Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2000-08-16
2001-12-04
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S422000, C528S499000
Reexamination Certificate
active
06326460
ABSTRACT:
This invention relates to a process for extracting polyamide particles, or polymer particles comprising polyamides, with aqueous extractants.
As-polymerized polyamides and especially nylon-6 contain low molecular weight extractables comprising monomers and oligomers because of the chemical equilibria which develop in the polymer melt. To prevent any impairment of product quality and of processing properties, for example during injection or extrusion molding or during spinning, the extractables content has to be lowered. The requisite extraction is usually carried out with water at elevated temperatures, as described in DE-A 2 501 348, for example. The aqueous extract is concentrated and recycled into the polymerization.
To ensure adequate extraction of the polyamide and especially a diminishment of critical oligomers and especially dimers frequently requires long residence times in the extraction stage and hence large extraction columns, which not only appreciably raises the level of capital investment required but also adversely affects the flexibility of the process.
Extracting polyamide chips with caprolactam, as described in JP-A-72 26 438, for example, is disadvantageous, since caprolactam is a comparatively costly material and need not necessarily be available for use.
It is an object of the present invention to provide an extraction process which, on the one hand, shortens the extraction time compared with extraction with pure water and improves the extraction efficiency and, on the other, ideally dispenses with the use of caprolactam as extracting solvent.
We have found that this object is achieved according to the invention by a process for extracting polyamide particles, or polymer particles comprising polyamides, with aqueous extractants, which comprises using aqueous solutions of aminonitriles and optionally further polyamide-forming monomers, polyamide-forming oligomers or mixtures thereof as aqueous extractants.
The extraction is carried out by first contacting the polyamide particles, or polymer particles comprising polyamides, especially the polymer chips or similar shaped articles, with the extractant in order that the undesired low molecular weight constituents may be extracted from the chips. In a further step, the chips are removed from the extractant and freed from extractant residues, for example by rinsing with water. If desired, a further extraction of the chips with or without the addition of aminonitrile or polyamide-forming monomers or oligomers may take place. Depending on the desired product specification, extraction quality can be set within wide limits through the combination of the aforementioned steps as a function of equipment preconditions and the chosen parameters such as extractant concentration, chip/extractant ratio, temperatures and residence times.
The extraction of the invention may be carried out in one or more stages, depending on the equipment available. The aforementioned stages and their sequence may be carried out either batchwise, i.e., in succession in a single reactor, or continuously, i.e., simultaneously in successive reactors. It will be appreciated that it is also possible for some of the stages to be carried out continuously and the remaining stage(s) batchwise.
If the extraction is carried out continuously, the extractant and the polymer can pass both cocurrently and countercurrently. Preferably, the extraction is carried out counter currently i.e., the polyamide particles, or polymer particles comprising polyamides, and the aqueous extractant are passed countercurrently.
In a preferred embodiment, the extraction is carried out in a plurality of stages, and the extractants used in the different stages have different compositions. It is possible, for example, to carry out a preextraction with an extractant comprising aminonitrile, polyamide-forming monomers and/or oligomers and water, followed by an extraction stage which is free of aminonitrile, monomers and/or oligomers. The advantage with this embodiment is the reduction in the influence of impurities or, to be more precise, the avoidance of chip surface contamination due to the extractant. This two-stage embodiment is preferably carried out in a single apparatus.
The polyamide chips obtained after the polymerization and subsequent pelletization stage are fed to a continuous extraction column via a transportation water circuit. The chips are separated from the transporting water by a separating means (a sieve) and fall into the extractor head. The chips pass downwardly through the extraction tower under gravity and are freed along the way from low molecular weight constituents by extraction. Extracting solvent or water is continuously added at the base of the extraction column and passes upwardly through the extraction column in countercurrent, becoming loaded with monomers and oligomers on the way. The laden extractant is taken off at the top of the column and educted as extract water efflux. If desired, this is followed by an extract water workup or a recycle into the feed stream.
The extractant used is an aqueous solution of aminonitriles and optionally polyamide-forming monomers and/or polyamide-forming oligomers. The aminonitrile content in the extractant is chosen in such a way that complete miscibility is present in the extractant used, i.e., no separation occurs in the extractant. The level of aminonitriles, polyamide-forming monomers and polyamide-forming oligomers suitably totals from 5 to 95% by weight, based on the total weight of the aqueous solution. The aminonitrile concentration is within the range from 1 to 100% by weight, preferably within the range from 30 to 100% by weight, particularly preferably within the range from 50 to 100% by weight, based on the total weight of the nonaqueous compounds. The concentration of polyamide-forming monomers is within the range from 0 to 99% by weight, preferably within the range from 0 to 70% by weight, particularly preferably within the range from 0 to 50% by weight, based on the sum total of nonaqueous compounds. The concentration of polyamide-forming oligomers is within the range from 0 to 60% by weight, preferably within the range from 0 to 40% by weight, particularly preferably within the range from 0 to 20% by weight, based on the sum total of nonaqueous compounds. If at least 1% by weight, preferably at least 5% by weight, of further monomers and/or oligomers is present, the amount of aminonitriles decreases accordingly. Preferably, no further monomers and/or oligomers are present.
Two possible extraction columns are illustrated in the drawing in FIGS.
1
/
2
and
FIG. 3
, respectively. The column can also represent a combination of the two variants.
REFERENCES:
patent: 4978743 (1990-12-01), Selbeck et al.
patent: 2501348 (1976-07-01), None
patent: 3534817 (1987-04-01), None
patent: 289471 (1991-05-01), None
patent: 4324616 (1995-01-01), None
patent: 19505150 (1996-08-01), None
patent: 308774 (1989-03-01), None
patent: 7226438 (1968-04-01), None
Derwent Abstract AN-95-078098 (JP 930172565, Jun. 18, 1993).
Hildebrandt Volker
Mohrschladt Ralf
Warzelhan Volker
BASF - Aktiengesellschaft
Keil & Weinkauf
Sergent Rabon
LandOfFree
Method for extracting polyamide particles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for extracting polyamide particles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for extracting polyamide particles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2597533