Ultrasound to Enhance a Liquid-Liquid Reaction

Abstract

Liquid-liquid mass transfer with ultrasound was investigated experimentally during the hydrolysis of n-amyl acetate. Power ultrasound is supposed to improve the yield and kinetics of such multiphase chemical reactions thanks to the mechanical effects of cavitation. Indeed, implosion of micro-bubbles at the vicinity of the liquidliquid interface generates disruption of this surface, and enhances mixing in the liquid around the inclusion, thus improving mass transfer between the two phases. This effect has been demonstrated here on the hydrolysis of namyl acetate by sodium hydroxide, a rather slow reaction but influenced by mass transfer; the reaction is carried out in a glass jacketed reactor, 500 mL of volume, equipped with a Rushton turbine and a 20 kHz sonotrode dipping in the solution. The ester is initially pure in the organic dispersed phase, and sodium hydroxide has an initial concentration of 300 mol/m 3 ; one of the products, pentanol partitions between the two phases and the sodium salt stays in the aqueous phase. The initial apparent reaction rate is measured from the record of the conductivity giving the concentration of alkali versus time. The reaction rate was always found to increase when ultrasound is superimposed to mechanical stirring (at 600 rpm), with a positive influence of input power (20 and 50 W). When varying initial concentration (300 and 600 mol/m 3 ), temperature (36 and 45°C) and ultrasound emitter (sonotrode or cuphorn), the benefit of ultrasound over mechanical agitation was systematic. The only case of a weak influence of ultrasound was the sonication of a dense medium, containing 23% of organic phase and impeding the propagation of ultrasound.

Prilezhaev epoxidation of oleic acid in the presence and absence of ultrasound irradiation

“…However, a number of sources declare an opposite effect in multiphase reactions, since the implosion of micro-bubbles in the vicinity of the liquid-liquid interface generates disruption of this surface, thus enhancing mixing and interfacial mass transfer. 26,27 Catalyst durability In order to check the possible spontaneous deactivation of the solid catalyst, experiments were conducted at 60°C with water (only) at different ultrasound amplitudes (60% and 90%). The catalyst was placed inside the RBR basket and the system was irradiated for 6 h in periods of 1 min on and 1 min off.…”

From Batch to Continuous Chemical Synthesis—A Toolbox Approach

“…An example is the impeller of a continuous stirred tank reactor (CSTR) that is driven by an external engine. In mini and microchannels, actuators and pulsing walls work with mechanical energy, while ultrasounds, microwaves, and piezoelectric systems have also shown mixing enhancement capabilities. , Passive techniques are generally simpler and offer lower possibility of mechanical malfunction and are thus preferred at the smaller scales over miniaturization of active techniques.…”

5. From batch to continuous chemical synthesis – a toolbox approach

“…For advective methods, flow through curved channels is among the simplest of these techniques, which can generate vortices and droplet/bubble recirculation in multiphase systems [16][17][18][19][20]. In mini and microchannels, actuators and pulsing walls work with mechanical energy, while ultrasounds, microwaves and piezoelectric systems have also shown mixing enhancement capabilities [22,23]. Active methods function with an external source of energy.…”