U.S. patent application number 09/934029 was filed with the patent office on 2002-07-25 for reactive rectification.
Invention is credited to Bachmann, Rolf, Dikow, Edmund, Gottschalk, Lutz, John, Gerald, Mendoza-Frohn, Christine, Prein, Michael, Ronge, Georg.
Application Number | 20020099163 09/934029 |
Document ID | / |
Family ID | 7661011 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020099163 |
Kind Code |
A1 |
John, Gerald ; et
al. |
July 25, 2002 |
Reactive rectification
Abstract
A process for producing polycarbonate is disclosed. Accordingly
a pre-reaction mixture containing a bis(hydroxyaryl) compound and a
diaryl carbonate is formed and introduced through the top of a
reactive rectification column under condition calculated to bring
about a reaction. The resulting hydroxyaryl is eliminated and
diaryl carbonate in vapor form is introduced at the bottom of the
reactive rectification column.
Inventors: |
John, Gerald; (Dusseldrf,
DE) ; Dikow, Edmund; (Koln, DE) ;
Mendoza-Frohn, Christine; (Erkrath, DE) ; Ronge,
Georg; (Dusseldorf, DE) ; Bachmann, Rolf;
(Gladbach, DE) ; Gottschalk, Lutz; (Koln, DE)
; Prein, Michael; (Braschaat, BE) |
Correspondence
Address: |
BAYER CORPORATION
PATENT DEPARTMENT
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
7661011 |
Appl. No.: |
09/934029 |
Filed: |
August 21, 2001 |
Current U.S.
Class: |
528/196 |
Current CPC
Class: |
B01D 3/009 20130101;
Y10T 428/24273 20150115; C08G 64/307 20130101; C08G 64/205
20130101; Y02P 20/10 20151101 |
Class at
Publication: |
528/196 |
International
Class: |
C08G 064/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2000 |
DE |
100 52 874.0 |
Claims
What is claimed:
1. A process for producing polycarbonate comprising (i) forming in
a pre-reaction unit a mixture containing a bis(hydroxyaryl)
compound and a diaryl carbonate, (ii) introducing said mixture
through the top of a reactive rectification column under condition
calculated to bring about a reaction of said bis(hydroxyaryl)
compound with said diaryl carbonate to yield hydroxyaryl, (iii)
eliminating the hydroxyaryl obtained in (ii) and (iv) introducing
diary carbonate in vapor form at the bottom of said reactive
rectification column.
2. The process of claim 1 wherein the bis(hydroxyaryl) compound is
bisphenol A and the diaryl carbonate is diphenyl carbonate.
Description
FIELD OF THE INVENTION
[0001] This application relates to a process for the production of
polycarbonate by the melt transesterification process using
reactive rectification.
BACKGROUND OF THE INVENTION
[0002] Production of polycarbonates by melt transesterification
proceeds by reacting bisphenols [bis(hydroxyaryl) compounds],
preferably bisphenol A, with diaryl carbonates, preferably diphenyl
carbonate, with elimination of the hydroxyaryl component from the
carbonic acid diester; when diphenyl carbonate is used, phenol is
eliminated. By sustained continuous or discontinuous removal of the
hydroxyaryl component, for example phenol, the reaction equilibrium
is shifted, making the formation of high molecular weight
polycarbonates possible. A distinction is generally drawn in this
connection between the so-called low viscosity stages at the
beginning of the reaction, during which polycarbonate oligomers are
formed and a large proportion of the liberated hydroxyaryl is
separated and the so-called high viscosity stages, during which
highly viscous polycarbonates are obtained towards the end of the
reaction using special surface-forming apparatus. Separation of the
hydroxyaryl in the low viscosity stages generally proceeds by
distillation. It is known that a stirred-tank reactor with an
attached distillation column can be used. The disadvantage of this
method is that the process is performed batchwise and not by
distillation and that the long residence times in the stirred-tank
reactor may result in damage to the product. Alternatively, the
hydroxyaryl may be separated in a multistage evaporator cascade,
for example of falling film evaporators. One disadvantage of this
continuous process is that, on flash evaporation in such apparatus,
relatively large quantities of diaryl carbonate are also evaporated
and therefor lost from the reaction mixture. As a result an excess
of diaryl carbonate has to be supplied to the process. In addition
the evaporator cascade entails considerable plant and equipment
costs and complexity.
