Heat Pipe Mediated Control of Fast and Highly Exothermal Reactions
Nadin Ehm, Holger Löwe
Johannes Gutenberg-University Mainz, Institute for Organic Chemistry, Duesbergweg 10-14,
55128 Mainz, Germany, Tel.: + 49 6131 39 27050, e-mail: [email protected]; [email protected]
Introduction
O
N
N
+
S
O
Long latency period of 15 seconds, Ea = 89 kJ mol-1
O
N + N
O
(2)
(1)
EtSO4
∆H = 130 kJ mol-1
Very fast and highly exothermal,
(3)
Second order kinetics
[2]
[2]
[3]
The synthesis of [EMIM]EtSO4 (1-ethyl-3-methylimidazolium ethyl-sulfate) (3) from the respective reactants 1-methyl-imidazole (2) and diethylsulfate (3) suffers from the highly
exothermal and self-accelerating reaction [1;2]. Recently we investigated the applicability of heat pipes for cooling highly exothermal reactions [4]. Heat pipes are advantageous due to
their fast dynamic cooling and heating behavior. By heating the reactor via heat pipes connected to an external heat source (hot air stream), the reaction can be stabilized inside of
the reactor. The reaction becomes self-stable (at 100°C), but due to the dynamic cooling of the heat pipes the temperature at the hot end is remarkably higher depending on the
reaction heat release.
Experimental setup
MIM
0.3 ml/min
RT
Temperature measurements
TR
TR
200
R1
P1
B1
Surface area: 970 mm2
TR
DES
0.5 ml/min
RT
[EMIM]EtSO4
0.8 ml/min
40°C
150
P2
B3
Heat pipe heat transport
TR
290 mm3
T/[°C]
B2
Volume:
TR
cooling fins
Stepwise increasing of the reactor temperature by an external heat source yields
to an optimal operating temperature.
100
50
The best product quality results in section II, III, VII and VIII corresponding to the
lowest temperature in the collecting basin. In section IV, V and VI coloration
occurs. In I and IX impurities appear.
II
I
III
V
IV
VI
IX
VIII
VII
0
0
50
100
t [min]
150
200
∆T
High flexibility
Explosion view (right) of the used
heat pipe controlled micro reactor.
Heat transport in sonic sound velocity
due to physical reasons (left).
Temperature measuring spots for
the temperature curves are marked.
heating zone
cooling zone
transport zone
vaporization
return in capillary structure
channel:
external heat source
4
12
defined volume (3ml)
collecting basin
condensation
140
An uncontrolled reaction in the collecting basin without external heating can be
avoided.
120
T [°C]
100
The highest temperature is present in the withdrawal channel and falls below the
temperatures in the micro channels during permanent heating (intercepts of blue
line in a).
90
80
80
80
31
t/min
32
33
34
35
70
60
60
27
40
Finally the temperature in channel 4 exceeds all temperatures. The reaction is
shifted into the first micro channels (intercepts of orange line in b).
a
T/°C
During heating via the heat pipe system the temperature curves show typical
characteristics (right).
b
T/°C
100
t/min
28
29
30
31
20
0
10
20
30
t [min]
40
50
Summary
After stepwise heating of the
reactor, the optimal operating temperature can be
found by plotting the outlet
temperature as a function of
the operating temperature.
130°C
Yellow, impurities
collecting basin temperature T [°C]
Results
140
The used set-up allows a self- mediated control of highly exothermal
reactions.
120
100
The dynamic cooling and heating behavior of the used heat pipes allows
an independent increase of volume flow.
80
60
Due to optimization of operating temperature of 85-110°C best product
quality was achieved.
40
optimal
operating temperature
20
room temperature
0
20
40
60
80
100 120
operating temperature T [°C]
140
+
N + N
55°C
Pale yellow
44°C
Pale yellow
40°C
Almost colorless
The final product appears as a clear non-colorized liquid indicating that no
hot-spots occur inside the reactor.
160
EtSO4
References
[1]
[2]
[3]
[4]
A. Renken, V. Hessel, P. Löb, R. Miszczuk, M. Uerdingen and L. Kiwi-Minsker, Chem. Eng.
Proc., 2007, 46, 840-845.
H. Löwe, R. D. Axinte, D. Breuch, C. Hofmann, J. H. Petersen, R. Pommersheim and A. Wang,
Chem. Eng. J., 2010, 163, 429-437.
A. Große Böwing and A. Jess, Chem. Eng. Sci., 2007, 62, 1760-1769.
H. Löwe, R. D. Axinte, D. Breuch, T. Hang and C. Hofmann, Chem. Eng. Technol., 2010, 33,
1153-1158.