One-step synthesis of N-methylaniline by hydroalkylation of nitrobenzene over oxide catalysts

Article abstract of DOI:10.1134/S0965544114060024

The reaction of nitrobenzene hydroalkylation with methanol forming N-methylaniline as the main product has been studied. Alumina modified with copper and chromium compounds deposited by incipient wetness impregnation has been examined as the catalyst. It has been shown that the reductive alkylation of nitrobenzene with methanol is preferable to conduct at a temperature of 250°C, a feed weight hourly space velocity of 1 to 2 h^-1, a methanol: nitrobenzene molar ratio of 3 to 4, and hydrogen: nitrobenzene molar ratio of 3-6. It has been found that promotion of the copper-containing catalyst with chromium leads to enhancement of the catalyst activity and facilitates an increase in selectivity for N-methylaniline.

Full text of DOI:10.1134/S0965544114060024

ISSN 0965ꢀ5441, Petroleum Chemistry, 2014, Vol. 54, No. 6, pp. 438–444. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © M.V. Belova, O.A. Ponomareva, I.I. Ivanova, 2014, published in Neftekhimiya, 2014, Vol. 54, No. 6, pp. 448–454.
OneꢀStep Synthesis of
NꢀMethylaniline by Hydroalkylation
of Nitrobenzene over Oxide Catalysts
a
a, b
a, b
M. V. Belova , O. A. Ponomareva , and I. I. Ivanova
a
Moscow State University, Moscow, Russia
eꢀmail: belova.msu@gmail.com
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
b
Received May 27, 2014
Abstract—The reaction of nitrobenzene hydroalkylation with methanol forming
Nꢀmethylaniline as the
main product has been studied. Alumina modified with copper and chromium compounds deposited by
incipient wetness impregnation has been examined as the catalyst. It has been shown that the reductive alkyꢀ
lation of nitrobenzene with methanol is preferable to conduct at a temperature of 250°C, a feed weight hourly
–1
space velocity of 1 to 2 h , a methanol : nitrobenzene molar ratio of 3 to 4, and hydrogen : nitrobenzene
molar ratio of 3–6. It has been found that promotion of the copperꢀcontaining catalyst with chromium leads
to enhancement of the catalyst activity and facilitates an increase in selectivity for ꢀmethylaniline.
N
Keywords: hydroalkylation,
Nꢀmethylaniline, nitrobenzene, oxide catalysts
DOI: 10.1134/S0965544114060024
NꢀMethylaniline is widely used in various indusꢀ chain and the benzene ring to yield
Nꢀsubstituted
tries as a reactant for synthesis of organic compounds; anilines and various toluidines, respectively. The
an additive in manufacture of synthetic rubbers; and direction of the process depends on the reaction conꢀ
raw material in the production of paints, varnishes, ditions, the catalyst, and the strength of its acid sites.
pharmaceuticals, explosives, and nitrocellulose powꢀ
der stabilizers [1]. However, it has found main applicaꢀ
tion in the oil refining industry as an effective antiꢀ
knock additive for petroleum fuels that makes it possiꢀ
ble to increase the octane number (ON) and produce
highꢀoctane gasolines, including those based on lowꢀ
octane feedstock [2].
The alkylation of aniline was studied over various
types of catalytic systems: oxide catalysts [2], spinels
[
[
15–17], zeolites with different framework types
1, 18], aluminophosphates [19], and mesoporous
materials [20]. According to published data [20], Cꢀ
alkylation occurs primarily on catalysts with strong
acid sites whereas the main product of alkylation on
Nowadays Nꢀmethylaniline is manufactured in the catalysts with weak and mediumꢀstrength acid sites or
industry in two steps: the hydrogenation of nitrobenꢀ basic sites is
Nꢀmethylaniline.