[0003] The object was to provide a simpler process for the
production of polycarbonate using the melt transesterification
process by reacting diaryl carbonates (DAC) with bisphenols
[bis(hydroxyaryl) compounds]. Description of the figures
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a schematic description of the inventive process.
Accordingly reaction unit (reactive rectification column) (1) has
an upper inlet (2) a lower inlet (3) and a discharge location, or
outlet unit (13). (4) indicates an evaporator for diaryl carbonate;
(5) is the pre-reaction unit. A final falling film evaporator unit
(9) connected downstream from (1) has a separate enrichment column
(10) that includes a condenser (12) and enrichment column (11).
Optional enrichment section (6) positioned at the top of reactive
rectification column (1) includes a condensing unit (8) and an
enrichment column (7).
SUMMARY OF THE INVENTION
[0005] It has now surprisingly been found that the low viscosity
stage may be performed with reactive rectification columns, in
particular only one reactive rectification column. As a result it
is possible to simplify the plant, to reduce residence times and
consequently reduce product contamination by more effective removal
of hydroxyaryl, to exercise greater control over product quality by
means of the ratio of DAC introduced into a pre-reaction unit to
DAC introduced in vapor form, and to reduce the required excess of
DAC in comparison with the falling film evaporator cascade, with a
consequent reduction in circulating volumes.
DETAILED DESCRIPTION OF THE INVENTION
[0006] The present invention accordingly provides a process for the
production of polycarbonate oligomers by reacting bis(hydroxyaryl)
compounds (bisphenols) and diaryl carbonates (DAC) with elimination
of the hydroxyaryl component from the DAC and with introduction of
pure DAC vapor countercurrently to this pre-reaction mixture.
Preferred bisphenol components which are used individually or as
mixtures are 2,2-bis(4-hydroxyphenyl)propane (BPA),
1,1-bis(4-hydroxyphenyl)-3,3,5-tri- methylcyclohexane,
4,4'-dihydroxybiphenyl or 1,3-bis(1-(4-hydroxyphenyl)-1-
-methylethyl)benzene. BPA is particularly preferably used as the
bisphenol component and diphenyl carbonate as the diaryl carbonate
component.
[0007] The pre-reaction mixture is preferably introduced into the
upper part (2) of a reactive rectification column (1) and the DAC
vapor into the lower part (3) of the reactive rectification column
(1).
[0008] The hydroxyaryl generated during the reaction of
bis(hydroxyaryl) compounds with DAC is discharged from the reactive
rectification column, preferably at the top (13) of the reactive
rectification column. The partial pressure of the hydroxyaryl in
the DAC introduction section (3) is zero. Since, in comparison with
DAC, the corresponding hydroxyaryl is a low-boiling compound, it is
displaced from the liquid phase by distillation and replaced by DAC
from the vapor phase. As a result, in the preferred processing
method, the vapor stream is continuously being concentrated from
the bottom upward with hydroxyaryl and DAC increasingly passes into
the liquid phase, where it is available for the reaction. In the
preferred embodiment, all the energy required for vaporizing the
hydroxyaryl formed in the reactive rectification column is
introduced by the vapor-form DAC, i.e., thus by an evaporator (4),
which does not come into contact with the polycarbonate. It is
accordingly possible to dispense with any input of energy by hot
evaporator surfaces which come directly into contact with the
reaction product.
