Solvent extraction (also known as liquid-liquid extraction or partitioning) is a method of separating chemicals on their differing solubilities in two immiscible liquids. The liquids are usually aqueous and organic and this is well suited to electrical tomographic measurements.
The two step process involves intensive mixing to enable transfer of the target materials between the two phases, followed by a settling period.
As well as needing to ensure good phase transfer, the settling process can present challenges, with certain sectors (such as flavour extraction) taking more than 24 hours. Other important sectors include speciality chemicals, pharmaceuticals, nuclear reprocessing, vegetable oil production and bio-diesels.
An ITS linear probe is inserted in the process vessel and is able to measure the dynamics and quality of mixing (based on an aqueous continuous phase).
Following mixing, the same probe can be used to measure the development of the organic / aqueous interface. This can be difficult to achieve in many processes, particularly where both phases are opaque (or black-on-black), leading to product being lost to waste (particularly expensive in processes such as pharmaceuticals). Process challenges can relate to oiling out of emulsions (where the system stabilises and fails to separate). A further complication can arise where the phases invert which can lead to hazardous conditions in downstream processes.
It should be noted that ITS is not yet able to apply its technology in molten metal based separations.