U.S. patent application number 09/682560 was filed with the patent office on 2003-03-20 for production of low-particulate bisphenol and use thereof in the manufacturing of polycarbonate.
Invention is credited to Blubaugh, James Cristopher, Chen, Fang Christine, Kissinger, Gaylord Michael, Nance, Darlene Hope, Ordonez, Juan Rodriguez, Quintana, Jose M., Stokes, Edward Brittain.
Application Number | 20030055296 09/682560 |
Document ID | / |
Family ID | 24740222 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030055296 |
Kind Code |
A1 |
Kissinger, Gaylord Michael ;
et al. |
March 20, 2003 |
PRODUCTION OF LOW-PARTICULATE BISPHENOL AND USE THEREOF IN THE
MANUFACTURING OF POLYCARBONATE
Abstract
Low-particulate dihydric aromatic compounds such as bisphenol-A
that can be used in the synthesis of low-particulate polycarbonates
are prepared by introducing into a desorber column containing a
non-aggregate packing material an adduct of bisphenol and phenol
and optionally a stripping gas. The column is maintained at an
operating temperature that is sufficiently high and an operating
pressure that is sufficiently low such that the adduct is
distilled. The stream of phenol and the stripping gas is recovered
from the top of the column. A second stream containing bisphenol
that is substantially free of added particulate matter is recovered
from the bottom of the column. This purified stream of bisphenol-A
can further be used in a method of producing optical-grade
polycarbonate.
Inventors: |
Kissinger, Gaylord Michael;
(Evansville, IN) ; Chen, Fang Christine;
(Evansville, IN) ; Blubaugh, James Cristopher;
(Evansville, IN) ; Nance, Darlene Hope; (Mt.
Vernon, IN) ; Stokes, Edward Brittain; (Schenectady,
NY) ; Ordonez, Juan Rodriguez; (Madrid, ES) ;
Quintana, Jose M.; (Murcia, ES) |
Correspondence
Address: |
OPPEDAHL AND LARSON LLP
P O BOX 5068
DILLON
CO
80435-5068
US
|
Family ID: |
24740222 |
Appl. No.: |
09/682560 |
Filed: |
September 19, 2001 |
Current U.S.
Class: |
568/749 |
Current CPC
Class: |
C07C 37/74 20130101;
C08G 64/24 20130101; C08G 64/307 20130101; B01J 2219/00006
20130101; C07C 37/74 20130101; C07C 39/04 20130101; C07C 37/74
20130101; C07C 39/16 20130101 |
Class at
Publication: |
568/749 |
International
Class: |
C07C 029/10 |
Claims
1. A method of producing a low-particulate dihydric aromatic
compound, comprising the steps of: (a) introducing into a desorber
column possessing a non-aggregate packing material an adduct of a
dihydric aromatic compound and phenol; (b) providing an operating
temperature range in the desorber column that is sufficiently high
and an operating pressure in the column that is sufficiently low
such that the adduct is distilled; (c) discharging from the
desorber column a first stream containing substantially all of the
phenol; and (d) discharging from the desorber column a second
stream containing substantially all of the dihydric aromatic
compound; whereby the second stream is substantially free of
particulate matter added in the desorber column.
2. The method of claim 1, wherein the non-aggregate packing
material is selected from the group consisting of borosilicate
glass, stainless steel, zirconia, and polytetrafluoroethylene.
3. The method of claim 1, wherein the non-aggregate packing
material is made from borosilicate glass.
4. The method of claim 1, wherein a stripping gas is introduced to
the column in countercurrent flow to the adduct.
5. The method of claim 4, wherein the stripping gas is selected
from the group consisting of nitrogen, carbon dioxide and
steam.
6. The method of claim 4, wherein the dihydric aromatic compound is
a bisphenol.
7. The method of claim 4, wherein the dihydric aromatic compound is
bisphenol-A.
8. The method of claim 7, wherein the operating temperature range
in the column is about 172 to about 217.degree. C.
