Intensified Liquid-Liquid Extraction Technologies in Small Channels: A Review

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.