ethylene glycol ethyl
ether, ethylene glycol benzyl ether, diethylene glycol, triethylene
glycol, alkyl formate, alkyl acetate, alkyl propionate, oxalates,
alkyl lactate, carbonates, benzoates, and others.
REMOVING IMPURITIES AND EXCESSIVE BASE COMPOUND
[0063] This step removes impurities by pretreating, precipitating,
separating, and washing the cake. Impurities may be removed by
solution pretreatment and crystallization by cooling as taught in
the prior art. In addition, the instant invention provides new
processes to remove both the impurities and excessive base compound
from the washed cake.
[0064] Solution pretreatment is to remove the impurities that can
be easily separated from solution, such as colorants or additives
by activated carbon, insolubles by filtration, or floats by
overflowing or scraping. Processes that separate this kind of
impurities are already well known, and the invention is not
restricted to any specific one. If the crude does not contain this
kind of impurity, solution pretreatment is not required.
[0065] Crystallization is to remove the impurities that are
difficult to be separated and have close physical and chemical
properties with the product. The solubility of impurity salt is
either lower or higher than the product salt at a given temperature
and solution composition. By the variation of solution temperature
and/or composition, the impurity having lower solubility is
precipitated first and separated from the others. Precipitating the
product salt separates it from those having higher solubility by
leaving them in mother liquor.
[0066] Prior art uses crystallization by cooling to separate
impurities, and the salt is separated by usual process, such as
filtration or centrifugation. It requires several large
crystallizers for crystallization because long residence time is
needed for growing crystals from mother liquor. The alternative is
crystallization by controlling composition with cooling to reduce
residence time requirement. After completely dissolving the crude
acid and before crystallization, it removes a predetermined amount
of solvent by usual processes, such as evaporation or distillation,
so that the cooled slurry still contains sufficient mother liquor
to separate the impurities. It reduces but still requires
significant residence time for crystallization. Both try to keep as
much impurities in mother liquor as possible for the separation
from the purified salt.
[0067] The prior art usually uses base compound to wash filter salt
because the dissolving solvent dissolves the salt immediately.
However, the washing efficient is low due to the high viscosity of
salt. Besides, it saturates the salt with excessive base compound
and increases the content of base compound in the finished product.
Other prior art teaches using aliphatic hydrocarbons or aromatic
hydrocarbons as washing solvent. It simply replaces the solvent in
crystal and provides no extraction power, and may present in the
finished product as other contaminant.
[0068] The instant invention uses base-extraction solvent to remove
both excessive base compound and impurities from the salt. The new
process includes washing and leaching with base-extraction solvent,
crystallizing salt in the presence of a base-extraction solvent,
precipitating product in the presence of a base-extraction solvent,
crystallization with direct-extraction from salt, and
crystallization with resalting and salt base-substitution.
[0069] Most base-extraction solvents do not convert salt to acid.
However, some may if the pure solvent is used to wash the filter
carbonyl basic salt, but mixing the salt-converting base-extraction
solvent with the base compound in a proper proportion reduces the
salt conversion. For instance, mixing methanol with 50% NMP to wash
the filter salt significantly reduces salt conversion. The washed
cake is preferred to be retained as salt.
[0070] More specifically, the base-extraction solvent is water,
hydrogen peroxide, alcohol, ether, phenol, ketone, ester, and
others. The alcohol, ether, ketone, and ester are defined
previously. The base-extraction solvent may be used alone or as a
mixture of two or more in any proportion, and the solvent may be
used in liquid or vapor state. The preferred base-extraction
solvent is water, methanol, ethanol, alkylene glycol, acetone,
tetrahydrofuran or tetrahydropyran. Since the targeted crystalline
in this step is purified salt, the used dissolving solvent is
excluded. In the next step, the targeted crystalline is product
acid and it may include the used dissolving solvent.
[0071] The color of most impurity salts are non-white and the odor
of excessive base compound is ammoniacal, using base-extraction
solvent to wash or leach the filter cake improves the salt
significantly in both of the color and odor compared with the salt
washed by other solvents, such as base compound or hydrocarbons. By
definition, leaching is different from washing filter cake (Perry's
Chemical Engineering Handbook, 6.sup.th Edition, Page 19-48).
Processes for washing and leaching are very well known, and the
invention is not limited to any specific one.
[0072] The base-extraction solvent may also be added to the
solution after complete dissolution of the crude acid. The presence
of base-extraction solvent during crystallization reduces the
inclusion of base compound and simultaneously extracts impurities
and base compound from the salt. In addition, the presence of
base-extraction solvent in the solution changes crystallization
mechanism, such as shape, size, and rate. For instance, adding
methanol, acetone, or tetrahydrofuran, changes the shape and
increases the size of crystals from NMP-PTA salts.
[0073] The purified product can be precipitate in the presence of a
base-extraction solvent by adding an acid-substitution solvent to
the solution. The presence of a base-extraction solvent extracts
impurities and base compound from the precipitate. The present
invention discovers that water is a base-extraction and also an
acid-substitution solvent for carbonyl basic salts because it
precipitates product directly from a saturated solution, but other
base-extraction solvents, such as methanol, precipitate salt in a
range of solution composition. However, the solubility of 4-CBA and
NMP salt in water is about 10 times lower than methanol. Compared
with washing to convert salts in the prior art, precipitating
product in the presence of a base-extraction solvent has better
control of salt conversion and crystal size by adjusting
temperature, agitation, composition, and residence time. An
acid-substitution solvent is added to precipitate product without
the presence of a base-extraction solvent in the prior art.
