USOO9518006B2

(12) United States Patent (10) Patent No.: US 9,518,006 B2

Pennemann et al. (45) Date of Patent: Dec. 13, 2016

(54) METHOD FOR PRODUCING (58) Field of Classification Search

DAMNOTOLUENE None
See application file for complete search history.
(71) Applicant: Covestro Deutschland AG, Leverkusen (56) References Cited
(DE)
U.S. PATENT DOCUMENTS
(72) Inventors: Bernd Pennemann, Bergisch Gladbach
(DE); Amgad Salah Moussa, Cologne 3,093,685 A 6, 1963 Hort et al.
(DE); Bastian Mahr, Bergisch 3,136,818 A 6/1964 Sperber et al.
Gladbach (DE) 3,636,152 A 1/1972 Szigeth
4,740,621 A 4, 1988 Adams et al.
(73) Assignee: Covestro Deutschland AG, Leverkusen 5,808,157 A 9/1998 Langer et al.
(DE) (Continued)
FOREIGN PATENT DOCUMENTS
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35 DE 3734344 A1 4f1989
U.S.C. 154(b) by 0 days. EP O748790 A2 12/1996

(21) Appl. No.: 15/027,327 (Continued)

OTHER PUBLICATIONS
(22) PCT Filed: Oct. 2, 2014
Cartolano, A. R. and Vedage, G. A., 2004, Amines by Reduction,
(86) PCT No.: PCT/EP2014/071125
Kirk-Othmer, Encyclopedia of Chemical Technology, John Wiley &
S 371 (c)(1), Sons Inc; 5th edition; Jan. 31, 2004, vol. 2, pp. 478; (p. 484 and p.
(2) Date: Apr. 5, 2016 485).
(Continued)
(87) PCT Pub. No.: WO2O1S/OS2O68
Primary Examiner — Clinton Brooks
PCT Pub. Date: Apr. 16, 2015 (74) Attorney, Agent, or Firm — Donald R. Palladino
(65) Prior Publication Data (57) ABSTRACT
US 2016/02444.02 A1 Aug. 25, 2016 The invention relates to an industrial-scale method for the
vapor-phase hydrogenation of dinitrotoluene (DNT).
(30) Foreign Application Priority Data According to said method, a stream containing DNT is
sprayed into a carrier-gas stream containing hydrogen,
Oct. 8, 2013 (EP) ..................................... 13187648 optionally in the presence of an atomizing gas, unevaporated
liquid droplets are extracted from the Substantially gaseous
(51) Int. C. stream that is obtained and the resultant gas stream is
CD7C 209/36 (2006.01) catalytically hydrogenated to form diaminotoluene.
(52) U.S. C.
CPC ................................... C07C 209/36 (2013.01) 7 Claims, 6 Drawing Sheets
 US 9,518,006 B2
Page 2

(56) References Cited

U.S. PATENT DOCUMENTS
5,877,350 A 3/1999 Langer et al.
5,962,365 A 10/1999 Langer et al.
6,359,177 B1 3/2002 Brady et al.
7.307,190 B2 12/2007 Pennemann et al.
7,595.424 B2 9/2009 Vanoppen et al.
8, 110,073 B2 2/2012 Pennemann et al.
9,067,864 B2 6, 2015 Sommer et al.
2008. O146847 A1 6, 2008 Pohl et al.
2011/0275858 A1 11/2011 Coelho Tsou et al.

FOREIGN PATENT DOCUMENTS

GB 599.252 3, 1948
GB 832939 4f1960
GB 14903.13 11/1977

OTHER PUBLICATIONS
Perry's Chemical Engineers' Handbook, 8th edition, Section 19;
Reactors, 2007 (pp. 19-1 to 19-61).
Perry's Chemical Engineers' Handbook, 7th edition, Section 23;
Chemical Reactors, 1999 (pp. 23-1 to 23-62).
Richter, Thomas; “Zerstauben von Flussigkeiten', expert Verlag,
Renningen, 2004, Chapters 34 (pp.39-42), 1.3 (pp. 54-56), 44 (pp.
57-65), 5.7 (pp. 80-84) and 65 (pp. 101-117).
Wozniak, Gunter; "Zerstaubungstechnik'; Springer, 2003, Chapters
5.1, 5.2, 5.3, 54 and 5.5 (pp. 59-87).
U.S. Patent Dec. 13, 2016 Sheet 1 of 6 US 9,518,006 B2

5/0 0€
0 09

Fig. 1
U.S. Patent Dec. 13, 2016 Sheet 2 of 6 US 9,518,006 B2

7OOO

Fig. 1 a
U.S. Patent Dec. 13, 2016 Sheet 3 of 6 US 9,518,006 B2

200 - 9 1. 200 - 9

FIG 1b.
U.S. Patent Dec. 13, 2016 Sheet 4 of 6 US 9,518,006 B2

33 O
O
O
O

-N 3
d

FIG. 2
U.S. Patent Dec. 13, 2016 Sheet S of 6 US 9,518,006 B2

O
N

N N
S.

