GB585076A - Process for the production of meta-xylene - Google Patents

Abstract

Meta-xylene in substantially pure from is recovered from a mixture of xylenes containing principally meta- and para-xylenes, by diluting said mixture with a relatively volatile inert diluent having a freezing point below -58.5 DEG C., cooling the diluted mixture suitably to below -58.5 DEG C., and removing crystals of para-xylene formed thereby, evaporating the diluent from the remaining liquid and again cooling the liquid, suitably to about -50 DEG to -56 DEG C. and removing the resulting meta-xylene crystals. The diluent may be used in the proportion of 1/5 to 2 volumes, or preferably 1/3 to 1 volume, per volume of mixed xylenes. Diluents specified are methyl, ethyl and isopropyl alcohols; acetone and methyl ethyl ketone; toluene; aliphatic hydrocarbons such as n-pentane, iso-pentane, pentenes, butenes, butanes, propane, propylene, ethane and ethylene. A suitable xylene mixture is obtained by fractionally distilling an aromatic fraction B.P. 136-144 DEG C. derived from petroleum oil, and collecting the meta/para fraction of B.P. 138 DEG to 141 DEG C. The crystallization process may be carried out in a jacketted kettle with cooling or by auto-refrigeration using the diluent, for example, liquid ethylene as the refrigerant. In a typical process, 1 volume of mixed xylenes (21 per cent. para, 71 per cent. meta, 8 per cent. other C8 aromatics) is mixed with 1 volume of n-pentane, cooled to -70 DEG C. and the para-xylene crystals so obtained removed; the filtrate is fractionally distilled to remove the diluent and the residue cooled to -52 DEG C. and then filtered, in this manner 70 per cent. of the p-xylene and 27 per cent. of the m-xylene present in the original mixture are recovered substantially pure.ALSO:Meta-xylene in substantially pure form is recovered from a mixture of xylenes containing principally meta- and para-xylenes by diluting said mixture with a relatively volatile inert diluent having a freezing point below - 58.5 DEG C., cooling the diluted mixture, suitably to a temperature below - 58.5 DEG C., removing crystals of para-xylene thereby formed, evaporating the diluent from the remaining liquid and again cooling the liquid, suitably to about - 50 DEG to - 56 DEG C. and removing the resulting metaxylene crystals. The diluent may be used in the proportions of 1/5 to 2 volumes or, preferably, 1/3 to 1 volume per volume of mixed xylenes. Diluents specified are methyl, ethyl or isopropyl alcohol; acetone and methyl ethyl ketone; toluene; aliphatic hydrocarbons such as n-pentane, isopentane, pentenes, butenes, butanes, propane, propylene, ethane and ethylene. A suitable xylene mixture may be obtained by fractionally distilling an aromatic fraction of boiling range 136 DEG to 144 DEG C. derived from petroleum oil distillation and collecting the meta/para xylene fraction boiling at 138 DEG to 141 DEG C. The crystallisation process may be carried out in a cooled kettle or by means of auto-refrigeration using the diluent, for example, liquid ethylene as the refrigerant. In a typical example, 1 volume of mixed xylenes (21 per cent para, 71 per cent meta, 8 per cent other C8 aromatics) together with 1 volume of n-pentane were cooled to - 70 DEG C., the para crystals which had formed were removed; the filtrate was then fractionally distilled to remove the n-pentane and the residue cooled to - 52 DEG C. and filtered; in this manner 70 per cent of the p-xylene and 27 per cent of the m-xylene present in the original mixture were recovered in pure form.