However, the product purity is low because most impurities
precipitate with the product.
[0074] Removing most or all solvents out of the solution by
evaporation or flashing obtains solid or slurry of salt. Since
impurities are not vaporized under normal operating conditions,
they all remain with the salt. This is a situation to be avoided by
the crystallization of prior art that keeps impurities in mother
liquor for separation. However, the invention unexpectedly and
surprisingly finds that the base-extraction solvent can extract
most of impurities and excessive base compounds from the salt.
Thus, this crystallization process completely eliminates the
residence time requirement for crystallization. Its product
recovery efficiency depends on the solubility of the salt in the
base-extraction solvent and the amount of dissolving solvent
remained in the slurry. Unlike the crystallization of prior art,
the crystallization with direct-extraction from salt does not cool
the solution for crystallization. The mother liquor in slurry may
or may not be separated from the salt before adding base-extraction
solvent. The extracted solution is then separated from the salt by
usual separation processes.
[0075] Redissolving the precipitate in the dissolving solvent or
base compound and recrystallizing the solution for one or more
times will remove impurities to undetectable level by the current
standard HPLC method or to meet polymer grade specification for a
crude acid having higher impurities. Thus, crystallization with
resalting comprises the steps of crystallizing the salt from the
dissolved solution of the crude acid; separating, washing, and
redissolving the salt; recrystallizing the salt from the solution;
and separating and washing the salt by usual process. Preferably,
the salt is completely dissolved before recrystallization. If the
washed cake contains product acid from using electromagnetic waves
or washing with a salt-converting base-extraction solvent, the acid
may or may not be separated from the salt or redissolved by the
base compound for resalting. Any previously discussed
crystallization process can be used for crystallization and
reprecipitation. However, it is preferable to use the
crystallization with direct-extraction from salt for both of
crystallization and recrystallization. If precipitating product in
the presence of a base-extraction solvent is used, it is preferred
to be the last crystallization step. The number of resalting is not
specifically limited, and preferably 1-2 times.
[0076] The base-extraction solvent used in the previously discussed
processes for removing impurity may or may not be the same. The
amount used is 0.1-100, preferably 1-10, moles per mole of the
carboxylic functional group. For ether basic salts, the preferred
base-extraction solvent is methanol or ethanol. For carbonyl basic
salts, alkylene glycol, acetone, tetrahydrofuiran, or
tetrahydropyran is also preferred.
[0077] Salt base-substitution is a method that enhances product
recovery by substituting the base compound of a first salt with the
base compound of another salt. As discussed previously, carbonyl
basic salts are more difficult and expensive to prepare but easier
and cheaper to recover. For instance, preparing an NMP-PTA salt is
several times more expensive than a morpholine-PTA salt, but it can
be recovered by less expensive water. The instant invention
discovers that the base compound of a salt can be substituted by
another base compound having higher boiling temperature, and
therefore, an ether basic salt or a common salt can be converted to
a carbonyl basic salt. Thus, a salt can be prepared by a more
economic base compound and converted to another salt for more
economic product recovery. The salt to be converted is mixed with a
substituting base compound with or without the presence of a
dissolving solvent. The substituted base compound and/or the
dissolving solvent are then removed from the solution by usual
separation processes, such as evaporation or distillation, using
conventional heating or electromagnetic waves. The substituted salt
is precipitated by cooling from the solution with or without the
presence of a base-extraction solvent or prepared by
direct-extraction from the salt. A dissolving solvent, such as
water, may be used to dissolve the unconverted salt that is then
recycled or converted in a series of steps. Salt base-substitution
also includes changing salt crystalline, such as shape or size, in
the presence of another base compound. The amount of substituting
base compound used may vary from 0.1-100, preferably 1-10, mole per
mole of the carboxylic functional group.
[0078] In addition of washing with a non-salt-converting
base-extraction solvent, the filter cake can be washed with a
salt-converting base-extraction solvent or an acid-substitution
solvent. This can be considered as a combined step of washing and
the acid-substitution of the next step, and it is Lee's approach.
However, washing has only little control on salt conversion and
product properties. The instant invention prefers to either
precipitate purified product during crystallization before
filtering or separate the precipitate as a salt to be converted in
the next step because both have better control on salt conversion,
the extraction of base compound and impurities from the recovered
product, and product particle size. For some basic salts, product
particle size may be affected by salt particle size that can be
controlled by spray drying, adjusting composition, residence time,
temperature, agitation, or others.
[0079] Thus, processes for removing impurities comprises solution
pretreatment, crystallization by cooling, crystallization by
controlling composition with cooling, crystallizing salt in the
presence of a base-extraction solvent, precipitating product in the
presence of a base-extraction solvent, crystallization with
direct-extraction from salt, crystallization with resalting, salt
base-substitution, washing with a base-extraction solvent, leaching
with a base-extraction solvent, or all possible combinations of
these processes. In addition to removing impurities from the crude
acid, excessive base compound is also removed from the washed cake
to reduce the content of base compound in the finished product
prepared by the following step.