[0009] Pre-condensation is preferably performed in a separate
pre-reaction unit (5). In this case, the pre-reaction unit is
operated with a large DAC deficit and DAC is constantly re-supplied
by the vapor phase in the reactive rectification column. The
hydroxyaryl formed in the pre-reaction unit may in part be
vaporized by flashing off in the reactive rectification column or
has partially been already vaporized in the pre-reaction unit
(5).
[0010] Alternatively, it is, of course, possible to introduce
additional energy into the reactive rectification column to ensure
improved vaporization of the hydroxyaryl or for control purposes by
means of evaporator surfaces at the bottom of the reactive
rectification column or heat exchangers in the reactive
rectification column between the mass transfer elements.
[0011] Instead of introducing the entire quantity of DAC into the
reaction zone from beneath, this stream may also be split and
introduced in part at one or more points in the central portion of
the reaction zone.
[0012] After this reactive rectification column, in order to take
the reaction to completion, a final falling film evaporator unit
(9) is preferably connected downstream. This unit is operated at
reduced pressure in comparison with the reactive rectification
column and has a separate condenser (12). It is, however, also
possible to proceed without or with two or more evaporator units.
In this case too, as described below for the reactive rectification
column, an enrichment section (10), consisting of a condenser (12)
and enrichment column (11) may optionally be operated in order to
concentrate the secondary product vapor streams which are
generated.
[0013] The final falling film evaporator unit may, of course, also
be operated at the same pressure as the reactive rectification
column. In this case, it is possible to dispense with separate
vapor condensation, as the vapors are introduced directly at the
base of the reactive rectification column.
[0014] It is entirely possible to utilize the enthalpy of the
hydroxyaryl which leaves the top the reactive rectification column
or the final falling film evaporator in vapor form for the
purification thereof. In this case, savings are made with regard to
additional energy and apparatus, for example, as described
below:
[0015] The reactive rectification column is optionally operated
with an enrichment column (6) to concentrate the escaping
hydroxyaryl. At the top of the enrichment column, the hydroxyaryl
is condensed in a condensing unit (8) and, on the basis of a reflux
ratio selectable as a function of the required purity, partially
discharged. As a result, the energy introduced with the DAC may be
utilized not only for separating the hydroxyaryl but also for
purifying it. The reflux is returned to the enrichment column (7).
The liquid stream leaving the bottom of the enrichment section is
discharged entirely or in part and may, optionally together with
the condensed vapors from the final falling film evaporator, be
sent for working-up in a separate, distinctly smaller quantity.
[0016] Alternatively, the vapors from the final falling film
evaporator and the reactive rectification column may be combined at
the lower pressure level, ie., in general at the pressure level of
the final falling film evaporator. This combined vapor stream is
introduced in vapor form into a separate enrichment column. Under
certain circumstances, the feed points for the individual vapor
streams may be located at differing points on this enrichment
column.
[0017] If homogeneous catalysts are used, they are introduced
entirely or in part into the pre-reaction unit. The remaining
proportion is apportioned directly above or also at a lower point
into the reaction section of the reactive rectification column.
High-boiling or non-volatile catalysts are preferred as any
transition into the gas phase may give rise to problems in the
optionally installed distillative top section. Homogeneously
dissolved catalysts which may be used are suitable soluble basic
compounds, such as for example alkali metal or alkaline earth metal
hydroxides or carbonates or basic organic compounds containing N or
P. Basic quaternary ammonium or phosphonium salts are preferably
used, such as for example tetraalkylammonium hydroxides or
tetraarylphosphonium phenolates. Conventional mass transfer
elements may here be used as column internals, wherein the
intention is to ensure not only intensive mass transfer between the
vapor and liquid but also a sufficiently long residence time for
the reaction to proceed. Various column plates or ordered or random
packing known to the person skilled in the art are thus suitable.
