Oscillatory-flow baffled reactors

Figure 5.14 Sketch Oscillatory flow baffle reactor, flow visualization and industrial unit Source Courtesy of http //www.nitechsolutions.co.uk...

Formulation of multi-component emulsions and mixtures are of interest in chemical and industrial processes (Vilar, 2008 Vilar et al., 2008). Standard stirred tank reactors (STR) and oscillatory baffled reactors (OBR) are traditional methods for the formulation of liquid-liquid mixtures and liquid-solid emulsions. Compared with STR, oscillatory baffled reactors provide more homogeneous conditions and uniform mixing with a relatively lower shear rate (Gaidhani et al., 2005 Harrison and Mackley, 1992 Ni et al., 2000). Figure 17 is a sketch of a typical oscillatory baffled reactor. It consists of the reactor vessel, orifice plate baffles, and an oscillatory movement part. The orifice plate baffles play an important role in the OBR for the vertex generation in the flow vessels as well as the radial velocities of the emulsions and mixtures. They are equally spaced in the vessel with a free area in the center of each baffle... 

Figure 17 Sketch of the oscillatory baffled reactor (top) and flow within baffled sections (bottom).

Stonestreet, P. Van Der Veeken, P.M.J. The effect of oscillatory flow and bulk flow components on residence time distribution in baffled tube reactors. Chem. Eng. Res. Des. 1999, 77 (A8), 671-684. 

Solano, J.P., Herrero, R., Espin, S. et al. (2012) Numerical study of the flow pattern and heat transfer enhancement in oscillatory baffled reactors with helical coil inserts. Chemical Engineering Research and Design, 90,732-742. 

The oscillatory baffled reactor (OBR), illustrated in Figure 5.13, is a novel form of continuous plug flow reactor, in which tubes fitted with equally-spaced, low-constriction orifice plate baffles have an oscillatory motion (range 0.5 to 10 Hz) superimposed upon the net flow of the process fluid. 

Dr Adam Harvey at Newcastle University (Harvey, 2006) is examining the use of oscillatory baffle reactors as components to intensify the production of biodiesel fuels. The research at Newcastle University uses rapeseed oil as the feedstock, the atfiaction being generally that it is a renewable energy source, it reduces CO2 emissions and pollution and it attracts tax relief in the UK at present. The range of PI projects in this area include a portable plant, solid catalysts (which allow a reduced number of process steps compared to liquid catalysts), the development of a reactive extraction process direct from the oilseeds, examination of cold flow properties and the production of biodiesel from algae. 

The oscillatory baffle reactor/oscillatory flow reactor (OBR/OFR) types are seen as for niche applications, where one wants to convert a long residence time batch process to a continuous one. In the case of biodiesel, Dr Harvey indicates that a conversion could be carried out in 10 minntes, compared to 1-6 hours in continnons indnstrial processes. One variant is shown, by means of a flow diagram, in Figure 10.20, while Figure 10.21 shows components of the OFR. The aim is to make the plant portable so that it will fit into a standard shipping container. The unit could be sold worldwide to, for example, formers to produce their own fuel locally. 

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. 

Reactor configurations other than conventional stirred tanks have been proposed for suspension polymerization. Draft tubes, or internal loops , can be used for suspension polymerization [102], but drop size changes can occur [103] and flow patterns may be complicated [104]. Tanaka et al. [105] used a loop reactor for the suspension polymerization of styrene. They employed a double agitation method to control the transient droplet diameter distribution and the final particle size distribution. Ni et al. [106] developed an oscillatory baffled reactor for batch suspension polymerization of methyl methacrylate. Fluid mixing was achieved by eddies that are generated when a fluid passes through a set of equally spaced, stationary, orifice baffles that are located inside a tube. Periodically formed vortices were con-... 

In the time or temporal domain, periodicity in operation is incorporated to realize all four principles of PI. A combination of adsorption-reaction-desorption on catalyst surface by periodic forcing of temperatures and pressures demonstrates the application of first principle. Oscillatory baffled flow reactor enhances uniformity, and illustrates the second PI principle. The application examples for third and fourth PI principles are pulsation of feed in trickle bed reactors enhancing the mass transfer rates, and flow reversal in reversed flow reactors shifting the equilibrium beyond limitations respectively. Switching from batch to continuous processing also result in realization of second and third PI principles. 

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