Sonochemistry is the use of ultrasound to enhance or alter chemical reactions. Sonochemistry in the true sense of the term occurs when ultrasound induces “true” chemical effects on the reaction system, such as forming free radicals which accelerate the reaction. However, ultrasound may have other mechanical effects on the reaction, such as increasing the surface area between the reactants, accelerating dissolution, and/or renewing the surface of a solid reactant or catalyst. This comprehensive review summarizes several topics of study in the sonochemical literature, including bubble dynamics, factors affecting cavitation, the effects of ultrasound on a variety of chemical systems, modeling of kinetic and mass-transfer effects, the methods used to produce ultrasound, proposed cavitation reactors, and the problems of scaleup. The objective of this paper is to present a critical review of information available in the literature so as to facilitate and inspire future research in the field of sonochemistry.

Sonochemistry: Science and Engineering

https://www.researchgate.net/file.PostFileLoader.html?id=53e9e550d3df3edb538b45ab&assetKey=AS%3A273579713728525%401442237896090

Polyethylene glycol and solutions of polyethylene glycol as green reaction media

This paper covers the recent research carried out by the authors on the chemical recycling of poly(ethylene terephthalate) (PET) taken from post-consumer soft-drink bottles. The chemical recycling techniques used are critically reviewed and the authors' contribution is highlighted. Hydrolysis in either an alkaline or acid environment was employed in order to recover pure terephthalic acid monomer that could be repolymerized to form the polymer again. Alkaline hydrolysis was carried out in either an aqueous NaOH solution or in a non-aqueous solution of KOH in methyl cellosolve. A phase-transfer catalyst was introduced in alkaline hydrolysis, in order that the reaction takes place at atmospheric pressure and in mild experimental conditions. The reaction kinetics were thoroughly investigated, both experimentally and theoretically, using a simple, yet precise, kinetic model. Moreover, glycolysis was examined as an effective way for the production of secondary value-added materials. The glycolysated PET products (oligomers) can be used as raw materials for the production of either unsaturated polyester resins (UPR) or methacrylated oligoesters (MO). UPR can subsequently be cured with styrene in ambient temperature to produce alkyd resins used as enamel paints or coatings. MO are potential monomers that can be cured either by UV irradiation or temperature to produce formulations used as coatings for wood surfaces, paints, or other applications. Thus, recycling of PET does not only serve as a partial solution to the solid-waste problem, but also contributes to the conservation of raw petrochemical products and energy.

Chemical Recycling of Poly(ethylene terephthalate)

Comparison of the effects of ultrasound and mechanical agitation on a reacting solid-liquid system

In the present paper state-of-the art and perspectives of ultrasound-assisted (UA) biodiesel production from different oil-bearing materials using acid, base and enzyme catalysts are critically discussed. The ultrasound action in biodiesel production is primarily based on the emulsification of the immiscible liquid reactants by microturbulence generated by radial motion of cavitation bubbles and the physical changes on the surface texture of the solid catalysts generating new active surface area. The importance of ultrasound characteristics and other process variables for the biodiesel yield and the reaction rate is focused on. UA transesterification is compared with other techniques for biodiesel production. Several different developing methods reducing the biodiesel production costs such as the optimization of process factors, the development of the process kinetic models, the use of phase transfer catalysts, the application of the continuous process, the design of novel types of ultrasonic reactors and the in situ ultrasound application in transesterification of oily feedstocks are also discussed.

Biodiesel production by ultrasound-assisted transesterification: State of the art and the perspectives

Phase transfer catalysis (PTC) uses catalytic amounts of phase transfer agents which facilitate interphase transfer of species, making reactions between reagents in two immiscible phases possible. PTC is used widely in the synthesis of various organic chemicals in both liquid-liquid and solid-liquid systems. Existing literature on PTC is chemistry-intensive and a mere handful of recent articles constitute the entire information on engineering analysis. This article reviews the field comprehensively by combining the existing knowledge from chemistry with insights into mechanistic and kinetic analysis and mathematical modeling of soluble and insoluble PTC. By its very nature, PTC involves a series of equilibrium and mass-transfer steps, beside the two main reactions. Neglect of mass-transfer effects can grossly overpredict the conversion of a PTC mediated reaction. A practical way of using PTC, which enables easy separation, is to immobilize the catalyst on a solid support. Mass-transfer limitations and higher costs, however, have precluded its commercial use so far, requiring further analysis of mass-transfer limitations in these complex three-phase systems. The use of PTC, combined with other rate enhancement techniques like sonochemistry, microwaves, electroorganic synthesis, and photochemistry, is being increasingly explored. Applications in this area in the manufacture of organic intermediates and fine chemicals seem almost unlimited.

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Sanjeev D. Naik

Papers

Phase Transfer Catalysis: Chemistry and Engineering

Mathematical modeling of solid-liquid phase-transfer catalysis

Rate enhancements in a solid-liquid reaction using PTC, microphase, ultrasound and combinations thereof