Patent GB-607949-A (GB)
Title: Improved process for the solvent extraction of aromatics from hydrocarbon mixtures
IPC: C10G21/08
Filed: 1943-01-06
Abstract: <PICT:0607949/III/1> Aromatic hydrocarbons are separated from oils containing them or from one another by a solvent-extraction process of the kind described in Specification 607,945, i.e. by a single or multi-stage extraction with liquid ammonia to which there is added, in at least one of the stages, a minor proportion of an agent which reduces its solvent power, e.g. water, ethylene glycol, formamide, ethylene diamine, or naphthenic or paraffinic hydrocarbons.  Such an agent may be added at more than one point in the process, so that its concentration increases as the process proceeds.  In one form of the process, the initial mixture is first extracted with liquid ammonia itself or with liquid ammonia containing a minor proportion of an agent which increases its solvent power, e.g. a higher glycol, an ether or ether-alcohol, methanol or other alcohol, an alcohol-amine, aniline, pyridine, or any of the methylamines, and the extract so obtained is then treated as indicated above.  The process is particularly applicable to mixtures of narrow molecular-weight range, e.g. a range of 15-30.  Examples are given in which single aromatic hydrocarbons are separated from mixtures containing them (see Group IV (b)) and also an example in which aromatics are removed from a relatively viscous hydrocarbon oil by extraction with liquid ammonia containing methylamine followed by treatment of the extract with an agent which reduces the solvent power of the ammonia.  An arrangement of plant is described in which the mixture to be treated is supplied by line 10 to a tower 11 down which it flows in countercurrent to solvent supplied by line 16, the solvent comprising liquid ammonia and a little water.  The extract from tower 11 is passed through a heat-exchanger 18 and heater 21 to a tower 22, in which the solvent power of the solvent is further reduced by water supplied through lines 23.  The residual extract from the tower 22 passes through a settler 27, solvent-evaporator 32 and heat-exchanger 40 to a still 41, in which the remainder of the ammonia is removed.  The residue from the still consists of the extracted aromatic hydrocarbons and some water, and this is passed to a settler 49, from which the hydrocarbons are removed at 50.  Ammonia from the evaporator 32 and the still 41 is condensed at 34 and returned to a storage tank 13. Water separated in the settler 49 is returned to storage tank 12. The raffinate from the tower 22 is returned by line 24 to tower 11, the raffinate from which passes to a still 57 in which ammonia is removed and returned through condenser 59 to tank 13. The residue from the still 57 passes to a settler 64 from which the hydrocarbon raffinate is withdrawn through line 65. Specifications 607,946, 607,947 and 607,948 also are referred to.  The Specification as open to inspection under Sect. 91 includes an example in which aromatics are recovered from a kerosene fraction by extraction with liquid ammonia containing a little methylamine followed by extraction of the extract with liquid ammonia.  This subject-matter does not appear in the Specification as accepted.ALSO:Aromatic hydrocarbons are separated from oils containing them or from one another by a solvent-extraction process of the kind described in Specification 607,945, [Group III], i.e. by a single or multi-stage extraction with liquid ammonia to which there is added, in at least one of the stages a minor proportion of an agent which reduces its solvent power, e.g. water, ethylene glycol, formamide, ethylene diamine, or naphthenic or paraffinic hydrocarbons.  Such an agent may be added at more than one point in the process, so that its <PICT:0607949/IV(b)/1> concentration increases as the process proceeds.  In one form of the process, the initial mixture is first extracted with liquid ammonia itself or with liquid ammonia containing a minor proportion of an agent which increases its solvent power, e.g. a higher glycol, an ether or ether-alcohol, methanol or other alcohol, an alcohol-amine, aniline, pyridine, or any of the methylamines, and the extract so obtained is then treated as indicated above.  The process is particularly applicable to mixtures of narrow molecular-weight range, e.g. a range of 15-30. Examples are given in which (1) benzene is extracted from a mixture with cyclohexane by means of liquid ammonia containing a little water; (2) toluene is extracted from a mixture with methylcyclohexane by a process in which the mixture is first treated with liquid ammonia containing a small proportion of ethylene glycol and the extract is treated with liquid ammonia containing a higher proportion of ethylene glycol; (3) a mixture of isopropylbenzene and nonane is extracted with liquid ammonia containing a little methylamine, and water is added to the extract to produce a final extract containing the isopropylbenzene; (4) methylnaphthalene is separated from paraffins of similar boiling range by a process similar to that of example 3; (5) styrene is separated from xylenes by extraction with liquid ammonia containing a little water; (6) toluene is separated from hydrocarbons of comparable boiling point by means of liquid ammonia containing a little cetane, decane, or decahydronaphthalene.  These separations are effected at atmospheric or slightly raised temperature under pressure.  An arrangement of plant is described in which the mixture to be treated is supplied by line 10 to a tower 11 down which it flows in counter current to solvent supplied by line 16, the solvent comprising liquid ammonia and a little water.  The extract from tower 11 is passed through a heat-exchanger 18 and heater 21 to a tower 22, in which the solvent power of the solvent is further reduced by water supplied through lines 23.  The residual extract from the tower 22 passes through a settler 27, solvent-evaporator 32 and heat-exchanger 40 to a still 41, in which the remainder of the ammonia is removed. The residue from the still consists of the extracted aromatic hydrocarbons and some water, and this is passed to a settler 49, from which the hydrocarbons are removed at 50.  Ammonia from the evaporator 32 and the still 41 is condensed at 34 and returned to a storage tank 13.  Water separated in the settler 49 is returned to storage tank 12.  The raffinate from the tower 22 is returned by line 24 to tower 11, the raffinate from which passes to a still 57 in which ammonia is removed and returned through condenser 59 to tank 13.  The residue from the still 57 passes to a settler 64 from which the hydrocarbon raffinate is withdrawn through line 65. Specifications 607,946, 607,947 and 607,948 also are referred to.