9. The method of claim 8, wherein the operating pressure of the
column is in a range from about 35 to about 810 mm Hg.
10. The method of claim 4, wherein the operating temperature range
in the column is about 172 to about 217.degree. C.
11. The method of claim 10, wherein the operating pressure of the
column is in a range from about 35 to about 810 mm Hg.
12. The method of claim 4, wherein the operating pressure of the
column is in a range from about 35 to about 810 mm Hg.
13. The method of claim 4, wherein the operating pressure of the
column is below atmospheric pressure.
14. The method of claim 1, wherein less than 20,000 particulates
per gram of bisphenol are added in the desorber column.
15. A method of manufacturing low-particulate polycarbonate,
comprising the steps of: (a) preparing a dihydric aromatic compound
by a method comprising the steps of: (i) introducing into a
desorber column possessing a non-aggregate packing material an
adduct of a dihydric aromatic compound and phenol; (ii) providing
an operating temperature range in the desorber column that is
sufficiently high and an operating pressure in the column that is
sufficiently low such that the adduct is distilled; (iii)
discharging from the desorber column a first stream containing
substantially all of the phenol; and (iv) discharging from the
desorber column a second stream containing substantially all of the
dihydric aromatic compound; whereby the second stream is
substantially free of particulate matter added in the desorber
column; and (b) reacting the dihydric aromatic compound from the
second stream with a derivative of carbonic acid to form a
polycarbonate to form a low-particulate polycarbonate.
16. The method of claim 15, wherein the non-aggregate packing
material is selected from the group consisting of borosilicate
glass, stainless steel, zirconia, and polytetrafluoroethylene.
17. The method of claim 15, wherein the non-aggregate packing
material is made from borosilicate glass.
18. The method of claim 15, wherein a stripping gas is introduced
to the column in countercurrent flow to the adduct.
19. The method of claim 18, wherein the operating temperature range
in the column is about 172 to about 217.degree. C.
20. The method of claim 18, wherein the operating pressure of the
column is in a range from about 35 to about 810 mm Hg.
21. The method of claim 18, wherein the operating pressure of the
column is less than atmospheric pressure.
22. The method of claim 18, wherein the stripping gas is selected
from the group consisting of nitrogen, carbon dioxide and
steam.
23. The method of claim 15, wherein the derivative of carbonic acid
is a carbonic diester.
24. The method of claim 23, wherein the carbonic diester is
diphenyl carbonate.
25. The method of claim 15, wherein the derivative of carbonic acid
is a carbonyl halide.
26. The method of claim 25, wherein the carbonyl halide is carbonyl
chloride.
27. The method of claim 15, wherein less than 20,000 particulates
per gram of bisphenol are added in the desorber column.
28. A facility for separation of an adduct of a dihydric phenol and
phenol into separate streams of dihydric phenol and phenol,
comprising a source of the adduct and a desorber column connected
to the source of adduct, said desorber column being packed with a
non-aggregate packing material.
29. The facility of claim 28, wherein the non-aggregate packing
material is selected from the group consisting of borosilicate
galls, stainless steel, zirconia and polytetrafluoroethylene.
30. The facility of claim 28, wherein the non-aggregate packing
material is made from borosilicate glass.
31. The facility of claim 28, further comprising a source of
stripping gas, connected to the desorber column to introduce
stripping gas in counter-current flow to the adduct.
32. The facility of claim 31, wherein the source of stripping gas
supplies a stripping gas selected from the group consisting of
nitrogen, carbon dioxide and steam.
33. The facility of claim 28, wherein the source of adduct supplies
an adduct of a bisphenol and phenol.
34. The facility of claim 33, wherein the bisphenol is
bisphenol-A.
35. The facility of claim 28, further comprising a ring pump
connected to the desorber column for maintaining sub-atmospheric
pressure in the desorber column during operation.
36. The facility of claim 35, wherein the non-aggregate packing
material is selected from the group consisting of borosilicate
galls, stainless steel, zirconia and polytetrafluoroethylene.
