Patent GB-894133-A (GB)
Title: Multistage xylene separation process
IPC: C07C7/14
Filed: 1959-03-04
Abstract: <PICT:0894133/III/1> Paraxylene of more than 95% purity is separated from a mixture by successively forming a crystal slurry and separating the crystals from the slurry 3-12 times, at least part of the mother liquor from each separation stage except the first being recycled to the preceding stage and the temperature being progressively increased from -75 DEG  - -120 DEG C. in the first separation stage to 0 DEG -55 DEG  C. in the final separation stage. The paraxylene contains at least one other xylene isomer, the proportion of paraxylene being in excess of that necessary to form a eutectic mixture.  The second slurry may be formed from the crystals separated from the first slurry by partial melting, by complete melting followed by partial crystallization, or by the addition of a solvent.  The non-paraxylene content of the crystals is preferably decreased by 50-98% at each stage.  The mixture of isomers treated may be a coke oven distillate containing at least 75% of xylene or a catalytically reformed naphtha distillate having a b.p. of 275 DEG -300 DEG F. and a xylene content of 50-60%.  The xylene content is preferably increased to at least 95% by solvent extraction. Orthoxylene is preferably removed by distillation in a column having more than 35, preferably at least 60, theoretical plates. Methanol may be added to the feed to prevent ice plugging (U.S.A. Specification 2,659,763).  As shown, a xylene feed is passed through a drier 11 and a slurry-forming cooler 14 into a centrifugal separator 17.  The feed passes to the cooler 14 after mixing with methanol via a line 12, a portion of the slurry from the cooler 14 via a line 15, and a portion of the mother liquor from a centrifugal separator 25 via line 27.  Solid from the separator 17 is passed through a slurry tank 20, wherein it is mixed with a portion of the mother liquor from the separator 25 via a line 21 and a portion of the mother liquor from a centrifugal separator 31 via a line 33, into the separator 25 via a line 22 and a cooler 23.  Solid from the separator 25 is passed through a slurry tank 28, wherein it is mixed with a portion of the mother liquor from the separator 31, into the separator 31 via a line 30.  Solid is passed from the separator 31 through a melt tank 34 as the desired product.  Mother liquor may be removed from the system via lines 27 and 29 instead of being recycled.ALSO:Paraxylene of more than 95% purity is separated from a mixture by successively forming a crystal slurry and separating the p crystals from the slurry 3-12 times, at least part of the mother liquor from each separation stage except the first being recycled to the preceding stage <PICT:0894133/IV (b)/1> and the temperature being progressively increased from -75 DEG C. to -120 DEG C. in the first separating stage to 0 DEG C.-55 DEG C. in the final separation stage. The paraxylene contains at least one other xylene isomer, the proportion of paraxylene being in excess of that necessary to form a eutectic mixture.  The second slurry may be formed from the crystals separated from the first slurry by partial melting, by complete melting followed by partial crystallization, or by the addition of a solvent.  The non-paraxylene content of the crystals is preferably decreased by 50%-98% at each stage.  The mixture of isomers treated may be a coke oven distillate containing at least 75% of xylene or a catalytically formed naphtha distillate having a b.p. of 275 DEG F.-300 DEG F. and a xylene content of 50%-60 DEG .  The xylene content is preferably increased to at least 95% by solvent extraction.  Orthoxylene is preferably removed by distillation in a column having more than 35, preferably at least 60, theoretical plates.  Methanol may be added to the feed to prevent ice plugging (U.S.A. Specification 2,659,763).  As shown, a xylene feed is passed through a dryer 11 and a slurryforming cooler 14 into a centrifugal separator 17.  The feed passes to the cooler 14 after mixing with methanol via a line 12, a portion of the slurry from the cooler 14 via a line 15 and a portion of the mother liquor from a centrifugal separator 25 via a line 27.  Solid from the separator 17 is passed through a slurry tank 20, wherein it is mixed with a portion of the mother liquor from the separator 25 via a line 21 and a portion of the mother liquor from a centrifugal separator 31 via a line 33, into the separator 25 via a line 22 and a cooler 23.  Solid from the separator 25 is passed through a slurry tank 28, wherein it is mixed with a portion of the mother liquor from the separator 31, into the separator 31 via a line 30.  Solid is passed from the separator 31 through a melt tank 34 as the desired product.  Mother liquor may be removed from the system via lines 27 and 29 instead of being recycled.