Greener Processing Routes for Reactions and Separations Based on Use of Ultrasound and Hydrodynamic Cavitation
Cavitational reactors, based on the use of ultrasound and fluid energy as the alternate energy source, offer significant promise for the intensification of physical and chemical processing applications. The chapter provides a detailed overview of the greener processing approaches for different chemical reactions as well as separations, highlighting the basic mechanisms for the expected intensification. The chapter also explains the different configurations of cavitational reactors that have been commonly used along with possible recommendations for designs suitable for large-scale processing. It appears that multiple frequency, multiple transducer-based sonochemical reactors and orifice plate type configurations, in the case of hydrodynamic cavitation, appear to be most suitable designs for large-scale processing. Guidelines for the selection of optimal operating/geometric parameters have also been provided. The two approaches of inducing cavitation (acoustic and hydrodynamic cavitation) have been compared on the basis of the energy transfer efficiencies and expected benefits for the specific application. It has been established that hydrodynamic cavitation reactors are more energy efficient for the specific applications discussed in the work. The major applications discussed in the work include chemical synthesis, wastewater treatment, crystallization, adsorption, distillation and extraction. The discussion is concentrated on clearly quantifying the expected benefits in comparison to the conventional approaches, as far as possible. Overall, it appears that considerable economic savings are possible based on the effective utilization of the spectacular effects of cavitation in chemical and physical processing.