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Liquid-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. Since most investment and operating costs are associated with the solvent recovery steps, it is very important to consider and study this aspect when designing the entire process.

In a typical extraction process about 3% of the operating cost is in the extractor, with the remaining 97% in solvent recovery. 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.

Chemical
     o Washing of acids/bases, polar compounds from organics

Pharmaceuticals
     o Recovery of active materials from fermentation broths
     o Purification of vitamin products

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

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

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

Petrochemicals
     o Separation of olefins/parafins
     o Separation of structural isomers

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

Metals Industry
     o Copper production
     o Recovery of rare earth elements

Inorganic Chemicals
     o Purification of phosphoric acid

Nuclear Industry
     o Purification of uranium