d
N
O

T8

FIG. 3
U.S. Patent Dec. 13, 2016 Sheet 6 of 6 US 9,518,006 B2

OZ
FIG. 4
 US 9,518,006 B2
1. 2
METHOD FOR PRODUCING explicitly warns against the gas-phase hydrogenation of
DAMNOTOLUENE starting materials having relatively high proportions of dini
tro compounds.
CROSS-REFERENCE TO RELATED DE-B 1809 711 is concerned with a process for the
APPLICATIONS gas-phase hydrogenation of nitro compounds and in particu
lar addresses the problem of uniform introduction of liquid
This Application is a National Phase Application of nitro compounds into a hot gas stream by atomization,
PCT/EP2014/071125, filed Oct. 2, 2014, which claims pri preferably at constricted places directly upstream of the
ority to European Application No. 13187648.4, filed Oct. 8, reactor. The danger of possibly incomplete vaporization of
2013, each of which being incorporated herein by reference. 10
the nitro compound is not mentioned. Although this docu
FIELD
ment speaks in general terms of nitro compounds, it gives a
specific example only for nitrobenzene. The process param
eters mentioned in the document are optimized for nitroben
The invention relates to an industrially implementable Z.
process for the gas-phase hydrogenation of dinitrotoluene 15
DE-A 3 636 984 describes a process for the coupled
(DNT), in which a DNT-containing stream is, optionally in production of nitroaromatics and dinitroaromatics from the
the presence of an atomizing gas, sprayed into a hydrogen corresponding hydrocarbons by nitration and Subsequent
containing carrier gas stream, the essentially gaseous stream hydrogenation. The hydrogenation is carried out in the gas
obtained is freed of unvaporized liquid droplets and the phase attemperatures of from 176 to 343.5°C. A description
resulting gas stream is catalytically hydrogenated to form is given of an apparatus for the gas-phase hydrogenation
toluenediamine. which consists essentially of two reactors connected in
BACKGROUND series with intermediate cooling and intermediate introduc
tion of starting material, but nothing is said about the size
and structure of these. The problems of decomposition of
Aromatic amines are important intermediates which have 25
dinitrotoluene is not addressed in the document.
to be available cheaply and in large amounts. Plants having The documents EP 0 696 573 A1 EP 0 696 574 A1, EP
very large capacities therefore have to be built for, for 0 748 789 A1 EP 0 748 790 A1 and DE 10 2006 035 203
example, the hydrogenation of dinitrotoluene (hereinafter A1 are concerned with a gas-phase process for the hydro
also referred to as DNT). The hydrogenation product tolu genation of aromatic nitro compounds which is carried out
enediamine (hereinafter also referred to as TDA) is an 30
under purely adiabatic conditions. EP 0696574 A1 describes
important intermediate in the preparation of tolylene diiso the process for preparing aromatic amines, in which a gas
cyanate which is of great importance in polyurethane chem mixture consisting of nitroaromatics and hydrogen is passed
istry. There are numerous publications relating to the prepa over the catalyst under adiabatic conditions, in a quite
ration of toluenediamine. By far the largest part of the prior general way. According to the other documents mentioned,
art is concerned with the hydrogenation of dinitrotoluene in 35
particular advantages are in each case achieved in the
the liquid phase. Known processes include a “single-phase' processes by changing various parameters. The processes
process, either without further solvent (see, for example, are applicable to nitroaromatics of the general formula
U.S. Pat. No. 3,093,685) or using solvents which dissolve
both DNT and the TDA/water mixture formed, for example
simple aliphatic alcohols (e.g. methanol). In addition, there 40
are also “two-phase' processes in which solvents (e.g.
hydrocarbons) which dissolve DNT but not the TDA/water
mixture formed are used, so that phase separation occurs;
see, for example, GB 1 490 313. The catalyst (for example
X / X
Pd/C, Raney Ni, Ni/SiO, etc.) is usually slurried in the 45 where R2 and R3 can be, inter alia, a methyl group.
liquid phase (therefore also referred to as “slurry-phase However, the focus of said documents is on aniline (the
process”). Possible reactors are, for example, loop reactors examples are concerned with the hydrogenation of nitroben
or stirred vessels (see, for example, US 2011/295.039 A1). Zene). The documents mentioned do not go into particular
All industrially relevant processes at present work in the aspects of the hydrogenation of dinitrotoluene.
liquid phase. Liquid-phase hydrogenation processes at 50 GB 832,939 is concerned specifically with the hydroge
elevated temperatures and the gas-phase hydrogenation of nation of dinitro compounds in the gas phase. This document
dinitrotoluene do not play any role industrially because of discloses the use of nickel sulfide catalysts on an aluminum
the potential hazards resulting from the thermal instability oxide Support material. According to the document, the use
of in particular, technical-grade dinitrotoluene. The gas of these makes an unexpectedly rapid reaction in excellent
phase hydrogenation of nitroaromatics having little Volatil 55 yields possible. The document does not go into process
ity and/or temperature sensitivity is considered to be critical engineering details in respect of vaporization. The hydro
in the literature (see, for example, Cartolano, A. R. and genation is carried out at ambient pressure and temperatures
Vedage, G. A., 2004, Amines by Reduction, Kirk-Othmer, of about 220° C. (cf. examples), i.e. below the decomposi
Encyclopedia of Chemical Technology, John Wiley & Sons tion temperature of liquid pure dinitrotoluene.
Inc.; 5' edition (Jan. 31, 2004), Vol. 2, page 478 and page 60 DE 3734344 A1 describes the conversion of dinitrotolu
484, Online-ISBN: 9780471238966). ene (DNT) in the gas phase into toluenediamine (TDA).
GB 599,252 and U.S. Pat. No. 3,136,818 describe pro DNT is vaporized in an inert, hot carrier gas within from 2
cesses for preparing aromatic monoamines, in particular to 120 seconds to give a mixture which is composed of
aniline, in the gas phase by hydrogenation in a fluidized-bed vaporized DNT and carrier gas and has a temperature of
reactor. Since mononitroaromatics are substantially more 65 from 150 to 250° C. As suitable types of vaporizer, mention
stable than dinitroaromatics, uncontrolled thermal decom is made of thin film evaporators having Smooth tubes, short
position does not present a significant problem. GB 599.252 path evaporators, falling film evaporators without circula
 US 9,518,006 B2
3 4
tion of liquid and single-coil helically coiled tube evapora 2011/0275858 A1). For this purpose, the hydrogenation was
tors. The low volatility and ready decomposition of DNT carried out at a temperature of 185°C., which was possible
and the explosion risk associated therewith are mentioned. in a safe manner under the following conditions:
Measures for avoiding decomposition or for avoiding accu 1. A reactor having an internal heat-exchange Surface and
mulation of high-boiling, thermally sensitive impurities are an external circuit with removal of heat was used.
not described since they presumably were not a problem 2. DNT was introduced into the catalyst suspension by
because of the short time of the experiment of a few hours means of a driving nozzle below the surface of the
and possibly because of the purity of the starting materials liquid.
used in the experiments carried out. The possible presence of 3. The average DNT concentration in the reactor was
nonvolatile components in the DNT is mentioned only 10
limited to a value of less than 1000 ppm.
insofar as the vaporization process can theoretically be used 4. The hydrogen concentration including the hydrogen in
for separation into DNT and nonvolatile components. The the external circuit was set to a value of greater than 1%
hydrogenation is, according to this document, carried out in by volume, preferably greater than 3% by volume.
the temperature range from 200 to 450° C. and preferably at
atmospheric pressure. 15 Adherence to these conditions is essential to the process
It is not possible to derive any technical concept for an described, because, inter alia, nitro and nitroso compounds
economical reaction on a large scale from the literature can decompose explosively in the presence of TDA at
sources which expressly refer to the possibility of hydroge elevated temperatures (DE 10 2005 008 613 A1). However,
nating DNT in the gas phase. The literature (in particular GB the third and fourth conditions in particular can in the case
832939 and DE 3734344 A1) does not address either the of industrial production at a temperature of 185°C. or above
