Classical thermo-analytical micro methods (DTA, DSC) are still very useful for process work, but medium scale instruments based on heat flow measurement are attaining an increasingly important role in this domain.
As in many areas, development of reaction calorimetry for industrial applications was driven by needs and by available means (technical capabilities).
The needs have been fairly constant over the past decades. There are data needs:
-Heat release rates
-Heat of desired reactions and decompositions
-Heat capacities and heat transfer capacities
It took the specialists of calorimetry a long time to recognize and to accept the operational needs, namely:
-Working under controlled temperature conditions (constant temperature, temperature ramps)
-Adding components during runs (continuously or in portions)
-Simulation of industrial mixing conditions
The main driving force for the development of process oriented calorimetric instruments was the evolution of electronic hardware which made the control of heat flow on a (non micro) laboratory scale easy.
The paper gives an overview on the principles of heat flow control and reviews the developments of the fifties and sixties, when the matching of heat flow with heat release by reactions was the goal.
With the advent of fast and powerful laptop computers, the focus has shifted. Now, the deduction of true heat release rates from signals which may be badly distorted, is the goal.
Some recent developments are reviewed and the hope is expressed that calorimetric equipment, inexpensive enough to be affordable for every laboratory engaged in process work, will be available soon.
Authors:Sridhar Vethathiri Pakkirisamy, Surianarayanan Mahadevan, Sivapirakasam Suthandathan Paramashivan, and Asit Baran Mandal
Fireworks mixtures are vulnerable to thermal hazards. ARC data are used for determining the ceiling temperature for processing, handling and transportation of hazardous materials. Accordingly, the practice adopted is that the
Reaction calorimetry strongly penetrated process development laboratories in the fine chemicals industry. Applications of calorimetry to different fields of process optimization, chemical reactions and physical unit operations were developed. Applications were first developed in the field of process safety. The thermal data of reaction obtained in the calorimeters allow us to check if a reaction will be controllable at full scale under normal operating conditions and in case of equipment failure. Further, the accurate temperature control and heat flow measurement opened the door to more engineering related data, in the fields of phase equilibria like vapour liquid, solubilities, crystallization and also in the mixing techniques. Some examples of developments in these different fields will be reviewed.
Authors:Qingsheng Wang, William Rogers, and M. Mannan
Reaction hazards remain the most serious concern in the chemical industry in spite of continual research and attention devoted
to them. Many commercial calorimeters, such as the Differential Scanning Calorimetry (DSC), are useful screening tools for
thermal risk assessment of reaction hazards. Some important thermodynamic and kinetic parameters, including onset temperature,
adiabatic time to maximum rate, and maximum adiabatic temperature, were analyzed in this paper. A kinetic-based model under
adiabatic conditions was developed, and the adiabatic time to maximum rate was estimated. Correlations between onset temperature
(To) and activation energy (Ea), and between onset temperature (To) and adiabatic time to maximum rate (TMRad) were found, and were illustrated by some examples from the previous literature. Based on the heat of reaction and the adiabatic
time to maximum rate, a thermal risk index (TRI) was defined to represent the thermal risk of a specific reaction hazard relative
to di-tert-butyl peroxide (DTBP), and the results of this index were consistent with those of the reaction hazard index (RHI). The correlations
and the thermal risk index method could be used as a preliminary thermal risk assessment for reaction hazards.
Authors:Hanspeter Sprecher, M. Nieves Pérez Payán, Michael Weber, Goekcen Yilmaz, and Gregor Wille
The synthesis and utilisation of acyl azides in a flow apparatus combined with an automated extraction unit is described. This process safely provides multi-100 g quantities of a labile diacyl azide (3) as an intermediate that could not be generated safely by classic batch methods. Its subsequent conversion to the desired amine (4) represents an example for process intensification. The same set-up with an output capacity of >30 g/h was used for the unattended synthesis of benzoyl azide as the final product in solution (tert-butyl methyl ether (TBME), 0.5 M).
A Grignard reaction of reactantA and phenyl magnesium chloride is used to make a pharmaceutical intermediate at the production scale. The elimination of protecting groups onA was proposed as a means to reduce synthesis costs. This new synthesis route, however, had process efficiency and safety issues associated with it: (1) build-up of unreactedA in the reactor, (2) influence ofA's particle size on the reaction rate, (3) the sensitivity of the reaction rate to the reaction temperature and to the (changing) solvent composition, and (4) the highly exothermic nature of the reaction.
The Mettler RC1 Reaction Calorimeter was used to quantify the influence of solvent composition, temperature, and particle size on the reaction rate. Results indicated a dramatic effect of solvent composition and reaction temperature on the reaction rate; for example, over a temperature range of just 30°C, the reaction time decreased from more than a day to just a few minutes. At such high reaction rates, the vessel jacket could not remove the reaction heat sufficiently and the internal temperature rose adiabatically.
These results were used to make process design and operation recommendations for safe and efficient plant operation with this modified Grignard reaction system.
In the investigation of foods by thermal analysis and calorimetric techniques, many physico-chemical effects can be observed in the temperature range between –50 and 300°C. These thermal phenomena may be either endothermic, such as melting, gelatinization, denaturation, evaporation or exothermic, such as crystallization, oxydation, fermentation. Glass transitions are observed as a shift in the base line; this information, associated with water content and water activity determinations, is of particular interest in relation to storage of food powders but also for gas retention in powders foreseen to foam when dissolved.The thermal behavior of foods strongly depends on their composition; we therefore present first the thermal characteristics of the major food constituents: carbohydrates, lipids, proteins, water and then of raw and reconstituted food.
Semi-batch reactors are widely spread in the fine chemicals and specialties industry. The reason is that, compared to the
pure batch operation, the feed of at least one of the reactants provides an additional way of controlling the reaction course,
which represents a safety factor and increases the constancy of the product quality. Process temperature and feed rate can
be optimized to satisfy safety constraints, i.e. cooling capacity and allowable accumulation. An economically better way of
operating a semi-batch reactor is to adapt the feed rate to the allowed accumulation of reactants. An experimental method
based on calorimetry will be presented and illustrated by an example.