298
F Reaction Calorimetry
For calorimeters operating with isothermal and dynamic temperature control, the
heat balance can be simplified to the case of an ideal heat flow:
˙
q r = ˙
q c
( ˙
q acc = 0)
(F.3)
The other fundamental aspect that characterizes different calorimetric methods is
the scale of the sample. This is also an important factor in choosing an appropriate
calorimetric method. For the investigation of decomposition reactions, microcalorimetry is suitable since it can safely measure very small heat fluxes from a
scaled-down version of the reaction mixture (e.g., in the milligram range).
In contrast, macro-calorimetry is a technique designed for samples in the gram
range, and bench-scale calorimetry is for samples in the kilogram range. These
allow for the running of experiments closer to industrial operating conditions and
are more suitable for the study of desired reactions during process development and
scale-up.
Comparing these techniques, micro-calorimetry is a more cost-effective and
time-saving approach than the other two. It also presents advantages from a safety
perspective given the small reaction sizes. However, during micro-calorimetry only
the temperature can be controlled, meaning that the effect of other variables such as
stirring, dosing, etc., cannot be assessed using this technique.
For an accurate study of the desired reaction under real process conditions,
macro- or bench-scale calorimetry should be the method of choice.
In the next section, the basic principles of differential scanning calorimetry are
introduced as a micro-calorimetry technique widely used in the field of process
safety for screening purposes. Further general information about calorimetry and
other specific calorimetric techniques can be found in Stoessel (2008).
F.2
Differential Scanning Calorimetry
Differential scanning calorimetry (DSC) is a micro-calorimetric technique used for
the determination of heats of reaction (e.g., for both desired and decomposition
reactions) and of the approximate temperature intervals in which these reactions
take place. DSC is, therefore, a suitable technique for the identification of thermal
hazards at the early stages of process development.
The sample size in DSC is usually between 1 and 20 mg, and the temperature
control mode can be dynamic or isothermal. The differential calorimeter consists
of a temperature-controlled oven containing a crucible holding a sample of the
substance as well as a reference crucible, as shown in Fig. F.1.
During the measurement, the temperature difference (T ) between the two
crucibles is recorded as a function of time, with the temperature of the heating
element either remaining constant (isothermal mode) or increasing over time
(dynamic mode). T becomes proportional to the thermal response of the sample.
Closed and pressure-resistant crucibles are used to avoid material and thermal
distortions caused by the evaporation of volatile components.
F Reaction Calorimetry
For calorimeters operating with isothermal and dynamic temperature control, the
heat balance can be simplified to the case of an ideal heat flow:
˙
q r = ˙
q c
( ˙
q acc = 0)
(F.3)
The other fundamental aspect that characterizes different calorimetric methods is
the scale of the sample. This is also an important factor in choosing an appropriate
calorimetric method. For the investigation of decomposition reactions, microcalorimetry is suitable since it can safely measure very small heat fluxes from a
scaled-down version of the reaction mixture (e.g., in the milligram range).
In contrast, macro-calorimetry is a technique designed for samples in the gram
range, and bench-scale calorimetry is for samples in the kilogram range. These
allow for the running of experiments closer to industrial operating conditions and
are more suitable for the study of desired reactions during process development and
scale-up.
Comparing these techniques, micro-calorimetry is a more cost-effective and
time-saving approach than the other two. It also presents advantages from a safety
perspective given the small reaction sizes. However, during micro-calorimetry only
the temperature can be controlled, meaning that the effect of other variables such as
stirring, dosing, etc., cannot be assessed using this technique.
For an accurate study of the desired reaction under real process conditions,
macro- or bench-scale calorimetry should be the method of choice.
In the next section, the basic principles of differential scanning calorimetry are
introduced as a micro-calorimetry technique widely used in the field of process
safety for screening purposes. Further general information about calorimetry and
other specific calorimetric techniques can be found in Stoessel (2008).
F.2
Differential Scanning Calorimetry
Differential scanning calorimetry (DSC) is a micro-calorimetric technique used for
the determination of heats of reaction (e.g., for both desired and decomposition
reactions) and of the approximate temperature intervals in which these reactions
take place. DSC is, therefore, a suitable technique for the identification of thermal
hazards at the early stages of process development.
The sample size in DSC is usually between 1 and 20 mg, and the temperature
control mode can be dynamic or isothermal. The differential calorimeter consists
of a temperature-controlled oven containing a crucible holding a sample of the
substance as well as a reference crucible, as shown in Fig. F.1.
During the measurement, the temperature difference (T ) between the two
crucibles is recorded as a function of time, with the temperature of the heating
element either remaining constant (isothermal mode) or increasing over time
(dynamic mode). T becomes proportional to the thermal response of the sample.
Closed and pressure-resistant crucibles are used to avoid material and thermal
distortions caused by the evaporation of volatile components.