Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-12-21
2004-09-14
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S125000, C528S126000, C528S127000, C528S145000, C528S149000, C528S170000, C528S491000, C528S497000, C528S500000, C528S503000, C210S633000, C210S634000, C210S660000
Reexamination Certificate
active
06790934
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to methods for purification of aromatic polyethers, and more particularly to methods for purification of aromatic polyetherimides.
Various types of aromatic polyethers, particularly polyetherimides, polyethersulfones, polyetherketones, and polyetheretherketones have become important as engineering resins by reason of their excellent properties. These polymers are typically prepared by the reaction of salts of dihydroxyaromatic compounds, such as bisphenol A (BPA) disodium salt, with dinitroaromatic molecules or dihaloaromatic molecules. Examples of suitable dihaloaromatic molecules include bis(4-fluorophenyl) sulfone, bis(4-chlorophenyl)sulfone, and the analogous ketones and bisimides as illustrated by 1,3-bis[N-(4-chlorophthalimido)]benzene.
According to U.S. Pat. No. 5,229,482, the preparation of aromatic polyethers by displacement polymerization may be conducted in the presence of a relatively non-polar solvent, using a phase transfer catalyst which is substantially stable under the temperature conditions employed. Suitable catalysts include ionic species such as guanidinium salts. Suitable solvents disclosed therein include o-dichlorobenzene, dichlorotoluene, 1,2,4-trichlorobenzene and diphenyl sulfone.
It is desirable to isolate aromatic polyether from a reaction mixture (or other type of mixture such as recovery from a mixed recycle stream solution) free from contaminating species that may affect the polymer's final properties in typical applications. In a typical halide displacement polymerization process contaminating species often include alkali metal halide and other alkali metal salts, residual monomer species, and residual catalyst species. For maximum efficiency of operation it is desirable to recover any solvent employed and other valuable compounds such as catalyst species, and to provide waste streams which do not contaminate the environment. In particular it is often desirable to recover alkali metal halide, especially sodium chloride, for recycle to a brine plant for production of sodium hydroxide and chlorine.
Many conventional techniques are used to purify polymer-containing organic solutions. For instance, extraction with water and settling by gravity in a mixer/settling tank have been used for removal of aqueous-soluble species. However, water extraction methods will not work when the water phase emulsifies with or does not phase separate efficiently from the organic phase. The particular case of polyethers in chlorinated aromatic hydrocarbon solvents often presents special difficulties when mixing with water and separating by settling. Depending upon such factors as polymer concentration and temperature, the organic solution may be particularly viscous making efficient washing with an aqueous phase difficult. Variations in either temperature of operation in the range of about 20-180° C. or in polymer concentration may promote settling due to density differences, but the presence of surface-active functional groups on the polymer may still promote emulsification, particularly the presence of ionic end-groups such as phenoxide and/or carboxylate left uncapped from the polymerization process. Another constraint is that the time for separation of the aqueous and organic phases must be fast, preferably on the order of minutes, so that separation rates do not slow down production. A method is needed that minimizes emulsification and is relatively fast for phase separation of the water and organic phases.
Dry filtration via filters or membranes has also been employed for the removal of relatively large suspended solids from polymer-containing organic solutions. The advantage is that no process water is needed, but the disadvantage is that the filter type has to be chosen carefully to avoid a high pressure drop as the solids cake builds. Filtration is not feasible if the solid particles plug, blind, or go through the porous filter media. Easy back flushing of the filter is also required for fast turn-around and repeated use. Alkali metal halides, such as sodium chloride, are typically insoluble in organic solvents such as chlorinated aromatic-hydrocarbons, but such halides may be present as small suspended solid crystals that are difficult to remove by standard filtration methods. Furthermore, residual monomer species such as alkali metal salts of monomer or complexes of catalyst and monomer may also be present which often cannot be efficiently removed by filtration alone.
Because of the unique separation problems involved, new methods are needed for efficiently separating aromatic polyether products from contaminating species in chlorinated aromatic hydrocarbons. Methods are also required for recycling the solvent arid for recovering useful catalyst and alkali metal halide species from any final waste stream.
BRIEF SUMMARY OF THE INVENTION
After careful study the present inventors have discovered methods for purifying aromatic polyethers prepared in water-immiscible solvents with a density ratio to water of greater than about 1.1:1 at 20-25° C. These new methods also provide efficient recovery of solvent, alkali metal halide, and valuable catalyst species.
In one of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and (iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110° C. and a density ratio to water of greater than 1.1:1 at 20-25° C., comprising the steps of:
(a) quenching the mixture with acid; and
(b) at least one step of contacting a polyether-containing organic phase with water and separating a water-containing phase from the organic phase, which step comprises using at least one of a liquid/liquid centrifuge, a solid/liquid centrifuge, a counter-current contact apparatus, a liquid-liquid extractor, a liquid-liquid continuous extractor, an extraction column, a static mixer, a coalescer, a homogenizer, or a mixing/settling vessel.
In another of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and (iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110° C. and a density ratio to water of greater than 1.1:1 at 20-25° C., comprising the steps of:
(a) subjecting the mixture to at least one solid separation step;
(b) quenching the mixture with acid; and
(c) extracting the organic solution at least once with water.
In still another of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and (iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110° C. and a density ratio to water of greater than 1.1:1 at 20-25° C., comprising: at least one solid separation step, and at least one ion exchange step.
In still another of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and (iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110° C. and a density ratio to water of greater than 1.1:1 at 20-25° C., comprising the steps of:
(a) providing to the mixture an amount of water in a range between about 0.005 wt. % and about 10 wt. % based on weight of polyether;
(b) mixing the phases, wherein a portion of alkali metal halide is in a form that can be separated by a solid separation step following mixing; and
(c) subjecting the mixture to at least one sol
Ayala Raul Eduardo
Brunelle Daniel Joseph
Freshour Amy Rene
Fyvie Thomas Joseph
Hall David Bruce
Acquah Samuel A.
Cabou Christian G.
General Electric Company
Johnson Noreen C.
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