37. The facility of claim 35, wherein the non-aggregate packing
material is made from borosilicate glass.
38. The facility of claim 35, further comprising a source of
stripping gas, connected to the desorber column to introduce
stripping gas in counter-current flow to the adduct.
39. The facility of claim 38, wherein the source of stripping gas
supplies a stripping gas selected from the group consisting of
nitrigen, carbon dioxide and steam.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates to the production of low
particulate bisphenols and to the use of such bisphenols in the
manufacturing of high-quality, low-particulate polycarbonates
intended for optical-grade products.
[0002] There are two common methods for manufacturing
polycarbonates, the interfacial method and the melt
polycondensation method. The interfacial method involves the
reaction of a dihydric aromatic compound with a carbonyl halide,
such as between bisphenol-A and phosgene. A primary disadvantage of
the interfacial method is the use of phosgene and the use of a
large amount of solvent. The melt polycondensation method uses a
transesterification reaction between a dihydric aromatic compound
and a diester of carbonic acid, such as diphenyl carbonate. The
melt method avoids the disadvantages of the interfacial method and
also eliminates chlorine from the process which is desirable
because chlorine can lead to a less consistent color in the
polycarbonate.
[0003] Bisphenol-A is the preferred dihydric compound in the
synthesis of polycarbonate, and as such, much attention has been
directed at developing methods for the purification of bisphenol-A.
U.S. Pat. No. 4,447,655 describes a method for the purification of
bisphenol-A through the use of a water/bisphenol-A crystal slurry.
U.S. Pat. No. 4,798,654 is directed at a distillation column
whereby recycling of the distillate leads to purified bisphenol-A.
U.S. Pat. No. 4,931,146 involves the purification of bisphenol-A
with steam-stripping in a multi-tubular packed column. In general,
processes for the production and purification of bisphenols are
well known, and are described inter alia in U.S. Pat. Nos.
4,107,218; 4,294,994; 5,210,329; 5,243,093; 5,245,088; 5,288,926;
5,368,827; 5,786,522; and 5,874,644.
[0004] High quality polycarbonate that has low levels of
particulate matter is desirable in the manufacturing of DVD"s,
CD-ROM"s, ophthalmic lenses, or other optical-grade products. The
micron-sized particles that can be introduced in the process of
manufacturing polycarbonate have the undesirable effect of
scattering light. In the case of optical disks, this scattering of
light introduces noise. Therefore, methods of removing these
particulates is extremely desirable and several patents are
consequently directed at this objective.
[0005] U.S. Pat. No. 6,008,315 discloses a method for producing
bisphenol-A that has low particulate impurities by using a calcined
metal filter. U.S. Pat. No. 6,197,917 discloses the use of a
fluorine resin membrane to filter micron-sized particles from a
molten mixture of bisphenol-A with a carbonic diester. Combining
the bisphenol-A and carbonic diester increases the efficiency of
filtering with the fluorine resin membrane.
[0006] A different approach to eliminating particulates in the
manufacturing of polycarbonate via the melt polycondensation method
is disclosed in U.S. Pat. No. 6,204,352. In this process, the
entire apparatus that is used in the synthesis of the polycarbonate
is made of various alloys of nickel or stainless steel. These
alloys were developed to prevent the discoloration of polycarbonate
and further refined to eliminate the presence of metallic
particulates in the polycarbonate.
