Hydrogenation of 2,4-dinitrotoluene to 2,4-diaminotoluene over platinum nanoparticles in a high-pressure slurry reactor

Article abstract of DOI:10.1080/00397911.2010.486510

More stringent requirements for reducing the content of aromatics have brought increasing attention to new catalysts involved in hydrotreating process. The dependence of the 2,4-dinitrotoluene hydrogenation rate on catalyst particle size and kinetic parameters in ethanol-water-diaminotoluene three-component solvent over Pt/C nanoparticle catalyst has been studied. The investigation of the effect of particle size of catalyst on the rate of the reaction corresponds to the zero reaction order. An optimum set of conditions for reaction occurrence is established.

Full text of DOI:10.1080/00397911.2010.486510

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Hydrogenation of 2,4-Dinitrotoluene
to 2,4-Diaminotoluene over Platinum
Nanoparticles in a High-Pressure Slurry
Reactor
Mohammad Reza Saboktakin a b , Roya M. Tabatabaie a , Abel
Maharramov b & Mohammad Ali Ramazanov b
a Nanostructured Materials Synthesis Laboratory, International
Research Institute of Arian Chemie Gostar , Tabriz , Iran
b Nanotechnology Research Center, Baku State University , Baku ,
Azerbaijan
Published online: 30 Mar 2011.
To cite this article: Mohammad Reza Saboktakin , Roya M. Tabatabaie , Abel Maharramov &
Mohammad Ali Ramazanov (2011) Hydrogenation of 2,4-Dinitrotoluene to 2,4-Diaminotoluene
over Platinum Nanoparticles in a High-Pressure Slurry Reactor, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 41:10, 1455-1463,
DOI: 10.1080/00397911.2010.486510
To link to this article: http://dx.doi.org/10.1080/00397911.2010.486510
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Synthetic Communications1, 41: 1455–1463, 2011
Copyright # International Research Institute of Arian Chemie Gostar
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.486510
HYDROGENATION OF 2,4-DINITROTOLUENE TO
2,4-DIAMINOTOLUENE OVER PLATINUM
NANOPARTICLES IN A HIGH-PRESSURE
SLURRY REACTOR
Mohammad Reza Saboktakin,1,2 Roya M. Tabatabaie,1
Abel Maharramov,2 and Mohammad Ali Ramazanov2
1Nanostructured Materials Synthesis Laboratory, International Research
Institute of Arian Chemie Gostar, Tabriz, Iran
2Nanotechnology Research Center, Baku State University, Baku, Azerbaijan
GRAPHICAL ABSTRACT
Abstract More stringent requirements for reducing the content of aromatics have brought
increasing attention to new catalysts involved in hydrotreating process. The dependence
of the 2,4-dinitrotoluene hydrogenation rate on catalyst particle size and kinetic parameters
in ethanol–water–diaminotoluene three-component solvent over Pt/C nanoparticle catalyst
has been studied. The investigation of the effect of particle size of catalyst on the rate of the
reaction corresponds to the zero reaction order. An optimum set of conditions for reaction
occurrence is established.
Keywords 2,4-Dinitrotoluene; hydrogenation; initial rate of hydrogenation; Pt=C
nanoparticles
INTRODUCTION
The catalytic hydrogenation of the compounds containing nitro groups with
different substituents was investigated in liquid and gas phases over different types
of catalysts using different solvents and compositions.[1,2] A nitro group catalytic
Received December 8, 2009.
Address correspondence to Mohammad Reza Saboktakin, International Research Institute of
Arian Chemie Gostar, Tabriz, Iran. E-mail: saboktakin123@yahoo.com
1455

