Patent GB-466730-A (GB)
Title: A process for extracting a liquid mixture with the aid of a selective solvent
IPC: C10G21/02
Filed: 1936-02-19
Abstract: <PICT:0466730/III/1> Liquid mixtures containing three components A, B, C of progressive solubility in a solvent S are extracted with this solvent to form an extract (B+C) in S which is then submitted to further treatment whereby two phases are obtained (a) a phase rich in B and (b) a phase rich in C and containing substantially all of the solvent S, the phase (b) being returned to the first extraction stage, after removal of a part of S if desired.  In the main extraction, this phase (b) will dissolve B mainly, leaving A and C. The further treatment of the extract consists in freezing or adding a second solvent L which is substantially immiscible with S and is a solvent for B.  In the Figure, 1 and 3 are an extraction and a washing system respectively in which two liquids are fed in countercurrent, and consist of contact towers, multi-stage mixers and settlers, or centrifuges.  A mixture of three components A, B, C of which A is the least soluble and C the most soluble in a solvent S, is admitted to the middle of the extraction column 1 through which flows a solvent containing the solvent S from a pipe 13.  The raffinate phase is withdrawn through a pipe 15 and the extract phase (S + B + C) through a pipe 17.  The raffinate passes to a still 5 where (A + C) is freed from solvents.  The extract passes to the washing apparatus 3 where it is extracted in countercurrent with a solvent L supplied from a storage tank 19. Solvent S is also introduced through a pipe 27 whereby the extract consisting mainly of B dissolved in L is freed from small amounts of C.  The washed extract (L + S + B) is withdrawn through pipe 29 and passes to a still 7 where B is freed from solvents (L + S) which may be distilled off separately or together.  A part of the extract B may be returned to the extraction zone whereby the first extract is freed from small amounts of A.  The second raffinate (S + C + L) is withdrawn through a pipe 41 and is used as solvent in the extraction stage, or a part of the solvent may be removed in a still 9.  The extract and washing towers may be provided with a temperature gradient control.  The process may be used to separate hydrocarbon mixtures such as lubricating oil or a mixture of paraffins, secondary olefines and tertiary olefines, using as solvent (S), liquid sulphur dioxide, furfural, nitrobenzene, "Chlorex" (Registered Trade Mark) phenols or isoquinoline.  The second solvent (L) may be a non-polar solvent for example, propane, butane, pentane.  Example: a lubricating oil distillate is extracted at 10 DEG  C. with twice its volume of crude cresol in counter-current.  The extract containing the most soluble and intermediately soluble components is treated in an extraction apparatus consisting of a series of four mixers and settlers.  The extract is introduced into the second or third mixer, cresol at one end of the series and propane at the other.  The propane removes small amounts of the least soluble component, and any other components contained in this extract are removed by the cresol whereby the extract in cresol contains the two more soluble components only.  This is cooled with or without a small amount of water or gasoline, to form layers whereby the most soluble component contained in the cresol is separated from the component of intermediate solubility.  The cresol solution is returned to the first extraction process.  The raffinate containing the most and least soluble components consists of a refined lubricating oil. Specifications 380,954 and 445,290 are referred to.