Recovery from the liquid phase

The separation and subsequent recovery of one liquid from another is perhaps one of the most regular activities within the chemical industry and a number of methods have been developed to achieve this process. Two principal categories can be identified of relevance to solvents which are the recovery of a solvent from water, which includes drying, and the separation of one solvent from another. The techniques relevant to each case are discussed below. 

In the separation of large volumes at high flow rates then large, shallow rectangular basins, fitted with a plate to ensure rapid coalescence, should be used. Decanting is not a suitable process for separation of emulsions. However it is an ideal method for chlorinated solvents and hydrocarbon solvents with water solubilities of less than 0.2%. Clearly there is a limit to the performance of decanting and in instances of solubility between water and solvent it is not an appropriate method. 

Other methods suitable for the separation of solvents and water are the use of air or steam to strip out the solvent from the aqueous phase [19]. 

3 Stripping. This technique is particularly useful for the recovery of low concentrations of solvents with low water solubilities and/or high volatilities with respect to water. Recapture of the solvent from the air stream can be accomplished by an adsorption process, such as activated carbon, as described above. This is a limitation of the system as the concentration of the solvent in the vapour phase may be very low resulting in excessive cost and complexity. The use of steam as the stripping medium results in easier methods for liberation of the solvent. Thus, for solvents which are immiscible with water then several methods, such as decanting, are now more appropriate as the proportion of solvent to water has increased. 

A method for removing water from solvents which is appropriate for both the bench and industrial scale operations is adsorption. 

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