In chemical, pharmaceutical, food and other industries, extraction technology plays a vital role. Among them, multi-stage countercurrent extraction and continuous countercurrent extraction are two mainstream extraction technologies, each with unique characteristics and advantages.

Multi-stage countercurrent extraction: efficient and stable separation technology

Multi-stage countercurrent extraction is a continuous separation technology used to extract and separate different components from a mixed liquid. The principle is to continuously add raw materials and extractants to the multi-stage countercurrent extraction system so that the raw materials and extractants flow in reverse in the multi-stage tower structure to achieve component separation. The light and heavy phases in each stage of the extraction equipment are balanced as much as possible through the parallel flow mode, and then after phase separation, they enter the two stages of extraction equipment before and after the stage in opposite directions. Therefore, by increasing the number of stages, the extraction efficiency can be significantly improved to achieve the target yield. Mixer settlers and centrifugal extractors are typical multistage countercurrent extraction equipment.

Multistage countercurrent extraction has the advantages of high separation efficiency, high recovery rate, and low energy consumption. In the chemical industry, it is often used for the separation and purification of organic solvents, such as ethanol, acetone, ethyl acetate, etc. In the food industry, multistage countercurrent extraction is used to extract vegetable oils, caffeine, tea polyphenols, etc. In addition, it is also widely used in the pharmaceutical industry to separate and purify the active ingredients in drugs and improve the purity and yield of drugs.

Multi-stage countercurrent extraction is introduced by taking the centrifugal extractor as an example. The CWL-M series centrifugal extractor first uses the centrifugal force principle to separate very quickly and has a larger processing capacity; secondly, the optional materials include polytetrafluoroethylene, stainless steel, PP materials, etc., to meet different corrosion resistance requirements. These are completely different from column equipment such as pulse extraction columns.

Continuous countercurrent extraction: a new option for flexible and efficient extraction

Continuous countercurrent extraction is a more flexible extraction technology. It usually relies on specific equipment, such as column equipment such as pulse extraction columns. In this technology, the light and heavy phases enter the equipment from the upper and lower ends respectively, and flow in a relatively countercurrent manner under the action of external force fields such as gravity or centrifugal force. Through pulses or stirring, the dispersed phase is dispersed into droplets and turbulent, thereby completing the mass transfer operation between the two phases.

The advantage of continuous countercurrent extraction is that it can usually achieve multiple theoretical levels in one device, thereby improving the extraction efficiency. However, this technology also has some limitations. Due to the countercurrent flow of the two phases, the relative shear force between the phases is large, which makes it easy for the dispersed phase droplets to be entrained by the continuous phase and cause back mixing. When the two-phase flux is large, the droplets are smaller, the back mixing is more serious, and it may eventually lead to flooding and failure to operate normally. This limits the application of continuous countercurrent extraction equipment in engineering.

In practical applications, the choice of extraction equipment needs to be determined based on specific extraction requirements and conditions. Multistage centrifugal countercurrent extraction is suitable for situations with large processing volume and high separation requirements. It is also necessary to consider factors such as the equipment's footprint, separation speed, and material corrosion resistance.
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