Liquid Extraction

Updated : 01-07-2017 Published : by :
Chemical Engineering Seminars

Many processes in chemical engineering require the separation of one or more of the components of a liquid mixture by treating the mixture with an immiscible solvent in which these components are p...

Many processes in chemical engineering require the separation of one or more of the components of a liquid mixture by treating the mixture with an immiscible solvent in which these components are preferentially soluble. In some cases purification of a liquid may be the function of the process, in others the extraction of a dissolved component for subsequent processes may be the important aspect. An example of the former is the preparation of the pure organic liquids from products of the oil industry. Liquid-liquid extractions may also be used as energy saving processes by, for example, eliminating distillation stages. It is possible, of course that the substance of interest may be heat-sensitive anyway and that distillation is accordingly an unacceptable process.

When separation by distillation is ineffective or very difficult, liquid extraction is one of the main alternatives to consider. Close-boiling mixtures or substances that cannot withstand the temperature of the distillation, even under a vacuum, may often be separated from impurities by extraction, which utilizes chemical differences instead of vapor pressure differences. For example, penicillin is recovered from fermentation broth by extraction with a solvent such as butyl acetate. Another example for liquid extraction is recovering acetic acid from dilute aqueous solutions; distillation would be possible in this case, but the extraction step considerably reduces the amount of water to be distilled.

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