REMOVING RESIDUAL BASE COMPOUND WHILE MAKING PURIFIED PRODUCT
[0080] This step recovers product from the salt in the washed cake
if the amount of salt is significant, and/or removes residual base
compound before making finished product. Processes for recovering
product from purified salt comprises acid substitution; thermal
decomposition; or electrolysis. Preferably, the product is
recovered in the presence of base-extraction solvent. Because
solution composition and temperature, agitation, and residence time
may affect the particle shape and size of product, and they are
preferably optimized with the extraction of base compound and
impurities.
[0081] Acid Substitution
[0082] To convert the salt to product, an acid-substitution solvent
is added to substitute and precipitate the product acid. The salt
may be mixed with a base-extraction solvent. It is preferred to
completely dissolve ether basic salts and common salts before
adding an acid-substitution solvent, and the preferred solvent is
water, methanol, ethanol, alkylene glycol, or a mixture of these.
Carbonyl basic salts are insoluble in most solvents, and water is a
preferred acid-substitution solvent. Water is preferably added in
the presence of the base-extraction solvent, such as methanol,
ethanol, acetone, tetrahydrofuran, or tetrahydropyran. Acid
substituttion may be conducted under electromagnetic waves. Acid
substitution with a base-extraction solvent reduces the inclusion
of base compound and impurities in the recovered product.
[0083] An acid-substitution solvent may be an aliphatic carboxylic
acid, an inorganic acid, water, or others. An aliphatic carboxylic
acid may be formic acid, acetic acid, propionic acid, butyric acid,
glycolic acid, lactic acid, malic acid, tartaric acid, mesotartaric
acid, citric acid, monochloroacetic acid, monobromoacetic acid,
mononitroacetic acid, trifluoroacetic acid, and trichloroacetic
acid; and an inorganic acid may be nitric acid, hydrochloric acid,
hydrogen bromide, hydrogen iodide, sulfuric acid, phosphoric acid,
and perchloric acid. As discussed before, water or a
base-extraction solvent can be an acid-substitution solvent for
carbonyl basic salts. An acid-substitution solvent can be a mixture
of these acids in any proportion, or a mixture of these acids with
a dissolving solvent or a base-extraction solvent in a proportion
that the acid is greater than 1% by weight.
[0084] For ether basic salts or common salts, the preferred
acid-substitution solvent is aliphatic carboxylic acid, and the
most preferable is acetic acid. For carbonyl basic salts, water is
preferred. The amount of acid-substitution solvent added is 0.5-100
mole per mole of carboxylic functional group in the aromatic
polycarboxylic acid. It is usually added in an amount of slightly
more than the mole parts of the carboxylic functional group.
[0085] Thermal Decomposition
[0086] Heat is added to the purified salt to thermally decompose
the base compound in a range of temperature between 50-350.degree.
C. The salt may be mixed with a base-extraction solvent having
desired boiling temperature that can also be adjusted by pressure.
The preferred base-extraction compound is water, steam, or an
alcohol. The heat may be added by heat transferring, such as
thermal conduction, or direct contacting with a heating medium.
[0087] In addition to the conventional process of heating, the salt
may be thermally decomposed under electromagnetic waves.
Preferably, the salt is mixed with a base-extraction solvent, such
as water, steam, or an alcohol, in any proportion that may dissolve
or acid-substitute the salt and absorb the wave to assist the
decomposition. The wave thermally agitates the molecules and
separates them from the product crystalline that is transparent to
the wave, and decomposes the solution to a mixture of recovered
product and unconverted salt. Maintaining a proper solvent
concentration and temperature allows the solution to be decomposed
continuously by the wave. The base-extraction solvent may also be
added in a series of steps to the mixture for further
decomposition. The unconverted salt may be separated from the
recovered product by dissolving in a solvent, and the filtrate is
recycled or thermally decomposed by the wave in a series of steps.
Thus, this process may be used for batch or continuous processing.
Thermal decomposition by electromagnetic waves requires
significantly less energy and residence time compared with the
conventional process. For instance, the residence time is estimated
to be about 0.04-0.6 hours compared to about 2-12 hours of
conventional processes. In addition, adding heat from inside out
reduces the chance of including base compound in the recovered
crystalline.
[0088] The decomposed base compound is preferred to be separated
from the recovered product by usual processes, such as evaporation,
suction under vacuum, distillation, absorbent, carrying by inert
gas, steam, or a dissolving solvent, etc.
[0089] For carbonyl basic salts, thermal decomposition by direct
contacting the salt with steam or by electromagnetic waves using
water or steam as base-extraction solvent is preferred because it
thermally decomposes and acid-substitutes the salt simultaneously.
Its product particle size is then determined by salt particle size
that is easier to control. Furthermore, this eliminates a step of
filtration and the step of drying and pneumatically carrying by
thermally decomposing and evaporating the residual salt and
solvents in an alkylene glycol to be discussed below.
[0090] Electrolysis
[0091] Electric current is applied to a solution formed by
dissolving the purified salt in a base-extraction solvent so that
the cathode is concentrated with basic cations whereas the anode is
concentrated with acidic anions. The product acid is precipitated
around the anode if the applied electric current is sufficiently
large enough. The alternative is to add acid-substitution solvent
or heat around the favorable electrode to precipitate the product
acid while keeping the basic cations apart under a moderate
electric field to reduce the inclusion of base compound. The
electrodes are separated by usual processes to minimize the
disturbance of ions around the other electrode. The electrolysis is
similar to the well-known electrolytic production of metal
elements, and the invention is not limited to any specific
electrolysis process. The magnitude of electric current used is not
particular limited, it depends on the desired production rate or
electric field to separate the ions. The electrode may use a
material that is not reactive with the ions and not dissolved
itself into solution to contaminate the product, or a material that
can deposit the basic cation on the electrode for separation. The
preferred base-extraction solvent is methanol, ethanol, alkylene
glycol, or a mixture of these.
