Organic compounds -- part of the class 532-570 series – Organic compounds – Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
1999-10-28
2001-07-17
Kifle, Bruck (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Unsubstituted hydrocarbyl chain between the ring and the -c-...
Reexamination Certificate
active
06262259
ABSTRACT:
The present invention relates to the preparation of a lactam by cyclizing hydrolysis of the corresponding aminonitriles.
Aliphatic lactams, such as in particular epsilon-caprolactam, are base compounds for the preparation of polyamides (polyamide 6 from caprolactam).
One of the known means for preparing these lactams consists in carrying out a cyclizing hydrolysis of the corresponding aminonitriles, more particularly of unbranched aliphatic aminonitriles, by passing in the vapour phase with water over a solid catalyst.
Thus, U.S. Pat No. 2,357,484 describes a process for vapour phase lactam preparation, which consists in passing a mixture of water and aminonitrile over a dehydration catalyst, such as activated alumina, silica gel or boron phosphate.
U.S. Pat. No. 4,628,085 has provided a process for vapour phase lactam preparation, which consists in bringing an aliphatic or aromatic aminonitrile and water into contact with a silica-based catalyst, in the form of spherical particles having a BET surface greater than 250 m
2
/g and a mean pore diameter less than 20 nm, and generally in the presence of hydrogen and ammonia.
The catalysts used in the processes of the prior art can make it possible, if appropriate, to, obtain good selectivities towards lactam. On the other hand, their deactivation can also be fast, which constitutes a very great handicap in an industrial implementation of the said processes.
In addition, the process according to U.S. Pat. No. 4,628,085 uses a very complex reaction mixture, requiring, at the end of the reaction, separation and recycling operations which greatly complicate the said process.
The present invention provides new alumina catalysts which, while resulting in good selectivity in the reaction for conversion of aminonitriles to lactams, have a long lifetime and therefore require less frequent regeneration.
More precisely, the invention consists of a process for the preparation-of lactams by vapour phase reaction of an aliphatic aminonitrile of general formula (I):
N≡C—R—NH
2
(I)
in which R represents an alkylene radical having from 3 to 12 carbon atoms, with water in the presence of a solid catalyst, characterized in that the catalyst is an alumina having a specific surface, measured by the BET method, greater than or equal to 10 m
2
/g.
The alumina used in the process of the invention preferably has a specific surface equal to or less than 500 m
2
/g.
The most important among the aminonitriles of formula (I) are those which result in lactams which serve as starting material in the preparation of polyamides 4, 5, 6 and 10, that is to say those in the formula of which the symbol R represents a linear alkylene radical having 3, 4, 5 or 9 carbon atoms.
The preferred compound of formula (I) is 6-aminocapronitrile (or epsilon-aminocapronitrile), which results in caprolactam, the polymerization of which provides polyamide 6.
The aluminas which can be used in the present process are first of all aluminas having a specific surface greater than or equal to 10 m
2
/g and less than or equal to 280 m
2
/g, as well as a volume for the pores with a diameter greater than 500 angstroms which is greater than or equal to 10 ml/100 g.
The BET specific surface is a specific surface determined by nitrogen adsorption in accordance with ASTM standard D 3663-78 based on the Brunauer-Emmett-Teller method described in the periodical “The Journal of the American Society”, 60, 309 (1938).
The volume for the pores with a diameter greater than 500 Å represents the cumulative volume created by all the pores with a size greater than a diameter of 500 Å. This volume is measured by the mercury penetration technique, in which Kelvin's law is applied.
The aluminas of this first family preferably exhibit a volume for the pores with a diameter greater than 500 Å which is greater than or equal to 20 ml/100 g and more preferentially still greater than or equal to 30 ml/100 g.
The aluminas of this first family also preferably exhibit a specific surface greater than or equal to 50 m
2
/g.
The aluminas which-can be used in the present process are also aluminas having a specific surface greater than or equal to 50 m
2
/g and less than or equal to 280 m
2
/g, as well as a volumne for the pores with a diameter greater than 70 angstroms which is greater than or equal to 30 ml/100 g.
The aluminas of this second family preferably exhibit a volume for the pores with a diameter greater than 70 Å which is greater than or equal to 45 ml/100 g.
The aluminas of this second family also preferably exhibit a specific surface greater than or equal to 80 m
2
/g.
The aluminas which can be used in the present process are also aluminas having a specific surface greater than or equal to 280 m
2
/g and a total pore volume greater than or equal to 15 ml/100 g.
The aluminas of this third family preferably exhibit a total pore volume greater than or equal to 22 ml/100 g and more preferentially still greater than or equal to 30 ml/100 g.
The aluminas are also characterized by their acidity.
This acidity can be measured by the test of isomerization of 1-butene to 2-butene.
This test is based on the isomerization reaction of 1-butene to a mixture of cis-2-butene and trans-2-butene at a temperature T (T=400° C. in the present case).
The isomerization reaction is a thermodynamic equilibrium. Two constants may be defined:
the theoretical equilibrium constant Kth(T) determined by the calculation:
Kth
(
T
)
=
[
cis
-
2
-
butene
]
eq
+
[
trans
-
2
-
butene
]
eq
[
1
-
butene
]
eq
+
[
cis
-
2
-
butene
]
eq
+
[
trans
-
2
-
butene
]
eq
where [butene]eq represents the concentration of each of the isomers in equilibrium at the temperature T;
the true equilibrium constant K(T) determined by the result of the measurements:
K
(
T
)
=
[
cis
-
2
-
butene
]
+
[
trans
-
2
-
butene
]
[
1
-
butene
]
+
[
cis
-
2
-
butene
]
+
[
trans
-
2
-
butene
]
where [butene] represents the concentration of each of the isomers at the outlet of the reactor at the temperature T.
The isomerizing power A of the alumina is defined by the activity with respect to the equilibrium:
A
(
T
)
=
K
(
T
)
Kth
(
T
)
×
100
In practice, the test is carried out in a vapour phase reactor, operating in pulsed mode, into which 500 mg of ground alumina (particles of between 400 and 500 &mgr;m) are introduced. The alumina is conditioned for 2 hours at 250° C. under a helium stream with a flow rate of 2.5 liters/hour. The alumina is then brought to a temperature of 400° C. and 1 milliliter of 1-butene is injected into the helium flow upstream of the alumina. Analysis of the output gases is carried out by gas phase chromatography and makes it possible to measure the amounts of 1-butene and of cis- and trans-2-butene recovered.
This isomerizing power A is corrected for the isomerizing power obtained under the same conditions with the empty reactor. The corrected isomerizing power A
c
represents the acidity of the said aluminas.
When the alkali metal or alkaline-earth metal content present in the alumina is less than 60 mmol per 100 g of alumina, the higher the A
c
value, the greater the acidity of the alumina.
Generally, the aluminas are obtained by dehydration of gibbsite, of bayerite, of nordstrandite or of their various mixtures. Reference may be made, for example, to the Kirk-Othmer encyclopedia, volume 2, pages 291-297.
The aluminas used in the present process can be prepared by bringing a hydrated alumina, in finely divided form, into contact with a hot gas stream at a temperature of between 400° C. and 1000° C., then keeping the hydrate and the gases in contact for a period ranging from a fraction of a second up to 10 seconds and finally separating the partially dehydrated alumina and the hot gases. Reference may in particular
Cotting Marie-Christine
Gilbert Laurent
Laurain Nathalie
Nedez Christophe
Burns Doane Swecker & Mathis L.L.P.
Kifle Bruck
Rhoneapoulenc Fiber & Resin Intermediates
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