1456
M. R. SABOKTAKIN ET AL.
hydrogenation in substituted nitro compounds is the base for synthesizing a number
of products of thin organic synthesis and aromatic amines in particular.[3] It is well
known that nitro compounds’ hydrogenation product, amine, is widely used in syn-
thesis of various dyes. The rate and the selectivity of aromatic nitrocompounds’
hydrogenation depend upon different factors such as temperature, hydrogen press-
ure, type and concentration of catalyst, and a hydrated compound. It is known that
if hydrogen pressure is increased, hydrogenation rates of nitro compounds are
increased as well.[4,5] When hydrogen adsorption is not a limiting stage of the process
and the reaction proceeds at a low concentration of a hydrated compound, the nat-
ure of the reaction rate depends on the pressure of hydrogen, which is determined by
the isotherm form of hydrogen adsorption.[6] Different authors have showed that the
degree of diffusion-retarding influence significantly affects the character of hydro-
genation rate and hydrogen pressure dependence.[7,8]
The main purpose of this study was to evaluate the effects of thermodynamic
parameters on the rate of 2,4-dinitrotoluene hydrogenation by Pt=C nanoparticle
catalyst, taking into account the diffusion-retarding kinetic region and adsorption
factors in ethanol–water–dinitrotoluene solvent.[9,10] The synthesis of 2,4-diaminoto-
luene performed by catalytic hydrogenation of 2,4-dinitrotoluene suffers from three
major disadvantages: (a) formation of several side products, (b) use of highly corre-
sive reagents like suforic acid, and (c) difficulties in separation and purification of
2,4-diaminotoluene from the reaction mass in pure form.[11,12]
The catalytic hydrogenation of 2,4-dinitrotoluene is an alternative route for the
synthesis of 2,4-diaminotoluene, which obviates these problems to some extent.[13,14]
The starting material for this route (i.e., 2,4-dinitrotoluene) can be obtained by direct
nitration of toluene. Conventionally, the reduction step is accomplished using
Fe-acid reducing agent. The major disadvantage of the conventional process is that
it uses large amounts of Fe and produces almost an equivalent amount of Fe-FeO
sludge, which poses serious waste-disposal problems.[15]
MATERIALS AND METHODS
Materials
2,4-Dinitrotoluene, 1% Pt=C, 1% Pd=C, 1% Pt=Al2O3, and 1% Ni=C catalysts
were purchased from Aldrich Chemicals, USA. Nanoparticles (1% Pt=C, 1% Pd=C,
1% Pt=Al2O3, 1% Ni=C) were prepared by the Nanotechnology Research Center of
Baku State University. Other supported catalysts such as 1% Pt=SiO2 were prepared
using standard literature procedures. Hydrogen gas was supplied by Azar Oxide Iran
Ltd. Solvents obtained from Merck Chemicals, high-performance liquid chromato-
graphy (HPLC)–grade water, and acetonitrile (Merck Chemicals) were used as received.
Analytical Measurements
The analysis of all liquid samples was carried out using a Hewlett-Packard gas
chromatograph model 6890 equipped with HP-1 capillary column (30 m long,
0.32 mm in diameter) and flame ionization detector (FID). The analytical conditions
were as follows: column temperature: 433 K, injection temperature: 523 K, detector
temperature (FID): 523 K, and carrier gas (nitrogen) flow rate 30 ml=min. The

