Abstract
A significant development in the theory of countercurrent extraction will be presented in this article. New expressions of the term in countercurrent extraction process analysis, “Adjacent Stage Impurity Ratio” (ASIR), are deduced. Furthermore, based on the term together with mass balance and extraction equilibrium, the conditions where a given countercurrent extraction separation operation can have minimum amounts of both extracting solvent and scrubbing agent solution can be estimated, and the equations of the two minimum amounts can be deduced. It was found that the equations for a two-component separation using a single aqueous or organic feed are exactly the same as they appeared in the theory initially established in 1970s. Unlike its earlier version, the present derivation does not involve feed-stage-composition hypothesis, and also has the advantage of dealing with a double-feed system where both aqueous and organic feeds are simultaneously employed whereas the earlier theory can only analyze a separation using a single aqueous or organic feed.
Highlights
The theory of countercurrent extraction was primarily established in 1970s [1]-[5]
We presented different expressions of the term of Adjacent Stage Impurity Ratio from before [20], and in the absence of feed-stage-composition hypothesis, we derived the equations of Smin and Wmin which are found to have the same forms as they previously appeared for a two-component separation using a single feed
Smin should correspond to the flowrate of extracting solvent resulting that the content of impurity A in the final raffinate just reaches the requirement while the lowest value of Adjacent Stage Impurity Ratio” (ASIR) in extraction section keeps 1, which is the basic principle to derive the equation of Smin
Summary
The theory of countercurrent extraction was primarily established in 1970s [1]-[5]. The theory was initially applied to the design of extraction separation processes of rare earths (REs), and contributed a lot to the rapid development of RE separation industry in China [6]-[13]. It is necessary to clearly know the minimum amount of extracting solvent (denoted hereafter as Smin) and the minimum amount of scrubbing agent solution (denoted hereafter as Wmin) which represents the limit of chemical consumption for a given separation. The equations of Smin and Wmin for a two-component separation using a single aqueous or organic feed were previously given in the theory of countercurrent extraction based on several hypotheses [3] [5]. We presented different expressions of the term of Adjacent Stage Impurity Ratio from before [20], and in the absence of feed-stage-composition hypothesis, we derived the equations of Smin and Wmin which are found to have the same forms as they previously appeared for a two-component separation using a single feed. The present work will support the design of hyperlink extraction processes together with our previous articles [21] [22]
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