[0092] The recovered product crystalline may be separated by usual
processes, and the filter cake is washed by a base-extraction
solvent, an acid-substitution solvent, or a mixture of the solvents
in any proportion. Some recovered products may be directly treated
without separation by the following step.
[0093] Prior art uses only washing to remove residual base compound
or convert salt to product, and it is insufficient to remove the
base compound to a satisfactory level. The finished product has
high content of residual base compound because the washed cake
contains significant excessive base compound, the product is
recovered without extracting residual base compound from
crystalline, the purified solution containing excessive base
compound is directly used for thermal decomposition, the base
compound is refluxed to the thermally decomposed solution, or using
washing for salt conversion by leaving unconverted salt in product,
etc.
[0094] On the other hand, the invention tries to reduce the
residual base compound by removing excessive base compound from the
salt and extracting the residual compound from the recovered
product. However, it is inevitable for the recovered product to
contact base compound because it is a constituent of salt. Thus,
these efforts can reduce but cannot totally remove the residual
base compound from the recovered product. Some of the previous
steps for removing base compound may be eliminated by having higher
residual base compound in the recovered product. Since removing the
residual base compound is a difficult process. Therefore, it is
preferred to minimize the residual base compound in the recovered
product.
[0095] The invention provides the following new processes for
removing the residual base compound from the recovered product to
make a finished product suitable for making polyesters. The new
processes includes leaching; stripping; thermal agitating with
electromagnetic waves; evaporation with thermal decomposition; or a
combination of these processes.
[0096] The recovered product may be leached by mixing with a
base-extraction solvent at a predetermined amount and temperature
and re-filtered for one or more times. Processes for leaching or
stripping traced solvent from filter cake are already well known,
and the invention is not limited to any specific one. Leaching or
stripping removes only the absorbed or entrapped but not the
included base compound.
[0097] Thermal agitating with electromagnetic waves applies the
wave to the recovered product or a mixture of the product with a
base-extraction solvent. The process is similar to thermal
decomposition by electromagnetic waves with emphasis on removing
the residual salt included inside the recovered product. The wave
is selectively absorbed by the residual base compound and solvents
that induces thermal agitation to heat and drive the ions, whether
adsorbed on surfaces or included inside crystals, out of the
crystalline transparent to the wave. The decomposed base compound
and other solvents are then separated as vapor; as liquid by an
absorbent; or leached away by a base-extraction solvent surrounding
the crystalline. The base extraction solvent may be added
continuously or seriously to the cake for a predetermined duration
or number of time to assist the decomposition of traced salt. This
process removes the residual base compound and dries the product
crystalline simultaneously.
[0098] Evaporation with thermal decomposition evaporates residual
solvents, such as water or acetic acid, and thermally decomposes
the residual base compound between 50-350.degree. C., and
preferably 90-210.degree. C. The recovered product is mixed with a
monomer to be reacted with the product acid to make a polyester,
the polyester with a size of chain varying from 1-100 basic units,
or a base-extraction solvent, such as water at elevated
temperature. Preferably, it is mixed with the monomer, and alkylene
glycol is the most typical monomer that will be used for
illustration in the instant invention. The high boiling temperature
of alkylene glycol is used to thermally decompose the residual salt
and evaporate the residual solvent out of the solution. In
addition, alkylene glycol is a structural unit of polyester, the
solution or the filter cake can be directly used for producing the
polyester. This makes the drying and pneumatically carrying steps
unnecessary. If a polyester plant is not integrated with the
purification plant, then this process can be conducted at either
site. It is preferred to use heat transferring or thermal agitating
under electromagnetic waves to avoid introducing another component.
The evaporated residual solvent is removed by suction or other
proper process. The preferred amount of alkylene glycol is the
amount required for polymerization so that the treated solution can
be directly used for making polyesters. This step can also be used
in the predominant process to eliminate the drying and
pneumatically carrying steps by mixing the pre-dried finished
product with an alkylene glycol. The treated solution is different
from the decomposed solution in product recovery that contains
significant amount of base compound and other solvents and is
unsuitable for making polyesters.
[0099] The base-extraction solvent used in product recovering,
washing, leaching, stripping, thermal agitating with
electromagnetic waves, or evaporation with thermal decomposition
may or may not be the same. The amount of base-extraction solvent
used is not particular limited, preferable in 0.5-1000 mole per
mole of the carboxylic functional group.
[0100] If evaporation with thermal decomposition by alkylene glycol
is not used to remove residual base compound, or if it is
necessary, the purified product is dried to remove the residual
solvents by blowing inert gas as in the predominant process. The
alternative is to dry by using electromagnetic waves as described
previously.
[0101] The purification method by solvent extraction may be
conducted under an atmosphere of air, steam, inert gas, such as
nitrogen, argon, or helium, or reductive gas, such as hydrogen or
lower hydrocarbon gas. The method can be used for batch,
semi-batch, or continues processing.
