Kinetics of highly selective catalytic hydrogenation of 2,3,5-trimethylbenzoquinone on Raney nickel catalyst

Article abstract of DOI:10.1021/op990074z

This work focuses on the catalytic hydrogenation of 2,3,5-trimethylbenzoquinone (TMBQ) to 2,3,5-trimethylhydroquinone (TMHQ). Kinetic interpretation has been made by studying the important process parameters using Raney nickel as the catalyst. Thus, at 100% TMBQ conversion level, as high as 100% selectivity to TMHQ was accomplished. Experimentation was performed to acquire the most suitable process conditions from the viewpoint of process research and development.

Full text of DOI:10.1021/op990074z

Organic Process Research & Development 2000, 4, 254−258
Articles
Kinetics of Highly Selective Catalytic Hydrogenation of
2,3,5-Trimethylbenzoquinone on Raney Nickel Catalyst
Sudip Mukhopadhyay,† Kavita H. Chandnani, and Sampatraj B. Chandalia*
Chemical Engineering DiVision, UniVersity Department of Chemical Technology, UniVersity of Mumbai,
Mumbai - 400 019, India
Scheme 1
Abstract:
This work focuses on the catalytic hydrogenation of 2,3,5-
trimethylbenzoquinone (TMBQ) to 2,3,5-trimethylhydroquinone
(TMHQ). Kinetic interpretation has been made by studying the
important process parameters using Raney nickel as the
catalyst. Thus, at 100% TMBQ conversion level, as high as
100% selectivity to TMHQ was accomplished. Experimentation
was performed to acquire the most suitable process conditions
from the viewpoint of process research and development.
panol - laboratory reagent grade; Raney nickel and Pd/C -
technical grade (Ms. Kalin Industries (India) Ltd, Mumbai).
Experimental Setup. Hydrogenation of 2,3,5-trimethyl-
benzoquinone was carried out in a 100 mL Hastelloy
autoclave (Parr Instrument Company, U.S.A.). It was equipped
with a magnetically driven, six-bladed turbine impeller, an
electric heater, two baffles, and a cooling coil. The pressure
gauge, pressure release valve, safety head port, sampling
valve, and gas inlet were all situated on the top head. The
sample port was connected to a condenser to minimize the
solvent loss during sampling. Hydrogen gas was supplied
from a cylinder. The temperature was measured by a
chromium-aluminum thermocouple hemmed in a thermo-
well and regulated by a temperature indicator-controller.
Experimental Procedure. In a typical experiment, 5 g
of 2,3,5-trimethylbenzoquinone, 0.5 g of Raney nickel
catalyst, and 50 mL of methanol were charged to the
autoclave and were repeatedly purged with hydrogen gas (0.2
MPa) at room temperature. The reaction temperature was
maintained at 100 °C by controlling the flow rate of cooling
water in the internal coil and the heating rate. The autoclave
was pressurized with hydrogen gas to 3.5 MPa, and agitation
was initiated. The time of reaction was deemed to be from
this instance. A steady pressure was maintained throughout
the reaction period. After the stipulated reaction time, the
reaction mixture was filtered to remove the catalyst and then
distilled under reduced pressure to isolate the product, TMHQ
(99.5% purity).
Introduction
2,3,5-Trimethylhydroquinone (TMHQ) is a precursor for
the synthesis of R-tocopherol, commercially known as
vitamin E which, besides its anti-sterility effect, presently
appears to have an active role in cell aging processes and is
employed as an anti-wrinkle agent. TMHQ is prevalently
synthesized by hydrogenation of TMBQ over noble metal
catalysts.1-4
Although the chemistry of the reaction (Scheme 1) has
been well-studied, the information pertaining to the kinetics,
optimum process conditions, and life of the catalyst are not
well documented. This work, therefore, is an attempt to study
the kinetics of the reaction as well as to optimize the process
conditions from a reaction engineering perspective.
Experimental Section
Materials. TMBQ was prepared in laboratory by air
oxidation of 2,3,5-trimethylphenol,5-8 methanol, and 2-pro-
* Corresponding author.
† Present address: c/o Professor A. T. Bell, Department of Chemical
Engineering, University of California at Berkeley, California, U.S.A.
(1) Hoever, H.; Biller, E. Ger. Offen., 2,225,543, 1973; cf. Chem. Abstr. 1993,
80, 70533.
(2) Yui, T.; Ito, A. EP 264,823, 1988; cf. Chem. Abstr. 1988, 109, 75724.
(3) Kijima, S.; Konita, T.; Hamamura, K. JP 73 49,732, 1973; cf. Chem. Abstr.
1973, 79, 136794.
(4) Baudouin, M.; Perron, R. Ger. Offen. 2,646,172, 1977; cf. Chem. Abstr.
1977, 87, 134531.
(5) Smith, L. I. J. Am. Chem. Soc. 1934, 56, 472.
(6) Kimura, I.; Onodera, K. JP 02 268,132, 1990; cf. Chem. Abstr. 1991, 114,
121741.
(7) Kimura, I.; Onodera, K. JP 02 270, 839, 1990; cf. Chem. Abstr. 1991, 114,
121742.
Analysis. Samples of 1-2 mL withdrawn at regular
intervals of time were analyzed by HPLC using a MERCK
50983, Lichrospher 100 RP-18 column. The mobile phase
used was a methanol- water (65:35) mixture, and the flow
rate was maintained at 1 mL/min. The analysis was done at
230 nm. Calibration was done by using standard TMBQ
(99.9% purity) and TMHQ (99.7%) samples.
(8) Chandnani, K. H.; Mukhopadhyay, S.; Chandalia, S. B. J. Chem. Technol.
Biotechnol. 2000, in press.
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10.1021/op990074z CCC: $19.00 © 2000 American Chemical Society and The Royal Society of Chemistry
Published on Web 05/20/2000

