Reaction and catalyst deactivation kinetics of the - CPI Research ...

REACTION AND CATALYST DEACTIVATION KINETICS OF
THE ALDOL CONDENSATION OF ACETONE
Deliverable 21
Workpackage 6
Technical Report
Name of Partner:
DSM
Authors:
Remko Bakker, Geert Hangx, Gerard Kwant, Harrie Maessen, Peter Markusse
Date:
15/02/01
PROGRAMME GROWTH
Intelligent Column Internals for Reactive Separations (INTINT)
Project No. GRD1 CT1999 10596
Contract No. G1RD CT1999 00048

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Deliverable 21 Issued: 15.02.01
1 SUMMARY 2
2 INTRODUCTION 2
3 EXPERIMENTAL 3
4 RESULTS AND DISCUSSION 4
5 CONCLUSIONS AND RECOMMENDATIONS 7
6 REFERENCES 8
1 Summary
Several catalysts were tested for reaction system 3: the aldol condensation of acetone towards diacetone
alcohol (DAA). The original catalyst, that was chosen based on literature studies, proved to be
too vulnerable towards deactivation. Four other catalysts were tested, of which barium hydroxide
crystals gave the best results with respect to catalytic activity and catalyst lifetime. However, catalyst
deactivation is still very fast, which makes application in a reactive distillation column virtually
impossible, despite several measures that were taken to improve catalyst stability. Therefore it is
recommended that another reaction system be chosen instead of the aldol condensation of acetone.
The esterification of ethanol and acetic acid towards ethyl acetate is suggested.
2 Introduction
The reaction studied is the aldol condensation of acetone (AC) towards diacetone alcohol (DAA),
see equation 1:
O O O OH
+
OH- OH- AC AC DAA
This reaction is reversible, and the equilibrium composition depends on temperature. A consecutive
reaction is the dehydration of DAA, which results in mesityl oxide (MO), see equation 2:
(1)

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Deliverable 21 Issued: 15.02.01
O OH O
DAA MO
MO formation is also reversible, but the equilibrium is very much on the side of MO 1 . At the low
concentrations of water and MO observed, the reverse reaction (MO + H2O DAA) can be neglected
2 . Both DAA and MO can undergo aldol condensation with acetone, DAA or MO, forming
heavier products such as isophorone and isoxylitone.
The intrinsic kinetics of the reaction system are more or less known from literature: the formation
of DAA from AC is second order in AC, the formation of AC from DAA is first order in DAA, and
the formation of MO from DAA is also first order in DAA 2 . All three reactions are base catalysed.
For porous particles with typical particle diameter 1 mm, intra-particle diffusion is expected to be
very important. Diffusion limitation promotes the formation of MO.
The objective of this study is
1. To find an appropriate catalyst for the aldol condensation of acetone,
2. To find kinetic parameters for the reactions described above (DAA and MO formation), and
3. To describe catalyst deactivation quantitatively.
3 Experimental
OH- OH- + H H2O 2O
Five catalysts were tested: three ion exchange resins (Amberlite IRA900, Amberlyst A26OH, and
Amberlyst A15), zirconia supported barium hydroxide, and pure barium hydroxide. The ion exchange
resins were purchased from Rohm & Haas. Amberlite IRA900 and Amberlyst A26OH are
anion exchange resins, containing quaternary ammonium groups. In the active form the counter ion
is hydroxide. Amberlite IRA900, which was also used in reference 1, was purchased in the chloride
form, and had to be pre-treated with 1.5 M sodium hydroxide solution 2 . Amberlyst A15 is a cation
exchange resin, containing sulfonic acid groups. Zirconia supported barium hydroxide was prepared
at DSM Research by impregnating porous zirconia (ZrO2) with a barium hydroxide (Ba(OH)2) solution.
The barium hydroxide content of the catalyst was 11 wt%. The pure barium hydroxide catalyst
consisted of crystalline Ba(OH)2.8H2O. The typical particle diameter of all catalysts was 0.6-1.4
mm.
The experimental set-up consisted of a thermostated jacketed glass tube, inner diameter 5 mm.
Typically 1-2 g of catalyst was used, and a constant acetone flow rate of 2-8 ml/min was applied.
The reactor was kept at 40-54 °C. The effluent was analysed off-line by GC, using a flame ionisation
detector. The acetone was distilled over sodium carbonate prior to use, in order to remove
traces of acids. The experiments were performed under nitrogen atmosphere.
(2)

