Note: Descriptions are shown in the official language in which they were submitted.
CA 02337858 2001-O1-16
0050/49207
IMPROVED METfiOD F17R SIMULTANEOUS PRODUCTION OF 6-AMINOCAPRONITRILE
AND HEXAMETHYLENEDIAMINE
Specification
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
cl) distillatively removing 6-aminocapronitrile, and then
dl) 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
dl) 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.
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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 A1203), but in
particular according for example to US 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 US 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 US 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 US
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.
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Recycled ACCPE may become hydrogenated to 2-aminomethyl-
cyclopentylamine (AMCPA), which is an impurity when the product
of value is hexamethylenediamine. US-A 3696153 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, US
2,762,835, US 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/1 of cat. x h.
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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 to higher 6-aminocapronitrile selectivities.
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The amount of catalyst is generally chosen so that the cobalt,
ruthenium, rhodium, iron or nickel quantity is within the range
from 1 to 50% by weight, preferably within the range from 5 to
20% by weight, based on the amount of dinitrile used.
5
The catalysts can be used as fixed bed catalysts in upflow or
downflow mode or as suspension catalysts.
In a further preferred embodiment, adiponitrile is partially
hydrogenated to 6-aminocapronitrile at elevated temperature and
elevated pressure in the presence of a solvent and of a catalyst
by using a catalyst comprising
1) a compound based on a metal selected from the group
consisting of nickel, cobalt, iron, ruthenium and rhodium,
ii) from 0.01 to 25% by weight, preferably from 0.1 to 5% by
weight, based on a), of a promoter based on a metal selected
from the group consisting of palladium, platinum, iridium,
osmium, copper, silver, gold, chromium, molybdenum, tungsten,
manganese, rhenium, zinc, cadmium, lead, aluminum, tin,
phosphorus, arsenic, antimony, bismuth and rare earth metals,
and also
iii)from 0 to 5% by weight, preferably from 0.1 to 3% by weight,
based on i), of a compound based on an alkali metal or an
alkaline earth metal.
Preferred catalysts are those in which component i) comprises at
least one compound based on a metal selected from the group
consisting of nickel, cobalt and iron in an amount within the
range from 10 to 95% by weight, and also ruthenium and/or rhodium
In an amount within the range from 0.1 to 5% by weight, each
based on the sum total of components i) to iii), component ii)
comprises at least one promoter based on a metal selected from
the group consisting of silver, copper, manganese, rhenium, lead
and phosphorus in an amount within the range from 0.1 to 5% by
weight, based on i), and component iii) comprises at least one
compound based on the alkali metals and alkaline earth metals
selected from the group consisting of lithium, sodium, potassium,
cesium, magnesium and calcium in an amount within the range from
0.1 to 5% by weight.
Particularly preferred catalysts are those comprising
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i) a compound based on iron such as iron oxide, and
ii) from 0 to 5~ by weight based on i) of a promoter based on an
element or 2, 3, 4, 5 or 6 elements selected from the group
consisting of aluminum, silicon, zirconium, vanadium,
manganese and titanium, and also
iii)from 0 to 5~ by weight, preferably from 0.1 to 3~ by weight,
in particular from 0.1 to 5~ by weight, based on i) of a
compound based on an alkali or alkaline earth metal,
preferably selected from the group consisting of lithium,
sodium, potassium, rubidium, cesium, magnesium and calcium.
The preferred catalysts may be solid or supported catalysts.
Suitable support materials include for example porous oxides such
as aluminum oxide, silicon dioxide, alumosilicates, lanthanum
oxide, titanium dioxide, zirconium dioxide, magnesium oxide, zinc
oxide and zeolites and also activated carbon or mixtures thereof.
They are generally prepared by precipitating precursors of
components a) together with precursors of the promoters,
components ii), and if desired with precursors of components iii)
in the presence or absence of support materials (depending on
which type of catalyst is desired), if desired processing the
resulting catalyst precursor into extrudates or tablets, drying
and subsequently calcining. Supported catalysts are generally
also obtainable by saturating the support with a solution of
components i), ii) and if desired iii), the individual components
being added simultaneously or in succession, or by spraying the
components i), ii) and if desired iii) onto the support in a
conventional manner.
