Sonoreactor

Controlled process ultrasound doses can be used to promote a broad range of effects which can modify materials, including surface cleaning, fragmentation, crystallisation, deagglomeration, emulsification, mixing and production of free radicals. Process ultrasound can be used for:

• Ultrasonic reactors – used for batch and flow processes in material production
• Sonocrystallisation – applied ultrasound to steer crystallisation, enhance nucleation and control polymorphs.
• Sonomilling – use of cavitation to break particles or crystals.
• Exfoliation – use of cavitation to exfoliate 2-D materials.
• Sonochemistry – use of ultrasound to enhance chemical reactions or generate radicals to promote polymerisation.

Most of these processes are driven by acoustic cavitation. Acoustic cavitation is the stimulated expansion, contraction and collapse of microbubbles in a liquid, under the influence of a driving acoustic field. The most common way cavitation is generated is using either sonic horns or sonic baths. These devices use piezoelectric transducers to generate the acoustic fields and resulting cavitation.

Challenges

Off-the-shelf devices make directly studying cavitation-driven processes challenging as they have fixed frequencies, are relatively inconsistent and unstable, and offer only rudimentary output control. Cavitation measurement, control and scaling can make industrial implementation of acoustic cavitation difficult. Utilising ultrasound techniques for materials processing can lead to other challenges related to energy efficiency of the process, and the yield achievable by and the scalability of that process

Off-the-shelf devices make directly studying cavitation-driven processes challenging as they have fixed frequencies, are relatively inconsistent and unstable, and offer only rudimentary output control.

NPL has unique capabilities related to ultrasound metrology and cavitation characterisation, including the development of the NPL ‘Sonoreactor’. This can enable industry to maximise the benefits of process ultrasound.

More sophisticated process ultrasound is an important tool to make better products and create novel process routes. NPL’s Sonoreactor capabilities include a reference cavitation vessel, a unique, 17 litre vessel operating at six-frequencies in the range 21-136 kHz. A second 25 litre vessel combines a focused MHz transducer with rings of kHz sources, creating high intensity, controllable cavitation pressure points within the vessel. NPL’s Sonoreactor knowledge includes patents filed in several jurisdictions (WO2020021248), plus knowhow related to the generation, characterisation and scale-up of controlled ultrasonication, and access to novel cavitation metrology solutions to support improved process control.

The controllable cavitation field generated by the sonoreactor enables the control of particle size, several industrial sectors (e.g. pharmaceuticals and nanomaterials production) face challenges related to effectiveness of particle size control, energy efficiently and at scale.

• NPL's Sonoreactor maintains the materials in a “sweet spot” reaction zone, which enable continuous processing and greater yield on significantly larger scales, and can reduce the energy requirement to process a sample versus other techniques.
• It can utilise common, less toxic surfactants than may be required for alternative processes which can make production safer with less potential environmental impact.
• It can be implemented at different sizes to enable scale up of process ultrasound, and for potential plant integration.

A side-view schematic of a cylindrical graphene sonoreactor that uses a HIFU transducer to lift and focus graphite through the central pressure peak of the sonoreactor’s ring of transducers, generating a continuous toroidal vortex (black arrows) of graphite

A top view of the sonoreactor design

NPL’s Sonoreactor capabilities can support industry to achieve more efficient production of high-quality, high-yield products, for instance in the advanced materials, pharmaceuticals and food and drink sectors. NPL is keen to partner with industrial, research and academic stakeholders to realise and exploit the potential of the technology through the development of systems suitable for installation within industry.

For more information please contact us.

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