SUMMARY OF INVENTION
[0007] The present invention relates to a method of producing a
low-particulate bisphenol-A stream that can be used in the
synthesis of polycarbonate. The method comprises the following
steps:(a) introducing into a desorber column containing a
non-aggregate packing material an adduct of a dihydric aromatic
compound and phenol;(b) providing an operating temperature range in
the desorber column that is sufficiently high and an operating
pressure in the column that is sufficiently low such that the
adduct is distilled;(c) discharging from the desorber column a
first stream containing substantially all of the phenol; and(d)
discharging from the desorber column a second stream containing
substantially all of the dihydric aromatic compound; whereby the
second stream is substantially free of added particulate matter as
compared to the adduct stream introduced to the column. The
invention can be applied in the context of a vacuum distillation
column, or may utilize a stripping gas which is introduced in
countercurrent flow relative to the adduct. The resulting stream of
dihydric aromatic compound can further be used in a method of
producing optical-grade polycarbonate.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 shows a schematic representation of a bisphenol-A
plant in accordance with the art, with particulate levels at
various points in the process indicated;
[0009] FIG. 2 shows a column charged with a borosilicate packing
material that can be used for the distillation of an adduct of a
dihydric aromatic compound and phenol;
[0010] FIG. 3 shows particulate levels in feed and bottoms samples
from a pilot scale desorber column with two types of packing;
and
[0011] FIG. 4 shows particle counts as a function of particle size
for several types of packing material.
DETAILED DESCRIPTION
[0012] The present invention relates to the preparation of
polycarbonate, and to the control of levels of particulate
materials in polycarbonate products. It will be appreciated that in
any process for manufacturing polycarbonates there may be various
sources of particulates. The present invention is directed to
addressing only one of these sources. Thus, the present invention
is directed towards the production of high-quality polycarbonate
that is substantially free of particulate matter derived from the
bisphenol component of the reaction mixture used in forming the
polycarbonate through the use of a bisphenol product with low
particulate levels.
[0013] Bisphenol having low particulate levels can be prepared by a
method according to the invention for producing purified bisphenol
that comprises the steps of:(a) introducing into a desorber column
possessing a non-aggregate packing material an adduct of a dihydric
aromatic compound and phenol;(b) providing an operating temperature
range in the desorber column that is sufficiently high and an
operating pressure in the column that is sufficiently low such that
the adduct is distilled;(c) discharging from the column a first
stream consisting essentially of phenol; and(d) discharging from
the desorber column a second stream containing substantially all of
the dihydric aromatic compound. The second stream is substantially
free of added particulate matter, as compared to the introduced
adduct, and can be used in a method of producing optical-grade
polycarbonate.
[0014] The method of the invention can be practiced in a vacuum
distillation column with packed section. Alternatively, the
invention may be practiced using a stripping gas. In this case, the
stripping gas is introduced in countercurrent flow relative to the
adduct and is substantially recovered as part of the second
stream.
[0015] There are no particular restrictions on the dihydric
aromatic compound that can be used in the production of the
high-quality polycarbonate and numerous species of dihydric
aromatic compounds are known for this purpose in the art. For
example, a bisphenol having structure I may be used: 1
[0016] wherein R.sup.1 is independently at each occurrence a
halogen atom, nitro group, cyano group, C.sub.1-C.sub.20 alkyl
group, C.sub.4-C.sub.20 cycloalkyl group, or C.sub.6-C.sub.20 aryl
group; n and m are independently integers 0-3; and W is a bond, an
oxygen atom, a sulfur atom, a SO.sub.2 group, a C.sub.1-C.sub.20
aliphatic radical, a C.sub.6-C.sub.20 aromatic radical, a
C.sub.6-C.sub.20 cycloaliphatic radical or the group 2
[0017] wherein R.sup.2 and R.sup.3 are independently a hydrogen
atom, C.sub.1-C.sub.20 alkyl group, C cycloalkyl group, or C C aryl
group; or R.sup.2 and R.sup.2 together form a C C.sub.20
cycloaliphatic ring which is optionally substituted by one or more
C.sub.1-C.sub.20 alkyl, C.sub.6-C.sub.20 aryl, C.sub.5-C.sub.20
aralkyl, C.sub.5-C.sub.20 cycloalkyl groups or a combination
thereof. Suitable bisphenols I for use in the method of the present
invention include bisphenol-A;
2,2-bis(4-hydroxy-3-methylphenyl)propane;
2,2-bis(3-chloro-4-hydroxypheny- l)propane;
2,2-bis(3-bromo-4-hydroxyphenyl)propane;
2,2-bis(4-hydroxy-3-isopropylphenyl)propane;
1,1-bis(4-hydroxyphenyl)cycl- ohexane;
1,1-bis(4-hydroxy-3-methylphenyl) cyclohexane; and
1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
[0018] The dihydric aromatic compound which is produced and used in
the invention may also be a modified (i.e., functionalized)
compound. For example brominated bisphenols may be used to
introduce bromine into the final polycarbonate to reduce
flammability.