Suitable precursors for components i) generally include readily
water-soluble salts of the aforementioned metals such as
nitrates, chlorides, acetates, formates and sulfates, preferably
nitrates. Suitable precursors for component ii) generally include
readily water-soluble salts or complexes of the aforementioned
metals such as nitrates, chlorides, acetates, formates and
sulfates and also especially hexachloroplatinate, preferably
nitrates and hexachloroplatinate.
Suitable precursors for components iii) generally include readily
water-soluble salts of the aforementioned alkali metals and
alkaline earth metals such as hydroxides, carbonates, nitrates,
chlorides, acetates, formates and sulfates, preferably hydroxides
and carbonates.
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They are generally precipitated from aqueous solutions,
selectively by addition of precipitants, by changing the pH or by
changing the temperature.
The catalyst prematerial thus obtained is usually dried,
generally at from 80 to 150 °C, preferably at from 80 to 120 °C.
Calcination is customarily carried out at from 150 to 500 °C,
preferably at from 200 to 450 °C, in a gas stream comprising air
or nitrogen.
After calcination, the catalyst material obtained is generally
activated by exposing it to a reducing atmosphere, for example by
exposing it for from 2 to 24 hours to a hydrogen atmosphere or to
a gas mixture comprising hydrogen and an inert gas, such as
nitrogen, at from 80 to 250 °C, preferably at from 80 to 180 °C,
in the case of catalysts based on ruthenium and rhodium as
components i), or at from 200 to 500 °C, preferably at from 250 to
400 °C, in the case of catalysts based on one of the metals
selected from the group consisting of nickel, cobalt and iron as
component I). The catalyst space velocity here is preferably
200 1/1 of catalyst.
Advantageously, the activation of the catalyst is carried out
directly in the synthesis reactor, since this customarily
dispenses with an otherwise necessary intermediary step, i.e.,
the passivation of the surface, customarily at from 20 to 80 °C,
preferably at from 25 to 35 °C, by means of oxygen/nitrogen
mixtures such as air. The activation of passivated catalysts is
then preferably carried out in the synthesis reactor at from 180
to 500 °C, preferably at from 200 to 350 °C, in an atmosphere
comprising hydrogen.
The catalysts may be used in a reactor R1 as fixed bed catalysts
in upflow or downflow mode or as suspension catalysts (see
Figure 1).
If the reaction is carried out in a suspension, it is customary
to choose temperatures within the range from 40 to 150 °C,
preferably within the range from 50 to 100 °C, particularly
preferably within the range from 60 to 90 °C; the pressure is
generally chosen within the range from 2 to 30 MPa, preferably
within the range from 3 to 30 MPa, particularly preferably within
the range from 4 to 9 MPa. The residence times are essentially
dependent on the desired yield, selectivity and the desired
conversion; the residence time is customarily chosen so as to
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maximize the yield, for example within the range from 50 to 275
minutes, preferably within the range from 70 to 200 minutes.
In the suspension procedure, it is advantageously possible to use
in particular liquid diluents, advantageously primary, secondary
or tertiary amines, such as monoamines, diamines and triamines
having from 1 to 6 carbon atoms, for example trimethylamine,
triethylamine, tripropylamine and tributylamine, or alcohols,
especially methanol and ethanol, preferably ammonia, or mixtures
thereof. It is advantageous to choose an adiponitrile
concentration within the range from 10 to 90~ by weight,
preferably within the range from 30 to 80g by weight,
particularly preferably within the range from 40 to 70o by
weight, based on the sum total of adiponitrile and diluent.
The amount of catalyst is generally chosen so that the catalyst
quantity is within the range from 1 to 50% by weight, preferably
within the range from 5 to 20o by weight, based on the amount of
adiponitrile used.