4 Results and discussion
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Deliverable 21 Issued: 15.02.01
Most experiments were performed at 40 °C. At this temperature the equilibrium concentration of
DAA (not regarding MO formation) is about 7.1 wt% (0.495 mol/l), and at 54 °C the equilibrium
DAA concentration is 4.3 wt% (0.27 mol/l) 2 . Within 10 minutes after start-up, the equilibrium DAA
concentration was reached in the reactor outlet for most experiments, except the ones using Amberlyst
A15 and Ba(OH)2/ZrO2. However, after a certain amount of time the DAA concentration decreased,
which indicates catalyst deactivation. The concentrations of DAA and MO as a function of
time are depicted in the figures below. It should be noted that a decrease in exit DAA concentration
from 95% of equilibrium to 50% of equilibrium corresponds with an 80% decrease in catalyst activity.
DAA conc. [mol/l]
0.6
0.5
0.4
0.3
0.2
0.1
0
cDAA
[mol/l]
cMO [mol/l]
0 100 200
time [min]
300 400
0.012
0.01
0.008
0.006
0.004
0.002
0
MO conc. [mol/l]
Figure 1 (left). Experiment with 1.4 ml Amberlite IRA900, acetone feed 7.5 ml/min, 40 °C.
Figure 2 (right). Experiment with 1.4 ml Amberlyst A26OH, acetone feed 3.75 ml/min, 40 °C.
In both figures DAA concentration on left y-axis, and MO concentration on right y-axis.
The cation exchange resin Amberlyst A15 showed very low activity: the maximum DAA concentration
measured for 1.6 ml catalyst, acetone feed 3.75 ml/min, 40 °C, was 0.07 wt%. No MO was
observed. The anion exchange resins Amberlite IRA900 and Amberlyst A26OH were also used
after exposure to air during 24 hours. Both catalysts were completely deactivated after this treatment.
This vulnerability to air is known from literature, and is attributed to absorption of CO2,
which neutralises the active sites 3 . Attempts to reactive the catalysts by dosing 2 wt% triethyl amine
in the feed, in order to remove acidic compounds, gave adverse results.
DAA conc. [mol/l]
0.6
0.5
0.4
0.3
0.2
0.1
0
cDAA
[mol/l]
cMO [mol/l]
0 500 1000
time [min]
1500 2000
0.06
0.05
0.04
0.03
0.02
0.01
0
MO conc. [mol/l]

DAA conc. [mol/l]
0.12
0.1
0.08
0.06
0.04
0.02
0
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Deliverable 21 Issued: 15.02.01
cDAA
[mol/l]
cMO [mol/l]
0 500 1000 1500
time [min]
0.003
0.002
0.001
Figure 3 (left). Experiment with 1.3 ml Ba(OH)2/ZrO2, acetone feed 3.75 ml/min, 40 °C.
Figure 4 (right). Experiment with 1.5 ml Ba(OH)2.8H2O, acetone feed 2.0 ml/min, 40 °C.
In both figures DAA concentration on left y-axis, and MO concentration on right y-axis.
Several causes for catalyst deactivation are possible:
0
MO conc. [mol/l]
1. An acidic component in the acetone feed, which neutralises the catalyst;
2. Catalysed degradation of acetone or a reaction product, which causes acid formation, which
neutralises the catalyst;
3. A component in the acetone feed, which polymerises on the catalyst and blocks its active
sites;
4. Catalysed polymerisation (or aldol condensation) of a reaction product (e.g. mesityl oxide),
which blocks the active sites;
5. Heat accumulation inside the catalyst due to exothermic reactions, which cause catalyst degradation.
Podrebarac et al. 2 attributed the deactivation of Amberlite IRA900 during the aldol condensation of
acetone to acids in the acetone feed (option 1) and pore blockage by higher aldol condensation
products (option 4). Most of the mechanisms mentioned above apply to inorganic catalysts as well,
except perhaps heat induced degradation. The deactivation mechanisms, their implications for the
reaction rates, and possible countermeasures are discussed below.
Acids in the acetone feed are unlikely to have passed the pre-treatments: neutralisation with sodium
carbonate and subsequent distillation. The deactivation would be linear: after a certain amount of
feed has passed the catalyst, it is completely neutralised and deactivated. A higher feed rate causes a
proportionally higher deactivation rate. This type of deactivation could be prevented and/or reversed
by adding a base (e.g. an amine or a hydroxide). Acid production by the catalyst itself results
in an exponential deactivation curve if the active sites for aldol condensation are the same as the
active sites for acid production. If the rate of acid production is proportional to the concentrations of
DAA, MO or a higher product, deactivation should be faster at lower feed rates. As in the previous
case, deactivation could be prevented and/or reversed by adding a base.
It can be assumed that the poisoning polymers formed are higher aldol condensation products,
which has been suggested as a source of catalyst deactivation 24 . The active sites for aldol condensa-
DAA conc. [mol/l]
0.6
0.5
0.4
0.3
0.2
0.1
0
cDAA
[mol/l]
cMO [mol/l]
0 1000 2000
time [min]
3000 4000
0.06
0.05
0.04
0.03
0.02
0.01
0
MO conc. [mol/l]

