Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2001-01-02
2002-02-12
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
Reexamination Certificate
active
06346641
ABSTRACT:
The present invention relates to a process for the coproduction of 6-aminocapronitrile and hexamethylenediamine starting from adiponitrile by
a) hydrogenating adiponitrile in the presence of a catalyst comprising an element of the eighth transition group as catalytically active component, to obtain a mixture comprising 6-aminocapronitrile, hexamethylenediamine, adiponitrile and high boilers,
b) distillatively removing hexamethylenediamine from the mixture comprising 6-aminocapronitrile, hexamethylenediamine, adiponitrile and high boilers, and either
c1) distillatively removing 6-aminocapronitrile, and then
d1) distillatively removing adiponitrile, or
c2) simultaneously distillatively removing 6-aminocapronitrile and adiponitrile into separate fractions,
characterized by base of column temperatures below 185° C. in steps d1) or c2).
It is known to hydrogenate adiponitrile in the presence of elements of the eighth transition group, especially in the presence of predominantly iron, cobalt, nickel, ruthenium or rhodium catalysts, solvents such as, for example, ammonia, amines or alcohols, and optionally additives such as, for example, inorganic bases to obtain mixtures comprising 6-aminocapronitrile, hexamethylenediamine and unconverted adiponitrile. The catalysts used are catalysts homogeneously dissolved in the liquid phase or fixed bed catalysts used as fixed bed or in suspension.
Iron catalysts, which are generally used as fixed bed catalysts in the liquid phase at high pressure, are described for example in DE 4235466, WO 96/20166, WO 96/20043 and DE 19636767. Cocatalysts are known for example from DE 954416, WO 96/20166 and DE 19636768. Nickel catalysts are used according to DE 848654 for example as supported catalysts (nickel on Al
2
O
3
), but in particular according for example to U.S. Pat. No. 2,762,835, WO 96/18603 and WO 97/10052 in the form of doped or undoped Raney nickel. Ruthenium fixed bed catalysts are known from U.S. Pat. No. 3,322,815, homogeneously dissolved ruthenium catalysts from WO 96/23802 and WO 96/23804. Rhodium catalysts, for example rhodium on magnesium oxide, are mentioned in U.S. Pat. No. 4,601,859 for example.
The partial hydrogenation of adiponitrile to form mixtures of 6-aminocapronitrile, hexamethylenediamine and unconverted adiponitrile is carried out in order that 6-aminocapronitrile and hexamethylenediamine may be obtained in a desired ratio which is adjustable through suitable choice of the reaction conditions. 6-Aminocapronitrile can be cyclized, for example according to U.S. Pat. No. 5,646,277, into caprolactam in the liquid phase in the presence of oxidic catalysts. Caprolactam is the precursor for nylon-6, and hexamethylenediamine is one of the two intermediates for manufacturing nylon-6,6.
DE-A 19548289 discloses a process for the coproduction of 6-aminocapronitrile and hexamethylenediamine by hydrogenation of adiponitrile in the presence of a catalyst to partial conversion, the removal of hexamethylenediamine and 6-aminocapronitrile from the mixture and conversion of 6-aminocapronitrile into caprolactam and also recycling into the process of a portion consisting essentially of adiponitrile.
The disadvantage with these processes is that the adiponitrile recovered in the course of the workup of the reaction effluent contains undesirable by-products, especially amines, such as 1-amino-2-cyanocyclopentene (ACCPE), 2-(5-cyanopentylamino)tetrahydroazepine (CPATHA) and bishexamethylentriamine (BHMTA).
According to the processes described, the by-products are impossible to separate from adiponitrile by distillation because of the formation of azeotropes or quasi-azeotropes. The result is, especially if the adiponitrile is recycled, a buildup of the by-products in the overall process.
Recycled ACCPE may become hydrogenated to 2-aminomethyl-cyclopentylamine (AMCPA), which is an impurity when the product of value is hexamethylenediamine. U.S. Pat. No. 3,696,153 discloses that AMCPA is very difficult to separate from hexamethylenediamine.