[0102] Recycling improves the efficiency of product recovery and
solvent usage. For instance, filtrates may be recycled or used for
washing or leaching to a previous step to reduce the solvent
requirement and improve product recovery. The recycling filtrates
may be treated or untreated. The filtrate may be treated by any
suitable process, such as distillation, filtration, centrifugation,
sedimentation, evaporation, cooling, adding more solvent, or any
combination of these processes. Processes for recycling to improve
efficiency are already well known, the method will not be limited
to any specific one.
[0103] The impurities from the disclosed method are, unexpectedly
and surprisingly, undetectable by current standard HPLC method.
Compared with the product purity from the prior art, the difference
is about two orders of magnitude. The color from intentionally
burnt sample meets the current standard, it implies that the base
compound has been removed to a satisfactory level. PTA in lower
impurity provides many potential advantages: larger molecular
weight in polymerization, stronger and finer fiber, less oxygen
penetration through bottles, faster spinning speed for producing
fibers, and many more advantages yet to be discovered.
DESCRIPTION OF A PREFERRED PROCESS FOR PRODUCING HIGH PURITY
AROMATIC POLYCARBOXYLIC ACIDS
[0104] A new combination of the purification method discussed above
with the prior art of oxidation and the recovery of solvents and
catalysts provides a process with substantially less capital and
production costs. The process can be applied for all aromatic
polycarboxylic acids produced through the oxidation of the
corresponding alkyl group with molecular oxygen. Examples of such
acids are PTA, IPA, TMA, 2,6-NDA, 2,7-NDA, and others. Since PTA is
the most typical process and it will be used for illustrations.
[0105] The combination reduces two sets of process steps into one
set to produce aromatic polycarboxylic acid in high purity. This is
accomplished by taking advantages of the following special features
and advantages found in the disclosed purification method.
[0106] 1) In addition to CTA, the purification method may directly
take the reactor effluent as feed without separating CTA. The
effluent contains other material, such as catalysts (including
catalyst promoters) and acetic acid, that can be separated from the
product in the purification process. This allows reducing two sets
of process steps in the predominant process to one set to
significantly reduce the capital and production costs.
[0107] 2) The prior art has to consider factors such as viscosity,
particle size, product recovery, and inclusion of impurity that can
be circumvented by the proposed crystallization with
direct-extraction from salt. In addition, the base-extraction
solvent can be used to adjust the viscosity of slurry for
separation and transportation.
[0108] 3) The purification method can remove more impurities than
the hydrogenation unit in the predominant process. This allows the
oxidation reactor to operate at more economical condition, such as
a severity for lower hydrocarbon combustion and catalyst
consumption, etc.
[0109] 4) The purification method does not require crystallizer for
crystallization.
[0110] 5) The purification method may eliminate drying and
pneumatically carrying steps by using evaporation with thermal
decomposition by alkylene glycol.
[0111] 6) The purification method uses physical separation rather
than chemical reaction to remove impurities, this requires less
capital and production costs for purification.
[0112] 7) The purification method produces product purity
significantly higher than the predominant process. This provides
many potential advantages as described previously.
[0113] The invention takes these synergistic advantages and
unobvious features to provide an unsuggested combination that
requires substantially less capital and production costs. The
combination comprises oxidizing; dissolving crude acid; removing
impurities and base compound from the purified salt; removing
residual base compound while recovering purified product from the
salt; and recovering solvents and catalysts. The process steps are
described as follows:
OXIDIZING
[0114] This step produces aromatic polycarboxylic acids through the
oxidation of the corresponding alkyl group with molecular oxygen.
The oxidation of aromatic polycarboxylic acid has been extensively
studied in the last 50 years, the invention may use any previously
known prior art and is not limited to any specific one.
[0115] A process developed by Mid-Century is a widely adopted
oxidizing process which uses acetic acid as a solvent to assist
slurry mixing and circulation; heavy metals, e.g., cobalt and
manganese, as catalysts; and a bromine-containing compound as
promoter. Reaction conditions are generally in the range of
175-230.degree. C. and 1500-3000 kPa.
[0116] The feed may include recycles containing catalysts, reactor
solvent, or intermediate products from the steps of dissolving a
salt formed by crude acid with a base compound in a dissolving
solvent; removing impurities and base compound from the purified
salt; and recovering solvents and catalysts.
DISSOLVING CRUDE ACID
[0117] Dissolving the crude aromatic polycarboxylic acid in a base
compound has already been described. As discussed previously, the
purification method can take reactor effluent or CTA from the
predominant process as a crude acid. Therefore, there are many
alternatives between the two extremes to prepare the crude acid.
For instance, if the slurry from flashed reactor effluent is used
as a crude acid, then the reactor solvent and catalysts will be
presented in filtrates with impurities that can be subsequently
recovered in the step of recovering solvents and catalysts. The
alternative is to separate reactor solvent and catalysts from the
crude acid by processes taught in previously known prior art, such
as flashing, evaporation, heating/cooling, crystallization,
filtration, centrifugal classifier, distillation, classification
column, fluid hydrocyclone, a cyclone separator, settling,
replacement of mother liquor with water, membrane, or from any
intermediate step of preparing CTA in the predominated process. The
separated mother liquor is either recycled to reactor or sent to
the step of recovering solvents and catalysts. The instant
invention is not limited to any specific process for separating the
reactor effluent. However, one of preferable separating processes
is to evaporate most of mother liquor out of the flashed reactor
effluent, and recycle a small portion of mother liquor containing
catalysts separated from the crude acid. The evaporation may or may
not de conducted under electromagnetic waves. This approach
recovers most of crude acid from reactor effluent without using
crystallization.
