Patent GB-477050-A (GB)
Title: A process for the solvent extraction of liquid mixtures
IPC: B01D11/04
Filed: 1936-06-25
Abstract: <PICT:0477050/III/1> <PICT:0477050/III/2> The least soluble component A of a liquid mixture containing at least three miscible components A, B, C, which are progressively soluble in a solvent, is extracted by first submitting the mixture to simple extraction with a selective solvent from the most soluble component (C), and then extracting the raffinate (A + B + some solvent) in a main extraction zone with a selective solvent for B under rectifying-extraction conditions as described in Specifications 355,294, 380,954, 417,617, 424,867. These extraction processes include treating the extract in the second stage by back-washing with the final extract (B) with or without a temperature gradient, (2) back-washing with the final raffinate (A) using a temperature gradient, for example stage cooling with separation of raffinate at each stage, (3) extraction with a selective solvent for A in countercurrent; a temperature gradient may be employed.  The selective solvent for B is preferably less selective than that used in the first stage, but the sam solvent may be used in both stages if the temperature of extraction in the first stage is lower (e.g. 20 DEG  C. lower) than the second. Mixtures which are treated are, petroleum oils containing paraffins (A) naphthenes (B) and aromatics and asphaltenes (C), especially oils containing a relatively large amount of low viscosity index oils; fatty oils, mixtures of alcohols, or of alcohols with parent olefines, chlorine compounds or fatty acids; polymerized fatty oils, fatty acids, aldehydes or hydrocarbons such as polymerized isobutylene oxidation products of paraffin wax containing alcohols, acids, aldehydes and acid anhydrides. Selective solvents for the first stage are liquid sulphur dioxide, aliphatic compounds containing 6 carbon atoms or less with one polar group, or iso- or hetero-cyclic compounds with more than one polar group.  Examples, b b <1>-dichlorethyl ether, furfurol, phenol, formamide, crotonaldehyde, methyl rhodanide, propionitrile, acetonitrile, nitrobenzene, nitromethane, resorcinol, pyrogallol nitrophenol, nitroaniline, dinitrochlor benzene, nitrobenzaldehyde, 3 : 4-diamino acenaphthene, acenaphthene quinone, naphthalene dicarbonic acid. Selective solvents for the second stage are, phenols, cresols, nitrobenzene, benzyl alcohol, aniline, acetophenone, toluidine, benzaldehyde, naphthylamine, naphtonitrile, fluorenone, amino pyridine, thipohene aldehyde, used alone or in admixture with a more selective solvent if the solvent power is too great.  If the solvent power is too low, diluents such as chloroform, benzene, cyclohexane, naphthalene, tetrahydronaphthalene, furane, liquid butane, carbon disulphide, pyridine or quinoline are added. According to Fig. I, oil is fed from a tank 1 to a mixer 8 where it is mingled with liquid propane from a tank 2.  The mixture passes to a settling chamber 4, where asphalt is deposited, and the oil solution passes to an extraction column 5 where it is submitted to simple extraction at low temperature with a highly selective solvent from a tank 3.  A part of the oil solution passes to a fractionating column 13 where some of the propane is removed.  The extract is obtained free from solvent in a column 25.  The raffinate is freed from selective solvent in a fractionating column 20, and then passes to the centre of a rectifying extraction column 6 which may be a packed tower, or a series of interconnected mixing and settling zones, in which extract and raffinate phases are in counterflow, and contains a long washing zone.  The selective solvent is admitted from a tank 3<1> and may contain some extract from column 5 admitted through a pipe 29.  The final raffinate is withdrawn at 31 and freed from solvent in a column 32, and may receive a further light extraction with the selective solvent in a tower 38.  The extract phase is washed in the lower part of the column with an auxiliary solvent, e.g. propane, admitted through a line 42, or this washing may be effected in a separate column.  The final extract is freed from solvent in a column 49.  The extract may be concentrated during washing by distilling a part of the extract to remove solvent and returning the extract to the column.  Fig. III shows heat-exchangers 54, 55, 56 giving a decreasing temperature gradient whereby efficiency of extraction is increased and an auxiliary solvent is unnecessary.  Part of the extract is concentrated in a column 49 and is returned to the column 6.  The cooling throws out components which then rise in the column and act as washing-agent.