Figure 2. Effect of hydrogen partial pressure on the rate of
reaction. Reaction conditions: initial concentration of TMBQ,
10% w/v; catalyst loading, 1% w/v; temperature, 100 °C;
speed of agitation, 1000 rpm; solvent, methanol; reaction
volume, 50 mL.
Figure 1. Effect of speed of agitation on the rate of reaction.
Reaction conditions: initial concentration of TMBQ, 10% w/v;
catalyst loading, 1% w/v; temperature, 100 °C; hydrogen partial
pressure, 3.5 MPa; solvent, methanol; reaction volume, 50 mL.
Results and Discussions
Definitions. OWerall ConWersion. The conversion is
defined as the ratio of the total moles of the TMBQ reacted
to the moles of the TMBQ taken initially in the reaction.
SelectiWity. The selectivity with respect to TMHQ is
defined as the ratio of the moles of TMBQ reacted for the
formation of TMHQ to the moles of TMBQ reacted.
Process Parameter Studies. Different significant process
parameters were studied to acquire the most suitable reaction
conditions and thus to formulate a kinetic interpretation.
Effect of Speed of Agitation. To ascertain whether the
effect of mass transfer is exclusively eliminated, the speed
of agitation was varied from 500 to 1400 rpm. There was a
significant change in the overall conversion when the agitator
speed was increased from 500 to 1000 rpm, indicating the
presence of the mass transfer limitation for the diffusion of
hydrogen from the gas-liquid interface to the bulk liquid.
When the speed of agitation was further increased to 1400
rpm, there was no consequential change in the overall
conversion (Figure 1), showing that mass transfer effects
were mostly eliminated at or above 1000 rpm and the data
represent the true kinetics of the process. Further reactions
were studied at 1000 rpm.
Figure 3. Effect of initial concentration of TMBQ on the rate
of reaction. Reaction conditions: catalyst loading, 1% w/v;
temperature, 100 °C; hydrogen partial pressure, 3.5 MPa; speed
of agitation, 1000 rpm; solvent, methanol; reaction volume,
50 mL.
Effect of Partial Pressure of Hydrogen. When the hydro-
gen pressure was increased from 0.2 to 3.5 MPa, it was
observed that the % conversion increased (Figure 2). With
a further increase in hydrogen pressure to 4.0 MPa there was
no change in the conversion level. Therefore,further reactions
were performed at the hydrogen partial pressure of 3.5 MPa.
Effect of Initial Concentration of TMBQ and Period of
Reaction on the Rate of Hydrogenation. The conversion of
TMBQ hardly increased when the initial concentration was
varied from 5% w/v to 15% w/v (Figure 3).
With an increase in the reaction period from 15 to 120
min, for a given initial concentration of the reactant, the con-
version of TMBQ increased from 43 to 100% (Figure 3).
Effect of Temperature. The reaction temperature was
varied from 60 to 110 °C (Figure 4). At 60 °C, the reaction
rate was observed to be very slow, and only 22% conversion
at 60 min was obtained. With an increase in temperature to
Figure 4. Effect of temperature on the rate of reaction.
Reaction conditions: initial concentration of TMBQ, 10% w/v;
catalyst loading, 1% w/v; speed of agitation, 1000 rpm;
hydrogen partial pressure, 3.5 MPa; solvent, methanol; reaction
volume, 50 mL.
110 °C, the conversion of TMBQ increased to 97% at 60
min.
Effect of Catalyst Loading. The catalyst loading ex-
pressed as the wt % of catalyst based on the total reaction
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255

