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Comparison of the differences between multi-stage countercurrent extraction and continuous countercurrent extraction

Feb 23, 2024

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In chemical, energy, mining and other industrial production, the operation of separating liquid mixtures is often involved, in which a liquid solvent (extraction agent) that is insoluble or partially miscible with the liquid mixture (mixed liquid) to be separated is added to form a In a two-phase system, the operation in which more soluble components (solutes) enter the solvent phase (extraction phase) to achieve separation is called liquid-liquid extraction by taking advantage of the differences in the distribution of each component in the mixed liquid between the two phases.

 

In order to improve the recovery efficiency of target products, most liquid-liquid extractions in industrial production adopt countercurrent operation mode. Counter-current extraction mode can be divided into multi-stage counter-current extraction and continuous counter-current extraction.

 

1. What is multi-stage counter-current extraction? What equipment does multi-stage counter-current extraction mainly include?

Mixing and clarifying tanks and centrifugal extractors are typical multi-stage countercurrent extraction equipment. The principle is that the light and heavy phases in each stage of extraction equipment achieve phase balance as much as possible through the co-current mode, and then after phase separation, they enter the two stages of extraction equipment before and after the equipment in the opposite direction. Therefore, in a multi-stage extraction process, the extraction efficiency can be improved by increasing the number of stages to achieve the target yield.

 

2. What is continuous countercurrent extraction? What kind of extraction equipment is typical for continuous countercurrent extraction?

Column equipment such as pulse extraction columns are typical continuous countercurrent extraction equipment. Its principle is that the light and heavy phases enter the equipment from the upper and lower ends respectively. Under the action of external force fields such as gravity or centrifugal force, the light and heavy phases flow relatively countercurrently. At this time, the dispersed phase is dispersed into droplets and turbulent through pulses or stirring. Complete the mass transfer operation between the two phases.