We will soon have a new HEL Phi-TEC Adiabatic Reaction Calorimeter up and running. Hopefully this will help solve some nagging questions I have about the thermal stability of certain compounds. Time to maximum rate (TMR) is a useful parameter and ARC testing helps to find this value.
I have spent a good deal of time with the Mettler-Toledo RC1 and have found it to be very useful in process development. There is a tendency for chemists to design exothermic reactions to start at low temperature and at perhaps some point raise the temperature to take the reaction to completion. The RC1 will indicate accumulation of energy in a vessel following a charge. By varying the temperature of the reaction mass and modulating the dosing rate it is possible to find a reaction temperature and feed rate that affords a steady state (or manageable, at least) output of power with minimal energy accumulation.
With the reactions I have been studying it has become apparent that sometimes a preference for low temperature (-30 C to 0 C) by the chemist may in fact be based on habit rather than need.
Naturally, the thermal picture is not the entirety of the problem. Product stability in the reaction mass and residence time at temperature play a role in how the process is configured. But a reaction calorimeter can help find threshold temperatures below which the reaction substantially shuts down.
The RC1 measures heat of reaction in Joules and power in Watts. After some time on the instrument one comes to view a reaction mass as a power generator or an absorber. Power is reported in Watts and is indicated by the magnitude of the deflection of the power curve from baseline. Joules of energy are calculated from the area under the power curve.
The instrument has a calibration routine where it determines the Cp of the vessel contents. If you have the reaction mass, heat of reaction, and Cp, you can calculate the adiabatic temperature rise for a given dose of reactant. This is an extremely useful element in sketching out the safe operating parameter space of a reaction.
Safety is a political concept. Safety has no basis in physics. It is an artifact of anthropology. It is a fuzzy construct defined by a magnitude of “likelihood” and type of consequence individuals and organizations are willing to absorb to obtain a particular outcome. But when you sit down in a meeting with thermokinetic data and solid interpretation, all of the stakeholders in a plant can brainstorm and home in on a fairly rational and agreed upon process profile. This is politics at its finest- data driven and substantially rational.