Solvent extraction is a key separation process in several industries. Mixer-settlers and agitated or pulsed columns are mainly used as liquid-liquid contactors. However, these units require large solvent inventories and long residence times, while flow fields are often not uniform and mixing is poor. These drawbacks can be overcome with process intensification approaches where small channel extractors are used instead. The reduced volumes of small units in association with the increased efficiencies facilitate the use of novel, often expensive, but more efficient and environmentally friendly solvents, such as ionic liquids. The small throughputs of intensified contactors, however, can limit their full usage in industrial applications, thus robust scale-up strategies need to be developed. This paper reviews promising intensified technologies for liquid-liquid extractions based on small channels. In particular, extractions in single channels and in confined impinging jets are considered. The increase in throughput via scale-out approaches with appropriate manifolds is discussed, based on the use of many channels in parallel. The combination of small channels and centrifugal forces is exploited in counter-current chromatography (CCC) systems where many mixing and settling steps are combined within the contactors. Scale up is possible via centrifugal partition chromatography (CPC) configurations.

In this work, the extraction of U(VI) by tributyl phosphate (TBP) is studied in small channels of different sizes, operated in segmented flow. The variables analysed include the channel diameter (1 to 4 mm I.D.), mixture velocity (1.06 to 4.24 cm s -1 ), volume fraction of the continuous phase (between 0.200 and 0.500), and concentration of extractant (TBP 30% v/v in kerosene and TBP 100%). The hydrodynamic characteristics of the flow, such as plug and slug lengths, specific interfacial area, and dispersed phase holdup, were obtained experimentally using high-speed imaging, while the pressure drop was measured with a differential pressure transducer. These parameters were correlated to the studied variables.The concentration of uranium in the aqueous phase was measured with UV-Vis spectroscopy, and the mass transfer coefficients were compared with the predictions of a numerical model of segmented flow developed in Comsol Multiphysics, with good agreement.

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Among the various interventions proposed to remediate the health and security effects of climate change by solar radiation protection is the proposal to enhance natural ocean whitecap formation. Compared to other solar protection interventions, this is technically simple and quickly terminated. However it has a drawback: even if the energy be obtained from wind or wave, the power demand to maintain a foam raft determines the capitalization of equipment. The average power demand is inversely related to foam lifetime which can be prolonged by surfactants preferably derived from ingenerate resources. Here we estimate the associated energy and power demands by identifying the parameters that can be adjusted to moderate the capital cost of implementation. Before dividing by efficiency factors, the range of power demand for an intermediate areal energy requirement of 5 MJ/km 2 of ocean varies from 6 to 30 W/km 2 for foam lifetime of 10 to 2 days. The most likely route to deployment is through merchant ship lubrication using bubbly liquids which both reduces fuel consumption and creates an extended wake and is perhaps an example of technical symbiosis.