zene with hydrogen followed by alkylation of the proꢀ
Since both processes can be carried out on similar
catalytic systems under close conditions and there is a
continuous growth of demand for aniline produced
from nitrobenzene, it is of interest to study the feasibilꢀ
duced aniline to Nꢀmethylaniline [3]. There are many
publications in the scientific literature on each of these
steps. The most frequently used nitrobenzene reducꢀ
tion catalysts are metal containing catalysts based on
palladium on various supports (hydrotalcite [4], MgO ity of production of
Nꢀmethylaniline by reductive
[
[
5],
8, 9] or molecular sieve MCMꢀ41 [10]), or nickel (on data on this process have been reported in the open
ꢀAl O [11], SiO [12], or carbon fiber [13] supports). press so far. In some papers [21–23], the possibility of
γ
ꢀAl O [5, 6], C [7]), platinum (supported on C alkylation of nitrobenzene in one step. Rather scanty
2 3
γ
2
3
2
It should be noted that catalysts based on Group VIII obtaining of
Nꢀmethylaniline via reductive alkylation
metals, such as Pd, Pt, or Ni, are capable of reducing of nitrobenzene over copper catalysts is described.
not only the nitro group, but also double bonds in the Starovoitov et al. [21] used for this purpose an indusꢀ
benzene ring. In the vaporꢀphase process, silica gelꢀ trial copper–zinc–chromium oxide catalyst or the
supported copper is also used as a catalyst [14], which
unlike Group VIII metals, can mediate the selective
hydrogenation of the nitro group with the double carꢀ
bon–carbon bonds remaining intact.
copper–zinc catalyst designed for lowꢀtemperature
conversion of carbon monoxide; the process was conꢀ
ducted in the presence of hydrogen at a nitrobenzene :
alcohol : hydrogen molar ratio of 1 : 1–5 : 3–10. Gorꢀ
The process of aniline alkylation with methanol bunov and coworkers [22] proposed to run the reducꢀ
can proceed via two routes: the alkylation of the side tive alkylation of nitrobenzene and aniline in a
438

ONEꢀSTEP SYNTHESIS OF
N
ꢀMETHYLANILINE BY HYDROALKYLATION
439
Table 1. Physicochemical characteristics of catalysts
2
3
Sample
Ssurf, m /g
Vpore, cm /g
Cu, wt %
Cr, wt %
a0
, mol NH /g
µ
3
Al O
160
109
105
96
0.25
0.20
0.19
0.16
–
–
–
100
160
220
270
2
3
Cu(7.5)/Al O
7.5
7.5
7.5
2
3
Cu(7.5)Cr(1)/Al O3
1.0
5.0
2
Cu(7.5)Cr(5)/Al O3
2
medium of the hydrogen and CO2 mixture obtained by perature was raised to 800
the gasꢀphase condensation of methanol with water. °C/min. The change in heat conductivity of the gas
In this study, the oneꢀstep synthesis of
ꢀmethylaꢀ stream during hydrogen absorption by the sample was
niline by hydroalkylation of nitrobenzene with methaꢀ measured with a thermal conductivity detector.
nol on oxide catalysts composed of alumina modified
°С at a heating rate of
8
N
Catalytic experiments on nitrobenzene hydroalkyꢀ
with copper and chromium compounds was investiꢀ lation with methanol were carried out in a tubular
gated. An attempt to rationalize the dependence of the downꢀflow reactor at atmospheric pressure in the
main parameters of the reductive nitrobenzene methꢀ gas–liquid phase mode in a hydrogen stream at a temꢀ
ylation process upon the reaction conditions and raw perature ranging within 200–275°
С
,
a
feed
weight hourly space velocity (WHSV) of 1.3–
3.0 gfeedstock/(gcatalyst · h), a nitrobenzene: methanol
material composition was made.
2
molar ratio of 1 : 1 to 1 : 4, and a hydrogen : nitrobenꢀ
zene molar ratio of 6 : 1 to 2 : 1.