The partial hydrogenation can also be carried out batchwise or
continuously over a fixed bed catalyst in the downflow or upflow
mode, in which case it is customary to choose a temperature
within the range from 20 to 150 °C, preferably within the range
from 30 to 90 °C, and a pressure which is generally within the
range from 2 to 40 MPa, preferably within the range from 3 to
MPa.
30 It is advantageously possible to use in particular liquid
diluents, advantageously primary, secondary or tertiary amines,
such as monoamines, diamines and triamines having from 1 to 6
carbon atoms, for example trimethylamine, triethylamine,
tripropylamine and tributylamine, or alcohols, especially
methanol and ethanol, preferably ammonia, or mixtures thereof.
In a preferred embodiment, ammonia is used within the range from
1 to 10 g, preferably from 2 to 6 g, per g of adiponitrile. It is
preferable to employ for this a catalyst space velocity within
the range from 0.1 to 2.0 kg, preferably within the range from
0.3 to 1.0 kg, of adiponitrile/1 x h. Here, too, the conversion
and hence the selectivity can be controlled by changing the
residence time.
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It is advantageous to add basic additives, especially hydroxides,
carbonates or alkoxides of alkali or alkaline earth metals or
mixtures of such compounds, in the hydrogenation of step a).
If a diluent was added in step a), it may advantageously be
removed between step a) and step b) in a conventional manner,
preferably by distillation, and be reused, for example in
step a).
The hydrogenation effluent of the present invention can be worked
up in two sequences of steps (see Figures 1 and 2).
The reaction effluent initially has hexamethylenediamine removed
from it together with the by-product hexamethyleneimine
(step b)). This can take place in two or more columns, preferably
one column (K 1).
In a preferred embodiment, the base of column temperature in step
b) should be below 185°C, preferably below 180°C, but the low
vapor pressure of the compounds to be separated means that the
base of column temperature should not be less than 100°C,
preferably not less than 130°C. The pressures at the base of the
column should advantageously be within the range from 0.1 to 100,
especially from 5 to 40, mbar. The residence times of the bottom
product in the distillation of step b) should preferably be
within the range from 1 to 60, especially 5 to 15, minutes.
The bottom product obtained from the distillation of step b) can
be worked up in two alternative ways, step sequence cl) and dl)
or step c2).
According to step c2 (Figure 1), the bottom product is fed into a
column K 2, where 6-aminocapronitrile is removed overhead,
adiponitrile is removed in a sidestream takeoff and high boilers
(HS) are removed via the bottom product.
The base of column temperature in step c2) of the present
invention is below 185°C, preferably below 180°C, but the low
vapor pressure of the compounds to be separated means that the
base of column temperature should not be less than 100°C,
preferably not less than 130°C. The pressures at the base of the
column should advantageously be within the range from 0.1 to 100,
especially from 5 to 40, mbar. The residence times of the bottom
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product in the distillation of step c2) should preferably be
within the range from 1 to 60, especially 5 to 15, minutes.
In step sequence cl)/dl) (Figure 2), the bottom product is fed
5 into a column K 2a, in which the 6-aminocapronitrile is
distillatively removed overhead (step cl)), the bottom product is
fed into a column K 2b, where adiponitrile is removed
distillatively overhead (step dl)) and high boilers (HS) are
removed via the bottom product.
In a preferred embodiment, the base of column temperature in step
cl) should be below 185°C, preferably below 180°C, but the low
vapor pressure of the compounds to be separated means that the
base of column temperature should not be less than 100°C,
preferably not less than 130°C. The pressures at the base of the
column should advantageously be within the range from 0.1 to 100,
especially from 5 to 40, mbar. The residence times of the bottom
product in the distillation of step cl) should preferably be
within the range from 1 to 60, especially 5 to 15, minutes.
The base of column temperature in step dl) of the present
invention is below 185°C, preferably below 180°C, but the low
vapor pressure of the compounds to be separated means that the
base of column temperature should not be less than 100°C,
preferably not less than 130°C. The pressures at the base of the
column should advantageously be within the range from 0.1 to 100,
especially from 5 to 40, mbar. The residence times of the bottom
product in the distillation of step dl) should preferably be
within the range from 1 to 60, especially 5 to 15, minutes.
