Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2000-07-11
2002-03-19
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C528S310000
Reexamination Certificate
active
06359020
ABSTRACT:
The present invention relates to a process for producing polyamides from aminonitriles and aqueous media at elevated temperature and elevated pressure.
This invention further relates to the use of aqueous monomer and oligomer extracts obtained from polyamide production by extraction of the polymer with water.
The polymers formed in polyamide production by polymerization of, for example, &egr;-caprolactam contain low molecular weight fractions composed of caprolactam and oligomers thereof. In practice, these low molecular weight fractions are removed by extraction with hot water. The caprolactam can be recovered from these extraction waters (aqueous monomer and oligomer extracts), purified and, if desired, reintroduced into the polymerization. It is also possible to add lyzing reagents to convert the oligomers in the extract waters into caprolactam which may likewise be isolated, purified and reused.
DE-A-25 01 348 describes a process for producing polyamides from &egr;-caprolactam including a step of extracting with a solvent after the polymerization. The extract, containing monomers and oligomers, is concentrated in the absence of atmospheric oxygen in an apparatus in which the extract-contacting surfaces are constructed in materials which are inert under the conditions of the concentrating step. The concentrate obtained is polymerized without further purification or fractionation, alone or together with other polyamide-forming starting materials.
U.S. Pat. No. 3,459,640 describes a process for recovering purified caprolactam from polycaproamide extraction solutions. The crude caprolactam is passed through a heat exchanger and then into a separator where purified caprolactam is distilled off under reduced pressure. The caprolactam can be returned into the reaction.
U.S. Pat. No. 5,077,381 describes a process for producing polyamides from amide monomers wherein unconverted amide monomers and oligomers are extracted, the relative proportion of oligomers in the extract is reduced by heat treatment at 220 to 290° C., and the extracted portion of the reaction mixture is returned into the reaction.
In EP-A-0 608 454, polyamide-6 wastes or oligomer-containing polyamide-6 wastes or oligomeric lactam residues are recovered by subjecting them to a depolymerizing hydrolysis in a pressure reactor in the presence of added water.
All the processes mentioned have the disadvantage that the extract water has to undergo a workup, in multiple stages in some instances, before the entire extract or constituents thereof, especially caprolactam, can be used for renewed polymerization. The processes which envisage removal, workup and recycling of caprolactam have the additional disadvantage that the oligomers in the extract waters are not worked up, but have to be disposed of. Furthermore, the aforementioned processes for recycling extract water assume the use of a process step for hydrolytic polymerization of the extract water concentrate or of a mixture of extract water constituents and caprolactam.
It is an object of the present invention to provide a process for recycling extract water, i.e. aqueous monomer and oligomer extracts obtained from polyamide production by extraction of the polymer with water, by using the aqueous extract solutions in the polymerization ideally directly without prior workup, concentrating or removal steps. The process shall moreover avoid the disadvantages of existing processes.
We have found that this object is achieved according to the invention by the use of aqueous monomer and oligomer extracts obtained from polyamide production by extraction of the polymer with water for producing polyamides by direct reaction with aminonitriles.
The invention also provides a process for producing polyamides by reacting at least one aminonitrile with aqueous monomer and oligomer extracts obtained from polyamide production by extraction of the polymer with water.
According to the invention, the aqueous monomer and oligomer extracts are returned into the polymerization without further workup steps. Accordingly, no concentrating, fractionation or purification is necessary.
The inventive process for recycling the aqueous extracts can be carried out batchwise or continuously.
Preference is given to converting a reaction mixture comprising aqueous monomer and oligomer extracts, aminonitrile and water into polyamide in a multiphase production process. The composition of the reaction mixture depends on the extractables contents of the aqueous extract. According to the invention, the water content of the reaction mixture is within the range from 10 to 80% by weight, preferably within the range from 25 to 60% by weight.
Preference is given according to the invention to such a process for producing a polyamide by reaction of at least one aminonitrile with water as comprises:
(1) reacting at least one aminonitrile with an aqueous medium at a temperature from 90 to 400° C. and a pressure from 0.1 to 35×10
6
Pa to obtain a reaction mixture,
(2) further reacting the reaction mixture at a temperature from 150 to 400° C. and a pressure which is lower than the pressure in step 1, the temperature and the pressure being selected so as to obtain a first gas phase and a first liquid or a first solid phase or a mixture of first solid and first liquid phase, and separating the first gas phase from the first liquid or the first solid phase or from the mixture of first liquid and first solid phase, and
(3) admixing the first liquid or the first solid phase or the mixture of first liquid and first solid phase with a gaseous or liquid phase comprising an aqueous medium at a temperature from 90 to 370° C. and a pressure from 0.1 to 30×10
6
Pa to obtain a product mixture, the aqueous medium used in step 1 and/or 3 being aqueous monomer and oligomer extracts obtained from polyamide production by extraction of the polymer with water, and otherwise water.
The process may comprise, additionally or instead of step 3, the following step:
(4) postcondensing the product mixture at a temperature from 200 to 350° C. and a pressure which is lower than the pressure of step 3, the temperature and pressure being selected so as to obtain a second, water- and ammonia-comprising gas phase and a second liquid or second solid phase or a mixture of second liquid and second solid phase, which each comprise the polyamide.
Thus, the aqueous monomer and oligomer extracts can be returned into step 1, step 3 or into both steps of the process. If the aqueous extract is not used, water can be used instead.
The aminonitrile in the mixture can be in principle any aminonitrile, i.e., any compound having both at least one amino group and at least one nitrile group. &ohgr;-Aminonitriles are preferred, especially &ohgr;-aminoalkyl nitrites having from 4 to 12 carbon atoms, more preferably 4 to 9 carbon atoms, in the alkylene moiety, or an aminoalkylaryl nitrile having from 8 to 13 carbon atoms, preferred aminoalkylaryl nitrites being aminoalkylaryl nitriles which have an alkylene group of at least one carbon atom between the aromatic unit and the amino and nitrile group. Especially preferred aminoalkylaryl nitriles are those which have the amino group and nitrile group in the 1,4 position relative to each other.
The &ohgr;-aminoalkyl nitrile used is preferably a linear &ohgr;-aminoalkyl nitrile in which the alkylene moiety (—CH
2
—) preferably contains from 4 to 12 carbon atoms, more preferably from 4 to 9 carbon atoms, such as 6-amino-1-cyanopentane (6-aminocapronitrile), 7-amino-1-cyano-hexane, 8-amino-1-cyanoheptane, 9-amino-1-cyanooctane, 10-amino-1-cyanononane, particularly preferably 6-aminocapronitrile.
6-Aminocapronitrile is customarily obtained by hydrogenation of adiponitrile according to known methods, described for example in DE-A 836,938, DE-A 848,654 or U.S. Pat. No. 5,151,543.
Of course, it is also possible to use mixtures of a plurality of aminonitriles or mixtures of an aminonitrile with further comonomers, such as caprolactam or the below-defined mixture.
In a particular embodiment, especially if copolyamides o
BASF - Aktiengesellschaft
Keil & Weinkaup
Michl Paul R.
LandOfFree
Method for producing polyamides from aminonitriles 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 producing polyamides from aminonitriles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing polyamides from aminonitriles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2829273