The research concerning the chemical reaction engineering plays a key role in the exploitation of new kinds of reactors able to work in increasingly more efficient & sustainable ways. In the past decades, considerable efforts from researchers have been addressed to the study of externally influenced processes,ie all the reactions whose extent could be enhanced by any kind of externally applied force field such as photocatalysis, microwave-assisted processes & sonochemistry. In the latter case high frequency sound waves (ultrasounds) have been used to generate desirable effects, which are locally concentrated high temperature, pressures & the subsequent formation of extremely reactive species (mainly radicals). This is possible because when ultrasounds propagate in a liquid medium the sudden pressure change due to the acoustic pressure oscillation creates gas/vapour bubbles that under certain conditions can grow in size & finally implode. This phenomenon is well known with the name of cavitation & has been deeply studied from both theoretical & experimental points of view.
While chemical effects of ultrasound have been widely exploited there is little focus on the use of low frequency sound waves to increase chemical efficiencies. Whist some theoretical studies predict that high wavelengths generate amplitude oscillations too slow for the bubble to behave adiabatically & hence lead to cavitation there is a lack of experimental evidence demonstrating whether low frequency sound waves have any influence on chemical reactions. In fact, no such experiment has been reported in literature, either related to simple propagation of low frequency sound waves in a liquid batch system or developing devices to exploit sound properties such as constructive interference (i.e. generating standing waves). The presence of impurities can enhance the cavity inception but the effects of pressure oscillation in presence of a gas bubble flow have been poorly investigated. It can be preliminarily concluded that low frequency sound waves can be successfully used to positively influence chemical reactions. This perspective is even more attractive given the development of new devices known as thermos-acoustic engines to produce low frequency sound waves. This new technology allows production of high intensity infrasound by exerting a thermal cycle on a gas in presence of a stack whose extremities are in contact with a hot & a cold heat exchanger respectively. It could be used to generate the force field that is responsible of the enhancement of the reaction activity, thus avoiding expensive devices that are normally used for the production of ultrasounds & drastically cutting the process costs. Finally, the effectiveness of this novel system could be evaluated in biofuel process, where the promotion of bond breakage & molecular weight decrease by cavitation could be useful in improving their quality. The production of new generation biofuels is a target in the chemical engineering research &, currently, the scientific world is facing some significant limitation such as the high oxygen content that makes them not suitable to be blended with crude oil derived fuels in existing engines.
Deliverables -
- Thermally generated low frequency sound waves-assisted chemical reactor
- Biofuel production & refining micro-scale pilot plant
Outcomes -
- Opening of a new field of sonochemistry (low frequency driven)
- Development of processes for production of biofuels & improvement of their quality