| 摘要 |
1,208,364. Para-xylene. SINCLAIR RESEARCH Inc. 25 April, 1968 [22 May, 1967], No. 19614/68. Heading C5E. Para-xylene of at least 99 mole per cent purity is obtained from a C 8 aromatic hydrocarbon mixture containing 5-50% para-xylene and other xylene isomers by cooling the mixture to crystallize substantially only para-xylene (e.g. at from - 60‹ to - 100‹ F.), separating a para-xylene cake by centrifugation, melting the cake and recrystallizing substantially only the para-xylene (e.g. at 0-40‹ F.), separating a second para-xylene cake of less than 99% purity by centrifugation, and washing the second cake with toluene in an amount sufficient to provide a para-xylene product of at least 99% purity, and at a temperature at least as high as that of the cake from the second centrifugation. The second cake normally contains up to 10 wt. per cent occluded liquid, and the amount of toluene wash is suitably 0À25-3 parts per part of said liquid, preferably an amount such that no toluene breakthrough occurs. Both the filtrate from the second centrifugation and. the wash effluent (after removal of any toluene) may be recycled to the first crystallization, and part of the filtrate may be recycled to the second crystallization. |