Different types of trays like bubble trays, sieve trays and valve
trays and sheet metal packing may be used. If very long residence
times are needed special tray-designs with great hold up (e.g.,
U.S. Pat. No. 5,026,549 incorporated herein by reference,
Thormann-tray from Julius Montz, Germany) or special packing
designs with great holdup (e.g., packing for heterogeneous
catalytic reactions like DE19701045, U.S. Pat. No. 5,467,817,
incorporated herein by reference) are preferred.
[0018] If solid catalysts are used, they are introduced in a manner
known to the person skilled in the art into the mass transfer
elements, such as for example in ordered or random catalytic
packing with a fabric structure to accommodate heterogeneous
catalysts or alternatively in specific apparatus in distillation
trays. Examples of such column internals are described in patents
EP-A 670 178; EP-A 461 855; U.S. Pat. No. 5,026,549; U.S. Pat. No.
4,536,373; WO 94/08681; WO 94/08682; EP-A 470 655; WO 97/26971;
U.S. Pat. No. 5,308,451; EP-A 755 706; EP-A 781 829; EP-A 428 265;
EP-A 448 884; EP-A 640 385; EP-A 631 813; WO 90/02603; WO 97/24174;
EP-A 665 041; EP-A 458 472; EP-A 476 938.
[0019] Metal oxides or for example solid basic anion exchange
resins may be used as the solid catalysts.
[0020] The temperature of the DAC supplied in vapor form is between
the boiling point of the DAC at the pressure prevailing in the
reactive rectification column and 300.degree. C., particularly
preferably up to 270.degree. C.
[0021] The temperature of the mixture supplied in liquid form
preferably from a pre-reaction unit is between 100 and 250.degree.
C., particularly preferably between 140 and 210.degree. C.
[0022] The temperature in the reactive rectification column is
established on the basis of the selected pressure and the selected
feed conditions and is between 130 and 230.degree. C. in the area
of the liquid feed and between 180 and 270.degree. C. in the lower
zone of the reactive rectification column.
[0023] The temperature in the final falling film evaporator may be
adjusted separately on the basis of the reduced pressure and is
between 180.degree. C. and 320.degree. C., particularly preferably
between 200 and 290.degree. C.
[0024] The pressure established in the reactive rectification
column at the upper end of the reaction section is between 20 and
500 mbar, particularly preferably between 30 and 200 mbar. The
selected pressure has a particular impact upon the temperatures and
thus upon the rate of reaction and product quality and, via the
temperature, upon the viscosity and thus the fluid dynamics in the
reactive rectification column.
[0025] The pressure established in the final falling film
evaporator is determined in accordance with admissible temperatures
for good product quality and is between 5 and 200 mbar,
particularly preferably between 10 and 60 mbar.
[0026] The molar ratio of the total quantity of DAC introduced into
the pre-reaction unit and the reactive rectification column (i.e.,
in the pre-reaction unit and feed in vapor form) to the quantity of
bis(hydroxyaryl) compounds is 0.95-1.5, particularly preferably
1.0-1.2.
[0027] 0% to 60%, particularly preferably 2% to 30% of the entire
DAC feed are introduced into the pre-reaction unit. The remainder
is introduced into the reactive rectification column by the feed in
vapor form. The instance with 0% DAC corresponds to a reactive
rectification column without a pre-reaction unit, into which the
pre-heated bis(hydroxyaryl) compound is introduced.
[0028] The greater part of the total amount of hydroxyaryl formed
is flashed off in the reactive rectification column or stripped out
by DAC in vapor form. The ratio of the hydroxyaryl stripped out in
the final falling film evaporator to the total amount of
hydroxyaryl formed is 0.1 %-20%, particularly preferably
0.1%-10%.
[0029] Typical residence times in the pre-reaction unit are 1 min.
to 60 min., particularly preferably 1 min. to 15 min.
[0030] Average residence times of the reaction mixture in the
reactive rectification column are 3 min. to 80 min., particularly
preferably 5 min. to 30 min.