EXPERIMENTAL
The catalyst was prepared by the simultaneous
The products were analyzed by GLC on a Kristall
incipient wetness impregnation of ꢀAl O (Redkino
γ
2 3
2
000M chromatograph (Chromatec Analytic) using a
flame ionization detector and a fused silica capillary
column ( = 30 m) coated with SEꢀ30; the carrier gas
catalyst plant) with aqueous solutions of the nitrates
Cu(NO3)2 and Cr(NO3)3 taken in amounts to obtain
loadings of 7.5 wt % Cu and 1 or 5 wt % Cr. The resultꢀ
l
was nitrogen. The products were identified with a
Thermo DSQꢀII mass spectrometer combined with a
Trace GC Ultra gas chromatograph equipped with a
ing samples were dried at 100
stream at 375 for 4 h, and in situ reduced for 20 min
at 250 in a hydrogen stream prior to the experiment.
°С, oxidized in an air
°С
°
С
5
0ꢀm fused silica capillary column coated with the
Lowꢀtemperature nitrogen adsorption isotherms
were recorded with a Micromeritics ASAP2000 autoꢀ
mated porosimeter. Preliminarily, all the samples were
OVꢀ101 phase. Chromatogram recording and processꢀ
ing were performed using a HewlettꢀPackard hardware
and software system.
⎯
3
evacuated at 350
pore volume was calculated from the amount of nitroꢀ
gen sorbed at a relative pressure of p0=0.945
°С to 10 Pa. The total adsorptive
p/
.
RESULTS AND DISCUSSION
Catalyst Properties
The acidic properties of the catalysts were studied
using temperatureꢀprogrammed desorption of ammoꢀ
nia (NH3 TPD) on a Unisit USGAꢀ101 sorption anaꢀ
The physicochemical characteristics of the samꢀ
lyzer. The sample was calcined in a flow of dry helium ples, which were metal oxides deposited on alumina by
at 550
Adsorption of ammonia was performed for 15 min at The data in the table show that the deposition of metꢀ
in a 1 : 1 mixture with nitrogen. The physisorbed als in an amount of 7.5–12.5 wt % on Al leads to a
ammonia was removed by purging with dry helium at decrease in the surface area of the samples by
00
for 1 h. The NH3 TPD experiments were conꢀ about 40%.
ducted in the temperature range of 60 to 700 in a
The amount and strength of acid sites of the oxide
dry helium stream (flow rate of 30 mL/min) at a heatꢀ catalysts were determined using the ammonia temperꢀ
ing rate of °C/min.
atureꢀprogrammed desorption technique. Figure 1
°С
and then cooled to room temperature. incipient wetness impregnation are given in Table 1.
6
0°C
O
2 3
1
°С
°
С
8
The redox properties of the catalysts were examꢀ shows NH3 TPD curves of the initial alumina, the copꢀ
ined using the technique of temperatureꢀprogrammed perꢀcontaining sample Cu(7.5)/Al O3, and the bimeꢀ
2
Cu(7.5)Cr(1)/Al O3
reduction by hydrogen (H2 TPR) on the Unisit tallic
catalysts
and
2
USGAꢀ101 analyzer. A weighed catalyst sample was Cu(7.5)Cr(5)/Al O3. The curves display one broad
2
placed in a fusedꢀsilica reactor and subjected to preꢀ peak corresponding to weak acid sites and acid sites of
treatment comprising holding the sample for 1 h at medium strength with Tmax in the range of 150–250
75 in an argon stream and cooling to room temꢀ The alumina and the copperꢀcontaining samples are
perature in an Ar stream. Then, a mixed stream conꢀ characterized by a low amount of weak and mediumꢀ
taining 3.5% hydrogen in argon was passed through strength acid sites of 100 and 150 mol/g, respectively.
the reactor at a flow rate of 10 mL/min and the temꢀ The introduction of chromium led to an increase in
°С.
3
°С
µ
PETROLEUM CHEMISTRY Vol. 54
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2014

440
BELOVA et al.