hurdles to be overcome in implementing an industrial DNT lead to great practical problems in the design and operation
hydrogenation process or the utilization of the advantages of a liquid-phase process. Matching of the individual param
potentially associated with Such a process. eters to one another is difficult to realize. As will be
In respect of the industrial production of TDA by a explained in more detail below, the present invention makes
gas-phase process, it has to be noted that DNT of technical 25 it possible to maintain a temperature of 185°C. or above so
grade purity can have a higher proportion of relatively that high-pressure steam can be obtained in a gas-phase
nonvolatile accompanying components than DNT which is process without comparable practical limitations.
used in small batches for laboratory experiments. For eco In addition, gas-phase processes have a series of other
nomic reasons, it is desirable to be able to use technical advantages. Thus, separation of the catalyst from the product
grade DNT without complicated and expensive prepurifica 30
is easier since the product leaves the reactor in gaseous form
tion. This requires particular measures in the vaporization of while the catalyst remains in the reactor. Scale-up of the
DNT in industrial production plants. process is also simpler in the case of gas-phase reactors than
None of the abovementioned documents gives any indi in the case of the reactors customary in the slurry-phase
cation that systematic steps have been undertaken in order to process. Since mechanical stirring is not necessary in the
allow safe vaporization and gas-phase hydrogenation of 35
dinitrotoluene of technical-grade purity for long periods of gas-phase process, the risk of plant downtimes due to caking
operation and on an industrial scale, without DNT or its on the stirrer and also the energy consumption is lower. In
accompanying components decomposing in an uncontrolled addition, gas-phase reactors are simpler to clean than stirred
manner. Little information is likewise given about vessels.
a) critical temperature limits for avoidance of thermal 40 A further advantage of an industrial TDA synthesis in the
decomposition of DNT, gas phase arises from the possibility of Subjecting the
b) handling accompanying materials which vaporize with gaseous product to a prefractionation (including isomer
difficulty or not at all and have a hazard potential (e.g. separation) in a simple way by fractional condensation at
picric acid, cresols, trinitrotoluene (TNT)), different temperatures. Each of the condensate fractions
c) avoidance of the accumulation of unvaporized materi 45 obtained in this way can be fed in at a different place
als which have a hazard potential in the unvaporized matched precisely to this fraction in the Subsequent distil
state (DNT, TNT, etc.) and lation sequence. This gives the possibility of considerably
d) ensuring complete conversion of DNT before the simplifying the distillation compared to the customary dis
product gas stream is cooled. tillation of the product from a liquid-phase process (up to six
The hydrogenation of DNT liberates large quantities of 50
columns, see, for example, U.S. Pat. No. 6,359,177 B1).
energy. In the conventional liquid-phase process, hydrogen There was therefore a need to provide a process for
is introduced at an absolute pressure of from about 20 to 100 carrying out the hydrogenation of DNT of technical-grade
bar and the reactors are operated at this pressure; see, for purity in the gas phase, which can be implemented on an
example, US 2008/0146847 A1 (100 bar pressure and a industrial scale and thus make it possible to actually make
temperature of 150° C.). Owing to the low temperature level, 55
use of the many advantages of a gas-phase hydrogenation, in
utilization of the energy to be removed is possible and/or particular the opportunity of obtaining high-pressure steam
economical to only a very limited extent. If the hydrogena
tion reaction were to be able to be carried out at a higher and the simplified work-up by fractional condensation, and
temperature so that higher-pressure steam were to be able to thereby to significantly increase the energy efficiency of the
be generated, this would have great economic value. This 60 process. The particular challenge was to avoid the risk of
applies particularly to integrated systems comprising a plu uncontrolled decomposition of DNT and its accompanying
rality of production plants in which Steam obtained in one components.
process can be utilized in other processes (for example for
heating the starting materials to the reaction temperature). SUMMARY
Recently, carrying out the liquid-phase hydrogenation with 65
out solvent at a temperature which allows the production of Taking into account what has been said above, the present
steam at a pressure level of 4 bar has been reported (US invention provides a continuous process for preparing tolu
 US 9,518,006 B2
5 6
enediamine by hydrogenation of dinitrotoluene in the gas (V) recirculation of at least part of the hydrogen-comprising
phase, which comprises the steps gas phase (7) obtained in step (IV) into the first vapor
(I) spraying of a dinitrotoluene-comprising stream (1, 11, ization apparatus (1000, 1010) of step (I).
12) into a hydrogen-containing carrier gas stream (2, 21. In this context, a vaporization apparatus is any apparatus
22) in a vaporization apparatus (1000, 1010, 1020), where 5 which is suitable for spraying the DNT stream 1 (11,12) into
a) the temperature of the dinitrotoluene-comprising the carrier gas stream (the “feed hydrogen' stream) 2 (21.
stream (1, 11, 12) is from 70° C. to 150° C., preferably 22) and very completely vaporizing the DNT. In the embodi
from 80° C. to 100° C., and the temperature of the ment shown in FIG. 1, solid lines, the “feed hydrogen
hydrogen-containing carrier gas stream (2, 21, 22) is stream 2 is, for example, a mixture of “recycle gas hydro
from 140° C. to 300° C., preferably from 180° C. to 10 gen’ 7 and fresh hydrogen 200; in the embodiment shown in
240° C., FIG. 1 with broken lines, it is identical to the recycle gas
b) the absolute pressure of the dinitrotoluene-comprising hydrogen (7). The vaporization apparatus comprises at least
one apparatus for spraying the stream 1 (11, 12) into the
stream (1, 11, 12) is from 3.0 bar to 30 bar, preferably stream 2 (21, 22). In the simplest case, the vaporization
from 4.0 bar to 20 bar, and the absolute pressure of the 15 apparatus comprises merely a pipe through which the stream
hydrogen-containing carrier gas stream (2, 21, 22) is 2 (21, 22) flows and into which an apparatus through which
from 1.0 bar to 10 bar, preferably from 3.0 bar to 6.0 stream 1 (11, 12) is sprayed in opens. An 'apparatus for
bar, where the pressure of the dinitrotoluene-compris spraying is preferably a nozzle (see below for details).
ing stream (1, 11, 12) is higher than that of the The first vaporization apparatus (1000, 1010) refers, when
hydrogen-containing carrier gas stream (2, 21, 22), a plurality of reaction spaces connected in series are used
preferably from 0.01 bar to 10 bar higher, and thus also when a plurality of vaporization apparatuses
c) the molar ratio of hydrogen to DNT is from >6.0:1 to arranged in series in the flow direction of the reaction
900:1, preferably from 60:1 to 500:1, mixture are used (cf., for example, FIG. 3), to the first
so that dinitrotoluene is vaporized within from 0.010 s to vaporization apparatus in the flow direction of the reaction
100 s, preferably within from 0.010 s to 3.0 s, with at 25 mixture, i.e. in the embodiment shown in FIG. 3 the vapor
least 95.0% by mass, preferably at least 99.5% by mass, ization apparatus 1010. In the case of a plurality of reaction
in each case based on the total mass of all the dinitro spaces connected in parallel and thus also a plurality of
toluene present in the dinitrotoluene-comprising stream vaporization apparatuses connected in parallel, all vaporiza
(1, 11, 12), being brought into the gas phase and an tion apparatuses arranged first in the flow direction of the
essentially gaseous stream (3, 31, 32) which comprises 30 reaction mixture are “first vaporization apparatuses' within
dinitrotoluene and hydrogen and may also contain the meaning of step (V). If only one reaction space and thus
proportions of unvaporized, relatively nonvolatile also only one vaporization apparatus is present (cf., for
accompanying components of the dinitrotoluene being example, FIG. 1), this vaporization apparatus is naturally
also “the first vaporization apparatus within the meaning of
obtained in this way: 35 step (V).
