Patent GB-717725-A (GB)
Title: Improvements in or relating to the separation of mixtures of organic compounds
IPC: C10G21/02
Filed: 1952-07-18
Abstract: <PICT:0717725/IV (b)/1> In separating a mixture of organic compounds with a selective solvent having greater solubility for one class of compound (Class A) than for another (Class B) contained therein, and wherein the mixture is introduced into an extraction zone at an intermediate point and contacted in counter-current with the solvent, a raffinate containing substantially Class B component is removed at the end at which the solvent is introduced, an extract comprising Class A component in the solvent is removed at the other end and Class A component recovered by fractional distillation, the extract is substantially freed, prior to removal, from residual Class B component by introducing a Class B compound which is more volatile than the Class B component of the mixture into the extraction zone at a point closer to the point of removal of the extract than to the point of introduction of the mixture and displacing said residual Class B component into the raffinate phase, the extract so freed is introduced to the top of a fractional distillation zone, substantially all the volatile Class B compound is vaporized, removed from the top of said zone and returned to the extraction zone at a point near the point of removal of the extract therefrom, Class A component substantially free from both Class B type compounds and from solvent is removed as a side stream, and the distillation residue comprising the solvent is removed at the bottom and returned to the extraction zone.  The selective solvent may be a mixture of primary and secondary solvents, the secondary solvent distilling at least partly with the volatile Class B or with the Class A solvent. In separating aromatics from hydrocarbon mixtures, diethylene glycol containing 5-15 per cent of water is preferred.  Phenol, thiophene, mercaptans, and sulphides may be separated from hydrocarbons; compounds containing monocarboxylic, nitro, amino, sulpho or hydroxyl groups from symmetrical disubstituted compounds; mono-olefins from paraffins, aromatics from olefins, and polynuclear aromatics from mono-nuclear.  Fractions of petroleum distillates, especially a C6 fraction containing benzene, hexanes and heptanes or a toluene-heptane-octane mixture may be treated.  Selective solvents include alcohols, glycols and their ethers and esters, phenols, and organic acid esters.  Preferred polyoxyalkylene glycols have the formula HO(CnH2nO)xH where n is from 2 to 5, and x from 2 to 15. Secondary solvents include water, furan, furfural, furfuryl alcohol, cyanides, perfluoro and mixed perhalo-hydrocarbons, acids and alcohols.  A benzene-containing petroleum fraction boiling from about 40-80 DEG  C. is fractionated in column 1 and a bottoms fraction containing benzene fed, after heating to 100-150 DEG  C. and compressing to 5-25 atmospheres, to extraction column 10 through line 9 in counter-current to diethylene glycol and water introduced by lines 11, 12 respectively.  Raffinate, washed free of primary solvent by the water, leaves at 15.  The extract meets a more volatile paraffinic fraction, e.g. the side cut from column 1, fed by line 18, and the less volatile paraffins are displaced thereby prior to the extract leaving by line 19.  It is transferred to stripper 21 operating at a lower pressure where the volatile paraffins are removed by line 22, cooled and fractionated to separate water by line 29, and paraffins by line 28, these being recycled to column 10 with the side cut from column 1.  A side cut from line 33 of stripper 21 is fed to fractionator 34 giving pure benzene overhead at line 36 and water at line 37.  The water from lines 29, 37 may be fed by line 46 to a reboiling section of column 21 whereby residual benzene is released.  Alternatively, volatile paraffins from line 28 may be used similarly.  The residue comprising primary solvent from stripper 21 is recycled to column 10 by line 51.  The necessary water fed by line 12 to column 10 is recycled by line 30. Examples describe the use of the above apparatus to recover benzene or toluene from a hydroformed gasoline fraction using diethylene glycol containing about 15 per cent of water, and to remove sulphur-containing compounds, viz. mercaptans, thiols and sulphides, from a gasoline fraction containing paraffins, naphthenes, olefins and aromatics, the water content of the glycol solution being 30 per cent.ALSO:In separating a mixture of organic compounds with a selective solvent having greater solubility for one class of compound (Class A) than for another (Class B) contained therein the mixture is introduced into an extraction zone at an intermediate point and contacted in counter-current with the solvent, a raffinate containing substantially Class B component is removed at the end at which the solvent is introduced, an extract comprising Class A component in the solvent is removed at the other end and Class A component recovered by fractional distillation, the extract is substantially freed, prior to removal, from residual Class B component by introducing a Class B compound which is more volatile than the Class B component of the mixture into the extraction zone at a point closer to the point of removal of the extract than to the point of introduction of the mixture and displacing said residual Class B component into the raffinate phase, the extract so freed is introduced to the top of a fractional distillation zone, substantially all the volatile Class B compound is vaporized, removed from the top of said zone and returned to the extraction zone at a point near the point of removal of the extract therefrom, Class A component <PICT:0717725/III/1> substantially free from both Class B type compounds and from solvent is removed as a side stream, and the distillation residue comprising the solvent is removed at the bottom and returned to the extraction zone.  The selective solvent may be a mixture of primary and secondary solvents, the secondary solvent distilling at least partly with the volatile Class B or with the Class A solvent.  In separating aromatics from hydrocarbon mixtures, diethylene glycol containing 5-15 per cent. of water is preferred. Phenol, thiophene, mercaptans and sulphides may be separated from hydrocarbons; mono-olefins from paraffins; aromatics from olefins; and poly-nuclear aromatics from mono-nuclear.  Fractions of petroleum distillates, especially a C6 fraction containing benzene, hexanes and heptanes or a tolueneheptane-octane mixture may be treated. Selective solvents include alcohols, glycols and their ethers and esters, phenols and organic acid esters.  Preferred polyoxyalkalene glycols have the formula HO(Cn H2n O)x H where n is from 2 to 5, and x from 2 to 15.  Secondary solvents include water, furan, furfural, furfuryl alcohol, cyanides, perfluoro and mixed perhalo-hydrocarbons, acids and alcohols.  A benzene-containing petroleum fraction boiling from about 40-80 DEG C. is fractionated in column 1 and a bottoms fraction containing benzene fed, after heating to 100-150 DEG C. and compressing to 5-25 atm., to extraction column 10 through line 9 in counter-current to diethylene glycol and water introduced by lines 11, 12 respectively.  Raffinate, washed free of primary solvent by the water, leaves at 15.  The extract meets a more volatile paraffinic fraction, e.g. the side cut from column 1, fed by line 18, and the less volatile paraffins are displaced thereby prior to the extract leaving by line 19.  It is transferred to stripper 21 operating at a lower pressure where the volatile paraffins are removed by line 22, cooled and fractioned to separate water by line 29 and paraffins by line 28, these being recycled to column 10 with the side cut from column 1.  A side cut from line 33 of stripper 21 is fed to fractionator 35 giving pure benzene overhead at line 36 and water at line 37.  The water from lines 29, 37 may be fed by line 46 to a reboiling section of column 21 whereby residual benzene is released.  Alternatively, volatile paraffins from line 28 may be used similarly.  The residue comprising primary solvent from stripper 21 is recycled to column 10 by line 51.  The necessary water fed by line 12 to column 10 is recycled by line 30.  Examples describe the use of the above apparatus to recover benzene or toluene from a hydroformed gasoline fraction using diethylene glycol containing about 15 per cent. of water, and to remove sulphur-containing compounds, viz. mercaptans thiols and sulphides, from a gasoline fraction containing paraffins, naphthenes, olefins and aromatics, the water content of the glycol solution being 30 per cent.