A reaction calorimeter

Calorimeter

A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal microcalorimeters, titration calorimeters and accelerated rate calorimeters are among the most common...

 is an instrument

Measuring instrument

In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

 that measures the amount of energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 released

Exothermic

In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...

 or absorbed

Endothermic

In thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the prefix endo- and the Greek word thermasi,...

 by a reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

. These measurements provide a more accurate picture of such reactions.

Applications

• Safety
  Safety
  Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...
  
  :- When considering scaling up a reaction to large scale from lab scale, it is important to understand how much heat is released. At a small scale heat released may not cause a concern, however when scaling up, that heat can build up and be extremely dangerous.

• Crystallization
  Crystallization
  Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid...
  
  :- Crystallizing a reaction product from solution is a highly cost effective purification
  Purification
  Purification is the process of rendering something pure, i.e. clean of foreign elements and/or pollution, and may refer to:* List of purification methods in chemistry* Water purification** Organisms used in water purification...
  
   technique. It is therefore valuable to be able to measure how effectively crystallization is taking place in order to be able to optimise it. The heat absorbed by the process can be a useful measure.

• Kinetics
  Chemical kinetics
  Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition...
  
  :- The energy being released by any process in the form of heat is directly proportional to the rate of reaction and hence reaction calorimetry
  Calorimetry
  Calorimetry is the science of measuring the heat of chemical reactions or physical changes. Calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat...
  
   (as a time resolved measurement technique) can be used to study kinetics.

• Process Development:- The use of reaction calorimetry in process development has been historically limited due to the cost implications of these devices however calorimetry is a very fast and easy way to fully understand the reactions which are conducted as part of a chemical process
  Chemical process
  In a "scientific" sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by somebody. Such a chemical process commonly involves a chemical reaction of some sort...
  
  .

Heat Flow

Heat flow calorimetry works by looking at the heat flowing across the reactor wall and quantifying this in relation to the other energy flows within the reactor.



where
= process heating (or cooling) power (W) = overall heat transfer coefficient (W/(m²K)) = heat transfer area (m²) = process temperature (K) = jacket temperature (K)

Heat flow calorimetry allows the user to measure heat whilst the process temperature remains under control. While the driving force Tr-Tj is measured with a relatively high resolution, the overall heat transfer coefficient U or the calibration factor UA respectively, is determined by means of calibration before and after the reaction takes place. The calibration factor UA (or the overall heat transfer coefficient U) are affected by the product composition, process temperature, agitation rate, viscosity, and the liquid level. Good accuracy can be achieved with experienced staff who well know the limitations and how to get the best results from the instrument.

RTCal

Calorimetry in Real Time:- RTCal is a patented measuring technique which is based on heat flux sensors that are located on the wall of the reactor vessels. The sensors measure heat across the reactor wall directly and thus, the measurement is independent of temperature, the properties or the behavior of the reaction mass. Heat flow as well as heat transfer information are obtained immediately without any calibrations during the experiment.

Heat Balance

The cooling/heating jacket controls the temperature of the process. Heat is measured by monitoring the heat gained or lost by the heat transfer fluid.



where
= process heating (or cooling) power (W)
= mass flow of heat transfer fluid (kg/s)
= specific heat of heat transfer fluid (J/(kg K))
= inlet temperature of heat transfer fluid (K) = outlet temperature of heat transfer fluid (K)

Heat balance calorimetry is, in principle, the ideal method of measuring heat since the heat entering and leaving the system through the heating/cooling jacket is measured from the heat transfer fluid (which has known properties). This eliminates most of the calibration problems encountered by heat flow and power compensation calorimetry. Unfortunately, the method does not work well in traditional batch vessels since the process heat signal is obscured by large heat shifts in the cooling/heating jacket.

Power Compensation

A variation of the 'heat flow' technique is called 'power compensation' calorimetry. This method uses a cooling jacket operating at constant flow and temperature. The process temperature is regulated by adjusting the power of the electrical heater. When the experiment is started, the electrical heat and the cooling power (of the cooling jacket) are in balance. As the process heat load changes, the electrical power is varied in order to maintain the desired process temperature. The heat liberated or absorbed by the process is determined from the difference between the initial electrical power and the demand for electrical power at the time of measurement. The power compensation method is easier to set up than heat flow calorimetry but it suffers from the similar limitations since any change in product composition, liquid level, process temperature, agitation rate or viscosity will upset the calibration. The presence of an electrical heating element is also undesirable for process operations. The method is further limited by the fact that the largest heat it can measure is equal to the initial electrical power applied to the heater.
or
- current supplied to heater - voltage supplied to heater - current supplied to heater at equilibrium (assuming constant voltage / resistance)

Constant Flux

A recent development in calorimetry however is that of constant flux cooling/heating jackets. These use variable geometry cooling jackets and can operate with cooling jackets at substantially constant temperature. These reaction calorimeters tend to be much simpler to use and are much more tolerant of changes in the process conditions (which would affect calibration in heat flow or power compensation calorimeters).

The equation used within COFLUX calorimetry is the same as in heat balance.