[0019] FIG. 1 shows a schematic representation of a bisphenol plant
using alumina (Coors AD995, 99.5% alumina) packing in the phenol
desorber column. Measurements of particle levels were taken at the
points indicated by the arrows, and the measurement amounts of
particulates in the 0.5 to 50 .mu.m size range per gram of sample
are indicated in the adjacent boxes. As shown, the alumina desorber
column is a significant source of particulates. Subsequent studies
conducted in connection with the present invention established that
silica, alumina and magnesium packing materials conventionally used
as column packing for the separation of bisphenol:phenol adducts
all undergo deterioration, giving rise to increased levels of
undesirable particulates in the product bisphenol stream. The
precise mechanism for this deterioration is not known, although it
presumably arises from thermal shocking, chemical corrosion,
mechanical friction, or some combination thereof. Regardless of the
mechanism, the deterioration was readily observable in a
6,000.times.scanning electron micrograph (SEM) of the surface of a
used alumina ceramic ball. The micrograph showed a highly texured
surface, with structures on the order of 1 .mu.m in size,
reminiscent of a coral-encrusted ocean floor. The surface fragility
of alumina ceramic balls was further reflected in a
10,000.times.SEM of the surface of an ultrasonified alumina ceramic
ball. In this case, the surface was covered with broken-up chunks,
having sizes on the order of 2 .mu.m. The present invention reduces
the amount of added particles at this stage in the process through
the selection of "non-aggregate" packing materials which are less
susceptible to these factors as a result of their physical
structure.
[0020] As used in the specification and claims of this application,
the term "non-aggregate packing material" refers to a
non-polycrystalline material that is substantially devoid of
grain-boundary regions that are subject to separation or fracture
under the conditions of temperature and pressure found in the
desorber column. It will be appreciated that the term
"non-aggregate" does not mean that there are no locations where
focused fracture might occur under more extreme conditions. Lacking
weak (in the context of the desorber column conditions)
grain-boundary regions and an "aggregate" of micro-crystals,
"non-aggregate" materials are not susceptible to the exfoliation of
microscopic crystalline matter under the conditions found in the
desorber column. Examples of non-aggregate material include
borosilicate glass, stainless steel, zirconia, and
polytetrafluoroethylene. A preferred embodiment of the present
invention utilizes borosilicate glass as the column packing.
[0021] Use of non-aggregate substance as a packing material in the
column leads to the production of bisphenol that is substantially
free of added particulate matter. The amount of particles in a
bisphenol preparation can be determined by various techniques
including analytical particle counter instruments such as a
Hiac-Royco Particle Counter. As used in the specification and
claims of this application, the term "substantially free of added
particulate material" refers to bisphenol preparations which
contain on average less than 50,000 added particles/gm of bisphenol
product having a size of 0.5 to 50 .mu.m, more preferrably less
than 20,000 added particles/gm, as determined by the technique
described in Example 1 below. Thus, the method of the present
invention can lead to at least an 80% reduction of particulate
matter in a stream of bisphenol-A as compared to methods employing
columns packed with alumina or silica.
[0022] The selection of the column in accordance with the invention
is not specifically intended to reduce the amount of particulates
which may be present in the reactant streams introduced to the
desorber column. Rather, the invention addresses particles which
are added during the separation of bisphenol from phenol as a
result of the nature of the column packing, and thus provides
bisphenol which is substantially free of added particles, rather
than bisphenol having particulate levels below any specific
threshold. To maintain the overall quality of the bisphenol product
it may be desirable to include filters positioned downstream from
the bisphenol reactor, upstream from the bisphenol reactor or both
to capture particulates which may be derived from other sources.
