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Production of Crotonaldehyde from Acetaldol.

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Short Research Communication
Production of Crotonaldehyde from Acetaldol
S.Atalay* and F.S. Atalay
Department of Chemical Engineering, Ege Universa Bomova-lzmir; TURKEY
Optimum operating conditionsfor the production of crotonaldehydefrom acetaldol were
investigated and the kinetics of the reaction were determined. The most important
operating conditions were found to be the cracking time, the pH value of the reaction
mixture, and the initial concentration of acetaldol. The order of the reaction wasfound to
be I .8 with respect to the acetaldol concentration. The kinetic parameters were
determined lo be 20.583 (rn3/kmol)0*8/minfor the frequency factor, and 341 6.800
Wlkmolfor the activation energy.
Introduction
Crotonaldehyde (2-butenal, crotonic aldehyde, P-methylacrolein) is a valuable
material for the production of n-butanol, n-butyraldehyde, 2-ethylhexanal and
2ethylhexanol [ 1-81.
The technical manufacture of crotonaldehyde is mainly by aldol condensation of
acetaldehyde with either simultaneous or consecutive dehydration of the acetaldol
[2,9- 121:
2 CH3CHO-
CH3CH(OH)CH2CHO
Acetaldehyde
Acetaldol
CH$H(OH)CH2CHO +CH3CH = CHCHO + H20
Acetaldol
Crotonaldehyde
Crotonaldehyde may be produced at low temperature (10 to 25°C) by a batch
process, or at higher temperatures (20 to 50°C) in a continous process in the
presence of an alkaline catalyst. The reaction mixture containing acetaldehyde and
acetaldol is neutralized using a weak acid such as acetic acid. This mixture is fed to
batch reactors or a continuous still, and is maintained between 100-105°C for a
contact time of 2 hours at atmospheric pressure. A mixture of acetaldehyde, water
and crotonaldehydeis continuously removed as an azeotropic overhead product and
is condensed. Continuous distillation of this mixture is accomplished in a series of
stills. In the first still acetaldehyde is obtained as overhead, and the bottoms are fed
to a second still from which the water-crotonaldehyde azeotrope is removed as
distillate (at 84°C). The distillate composition is 24.3 w t % water and 75.7 wt.%
crotonaldehyde. This heterogeneous azeotrope is composed of a top layer and an
*Author for correspondence.
58
Production of Crotonalehydefrom Acetaldol
aqueous bottom layer. Crotonaldehyde may also be produced in a single stage in a
continuous manner and without the use of a catalyst, this process being more
applicableto large-scaleoperations121.
Experimental Study
The acetaldehyde-acetaldolmixture was neutralized, and its pH kept between 3.7 and
5.5 by the introduction of acetic acid. Preparation of the acetaldol has been
described elsewhere [13]. A known amount of the acidified mixture was charged
into a 500 ml batch reactor having three necks. The reactor temperature was
controIled by an electrical heater. One of the necks was connected to a packed
column (height of 500 mm) with a reflux condenser which was used to condense the
acetaldehyde vapors. The reaction mixture was &hydrated (cracked) by maintaining
the reactor at a constant temperature for between 1 to 4 hours at atmospheric
pressure. After dehydration, the mixture was distilled and the crotonaldehyde-water
azeoaope was removed at 84°C. The overhead distillate was separated into two
layers which were weighed and then analysed by gas chromatography with flame
ionisation detector using a Carbowax column. The top layer contained
crotonaldehyde, acetaldehyde and water. The bottom layer contained acetaldehyde,
unconverted acetaldol and water.
Results
The mass of acetaldol charged into the reactor was known, hence the yield and the
conversion of acetaldol to crotonaldehyde were calculated fiom the composition and
mass of the top layer. The experimental conditions and the conversions and yields
are given in Table 1. In the calculations, the top layer composition was assumed to
be 75.7 w t % crotonaldehyde and 24.3 wt.% water [lo]. The results presented in
Table 1 illustrate the importance of the cracking time, pH, and the initial acetaldol
concentration, upon the production of crotonaldehyde.
