Cavitation chemical processing applications

Gogate PR (2008) Cavitational reactors for process Intensification of chemical processing applications A critical review. Chem Eng Proc 47 515-527... 

Cavitation can be used in chemical processing applications to obtain the following [151] ... 

It is important to cite the following critical issues while selecting the application of cavitating conditions for intensification of chemical processing applications [151] ... 

Gogate, P.R. (2007). Cavitational reactors for process intensification of chemical processing applications a critical review. Chemical Engineering Processing, doi 10.1016/j.cep. 2007.09.014.. 

Intensification can be achieved using this approach of combination of cavitation and advanced oxidation process such as use of hydrogen peroxide, ozone and photocatalytic oxidation, only for chemical synthesis applications where free radical attack is the governing mechanism. For reactions governed by pyrolysis type mechanism, use of process intensifying parameters which result in overall increase in the cavitational intensity such as solid particles, sparging of gases etc. is recommended. 

Since 1945 an increasing understanding of the phenomenon of cavitation has developed coupled with significant developments in electronic circuitry and transducer design (i. e. devices which convert electrical to mechanical signals and vice versa). As a result of this there has been a rapid expansion in the application of power ultrasound to chemical processes, a subject which has become known as Sonochemistry . 

The possibility of using sound energy in chemistry was established more than 70 years ago. By definition, sonochemistry is the application of powerful ultrasound radiation (10 kHz to 20 kHz) to cause chemical changes to molecules. The physical phenomenon behind this process is acoustic cavitation. Typical processes that occur in sonochemistry are the creation, growth and collapse of a bubble. A typical laboratory setup for sonochemical reactions is shown in Fig. 8.17. More details of sonochemistry and the theory behind it can be found elsewhere. - ... 

Ultrasound can thus be used to enhance kinetics, flow, and mass and heat transfer. The overall results are that organic synthetic reactions show increased rate (sometimes even from hours to minutes, up to 25 times faster), and/or increased yield (tens of percentages, sometimes even starting from 0% yield in nonsonicated conditions). In multiphase systems, gas-liquid and solid-liquid mass transfer has been observed to increase by 5- and 20-fold, respectively [35]. Membrane fluxes have been enhanced by up to a factor of 8 [56]. Despite these results, use of acoustics, and ultrasound in particular, in chemical industry is mainly limited to the fields of cleaning and decontamination [55]. One of the main barriers to industrial application of sonochemical processes is control and scale-up of ultrasound concepts into operable processes. Therefore, a better understanding is required of the relation between a cavitation coUapse and chemical reactivity, as weU as a better understanding and reproducibility of the influence of various design and operational parameters on the cavitation process. Also, rehable mathematical models and scale-up procedures need to be developed [35, 54, 55]. 

Sonochemical destruction is a process for the destruction of volatile organic compounds (VOCs) in water using ultrasound. The technique is being researched for the treatment of contaminated ground and process water. Sonochemistry in liquids is the inducement of chemical reactions by the application of ultrasound energy acoustic cavitation results in the formation of hot spots of intense temperature and pressure that cause the destruction of VOCs. 

It was observed that, under equal conditions, the yields of copper complexes are always higher in comparison with those of nickel. An increase in donor force of the solvent applied leads to more rapid formation of complexes an increase in viscosity leads to its delay. According to the physical-chemical study, the formed products are the same as those prepared by conventional methods from corresponding metal salts and ligands. It was established that a multimolecular layer of crystalline product is formed in the border metal-solution. Diffusion of metal atoms takes place through this layer due to cavitation processes [738], Another application of ultrasonic treatment for optimization of traditional synthetic methods is presented in the Experimental Procedures at the end of this section. 

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