About Extraction

Liquid Extraction HierarchyLiquid-liquid extraction is a powerful separation technique that falls right behind distillation in the hierarchy of separation methods (see figure on the right).

Reasons to use extraction:

Separation not feasible by distillation
Break azeotropes
Energy requirements of distillation are prohibitive
A complex distillation sequence is required
The material is heat sensitive
The material is non-volatile

The general rule: If a separation can be made economically by distillation, there is no reason to consider extraction. However, in situations where distillation is not feasible for reasons such as a complex process sequence, high investment or operating costs, heat sensitive materials, or low volatility, extraction is often the best technology to use.

Extraction frequently involves additional steps to recover and recycle the solvent. A typical extraction process is shown below. About 3% of the operating cost is in the extractor, with the remaining 97% in solvent recovery. Also, the majority of the capital cost is in the equipment downstream of the extraction column. Therefore, it is extremely important to consider the solvent recovery aspects early in the project since they play such an important role in overall process economics.

Typical Liquid-Liquid Extraction

Liquid-Liquid Extraction Applications by Industry

Washing of acids/bases, polar compounds from organics
Recovery of acrylic acid

Recovery of carboxylic acids from biomass such as fermentation broths
Recovery of oil from algae broths

Scheibel Column for Liquid ExtractionPharmaceuticals
Recovery of active materials from fermentation broths
Purification of vitamin products

Effluent Treatment
Recovery of phenol, DMF, DMAC
Recovery of acetic acid from dilute solutions

Polymer Processing
Recovery of caprolactam for nylon manufacture
Separation of catalyst from reaction products

Lube oil quality improvement
Separation of aromatics/aliphatics (BTX)

Liquid Extraction for the Food IndustryPetrochemicals
Separation of olefins/parafins
Separation of structural isomers

Food Industry
Decaffeination of coffee and tea
Separation of essential oils (flavors and fragrances)

Metals Industry
Recovery of cobalt and nickel
Recovery of rare earth elements

Inorganic Chemicals
Purification of phosphoric acid

Nuclear Industry
Purification of uranium