To further reduce the level of by-products in the recovered
adiponitrile, the process of the present invention makes it
advantageously possible to feed an organic or inorganic acid
batchwise or preferably continuously into the bottom region of
the column K 2b or for the adiponitrile obtained downstream of
columns K 2 or K 2b to be purified, batchwise or preferably
continuously, with an organic or inorganic acid.
The adiponitrile obtained by either alternative may
advantageously be used in the partial hydrogenation to form
6-aminocapronitrile and hexamethylenediamine, for example by
recycling into step a) of the process of the invention, or into a
process for complete hydrogenation to hexamethylenediamine.
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Surprisingly, recycling the adiponitrile recovered by the process
of the present invention into the partial hydrogenation process
was found to lead to considerable advantages in the
hydrogenation, the distillative purification of
hexamethylenediamine and the onstream time of the hydrogenation
catalyst because the present invention has reduced the level of
1-amino-2-cyanocyclopentene in the recycled adiponitrile.
Example 1:
a) Preparation of an iron hydrogenation catalyst
The partial hydrogenation of adiponitrile to 6-aminocapronitrile
and hexamethylenediamine was carried out using an iron catalyst
which was based on a magnetite ore and prepared according to
Example 2 a) of DE 19636767. The particle size fraction used
ranged from 3 to 5 mm.
b) Partial hydrogenation of adiponitrile
A tubular reactor (180 cm in length and 30 mm in internal
diameter) was packed with 720 ml (1630 g) of the catalyst
material prepared according to a) and reduced in a 500 standard
1/h hydrogen stream under atmospheric pressure. The temperature
was raised from 30 °C to 340 °C over 24 hours and then
maintained
at 340 °C for 72 hours.
After the temperature was lowered, the reactor was fed at 250 bar
and 90 °C feed temperature with 330 g/h of ADN, 1200 g/h of
ammonia and 140 standard 1/h of hydrogen.
The hydrogenation was operated for 1500 hours under the stated
conditions. Throughout the entire duration of the run, an ADN
conversion of 60o gave a constant total selectivity (sum total of
the selectivities of 6-aminocapronitrile and hexamethylene-
diamine) of 990. The 6-aminocapronitrile selectivity decreased
from 50% to 48.50 in the course of the run.
c) Workup of hydrogenation effluent
Hydrogenation effluents were collected during the run for the
workup, which was carried out batchwise.
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First, ammonia was distilled out of the effluents overhead in a
column having 20 theoretical plates. The bottom product obtained
was a mixture which, according to analysis by gas chromatography,
was 30 mold 6-aminocapronitrile, 39 mold adiponitrile and 30 mold
hexamethylenediamine. The most significant by-product by volume
was hexamethyleneimine.
On processing 1000 g of the bottom product in the same column,
296 g of hexamethylenediamine were removed overhead at a base of
column temperature of 180°C and found to contain about 0.5~ by
weight of hexamethyleneimine.
695 g of the bottom product obtained were distilled in a
continuously operated column in such a way as to remove around
305 g of 6-aminocapronitrile overhead, 380 g of adiponitrile via
a sidestream takeoff and 10 g of adiponitrile-comprising high
boilers as bottom product. The distillation was carried out at a
top of column pressure of from 20 to 40 mbar.
The base of column temperature was varied by varying the top of
column pressure. The reflux ratio was 2 . 1. Table 1 shows the
dependence of the 1-amino-2-cyanocyclopentene quantity in the
adiponitrile of the sidestream takeoff as a function of the base
of column temperature.
Table 1
Base of column ACCPE
temperature
i
(C)
(PPm)
198.5 12300
184.9 11300
184.2 8900
1822 3600
182.0 3200
180.9 2700
180.5 2700
180.0 2800
178.2 2800
1) ppm of 1-amino-2-cyanocyclopentene based on adiponitrile
obtained in sidestream takeoff
