Adiabatic Pressure Dewar-Based Calorimetry
Creators: name: Harris, Malcolm Terry-Guy
Publisher: name: London South Bank University
Year: 1995

description: The use of a Dewar-based vessel to study the thermal stability of single substances, and reaction mixtures is based on a well-established technique. The existing experimental calorimeters developed at South Bank University, although suitable for studying small samples of single substances were limited in their application. Hence, a need arose for developing a modified Dewar-based calorimeter, with all the features of existing calorimeters. The instrument addressed most of the old constraints associated with the old Dewar systems, such as the limited use of control and monitoring instrumentation for controlled process operation and data-logging, and the unavailability of integral feed and dump tanks. This computer controlled calorimeter was designed, commissioned, and used to study a range of industrial reactions under adiabatic conditions. The Dewar-based calorimeter is reliable, accurate, and possesses a high degree of sensitivity. It is inexpensive to construct and versatile in operation. The stainless steel Dewar possesses an average heat loss rate of 107.9 W m'K" at 80°C compared with 2.0 x 10+ m? (200 ml) and 5.0 x 10* m’ (500 ml) glass Dewars that possess lower heat loss rates of 77.0 W m'K" and 30.0 W m'K" respectively. The adiabatic nature of the Dewar-based calorimeter allows the runaway condition to be imitated from the maloperation of the batch reactor, that can arise from the loss of cooling or agitation failure. The Dewar can also operate up to 20 bar (300 Psig), and has demonstrated the ability to perform thermodynamic, kinetic, and emergency vent sizing tests on reaction mixtures under batch and semibatch operation. Although the chemical investigations have been restricted to reaction mixtures the instrument can also be adapted to study single substances. The heat of reaction determination experiments that were conducted for the Mono-nitration of Toluene and for Styrene Polymerisation using t-butyl catechol inhibitor revealed a mean heat of reaction and of polymerisation values of 144.66 kJ mol! at 45°C and 80.71 kJ mol! at 85°C respectively. This was 7.1 % and 7.9 % higher than the experimental values that were obtained from the ICI adiabatic Dewar and the Mettler RC1. The kinetic studies on Butan-2-ol and Propanoic Anhydride esterification reaction indicated a second order reaction with pre-exponential factor and activation energy of 4.7 x 10° m’ mols" at 309-400 K and 5.68 x 10* J mol! for the uncatalysed reaction, and 7.1 x 10® m? mols and 8.33 x 10* J mol" for the catalysed reaction respectively. The results were shown to be in good agreement with those obtained from commercial instruments. The mean vent sizes for the uncatalysed and catalysed Methanol/Acetic Anhydride esterification reaction was found to be 164 mm (6.48") and 193 mm (7.6") respectively. The result for the uncatalysed case was shown to be slightly underestimated compared with the RSST and the ICI adiabatic calorimeters. This thesis has attempted to show that the Adiabatic Dewar-based Calorimeter can be used for the investigation of the thermochemistry (heat of reaction), simple overall reaction kinetic studies, as well as providing pressuretemperature-time data to assist the design of emergency relief systems for the sizing of vents for reaction mixtures.