Note: Descriptions are shown in the official language in which they were submitted.
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USE OF MODIFIERS IN A DINITRILE HYDROGENATION PROCESS AT HIGH PRESSURES
FIELD OF THE INVENTION
The present invention concerns the hydrogenation of aliphatic
s dinitriles to produce diamines and/or aminonitriles, e.g. adiponitrile to
produce hexamethylenediamine and/or 6-aminocapronitrile.
BACKGROUND OF THE INVENTION
Dinitriles are common feedstocks to the chemical, pharmaceutical,
and agrochemical industries. Through hydrogenation they can be
io converted to diamines and/or aminonitriles, which are used in or as
polymer intermediates, surfactants, chelatirig agents, and chemical
synthesis intermediates. As a particular example, adiponitrile can be
converted to 6-aminocapronitrile and/or hexamethylenediamine by
.hydrogenation. Hexamethylenediarnine is an intermediate in the
is pr~duc~oon.of'f~yldi~"66.'"0-~=~di:nin~o~aproriitrsoe'~a~ii~e use'd'~a~
ate'
,;;,
intermediate in_the production of Nvlon 6. ..
Traditional methods of producing hexamethylenediamine include
hydrogenation of adiponitrile over a reduced iron oxide or cobalt oxide
catalyst at high pressures and temperatures. US6110856 describes the
2o use of cobalt and iron based catalysts in a process for the ~hydrogenafiion
of adiponitrile to a mixture of aminocapronitrile and '
hexamethylenediamine. The process does not produce aminocapronitrile
with high selectivity, yielding 37% aminocapronitrile at 75% adiponitrile
conversion. Low-pressure processes are known for the simultaneous'
as production of aminocapronitrile and hexamethylenediamine. US5,151,543
describes the hydrogenation of dinitriles, including adiponitrile in the
presence of a solvent. US6,258,745, US6,566,297, US6,376,714,
W099/47492 and W003/000651A2 all describe the hydrogenation of
dinitriles to aminonitriles in the presence of selectifying agents for low
3o pressure reactions, i.e. less than about 13.89 MPa (2000 psig).
For simultaneous production of aminonitrile and diamines, it would
be advantageous to employ a commercial equipment that is currently used
for hexamethylenediamine production and that operates at high pressures,
i.e. greater than 13.89 MPa (2000 psig). Additionally, it would be
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adv~tx~~~~eous~ to oipe~°'f~ese pfo~eas~I;i'h ~orre~~ea~etevti~~ity,~fo
aminocapronitrile than is possible under operating conditions taught in the
art.
SUMMARY OF THE INVENTION
The present invention is, therefore, a process of
hydrogenating a dinitrile for the simultaneous production of
aminocapronitrile and hexamethylenediamine, said process comprising:
treating the dinitrile with hydrogen in the present of a'catalyst and a
modifier at a pressure at least about 15.27 MPa (2200 psig), wherein said
1o catalyst comprises an element selected from the group consisting of~Fe,
Ru, Co, and Ni and said modifier is at least one member selected from the
group consisting of quaternary ammonium hydroxides, quaternary
ammonium cyanides, quaternary ammonium fluorides, quaternary
ammonium thiocyanides, quaternary phosphonium, hydroxides, carbon
is monoxide, and hydrogen cyanide.
DETAILED DESCRIPTION OF THE INVENTION
In~thev present. invention, an aliphatic or alicyclic dinitrile can be
hydrogenated to a diamine or a mixture of a diamine and an aminonitrile
using a catalyst at pressures greater than 15.27 MPa (2200 psig). For
2o example, adiponitrile can be hydrogenated to hexamethylenediamine or a
mixture of hexamethylenediamine and 6-aminocapronitrile. The process
employs one or more modifiers to maintain or improve the selectivity of the
process for the production of aminonitrile. These modifiers may react with
the catalyst surface or may modify the reactivity of the dinitrile and/or
2s aminonitrile. The modifiers may comprise quaternary ammonium
hydroxide, cyanide, fluoride or thiocyanide salts, or quaternary
phosphonium hydroxide salts or carbon monoxide or hydrogen cyanide.
Notably, the modifiers of the present invention are not expected to build-up
in the incinerator firebricks, nor are they expected to require disposal via
3o deep-wells, when they or their decomposition products are removed from
the crude product obtained from the said hydrogenation of dinitrile.