Such filters may, for example, be fluorine resin membranes or
calcined metal filters as known in the art.
[0023] To practice the method of the present invention, a column is
charged with a non-aggregate packing material. The packing material
may be of any shape, such as without limitation spheres, saddles,
or Raschig or Pall rings, and be of any size, without limitation,
that is currently known in the art. The selected packing material
should have a void volume such that, at the flow rate of gas
employed, the column operates with fluid at the top of the column.
Furthermore, in the case of denser packing materials, such as
stainless steel, it is desirable to use hollow balls to avoid undue
weight on the column. The column itself may suitably be made of
stainless steel, for example 316 or 304 stainless, or glass, or it
may be glass lined. Column materials which are themselves sources
of particulates are suitably avoided.
[0024] As shown in FIG. 2, the column 10 has a first inlet 1 for
introducing an adduct containing, for example, phenol and a
dihydric compound such as bisphenol-A, and a second inlet 2 for
introducing nitrogen or some other stripping gas such as argon,
helium, nitrogen, carbon dioxide or steam. The stripping gas
operates in a counter-current mode where the flow of the stripping
gas is opposite to the adduct flow. To remove the distillation
products, the column 10 possesses a first outlet 3 at the top of
the column to remove a stream containing the stripping gas and
phenol, and a second outlet 4 at the bottom of the column to remove
a stream containing substantially particle-free bisphenol-A.
[0025] The adduct is appropriately introduced to the column 10 at
an elevated temperature to minimize thermal disruption of the
distillation system. Suitably, this temperature is in the range of
from about 95 to 220.degree. C., more preferably from 150 to
180.degree. C. The stripping gas may be introduced at ambient
temperature (i.e., around 20-25 .degree. C.), or may be pre-heated
to a temperature comparable to the temperature at the bottom of the
column, for example up to 220.degree. C. The adduct and stripping
gas are introduced at rates that account for the dimensions of the
column, namely volume and length; the volume, shape and flow
properties of the packing material; and, in general, operating
pressure and the rate of distillation of the adduct (i.e., the
removal of distillation products from the column).
[0026] The rate of distillation of the adduct is dependent upon the
temperature and pressure maintained in the column and the boiling
point properties of the adduct. In general, the adduct has a
nominal phenol to bisphenol ratio, but also has additional phenol
because it is in the form of a wet cake that is wet with phenol.
The amount of wetting phenol can be such that the actual ratio of
phenol to bisphenol-A in a wet nominally 1:1 adduct cake is in the
range of 45-70.8% BPA and 29.2-55% phenol, rather than the
theoretical composition of 70.8%BPA and 29.2% phenol. For
distilling an adduct of phenol and bisphenol-A in a nominal 1:1
ratio (regardless of the amount of additional phenol), distillation
occurs when the temperature at the bottom of the column is about
185.degree. C. and the pressure of the column is maintained at 760
mm of Hg. Decreasing the pressure in the column to below
atmospheric pressure allows for distillation to occur at a lower
temperature and increases the capacity of the column. The pressure
can be regulated by using a liquid ring pump to collect gas from
the top of the desorber column. The operating parameters of the
pump are balanced against the input flow rate of gas to the bottom
of the desorber column to achieve the desired pressure. The column
pressure may be maintained between a range of about 35 to about 810
mm Hg and the temperature adjusted accordingly to maintain the
distillation of the adduct. Reduced gas flow is generally required
when pressure is decreased to maintain separation efficiency. For
reduced pressure operation, the pressure is suitably in the range
of 35 to 750 mm Hg, more conventionally 250 to 750 mm Hg. Assuming
near atmospheric pressure, the temperature of the column is
maintained at a range (from the top of the column to the bottom) of
about 170 to about 220.degree. C. The ideal distillation rate is
achieved by maximizing the production of bisphenol-A, but
minimizing the concentration of phenol in the bisphenol-A
stream.
