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Documentation for Reaction Calorimeters
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What is Reaction Calorimetry?
Reaction calorimetry measures the heat released from a chemical reaction or physical process under process-like conditions and provides the fundamentals of the thermochemistry and kinetics of a reaction.
Calorimetric information is crucial when determining how chemical reactions can be transferred safely from lab to plant. Along with the chemical development workflow, reaction calorimetry provides the information needed for each of the individual steps and is subsequently converted into information to evaluate the risk, scalability and criticality of a process. Reaction calorimetry helps to identify issues related to heat and mass transfer or mixing, and allows the determination of the correct temperature, stirring or dosing profile online. Reaction calorimetry also uncovers unexpected behavior and makes other scalability issues visible and quantifiable.
What is Important to Obtain Good Calorimetric Data?
Fast responding thermostate with precise temperature control ensures the reaction proceeds along the desired pathway. Large cooling capacity with rapid heat removal copes with fast and violent reactions and large amounts of heat. Sensitive temperature measuring system ensures precise temperature control and accurate calculation of all heat information. Calculation algorithms take into account not just the measured data, but also physical factors such as heat capacity, heat accumulation, and heat of dosing. Integrated knowledge management and reporting are important to track all experimental information.
Decisive Factors Within Total Heat Flow Balance
Getting the most out of an experiment requires consideration of all possible heat flow terms.
- Heat Flow: heat flow across reactor wall
- Heat Accumulation: accumulated heat due to temperature variation
- Heat of Dosing: heat due to added material
- Heat of Calibration: calibration power
- Heat of Reflux: heat removed via condenser
- Heat of Stirring: energy input due to stirrer at changing viscosity or stirrer speed
- Heat Loss: heat loss through reactor lid assembly
What is the Heat Flow Principle and How Does it Work?
Applicable to all METTLER TOLEDO reaction calorimetry workstations, the heat flow principal is the most simple and robust method to determine the heat released by a chemical or physeical process. It is applicable under most conditions, is highly sensitive and offers excellent repeatability. The heat flow principle is based on the driving force (temperature difference between reaction mass and jacket temperature) which is converted into heat flow by means of the calibration factor. The calibration factor is determined by means of an electrical heater than emits a small amount of energy into the reaction mass.
The determination of heat flow is based on the temperature difference across the wall of the reactors and depends on the thermal conductivity and thickness of the reactor wall, the thermal resistance of the reaction mass film, the thermal resistance of the oil film. In a non-isothermal operation, some of the energy is stored in the reactor wall. As a result, the appreciable heat capacity of the reactor wall must be taken into account. A mathematical model is used to calculate the temperature distribution in the reactor wall and gives an (imaginary) jacket temperature.
What is the Importance of Accurate Specific Heat Data?
When a system heats up/cools down, energy is absorbed/released by the system, If energy is stored or accumulated, the temperature increases and descreses if it is released again. Note that it is not only chemicals that are heated up/cooled down. The total amount of accumulated heat depends on the amount of material, difference in temperature, and specific heat capacity of the material. The consequence is that the heat capacity of the material, the inserts, and the reactor wall need to also be taken into account.
Reaction Calorimetry Applications