(II) removal or targeted decomposition, preferably removal, Here, the statements that at least 95.0% by mass, based on
of the liquid droplets present in the essentially gaseous the total mass of all the dinitrotoluene present in the dini
stream (3, 31, 32) comprising dinitrotoluene and hydro trotoluene-comprising stream (1,11,12) are brought into the
gen from step (I) in an apparatus (2000, 2010, 2020) so gas phase step (I) and the gas stream 4 (41, 42) preferably
that the resulting gas stream (4, 41, 42) which comprises 40 contains not more than 1000 ppm of unvaporized droplets,
dinitrotoluene and hydrogen and has been depleted in based on the total mass of all the dinitrotoluene present in
liquid droplets preferably contains not more than 1000 the dinitrotoluene-comprising stream (1,11,12) step (II) in
ppm, particularly preferably not more than 500 ppm, very each case refer to DNT as such, i.e. without taking into
particularly preferably not more than 100 ppm, extraor account the impurities which are always present in techni
dinarily very particularly preferably not more than 50 45 cal-grade DNT. When stream 1 (11, 12) is, for example, a
ppm, of unvaporized droplets, based on the total mass of dinitrotoluene having a purity of 98% which is fed at a kg/h
all the dinitrotoluene present in the dinitrotoluene-com to the vaporization in step (I), at least 0.95:0.98 a kg/h of
prising stream (1, 11, 12); gaseous dinitrotoluene are fed with stream 3 (31. 32) to the
(III) reaction of the dinitrotoluene present in the gas stream droplet removal in step (II). The residual droplet content in
(4., 41, 42) which comprises dinitrotoluene and hydrogen 50 the gas stream (4, 41, 42) which comprises dinitrotoluene
and has been depleted in liquid droplets with hydrogen in and hydrogen and has been depleted in liquid droplets is
at least one reaction space (3000, 3010, 3020) in the preferably determined by laser-optical measurement, by
presence of a catalyst (100, 110, 120) at an absolute means of a capacitive measurement technique or by with
pressure of from 1.0 bar to 10 bar, preferably from 3.0 bar drawal of a representative Substream and determination of
to 6.0 bar, a temperature of from 140° C. to 300° C., 55 its droplet content by means of abovementioned techniques
preferably from 180° C. to 270° C., and a residence time or by collection and weighing of the droplets. The above
in the reaction space of from 0.1 s to 10s, preferably from described methods with which a person skilled in the art is
1.0 s to 5.0 S. So as to give a toluenediamine-containing familiar generally give the same results within normal error
gas stream (5, 51, 52), tolerances which do not detract from the reliability of the
(IV) separation of the toluenediamine-containing gas stream 60 result. Should different measurement methods nevertheless
(5, 52) obtained in step (III) after passing through the last give significantly different values, the result from the laser
reaction space (3000, 3020) into a toluenediamine-com optical measurement is decisive according to the invention.
prising liquid phase (6, 6a, 6b, 6c) and a hydrogen For the purposes of the present invention, the term reac
comprising gas phase (7) by condensation, preferably in tion space (step (III)) refers to the space in which DNT and
a condensation apparatus (4000), particularly preferably 65 hydrogen react with one another in the presence of the
by multistage condensation (4010, 4020, 4030) at a tem catalyst. The reaction space is located in an industrial
perature which decreases from stage to stage; and apparatus for carrying out chemical reactions, viz. the reac
 US 9,518,006 B2
7 8
tor. In the case of a reactor which is completely filled with extent have to be feared. Wherever gaseous DNT is present,
catalyst (for example in the form of a bed of catalyst i.e. in the vaporization apparatus and also in the reaction
spheres), the reaction space is identical to the interior space, a temperature of 300° C. must not be exceeded; in
volume of the reactor. When a plurality of reaction spaces addition, the residence time has to be kept short.
are present, these can be connected in series or in parallel. 5 The streams 1 (DNT) and 200 (fresh hydrogen) can also
The last reaction space refers in the case of a plurality of contain further constituents in addition to the essential
reaction spaces connected in series (cf., for example, FIG. 3) constituents DNT and hydrogen, respectively. In particular,
to the last reaction space in the flow direction of the reaction it can be advantageous to dissolve the technical-grade DNT
mixture, i.e. in the embodiment shown in FIG. 3 the reaction in a suitable solvent which is inert under the reaction
space 3020. Preference is given to only the toluenediamine 10 conditions and is covaporized. Suitable solvents are alcohols
containing gas stream obtained in this reaction space being (preferably selected from among methanol, ethanol and
separated into a gas phase (7) and a liquid phase (6). In the isopropanol). If a solvent is used, the proportion of techni
case of a plurality of reaction spaces connected in parallel, cal-grade DNT in the solution (1) is preferably from >0% by
all reaction spaces arranged last in the flow direction of the mass to <50% by mass, based on the total mass of 1. The
reaction mixture are “last reaction spaces' within the mean 15 hydrogen, too, does not have to be used in neat form, but can
ing of step (IV). In this case, the plurality of toluenediamine be diluted with other gases which are inert under the reaction
containing gas streams obtained in this way are preferably conditions of the hydrogenation. This can be effected either
combined before the condensation. If only one reaction by the hydrogen being mixed with an inert gas before being
space is present (cf., for example, FIG. 1), this is naturally mixed with the DNT-containing stream 1 or hydrogen and
also “the last reaction space within the meaning of step inert gas being introduced separately. Suitable inert gases
(IV). are, for example, noble gases, steam, CO, nitrogen; with
preference being given to nitrogen or steam. If the hydrogen
BRIEF DESCRIPTION OF THE DRAWINGS is diluted with such gases before contact with the DNT
containing stream 1, the proportion thereof in the stream 2
FIG. 1 illustrates a basic embodiment of the process of the 25 is preferably not less than 3 mol %, based on the total molar
present invention; amount of all compounds present in stream 2. For example,
FIG. 1a illustrates, in a section of the total process of the synthesis gas can also be used directly without the hydrogen
embodiment shown in broken lines in FIG. 1, a variant of the present therein being purified to high purities. If a condens
embodiment of FIG. 1 in which a two-fluid nozzle is used; able diluent gas (e.g. Steam) is used, this has the advantage
FIG. 1b illustrates a possible configuration of a two-fluid 30 that the Volume stream through the compressor decreases in
noZZle according to Some embodiments of the present inven comparison with incondensable carrier gas.
tion; The present process makes possible, in step (I), the
FIG. 2 illustrates a non-limiting example of a system for vaporization of technical-grade DNT on an industrial scale.
condensation and Subsequent work-up of a gaseous product Any proportions of liquid droplets still present in the stream
stream according to the present invention; 35 3 (31. 32) are made up quite predominantly to completely of
FIG. 3 illustrates an arrangement in which two adiabati relatively nonvolatile accompanying components in the
cally operated reactors having two vaporization apparatuses technical-grade DNT. The proportion of unvaporized drop
are connected in series according to some embodiments, of lets in stream 3 (31. 32) is therefore dependent to a sub
the present invention; and stantial extent on the purity of the DNT used. The “techni
FIG. 4 illustrates a process of the present invention 40 cal-grade DNT which is preferably used as DNT source for
described in Example 1. stream 1 (11, 12) in the process of the invention preferably
comprises:
DETAILED DESCRIPTION from 99.00% by mass to 99.94% by mass of DNT, with 2,4-
and 2,6-DNT making up the major part (>95% of the DNT
For the purposes of the present invention, residence time 45 present in 1);
in the reaction space is the ratio of the volume of the reaction >5 ppm of nitrocresols;
space through which the gas stream can flow to the Volume >20 ppm of trinitrotoluene:
stream exiting from the reaction space per unit time. >500 ppm of other impurities comprising, preferably con
The invention will be described in detail below. Various sisting of water, mononitrotoluene, Sulfuric acid and salts of
