Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-07-16
2004-04-06
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C264S176100, C264S219000, C524S599000, C524S611000
Reexamination Certificate
active
06716933
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to a process for working up organic solutions of polymers and more particularly to working up organic solutions contaminated by alkaline constituents.
BACKGROUND OF THE INVENTION
Polycarbonate, as an example of a polymer to be washed according to the invention, is produced in by far the majority of cases by the known interfacial process, which is described by way of example in the following publications
Schnell, “Chemistry and Physics of Polycarbonates”, Polymer Reviews, Volume 9, Interscience Publishers, New York, London, Sydney 1964, p. 33 ff;
D. C. Prevorsek, B. T. Debona and Y. Kesten, Corporate Research Center, Allied Chemical Corporation, Morristown, N.J. 07960: “Synthesis of Poly(ester Carbonate) Copolymers” in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 18 (1980), p. 75 ff;
D. Freitag, U. Grigo, P. R. Müller, N. Nouvertne', BAYER AG, “Polycarbonates” in Encyclopedia of Polymer Science and Engineering, Volume 11, Second Edition, 1988, p. 651 ff, and finally
Dres. U. Grigo, K. Kircher and P. R. Müller “Polycarbonate” in Becker/Braun, Kunststoff-Handbuch, Volume 3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser Verlag Munich, Vienna 1992, p. 118 ff and 138 ff
and also in EP-A 0 359 953 and many other patents.
These publications relate to the synthesis of polycarbonate by the so-called “interfacial process”, which takes place in a two-phase reaction mixture consisting of inorganic phase (water, alkali) and an organic phase (organic solvents, insoluble in water, mostly chlorinated hydrocarbons such as dichloromethane and/or chlorobenzene).
The product of that synthesis is an organic phase (herein after also called organic synthesis solution), which contains the polycarbonate in dissolved form, and an inorganic aqueous alkaline phase, which contains the salts formed in the synthesis, such as NaCl, sodium hydrogen carbonate, soda, additionally residues of the phenolates, bisphenolates and sodium hydroxide used, as well as catalysts and secondary products thereof, as well as water-soluble compounds originating as impurities from the starting materials or formed as by-product. If a different basic compound is used instead of NaOH, the aqueous alkaline phase contains the corresponding analogous salts or secondary products.
The aim of the working-up which follows is to separate off that inorganic aqueous phase as completely as possible and to remove the remaining, especially alkaline residues of the inorganic compounds, which are contained in the soluble and dispersed water content of the separated organic phase, as completely as possible from the organic phase. That is achieved by washing operations, which are optionally combined with acidification steps. Such purification operations are, if possible, carried out before concentration of the organic phase if heat processes are used for the purpose of concentration.
Similar problems are also known in the case of other polymers. Polymers whose synthesis solution can be acidified by the process according to the invention are, therefore, all polymers whose synthesis yields alkaline solutions or suspensions or emulsions. There may be mentioned by way of non-limiting examples polysulfones, polyether sulfones, polyphenylene oxides, or their suspensions, styrene copolymers, such as ABS, provided they are prepared in suspension, polycarbonates, polyester carbonates, polyether carbonates and polyethers.
Purification of the synthesis solution is achieved by washing that organic solution with water one or more times. That is generally carried out with the aid of one or more acidifications and washing with water, mostly in several steps.
The acidification includes either the entire alkaline potential of the synthesis or, preferably, after separation of the phases in the alkaline pH range, only the neutralization of residual constituents of the aqueous phase dissolved or, in admixture with residues of the aqueous phase, dispersed in the organic phase. There are used for such acidifications aqueous mineral acids, especially hydrochloric acid and phosphoric acid, or alternatively aqueous solutions of organic acids.
That washing and acidification is likewise the subject-matter of many patents and publications.
For example, EP-A 0 023 570 describes a process for working up the alkaline synthesis solution using separators that produce shear energy, optionally with the use of dispersing agents.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that, as the demands made of the polymer increase, the conventional methods of working up are no longer sufficient. Even the smallest traces of inorganic residues, especially alkali and catalyst residues, from the synthesis cause significant damage in the case of applications in which the polymer is exposed to high temperatures, optionally combined with moisture. Such damage may be micro-scratches, instability of the melt viscosity or, in extreme cases, the formation of white spots of hydrolyzed polymer. All such damage is known to the person skilled in the art.
In general, attempts are made to counter that phenomenon by means of suitable additives. However, the use of stabilizers as additives is limited by the loss of mechanical properties or, for example, by an adverse effect on the hydrolytic behavior of the stabilized polymer. The use of, for instance polycarbonate in the medical or food-related applications is therefore very limited for regulatory reasons.
Separation of the inorganic constituents, whether they be salt, salt of the catalyst or alkali from the synthesis of the polymer or water from the washing of the polymer synthesis solution, is also expedient because separation (salt, alkali) is no longer possible in the following working-up and compounding steps. In the case of the washing water, significant damage can be caused, for example, even by concentration of the polymer solution used to obtain the polymer out of the solution, where such concentration involves thermal steps such as distillations or flash steps, because the methylene chloride frequently used as solvent is susceptible to decomposition. The person skilled in the art is also familiar with such reactions.
Starting from those problems, the object is, therefore, to find a working-up process that leads to a significant reduction in the inorganic constituents, especially the alkaline constituents in the parts per billion (ppb) range in the organic polymer solution, before the polycarbonate solution is concentrated further in order to separate off the polymer.
Surprisingly, this object is achieved by a process for working up polymer synthesis solutions, which are obtained by an interfacial condensation process for manufacturing of polymers, in which the organic polymer-containing phase is separated off and acidified with acids that are homogeneously soluble in the organic phase—such as hydrogen halides, organic carboxylic and/or sulfonic acids having from 1 to 22 carbon atoms, which may optionally be branched or substituted, or their derivatives, such as, for example, halides or anhydrides, mineral acids, acid chlorides of mineral acids, especially such acids that have better solubility in water than in organic solvents or that react with water to form such components; preferably HCl gas, SO
2
, ortho/meta/poly-phosphoric acids and organic carboxylic and/or sulfonic acids having from 1 to 12 carbon atoms, which may optionally be branched or substituted; very particularly preferably HCl gas and phosphoric acid—and is then optionally washed with water as usual.
Within the context “homogeneous acidification” is understood as meaning acid compound in pure form or in solution in organic solvent added to organic phase, which contains the polymer, and dissolve homogeneously in the polymer solution.
That acidification step according to the invention be carried out instead of the usual washing of the polymer-containing solution with aqueous mineral acids or alternatively, in a preferred embodiment of the process according to the invention, it be
Alewelt Wolfgang
Bruynseels Frank
Ebert Wolfgang
Fritz Thomas
Jahn Dirk
Bayer Aktiengesellschaft
Boykin Terressa
Franks James R.
Gil Joseph C.
Preis Aron
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