HYDROGENATION OF 2,4-DINITROTOLUENE
1457
quantitative analytical procedure had relative accuracy within 2%. Calibration fac-
tors were determined by using liquid standards having known compositions of 2,4-
dinitrotoluene and 2,4-diaminotoluene. The water content in ethanol was measured
by the Karl-Fischer method.
Experimental Procedure
In a typical hydrogenation experiment, 1% Pt=C (8 mg, 0.2660 g=cm3), 2,4-
dinitrotoluene (2 mg, 0.4792 mol=cm3), and 30 ml ethanol (90%) were charged into
a clean autoclave. The contents were flushed with nitrogen to ensure removal of
traces of oxygen from the reactor. The reactor was then heated to 353 K under slow
stirring (100 rpm), and the temperature was allowed to stabilize at the desired set
point. Then, hydrogen gas was introduced to a desired level (2.72 Mpa), and the con-
tents were stirred vigorously (1000 rpm). The reactor was operated at a constant
pressure throughout the reaction period by supplying hydrogen from a reservoir ves-
sel, which was measured as a function of time using a digital pressure reducer. After
completion of the reaction, the reactor was cooled, and the excess gas was vented off.
The product 2,4-diaminotoluene (DAT) was separated as a solid product in the auto-
clave because of its low solubility in the reaction medium at room temperature. The
reaction mass was further diluted to 60 ml by acetonitrile, and the resulting solution
was analyzed on a gas chromotograph for DAT and 2,4-dinitrotoluene.
RESULTS
The hydrogenation of 2,4-dinitrotoluene using 1% Pt=C nanoparticles catalyst
was investigated in a batch slurry reactor in which concentration, time, and hydrogen
consumption data were obtained. The experimental results were expressed in terms
of initial hydrogenation rate and average catalytic activity. The initial hydrogenation
rate (RA) was calculated from the hydrogen consumption and time data, essentially
under low conversion conditions. The average catalytic activity (N) expressed as
kmol=kgh was defined as the amount of 2,4-dinitrotoluene consumed per unit weight
of the catalyst per hour, based on the time to achieve more than 99% conversion of
2,4-dinitrotoluene. In a few initial experiments, the amount of hydrogen consumed
was compared with the amount of 2,4-dinitrotoluene consumed, without formation
of any other side products in appreciable quantities.
Effect of Particle Size Catalyst
The activity of Pt transition-metal catalyst in the micro and nano sizes for the
hydrogenation of 2,4-dinitrotoluene to 2,4-diaminotoluene in ethanol (96%) solvent
was investigated at 353 K and 2.72 MPa of hydrogen pressure, and the results are
presented in Table 1. The results show that the initial hydrogenation rate and cata-
lytic activity increased for Pt=C catalyst at the nanoparticle size.
Effect of Solvent
The effect of solvent on the initial rate of hydrogenation and average catalytic
activity was also investigated using 1% Pt=C catalyst at 353 K. The solvents used for

1458
M. R. SABOKTAKIN ET AL.
Table 1. Effect of transition metal catalyst particle size on the initial rate of hydrogenation and catalytic
activity of hydrogenation of 2,4-dinitrotoluene
Samples
Catalyst
RA ꢀ 103 (kmol=m3 ꢁ sec)
N (kmol=kg ꢁ hr)
1
2
1% Pt=C (Micro size)
1% Pt=C (Nano size)
1.024
2.216
1.957
3.254
Reaction conditions: 2,4-dinitrotoluene 0.480 mol=cm3, ethanol (90%) 30 ml, catalyst: 0.266 g=cm3, H2
pressure: 2.72 MPa, temperature: 353 K, agitation: 1000 rpm.
this study include water, methanol, ethanol, and n-propanol. The results are pre-
sented in Table 2. The average catalytic activity and initial rate of hydrogenation
were greatest in water as a solvent and lowest for n-propanol. It was observed that
both hydrogenation rate and catalytic activity increased with increase in polarity of
the solvent. This conclusion was further supported by the effect of water content on
the catalytic activity and the initial rate of hydrogenation, which increased with
water content (Fig. 1).
Table 2. Effect of solvent on initial rate of hydrogenation and catalytic activity during hydrogenation of
2,4-dinitrotoluene
Samples
Solvent
Dielectric constant (e)
RA ꢀ 103 (kmol=m3 ꢁ sec)
N (kmol=kg ꢁ hr)
1
2
3
4
Water
78.5
32.6
24.3
20.1
1.325
1.170
1.096
0.774
3.066
2.160
1.960
1.790
Methanol
Ethanol
n-Prpanol
Reaction conditions: 2,4-dinitrotoluene 0.480 mol=cm3, catalyst: 0.266 g=cm3, H2 pressure: 2.72 MPa,
temperature: 353 K, agitation: 1000 rpm.
Figure 1. Effect of water content in ethanol on initial rate of hydrogenation and catalytic activity.

HYDROGENATION OF 2,4-DINITROTOLUENE
1459
Figure 2. Effect of hydrogen partial pressure on initial rate of hydrogenation and catalytic activity.
Effect of Hydrogen Pressure
The effect of hydrogen partial pressure on the initial rate of hydrogenation and
average catalytic activity was also studied in the range of 1.36 to 6.80 MPa at 353 K,
keeping all other parameters constant. The initial rate of hydrogenation increased
with hydrogen pressure up to 4.08 MPa and was unchanged after that. The average
catalytic activity also followed a similar trend. The results are presented in Fig. 2.
Effect of Substrate Concentration
The effect of 2,4-dinitrotoluene concentration on the initial rate of hydro-
genation and activity of the catalyst was studied in the range of 0.119 to
Figure 3. Effect of 2,4-dinitrotoluene concentration on initial rate of hydrogenation and catalytic activity.

