Search

Direct carboxylation of thiophene with CO2 has been achieved under a relatively mild solvent-free carbonate and carboxylate medium. This base-mediated medium can cleave the very weakly acidic C–H bond without using other limiting reagents, which is one indispensable step in the carboxylation reaction. Product yield varies with different carboxylate salts, and cesium pivalate is the most suitable base additive among targeted simple carboxylate salts. Furthermore, the detailed mechanism of this carboxylation reaction is studied, which involves initial proton abstraction, rendered by carbonate and C–C bond formation, by inserting CO2. The activation energy barrier of the C–H activation step is higher than the following CO2 insertion step, whether for the formation of the mono- and/or di-carboxylate, which indicates that the C–H deprotonation induced by the base is slow and the resulting carbon-centered nucleophile reacts rapidly with CO2. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review of the remarkable achievements by Chinese scientists and engineers who have contributed to the multiscale process design, with emphasis on the transport mechanisms in stirred reactors, extractors, and rectification columns. After a brief review of the classical theory of transport phenomena, this paper summarizes the domestic developments regarding the relevant experiments and numerical techniques for the interphase mass transfer on the drop/bubble scale and the micromixing in the single-phase or multiphase stirred tanks in China. To improve the design and scale-up of liquid-liquid extraction columns, new measurement techniques with the combination of both particle image velocimetry and computational fluid dynamics have been developed and advanced modeling methods have been used to determine the axial mixing and mass transfer performance in extraction columns. Detailed investigations on the mass transfer process in distillation columns are also summarized. The numerical and experimental approaches modeling transport phenomena at the vicinity of the vapor-liquid interface, the point efficiency for trays/packings regarding the mixing behavior of fluids, and the computational mass transfer approach for the simulation of distillation columns are thoroughly analyzed. Recent industrial applications of mathematical models, numerical simulation, and experimental methods for the design and analysis of multiphase stirred reactors/crystallizers, extractors, and distillation columns are seen to garnish economic benefits. The current problems and future prospects are pinpointed at last. [ABSTRACT FROM AUTHOR]