Equipment Spinning discs

Inverted microscope with EMCCD camera, equipped for TIRF or spinning-disc microscopy. 

There are a number of types of equipment associated with high-energy transfer to the reactants including microreactors, microwave reactors, radio frequency heating, electric pulses, ultrasonication, and spinning disc reactors. Some of these are briefly discussed later. 

High-gravity field Spinning disc reactor Heat transfer from liquid film Mass transfer in liquid film Reaction time Equipment size Impurities level... 

The chapter on mixers is comparatively short - not because mixers are unimportant, but because mixing is such an integral part of other intensive processes (heat exchange, reactions and crystallisation/precipitation as examples), that the topic is addressed continuously through other equipment and application chapters. The point is well made by Wu et al. (2(X)7) who stresses in their recent review that PI needs to be implemented via increased mixing, as well as heat and mass transfer - hence the success in this area of the spinning disc and the oscillatory baffle reactors. 

In most of the attractive examples of intensified process equipment (e.g. in-line mixers, spinning disc reactors, rotating packed-beds, micro-reactors, etc.) the fluid residence time is measured in seconds. Therefore, a process designer should consider the use of these devices, provided that the reactions are (or can be made to be) completed in this time frame. If this is not the case, then the fluid intensity should be detuned to match the relatively relaxed kinetic environment. In this event, with a continuous process, a simple tubular reactor with very modest flow velocities could provide adequate plug flow and residence times up to several hours. In the case of a number of biological processes, as an alternative example, substantial intensification can be achieved using a continuous oscillatory baffled reactor (COBR, see Chapter 5), where residence times may be at best minutes and could extend to hours. 

Figute 4.10. A basic photocentxidisc, as used to perform line start sedimentation smdies, has a thin layer of suspension added onto the free surface of the fluid in the spinning disc, a) Appearance of the photocentridisc. b) Side view of the equipment showing the suspension layer, c) Typical signal output from a photocentridisc. 

Armed with the PFS and the questions for the various process options the team can then discuss the most appropriate way forward. For example considering question 2, production staff may comment that this particular plant only runs on the day shift, so a 10-hour reaction is not viable the chemical engineer may conclude that the problem is likely to be one of mass transfer, and other reactor design options such as a spinning disc reactor should be considered. The SHE advisor may comment that not only is solvent 1 volatile but it is also moderately harmful and would require specialist handling equipment, hence it is very important to find an alternative. As waste minimization starts at the reaction stage it is critical to study this area in particular detail. Questions that can be asked include ... 

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