[0031] Residence times in the final falling film evaporator
including the associated equipment are 2 to 50 min., particularly
preferably 5 to 25 min.
[0032] In this manner, polycarbonate oligomers are obtained which
exhibit a relative solvent viscosity eta.sub.rel (measured on a
solution in dichloromethane containing 5 g of polymer per liter at
25.degree. C.) of 1.05 to 1.10, preferably of 1.06 to 1.08. The
content by weight of the phenolic OH terminal groups x.sub.PhOH in
the resultant polycarbonate oligomers is 4000-10000 ppm, preferably
5000-7000 ppm. The products obtained in this manner may be used as
prepolymers for the production of light-colored and solvent-free
polycarbonate, as for example described in EPA 719 814 or EPA
694572. To this end, the prepolymers, optionally with the addition
of a suitable catalyst, are condensation polymerized with continued
elimination of the hydroxyaryl compound from the diaryl components
to yield high molecular weight polycarbonate polymers.
[0033] The following Example is intended to illustrate the present
invention, but without restricting it.
EXAMPLE
[0034] 24.2 kg/h of mixture prepared from 94.4 wt. % of BPA, 5.6
wt. % of DPC and, relative to BPA, 1.5.multidot.10.sup.-3 mol % of
tetraphenylphosphonium phenolate as catalyst are introduced into a
pre-reaction unit and heated and, at 190.degree. C., reacted in a
pre-reaction to yield polycarbonate (PC). The residence time in the
pre-reaction unit was approx. 3 min. The resultant
phenol/BPA/DPC/PC mixture is introduced into the top of a reactive
rectification column. In so doing, a proportion of the hydroxyaryl
formed in the pre-reaction unit flashes off. The temperature in the
reactive rectification column around the input point is approx.
190.degree. C. Pure DPC is evaporated in a lateral falling film
evaporator and, at a temperature of 230.degree. C at the base of
the reactive rectification column, introduced at an input rate of
22.7 kg/h.
[0035] The reactive rectification column has a diameter of 100 mm
and is equipped with a conventional 350 m.sup.2/m.sup.3 sheet metal
packing. The total packing height is 13 m. The liquid is collected
and redistributed at three points. The reactive rectification
column is insulated by an adiabatic jacket. The reactive
rectification column is operated at 100 mbar. Pressure is measured
directly above the reaction zone. Temperature measurement points
are provided in the reactive rectification column, measuring from
the bottom upwards, after approx. 1.5 m and after 13 m of packing
for monitoring the temperature profile. The temperature at the
measuring point after 1.5 m is 232.degree. C., that at the
uppermost measuring point is 191.degree. C. The residence time in
the reactive rectification column is approx. 10 minutes.
[0036] The reaction liquid is discharged from the reactive
rectification column at the bottom and introduced into a 1.0
m.sup.2 falling film evaporator to take conversion to completion.
The falling film evaporator and its associated bottom pump receiver
are operated at 25 mbar and 272.degree. C. 27.1 kg/h of liquid
product consisting of polycarbonate oligomers may be withdrawn from
the falling film evaporator. The product is characterized by the
values eta.sub.rel=1.063 and x.sub.PhOH=6030 ppm. A total of 3.3
kg/h of vapor from the falling film evaporator, primarily
consisting of DPC and phenol, are condensed in a separate
condenser.
[0037] The vapor leaving the reactive rectification column is
passed through an empty 1 m length of glass tube of a diameter of
100 mm to a condenser. The glass tube is also provided with an
adiabatic jacket. 16.4 kg/h of vapor are condensed in the condenser
installed thereover, which is operated at a coolant-side
temperature of 50.degree. C. The condensate contains approx. 98 wt.
% phenol. In the laboratory, an enrichment section with mass
transfer elements is not provided.
[0038] Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely for that purpose and that variations can
be made therein by those skilled in the art without departing from
the spirit and scope of the invention except as it may be limited
by the claims.
* * * * *