[0118] The other source of crude acids may be from recycled
filtrates, treated or untreated, or from the step of recovering
solvents and catalysts.
REMOVING IMPURITIES AND EXCESSIVE BASE COMPOUND
[0119] Removing impurities has been described previously. As
discussed before, crystallization by controlling composition with
cooling can reduce the number of crystallizer, crystallization with
direct-extraction from salt eliminates the crystallizer for
crystallization.
[0120] The filtrate can be recycled to the other step, treated or
untreated, or sent to the step of recovering solvents and
catalysts. Some impurities have to be removed from this step to
avoid accumulation, and this can be accomplished by any proper
process. One of the examples is to evaporate solvents from a
selected filtrate containing significant amount of impurities, and
the bottom is then directly recycled or treated with a product
recovering step to convert the salt to impurities before
recycling.
REMOVING RESIDUAL BASE COMPOUND WHILE MAKING PURIFIED PRODUCT
[0121] This step has been described previously. If evaporation with
thermal decomposition by alkylene glycol is used to remove residual
base compound, then the drying and pneumatically carrying steps in
the state of art process will be unnecessary.
[0122] The particle sizes obtained from acid substitution are
generally finer, but more uniform, than those obtained from the
existing PTA processes. If alkylene glycol is used for removing the
traced basic compound, then the mixture can be used directly for
making PET. However, if it is necessary, re-dissolving and
re-crystallization can adjust the bulk density of PTA. This can be
achieved by a number of processes used in existing manufacturing
plants. The re-crystallized PTA are not only similar to current
commercial PTA in bulk density but also further purified to contain
fewer impurities.
RECOVERING SOLVENTS AND CATALYSTS
[0123] In addition to using previously known prior art for
recovering reactor solvent, water, catalysts, this step also
recovers base compound; base-extraction solvent; acid-substitution
solvent if it is used for recovering product and is different from
reactor solvent; and dissolving solvent if it is used and different
from water. Besides, residual impurities and product may possibly
present from direct recycling of filtrates from purification
steps.
[0124] Not all components have to be recovered to their pure forms.
Some may be recovered as a mixture. For instance, in the dissolving
crude acid step, the base compound and dissolving solvent can be
used as a mixture. Furthermore, if the mixture contains some
acid-substitution solvents, it does not have significant impact on
the efficiency of purification.
[0125] Among the solvents, some may form azeotropic mixture. If
acid substitution is used for recovering product then the base
compound and the acid solvent may form electrolytes. However,
processes for separating these components are already well known,
such as distillation, filtration, centrifugation, sedimentation,
evaporation, thermal decomposition, cooling, membrane, stronger
base substitution, stronger acid substitution, adding other
component to break an azeotropic mixture, and others. The invention
may also use electromagnetic waves for evaporation, distillation,
and thermal decomposition, and others.
[0126] Conclusion
[0127] Thus, the purification method of the instant invention
removes not only impurities from crude aromatic polycarboxylic
acids, it also provides procedures to remove the base compound used
for purification that will otherwise contaminate the finished
product. The invention solves an unsolved or unknown problem, and
it makes purification by solvent extraction practical.
[0128] The purification method reduces the number of crystallizers
for crystallization or totally eliminate them. Using alkylene
glycol to remove residual base compound eliminates the drying and
pneumatically carrying steps required in the prior art.
[0129] Compared to the purity of the prior art, the improvement of
product purity is about two orders of magnitude with undetectable
impurity by standard HPLC measurement. This provides many potential
advantages such as making new fibers that are stronger and finer,
increasing PET fiber production rate with higher spinning speed,
applying PET bottles for new uses by reducing oxygen penetration
rate, and many more advantages yet to be discovered.
[0130] By taking advantages of some special features and advantages
found in the purification method, the combination of the
purification method with the prior art in oxidation and the
recovery of solvents and catalysts reduces two sets of process
steps in the predominant process into one set. This unsuggested
combination substantially reduces capital and production costs to
produce high purity aromatic polycarboxylic acids.
[0131] In addition to aromatic polycarboxylic acids, the
purification method can be used for the purification of organic
acids containing impurities having close physical and chemical
properties. The impurities may have different number of acid
functional group; an acid group substituted by other functional
group; the acid functional group at different positions; or the
same acid group at the same position but with hydrogen substituted
by other functional group, etc.
[0132] Accordingly, the scope of the invention should be determined
not by the embodiments illustrated, but by the appended claims and
their legal equivalents. The invention is further illustrated by
the following examples.
REFERENCE EXAMPLE
[0133] A sample of crude terephthalic acid (CTA) from a PTA
manufacturer with the levels of impurities shown in Table 1 was
used in the experiments:
1 TABLE 1 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) 2436 1097 515
Where ppmw means parts per million by weight.