1460
M. R. SABOKTAKIN ET AL.
Table 3. Effect of temperature on initial rate of hydrogenation and
average catalytic activity
Temperature (K)
RA ꢀ 103 (kmol=m3 ꢁ sec)
N (kmol=kg ꢁ hr)
308
323
338
353
0.136
0.415
0.687
1.987
0.631
1.245
1.987
2.014
Reaction conditions: 2,4-dinitrotoluene 0.480 mol=cm3, ethanol
(90%) 30 ml, catalyst: 0.266 g=cm3,H2 pressure:2.72 MPa, agitation:
1000 rpm.
0.958 kmol=m3 at 353 K. It was observed that the initial rate of hydrogenation
increased with 2,4-dinitrotoluene concentration up to 0.479 kmol=m3, beyond which
it remained almost constant, as shown in Fig. 3.
Effect of Temperature
To study the effect of reaction temperature, the reactions were carried out in a
temperature range of 308 to 353 K, and hydrogenation as well as the average cata-
lytic activity increased with temperature. Table 3 shows the effect of temperature
on initial rate of hydrogenation and average catalytic activity.
DISCUSSION
The main aim of this research was kinetic studies and analysis of initial rate
data of hydrogenation of 2,4-dinitrotoluene with 1% Pt=C nanosized catalyst. The
preliminary experiments showed that with 1% Pt=C nanosized catalyst, initial hydro-
genation of 2,4-dinitrotoluene to DAT occurred selectively with material balance
agreement of more than 99%. Therefore, for all kinetic runs, the rate measurements
were followed by the observed hydrogen consumption and time data. It was also
noted that no hydrogenation occurred in the absence of a catalyst, indicating the
absence of any non catalytic reaction. A few initial experiments were obtained with
an average error of less than 3%. The hydrogenation of 2,4-dinitrotoluene is an
example of multiphase (gas–liqiud–solid) catalytic reaction system, and therefore it
was important to ensure that mass-transfer effects were either eliminated or
accounted for while determining the instrinsic reaction kinetics. To ascertain the
importance of mass-transfer effects, it was essential to know the solubility of hydro-
gen in aqueous ethanol. The solubility of hydrogen in ethanol (90%) and Pt=C
nanosized catalyst was measured using an absorption technique in a pressure auto-
clave. In a typical experiment for solubility measurement, a known volume of 90%
ethanol (30 mL) was charged into the reactor, and the contents were heated to a
desired temperature. After the thermal equilibrium was attained, the void space
above the liquid phase was pressurized with hydrogen to the required level
(Pinitial). The contents were then stirred vigorously until the gas–liquid equilibrium
was established. To ensure the gas–liquid equilibrium, the contents were stirred until
there was no further gas absorption. The final pressure in the reactor was recorded as