DE 19636766 discloses admixing the adiponitrile to be recycled with from 0.01 to 10% by weight of an acid, based on adiponitrile, or an acidic ion exchanger, to remove the adiponitrile from this mixture and to recycle it into the hydrogenation reactor. The addition of acid serves to neutralize nitrogenous basic by-products. The disadvantage with this method is the formation of salts, which have to be removed from the process and disposed of. This necessitates an additional process step.
It is an object of the present invention to provide a process for removing adiponitrile from an adiponitrile partial hydrogenation product mixture comprising adiponitrile, hexamethylenediamine, 6-aminocapronitrile and components having a boiling point above that of adiponitrile (“high boilers”) in a technically simple and economical manner while avoiding the disadvantages mentioned and recovering very pure adiponitrile.
We have found that this object is achieved by the process defined at the beginning.
The partial hydrogenation of adiponitrile can be carried out according to one of the known processes, for example according to one of the aforementioned processes described in 46018591, U.S. Pat. Nos. 2,762,835, 2,208,598, DE-A 848654, DE-A 9544161, WO 96/18603, WO 97/10052, DE-A 4235466 or WO 92/21650, by, in general, performing the hydrogenation in the presence of an element of the eighth transition group or mixtures thereof, such as nickel, cobalt, iron, ruthenium or rhodium catalysts. The catalysts can be used as homogeneously dissolved catalysts or as suspended or fixed bed supported or solid catalysts. Examples of suitable catalyst supports are aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide, activated carbons and spinels. Examples of suitable solid catalysts are Raney nickel and Raney cobalt, which may each be doped with further metals.
The catalyst space velocity chosen is typically within the range from 0.05 to 10 kg, preferably from 0.1 to 5 kg, of adiponitrile/l of cat. x h.
The hydrogenation is generally carried out at a temperature from 20 to 220° C., preferably within the range from 50 to 150° C., and at hydrogen partial pressures from 0.1 to 40 MPa, preferably from 0.5 to 30 MPa.
The hydrogenation is preferably carried out in the presence of a solvent such as ammonia, amines or alcohols, especially ammonia. The ammonia quantity chosen is generally within the range from 0.1 to 10 kg, preferably within the range from 0.5 to 3 kg, of ammonia/kg of adiponitrile.
The molar ratio of 6-aminocapronitrile to hexamethylenediamine and hence the molar ratio of caprolactam to hexamethylenediamine can be controlled by the particular adiponitrile conversion which is chosen. Preference is given to using adiponitrile conversions within the range from 10 to 90%, preferably within the range from 30 to 80%, in order that high 6-aminocapronitrile selectivities may be obtained.
In general, the sum total of 6-aminocapronitrile and hexamethylenediamine is within the range from 95 to 99%, depending on catalyst and reaction conditions, and hexamethyleneimine is the most significant by-product in terms of volume.
The catalysts used are preferably nickel, ruthenium, rhodium, iron and cobalt compounds, preferably those of the Raney type, especially Raney nickel and Raney cobalt. The catalysts can also be used in the form of supported catalysts, in which case suitable supports include for example aluminum oxide, silicon dioxide, zinc oxide, activated carbon or titanium dioxide (S. Appl. Het. Cat., 1987, 106-122; Catalysis, Vol. 4 (1981) 1-30). Raney nickel is particularly preferred.
The nickel, ruthenium, rhodium, iron and cobalt catalysts can advantageously be modified with metals of the groups VIB (cr, Mo, W) and VIII (Fe, Ru, Os, Co (only in the case of nickel), Rh, Ir, Pd, Pt) of the periodic table of the elements. According to observations to date, for example according to DE-A 2260978; Bull. Soc. Chem. 13 (1946) 208, the use of especially modified Raney nickel catalysts, for example chromium- and/or iron-modified, leads t
Achhammer Günther
Ansmann Andreas
Bassler Peter
Fischer Rolf
Luyken Hermann
McKane Joseph K.
Murray Joseph
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