Product Seperation (Downstream)

7/30/2019 Product Seperation (Downstream)

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STEAM DISTILLATION


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The dielectric constant is a measure of the degree of molar polarization of

a compound. If this value is known it is then possible to predict whether a

compound will be polar or non-polar, with a high value indicating a highly

polar compound

The final choice of solvent will be influenced distribution or partition coefficient

K where

K= Concentration of solute in extract / Concentration of solute in raffinate

The value of K defines the ease of extraction. There is a relatively high K

value, good stability product and good separation of the aqueous and vent

phases, then it may be possible to use a Smgle-stilge extraction system.

A value of 50 indicatles that the extraction should be Straightforward

whereas value of 0.1 shows that the extraction will be and that amultistage process will be necessary.


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The co-current system

There are n mixer/separator vessels in line and the raffinate goes from vessel

1 to vessel n.

Fresh solvent is added to each stage, the feed and extracting solvent pass

through the cascade in the same direction. Extract is recovered from each

stage.

Although a relatively large amount of solvent is used, a high degree of

extraction is achieved.


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A counter-current system

There. are a number of mixer/separators connected in series. The extracted

raffinate passes from vessel 1 to vessel n while the product-enriched solvent is

flowing from vessel n to vessel 1.

The feed and extracting solvent pass through the cascade in opposite

directions. The most efficient system for solvent utilization is counter-currentoperation, showing a considerable advantage

over batch and co-current systems.


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There are, however, a number of significant disadvantages in the utilization of

this technology:

(i) Phase equilibria of the solvent/solute system is complex, making design ofextraction conditions difficult.

(ii) The most popular solvent (carbon dioxide) is non-polar and is therefore

most useful in the extraction of non-polar solutes. Though cosolvents

can be added for the extraction of polar compounds, they will complicate

further downstream processing.

(iii) The use of high pressures leads to capital costs for plant, and operating

costs may also be high.


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Product Seperation (Downstream)