Suitable aliphatic or alicyclic dinitriles, for use herein, have the
general formula R(CN)2, wherein R~is a saturated hydrocarbylene group.
A saturated hydrocarbylene group~contains carbon and hydrogen atoms in
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branched or straight chains or rings and does not contain a double or triple
bond between any pair of carbon atoms. Preferred hydrocarbylene groups
contain from 2 to 25, more preferably 2 to 15, and most preferably 2 to 10
carbon atoms per group. In other words, preferred dinitriles contain from 4
s to 27, more preferably 4 to about 17, and most preferably 4 to 12, carbon
atoms per dinitrile molecule. The preferred type of hydrocarbylene group
is a linear alkylene group.
Examples of suitable dinitriles include, but are not limited to,
adiponitrile; methylglutaronitrile; succinonitrile; glutaronitrile; alpha,
io omega-heptanedinitrile; alpha, omega-octanedinitrile, alpha, omega
decanedinitrile, alpha, omega-dodecanedinitrile; and combinations of two
or more thereof. The preferred embodiment is adiponitrile (ADN).
The catalyst in the process is a hydrogenation catalyst suitable for
hydrogenating a dinitrile to a diamine or a mixture of diamine and
is aminonifirile. Preferred are cafalysts~based on the elements iron, cobalt-
nickel,,.or: ruth_e.nium and.combinations._there_of in. which the said
elements,.
can exist as metals or their~compounds. Most preferred is a catalyst
comprising iron. The catalytic element may comprise about 1 to 99 % of
the total catalyst weight, preferably about 50 to 85 wt%. The catalyst may
20 further comprise one or more promoters selected from the group
consisting of aluminum, silicon, titanium, vanadium, magnesium,
chromium, sodium,, potassium and manganese. The promoters may be
present in concentrations up to about 15% based on the total weight of the
catalyst, preferably. about 0.05 to 2 wt%.
2s While the degree of beneficial effects of this invention may vary with
the structure of the dinitrile, the identity of the catalytic element, and the
identity of the modifier, it is important to realize that even small
improvements in selectivity can have large economic impact for large-
scale industrial processes.
3o The catalytic element can also be supported on an inorganic
support~such as...~lum~na, magnesium oxide, and combinations thereof.
The element can be supported on an inorganic support by any means
known to one skilled in the art such as, for example, impregnation,
coprecipitation, ion exchange, and combinations of two or more thereof. If
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the catalytic element is supported on an inorganic support or is a
component of an alloy or a solid solution, the catalytic element is generally
present in the range of about 0.1 to about 60 wt% and preferably about 1
to about 50 weight percent, based on the total catalyst weight.
The catalyst can be present in any appropriate physical shape or
form. It can be in fluidizable forms, extrudates, tablets, spheres, or
combinations of two or more thereof. When employing the process using
a fixed bed catalyst, the catalyst is in the form of granules having a
particle
size in the range of about 0.76 to 10.2 mm (0.03 to 0.40 inch). When
io employing the process using a slurry-phase catalyst, the catalyst is in
finely divided form, preferably less than about 100 Nm in size, most
preferred range being about 20 to 75 Nm.
The molar ratio of catalyst.to. dinitrile can be any ratio as long as the
ratio can catalyze the selective hydrogenation of a dinitrile. The weight
us ratio of catalyst to dinitrile i~:g~ners~ly in the range: ~f frort~about
O:,OD'I~.1 ~1,,~~~~
to about 1:1, preferably about OJ001:1 to about 0.5:1.
The modifiers of the present invention can be selected from the
group consisting of quaternary ammonium hydroxide, quaternary
ammonium cyanide, quaternary ammonium fluoride, quaternary
2o ammonium thiocyanides, quarternary phosphonium hydroxide,~carbon
monoxide and hydrogen cyanide. The term quaternary describes a
nitrogen or phosphorous atom with four bonds to it and bearing a formal
charge of +1. The ammonium ion (NH4+) and tetraalkylammonium ions
are included within the definition of quaternary ammonium. More than one
2s modifier can be used in the reaction. Examples of suitable modifiers are
tetramethylammonium hydroxide, tetrabutylammonium cyanide,
tetraethylammonium fluoride, tetrabutylammonium thiocyanide and
tetrabutylphosphonium hydroxide. Preferred modifiers are quaternary
ammonium hydroxide and quaternary ammonium cyanide. Examples~of
3o suitable tetraalkylammonium hydroxide compounds are
tetramethylammonium hydroxide, tetraethylammonium hydroxide,
tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.