embodiments are, unless the context clearly indicates the 50 Sulfuric acid,
contrary, can be combined with one another as desired. in each case based on the total amount of the technical-grade
It has Surprisingly been found that gaseous mixtures of DNT 1 (11,12).
vaporized DNT and a hydrogen-containing carrier gas are The vaporization apparatus (1000, 1010, 1020) used has
more thermally stable than liquid DNT or solutions of DNT to ensure very complete vaporization of the DNT and at the
having a high concentration at the same (high) temperature. 55 same time short resonance time and minimal thermal stress
This applies even in the presence of TDA with which DNT ing of the liquid DNT. For this purpose, apparatuses in
can in principle undergo undesirable reactions. A significant which the DNT-containing stream 1 is sprayed into a hot
part of the process is therefore sufficiently complete vapor hydrogen-containing carrier gas stream 2 (21, 22) by means
ization of DNT. The process of the invention makes it of at least one spray apparatus (preferably a nozzle) ("spray
possible to bring at least 99.90%, preferably at least 99.95%, 60 vaporizer) are suitable for the purposes of the invention.
particularly preferably at least 99.99%, very particularly Here, the ratio of the molar flows of 1 to 2 (21, 22) is
preferably at least 99.995%, of the DNT into the gas phase preferably such that the proportion of DNT in 3 (31. 32) is
(steps (I) and (II)) before it is hydrogenated in the presence from 0.1 mol % to 10 mol %, particularly preferably from
of the catalyst in the reaction space to form TDA (step (III)). 0.8 mol % to 2.0 mol %, in each case based on the total
The maximum possible amount of unvaporized droplets of 65 molar amount of all compounds present in stream 3 (31. 32).
0.10%, based on the mass of all the dinitrotoluene present in The temperature of the carrier gas stream should be selected
1, is so low that no decomposition reactions to a dangerous so that as much DNT as possible can be vaporized, i.e. the
 US 9,518,006 B2
10
DNT partial pressure is very close to the saturation pressure hydrogen consumed in the hydrogenation can in this way be
at the prevailing exit temperature from the vaporizer, and at replaced in a simple and advantageous manner in continuous
the same time the maximum temperature of 300° C. allowed operation with very complete recycling of the process gas 7.
in the downstream reaction space at complete conversion of The mass ratio of stream 9 to stream 1 is preferably from
DNT is not exceeded. This gives a suitable temperature of 5 0.01 to 1, particularly preferably from 0.05 to 0.2. The
the hydrogen-containing carrier gas 2 at the inlet into the pressure drop over the nozzle is preferably from 1.0 bar to
vaporization apparatus of from 140° C. to 300° C., prefer 20 bar, particularly preferably from 3.0 bar to 9.0 bar, for
ably from 180° C. to 240° C. To achieve very rapid (within stream 9 and preferably from 0.1 bar to 20 bar, particularly
from 0.010 s to 100s, preferably within from 0.010 s to 3.0 preferably from 3.0 bar to 9.0 bar, for stream 1.
seconds) and complete (at least 95.0% by mass, preferably 10 In step (II), the already essentially gaseous stream 3 (31.
at least 99.5% by mass, of all DNTs present in 1 (11, 12)) 32) is freed further of liquid droplets because, inter alia, of
vaporization of the DNT, a DNT spray stream 1 (11, 12) the higher thermal sensitivity in the liquid phase. This is
having a very Small droplet size (average droplet diameter d preferably achieved by means of one or more of the follow
preferably in the range from 20 um to 200 um) and a uniform ing measures:
droplet size distribution has to be produced, as is possible 15 a) separation of the remaining droplets from stream 3 (31.
with customary one-fluid and in particular two-fluid nozzles. 32), e.g. by means of a Suitable separation unit. Such a
Suitable one-fluid nozzles are, for example, those separation unit can also be installed in the reactor itself.
described in Wozniak, “Zerstäubungstechnik'. Springer It is then located upstream of the actual reaction space.
2003 (in particular chapters 5.1, 5.3, 5.4 and 5.5) and Richter Suitable separation units are, for example, filters, knits,
“Zerstäuben von Flissigkeiten, expert Verlag, Renningen, deflection precipitators, cyclones and droplet precipi
2004 (in particular chapters 3.4, 4.3, 4.4 and 5.7). Tangential tators known to those skilled in the art. The separation
hollow cone nozzles, for example, are Suitable because of units are either dimensioned so that their function is
the relatively small droplet diameter produced and their ensured for the duration of a normal production cycle,
insensitivity to blockages. For smaller flow rates and even after which they are then cleaned or regenerated in a
Smaller droplet diameters, ultrasonic atomizer nozzles are 25 manner known to those skilled in the art (e.g. by
Suitable, also because of their variable operating range. burning-off), or a plurality separation units are con
However, the abovementioned requirements in terms of nected in parallel with one of these being in operation
droplet size and droplet size distribution can be satisfied while the others are cleaned or regenerated.
most simply by means of two-fluid nozzles. In a very b) targeted continuous or discontinuous decomposition of
particularly preferred embodiment, the invention therefore 30 the accumulated constituents to form nonhazardous
provides a process in which the spraying of the stream 1 (11. species, e.g. by Suitable introduction of energy and
12) into the carrier gas stream 2 (21, 22) in step (I) is effected controlled initiation of thermal decomposition.
by means of at least one two-fluid nozzle (7000) through Here, a) is preferred over b).
which, in addition to 1 (11,12), a stream of an atomizing gas Since DNT and TDA can react with one another, the
9 which is under a pressure which is from 1.0 bar to 20 bar 35 reaction conditions in step (III) have to be selected so that
higher, preferably from 3.0 bar to 9.0 bar higher, than the very complete conversion of the DNT is ensured within a
absolute pressure prevailing in the Surroundings on the short time. Here, the abovementioned conditions in respect
nozzle outlet side and preferably has the same temperature of pressure, temperature and the molar ratio of hydrogen to
as stream 2 is passed. Suitable two-fluid nozzles are DNT are of particular importance. Suitable catalysts are in
described, for example, in Wozniak, “Zerstäubungstechnik'. 40 principle the catalysts known to those skilled in the art for
Springer 2003 (in particular chapter 5.2) and Richter “Zer DNT hydrogenation, as long as they allow rapid conversion
stäuben von Flissigkeiten, expert Verlag, Renningen, 2004 of the DNT. According to the invention, solid catalysts are
(in particular chapter 6.5). The mixing of 1 (11, 12) and the used. In principle, all solid catalysts known to those skilled
atomizing gas stream (9) occurs, depending on the construc in the art for the hydrogenation of aromatic nitro compounds
tion of the two-fluid nozzle 7000, either in the nozzle 45 are suitable. Such catalysts are described in many publica
(“internally mixing nozzle”) or when the individual streams tions and comprise, as hydrogenation-active elements, Pd,
exit from the nozzle (“externally mixing nozzle''). In the first Pt, Ru, Fe, Co, Ni, Mn, Re, Cr, Mo, V, Pb, Ti, Sn, Dy, Zn,
case, a two-phase mixture of 1 (11, 12) and the atomizing Cd, Ba, Cu, Ag, Au, and compounds thereof. Sometimes as
gas stream (9) is produced in the nozzle 7000 and is sprayed oxides, sulfides or selenides and also in the form of a Raney
into the carrier gas stream 2 (21, 22). In the latter case, the 50 alloy, and also on inert Support materials, for example
streams containing DNT 1 (11,12) and atomizing gas (9) are Al2O, Fe2O/Al2O, SiO, Silicates, carbon, graphite, TiO,
sprayed separately from one another through channels in the CrOs. Mixed oxides of the elements mentioned are likewise
nozzle into the carrier gas atmosphere 2 (21, 22). Preference conceivable.
is given to using internally mixing two-fluid nozzles in Preference is given to using a catalyst (100, 110, 120)
which the streams 1 (11, 12) and 9 impinge on one another 55 comprising a ceramic Support, preferably Al-O, particularly
within the nozzle and leave the nozzle as a two-phase preferably C-Al-O. very particularly preferably C-Al-O
mixture. having a BET surface area of less than 40 m/g, preferably
In preferred embodiments, the invention provides a pro less than 20 m/g, particularly preferably less than 10 m/g,
cess in which steam, nitrogen, hydrogen, part of the hydro and
gen-comprising gas phase 7, part of the hydrogen-containing 60 (a) from 1.0 g to 100 g, preferably from 1.0 g to 50 g, of