0.30
0.25
0.20
0.15
0.10
0.05
0
12
4
3
1
0
8
6
4
2
2
3
1
2
1
2
1
0
1
00
150
200
250
300
350
T
, °C
50
150
250
350
450
T, °C
Fig. 1. TPD NH3 curves for Cu(7.5)Cr(X)/Al O catalysts:
Fig. 2. TPR H curves for Cu(7.5)Cr(X)/Al O samples:
2 2 3
2
3
(1
) Al O , (
2
) Cu(7.5)/Al O , (
3
) Cu(7.5)Cr(1)/Al O , and
(
(
1)
Cu(7.5)/Al O ,
(
2)
Cu(7.5)Cr(1)/Al O , and
2
3
2
3
2
3
2
3
2 3
2 3
(4
) Cu(7.5)Cr(5)/Al O .
3
) Cu(7.5)Cr(5)/Al O .
2
3
the amount of sites; the Cu(7.5)Cr(1)/Al O3 and curves to lower temperatures, thereby indicating either
2
Cu(7.5)Cr(5)/Al O samples had a0 = 220 and
2
3
a decrease in particle size of the metal oxide or weakꢀ
ening its interaction with the support. Furthermore,
the introduction of the second metal can lead to the
appearance of new peaks due to the reduction of its
2
70
on the chromiumꢀcontaining sample can be due to the
interaction of ammonia with the acid oxide CrO3
µ
mol/g, respectively. The high adsorption of NH3
.
Figure
2
presents H2 TPR curves for oxide to certain oxidation states. The deposition of
Cu(7.5)Cr(X)/Al O samples oxidized at 375°C. The Cr O3 in an amount of 1 wt % Cr onto CuOꢀmodified
2
3
2
temperatureꢀprogrammed reduction curve for the sinꢀ alumina did not result in a shift of the highꢀtemperaꢀ
gleꢀcomponent copper catalyst displays two distinct ture peak; however, the ratio between the areas of the
peaks. Luo et al. [24] believe that the first peak at 190–
00 is due to the reduction of fine copper particles
and the second peak at 250 is associated with the
reduction of larger particles. Table 2 presents values for
the hydrogen uptake in the Н2 TPR experiments and
the molar ratio of the hydrogen absorbed to the total
metals in the sample. The data in Table 2 show that the
amount of hydrogen consumed for the reduction of
the copper catalyst is almost equal to the theoretically
highꢀtemperature and lowꢀtemperature peaks
changed, suggesting either a decrease in the particle
size of CuO in the bimetallic samples or that the
reduction of chromia occurs at the same temperatures
2
°С
°С
of 180–200
°С. A similar reduction behavior of Al O3ꢀ
2
supported CuO in the case of modification with chroꢀ
mium oxide was observed in [27].
As the amount of the second metal is increased to
predicted amount required for the complete reduction 5 wt %, the tendency shown by the H2 TPR curve for
0
of CuO to Cu
.
Cu(7.5)Cr(1)/Al O3 becomes more pronounced, the
2
addition of 5 wt % chromium facilitates the reduction
of CuO. The H2 TPR curve of the copper–chromium
The addition of the second metal altered the shape
and the ratio of the peaks on the H2 TPR curves for
both samples with chromium contents of 1 and 5 wt %. sample displays one distinct reduction peak (T =
max
According to published data [25, 26], the introduction 200°C) with a shoulder at about 240°С attributed to
of the second metal can shift the peak on the H2 TPR the reduction of the bulk CuO phase [28].
Table 2. Hydrogen uptake in H TPR experiments on Cu(7.5)Cr(X)/Al O samples
2
2 3
Mol of H /mol of metal
2
Catalyst
Cu(7.5)/Al O
a
(Me),
µ
mol/g
a
(H2), µmol/g
theoretical*
experimental
1181
1324
1895
1283
1942
2488
1.0
4.0
4.0
1.1
5.0
4.6
2
3
Cu(7.5)Cr(1)/Al O3
2
Cu(7.5)Cr(5)/Al O3
2
*
The amount of hydrogen required for the reduction of the samples was calculated on the basis of the assumption that the oxides CuO
0
0
and CrO are reduced to Cu and Cr , respectively
3
PETROLEUM CHEMISTRY Vol. 54
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ONEꢀSTEP SYNTHESIS OF
N
ꢀMETHYLANILINE BY HYDROALKYLATION
441
Concerning Cr O3, some investigators [29, 30]
believe that chromium(III) oxide is not reduced at
2
90
80
temperatures below 500
oxide that is supposedly [31] reduced with hydrogen to
give Cr O . However, our calculation results show that
°С, but it is chromium(VI)
70
60
2
3
NꢀMethylaniline
0
CrO3 undergoes reduction to Cr (Table 2); presumꢀ
ably, the reduction of the oxide is promoted by the
presence of CuO.
