Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2000-01-06
2002-04-30
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
Reexamination Certificate
active
06380345
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field of the Invention
This invention relates to a production method of a polycarbonate resin, more particularly the production method of the polyearbonate resin enabling the reduction of a waste liquid and a long term continuous operation in an economically advantageous method by using an ejector as a method for removing reaction byproducts generated in the production of the polycarbonate resin by drawing for reducing a pressure thereof.
2. Description of the Related Arts
An aromatic polycarbonate resin is excellent in mechanical properties such as an impact resistance, etc., and also in heat resistance, transparency, etc., and widely used as a molding material.
As the production method of such aromatic polycarbonate resin, a method for directly reacting an aromatic dihydroxy compound such as bisphenol, etc., with phosgene (a boundary method), or a method for performing the transesterification reaction of the aromatic dihydroxy compound such as bisphenol with an aromatic carbonic acid diester such as diphenyl carbonate (a melting method), are known.
Among such production methods, the method for producing the polycarbonate resin by the transesterification reaction of the aromatic dihydroxy compound with the aromatic carbonic acid diester, is performed by heating the reaction mixture for elevating a reaction temperature from 150° C. which is the lowest temperature for initiating the transesterification reaction, gradually to approximately 350° C., using an organic acid salt, an inorganic acid salt, an oxide, a hydroxide, a hydride, an alcoholate or the like of a metal as a catalyst and also gradually reducing a reaction pressure from atmospheric pressure to 13.3×10
−6
MPa for distilling off generated reaction byproducts from the reaction mixture.
Therefore, it was necessary for a piping connecting a polymerization reactor with a vacuum pump, a vacuum trap and the vacuum pump used in the above process to provide a specific consideration for preventing clogging caused by a solidification in regard to a vapor of phenolic byproducts, decomposed materials by the reaction, and un-reacted materials and/or lowly polymerized materials accompanied therewith. Further, since the reaction byproducts contain reusable substances (effective components) such as phenolic compounds and aromatic carbonic acid diesters, it was important to recover and reuse thereof to economically produce polycarbonates by a transesterification process.
Regarding a process for collecting vapor of an aromatic monohydroxy compound as the byproduct of the trans-esterification reaction by a condensing apparatus, Japanese unexamined patent publication JP-6-73174A has proposed a process. However, such a process has a problem that it is hardly applicable in the case where the reaction is carried out under high vacuum like 666×10
−6
MPa (5 Torr) or lower. Especially, in a polymerization reactor (the latter stage polymerization reactor) for producing a polycarbonate having a viscosity average molecular weight of 10000 or more, which is operated under a reduced pressure of 666×10
−6
MPa or lower, reaction byproducts can not be collected in some cases in a liquid phase, thereby a trouble of clogging caused by solidification tends to occur, and a large number of efforts, for example, two condensers are placed in parallel, are necessary to perform a long term continuous operation, .
In addition, for these purposes, a process placing a scrubber between a polymerization reactor and a vacuum pump, as described in Japanese unexamined patent publication JP-6-065367, the publication WO97/38039 or the like, has been proposed; and a liquid sealing type vacuum pump is generally used as the vacuum pump.
However, in the melting method, with the view of keeping its economical advantages, it was extremely important to recover the reaction byproducts produced as byproduct and use them repeatedly by converting into the carbonic acid diester as a raw material for the polymerization.
That is, in the latter stage polymerization reactor, not only a transesterification reaction which accompanies the production of a monohydroxy compound as byproduct, but also a transesterification reaction which accompanies the production of an aromatic carbonic acid diester as byproduct occur. Since the aromatic carbonic acid diester produced as byproduct is the same compound as the aromatic carbonic diester which is used as the raw material of the polymerization, it becomes more advantageous to collect and recover the aromatic carbonic acid diester of the byproduct, and recycle it directly into the polymerization process from the view point of economy. However, in the process described in Japanese unexamined patent publication JP-6-065367A, which uses, for example, tetraethylene glycol as a scrubber liquid, there have been such problems in the recycling that the recovery percentages of the effective components decrease, and also a trace of third components such as tetraethylene glycol are mixed in the recovered effective components.
Under these circumstances, effective collecting processes have been investigated. The publication of WO97/38039 discloses a process using a phenol solution containing a melting point-lowering agent as a scrubber liquid in order to solve such problems, but still the influence of the melting point-lowering agent can not be avoided, and problems have remained with regard to the recovery of the effective components.
Further, in the description of the present invention, “reaction byproducts” means a mixture of a vapor of phenolic byproducts, decomposed materials by the reaction, accompanied un-reacted raw materials and/or lowly polymerized materials, which are drawn by a vacuum drawing system such as the vacuum pump from the polymerization reactor, and “condensed reaction byproducts” means that the reaction byproducts condensed in the vacuum drawing system.
Problem to be solved by this invention
However, in the above exchangeable type condenser used conventionally, since the reaction byproducts are removed by condensing on a heat conducting surface cooled at a melting point thereof or lower for condensing under vacuum between the polymerization reactor and the vacuum pump, a large heat conducting surface area is necessary to lead a large scale facility unavoidably. Also, there is large pressure fluctuation caused by the gradual clogging of piping passages by the solidification especially of the byproduct phenolic compound and aromatic carbonic acid diester compound among the reaction byproducts into a cotton like state on the heat conducting surface, and there is such a problem that the vacuum pump can not generate the vacuum because of the generation of the solidification, etc., at the moving parts in the vacuum pump by drawing a part of the reaction byproducts into it; and thereby a high exchanging frequency of the pump is required for preventing such a problem that the pump becomes unoperative, and the quality of the product is badly affected, and also the influence on the economy thereof can not be disregarded.
When a scrubber is used, it is installed between the polymerization reactor and the vacuum pump, and removes the reaction byproducts; however, the selection of a liquid to be used for scrubbing is difficult because it is desirably a substance having such characteristics that its vapor pressure is lower than the polymerization reaction pressure at its using temperature, it has a sufficient solubility for the drawn reaction byproducts, and also it does not react with the reaction byproducts dissolved in the scrubber liquid, and is easily separable from the monohydroxy compound and the aromatic carbonic acid diester after scrubbing. Further, since there are problems of a waste liquid treatment and the recovery of effective components which becomes complex in this process, the process is economically not feasible. Furthermore, the mingling of trace of the scrubber liquid components into the recovered monohydroxy compound and aromatic carbonic
Sasaki Katsushi
Sawaki Toru
Simonaru Masasi
Uenishi Kazuhiro
Boykin Terressa M.
Teijin Limited
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