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Deliverable 21 Issued: 15.02.01
tion are the same as the active sites for polymer production. Reactivation is difficult, and may be
impossible. Polymerisation of a feed component results in an exponential deactivation curve. A
higher feed rate probably causes a higher deactivation rate. Polymerisation of a reaction product
(DAA, MO) results in a deactivation rate that is proportional to both the number of remaining active
sites and to the actual DAA and/or MO concentration. According to the manufacturer (Rohm &
Haas), the anion exchange resins Amberlite IRA900 and Amberlyst A26OH (both in the hydroxide
form) are stable up to 60 °C. The heat of reaction is 14.65 kJ/mol 5 .
The experimental data with Ba(OH)2.8H2O as the catalyst at 40 °C could be described accurately
using a five CSTRs in series model, in which the kinetic equations that are given below were used:
2 AC → DAA R1 = feff k1 [AC] 2 (3)
DAA → 2 AC R2 = feff k2 [DAA] (4)
DAA → MO + H2O R3 = feff k3 [DAA] (5)
Deactivation dfeff/dt = feff kd ([DAA] + [MO]) (6)
All concentrations are in mol/m 3 ; the reaction rates are in mol/mcat 3 s. The parameters used are k1
4.9⋅10 -6 m 3 /mol s; k2 1.7 1/s; k3 1.3⋅10 -3 1/s; kd 1.2⋅10 -7 m 3 /mol s. The simulation is compared with
the experimental data in figure 5. It is observed that after 54 hours of reaction the simulated catalyst
activity feff has decreased to 0.3% of its original value. If the same deactivation model were applicable
to a system in which the DAA concentration was at equilibrium continuously, the catalyst
activity after 120 hours would only be 1.7⋅10 -11 times its original value. Obviously, this is not acceptable.
DAA conc. [mol/l]
0.6
0.5
0.4
0.3
0.2
0.1
0
0 500 1000 1500 2000 2500 3000 3500
time [min]
Figure 5. Experimental data (symbols) and simulation (lines) with 1.5 ml Ba(OH)2.8H2O, acetone
feed 2.0 ml/min, 40 °C.
The influence of the acetone feed rate is depicted in figure 6. Three experiments with Amberlyst
A26OH are shown, all at 40 °C. The experiment at the lowest feed rate is rather encouraging, since
the DAA concentration is still close to equilibrium after 1500 minutes. Judging from the MO concentration
profile, the catalyst activity has been decreased by only 60% in 25 hours. This indicates
that Amberlyst A26OH could have been a suitable catalyst, if it had not been extremely vulnerable
to CO2 from the air.
DAA
DAAcalc
MO
MOcalc
0.045
0.03
0.015
0
MO conc. [mol/l]