50
40
Aniline
3
2
1
0
0
0
Conversion of Nitrobenzene and Methanol on Oxide
Catalysts in the Presence of Hydrogen
N,NꢀDimethylaniline
40
60 80 100
Since the hydroalkylation of nitrobenzene on oxide
catalysts is a complex process, revealing the sequence
of product formation is an important task for controlꢀ
ling the selectivity of the reaction. In this study, the
kinetic analysis of the process was performed using the
Wojciechowski method [32], which suggests plotting
experimental selectivity curves, i.e., relating timeꢀ
averaged product yields to the feedstock conversion
0
20
Conversion, %
Fig. 3. Selectivity curves for the products of nitrobenzene
hydroalkylation with methanol on the Cu(7.5)Cr(5)/
O catalyst at 250°C and a nitrobenzene : methanol :
hydrogen molar ratio of 1 : 3 : 4.5.
Al
2 3
(
with varying contact time at a fixed catalyst to feedꢀ
stock weight ratio). By the shape of the curves, the
sequence of product formation and transformations of
the products can be evaluated. The products can be
primary or secondary and stable or unstable (intermeꢀ
diate).
with the hydrogenation and alkylation products,
methanol conversion products, such as dimethyl
ether, methane, alkanes, and С –С6 alkenes were
2
formed in the reaction. The methanol conversion into
gas did not exceed 7–10% in all the experiments.
The kinetic study was performed on the
Cu(7.5)Cr(5)/Al O catalyst at atmospheric pressure,
2
3
Т
= 250°C, and a reactant molar ratio of nitrobenzene :
Hydroalkylation of Nitrobenzene with Methanol
on MetalꢀContaining Catalysts
methanol : hydrogen = 1 : 3 : 4.5 in the wide range of
contact time of 0.8 to 0.043 h.
Figure 3 presents selectivity curves for all of the
substances produced during the reaction. The depenꢀ
dence of the yields of hydroalkylation products
Table 3 presents the results of catalytic experiments
on the catalysts Cu(7.5)Me(X)/Al O3. The addition of
2
chromium enhances the catalyst activity in compariꢀ
son with the copper catalyst: the conversion of
nitrobenzene increases from 33% over Cu/Al O to
(
aniline, Nꢀmethylaniline, N,Nꢀdimethylaniline) on
the conversion of nitrobenzene has a pattern characꢀ
teristic of primary and secondary products. Appaꢀ
rently, nitrobenzene hydrogenation initially gives
aniline (primary unstable product), which reacts with
2
3
8
4% on Cu(7.5)Cr(X)/Al O3. The bimetallic catalysts
2
are more active in the reductive alkylation of nitrobenꢀ
zene with methanol; it is possible that the introduction
of the second metal makes the dispersion state of CuO
in the samples optimal for hydroalkylation. The
enhancement of the alkylating activity of the chroꢀ
miumꢀdoped samples is consistent with the NH3 TPD
methanol to form
product). As a result of the reaction of
N
ꢀmethylaniline (secondary stable
Nꢀmethylaꢀ
niline with another methanol molecule, N,Nꢀdimethꢀ
ylaniline (secondary stable product) is formed.
It is worth noting that the Cꢀalkylation products data (Fig. 1), since the introduction of chromium led
were found in trace amounts under any selected conꢀ to an increase in the amount of acid sites in these samꢀ
ditions of the process on the test oxide catalysts. Along ples compared with the copper catalyst (Table 1).
