Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-01-18
2004-05-11
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C422S129000, C422S131000, C422S132000, C422S198000, C422S224000, C422S233000, C422S282000, C528S481000, C528S501000, C528S503000
Reexamination Certificate
active
06734282
ABSTRACT:
The invention relates to a process and an apparatus for separating polymers in solution from solids which are insoluble in the solution. The invention further relates to the separation of sulfur-containing polymers from undissolved solids.
In the preparation of polymers by polycondensation, solids are frequently formed as by-products, sometimes in a subsequent neutralization reaction. This applies, for example, to the preparation of polyphenylene sulfide (PPS) from sodium sulfide and p-dichlorobenzene in a polar solvent in accordance with the simplified reaction equation:
Na
2
S+C
6
H
4
Cl
2
→[—C
6
H
4
—C—]+2NaCl
In known processes, the sodium chloride by-product which is insoluble in the reaction mixture is removed after the reaction by repeated washing with water and subsequent filtration of the polymer. However, these and related processes for other high-performance polymers such as polyaramides, poly(ether)sulfones or polyether ketones have the disadvantage that large amounts of salt-containing wastewater are obtained.
DD-A-241 368 describes an apparatus for the removal of water-soluble solids. Here, undissolved solid is separated from an epoxy resin solution by means of a combined process comprising sedimentation and dissolution of the solid in water. In operation, the apparatus disclosed has a phase boundary between the water-imiscible polymer solution at the top and the water as extractant for the solid underneath in the middle region. Separation processes using this apparatus consequently produce dilute, aqueous salt solutions.
EP-A 0 220 490 describes hot filtration or centrifugation at temperatures above 210° C. for the separation of salt from PPS and a polar solvent. However, in industrial use, this method has the disadvantage that filtration apparatuses or centrifuges for this temperature range require costly constructions. At T>210° C. and the prevailing pressures, sealing moving, in particular rapidly rotating, components presents difficulties.
WO-A-96 11 968 describes the separation of the insoluble solids from dissolved polymers in order to recover filled polymers. In the method described there, the solids, for example glass fibers, are separated from the polymer solution by filtration. However, the known processes are capable of improvement since dilute washing liquors are obtained and the removal of the solid from the filter apparatuses is difficult, particularly at high temperatures under pressure.
It is an object of the present invention to provide a process and an apparatus by means of which solids are separated from dissolved polymers and the solid discharged has been substantially freed of polymers.
The object of the present invention is achieved by a process for separating a dissolved polymer from solids, wherein the solid is separated off by sedimentation and the sedimented solid is washed in countercurrent with a solvent.
It has been found that solids can be separated from dissolved polymers by sedimentation. According to the invention, a washing process simultaneously takes place in the sedimentation apparatus, by means of which the losses of polymer caused by adhesion of polymer solution to the solid can be minimized. The sedimentation and washing sequence can be repeated in a plurality of steps or stages until a prescribed residual content of polymer in the solution adherent to the solid is achieved.
The process of the invention can also be carried out simply at high temperatures and pressures. The separation process preferably occurs continuously without dilute washing liquors being obtained. The polymer concentration in the overflow from the sedimentation apparatus is greater than 50%, preferably greater than 70%, of the concentration at the inlet.
In the present context, the term polymer includes all macromolecular, predominantly organic compounds which dissolve in a solvent, if appropriate at elevated temperature under pressure.
The process of the invention is particularly suitable for polymers in whose preparation solids, for example salts, are formed as by-products and have to be separated off. The solids can be formed directly in the polycondensation process or in a subsequent neutralization of acids or bases. Examples of such processes are the preparation of polyaramides from diamines and diacid chlorides, of polycarbonates from diphenols or diphenoxides and phosgene, of polysulfones, polyether sulfones or polyether ketones from diphenoxides and dihalogenated aromatic hydrocarbons or the preparation of polyarylenesiloxanes from diaryidichlorosilanes and diphenoxides.
The process of the invention is of particular relevance for polymers which dissolve only at elevated temperature under pressure and in the case of which the removal of the solids therefore requires costly apparatus. Such polymers include, in particular, sulfur-containing polymers.
Sulfur-containing polymers are polymers comprising arylene sulfide units. The arylene constituents of the arylene sulfide units comprise monocyclic or polycyclic aromatics or linked aromatics. The aromatics can also contain heteroatoms. Examples of such aromatics, which may be substituted or unsubstituted, are benzene, pyridine, biphenyl, naphthalene, phenanthrene. Examples of substituents are C
1
-C
6
-alkyl, C
1
-C
6
-alkoxy, carboxyl, amino and sulfonic acid groups. Linked aromatics are, for example, biphenyl or aromatics joined by other bridges (arylene ethers).
Preferred sulfur-containing polymers are polyarylene sulfides, in particular polyphenylene sulfide.
Possible solids are all substances which, under the conditions under which the sedimentation apparatus is operated, are present in solid form and have a density different from the liquid mixture. Examples are salts, substances used as fillers, e.g. glass fibers, carbon fibers, titanium dioxide, gypsum or other solids.
Salts can be organic or inorganic, i.e. can consist of any combination of organic or inorganic cations with organic or inorganic anions. They have to be at least partially insoluble in the reaction medium and have a density different from that of the liquid reaction mixture. Typical representatives of the inorganic salts are the halides of alkali or alkaline earth metals which are frequently formed as by-product of a polycondensation. Typical representatives of organic salts are carboxylates of the alkali metals, of the alkaline earth metals, of ammonium or of organically substituted ammonium cations which are, according to the prior art, used as promoters in, for example, the preparation of sulfur-containing polymers. For the purposes of the present invention, carboxylates are the solids of aliphatic carboxylic acids, e.g. acetic acid or propionic acid, or aromatic carboxylic acids, for example benzoic acid, and also solids of polyfunctional carboxylic acids.
Apparatuses suitable for separating off the undissolved solids are ones which allow the solid which has been separated off to be washed with solvents. The separation is preferably carried out using an apparatus which makes it possible for the solid to be separated off to be washed in countercurrent in a number of stages and which can also be used at elevated pressures and temperatures and which allows effective washing of the solid to be separated off with small amounts of solvent, so that no highly dilute polymer solutions are formed. These objectives can be achieved by means of the sedimentation apparatuses described below.
The polymer concentration of the mixture to be separated is preferably up to 70% by weight. Particular preference is given to 10 -50% by weight. The polymer concentration in the liquid discharged together with the solid is from 0% to 70% of the concentration at the inlet, preferably from 0% to 10% and particularly preferably from 0% to 5%.
The sedimentation of the insoluble solid occurs at temperatures at which the polymers are liquid or in dissolved form. In the case of high-performance polymers which often dissolve only at elevated temperatures, the sedimentation apparatuses are operated at elevated temperatures and pre
Haubs Michael
Wagener Reinhard
Boykin Terressa
Connolly Bove & Lodge & Hutz LLP
Ticona GmbH
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