Sonochemical reaction vessels

Nanzai B, Okitsu K, Takenaka N, Bandow H, Tajima N, Maeda Y (2009) Effect of reaction vessel diameter on sonochemical efficiency and cavitation dynamics. Ultrason Sonochem 16 163-168... 

The chemical reactions induced by ultrasonic irradiation are generally influenced by the irradiation conditions and procedures. It is suggested that ultrasound intensity , dissolved gas , distance between the reaction vessel and the oscillator and ultrasound frequency are important parameters to control the sonochemical reactions. 

Figure 5.7 shows the effects of the distance from the oscillator to the bottom of the reaction vessel on the rate of Au(III) reduction, where the distance is changed from 3.5 to 4.5 mm [29]. It is clear that the rates of reduction are affected by the position of the reaction vessel. The rate of reduction became the maximum at a distance of ca. 3.8 mm. This was almost the same as the half-wavelength of the ultrasound (3.71 mm) used in this study. It is suggested that ultrasound is effectively transmitted into the reaction vessel at 3.8 mm distance. It should be noted that the position of the reaction vessel sensitively affects the efficiency of the sonochemical reduction. 

The cup-horn configuration, shown in Fig. 8, was originally designed for cell disruption but has been adopted for sonochemical studies as well (81). It has greater acoustic intensities, better frequency control, and potentially better thermostating than the cleaning bath. Again, however, it is very sensitive to the liquid levels and to shape of the reaction vessel. In addition, the reaction vessel faces a size restriction of 5 cm diameter. 

In 1983 Suslick reported the effects of high intensity (ca. 100 W cm, 20 kHz) irradiation of alkanes at 25 °C under argon [47]. These conditions are of course, well beyond those which would be produced in a reaction vessel immersed in an ultrasonic bath and indeed those normally used for sonochemistry with a probe. Under these extreme conditions the primary products were H2, CH4, C2H2 and shorter chain alk-l-enes. These results are not dissimilar from those produced by high temperature (> 1200 °C) alkane pyrolyses. The principal degradation process under ultrasonic irradiation was considered to be C-C bond fission with the production of radicals. By monitoring the decomposition of Fe(CO)5 in different alkanes it was possible to demonstrate the inverse relationship between sonochemical effect (i. e. the energy of cavitational collapse) and solvent vapour pressure [48],... 

Another important consideration when using baths to perform sonochemical reactions is that it may be necessary to stir the mixture mechanically to achieve the maximum effect from the ultrasonic irradiation. This is particularly important when using solid-liquid mixtures where the solid is neither dispersed nor agitated throughout the reaction by sonication alone and simply sits on the base of the vessel where it is only partially available for reaction. The reason that additional stirring is so important in such cases is that it ensures the reactant powder is exposed as fully as possible to the reaction medium during sonication. 

Figure 1. A glass reaction vessel suitable for most sonochemical reactions. The volume of the glass cell can be easily varied from 15 to 500 mL by replacing the cylindrical vessel with a round bottom flask.

Observation of the evolution of the nitrogen dioxide vapors led to a first improvement, by carrying out the reaction in a closed vessel, confirming that the actual oxidizing agent is NO2. The sonochemical reaction gives almost quantitative yields in 2 h, while the silent process requires 2 days (Fig. 38). 

An ultrasonic reactor designed for sonochemical reactions is shown in the figure below. The main improvement is that the reactor is attached directly to the transducer. This set-up allows a direct transmission of the acoustic energy to the solution. Other advantages are the elimination of substrate contamination by probe erosion and a reproducible adjustment of a reaction vessel on the high energy spot in water baths. 

Sonochemical Synthesis of M50 Type Steel Nanopowders. A dispersion of 15g (0.0765 mol) of Fe(CO)5, 0.66g of Cr(EtxC6H6-x)2, 0.75g (0.0015 mol) of CpMo(CO)3 and 1.0 g of polyoxyethylene sorbitan trioleate (surfactant) in dry decalin was sonicated at 50% amplitude for 7h at room temperature in a sonochemical reactor fitted with a condenser and gas inlet and outlet tubes connected to a mercury bubbler. The color of the solution turned dark and then black within a few minutes and this reaction mixture was sonicated until the formation of shiny metallic particles was observed on the walls of the reaction vessel. The sonication was then stopped and the decalin solvent was removed from the reaction flask via vacuum distillation. Fine black powder (Yield 4.448g) remained at the bottom of the reactor, which was then isolated, transferred to a vial and coated with mineral oil before the compaction. 

Careful design of the reaction vessel allows reactions to be carried out under inert atmospheres (Fig. 13) or at moderate pressures (< 10 atmospheres) (Fig. 14). Other workers have proposed modifications to allow the reaction mixture to be simultaneously stirred. These include use of a cell with a small indentation at the bottom or a glass rosette cell (Fig. 15). Luche and coworkers have carried out extensive investigations into sonochemical preparation of... 

One problem with photochemical treatment is that the method relies on good light transmission into the reaction medium. The slow coating of the transparent walls of the photoreactor vessel with biological or chemical deposits or coloration in the material to be treated causes loss in efficiency. A possible solution to the first of these problems is the use of ultrasound to protect the photoreactor walls against deposition of such materials [39]. Very general claims have been made in the patent literature relating to the possible combined use of photochemistry with sonochem-... 

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