carrier gas stream (2, 21, 22) or a mixture of two or more of at least one metal of groups 8 to 12 of the Periodic
the abovementioned gases is used as atomizing gas 9. Very Table of the Elements (numbering according to IUPAC
particular preference is given to using hydrogen (i.e. fresh recommendation of 1986), preferably Pd, Pt,
hydrogen 200, to be distinguished from the hydrogen (b) from 1.0 g to 100 g, preferably from 1.0 g to 50 g, of
containing stream 2 (21, 22), as atomizing gas 9. In the case 65 at least one metal of groups 4 to 6 and 12 of the Periodic
of a plurality of reactors connected in series, stream 200 is Table of the Elements, preferably Ti, V. Nb, Ta, Cr, Mo,
divided (210, 220, . . . ) over the various reactors. The W, and
 US 9,518,006 B2
11 12
(c) from 1.0 g to 100 g, preferably from 1.0 g to 20 g, of assist DNT vaporization and heat recovery in the isolation of
at least one metal of groups 14 and 15 of the Periodic the product, but lead to larger dimensions of the apparatuses
Table of the Elements, preferably Pb, Bi, and a higher energy consumption for compression. In par
per liter of bed volume of the ceramic support. ticular, the recycle stream is, on the industrial scale, limited
Further preferred catalysts comprise by the maximum sizes of available apparatuses, so that a
Pd and Rh or lower process pressure requires, at the same plant capacity
Ag and Rh and the same maximum recycle Volume stream, more reac
as hydrogenation-active elements, in each case on an inert tion stages.
Support, preferably Al-O, particularly preferably C-Al-O. Steam or nitrogen can be fed in in a targeted manner or be
The reaction over a solid catalyst can be carried out 10 left in the process in the desired concentrations by means of
largely isothermally (i.e. with removal of the heat of reac targeted discharge in order to increase the average molar
tion), e.g. in a shell-and-tube reactor or fluidized-bed reactor. mass of the recycle gas to be compressed (averaged over all
Suitable apparatuses are described in Perry's Chemical components present) in order to achieve more favorable
Engineers' Handbook, 8' edition, chapter 19, 2007, and 7" compression in vaporization and reaction.
edition, chapter 23, 1999, Mcgraw-Hill Professional. It is 15 The reaction products toluenediamine (TDA) and water
also possible to carry out the reaction adiabatically, e.g. in a are selectively removed from the toluenediamine-containing
fixed-bed reactor (as described in DE 10 2006 035 203 A1, gas stream by condensation in step (IV). In the case of a
especially in paragraphs 0006, 0020 and 0030 to plurality of reactors connected in series, this can occur either
0032). In an adiabatic reactor, an adiabatic temperature after each reactor or preferably only after the last reactor.
increase of from 50 K to 150 K is preferably set. To maintain Suitable apparatuses for this purpose are known to those
this temperature increase, the gas stream 4 has to be set skilled in the art and are, for example, air coolers or
appropriately (for example by means of a Sufficiently large shell-and-tube heat exchangers. Condensation preferably
excess of hydrogen). A person skilled in the art will know occurs fractionally in a plurality of condensers (4010, 4020,
how the required selection of the gas stream 4 can be 4030) connected in series with a gradually decreasing con
calculated. A combination of the various modes of operation 25 densation temperature, where the gas phase from one con
is likewise conceivable. denser is conveyed into the following condenser. In a
The removal of the heat of reaction is integrated in the preferred embodiment, condensation is carried out so that
reactor in the case of isothermally operated reactors (e.g. in from two to five, particularly preferably four, condensate
the case of shell-and-tube reactors having a cooling circuit fractions are obtained. In an embodiment having five con
(e.g. oil, water or salt melt) for removing the heat of 30 densate fractions 6a, 6b, 6c. 6d and 6e, the condensation
reaction). Adiabatically operated reactors are preferably temperature can, for example, be decreased gradually as
followed by apparatuses for the removal of heat (e.g. heat follows:
exchangers). The temperature level allows the heat to be 6a: condensation at from 175° C. to 195°C.,
removed to be utilized for heating suitable heat transfer 6b; condensation at from 145° C. to 165° C.,
media, e.g. for generating steam having a maximum pres 35 6c: condensation at from 129° C. to 149° C.,
sure, preferably from 3 to 10 bar (absolute). 6d: condensation at from 85° C. to 105° C.
Two or more reaction stages can be connected in series 6e: condensation at from 30° C. to 50° C.
with or without intermediate introduction of one or more The various condensate streams (6a, 6b, 6c,...) obtained
starting materials. If DNT is fed into each reactor, each in this way are preferably introduced separately from one
reactor preferably has a dedicated DNT vaporization stage. 40 another at different places into a downstream distillation
The gas exiting from the last reaction stage is, after Sub sequence. This distillation sequence can consist of conven
stantial removal of the reaction products and discharge of tional distillation columns (or an individual distillation col
undesirable components, advantageously recirculated to the umn) with which a person skilled in the art will be familiar.
vaporization and/or reaction stages in order to utilize starting In particularly preferred embodiments, the distillation
materials used in excess (i.e. the hydrogen), to assist vapor 45 sequence comprises
ization and to reduce the temperature increase in the reac 1. heat-integrated configurations such as columns having
tOrS. heat pumps or HIDICs (“heat integrated distillation
The connection of a plurality of reaction stages in series columns’) or
is particularly advantageous in the case of an adiabatic 2. thermally coupled columns such as columns having
reaction since the amount of DNT which can be reacted per 50 side stream stripping or rectification columns, side
stage can be limited firstly by the low vapor pressure and stream vaporizers or preseparation columns or pre
secondly by the adiabatic temperature increase. If a largely vaporizers, for example Petlyuk or Kaibel configura
isothermal reactor is used, the use of a preceding adiabatic tions, or dividing wall columns.
reaction stage, without intermediate cooling or with little In addition, the distillation columns can have a number of
intermediate cooling, can be advantageous in order to pre 55 pump liquid circuits.
heat the gas stream by means of the heat of reaction before If a plurality of condensate fractions 6a, 6b, etc., are fed
vaporization, so that the vaporization of DNT is made easier. to the same distillation column, preference is given to the
A particularly efficient embodiment of the process comprises fractions obtained at higher temperature being introduced
the alternate use of adiabatic and isothermal reaction stages into the distillation column above the fractions obtained at
since the particularly high exit temperature from the adia 60 lower temperature.
batic reaction stages can be utilized for vaporizing large The abovementioned distillation sequences are consider
amounts of DNT for reaction in the isothermal stages. It is ably cheaper to install and to operate than a TDA distillation
also conceivable to integrate steps (I) to (III) in one appa sequence according to the prior art having up to six distil
ratuS. lation columns.
The hydrogenation in step (III) is advantageously carried 65 A Substream is preferably discharged from the remaining
out at an absolute pressure of from 1.0 bar to 20 bar, incondensable gas stream in order to avoid accumulation of
preferably from 3.0 bar to 6.0 bar. Relatively low pressures Volatile undesirable components in the process. Subse
 US 9,518,006 B2
13 14
quently, the pressure is preferably increased and the com exchanger 5000. However, this will generally not be suffi
pressed stream is recirculated to the process (hydrogen ciently complete, so that a condenser 4000 is installed
containing gas stream 7). downstream.
The hydrogen-comprising gas phase 7 obtained in step FIG. 1a shows, in a section of the total process of the
(IV) is recirculated in step (V) to the first vaporization embodiment shown in broken lines in FIG. 1, a preferred
apparatus (1000, 1010). In a preferred embodiment, the variant of this embodiment in which a two-fluid nozzle 7000
hydrogen-comprising gas phase 7 is used to provide the is used. Fresh hydrogen 200 serves simultaneously as atom
hydrogen-containing carrier gas stream 2. This can be izing gas 9. The two-fluid nozzle opens directly into the
