Batch process for producing polyamides from aminonitriles

Details Batch process for producing polyamides from aminonitriles Batch process for producing polyamides from aminonitriles

2000-07-13

2001-10-30

Hampton-Hightower, P. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S312000, C528S313000, C528S329100, C528S342000, C528S324000

Reexamination Certificate

active

06310173

ABSTRACT:

The present invention relates to a batch process for producing polyamides from aminonitriles and water at elevated temperature and elevated pressure in the presence of a catalyst.
PRIOR ART
U.S. Pat. No. 4,629,776 describes a catalytic process for producing polyamides from &ohgr;-aminonitriles such as &ohgr;-amino-capronitrile (ACN). ACN is reacted with water in the presence of a catalytic amount of an oxidized sulfur compound as catalyst. Sulfuric acid is an example of the catalyst used.
U.S. Pat. No. 4,568,736 describes a similar catalytic process for producing polyamides. The catalyst used in this case is an oxygen-containing phosphorus compound, phosphoric acid or a phosphonic acid.
Complete removal of catalyst is practically not possible in either process. The presence of catalyst in the polymer can hinder the building of high molecular weight polymers and compromise later processing operations, for example spinning. Moreover, the level of volatiles in the polymers obtained is high, so that the polyamides are difficult to process.
EP-A-0 479 306 describes the production of polyamides from &ohgr;-aminonitriles. The &ohgr;-aminonitriles are reacted with water in the presence of an oxygen-containing phosphorus compound as catalyst. Once a reaction temperature from 200 to 260° C. has been obtained, ammonia and water are continuously removed by decompressing and at the same time water is continuously added, the pressure being selected within the range from 14 to 24×10
6
Pa (14-24 bar).
DE-A-43 39 648 relates to a process for producing caprolactam by reacting aminocarbonitriles with water in the liquid phase using heterogeneous catalysts. Suitable heterogeneous catalysts include acidic, basic or amphoteric oxides of the elements of main groups 2, 3 and 4 of the Periodic Table. Titanium dioxide can be used, for example. The catalyst is used in the form of extrudates, for example.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for producing polyamides from aminonitriles with improved hydrolysis of the reactants, especially of the acid amide groups, and improved molecular weight buildup. The catalyst used shall be very substantially removable from the reaction mixture and have high activity. In addition, the temperability of the polyamides obtained shall be improved.
DETAILED DESCRIPTION
We have found that this object is achieved according to the invention by a batch process for producing a polyamide by reaction of a mixture comprising at least one aminonitrile, and optionally monomers useful for polyamide production, with water, which comprises the following steps:
(1) reacting the mixture with water 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 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 the first gas phase is separated 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 water at a temperature from 150 to 370° C. and a pressure from 0.1 to 30×10
6
Pa to obtain a product mixture,
(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,
wherein step (1) is carried out in the presence of a Brönsted acid catalyst selected from a beta-zeolite catalyst, a sheet-silicate catalyst or a fixed bed catalyst consisting essentially of TiO
2
comprising from 70 to 100% by weight of anatase and from 0 to 30% by weight of rutile and in which up to 40% by weight of the titanium dioxide may be replaced by tungsten oxide, and steps (2) and (3) may be carried out in the presence of this catalyst.
Preferably, in the above process, in step (3), the gaseous or liquid phase comprising water is added in an amount from 50 to 1500 ml of water per 1 kg of first liquid or first solid phase or mixture of first liquid and first solid phase.
The present invention further provides a process for producing a polyamide by reaction of a mixture comprising at least one aminonitrile, and optionally monomers useful for polyamide production, with water, which comprises the following steps:
(1) reacting the mixture with water at a temperature from 90 to 400° C. and a pressure from 0.1 to 35×10
5
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 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 the first gas phase is separated from the first liquid or the first solid phase or from the mixture of first liquid and first solid phase, and
(3) postcondensing the first liquid or the first solid phase or the mixture of first liquid and first solid phase 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,
wherein step (1) is carried out in the presence of a Brönsted acid catalyst selected from a beta-zeolite catalyst, a sheet-silicate catalyst or a fixed bed catalyst consisting essentially of TiO
2
comprising from 70 to 100% by weight of anatase and from 0 to 30% by weight of rutile and in which up to 40% by weight of the titanium dioxide may be replaced by tungsten oxide, and step (2) may be carried out in the presence of this catalyst.
The principle of the process of the invention is described in DE-A-197 09 390, unpublished at the priority date of the present invention.
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;-Amino-nitrites are preferred, especially &ohgr;-aminoalkyl nitriles having from 4 to 12 carbon atoms, more preferably 4 to 9 carbon atoms, in the alkylene moiety, or an aminoalkyl-aryl nitrile having from 8 to 13 carbon atoms, preferred aminoalkylaryl nitrites being aminoalkylaryl nitrites 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-cyanohexane, 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 or branched or chain-lengthened polyamides are to be prepared, the following mixture is used instead of pure 6-am

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