Classifying – separating – and assorting solids – Electrostatic
Patent
1999-08-04
2000-10-31
Walsh, Donald P.
Classifying, separating, and assorting solids
Electrostatic
2091274, 209128, 209129, 209130, B03C 700
Patent
active
061405981
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the separation of particulate or pulverulent mixtures of organic polymers and salts, in particular sulfur-containing polymers and halides or carboxylates of alkali metals and alkaline earth metals.
In the preparation of polymers by polycondensation, salts are frequently formed as by-products, e.g. in a subsequent neutralization reaction. This also applies, inter alia, to the preparation of polyphenylene sulfide (PPS) from sodium sulfide and para-dichlorobenzene in a polar solvent according to the simplified reaction equation
In a known process, the mixture of solvent, polymer and salt present after the reaction is subjected to a flash evaporation to remove the solvent and a solids mixture of polymer and salt is obtained. The salt is removed from this mixture by washing with water and subsequent filtration of the polymer from the washing water. However, these and related processes have the disadvantage that large amounts of salt-containing wastewater are obtained.
For the separation of salts from PPS and a polar solvent, EP-0 220 490 describes a hot filtration or centrifugation at temperatures of above 210.degree. C. However, this procedure requires, in industrial implementation, special constructions of filtration apparatus or centrifuges for this temperature range. In particular, the sealing of the apparatus against the polar solvents used at T>210.degree. C. presents problems.
There is therefore a need for a process for separating salts from organic polymers which operates at moderate temperatures and does not generate large wastewater streams.
It is known that different plastics can be separated from one another by means of triboelectric separation, i.e. by separation of charged particles in a static electric field after they have been charged by mutual friction or friction with apparatus components. It is proposed, for example in DE-C-3 035 649 and in DE-C-4 225 977, for the separation of chemically different plastics within a recycling process. The feed materials used therein are mechanically commuted plastic moldings. Typical particle sizes are in the range from a few millimeters down to fractions of a millimeter, but do not extend down into the very fine particle range of, for example, less than 200 .mu.m. An apparatus for the triboelectric separation of purely inorganic, mineral solids in the very fine particle size range has been proposed in Powder Technology 86 (1996), 41-47.
It has surprisingly been found that triboelectric separation also gives very good results for solids mixtures of organic polymers and salts in the very fine particle size range down to d=10 .mu.m. The invention accordingly provides a process for the triboelectric separation of organic polymers and salts, in particular for the separation of such mixtures of organic polymers and salts having mean particle diameters of .ltoreq.200 .mu.m.
According to a preferred embodiment, the invention provides a process for the separation of sulfur-containing polymers of salts, in particular the halides or carboxylates of alkali metals or alkaline earth metals.
For the purposes of the present invention, the term organic polymer encompasses essentially all known macromolecular, predominantly organic materials. The process of the invention is of particular relevance to polymers which are prepared in a polycondensation process with direct formation of salts or of acids or bases which are to be neutralized subsequently. Examples of such processes are the preparation of polyaramides from diamines and diacid chlorides, of polycarbonates from diphenols or diphenoxides and phosgene, or polysulfones, polyether sulfones or polyether ketones from diphenoxides and dihalogenated aromatic hydrocarbons or the preparation of polyarylene siloxanes from diaryldichlorosilanes and diphenoxides. In particular, the term encompasses sulfur-containing polymers.
Sulfur-containing polymers are preferably polymers which comprise arylene sulfide units. The arylene constituents of the arylene sulfide units comprise monocyclic or
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Schonert Klaus
Semel Joachim
Wagener Reinhard
Miller Jonathan R.
Ticona GmbH
Walsh Donald P.
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