Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-08-16
2002-03-26
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, C528S328000, C528S332000, C528S335000, C528S336000
Reexamination Certificate
active
06362307
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to processes for producing polyamides from aminocarboxylic acid compounds, to the polyamides obtained and to the use thereof.
Polyamides can be produced not only from caprolactam but also, inter alia, from aminocapronitrile.
U.S. Pat. No. 2,245,129 describes a batchwise two-stage preparation of polycaprolactam from aminocapronitrile (“ACN”), and water at a temperature within the range from 150 to 300° C., governed by a specific temperature program as a function of the amount of water added, and a pressure of not more than 30 bar. The disadvantages of this process are the long reaction times (20 h in the first stage), the low viscosity of the resulting polycaprolactam and the high level of volatile bases (essentially primary acid amides) compared with a polycaprolactam produced from caprolactam.
U.S. Pat. No. 4,568,736 partly solves the problems described in U.S. Pat. No. 2,245,129 by the use of phosphorus- and sulphur-containing catalysts. The use of these catalysts improves the low space-time yield of the process described in U.S. Pat. No. 2,245,129. However, the level of volatile bases in all the products produced by this process is still too high, so that the polyamides are difficult to process and have a reduced carboxyl end group number. The stoichiometric discrepancy between the amino and carboxyl end groups in the products of the processes is responsible for their showing an insufficient degree of polymerization and a slow increase in molecular weight during tempering.
Furthermore, complete removal of the catalysts is virtually impossible, so that the chemical and physical behavior of the polymers produced using the catalysts, such as type and quantity of end groups or snap-off behavior during spinning, is adversely affected.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for producing polyamides without the disadvantages of the above processes. The process shall provide polyamides in high conversions, and the properties of the polyamides shall not be compromised by the presence of additional components which cannot be separated off.
We have found that this object is achieved by a process for producing polyamides by reacting aminocarboxylic acid compounds of the general formula I
H
2
N—(CH
2
)
m
—C(O)R
1
(I)
where R
1
is OH, O—C
1-12
-alkyl or NR
2
R
3
, where R
2
and R
3
are independently hydrogen, C
1-12
-alkyl or C
5-8
-cycloalkyl, and m is an integer from 3 to 12,
optionally in a mixture with aminonitriles and their hydrolysis products and optionally in the presence of water,
in a liquid phase at elevated pressure and elevated temperature in the presence of metal oxides as heterogeneous catalysts, the metal oxides being used in a form which permits mechanical removal from the reaction mixture and being removed from the reaction mixture during or after the polymerization.
In the process, the aminocarboxylic acid compounds or mixtures used may be obtained by complete or incomplete reaction of aminonitriles with water in a preceding stage. The proportion of aminocarboxylic acid compound(s) in the mixture to be polymerized is preferably not less than 75% by weight, particularly preferably not less than 95% by weight.
It was found that the reaction of aminocarboxylic acid compounds or mixtures comprising aminocarboxylic acid compounds and aminonitriles leads to polyamide in a faster and improved manner. The use of homogeneous catalysts which impair the product properties is avoided.
The starting materials used in the process of the invention are aminocarboxylic acid compounds of the general formula I
H
2
N—(CH
2
)
m
—C(O)R
1
(I)
where R
1
is —OH, —O—C
1-12
-alkyl or —NR
2
R
3
, where R
2
and R
3
are independently hydrogen, C
1-12
-alkyl or C
5-8
-cycloalkyl, and m is 3, 4, 5, 6. 7, 8, 9, 10, 11 or 12, optionally in a mixture with aminonitriles.
Particularly preferred aminocarboxylic acid compounds are those in which R
1
is OH, —O—C
1-4
-alkyl such as —O-methyl, —O-ethyl, —O-n-propyl, —O-i-propyl, —O-n-butyl, —O-sec-butyl, —O-tert-butyl and —NR
2
R
3
such as —NH
2
, —NHMe, —NHEt,—NMe
2
and —NEt
2
, and m is 5.
Very particular preference is given to 6-aminocaproic acid, methyl 6-aminocaproate, ethyl 6-aminocaproate, 6-amino(N-methyl)caproamide, 6-amino(N,N-dimethyl)-caproamide, 6-amino(N-ethyl)caproamide, 6-amino(N,N-diethyl)-capro-amide and 6-aminocaproamide.
The starting compounds are commercially available or preparable for example as described in EP-A-0 234 295 and Ind. Eng. Chem. Process Des. Dev. 17 (1978)9-16.
The aminonitrile used 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 nitriles having from 4 to 12 carbon atoms, more preferably 4 to 9 carbon atoms, in the alkylene moiety, or aminoalkylaryl nitriles having from 8 to 13 carbon atoms, preferred aminoalkylaryl nitriles being those which have an alkyl spacer 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. It is also possible to use mixtures of a plurality of aminonitriles.
The catalysts used for heterogeneous catalysis can be known metal oxides, such as zirconium oxide, aluminum oxide, magnesium oxide, cerium oxide, lanthanum oxide and preferably titanium dioxides, as well as beta zeolites and sheet-silicates for heterogeneous catalysis. Particular preference is given to titanium dioxide in the anatase polymorph. It was further found that silica gel, zeolites and doped metal oxides, the dopants being for example ruthenium, copper or fluoride, significantly improve the reaction of the starting materials mentioned. According to the invention, the heterogeneous catalyst has a macroscopic form which permits mechanical removal of the polymer melt from the catalyst, for example by means of sieves or filters. The invention proposes the use of catalyst in extrudate or granule form or in the form of a coating on packings and/or internals.
In another embodiment, the aminocarboxylic acid compounds are reacted with homogeneously dissolved acidic cocatalysts or a mixture of different catalytically active compounds in the presence of the abovementioned heterogeneous catalysts. Preferred cocatalysts for this purpose are acidic catalysts, such as the abovementioned carboxylic acids, terephthalic acid, adipic acid, propionic acid and isophthalic acid, or oxygen-containing phosphorus compounds, especially phosphoric acid, phosphorous acid, hypophosphorous acid, their alkali metal and alkaline earth metal salts and ammonium salts, or oxygen-containing sulphur compounds, especially sulphuric acid and sulphurous acid.
Preference is given to using a Brönsted acid catalyst selected from a beta zeolite catalyst, sheet-silicate catalyst or a titanium dioxide catalyst comprising from 70 to 100% by weight of anatase and from 0 to 30% by weight of rutile in which up to 40% by weight of the titanium dioxide may be replaced by tungsten oxide. The proportion of anatase in the titanium dioxide catalyst should be as high as possible. Preference is given to using a pure anatase catalyst. The catalyst preferably has a pore volume of from 0.1 to 5 ml/g, particularly preferably from 0.2 to 0.5 ml/g. The average pore diame
Hildebrandt Volker
Mohrschladt Ralf
BASF - Aktiengesellschaft
Hampton-Hightower P.
Keil & Weinkauf
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