effected by mixing fresh hydrogen 200 with the DNT vaporization apparatus 1000. A possible configuration of a
containing stream 1 (preferably in a two-fluid nozzle) before 10 two-fluid nozzle 7000 as internally mixing nozzle is shown
the resulting mixed stream is sprayed into the carrier gas in FIG 1b.
stream 2 (in this embodiment identical to the recycled gas The condensation in the apparatus 4000 is preferably
stream 7) (shown by broken lines in FIG. 1). As an alter carried out in Such a way that a preseparation of the crude
native, it is also conceivable (as shown by solid lines in FIG. TDA takes place at this early stage, which considerably
1) to combine fresh hydrogen (200) with the recycled 15 assists the Subsequent work-up (FIG. 2). For this purpose,
process gas stream 7 to form the carrier gas stream 2 before the product 5 which is obtained in gaseous form is separated
the DNT-containing gas stream 1 is sprayed in. In the case into a plurality of condensate fractions 6a, 6b, 6c, etc., by
of a plurality of reactors connected in series, the stream 7 is means of a fractional condensation in condensers (4010.
used directly only for providing the carrier gas stream 2 for 4020, 4030) connected in series with gradually decreasing
the first reactor. The carrier gas stream for the Subsequent temperature. The embodiment with three condensate
reactors is the toluenediamine-containing gas stream (51) or, streams as shown in the drawing is merely by way of
if this is, as is preferred, enriched with fresh hydrogen (200), example. Each of the resulting condensate fractions is fed to
as shown in FIG. 3, the stream 22 which naturally contains a different place matched precisely to this fraction in the
the constituents of the stream 7. distillation column 6000 in the subsequent distillation
The liquid phase 6 (or the liquid phases 6a, 6b, 6c, etc.) 25 sequence (step (VI)). In this way, various toluenediamine
obtained in step (IV) contains, apart from the target product fractions 8a, 8b, 8c and 8d which differ in terms of their
toluenediamine, mainly water and minor amounts of sec isomer composition and secondary component content are
ondary components. Stream 6 (or the liquid phases 6a, 6b, obtained.
6c, etc.) is preferably worked up by methods known per se FIG. 3 shows an arrangement in which two adiabatically
comprising distillation of the crude TDA in a further step 30 operated reactors 3110 and 3120 having two vaporization
(VI) in order to obtain pure toluenediamine. Suitable meth apparatuses 1010 and 1020 are connected in series instead of
ods are described, for example, in U.S. Pat. No. 6,359,177 one reactor 3100. The depiction of two reactors is purely by
and U.S. Pat. No. 7,307,190. This work-up can be simplified way of example; the actual number of the reactors to be
significantly by a Suitable prefractionation in step (IV). selected depends on many factors such as the desired
Various embodiments of the invention are illustrated 35 production capacity, the recycle gas Volume, etc. Preference
below with the aid of the drawings: is given to from 8 to 12 reactors being connected in series.
FIG. 1 shows, in greatly simplified form, a basic embodi The reaction route shown in FIG. 1 by broken lines can
ment of the process of the invention having only one reactor naturally likewise be used here and has not been drawn in
3100. Details such as compressors have not been shown for merely for reasons of clarity.
reasons of clarity. 40 Technical-grade DNT (1) is brought into the gas phase in
Technical-grade DNT (1) is brought into the gas phase in a vaporization apparatus 1010 or 1020 by spraying into the
a vaporization apparatus 1000 by spraying into the hydro hydrogen-containing carrier gas stream 21 or 22 (step (I)).
gen-containing carrier gas stream 2 (step (I), Solid lines). It Before entry into the respective reactor, the stream 31 or 32
is also conceivable to use the process gas stream 7 as is additionally freed of liquid droplets in an apparatus 2010
hydrogen-containing carrier gas stream 2 and mix fresh 45 or 2020 (step (II)) so as to obtain a gas stream 41 or 42. The
hydrogen 200 with the DNT stream 1 (broken lines) before hydrogenation takes place under adiabatic conditions in the
entry into the vaporization apparatus. Before entry into the reactors 3110 and 3120 (step (III)). The heat of reaction is
reactor, the stream 3 is freed of last liquid droplets in an reflected, except for Small unavoidable heat losses, quanti
apparatus 2000 (step (II)). The liquid stream 8 obtained in tatively in a temperature increase of the gas stream (adia
this way is, to avoid undesirable reactions, either cooled 50 batic temperature increase). The gaseous product stream 51
further quickly or subjected to controlled decomposition leaving the first reactor is cooled to the entry temperature in
(e.g. by irradiation with microwaves or controlled thermal the following stage with generation of steam in a down
decomposition brought about in another way; not shown in stream heat exchanger 5010. After passing through the last
the figure). The gas stream 4 is introduced into the reactor heat exchanger 5020, the product passes through a multi
3100. In the reaction space 3000, the hydrogenation takes 55 stage condensation and phase separation in 4000 (step IV).
place in the presence of the catalyst 100 (step (III)). The The streams 6a, 6b and 6c obtained here are worked up in
gaseous product stream 5 leaving the reactor is cooled in the step (VI) (not shown in the figure) to give pure TDA. The
heat exchanger 5000 by heat exchange with stream 7 and gas phase obtained is, after heat exchange with stream 52
condensed in the condensation apparatus 4000, giving a and optionally after discharge of a small part as purge stream
toluenediamine-comprising liquid phase 6 and a hydrogen 60 (not shown in the figure), recirculated as stream 7 to the
comprising gas phase 7. Stream 7 is, optionally after dis process (step (V)).
charge of a small proportion (not shown in the figure) in The process of the invention can be carried out in various
order to prevent accumulation of undesirable gases, mixed embodiments. The reaction in the reaction space 3000
with the fresh hydrogen 200 in order to obtain the hydrogen (3010, 3020) can, as mentioned above, be carried out
containing carrier gas stream 2. Stream 7 is preheated in the 65 adiabatically or isothermally. The catalyst 100 (110, 120)
heat exchanger 5000 by heat exchange with stream 5. Partial can be present in the form of a fixed bed or a fluidized bed.
condensation of the stream 5 can occur already in the heat The process can also be carried out in a plurality of stages
 US 9,518,006 B2
15 16
(i.e. in a plurality of reaction spaces 3010, 3020, . . . ) with in which a fractional partial condensation to give liquid
multiple addition of fresh DNT, with from two to 10 stages TDA-containing streams (6a, 6b, 6c) already occurred. The
being preferred. Here, the type of reaction space 3000 can gas stream which remained was partially liquefied in a
vary from stage to stage. For example, an embodiment in scrubber (4000) to give the TDA-containing liquid phase 6d.
which adiabatically and isothermally operated reaction 5 The overhead product from the scrubber (4000) was passed
spaces alternate (3010: adiabatic, 3020: isothermal, 3030: through a condenser (4010), the liquid phase obtained there,
adiabatic, etc.) is conceivable. Fixed-bed reactors and flu which consisted predominantly of water and minor propor
idized-bed reactors can also be combined with one another tions of low-boiling by-products and traces of TDA, partly
in a production plant, for example in an alternating fashion. recirculated to the scrubber and partly discharged. A small
In addition, apparatuses for removal of heat (heat 10
purge stream was taken off from the recycle gas stream (7)
exchangers) can be provided between the individual stages. leaving the condenser (4010) and the remaining recycle gas
Such apparatuses for removal of heat are preferably installed stream (7) was compressed (both not shown in the figure).
downstream of the adiabatically operated reaction spaces. In After heating by indirect heat exchange with the hot TDA
the case of isothermally operated reaction spaces, the gas stream 58 in 5080, the recycle gas stream (7) was fed as
removal of heat occurs in the reaction space itself. It is 15
carrier gas stream (21-7) to the vaporization of the DNT/
likewise possible for part or all of the heat of reaction from fresh hydrogen mixture (11+210) in the spray vaporizer
the preceding stage to be used for the (naturally endother
mic) vaporization of fresh DNT in each stage and thus to be (1010).