[0027] Distillation in the desorber column of the invention
produces two streams, one containing substantially all of the
phenol and one containing substantially all of the bisphenol. While
it will be appreciated that the ordinary goal of the desorber
column is to achieve the maximum degree of separation, for purposes
of the specification and claims of this application, a stream which
contains "substantially all" of the bisphenol or phenol will be one
which contains at least 80% of the identified component from the
adduct.
[0028] After producing the stream of low-particulate dihydric
aromatic compound, the dihydric aromatic compound is used in the
production of polycarbonate using either the interfacial method or
the melt polycondensation method. Thus, the present invention
contemplates a reaction of the purified bisphenol-A with a
derivative compound of carbonic acid, namely either carbonyl
chloride (phosgene) or any other carbonic diester known in the art,
such as those disclosed in U.S. Pat. No. 6,204,352. Specific
examples of carbonic diesters that can be used in the
transesterification reaction, either alone or in combination with
one another, include diphenyl carbonate, bis(methyl salicyl)
carbonate, ditolyl carbonate, bis(chlorphenyl) carbonate, m-cresyl
carbonate, dinaphthyl carbonate, bis(diphenyl) carbonate, diethyl
carbonate, dimethyl carbonate, dibutyl carbonate and dicyclohexyl
carbonate. Of these, diphenyl carbonate is particularly
favorable.
[0029] The method of the invention may be practiced in a facility
for separation of an adduct of a dihydric phenol and phenol into
separate streams of dihydric phenol and phenol, comprising a source
of the adduct and a desorber column connected to the source of
adduct in which the desorber column is packed with a non-aggregate
packing material such as borosilicate galls, stainless steel,
zirconia and polytetrafluoroethylene- . The facility may include a
source of stripping gas, for example, nitrogen, carbon dioxide or
steam, connected to the desorber column to introduce stripping gas
in counter-current flow to the adduct. The facility may also
include a ring pump connected to the desorber column for
maintaining sub-atmospheric pressure in the desorber column during
operation.
[0030] In the course of considering the benefits of the present
invention in reducing particulates, it was noted that the same
result might be achieved not through an actual reduction in
particulates but through the formation of particulates which were
effectively invisible in polycarbonate as a result of having the
same refractive index. To explore this possibility, we looked at
the refractive indices of various materials, as summarized in Table
1. The refractive index for polycarbonate was taken to be 1.586. As
is apparent from the difference in refractive indices, the absence
of measurable particles using borosilicate cannot be attributed to
an invisibility phenomenon. Nevertheless, if a column material were
identified which had the correct refractive index, this would serve
as an alternative approach to reduction of particulates in
bisphenol and resulting polycarbonate, even if the column material
were subject to deterioration.
[0031] [t1]
1TABLE 1 Material Refractive Index Difference from PC alumina 1.76
0.174 silica 1.55 -0.036 borosilicate (Sigmund 1.473 -0.113 Lindner
Type 3.3)
[0032] The invention will now be described further with reference
to the following non-limiting examples.
EXAMPLE 1
[0033] A column (packed column length 13 feet-7-{fraction (9/16)}
inches, interior diameter 10") was initially charged with about 5
to 6 ft.sup.3 (or about 200 to 250 kg) of alumina balls as a
packing material. After a period of operation, the alumina balls
were replaced with the same volume of comparably-sized borosilicate
glass balls. Throughout operation with either type of packing
material, nitrogen and a 1:1 adduct of bisphenol-A:phenol were
introduced in a countercurrent flow. The adduct was fed into the
column at a temperature of about 135 .degree. C. and a rate of 0.44
gpm. The gas flow rate of nitrogen was about 28 scfm/ft.sup.2 of
surface area of the column. The pressure of the column was
maintained at about 760 mm Hg. The temperature of the bottom of the
column was about 185.degree. C., while the temperature of the top
of the column was about 180.degree. C.