DAA conc. [mol/l]
0.5
0.4
0.3
0.2
0.1
0
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Deliverable 21 Issued: 15.02.01
0 500 1000 1500 2000
time [min]
0.1
0.08
0.06
0.04
0.02
0
MO conc. [mol/l]
DAA 7.5 ml/min
DAA 3.75 ml/min
DAA 2 ml/min
MO 7.5 ml/min
MO 3.75 ml/min
MO 2 ml/min
Figure 6. Experiments with Amberlyst A26OH at 40 °C: acetone feed 7.5 ml/min, 1.2 ml catalyst
(diamonds), acetone feed 3.75 ml/min, 1.4 ml catalyst (triangles), acetone feed 2 ml/min, 1.6 ml
catalyst (squares). DAA concentration (filled symbols) on left y-axis, and MO concentration (open
symbols) on right y-axis.
5 Conclusions and recommendations
In view of the results obtained with the various catalysts, it must be concluded that neither of the
catalysts tested for the aldol condensation of acetone are suitable for use in pilot plant experiments.
Since both organic and inorganic catalysts were examined, it can be expected that other base catalysts
will have the same deactivation behaviour. The search for a suitable catalyst could require a lot
of effort, and is not the scope of this project. Therefore, it is recommended to discontinue the work
on the aldol condensation of acetone, and to select a different model system 3. The reaction suggested
is the esterification of ethanol (CH3CH2OH, EtOH) and acetic acid (CH3COOH, AcOH),
resulting in the products ethyl acetate (CH3COOCH2CH3, EtOAc) and water (equation 7):
EtOH + AcOH ↔ EtOAc + H2O (7)
This reaction is an equilibrium reaction: the equilibrium constant K (see equation 8), which is not a
strong function of temperature, is approximately 4 5 .
K=[EtOAc][H2O]/[EtOH][AcOH] (8)
The reaction is acid catalysed, and as for most esterifications usually strong mineral acids (hydrochloric
acid, sulfuric acid) are used 5,6 . Cation exchange resins (typically containing sulfonic acid
groups, e.g. Amberlyst 15) are also widely used, because of their high activity and selectivity (possible
side reactions are alcohol dehydration and etherification) 5 . Catalyst deactivation appears to be
negligible. In practice the equilibrium is often forced towards the ester by azeotropic water removal
5 .

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Deliverable 21 Issued: 15.02.01
The reaction mechanism is well known: the ethyl acetate formation reaction is first order in ethanol
and acetic acid, and the reverse reaction (ethyl acetate hydrolysis) is first order in ethyl acetate and
water. Kinetic parameters for Amberlyst 15 and the system methanol/acetic acid/methyl acetate are
known 7 ; it is expected that the formation rate of ethyl acetate is about 40% lower 5 . The working
temperature will be around 70 °C, and atmospheric pressure will be used. The thermodynamics of
the system ethanol/acetic acid/ethyl acetate/water are well known.
6 Proposed work schedule
The above-mentioned results have been discussed on 31-01-2001 in Geleen by Górak, Kenig (both
University of Dortmund) and Moritz (Sulzer) together with the DSM team (Markusse, Hangx,
Maessen, Stankiewicz, Kwant). It has been agreed that the DAA system should not be further
evaluated as the results and conclusion presented above leave little hope for a quick and satisfactory
result. As the goal of the consortium is to develop internals and not a DAA process, further development
of the DAA system is not desirable. First is has been discussed to use one of the systems
already available in the project but is has been found that there is hardly any possibility to add valuable
experimental data since most has been covered by the partners already.
Therefore we propose that DSM will deliver the reaction kinetics of the ethyl acetate system (proposed
deliverable number 22) by 1 May 2001. If necessary, literature thermodynamic data will be
provided.
7 References
1. Kim, Y.K., Hatfield, J.D., J. Chem. Eng. Data, 30 (1985) 149-153
2. Podrebarac, G.G., Ng, F.T.T., Rempel, G.L., Chem. Eng. Sci., 52 (1997) 2991-3002
3. Astle, M.J., Zaslowsky, J.A., Ind. Eng. Chem., 44 (1952) 2867-2871
4. Kunin, R., Catalysis with ion exchange resins, in „Ion Exchange Resins, 2nd ed.“, R.E.
Krieger Publishing, Huntington NY (1972)
5. Ullmann’s Encyclopedia of Industrial Chemistry
6. Chemical Economics Handbook CD-ROM
7. Krafczyk, J., Gmehling, J., Chem. Ing. Technik, 66 (1994) 1372-1375