Chemical Engineering October 2014 - 50

Calorimeter
type
DSC
TGA
RSST
C80D
ARC
APTAC
VSP2
RC-1
Sample size Maximum temperature
(°C)
0.1 g
10 mg
10 mL
10 mL
5 mL
500 mL
120 mL
300
200
400
300
500
500
400
50-5,000 mL 300
For further accuracy, assessment
of reactive chemicals is performed
using adiabatic calorimeters,
such as the Automatic Pressure
Tracking Adiabatic Calorimeter
(APTAC, Figure 3) or the accelerating-rate
calorimeter (ARC, Figure
4), from Netzsch Group (Selb,
Germany; www.netzsch.com).
For larger-scale and conditiondependent
studies, isoperibolic
calorimeters and isothermal calorimeters,
such as the RC1e (Figure
5) from Mettler-Toledo (Greifensee,
Switzerland; www.mt.com) or the
HEL Simular [19] can be used.
Temperature-programmed equipment,
such as a differential-scanning
calorimeter (DSC) or the
C80D, is widely used to detect reaction
onset temperature and selfaccelerating
decomposition temperature.
The onset temperature
is the temperature where the exothermic
reaction can be detected by
the equipment in use. It should be
noted that the onset temperature
depends highly on the accuracy of
the applied equipment. Therefore,
different equipment may have a
different onset temperature for the
same reaction. DSCs can also measure
heat of reaction and time to
TABLE 1. COMPARISON OF CALORIMETERS [16]
Maximum pressure Operation mode
Sensitivity
N/A
1 bar
500 psig
350 bars
200 bars
2,000 psig
130 bars
300 bars
Temperature-scanning
Temperature-scanning
Temperature-scanning
Isothermal, heat-wait-search,
heat ramp
Heat-wait-search, heat-soaksearch,
Isothermal, heat ramp
Adiabatic
1 μW
100 μW
0.1 °C/min
Temperature-scanning, isothermal 0.1 μW
0.04 °C/min
0.05 °C/min
0.05 °C/min
Isothermal, isoperibolic, adiabatic 0.02 °C/min
Figure 3. Adiabatic equipment, such as the APTAC, can
be used to design safer work practices in reactive systems
based on the determination of thermodynamic parameters
over the whole reaction process
maximum rate [20]. TGA equipment
is usually used in combination with
other compositional analysis tools,
including flame-ionization, infrared
and mass-spectroscopy detectors,
making it a powerful technique for
identifying decomposition products
[16]. It can also be combined with a
DSC to detect and analyze the behaviors
associated with the generation
of volatile species.
The RSST is a pseudo-adiabatic
calorimeter used for rapid measurement
of a reaction's thermal behavior.
A sample is usually heated at a
constant rate, which can vary from
0.25 to 2°C per min. The calorimeter
can compensate for heat losses by
adding additional energy generated
from an electric heater [18, 21]. Parameters
that can be obtained from
the RSST include the detection
of exotherms, onset temperature,
onset pressure and rate of heat or
gas evolution.
An RSST can be used not only for
screening reactive chemicals, but
also for designing emergency relief
devices in conjunction with more
accurate calorimeters. This is done
by modeling pressure-relief scenarios,
such as loss of cooling, loss
of stirring, mischarge of reagents,
mass-loaded
upset, batch contamination
or
fi r e - e x p o s u r e
heating. An RSST
uses experimental
data, such as the
rates of temperature
and pressure
rise during a
runaway reaction,
to provide reliable
energy and
gas-release rates,
48 ChemiCal engineering www.Chemengonline.Com oCtober 2014
Netzsch
Figure 4. An accelerating-rate calorimeter
(ARC) maintains isothermal conditions
and can be used to determine
the likelihood of runaway reactions
Figure 5. The RC1e calorimeter is
suited for larger-scale and condition-dependent
studies because it can accommodate
very large sample sizes
which can be applied directly to
full-scale process conditions. The
knowledge generated from testing
can be used in the design stages for
the development of safer and more
efficient processes.
The RSST can be used to study
three types of reactive systems:
vapor, gassy and hybrid.
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Chemical Engineering October 2014

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