COMPARATIVE EXAMPLE 1
[0134] A CTA with similar composition from Table 1 is subject to a
conventional hydrogenation purification method as discussed in the
prior art to give a PTA product with the impurity level shown in
Table 2:
2 TABLE 2 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) 15
Undetectable 143
[0135] Similarly, the PTA product from another source contained the
levels of impurities shown in Table 3:
3 TABLE 3 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) 25 52 150
[0136] The impurity levels in the purified products represent
typical commercially available polymer-grade terephthalic acid.
COMPARATIVE EXAMPLE 2
Removing Impurities but Not Base Compound
[0137] A sample of 150 grams of CTA as described in Table 1 was
mixed with 198 grams of morpholine and 180 grams of water. The
solution was raised to 100.degree. C. to completely dissolve the
CTA and then cooled to room temperature for precipitation. The
slurry was filtered to separate from the mother liquor, and the
filter cake was subsequently washed with morpholine to obtain 196
grams of wet cake. The recovered solids were then mixed with 84
grams of water and 22 grams of morpholine. The solution temperature
was then raised to 110.degree. C. to evaporate 57 c.c. of
condensate, and the solution was then cooled to room temperature
for precipitation. The filter cake was subsequently washed with
morpholine to obtain 145 grams of purified salt. The salt was then
mixed with 235 grams of acetic acid and 14 grams of water to
precipitate PTA. The filter cake was washed by about 600 grams of
water. The wet cake was then dried in an oven at about 275.degree.
C. for 4 hours to obtain 40 grams of dried purified terephthalic
acid. Analysis with HPLC showed the impurities in Table 4. However,
the measured B-Value representing the color of cake was 6.5, four
times higher than the standard value of 1.6. This indicated the PTA
contained significant amount of morpholine.
4 TABLE 4 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) Undetectable
Undetectable Undetectable
COMPARATIVE EXAMPLE 3
Precipitating Product by Directly Adding Acetic Acid
[0138] A sample of 3 grams of CTA as described in Table 1 was
totally dissolved at room temperature into a solution containing
5.010 grams of triethylamine and 9.047 grams of methanol. 7.570
grams of acetic acid were then added to precipitate crystals, which
were then filtered and dried to 2.179 grams of terephthalic acid.
Analysis with HPLC showed the acid contained the impurities as
shown in the Table 5.
5 TABLE 5 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) 2471 844
471
EXAMPLE 1
Crystallization By Direct-extraction from precipitate with
Leaching
[0139] A sample of 40 grams of CTA as described in Table 1 was
mixed with 52 grams of morpholine and 48 grams of water. The
solution was heated to 110.degree. C. to dissolve the CTA and
evaporate 29 c.c. of condensate, and then cooled to room
temperature for precipitation. The filter cake was subsequently
washed and leached by methanol to obtain 55 grams of wet cake. The
wet cake was then mixed with 30 grams of methanol, and then 85
grams of acetic acid was added to the solution for precipitating
terephthalic acid. The wet cake was washed with 35 grams of
methanol, and leached with 35 grams of methanol for three times to
obtain 31.5 grams of wet cake. The wet cake was then dried in an
oven at about 250.degree. C. for 4 hours to obtain 24 grams of
dried cake. The B-Value of the cake was 2.73 that was still higher
the standard, and the analysis with HPLC showed the PTA containing
the impurities in Table 6.
6 TABLE 6 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) 20.8
Undetectable Undetectable
EXAMPLE 2
Crystallization with Resalting with Evaporating and Thermal
Decomposing
[0140] A sample of 925 grams of CTA as described in Table 1 was
dissolved in 1103 grams of morpholine and 1205 grams of water. The
solution was heated to 110.degree. C. and evaporated to about 404
c.c. of condensate and stopped before the sudden crystallization.
The solution was cooled to room temperature for 4 hours to
precipitate crystalline. 250 grams of ethanol was added to dilute
the slurry, and the filter cake was then washed and leached by
about 750 grams of ethanol to obtain 1455 grams of salt. 1005 grams
of the salt was dissolved in 465 grams of water. The solution was
heated to 109.degree. C. and suddenly crystallized after
evaporating about 280 c.c. of condensate. The salt was leached by
650 grams of ethanol, and the slurry was filtered and washed by 250
grams of ethanol to obtain 702 grams of purified salt. 35 grams of
the salt was dissolved in 40 grams of water and 40 grams of
ethanol, and 60 grams of acetic acid was then added to the solution
to precipitate the product crystalline. The filter cake was washed
and leached by about 200 grams of water for 3 times to obtain 27.5
grams of wet cake that was then mixed with 130 grams of EG. The
solution was heated to about 150-165.degree. C. under normal
pressure until no more brown liquid was condensed and separated
from the solution. The hot solution was then immediately filtered,
washed and leached by about 300 grams of water to obtain 15.4 grams
of wet cake. The cake was then dried in a microwave oven for 20
minutes set at median power level with an absorbent underneath the
cake, the cake was then dried in an oven at about 250.degree. C.
for 4 hours to obtain 11.6 grams of dried cake. The B-Value of the
cake was 1.58 that met the standard, and the analysis with HPLC
showed the PTA containing the impurities in Table 7.
