Process for production and recovery of paraxylene

A continuous process for separating a hydrocarbon, which crystallizes below -50 DEG F., from a liquid mixture containing other hydrocarbons, comprises maintaining the liquid mixture in at least two bodies of slurry containing crystals in mother liquor at crystallization temperatures, continuously passing the liquid mixture into the first body of slurry, continuously passing mother liquor and crystals from the first body into the second body of slurry, continuously withdrawing, separating and collecting crystals and mother liquor from the second, or last, body of slurry and recycling at least a portion of the crystals, so separated, to the first of the bodies of slurry. The process is described as applied to recovering paraxylene from a mixture containing paraxylene with metaxylene, orthoxylene, ethylbenzene, and small amounts of toluene, C9 aromatics and non-aromatics, but durene, cyclohexane, benzene, orthoxylene and naphthalene may be separated from mixtures according to examples. A feed stock is fractionated in towers A and B to concentrate the paraxylene contained therein, passed by a line 13 through a drier 15, a heat-exchanger 17 and a prechiller 19, mixed with recycled slurry introduced by a line 24, and passed through a scraped surface chiller C into a first crystallization vessel F, where it is held for 30 minutes to three hours at -80 DEG F. A slurry of paraxylene crystals and mother liquor is continuously withdrawn by a line 22, a part being recycled by line 24, and the remainder passed by a line 25 to a second crystallization vessel G where it is held for 30 minutes to 3 hours at -90 DEG F. to -105 DEG F. A slurry of paraxylene crystals and mother liquor is continuously withdrawn by a line 26, a part being recycled by a line 28 through a scraped chiller D for admixture with the slurry in line 25, the remainder passing by a line 30 to a first basket centrifuge J. A part of the filtrate from centrifuge J is passed by a line 31 to dilute the slurry in line 30, while the remainder passes to heat-exchanger 17. A filter cake is discharged from centrifuge J by a shoot 38, melted in a drum 39, a portion of the melt being passed by a line 43 containing a heater 44 to shoot 38, the remainder passing by a line 45 through a prechiller 46, a line 47, a heat-exchanger E and a line 48 to a third crystallization vessel H, where it is held for 30 minutes at -10 DEG to 20 DEG F. A slurry is continuously withdrawn by lines 55 and 56, a portio