Review of Research Topics for Scaling-up of Sonochemical Reactors (Sono-Reactors)

Abstract

This study is aimed to review the topics of chemical engineering to take in consideration for the scaling-up of reactors, in order to perform processes based on the application of the sonochemistry at industrial level. Sonochemistry is an emergent technology, defined as chemistry made with ultrasound. The characteristic ultrasound frequencies are in the range of 1-10MHz, and in particular for sonochemistry in the sub-range 16-100 KHz. Chemical effects of ultrasound exist when there are changes in the path- ays of reactions, yields and/or selectivities of the products due to the ultrasonic activation. At laboratory level, the sonochemistry has shown fantastic results, because it is based on the phenomenon of acoustic cavitation in liquids, thus, producing very high temperatures (some thousands of Kelvin degrees) and high pressures (some hundreds of atmospheres) during very short times (from tenths to hundreds of microseconds). Cavitation is the phenomenon with the most important effect for intensification of physical and chemical processing. Under these conditions, the yields of sonochemical reactions increase drastically, and their selectivities are improved, thus generating new mechanisms of reaction  involving inorganic and organic syntheses. It is not easy to reproduce experimental results of quantification of sonochemical intensity, which is significant for the efficient scaling-up of sonochemical reactors (sono-reactors) for the progress of industrial applications of sonochemistry. This technology has application at industrial level for the treatment of waste-water and black-water. Sonochemistry can be considered as Green Chemistry, presenting the following advantages: low waste, low consumption of materials and energy with optimized use of non-renewable resources and use of renewable energies. Designs of large-scale use sono-reactors are based on intuition mainly, and their yields are impossible to predict. Few studies were aimed about optimum design and scaling-up of sonochemical reactors. The implementation of sonochemistry at the industrial level will be feasible when the use of cavitational energy can be adequately controlled. There is a need for standardized sonochemical reactors in order to be able to compare the results of yield and selectivity of sonochemical reactions. For sonochemical reactors a pilot and industrial scale the required volumes are 100 dm3  and 1 m3  approximately. Polymerization reactions, must be developed in a discontinuous or semi-continuous regime (Batch or semi-batch sono-reactors respectively), considering the kinetic and thermodynamic topics of the reactor, as also the effects of viscosity on transport properties. Organo-metals reactions, they have to be developed in a semi-continuous or continuous regime. In order to improve the sonochemical processes, we must take in consideration the optimizations of production and economic, including the ultrasonic energy in the energy balances, as well as in the conditions of operation. Among limitations found are the modeling and simulation of 2-D and 3-D of ultrasound waves in liquid medium for the study of pressure fields behaviors in sonochemical reactors, considering the quantification of cavitation intensities and fluid circulation. Due to the high temperatures inside of sono-reactor (although be for a period of µs) and the associated safety hazards, application of thermal and electrical superconductors respectively, would be an important topic to investigate. The study of materials resistant to the stress by ultrasonic cavitation is also a new topic research open by sonochemistry.