Table 1. Effect of catalyst reusabilitya
% overall
conversion
%
catalyst
selectivity
fresh
first reuse
second reuse
90
82
71
90
100
99
99
second reused catalyst +
100
fresh catalyst
(10% w/w of total catalyst loading)
a Reaction conditions: initial concentration of TMBQ, 10% w/v; Raney nickel;
1% w/v; temperature, 100 °C; time, 60 min; hydrogen pressure, 3.5 MPa; solvent,
methanol; reaction volume, 50 mL.
Table 2. Effect of solventa
Figure 5. Effect of catalyst loadings on the rate of hydrogena-
tion. Reaction conditions: initial concentration of TMBQ, 10%
w/v; temperature, 100 °C; speed of agitation, 1000 rpm;
hydrogen partial pressure, 3.5 MPa; solvent, methanol; reaction
volume, 50 mL.
% overall
conversion
%
solvent
selectivity
2-propanol
ethanol
95
92
90
100
100
100
methanol
a Reaction conditions: Initial concentration of TMBQ, 10% w/v; catalyst
loading, 1% w/v; temperature, 100 °C; time, 60 min; hydrogen pressure, 3.5
MPa; speed of agitation, 1000 rpm; reaction volume, 50 mL.
Table 3. Material balance on isolation basisa
mol of TMBQ
%
overall
material
accounted for accounted for material balance
TMBQ (Input)
TMHQ
Unaccounted
0.2
0.1936
0.0064
99.9
96.8
3.2
96.8
a Reaction conditions: Initial concentration of TMBQ, 10% w/v; Raney nickel;
1% w/v; temperature, 100 °C; time, 150 min; hydrogen pressure, 3.5 MPa;
solvent, methanol; reaction volume, 300 mL.
Figure 6. Effect of different types of catalyst on the rate of
reaction. Reaction conditions: initial concentration of TMBQ,
10% w/v; temperature, 100 °C; catalyst loading, 1% w/v; speed
of agitation, 1000 rpm; hydrogen partial pressure, 3.5 MPa;
solvent, methanol; reaction volume, 50 mL.
be used, but methanol is cheaper than the other alcohols;
thus, it was worth considering using methanol as the solvent.
Material Balance. A complete material balance on
isolation basis is given in Table 3. The reaction was
performed in a 1 L autoclave. A 96.8% overall mass balance
was achieved on TMBQ (99.9% initial purity) under the
reaction conditions. The unaccounted material may be due
to distillation losses, and there was no residue formations.
Kinetics. The reactions were carried out at a high speed
of agitation to eliminate the mass transfer effects. No increase
was observed in the conversion level when the hydrogen
pressure was increased from 3.5 to 4.0 MPa. This indicates
that at or above 3.5 MPa pressure the reaction is insensitive
to a further increase in hydrogen pressure.
volume was varied from 0.1 to 1.25% w/v (Figure 5). The
per cent overall conversion increased significantly with the
increase in catalyst loading. The selectivity to the desired
product remained almost the same.
Effect of Different Types of Catalyst. The different
catalysts, Raney nickel and 10% Pd/C, were used for the
hydrogenation reaction. From Figure 6, it was observed that
in 60 min the conversion was 99% with Pd/C, whereas with
Raney nickel 90% conversion was accomplished. Although
the rate of hydrogenation with Pd/C was much higher than
with Raney nickel, due to the higher cost of Pd/C, Raney
nickel was used for practically all of the runs.
Effect of Catalyst Reusability. It was noticed that on
reusing the catalyst, the catalyst activity decreased consider-
ably (Table 1). In 60 min, 90% conversion was achieved
with the fresh catalyst. After a second use only 71%
conversion was obtained. As a solution, to the second time
reused catalyst 10% w/w of fresh catalyst was added and
used for a subsequent run. Under these conditions, the
conversion was almost identical to that of fresh catalyst.
Effect of solWent. Different solvents including methanol,
ethanol, and 2-propanol were considered for this reaction.
From Table 2, it is seen that any one of these solvents can
