Our company has long been known for characterizing outcomes our customers would rather not encounter but have to be ready for nonetheless. That would be sizing vents to safely handle runaway reactions, preventing and mitigating combustible dust explosion hazards, assessing the flammability potential of combustible gases and vapors or determining the thermal stability of reactive monomers and other chemical reagents. Understanding what you don’t want to do is a vital part of a process safety plan. So, too, is characterizing what you do want to do, and knowing what it takes to keep it that way.
In the case of a desired (exothermic) chemical reaction, we are talking about knowing the rate of heat production, how it scales and how it is affected by deviations, and whether said upsets can lead to any unwanted events. In process development, we are concerned with the ramifications of scaling this heat production rate, where and how it is to be removed and does the initial concept of the process jive with the projected performance at scale (addition times, addition orders, batch versus semi-batch operation). And, all of this must be studied under conditions where the effects of mass and heat transfer are well understood and controlled.
The accepted technique for gathering this type of data in the industry is known as reaction calorimetry. There have been many instruments developed over the years to accomplish such tasks and Fauske & Associates, LLC (FAI) maintains a variety of devices so we can be flexible and design the most appropriate experiment to gather the vital heat rate and adiabatic potential data you need for a safe scale up. Couple this with our vast experience in characterizing runaway reaction behavior using adiabatic and vent sizing calorimetry and we can deliver you a complete picture of a safe chemical process.
FAI currently has three reaction calorimeters of varying size and capability:
1. THT- RC
This device is reaction calorimetry in a vial. The reactor is simply a GC vial
or a metal pressure (SS or HC) cell, volume ~1.5 ml. Agitation is via magnetic stir bar. Temperature range is -5°C to 150 °C and pressures up to 10 bar are possible with the pressure cells. The instrument has a 5 W sensitivity and roughly ±110 mW heat flow limit. Modes of operation include isothermal with steps, titration with an integrated syringe pump, scan and hold (2°C/min max) and heat capacity determination. FAI is also developing this device for measuring binary compatibilities.
2. Mettler-Toledo RC1
The RC1 is a heat flow calorimeter. As such, the heat leaving or entering the jacketed reaction vessel is characterized by UA(Tr-Tj) where U is the overall heat transfer coefficient, A is the area of heat transfer and Tr and Tj are the temperature of the reactor and jacket, respectively. The temperatures are measured, A is known by geometry (stirred volume) and the heat transfer coefficient, U, is calibrated for by an immersed calibration heater before and after the reaction. Available temperature range is -73°C to +230°C, pressure ambient to 2 bar. Reactors are borosilicate glass, 500 ml or 1 liter. Agitation via overhead stirrer with a conventional Teflon® bearing or magnetic drive, glass or Hastelloy stirrers and baffles, the latter for difficult to stir systems. Automated reagent additions can be performed with integrated balances using positive displacement Teflon® diaphragm pumps or solenoid valves. With an inserted probe, pH monitoring and/or control is also possible. The RC1 is not just for batch or semi-batch operation. It has been used by the author to demonstrate continuous processing too.
The ChemiSens is a heat flux calorimeter that provides a true heat flow signal without requiring any calibration.
The heat transfer surface is entirely through the bottom of the reactor making use of Peltier technology and is independent of the heat transfer coefficient as defined above. FAI is the North American Distributor for the ChemiSens. The temperature range is -50°C to 200°C and the combination 316 stainless steel glass reactor has a pressure rating to 20 bar though reactors of other materials of construction and higher pressure ratings are available. Stirring is via a magnetically coupled drive (2000 rpm) with a variety of impellers and inserts. Additions can be performed using a pressure syringe pump. The pressure reactor has been outfitted for hydrogenation studies complete with a gas induction impeller, baffles and gas uptake rig. Operation under reflux with or without gas generation is also possible. The ChemiSens is best when operated in isothermal mode, however, FAI has done some creative temperature scanning work as well. A variety of inserts allow for batch injection of solids, torque measurement if desired.