| 摘要 |
<p>Meta-xylene is isomerized to para-xylene by contacting a meta-xylene-containing feed with a catalyst selected from the oxides and sulphides of metals of Group VI of the Periodic Table at a temperature in the range 800-1150 DEG F. in the presence of hydrogen, recovering para-xylene from the isomerized product and resubjecting the unconverted meta-xylene to the catalyst contacting treatment for further isomerization. The catalyst used is preferably an oxide or sulphide of chromium, tungsten or molybdenium on a carrier such as alumina, zinc oxide, silica, magnesia and spinel. Pressure is preferably in the range 50 to 500 lbs. per sq. in. gauge. The feed stock may be substantially pure meta-xylene or may be a meta-xylene containing fraction which contains other aromatic hydrocarbons having -8 carbon atoms in the molecule, for example, orthoxylene and ethylbenzene. The feed stock may also be a naphthenic hydrocarbon fraction boiling in the range 200-350 DEG F. Following the isomerization of meta-xylene to paraxylene the product may be subjected to a fractional distillation to remove all toluene and C9 and heavier aromatic hydrocarbons, leaving a product enriched in para-xylene from which the para-xylene may be separated by chilling to form a slurry of para-xylene in mother liquor and centrifuging this. The filtrate is mixed with the feed and subjected to recantact with the catalyst. In the example a meta-xylene concentrate containing 96 per cent by volume of meta-xylene is contacted with a supported molybdenum oxide catalyst in the presence of hydrogen; the C8 aromatic fraction obtained contained a mixture of ethyl benzene, orthoxylene, meta-xylene and para-xylene, the metaxylene from which was recycled.</p> |
