Patent GB-690301-A (GB)
Title: Improvements in or relating to the purification of para-xylene
IPC: C07C7/14
Filed: 1951-01-17
Abstract: <PICT:0690301/IV (b)/1> Para-xylene of over 90 per cent by weight purity is separated from a mixture with at least one other isomeric xylene, the para-xylene being in a minor proportion, by cooling the mixture to a temperature not as low as its first eutectic point to form a first slurry of para-xylene crystals in a mother liquor, centrifuging the slurry to form a cake comprising a major proportion but less than 85 per cent of para-xylene, melting the cake and cooling to a temperature not less than -20 DEG  F. to form a second slurry and centrifuging this slurry to form a second cake containing more than 90 per cent by weight of para-xylene.  The mother liquor in the second centrifuging stage may be recycled with the feed prior to the first or second centrifuging stages.  The preferred temperature ranges are -90 DEG  to -110 DEG  F. for the first chilling stage and 20 DEG  to -20 DEG  F. for the second chilling stage.  In the Figure the feed-stock in tank 11 is charged into a chiller 13 which may be operated at a temperature in the range between -90 DEG  and -110 DEG F.  The chilled xylene mixture is discharged into centrifuge 15 where it is separated into mother liquor and filter cake.  The filter cake is discharged into a melt tank 18 where the crystals are melted and are then discharged into a chiller 20 maintained at a temperature in the range 20 DEG  to -20 DEG  F.  A second slurry of para-xylene is formed and discharged into centrifuge 22. Para-xylene crystals of above 90 per cent purity are obtained. The mother liquor from the centrifuge 22 is divided into two portions, the first of which is recycled to the slurry from the second chiller to ensure its fluidity and the second portion is recycled to the first chiller.  The feed mixture may contain ethyl benzene in addition to xylenes.ALSO:<PICT:0690301/III/1> Para-xylene of over 90 per cent by weight purity is separated from a mixture with at least one other xylene, the paraxylene being in a minor proportion, by cooling the mixture to a temperature not as low as its first eutectic point to form a first slurry of para-xylene crystals in a mother liquor, centrifuging the slurry to form a cake comprising a major proportion but less than 85 per cent of para-xylene; melting the cake and cooling to a temperature not less than -20 DEG F to form a second slurry and centrifuging this slurry to form a second cake containing more than 90 per cent by weight of para-xylene.  The mother liquor in the second centrifuging stage may be recycled with the feed prior to the first or second centrifuging stages.  The preferred temperature ranges are -90 DEG  to -110 DEG F for the first chilling stage and 20 DEG  to -20 DEG F for the second.  In the Figure the feed stock in tank 11 is charged into a chiller 13 which may be operated at a temperature in the range -90 DEG  and -110 DEG F.  The chilled xylene mixture is discharged into centrifuge 15 where it is separated into mother liquid and filter cake.  The filter cake is discharged into a melt tank 18 where the crystals are melted and are then discharged into a chiller 20 maintained at a temperature in the range 20 DEG  to -20 DEG F.  A second slurry of paraxylene is formed and discharged into centrifuge 22.  Para-xylene crystals of above 90 per cent purity are obtained.  The mother liquor from the centrifuge 22 is divided into two portions, the first of which is recycled to the slurry from the second chiller to insure its fluidity and the second portion is recycled to the first chiller. The feed mixture may contain ethyl benzene in addition to xylenes.