Table 3. Results of experiments on nitrobenzene hydroalkylation with methanol
Yield, mol %
Catalyst
PhNO conversion, %
2
aniline
N
ꢀmethylaniline
N
,
N
ꢀdimethylaniline
toluidine
Cu(7.5)/Al O
33.5
83.1
83.6
24.0
25.6
25.6
9.2
56.0
56.4
0.3
3.3
0.9
–
2
3
Cu(7.5)Cr(1)/Al O3
0.4
0.7
2
Cu(7.5)Cr(5)/Al O3
2
Experimental conditions: 250
°
C, 5.75 g/(g h), PhNO : CH OH : H = 1 : 3 : 4.5 (by mole).
2
3
2
PETROLEUM CHEMISTRY Vol. 54
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442
BELOVA et al.
Influence of Reaction Conditions
90
80
70
60
50
40
30
20
10
3
The effect of temperature on nitrobenzene
hydroalkylation with methanol was studied at 200–
275°С on the Сu(7.5)Cr(5)/Al O3 catalyst at atmoꢀ
2
spheric pressure, a feed WHSV of 5.75 g/(g h), and a
nitrobenzene : methanol : hydrogen molar ratio of 1 :
: 4.5 (Fig. 5a). As the temperature increases, the
nitrobenzene conversion passes through a maximum
at 250 . The increase in the conversion at 200–
50 can be explained in terms of an increase in the
reaction rate with temperature. Since hydrogenation is
an exothermic process, the equilibrium during the furꢀ
ther rise in temperature is displaced toward the reacꢀ
tants and the conversion of nitrobenzene decreases.
The yields of hydroalkylation products also pass
through a maximum, which coincides with that of
nitrobenzene conversion. As the temperature
2
3
1
°С
2
°С
20
40
60
80
100
120
Time, min
Fig. 4. Time dependence of the nitrobenzene conversion
increases, alkylation is enhanced;
becomes the main product at 225
ylaniline appears as a product at a temperature above
250
N
ꢀmethylaniline
N,N
on Cu(7.5)Cr(X)/Al O catalysts at 250°C, 5.75 g/(g h)
2
3
°С
and ꢀdimethꢀ
and hydrogen: methanol : nitrobenzene molar ratio of 4.5 :
: 1. ( ) Cu(7.5)/Al O , ( ) Cu(7.5)Cr(1)/Al O , and (
Cu(7.5)Cr(5)/Al O .
3
1
2
3)
2
3
2 3
°С.
2
3
An increase in the feed weight hourly space velocity
from 1.3 t o 23.0 gfeedstock/(gcatalyst h) leads to a decrease
sion shows that all of the Cu(7.5)Сr(X)/Al O catalysts in nitrobenzene conversion from 99 to 4.5% (Fig. 5b).
The time dependence of the nitrobenzene converꢀ
2
3
are deactivated with time under the given reaction At the same time, the product ratio also depends on
conditions, with the conversion decreasing approxiꢀ the contact time. At the maximum contact time, alkyꢀ
mately by 20% during 2 h on stream (Fig. 4).
lation proceeds at a high rate and the main products
are ꢀmethylaniline and N,Nꢀdimethylaniline. As the
feed space velocity increases, the contribution of the
dialkylation products decreases and, at a WHSV above
N
The data on the activity and selectivity of the test
catalysts
lead
to
the
conclusion
that
Сu(7.5)Cr(5)/Al O is the best catalyst; therefore it
2
3
6
g/(g h), N,Nꢀdimethylaniline is not produced at all
was chosen for further investigation of the effect of the
reaction conditions and the feedstock composition on and the primary product aniline makes a progressively
the parameters of the process. increasing contribution to the reaction products.
100
(a)
100
(b)
1
80
60
40
20
80
60
40
20
1
2
2
3
3
4
4
0
2
00
225
250
275
0
5
10
15
20
25
°C
g/g h
Fig. 5. Influence of the reaction conditions on the parameters of the hydroalkylation process on the Cu(7.5)Cr(5)/Al O catalyst:
2
3
(
(
(
a) effect of the reaction temperature at 5.75 g/(g h) and a hydrogen: methanol : nitrobenzene molar ratio of 4.5 : 3 : 1 and
b) effect of the feed weigh hourly space velocity at 250°C and a hydrogen: methanol : nitrobenzene molar ratio of 4.5 : 3 : 1.
