Organic Process Research & Development 2001, 5, 158−166
Determination of Reaction Parameters Using a Small Calorimeter with an
Integrated FT-IR Probe and Parameter Fitting
J o¨ rg Pastr e´ , Andreas Zogg, Ulrich Fischer,* and Konrad Hungerb u¨ hler
Swiss Federal Institute of Technology ETH, Laboratory of Technical Chemistry, Safety and EnVironmental Technology
Group, CH 8092 Zurich, Switzerland
Abstract:
analytical techniques such as FT-IR (Fourier transform
infrared) spectroscopy. Combinations of FT-IR with standard
reaction calorimeters were already presented in the literature.1
The calorimetric signal reflects the sum of all physicochem-
ical changes of the reaction system that have an impact on
the heat balance of the system, such as, for example, thermal
conductivity or a change of viscosity, which result in a
change of the heat transfer coefficient and influence the
calorimetric signal in addition to the heat produced by the
different chemical reactions. The FT-IR measurements on
the other hand reflect the sum of all chemical changes of
the system, even when the heat production is rather small.
The vast amount of chemical information is displayed in the
about 2000 wavenumbers recorded.
Unfortunately the reaction calorimeters that can be
equipped with an IR probe require a large volume on the
order of 200-2000 mL, meaning a considerable consumption
of test substance. However, in early stages of process
development the available amount of reactants is often small,
and thus the use of commercially available reaction calo-
rimeters is impeded. Therefore, we developed a small
reaction calorimeter with power compensation, which allows
stirring, different dosing profiles, and the combination with
an IR dipper.
To identify optimal operating conditions of a chemical process,
knowledge on kinetic and thermodynamic parameters of the
main reactions is needed. In particular in the fine chemical
industry during the early phases of process development this
knowledge is usually low. One reason is that only small amounts
of substrate are available to perform the required calorimetric
and analytical experiments. Therefore, we present in this paper
a new prototype reaction calorimeter with a volume of 50 mL.
Despite its small volume, the reaction calorimeter is combined
with an IR-ATR probe to obtain augmented information from
semibatch experiments under isothermal conditions. Further-
more, we present a new method to analyze the calorimetric
measurements. The novelty of the approach is that all heat flows
in the calorimeter are modeled together with the chemical
reaction. For general reaction kinetics this reactor model cannot
be solved analytically, and thus, numerical methods are applied
for fitting the model parameters to the measurement data. In
contrast to the traditional method of thermal conversion the
rate constants and the heats of reaction are computed at the
same time. The new reaction calorimeter and the new evaluation
principle of the thermal signal were both tested using a single-
step second-order model reaction. Also the FT-IR data were
evaluated by fitting the parameters in the reactor model
numerically. The reaction parameters obtained with both
measurement techniques are in good agreement with values
published in the literature demonstrating the feasibility of the
approach.
The traditional way of evaluating the thermal signal is to
2
apply the principle of thermal conversion. In this approach,
during the dosing period of a semibatch experiment, the
dosing temperature and the heat capacity of the feed have
to be known. If heats of mixing appear during the dosing
period they have to be determined in a separate experiment.
Furthermore, if the reaction is not run until completion, which
can take a long time for second-order reactions, the extent
of conversion at the end of the experiments has to be
determined by another analytical technique such as gas
chromatography.
We present a new method to analyze the calorimetric
measurements. The novelty of the approach is that all heat
flows in the calorimeter are modeled together with the
chemical reaction. The reaction model is expressed in terms
Introduction
To identify the optimal operating conditions of a chemical
process (e.g., by modeling using flow-sheeting programs)
knowledge on kinetic and thermodynamic parameters, in the
following referred to as “reaction parameters”, for the most
important main and side reactions is needed. In early stages
of chemical process development the focus lies on determin-
ing scale-up factors and macro-kinetic parameters rather than
on gathering in-depth mechanistic insight.
However, a conventional method for investigating a
reaction during process development is reaction calorimetry.
Reaction calorimeters are used mainly for safety assessments
and for understanding most necessary scale-up factors such
as heat of reaction and conversion time curves at working
temperature.
(1) (a) Landau, R. N.; McKenzie, P. F.; Forman, A. L.; Dauer, R. R.; Futran,
M. Process Control Qual. 1995, 7, 133. (b) LeBlond, C.; Wang, J.; Larsen,
R. D.; Orella, C. J.; Forman, A. L.; Landau, R. N.; Laquidara, J.; Sowa, J.
R.; Blackmond, D. G.; Sun, Y.-K. Thermochim. Acta 1996, 289, 189. (c)
LeBlond, C.; Wang, J.; Larsen, R.; Orella, C.; Sunn, Y.-K. Top. Catal. 1998,
5, 149. (d) am Ende, D. J.; Clifford, P. J.; DeAntonis, D. M.; SantaMaria
C.; Brenek, S. J. Org. Process Res. DeV. 1999, 3, 319. (e) Ubrich, O.;
Srinivasan, B.; Lerena, P.; Bonvin, D.; Stoessel, F. J. Loss PreV. Process
Ind. 1999, 12, 485.
To gather additional information on a reaction, the
reaction calorimeters are often combined with in situ
(2) am Ende, D. J..; Clifford, P. J.; Northrup, D. L. Thermochim. Acta 1996,
289, 143.
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Vol. 5, No. 2, 2001 / Organic Process Research & Development
10.1021/op000072a CCC: $20.00 © 2001 American Chemical Society and The Royal Society of Chemistry
Published on Web 01/31/2001