The rate equation at 3.5 MPa hydrogen partial pressure
and a 0.5% w/v catalyst loading can be expressed as
-dC
dt
A ) kWPH2CA
(I)
-ln(1 - XA) ) kobst, where kobs ) kWPH2
(II)
It was deduced from the plot of -ln(1 - XA) vs t that, for
a given initial concentration of the reactant, the reaction is
first-order with respect to the TMBQ (Figure 7).
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Figure 10. -ln(1 - XA) vs t at different temperatures. Reaction
conditions: initial concentration of TMBQ, 10% w/v; speed of
agitation, 1000 rpm; hydrogen partial pressure, 3.5 MPa;
solvent, methanol; reaction volume, 50 mL.
Figure 7. -ln (1 - XA) vs t at different initial concentrations
of TMBQ. Reaction conditions: catalyst loading, 1% w/v;
temperature, 100 °C; hydrogen partial pressure, 3.5 MPa; speed
of agitation, 1000 rpm; solvent, methanol; reaction volume, 50
mL.
Figure 11. Arrhenius plot. Reaction conditions: initial con-
centration of TMBQ, 10% w/v; catalyst loading, 1% w/v; speed
of agitation, 1000 rpm; hydrogen partial pressure, 3.5 MPa;
solvent, methanol; reaction volume, 50 mL.
Figure 8. -ln(1 - XA) vs t at different catalyst loadings.
Reaction conditions: initial concentration of TMBQ, 10% w/v;
temperature, 100 °C; speed of agitation, 1000 rpm; hydrogen
partial pressure, 3.5 MPa; solvent, methanol; reaction volume,
50 mL.
diffusion of hydrogen from the bulk liquid to the solid is
estimated to be unimportant, the data appears to represent
the true kinetics of the process at a catalyst loading of 1.0%
w/v.
A plot of -ln(1 - XA) vs t at different temperature
(Figure 10), exhibit a linear relationship. The slope, kobs, when
divided by the corresponding hydrogen partial pressure and
gram of catalyst at 50 mL reaction size, the rate constant k
was found to be 2.9 × 10-4, 7.2 × 10-4, 2.08 × 10-3, and
3.33 × 10-3 min-1 MPa-1 g-cat-1 at 60, 80, 100, and 110
°C, respectively. The energy of activation was found to be
52 kJ/mol from the Arrhenius plot (Figure 11).
Conclusions
Figure 9. Initial rate constant vs catalyst loading. Reaction
conditions: initial concentration of TMBQ, 10% w/v; tem-
perature, 100 °C; speed of agitation, 1000 rpm; hydrogen
partial pressure, 3.5 MPa; solvent, methanol; reaction volume,
50 mL.
The hydrogenation of 2,3,5-trimethyl benzoquinone to the
corresponding hydroquinone, using Raney nickel as the
catalyst gave 100% selectivity at a conversion ratio of
100%.
The plot of -ln(1 - XA) vs t (Figure 8) at different
catalyst loading is plotted. The respective slopes of the line
are plotted against corresponding catalyst loading (Figure
9). It was observed that the initial rate increased with the
increase in catalyst loading. Since for the physical size of
the catalyst used and the conditions employed the role of
At a particular initial concentration of TMBQ, a temper-
ature of 110 °C, and a pressure of 3.5 MPa, the hydrogena-
tion reaction over Raney nickel follows first-order kinetics.
A model such as Langmuir-Hinshelwood could explain the
kinetic observations more clearly, taking account the adsorp-
tion effects on a heterogeneous catalyst.
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257

TMBQ
TMHQ
2,3,5-trimethylbenzoquinone
2,3,5-trimethylhydroquinone
The catalyst could be reused by adding 10% w/w of fresh
catalyst to the spent one to restore its activity under analogous
reaction conditions.
Notation
Acknowledgment
CA
XA
PH2
k
concentration of TMBQ, mol/L
fractional conversion of TMBQ
partial pressure of hydrogen, MPa
S.M. is grateful to the University Grants Commissions,
New Delhi, for the award of a Senior Research Fellowship.
-1
-1
rate constant, min MPa1- g-cat
Received for review August 19, 1999.
OP990074Z
t
time, min
W
wt of catalyst, g
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