1) nitrobenzene conversion, (2) aniline yield, (
3)
Nꢀmethylaniline yield, and (
4) N,Nꢀdimethylaniline yield.
PETROLEUM CHEMISTRY Vol. 54
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2014

ONEꢀSTEP SYNTHESIS OF
N
ꢀMETHYLANILINE BY HYDROALKYLATION
443
1
00
(b)
1
00
(a)
Nitrobenzene conversion
Yield of aniline
8
6
4
2
0
0
0
0
0
8
6
4
2
0
0
0
0
0
Yield of Nꢀmethylaniline
Yield of N,N
ꢀ
dimethylaniline
4.5
6
1
2
3
4
2
Methanol/nitrobenzene
Hydrogen/nitrobenzene
Fig. 6. Influence of the reactant ratio on the basic characteristics of the hydroalkylation process on the Cu(7.5)Cr(5)/Al O caꢀ
2
3
talyst at 250°C and 5.75 g/(g h): (a) effect of the methanol : nitrobenzene molar ratio (hydrogen : nitrobenzene = 4.5 : 1) and
b) effect of the hydrogen/nitrobenzene molar ratio (methanol : nitrobenzene = 3 : 1).
(
Influence of Reaction Mixture Composition
hydrogen = 1 : 3 : 4.5. During 3 h the catalyst operated
stably, the nitrobenzene conversion was 99.5%, and
The correlation between of the nitrobenzene conꢀ
version, the yields of the main products and the comꢀ
position of the reaction mixture are plotted in Fig. 6a.
Analysis of the results shows that the nitrobenzene
conversion remains at the level of 80% after adding an
excess of methanol; the dilution does not affect the
hydrogenation process. An increase in the methanol to
nitrobenzene molar ratio in the reaction mixture
favors the alkylation process: at a reactant ratio of 1 : 1,
aniline is the main product, having a yield of 79 mol
the
the
N
N
ꢀmethylaniline selectivity was 85 mol %, wherein
ꢀmethylaniline content in the alkylaniline fracꢀ
tion was 91 mol %.
Summing up a new process for the oneꢀstep proꢀ
duction of Nꢀmethylaniline has been proposed, which
is based on the vaporꢀphase hydroalkylation of
nitrobenzene with methanol in a downꢀflow reactor
over a bifunctional catalyst. According to catalytic
experiments, copperꢀcontaining oxide catalysts selecꢀ
tively reduce the nitro group to aniline and promotion
of the copper catalyst with chromium leads to
enhancement of the catalyst activity in the hydroalkyꢀ
lation of nitrobenzene and increases the selectivity for
%, which drops to 19 mol % as the methanol content
in the mixture is increased to 4 : 1. The yield of the
alkylation products increase with the methanol conꢀ
tent; at a methanol : nitrobenzene ratio of 4 : 1, the
amount of N,Nꢀdimethylaniline is significantly
greater. This dependence is explained by the easier
Nꢀmethylaniline. It has been found that optimal conꢀ
ditions for conducting the process of reductive alkylaꢀ
tion of nitrobenzene with methanol are the following:
temperature of 250°С, a feed weight hourly space
velocity of 1 to 2 h , a nitrobenzene : methanol molar
ratio of 3 to 4, and a hydrogen : nitrobenzene molar
ratio of 3–6.
addition of the second methyl group to
Nꢀmethylaꢀ
niline in the presence of a large excess of methanol.
–1
The influence of the molar concentration of hydroꢀ
gen on the nitrobenzene conversion and the product
yields is illustrated in Fig. 6b. There is a logical rise in
the nitrobenzene conversion from 57.5 to 99.8% with
an increase in the hydrogen content relative to
nitrobenzene from 2 : 1 to 6 : 1 in the system. The yield
of aniline passes through a maximum due to an
increase in the nitrobenzene conversion, and the
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No. 6
2014