[0034] Samples were taken periodically from the feed material and
the desorber column bottoms for particulate analysis. Samples were
caught in 16 ounce clean room prepared jars. About 20 g of sample
was caught in each jar. To this was added about 238 grams of HPLC
grade methanol. The exact amount of methanol needed was determined
as equal to grams of sample/(20/238). Particulates having a size of
from 0.50 to 50.0 .mu.m are counted in each sample with a
Hiac-Royco portable particle counter. Blanks of HPLC-grade methanol
were run prior to the sample and between each sample. The particle
count in the blanks was from 2,000 to 5,000 total particles.
[0035] FIG. 3 shows a comparison of the particulate levels in the
bottoms (-squares-) as compared to the feed (-diamonds-) before and
after the change in packing material. As shown, there is a
substantial increase in the particulate level in the column bottoms
using the ceramic packing material. On the other hand, the bottoms
samples obtained after the change to borosilicate glass packing
have essentially no added particulates.
[0036] Measurement on the quality of the product also showed an
interesting and unexpected improvement. During the portion of the
run with the alumina ceramic balls, the residual phenol level was
56 ppm, while the residual isopropenyl phenol (IPP) level was 53
ppm. In contrast, when borosilicate packing material was used, the
levels were 34 and 41 ppm respectively. Thus, changing the packing
results not only in reduced particulate levels, it also improves
the separation efficiency and reduces levels of side-reaction
products.
EXAMPLE 2
[0037] Bench scale tests were conducted in a 1 liter 3 neck flask.
The flask was heated with a mantle connected to a variable power
supply. A condenser was used to condense the phenol as it vaporized
during the experiment. Temperature control was accomplished by
first allowing the phenol to pass through the condenser and then,
when the desired boiling temperature was reached, starting a
45.degree. C. water flow through the condenser jacket to begin
total reflux. A temperature probe was used to get the actual liquid
temperature in the flask.
[0038] To simulate conditions of high thermal stress, packing
material was placed into the flask with an amount of liquid
material such that the packing was only partially immersed in the
boiling mixture (240-255.degree. C.). The exposed portion of the
packing comes into contact with the cooler phenol condensate
spilling down from the reflux condenser, thus simulating "thermal
shock" which could lead to deterioration of the packing.
[0039] A phenol/BPA mixture (roughly a 1:2 ratio) was used in each
experiment. The phenol/BPA mixture was added to the flask and
melted. After melting, a sample A was taken. The packing material
was then added to the flask and the temperature increased to the
desired temperature for the experiment. After the boiling point was
reached, another sample B was taken. Condenser water was applied to
start the reflux which was maintained for 2 hours. At the end of
this time, a final sample C was taken. Table 2 summarizes the
experimental conditions and the observed results. The "total
particulates" is calculated as the amount of particles per gram in
sample C minus the sum of the particulates in samples A and B. As
can be seen, the amount of added particulates is much less in the
case of the borosilicate glass packing material than in the AD995
alumina ceramic (Coors) used as a comparison. The amounts of
particulates are also higher than those observed in the actual
packed column tests, suggesting that the thermal stresses in the
bench test are more extreme than those which actually occur in the
column..
[0040] [t2]
2TABLE 2 weight percent Column Packing Temp (.degree. C.)
phenol/BPA Total Particulates None 255 30.83/69.17 109,610 alumina
(Run 1) 240 35.33/64.67 15,638,525 alumina (Run 2) 240 33.20/66.80
16,291,480 Borosilicate (Run 1) 251 38.68/61.32 566,960
Borosilicate (Run 2) 245 33.94/66.06 1,210,536
EXAMPLE 3
[0041] Zirconia balls were tested as packing material. The total
particulates observed (C-B) was 1,454,965 particles per gram.
EXAMPLE 4
[0042] Packing balls sold under the tradename CHIPTON
(Al.sub.2O.sub.3=13-17%; SiO.sub.2=74-78%; Na.sub.2O 2.5%;
B.sub.2O.sub.3=not detected; MgO=0.5%; other=5.5% were tested as
packing material. The total particulates observed (C-B) was
1,086,950 particles per gram.
* * * * *