Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-04-08
2003-09-02
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S198000, C526S062000, C526S063000, C526S064000, C526S065000, C526S067000, C526S071000
Reexamination Certificate
active
06613868
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for continuous production of polycarbonates and more particularly to the two-phase interface method.
SUMMARY OF THE INVENTION
A process for the production of polycarbonate is disclosed. The process, representing an improvement over the known interfacial polycondensation process entails introducing into the loop of a circulating reactor that additionally contains, a residence tank, an optional mixer, a pump, and a heat exchanger (i) an organic phase that contains a solvent for polycarbonate and phosgene and (ii) an aqueous phase that contains an aqueous lye solution, a dihydroxy compound and an optional monophenol to form an emulsion. Maintaining specified temperature and process conditions results in polycarbonate resin having good properties and in waste water that are characterized by their purity.
BACKGROUND OF THE INVENTION
The two-phase interface process has been successfully used for many years in the production of polycarbonates. The process permits production of thermoplastic polycarbonates for a range of application areas, such as data carriers (CD, DVD), optical applications or medical applications.
Good heat stability and minimal yellowing are often described as important qualities of the polycarbonate. Less attention has hitherto been paid to the quality of waste water created during polycarbonate production. The contamination of waste water with residual organic materials, such as residual phenols, is of particular importance when considering the further treatment of waste water, for example by a waste treatment plant or by ozonolysis, to oxidize the residual organic materials. There have however been a number of applications in which methods for subsequent waste water treatment with the aim of reducing the content of phenolic components are predominantly described—see, for example: JP 08 245 780 A (Idemitsu); DE 19 510 063 A1 (Bayer); JP 03 292 340 A (Teijin); JP 03 292 341 A (Teijin); JP 02 147 628 A (Teijin).
The contamination of waste water with residual organic materials, for example with bisphenols or phenols, may be kept to a minimum if a large excess of phosgene is used. However, this is not desirable for economic reasons.
When producing polycarbonates with reduced excess phosgene there is the risk that the bisphenol or the monophenol will not all react fully and will contaminate the waste water. There is the further risk that interface-active phenolic OH groups remaining in the polymer will complicate phase separation and washing. Consequently water-soluble impurities may not all be extracted from the organic phase. This may, in turn, adversely affect the quality of the product.
It is maintained that the production of high-quality polycarbonates by a continuous two-phase interface process and simultaneous low contamination of waste water was possible either only with considerable excess phosgene (uneconomical) or with phase separation problems—along with loss in quality of the polycarbonate—or by subsequent treatment of the waste water.
The Applicant's DE-A 42 27 372, disclosed the presently relevant arrangement of apparatus for the process according to the invention. In contrast to the teaching of the invention, however, no teaching may be inferred from DE-A 42 27 372 about the quantities and, in particular, the circulating conditions in which the educts are to be combined, let alone the fact that a particularly low content of residual organic materials, such as phenols and bisphenols, in waste water may be achieved by specially adjusted proportions and circulating conditions.
Starting from DE-A 42 27 372 the object is therefore to provide a process for producing high-quality products at the same time as a low content of organic materials in the waste water.
DETAILED DESCRIPTION OF THE INVENTION
It has now surprisingly been found that very high-quality polycarbonate, measured by the yellowness index and by the terminal phenolic OH group content, is obtained in a continuous process, the process resulting in only low concentration of residual organic materials (residual phenols) in its waste water. In the process, a circulating reactor and at least one tubular reactor that is connected downstream thereof are used as reactor arrangement. Also critical are the specified reaction conditions and the ratio of added starting components to the quantity of circulated reaction emulsion.
A circulating reactor includes a circulating loop, a pump for circulating the reaction emulsion, a heat exchanger and a residence tank. The residence tank is equipped with means for continuous removal of part of the emulsion. The feeding points for the organic phase and the aqueous phase are situated between the residence tank and the pump. In embodiments where an optional mixer is used, these feeding points may be at the mixer.
The “circulating reactor” is also shown schematically for the purpose of better understanding:
The tubular reactor includes mixing and residence zones and is connected down-stream of the residence tank.
A key feature of the inventive process is the relative purity of the waste water:
The water is characterized in that it contains only low concentration of residual organic materials (residual phenols).
The process is an improvement of the well know two-phase interface process where polycarbonate is prepared from diphenols, phosgene, chain terminators, catalyst and optionally branching agents in a mixture of aqueous/alkaline phase and organic solvent phase. The process entails
(a) introducing into the circulating loop of a circulating reactor that additionally contains, in sequence a residence tank, an optional mixer, a pump, and a heat exchanger, through at least one point downstream from the residence tank and up stream from said pump,
(i) an organic phase that contains a solvent for polycarbonate and phosgene and
(ii) an aqueous phase that contains an aqueous lye solution, a dihydroxy compound and an optional monophenol to form an emulsion, wherein the temperature throughout the reactor is lower than 60, preferably 55° C. to 25° C., and wherein residence time of the emulsion in the circulating reactor is at least 2, preferably 2 to 15 minutes and
(b) removing from the residence tank a portion of the emulsion and pumping said portion into at least one tubular reactor equipped with at least one mixing zone and at least one residence zone and subjecting said portion to total residence time of 2 to 40 preferably 2 to 30 minutes in the tubular reactor,
with the provisos that
(aa) the rate at which the total amount of aqueous and organic phases is introduced in (i) relate to the flow rate of the emulsion as 1:3 to 1:12 preferably 1:3 to 1:10 and that
(bb) the rate of removal of the portion in (b) corresponds to said rate of introduction, and that
(cc) the molar amount of phosgene introduced to the reaction relates to the theoretical amount that is needed for the reaction of phosgene with dihydroxy compounds and with the optional monophenols as 1.12/1 to 1.22/1, preferably 1.14/1 to 1.20, and that
(dd) lye in an amount of 15 to 40 preferably 20 to 35 percent relative to the total weight of lye used in the process according to dd) and ee) is introduced into the circulating loop, and that
(ee) lye in an amount of 85 to 60, preferably 80 to 65 percent relative to the total weight of lye used in the process according to dd) and ee) is introduced into said portion of the emulsion, and that
(ff) monophenol chain terminator is optionally added into said portion, and that
(gg) catalyst is added to the said portion after residence time of 1 to 20, preferably 1 to 15 minutes of said portion in the tubular reactor.
“Downstream” and “upstream” are always taken to mean in the flow direction of the emulsion inside the circulating reactor in the present context.
The content of the phenolic component of the untreated waste water of the reaction is less than 100 ppm, preferably less than 50 ppm, particularly preferably less than 20 ppm.
Suitable diphenols are those of formula HO—Z—OH, in which Z is an aromati
Heuser Jürgen
Kauth Hermann
Kords Christian
Bayer Aktiengesellschaft
Boykin Terressa M.
Gil Joseph C.
Preis Aron
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