HYDROGENATION OF 2,4-DINITROTOLUENE
1461
Pfinal. The vapor pressure of the solvent was subtracted in calculating the Pinitial and
Pfinal values. From the initial and final pressure readings, the solubility of the
hydrogen gas was calculated as
ðPinitial ꢂ PfinalÞ Vgas
S ¼
RTVL
where S is solubility of hydrogen (kmol=m3), Pinitial is initial pressure of hydrogen
(MPa), Pfinal is final pressure of hydrogen (MPa), VG is volume of gas (m3),VL is vol-
ume of liquid (m3), R is gas constant (m3MPakmolꢂ1Kꢂ1), and T is absolute tem-
perature (K). For calculating solubility, we assumed that under the equilibrium
conditions the volume expansion due to dissolved gas in the liquid phase was negli-
gible. The solubilities of hydrogen in ethanol (90%) and Pt=C nanosized catalyst
were measured at different partial pressures of hydrogen and temperatures. The
Henry’s law constant, H, was calculated as
S
H ¼
Pfinal
The solubility data were determined in a temperature range of 308–353 K, and the
results are presented in Table 4. The solubility of hydrogen was found to increase
with hydrogen partial pressure at all temperatures. The linear dependence of solu-
bility on the partial pressure was in accordance with Henry’s law. The values of
Henry’s constant calculated from these data using the equation are given in Table 5.
Analysis of initial rate data provides a first approach for understanding the
dependency of the reaction rate on individual parameters and also evaluating signifi-
cance of mass-transfer effects. As mentioned earlier, the initial rates were calculated
from the slope of the hydrogen consumption vs time plots during the initial period of
reaction such that the conversion of 2,4-dinitrotoluene was less than 10–15% and dif-
ferential conditions prevailed. The effect of catalyst particle size, hydrogen partial
pressure, and 2,4-dinitrotoluene concentration was studied in a temperature range
of 308–353 K. The effect of catalyst particle size on the initial rate at different tem-
peratures is shown in Fig. 4. The rate was found to vary with catalyst particle size
indicating that gas–liquid mass transfer resistance may not be significant under the
Table 4. Solubility of hydrogen in ethanol at different temperatures
308 K
P
323 K
338 K
353 K
S ꢀ 100
P
S ꢀ 100
P
S ꢀ 100
P
S ꢀ 100
1.456
2.697
3.564
4.365
6.357
7.584
4.96
9.36
1.657
2.987
3.457
4.356
7.125
7.254
5.32
10.25
12.34
16.35
21.98
24.32
1.421
2.978
3.641
4.361
5.874
7.125
5.24
10.36
12.98
15.98
20.97
25.90
2.154
3.547
3.657
4.368
6.381
7.254
7.36
11.98
13.97
15.99
23.15
27.95
11.97
15.32
21.36
25.38
P ¼ hydrogen pressure, MPa and S ¼ solubility, kmol=m3.

1462
M. R. SABOKTAKIN ET AL.
Table 5. Henry’s constant for hydrogen in ethanol (90%)
Temperature, K
H ꢀ 100, kmol=m3 ꢁ MPa
308
323
338
353
3.457
3.687
3.781
4.011
Figure 4. Effect of catalyst particle size on the initial hydrogenation rate: (a) microparticle catalyst, (b)
nanoparticle catalyst.
prevailing reaction conditions. To further confirm the significance of gas–liquid mass
transfer resistance, the effect of particle size on the rate of hydrogenation was stud-
ied. The results clearly indicate the hydrogenation rate was dependent on particle
size, and the reaction could be assumed to operate in the kinetic regime. The effect
of hydrogen partial pressure on the initial rate of hydrogenation was investigated at
different temperatures, and results are presented in Figure 2. The initial rate of
hydrogenation increased linearly with hydrogen partial pressure upto 4.08 MPa,
but further increase in hydrogen pressure did not affect the hydrogenation rate very
significantly at all the temperatures. The initial rate dependence on the partial press-
ure of hydrogen suggests that the surface reaction may be rate controlling.
The effect of 2,4-dinitrotoluene concentration on the initial rate of the reaction
was also investigated at different temperatures, and results are given in Figure 1. The
hydrogenation rate showed a first-order dependence at lower concentrations of
2,4-dinitrotoluene, beyond which it was independent of initial concentration of
2,4-dinitrotoluene.
CONCLUSIONS
The hydrogenation of 2,4-dinitrotoluene to DAT using 1% Pt=C nanparticle-
size catalyst was studied in a laboratory-scale slurry reactor. The experimental data
showed that the initial rates of hydrogenation and average catalytic activity

HYDROGENATION OF 2,4-DINITROTOLUENE
1463
increased with 1% Pt=C nanoparticle-size catalyst. The addition of water resulted in
an increase in the catalytic activity as well as initial rate of hydrogenation. The
kinetics of hydrogenation of 2,4-dinitrotoluene to DAT was investigated using 1%
Pt=C nanoparticle-size catalyst in a temperature range of 308–353 K, hydrogen
pressure between 1.33 and 6.8 MPa, initial 2,4-dinitrotoluene concentration between
0.119 and 0.958 kmol=m3, and agitator speed between 600 and 120 rpm.
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