Question

For an organic chemistry lab final report I need to include 1. Discussion of using liquid-liquid extraction as a method for separating unknown compounds in a mixture, 2. For what functional groups would this method be most useful, and 3. What are some instances where liquid-liquid extraction wouldn't be useful?

Answer 1

In a liquid-liquid extraction unit, a liquid stream (carrier) containing the component(s) to be recovered (solute) is fed into an extractor, where it contacts a solvent. The two liquids must be immiscible or only slightly miscible; this allows them to form a dispersion, with one liquid dispersed as droplets in the other.

Mass transfer occurs between the droplets (dispersed phase) and the surrounding liquid (continuous phase). In order for the two liquids to be subsequently separated, they must have different densities. The droplets then accumulate above or below the continuous phase, depending on the liquids’ relative densities. The boundary between the continuous phase and the droplet dispersion is referred to as the interface, and can be at the top or bottom of the extraction column.

Extraction processes are well suited to the petroleum industry because of the need to separate heat-sensitive liquid feeds according to chemical type (e.g. aliphatic, aromatic, naphthenic) rather than by molecular weight or vapour pressure.Other major applications exist in the biochemical or pharmaceutical industry, where emphasis is on the separation of antibiotics and protein recovery. In the inorganic chemical industry, they are used to recover high-boiling components such as phosphoric acid, boric acid, and sodium hydroxide from aqueous solutions.

Some examples are given below:

Extraction of nitrobenzene after reaction of HNO3 with toluene in H2SO4
Extraction of methylacrylate from organic solution with perchlorethylene
Extraction of benzylalcohol from a salt solution with toluene
Removing of H2S from LPG with MDEA
Extraction of caprolactam from ammonium sulfate solution with benzene
Extraction of acrylic acid from wastewater with butanol
Removing residual alkalis from dichlorohydrazobenzene with water
Extraction of methanol from LPG with water
Extraction of chloroacetic acid from methylchloroacetate with water