Use of Process-intensifying Parameters

Use of a combination of cavitation and advanced oxidation processes such as ozonation, chemical oxidation using hydrogen peroxide and photocatalytic oxidation. 

Considering the specific apphcation of chemical synthesis, the presence of solid catalyst (particles/salts in a typical concentration range of 1 to 10% by weight of the reactants optimization is recommended in the majority of the cases using laboratory-scale studies) in the sonochemical reactors results in intensification due to the following mechanisms  

Formation of increased cavitation nuclei due to a higher number of discontinuities in the liquid continuum as a result of the presence of particles to give a larger number of collapse events resulting in an increase in the number of free radicals. 

In a biphasic soUd-hquid medium irradiated by ultrasound power, major mechanical effects are the reduction of particles size, leading to an increased surface area, 

These liquid jets not only provide surface cleaning but also induce pitting and surface activation effects and increase 

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Intensification can be achieved using this approach of combination of cavitation and advanced oxidation process such as use of hydrogen peroxide, ozone and photocatalytic oxidation, only for chemical synthesis applications where free radical attack is the governing mechanism. For reactions governed by pyrolysis type mechanism, use of process intensifying parameters which result in overall increase in the cavitational intensity such as solid particles, sparging of gases etc. is recommended. 

Design of sonochemical reactors is a very important parameter in deciding the net cavitational effects. Use of multiple transducers and multiple frequencies with possibility of variable power dissipation is recommended. Theoretical analysis for predicting the cavitational activity distribution is recommended for optimization of the geometry of the reactor including the transducer locations in the case of multiple transducer reactors. Use of process intensifying parameters at zones with minimum cavitational intensity should help in enhancing the net cavitational effects. 

The estimation of Rav for characteristic parameter values shows that Rav where Aq = d/Re /" is the internal scale of turbulence. In a turbulent flow, both heat and mass exchange of drops with the gas are intensified, as compared to a quiescent medium. The delivery of substance and heat to or from the drop surface occurs via the mechanisms of turbulent diffusion and heat conductivity. The estimation of characteristic times of both processes, with the use of expressions for transport factors in a turbulent flow, has shown that in our case of small liquid phase volume concentrations, the heat equilibrium is established faster then the concentration equilibrium. In this context, it is possible to neglect the difference of gas and liquid temperatures, and to consider the temperatures of the drops and the gas to be equal. Let us keep all previously made assumptions, and in addition to these, assume that initially all drops have the same radius (21.24). Then the mass-exchange process for the considered drop is described by the same equations as before, in which the molar fluxes of components at the drop surface will be given by the appropriate expressions for diffusion fluxes as applied to particles suspended in a turbulent flow (see Section 16.2). In dimensionless variables (the bottom index 0" denotes a paramenter value at the initial conditions). 

To overcome current limitations and restrictions in the monobromination of aromatic compounds, microstmctured reactors were tested by Loeb and coworkers [26-28] under intensified process conditions. Due to the improved safety features of microreactors, parameter screenings were extended to elevated temperatures and pressures. Moreover, undiluted elemental bromine was used as bromination agent, discarding the use of catalysts and radiation. In particular, the competitions between (a) single versus multiple substitutions and (b) core versus side-chain substitutions were investigated. 

The system described in Fig. 1 could be used to develop new processes and process units by combining relevant phenomena according to specific goals and constraints. This would allow a creative approach and also specific requirements of each case could be taken into account. The modelling should be done together with simultaneous experimentation and therefore also mathematical software for parameter estimation, sensitivity analysis and experiment planning would be needed. The system would help in the development of models with different degree of details for specific purposes intensified units, multifunctional units, new chemical routes, properties of products etc. Such a tool would inevitably be a tool of experts, its use would require expertise. 

Ultrasound is used in a variety of industrial applications, with a very wide range of objectives. Low-intensity ultrasound (with typically /process control and nondestructive testing of products (Knorr et al., 2004 Leemans and Destain, 2009), whereas high-intensity ultrasound (with I of 10-1000 Wcm ) is applied to intensify processes, such as the inactivation of microorganisms (Lee et al., 2009), homogenization (Wu et al., 2001a), or drying (Mulet et al., 2003 see also Chapter 8 of this volume). These very different applications underline the fact that the parameters of ultrasound and its interaction with a product must be well understood in order to allow successful process development. 

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