Sonochemistry: How Ultrasound boots chemical reactions
It is a known fact that for most chemical reactions heat is required and that reactions proceed approximately twice as fast with an temperature increase of 10°C to 15°C. Since the last decades, the range of technical possibilities for heat input into liquids has been fairly amplified. Beside the traditional heating techniques, microwave and ultrasound technology have become established means. While all of these forms of energy result finally in heating, physical and chemical reactions are observed only during a few of these heating processes, so that they can be used for specific applications.
If ultrasonic irradiation is applied on liquids, this kinetic energy is converted by friction partly into heat. But if amplitudes und acceleration will be high enough, the phenomenon of so-called cavitation occurs. The liquid bursts and vacuum bubbles are generated during the alternating high-pressure and low-pressure cycles. When these small bubbles cannot absorb more energy, they implode during a high-pressure cycle, so that pressures up to 1000 bar and shock waves as well as liquid jets of up to 400 km/h are reached locally. These highly intense forces, caused by ultrasonic cavitation, take effect to the enclosing droplets and particles. The main objective of power ultrasonics consists in the use of cavitational forces, the heating is mostly a welcome side-effect.
Cavitation and the effects described above cause interparticular collision. Existing bondings are broken, particles are dispersed and deagglomerated. By that, new bonding can be formed. By the very fine, intensive mixing and dispersing of particles and droplets, the reaction time is significantly reduced. The larger the overall surface area of all reacting particles will be, the faster and more efficient a process will run. This is especially achieved by the particle size reduction and breakup of agglomerates in suspensions or by the shearing of droplets in emulsions. By ultrasonication, particles and droplets in micron- and nano-size can be achieved easily. A further effect of ultrasonic irradiation is the permanent cleaning of the catalysts, so they offer a larger active surface area whereby the amount of added catalyst can be reduced. Beside the catalytic speed-up, ultrasonication initiates also reactions which can be by input of other energy forms not achieved or can be just hardly obtained.
In the last few years, Hielscher has intensively investigated and developed the ultrasound technology and their applications so that the German company is capable to offer their customers a broad range of ultrasonic processors for applications in lab and industry. Many years of experience and know-how in ultrasound technology allow Hielscher Ultrasonics to advise their customers regarding the manifold sonochemical reactions, such as precipitation, homogeneous and heterogeneous catalysis, crystallization, sonochemistry of polymers or transesterification of oil and fat to biodiesel.
In the lab, not only the reduction of processing time and costs is an important factor, but also a fast supply of analysis’ results is a considerable criterion. For the quality control of production processes it is important to react due to fast analysis results as promptly as possible to the process.
Accordingly these requirements, Hielscher offers ultrasonic devices with manifold accessories not only for the fast sample preparation in the lab, such as the handhold or stand-mounted homogenizers or the recirculating “Sonostep”, but also for the inline sonication of large volume streams for industrial production. For example, Hielscher’s benchtop processor UIP1000hd (1000W, 20kHz) is capable to sonicate liquids in flow mode with a flow rate between 0.5 and 4.0 L/min, depending on the specific process. Hielscher’s UIP16000, the worldwide most powerful ultrasound device, processes between 12 to 50 mł/hr. All industrial devices are easy to handle and to operate; built at full industrial grade, they can be operated 24 hours per day (24h/7d). As the ultrasonic units can be installed as clusters, there is virtually no processing limit. While the energy consumption of lab applications is mostly negligible, it is a considerable coast factor of industrial processing. Therefore, a high efficiency and the optimization of the process parameters are essential. Ultrasonic processes can be generally scaled linear from lab or benchtop size up to any size of production process. Only the required ultrasonic power correlates linearly with the processed volume stream and will be realized by the number of Hielscher’s high-performance ultrasound equipment; all other parameters are completely constant. Hielscher supplies turnkey systems consisting of ultrasound generator, transducer, sonotrode, flow cell, electronic control, sound protection and explosion-proof (as needed).
The outstanding effectiveness in booting chemical effects and the various possibilities of sonochemical applications make ultrasound to a cutting-edge technology in the lab as well as in industry.
Suslick, K. S.; Skrabalak, S. E. (2008): "Sonocatalysis" In Handbook of Heterogeneous Catalysis, vol. 4; Ertl, G.; Knözinger, H.; Schth, F.; Weitkamp, J., Eds.; Wiley-VCH: Weinheim, 2008, pp. 2006-2017
Hielscher Ultrasonics GmbH
Tel. 03328 437 3
Fax: 03328 437 444