The kinetics of crotonaldehyde production were determined from the results
obtained at constant temperature, constant pH. and constant initial concentration.
The rate of the reaction was defined as:
Using a regression technique, the order of the reaction 'n' was found to be 1.8.
The rate constants at 80°C and 93°C were determined. The rate constant was defined
by the relation :
k = 20.583 exp(-3416.8/RT)
Nomenclature
C,
k
n
R
rA
T
Concentrationof acetaldol0<11101/m3)
Rate constant of reaction of acetaldol to crotonaldehyde (m3/ kmol)Od/min
Order of reaction (-)
Ideal gas constant (kT/kmol K)
Rate of reaction (km0i/m3 min)
Temperature(K)
59
SAtalay and FS.Atahy
Table 1 Conditionsfor production of crotonaldehydefromacetaldol and
calculated conversion (pressure = 1 am).
~~
Experiment
Number
1
2
3
4
5
6
7
a
9
10
11
12
13
14
15
Initial acetaldol Cracking
concentration
(kmovm3)xr 04
time
(min)
4.08
60
4.08
4.08
120
180
240
120
120
120
120
165
165
45
135
180
225
240
4.08
4.08
4.08
4.08
4.08
4.08
6.76
4.16
4.16
4.16
4.16
4.16
PH
Temperature
Yield
Conversion
(“C)
v4
W)
93
93
93
93
93
93
93
93
93
93
33.130
50.015
56.731
66.387
50.015
7i.m
63572
64.092
56.871
60.949
23.819
49.060
51.119
55.41 1
69.990
41.649
62.876
71.319
83.458
62.876
89.93
79.919
80.573
71.486
76.612
29.941
61.668
64.256
69.651
87.977
value
3.7
3.7
3.7
3.7
3.7
4.0
4.5
5.5
5.0
5.0
4.7
4.7
4.7
4.7
4.7
-
ao
80
80
ao
ao
References
1. Comils, B. and Mullen, A. 1980. Petrochemical Developments. Hydrocarbon Process.,
59(11), 93-102
2. Faith, F.L.,Keyes, D.B. and Clark, R.L. 1965. Industrial Chemicals,pp. 300-302, Wiley,
New York.
3. Groggins, P.H.1958. Unit Processes in Organic Synthesis, pp.574-577, McGraw-Hill,
New York.
4. Horn.0.1959. Reactions of Crotonaldehyde. Ind. Eng. Chem.,51(5),655-656.
5. Kirk-Othmer.1965. Encyclopedia of Chemical Technology, vo1.3. pp.286. Wiley. New
York.
6. Mcketta, 1.1. and Cunningham, W.A. 1977. Encyclopedia of Chemical Process and
Design, Vo1.5. pp.382-384. Marcel Dekker, New York.
7. Weissermal, K. and Arpe, H.J. 1978. Industrial Organic Chemistry, pp.162-167, VerlagChemie
8. Werner, B.. Baltes. H. and Mayer, D. 1957. UllmannS Encyclopedia of Industrial
Chemistry.Vol.A.8. pp.83-89. VCH. New York
9. Les Usines de Melle. 1949. Aldol and crotonaldehyde,British Patent. no. 630,904.
10. Kirk-Othmer. 1965. Encyclopedia of Chemical Technology. vo1.6, pp.445-464. Wiley,
New York
11. McKetta. J.J and Cunningham, W.A. 1976. Encyclopedia of Chemical Process and
Design, Vol.1, pp.153-155. Marcel Dekker. New York.
12. McKetta, J.J and Cunningham, W.A. 1977. Encyclopedia of Chemical Process and
Design. Vo1.13, pp.231-237. Marcel Dekker. New York
13. Atalay, F.S. and Atalay, S. 1991. Kinetics of acetaldol production. Chemie Ingenieur
Technik, 63(9). 933-934.
Received: 9 November 1992;Accepted after revision: 27 August 1993.
60
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