Examples of suitable tetraalkylammonium cyanide compounds are
tetramethylammonium cyanide, tetraethylammonium cyanide and
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tetrabutylammonium cyanide. It should be noted that various hydrated
forms such as, for example, tetramethylammonium hydroxide
pentahydrate, are included within the meaning of tetraalkylammonium
hydroxide and tetraalkylphosphonium hydroxide.
The hydrogenation reaction can be conducted at a temperature
about 50 to 250°C and preferably about 90 to 180°C and at a
pressure
about 15.27 to 55.26 MPa (2200 to 8000 psig) total pressure with
hydrogen and preferably at about 20.78 to 34.58 MPa (3000 to 5000 psig).
In a preferred mode of operation, the process~is conducted continuously in
io a continuous stirred tank reactor (CSTR), a plug flow reactor (PFR); a
slurry bubble column reactor (SBCR),~or a trickle bed reactor. A
continuous stirred tank reactor, also known as a back-mixed reactor, is a
vessel in which the reactants are added in a continuous fashion and a flow
of product stream is continuously withdrawn from it. There is adequate
t~s <rvii~ing in tlie.>vesseb'~rovid~~i ~b:~~a :rnia~i<nyzd~5ice;.~ e.ig:;;.a
~echa~icar
agitator,ao that.~the composition.inside.the reactor is uniform and is the.
same as that in the product stream withdrawn. A plug flow reactor is a
tubular reactor in which the reactants' are added in a continuous fashion in
one end of the tubular reactor and the product is withdrawn in a
2o continuous fashion from the other end of the tube. There is no back-
mixing, i.e: the composition inside the reactor tube is not uniform. It is
possible to incorporate backmixing in PFRs by recycling a part of the
product flow back to the inlet of the reactor. It is also possible to achieve
plug flow reactor behavior by using multiple CSTRs is series. A slurry
2s bubble column reactor is a vessel, in which liquid reactants and gas are
continuously fed to the bottom of the reactor, while product is continuously
withdrawn from the top of the reactor. The gas is present in the reactor as
bubbles, which rise and simultaneously provide mixing for a solid
powdered catalyst (20 to 200 pm average particle sizes). The catalyst
3o may be removed continuously with the product and added continuously by
addition with the liquid feed. A trickle bed reactor is a tubular reactor in
which the catalyst is fixed while the reactants are added at the top of the
reactor and flow to the bottom where the product is continuously
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withdrawn. Gaseous reactants may flow cocurrently with the liquid or may
flow countercurrently from the bottom to the top of the reactor.
The preference for reactor is not meant to limit the invention, which
can also be conducted in batch mode.
The process can be operated in the absence or presence of a
solvent. In this invention, a solvent is defined as a substance that is added
to a reaction mixture and that serves to solvate one or more reaction
components, increases the volume of the reaction mixture, provides a
medium for transferring (or removing) the heat of reaction, and is either
to not incorporated in the final product or does not alter the properties of
the
final product. While not comprehensive, a list of solvents includes
ammonia; amines such as triethylamine; alcohols such as methanol,
ethanol; propanol, and butanol; ethers such as tetrahydrofuran and
dioxane; amides such diethylacetamide and N-methylpyrolidinone; and
S 1; J .,g t.~ ~,.= 3 W~,f :, p. ~. " 'k
is °este~~~°sucn~~ ~t~~l~ acei~~~~a1"nd ditzieth~ilaidip~te ~'he
'pr~fierred 's~iv~~t~i
ammonia., ~:~The solvent can. be present in. the. reaction mixture. in,
about~20.
to 90% by weight, preferably about ~30 to 50%~.
The modifier and ainitrile may be introduced to a reactor, which
contains catalyst, separately or as a premixed solution with a diamine, an
2o aminonitrile, water, a solvent or any combination thereof. The modifier
can be added in a weight ratio to dinitrile from about 1:5000 to 1:30,
preferably from about 1:2000 to 1:500.
