Countercurrent Extraction

A continuous extraction approach (though sometimes performed in a batch-wise manner) is counter-current extraction. In countercurrent extraction both phases are continuously added (or changed) and flow in opposite directions as the extraction progresses. (When only one phase is continuously added, the procedure becomes a crosscurrent extraction.) In the case of both countercurrent and crosscurrent extractions, the feed is repeatedly (continuously) contacted or washed with extracting solvent. The number of theoretical stages is maximized by using solvents with favourable distribution coefficients (see sub sequent discussion) or by increasing the solvent-to-feed ratio. Commonly, these processes employ up to eight theoretical stages. Although they have been replaced by chromatographic methods in many cases, countercurrent extractions are useful in that they use solvent only, without sorbents, and relatively mild conditions. They are favoured when the distribution coefficient is small. However, countercurrent extractions use large volumes of solvent and are not advantageous when large amounts of solute are to be isolated. The Craig countercurrent device, popularly used to study partition chromatography, is a discontinuous, differential migration process, since the extraction stages are performed step-wise rather than as continuous extractions.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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