7 TABLE 7 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) Undetectable
Undetectable Undetectable
EXAMPLE 3
Simulating Reactor Effluent Condition with Leaching
[0141] A sample of 150 grams of CTA as described in Table 1 was
dissolved at room temperature into a solution with composition
close to flashed reactor effluent compositions. The solution
contained 202 grams of morpholine, 191 grams of water, 29 grams of
48% hydrobromic acid, 0.23 grams of cobalt acetate tetrahydrate,
0.3 grams of magnesium acetic tetrahydrate, and 60 grams of acetic
acid. The temperature of this solution was raised to 110.degree. C.
to dissolve the CTA and evaporate 79 c.c. of condensate. The
solution was then cooled to room temperature for precipitation, and
the filter cake was subsequently washed and leached by methanol to
obtain 278 grams of wet cake. The wet cake was then mixed with 133
grams of water, and the solution temperature was then raised to
110.degree. C. to evaporate 88 c.c. of condensate, and the solution
was then cooled to room temperature for precipitation. The filter
cake was washed and leached by methanol to obtain 160 grams of wet
cake. The wet cake was then mixed with 160 grams of methanol, and
180 grams of acetic acid was then added to the solution for
precipitating terephthalic acid. The wet cake was washed and
leached with 500 grams of water, and leached with 35 grams of
methanol for 3 times to obtain 123 grams of wet cake. The wet cake
was dried in a microwave oven for 20 minutes set at median power
level with an absorbent underneath the cake, the cake was then
dried in an oven at about 250.degree. C. for 4 hours to obtain 73
grams of dried cake. The B-Value of the cake was 2.22, all metal
contents are less than standard specification, and analysis with
HPLC showed the PTA containing the impurities shown in Table 8
8 TABLE 8 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) Undetectable
Undetectable Undetectable
EXAMPLE 4
Thermal Decomposition by Electromagnetic Waves
[0142] A sample of 10.05 grams of purified salt from Example 2 was
dissolved in 6 grams of water. The solution was heated in a 600
watt-microwave oven for 3 minutes and the residual mixture
contained about 9.29 grams of solids. The solids was then mixed in
6.27 grams of water and heated in the oven for 3 minutes to obtain
8.82 grams of solids. The solids was then mixed in 6.66 grams of
water and heated for 3 minutes to obtain 8.49 grams of solids. The
solids was then mixed in 10.85 grams of water and heated in the
oven for 4 minutes to obtain 8.14 grams of solids. The solids was
then mixed in 9.59 grams of water and heated in the oven for 3
minutes to obtain 7.82 grams of solids. In each step, the reduction
of weight was from the salt decomposed.
EXAMPLE 5
Crude NDA
[0143] A sample of 150 grams of crude 2-6 and 2-7 NDA was mixed
with 161 grams of morpholine and 180 grams of water. The
temperature of this solution was raised to 110.degree. C. to
evaporate solvents by 86 c.c. The solution was then cooled to
precipitate crystals that were then filtered to separate from the
mother liquor. The filter cake was subsequently washed with a 10
wt. % water mixture in morpholine to obtain 186 grams of wet cake.
The wet cake is then re-dissolved in 72 grams of water and 18 grams
of morpholine, and the solution was then heated to vaporize 35 c.c.
of condensate. After cooling the solution for precipitation,
filtering, and washing with a mixture of solvent containing 10 wt.
% water in morpholine, 158 grams of wet cake was obtained. A
mixture of 16 grams of water and 158 grams of acetic acid was then
added to the purified salt to precipitate the product acid. It was
then filtered, washed with water, dried to obtain 85 grams of
purified acid. The crude NDA was purified to 99.993%. Analysis with
Capillary Electro-phoresis of the crude acid showed 11 peaks with
time and area at (8.86,3.824), (8.92,2.891), (8.92,5.518),
(9.06,10.038), (9.18,36.226), (9.45,18.536), (9.52,13.944),
(9.57,8.298), (11.87,0.106), (11.99,0.598). Electro-phoresis of the
purified acid showed 2 peaks with time and area at (9.49,99.993)
and (9.55,0.007).
EXAMPLE 6
Dissolving by Microwaves and Crystallization in Ethanol using
NMP
[0144] A sample of 12.5 grams of CTA as described in Table 1 was
mixed in 60 grams of NMP preheated in a 600 watt-microwave oven for
30 seconds. The CTA was completely dissolved in 3.5 minutes using
low power level of the oven. 13 grams of ethanol was added to
solution during crystallization by cooling the solution in an ice
bath for about 60 minutes. The salt was then filtered and washed by
the solvent mixed by 50% of ethanol and 50% NMP to obtain 26.2
grams of salt. The salt was mixed with 31 grams of NMP and
redissolved in the microwave oven for 2.7 minutes using low power
level. 15 grams of ethanol was added to solution during
crystallization by cooling the solution in an ice bath for about 60
minutes. The salt was then filtered and washed by the solvent mixed
by 50% of ethanol and 50% NMP to obtain 16 grams of purified salt.
3 grams of the purified salt was put between a stack of filter
paper socked with water. The microwave oven was set at low power
level to thermally decompose the purified until no change of the
weight to obtain 1.2 grams of PTA. Table 9 shows the impurity
analyzed with HPLC.
9 TABLE 9 4-CBA Benzoic Acid p-Toluic Acid PTA (ppmw) Undetectable
Undetectable Undetectable
[0145] The preceding examples were presented to facilitate an
understanding of the process of the present invention, and are not
intended to limit the scope of the present invention to specific
compounds or process steps. The scope of the invention is defined
by the claims that follow.
* * * * *