The yields of diamine and/or aminonitrile, e.g.
hexamethylenediamine and/or 6-aminocapronitrile; depend on operating
2s conditions including temperature; pressure, hydrogen flow rate, amount
and kind of catalyst, amount of modifier and space velocity and the like.'
For the purpose of this invention, the term "space velocity" is defined as
the unit weight of dinitrile fed into the reactor per hour, per unit weight of
the catalyst. Typically, the dinitrile should be added to the reactor such
3o that the space velocity of the dinitrile is within the range of about 0.5
to 20
h''. Most preferred space velocities may be readily determined by those
skilled in the art using conventional techniques.
While not meant to limit the invention by any theory, it is possible
that the modifier reacts with the el~ement(s) of the catalyst forming a,
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modifier/catalytic element complex. The resulting~complex may contain
the Group VIII element in its metallic state or perhaps in an oxidized state.
The reaction of modifier with the catalytic element may be irreversible but
more likely is a reversible equilibrium reaction. The interaction of the
modifier with the catalyst may alter the reactivity of the catalyst, improve
the selectivity for aminonitrile production, suppress secondary amine
oligomer formation and, perhaps, increase the lifetime of the catalyst.
The catalyst and modifier can be separately introduced into a
reactor to contact the.dinitrile; however, the catalyst may be precontacted
io with the modifier. This may be done in water and/or a solvent such as, for
example, an alcohol, ether, ester, ammonia, or combinations of two or
more thereof.
The molar ratio of hydrogen to dinitrile is not critical as long as
sufficient hydrogen is present to produce an aminonitriie and/or a diamine,
;i~~~ e:g fi-ahnino~~~prc~rDat~iIWa~id/h~fh~xa~n~ethylenddiamine
°Hyd~oger~vs~
generally used in.excess.
Diamine and/or aminonitrile, e.g. hexamethylenediamine and/or 6-
aminocapronitrile, can be recovered from the reaction products by typical
purification procedures such as. recrystallization or preferably,
distillation.
2o The unreacted dinitrile can be recycled back to the hydrogenation reactor
to obtain additional diamine and/or aminonitrile.
EXAMPLES
The hydrogenation of adiponitrile (ADN) may be described using a kinetic
2s model in which ADN is first converted to aminocapronitrile (ACN) andlthe
ACN is then converted to hexamethylenediamine (HMD), e.g.,
ADN ~ ACN ~ HMD
where each reaction step is a first order reaction, and the first step has a
rate constant 2k~ and the second step has a rate constant k2. In this
3o model a k~/k2=1 value describes a' non-selective catalyst and the
maximum yield of ACN will be 50°/a.,in a well-mixed batch reaction. It
is
desirable to maximize the k~/k2 value.
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Comparative Example 1. A 1-L stainless steel pressure vessel was
charged with 216 g of adiponitrile and 20g of a powdered, reduced iron
catalyst. The vessel was sealed, purged with hydrogen and charged with
225g ammonia. It was heated to 150°C and pressurized to 4500 psig (31
s MPa). As hydrogen was consumed, it was constantly replenished from a
pressurized cylinder to maintain an operating pressure of 4500 psig (31
MPa). After 70 min the reaction was stopped, and a sample was analyzed
via gas chromatography. The analysis showed that the reaction product
comprised 12 wt% adiponitrile (ADN), 45wt% 6-aminocapronitrile (ACN),
~o and 36wt% hexamethylenediamine. The k~/k2 value was 1.1.
Examples 2 to 4. The experiment of Example 1 was repeated except ~.2g
of a modifier chemical was added to the reaction mixture with the ADN.
The results are presented in Table 1. TBACN = tetrabutylammonium
la~ ,.cyaniae,eT~AI~~= re~raetr~yi~'mo~oni-um cydrtid~sri'l'~AFIP~=
tetramethylammonium hydroxide,pentahydrate..
Example ModifierTime Wt% Wt% Wt% k~/k~
of ~ ADN in ACN in HMD in
Reactionreactionreactionreaction
(min) product product product
1 None 70 12 45 36 1.1
2 TBACN 315 21 57 17 1.8
3 TEAF 180 21 54 21 1.4
4 TMAHP 120 M 11 51 ' 28 1.6
s