made directly useful. The condensation of the individual TDA fractions
occurred at the following temperatures:
EXAMPLES 6. 185° C.
6B. 1550 C.
Example 1 6c. 135° C.
6d 95° C.
Process Simulation by Means of Aspen Plus(R for a 25 These four streams were fed separately from one another
Process Having Eight Reactors Connected in into a distillation column having a convection vaporizer,
Series: FIG. 4 side offtake and overhead condenser (not shown in FIG. 4),
with the stream 6a being fed into the column 5 theoretical
39.8 metric tons of DNT (1) per hour were melted at from plates above the bottom. Stream 6b was fed in above 6a,
70° C. to 100° C., compressed to an absolute pressure of 30
stream 6c was fed in above 6b and stream 6d was fed in
from 10 to 20 bar and divided into eight streams (11, above 6c. The absolute pressure at the top of the distillation
12. . . . , 18). 2959 kg/h of fresh hydrogen (200) were column was 60 mbar. Four product streams were taken off:
supplied at the same absolute pressure and likewise divided gaseous overhead product comprising predominantly water
into eight streams (210, 220, . . . . 280). DNT streams (11, and low boilers;
12, ..., 18) and fresh hydrogen streams (210, 220, ..., 280) 35
liquid overhead product comprising predominantly o-TDA:
were mixed with one another in two-fluid nozzles (not
shown) in each case. The resulting mixed streams were fed a product which was taken off as side stream and comprised
to spray vaporizers (1010, 1020, ..., 1080). In the first spray predominantly m-TDA (25 metric tons per hour);
vaporizer, recycle gas (7; about 100 000 m/h) under an bottom product comprising predominantly high boilers.
absolute pressure of 4.2 bar was used as carrier gas stream 40 The energy consumption of the convection vaporizer was
(21) into which the DNT/fresh hydrogen mixture (11+210) 5.5 MW at 202° C.
was sprayed. The resulting predominantly gaseous mixed For such a distillation performance, the use of a plurality
stream (31) was conveyed through a droplet precipitator of distillation columns is required according to the prior art.
(2010). The residence time of the DNT between entry into This is made clear in the specialist literature; see, for
the spray vaporizer and entry into the droplet precipitator 45 example, Kirk-Othmer, Encyclopedia of Chemical Technol
was 0.25-0.35 second. In the embodiment shown, the appa ogy, John Wiley & Sons Inc.; 5' edition (Jan. 31, 2004), Vol.
ratus for droplet precipitation is integrated into the vapor 2, page 485, online ISBN: 9780471238966, where the use of
ization apparatus. Nonvaporizable components were taken three distillation columns for removal of water and isomer
off as liquid stream (81) at the bottom of the spray vaporizer separation is described. EP 1935871 A2 states that, by means
(1010). All resulting liquid streams of unvaporizable com 50
of a suitable energy saving connection with the reaction
ponents (81, 82. . . . , 88) were quickly cooled to a section, a calculated 10.9 MW of steam from outside is
temperature below 40°C. and safely disposed of (not shown required for water removal in order to obtain 25 t?h of
in the figure). The gas stream (41) from the spray vaporizer m-TDA product stream. According to U.S. Pat. No. 7.307.
was fed into the reactor 3110. In the reaction space 3010, 190 B2, the subsequent isomer separation can be brought
DNT was converted into TDA under adiabatic conditions. 55
The TDA-containing recycle gas stream (51) leaving the about in an energy-saving manner in a dividing wall column,
reactor was cooled to a temperature of 180° C. in a heat for which a prevaporizer power of a calculated 5.6 MW is
exchanger (5010) with generation of 6 bar steam and fed as required for obtaining 25 t?h of m-TDA product stream.
carrier gas stream (22) for the DNT/fresh hydrogen mixture According to the prior art, a total of at least 16.5 MW of
(12+220) to the next spray vaporizer (1020). The mixed 60 vaporizer power is accordingly required in at least two
stream (32) obtained is freed of droplets as described above columns for the fractionation of the total reaction mixture,
and converted into TDA in the reactor 3120. The further compared to 5.5 MW in the process of the invention. In
reaction in the reactors 3130 to 3180 was carried out addition, the distillation according to the invention in one
analogously with slightly different temperatures. column is cheaper in terms of apparatus and simpler to
The product gas stream (58) obtained after passage 65 operate than the two-column distillation sequence according
through the last reactor (3180) was passed through a plu to the prior art consisting of a column with heat integration
rality of heat exchangers (shown in simplified form as 5080) of the reaction section and also a dividing wall column.
 US 9,518,006 B2
17 18
The invention claimed is: 2. The process of claim 1, wherein the spraying of the
1. A continuous process for preparing toluenediamine by dinitrotoluene-comprising stream into the hydrogen-con
hydrogenation of dinitrotoluene in the gas phase, compris taining carrier gas stream in step (I) is carried out by means
1ng: of at least one two-fluid nozzle through which a stream of an
(I) spraying a dinitrotoluene-comprising stream into a atomizing gas which is under a pressure of from 1.0 bar to
hydrogen-containing carrier gas stream in a vaporiza 20 bar higher than the absolute pressure prevailing in the
tion apparatus, where Surroundings on the nozzle exit side is passed in addition to
a) the temperature of the dinitrotoluene-comprising the dinitrotoluene-comprising stream.
stream is from 70° C. to 150° C. and the temperature 3. The process of claim 2, wherein steam, nitrogen, fresh
of the hydrogen-containing carrier gas stream is from 10 hydrogen, part of the hydrogen-comprising gas phase, part
140° C. to 300° C., of the hydrogen-containing carrier gas stream or a mixture
b) the absolute pressure of the dinitrotoluene-compris of two or more of the abovementioned gases is used as
ing stream is from 3.0 bar to 30 bar and the absolute atomizing gas.
pressure of the hydrogen-containing carrier gas 4. The process of claim 1, wherein the condensation in
stream is from 1.0 bar to 10 bar, where the pressure 15
step (IV) is carried out fractionally with a gradually decreas
of the dinitrotoluene-comprising stream is higher ing condensation temperature so that a plurality of toluene
than that of the hydrogen-containing carrier gas diamine-comprising liquid phases are obtained.
stream, and 5. The process of claim 1, further comprising:
c) the molar ratio of hydrogen to dinitrotoluene is from
6.0:1 to 900:1, (VI) working UP the toluenediamine-comprising liquid
So as to give a stream comprising dinitrotoluene and phase and/or the toluenediamine-comprising liquid
hydrogen; phases obtained in step (IV) by distillation in order to
(II) removing or targetedly decomposing the liquid drop obtain pure toluenediamine.
lets present in the stream comprising dinitrotoluene and 6. The process of claim 5, wherein the condensation in
hydrogen from Step (I) to give a gas stream which 25 step (IV) is carried out fractionally with a gradually decreas
comprises dinitrotoluene and hydrogen and has been ing condensation temperature so as to give a plurality of
depleted in liquid droplets; toluenediamine-comprising liquid phases which are, in step
(III) reacting the dinitrotoluene present in the gas stream (VI), introduced separately from one another into various
which comprises dinitrotoluene and hydrogen and has places in the work-up by distillation.
been depleted in liquid droplets with hydrogen in at 30
7. The process of claim 1, wherein the dinitrotoluene in
least one reaction space in the presence of a catalyst at the dinitrotoluene-comprising stream has the following
an absolute pressure of from 1.0 bar to 10 bar, a composition:
temperature of from 140°C. to 300° C. and a residence
time in the reaction space of from 0.1 s to 10 s, so as from 99.00% by mass to 99.94% by mass of dinitrotolu
to give a toluenediamine-containing gas stream, 35 ene,
(IV) separating the toluenediamine-containing gas stream >5 ppm of nitrocresols,
obtained in step (III) after passing through the last >20 ppm of trinitrotoluene, and
reaction space into a toluenediamine-comprising liquid >500 ppm of other impurities comprising water, mono
phase and a hydrogen-comprising gas phase by con nitriotoluene, Sulfuric acid and salts of Sulfuric acid,
densation; and 40
in each case based on the total mass of the dinitrotoluene
(V) recirculating at least part of the hydrogen-comprising in the dinitrotoluene-comprising stream.
gas phase obtained in step (IV) into the first vaporiza
tion apparatus of step (I). k k k k k