to 600 rpm, and the reaction temperature Tr was set to 25
°C. In a second step 14.4 mL of 4 N H2SO4 (Fluka) was
added at 3.6 mL/min in the reactor. The experiment was
repeated three times. To determine qDos the heat capacity of
the feed mixture (3.61 kJ/kg‚K) was taken from Landolt-
Bo¨rnstein.19
Hydrolysis of Acetic Anhydride.
After having measured the reference background spectrum
for the IR spectrophotometer the reactor was filled with 35
mL of HCl 0.1 N (Titrisol, Merck). The stirrer speed was
turned on to 600 rpm, and the reaction temperature Tr was
set. Then 2 g of a mixture of 10.72 mmol of acetic anhydride
(Fluka) and 15.12 mmol of acetic acid (Sharlau) was added
with a constant dosing rate of 5 mL/min. The experiments
were carried out at three reaction temperature levels Tr )
25, 40 and 55 °C three times. To determine qDos, the heat
capacity of the feed mixture (1.83 kJ/kg‚K) was calculated
using the mass fraction and the heat capacities of the pure
components (acetic anhydride: cp ) 1.65 kJ/kg‚K and acetic
acid: cp ) 2.05 kJ/kg‚K).19
Figure 8. (CRC.v4): Neutralization experiment of NaOH with
H2SO4 at 25 °C. (a) For the heat flow signal the maximum
power of the reaction is about 550 W/L. The changing baseline
of the qcomp signal is mainly caused by the change of the heat-
transfer area due to the volume increase from the dosing of
the H2SO4. (b) The precision of the reaction temperature
control. The dosing period is indicated with the vertical lines.
pensated mathematically by supposing a linear change of
the heat-transfer area (UA). With the new calorimeter, this
mathematical correction is no longer needed because the
Acetylation of a Substituted Benzopyranol.
At the beginning of each acetylation experiment the empty
q
q
Comp signal is compensated by the heat balance measurement
Cooling. The q tot is calculated therefore without any
React
calibration or correction of the heat-transfer coefficient (eq
3, Table 2).
The integration of the q tRoetact gives a reaction enthalpy of
-134 ( 2 kJ/mol (mol of H2SO4), which is close to the
literature values of -134,4,17 -132,19 and -139.120 kJ/mol.
Figure 8b also shows the precision of the reaction temper-
ature control. The maximum reaction power of about 550
W/L is removed rapidly; as it can be seen from the Tr curve,
the temperature of the reactor content is only changing by
0.3 K over a short period of about 40 s at the beginning and
at the end of the dosing period.
reactor was purged with N2, and a reference background
spectrum for the IR spectrophotometer was measured. In a
second step a mixture of 22 mL of the substitute benzopy-
ranol and 5 mL of acetic anhydride was added to the reactor.
The stirrer speed was set to 600 rpm and the reactor
temperature Tr to 60 °C. In a third step 0.3 mL of a mixture
of 0.15 mmol of acetic anhydride (Fluka) and 0.05 mmol of
sulphuric acid (Fluka 98%) was added with a constant dosing
rate of 0.5 mL/min. To determine qDos the heat capacity of
the feed mixture (1.58 kJ/kg‚K) was calculated using the
mass fraction and the heat capacities of the pure components
(acetic anhydride: cp ) 1.65 kJ/kg‚K and acetic acid: cp )
2.05 kJ/kg‚K).19 The experiment was carried out three times.
Hydrolysis of Acetic Anhydride. Figure 9 shows the
tot
React
q
of the hydrolysis of the acetic anhydride at three
different temperature levels (25, 40, and 55 °C) (also here
the results are very similar to those of CRC.v34). As can be
seen, the deviation from the temperature set point is quite
tot
React
small. The q
at 25 °C shows a significant peak at the
Results and Discussion
beginning of the reaction. As reported by Zogg et al.,4 Becker
et al.21, Ko¨hler et al.,22 and Maschio et al.23 this peak
corresponds to the heat of mixing during the dosing phase.
Neutralization of NaOH with H2SO4. Figure 8 shows
the results of the CRC.v4 for the neutralization of the NaOH
with H2SO4 (results identical to those of CRC.v34).
This very fast reaction provides an example of the change
of heat flow through the wall during reaction time. In this
case the heat-transfer area A is changing (eq 7, Table 2); the
large shift is caused by the dosing of 14.4 mL of H2SO4
into 26 mL of NaOH (change of A of about 55%).
As shown by Zogg et al.,4 if only the power compensation
signal would be available as in the case of conventional
calorimeters, this baseline change would have to be com-
(20) Schildknecht, J. Reaction Calorimeter for Applications in Chemical Process
Industries: Performance and Calibration. Thermochim. Acta 1981, 49, 87.
(21) Becker, F.; Walisch, W. Isothermal calorimetry with automatically controlled
Peltier-cooling and continuous integration of the compensation power.
(Isotherme Kalorimetrie mit automatisch gesteuerter Peltier-Ku¨ hlung und
fortlaufender Integration der Kompensationsleistung). Z. Phys. Chem. Neue
Folge. 1965, 46, 279.
(22) Ko¨hler, W.; Riedel, O.; Scherer, H. An isothermal Calorimeter controlled
by Heat Pulses. Part II: Examples for Calorimetric and Calorimetric-Kinetic
Measurements. (Ein mit Heizimpulsen Gesteuertes Isothermes Kalorimeter.
Teil II: Anwendungsbeispiele fu¨r Kalorische und Kalorisch-Kinetische
Messungen). Chem.-Ing.-Tech. 1973, 22, 1289.
(19) Landolt, H.; Bo¨rnstein, R.; Hellwege, K. H. Numerical Data and Functional
Relationships in Science and Technology, 6th ed.; Springer: Berlin, 1987;
Vol. 4, Part 4.
(23) Ampelli, C.; Di Bella, D.; Lister, D. G.; Maschio, G.; Stassi, A. Study of
the Hydrolysis of Acetic Anhydride by Means of a Simple, Low Cost
Calorimeter. RiV. Combust. 2001, 55, 292.
732
•
Vol. 8, No. 5, 2004 / Organic Process Research & Development