The effect of solution level on calorific and dosimetric results in a 70 kHz tower type sonochemical reactor

In order to design and optimise sonochemical reactors it is important to study the impact of liquid level, or path length, on the standing wave phenomena and the influence this has on temperature increase and OH radical rate of production. In this work, an ultrasonic tower type reactor operating at 70 kHz is investigated with results from variations to liquid levels reported. Calorimetry data was obtained using a modified reactor set up with temperature change monitored at selected points within the chamber. OH radical rate of formation was shown via chemical dosimetry, following the conversion of terephthalic acid (TA) to 2-hydroxyterephthalic acid (HTA). The results obtained have shown that changes in solution depth of a few millimetres significantly impacts on the interaction of the propagated and reflected waveforms with the results of calorific measurements and HTA rates of formation varying by 90% (750 J) and 88% (80 mmol dm(-3) min(-1)) between the operational extremes over the studied depth range.

The sono-degradation of phenanthrene in an aqueous environment

Polynuclear aromatic hydrocarbon (PAH) contamination has spread throughout the globe with background levels now found in virtually all sections of the ecosystem and environment. The mutagenic and/or carcinogenic properties attributed to many of these compounds, and frequency of occurrence and concentration in the environment, has driven research into safe methods of removing contamination, whilst avoiding the use of harmful solvents or the formation of even more hazardous compounds. Ultrasound is currently used in industry and research to propagate and accelerate chemical reactions, opening reaction pathways which otherwise would not be observed. In the study of the degradation of PAHs through ultrasonic irradiation, the breakdown of an aqueous solution of phenanthrene in a sonochemical reactor utilising a 30 kHz probe system, operating in batch mode, has been investigated. The phenanthrene molecule was studied and used as a model PAH molecule. It was chosen due to the structural similarities to many of the higher order PAHs currently recognised as being hazardous to health. The influence of several parameters on the degradation of phenanthrene are reported (power ultrasound energy, temperature and light). Qualitative analysis using HPLC and quantitative analysis using UV/Vis photo-spectrometry confirmed that a 88% reduction in the peak observed phenanthrene concentration was achieved over 240 min of sonocation. Whilst there was the potential for the formation of recalcitration and rearrangement products, no higher order PAHs were observed and a 80% reduction in total monitored UV fluorescence and hence, aromaticity/conjugation, was observed.

Effects of ultrasound energy on degradation of cellulose material

The rationale for selection of waste cellulose source and method for its degradation, such as ultrasound, aeration and coupled energy, is examined. Consideration is given to the availability of waste material for the conservation of global resources, pollution effects from energy forms and efficiency of energy transfer. Availability of the sources and possible ways of converting them to fuels, processes involved in its production and the possible effects on the environment are discussed. Manufactured cellulose and waste paper are used as the source for these experiments and the rationale behind their use in the environment is analysed. An ultrasound reactor that operates at 80 W and 38 kHz was used in breaking down the samples to produce glucose and other chemical species. One of the routes being explored is the further conversion of these molecules into fuel (alcohol).

High-speed video microscopy and computer enhanced imagery in the pursuit of bubble dynamics

The equipment and method for studying transient bubble dynamics are described in simple sonochemical reactors and presented using still frames from high-speed video microscopy (500 fps). Effects on aeration bubbles (mean size 1-3 mm diameter) and the cavitation induced species (< 0.5 mm diameter) are studied. The images are computer enhanced to improve interpretation of such features as the maximum ellipsoidal distortion at the nodal sound plane and spherical shape regain with due consideration of energy involved and expansion effects at the nodal sound plane. Also immersion depth/pressure effects, as the bubbles transcend the sound field column, in the cylindrical reactor, are recorded for evaluation of nodal and antinodal sound wave effects. Positions of the nodal and antinodal regions are marked using a novel tungsten halogen bulb technique and verified using the sonoelectroluminescent approach with the classical luminol/hydrogen peroxide chemistry which is enhanced under the sound field conditions.