| 摘要 |
In the production of a desired xylene isomers from a mixture of isomers comprising a distillation step for concentrating the xylene isomers from a mixture containing them, a separation step for recovering the desired isomer and an isomerization step for isomerizing the residue, the isomerization is effected by passing the vaporous xylene mixture free from permanent gases over a fixed bed of catalyst and passing the vaporous effluent without condensation to the distillation step. The initial feedstock may be fed into the distillation step or the isomerization provided the feed to the latter contains at least 50% by wt. of xylenes. If para-xylene is the desired product it is separated by crystallization. Isomerization is effected at 375-550 DEG C. over silica-alumina, halogenimpregnated silica-alumina or supported platinum. The first distillation after the isomerization is preferably a topping column followed by a tailing column and heat from the reaction effluent may be supplied to the reboilers or to the reaction feed. The catalyst is regenerated at intervals with an oxygen-containing gas at 450-550 DEG C., preferably increasing the temperature during the regeneration from the lower to the upper limit and increasing the oxygen content simultaneously, e.g. from 1% to 20% by volume. |
