Positive reactions
24 Feb 2005
The innovative concept of a constant flux reactor has just successfully come through its first field trials at a leading speciality chemicals producer. Mike Spear reports on this patented technology that can turn stirred tank reactors into precision calor
Constant flux control (Coflux) is a patented technology, developed by Hertfordshire-based Ashe Morris, that allows stirred tank reactors of virtually any size or type to be operated as precision calorimeters.
Its developers believe it offers a simple and versatile solution for on-line monitoring of chemical, physical and biological processes — claims that have now been borne out in the first field trials carried out by Clariant Chemicals at its plant in Horsforth, Leeds.
A constant flux reactor is essentially a vessel equipped with a heat exchange jacket for controlling heat flows into or out of the reactor.
But unlike conventional heat exchangers, a Coflux reactor varies the heating or cooling power by regulating the heat transfer area rather than the temperature of the heat transfer surface.
Instead of a single jacket, the heat transfer surface is comprised of multiple separate elements, each of which can be turned on or off by means of a motorised piston (or rotary) valve. By regulating the number of heating/cooling elements in service, the user can control temperature without altering the velocity or temperature of the heat transfer fluid.
The system used in the Clariant trials was a 10 litre constant flux reaction calorimeter with a Hastelloy body. Power and enthalpy data were monitored in real time and displayed on a Eurotherm 5180v data management unit.
Clariant carried out a series of test reactions in the trial unit and used the on-line monitoring features to track progress in real time.
The company's engineers were able to observe the rate of change (powder dissolution and reaction) throughout the experiments and could successfully detect the start and finish of each reaction step.
The results were very encouraging and Jim Wilson, Clariant's R&D manager at the Horsforth site, says 'an insight into the mechanics of the chemical reactions was provided due to the highly responsive online metrics'. Pointing to potential benefits arising from 'reduced cycle times and increased material efficiencies, as well as reduced energy requirements', he concludes that 'constant flux could be utilised to optimise synthesis processes within Clariant'.
Robert Ashe, a co-founder of Ashe Morris, points out that 'no calibration was required between experiments, and a single monitoring tool has been able to track continuously two entirely different unit operations [powder dissolution and reaction] without interruption. We believe that no other process monitoring techniques can match Coflux calorimetry for its combination of simplicity, reliability and versatility.'
In addition to its on-line monitoring role, the Coflux design also offers some major operational advantages. For example, greater uniformity of temperature can be achieved at the heat transfer surface, while the new jacket design for batch reactors can also deliver improved heat transfer capacity. The height of the cooling/heating fluid in the jacket can also be restricted to liquid-covered surfaces in the reactor. This prevents product from being damaged by extreme temperatures in the splash zone above the liquid surface.
Clariant is currently undertaking further reviews of Coflux in its technology centre in Switzerland. Further trials are also now in progress with other manufacturers, such as Astra-Zeneca, in the UK and US.
