GB675836A - A process for the isomerisation of xylenes and the resulting xylenes - Google Patents

Abstract

Xylenes are isomerized by contacting with from 0.2-6 moles. of steam or hydrogen per mole. of xylene at about 427-593 DEG C. and a liquid hourly space velocity of about 1-16, in the presence of a clay type cracking catalyst. Preferably ethyl benzene is also added. Acid treated clays or synthetic materials comprising silica with alumina, magnesia, zirconia or boric oxide are suitable catalysts. Any pressure, e.g. atmospheric up to 500 atm. or more, may be used. A mixture of isomers approaching the equilibrium composition may be treated to remove part of the o-xylene, e.g. by superfractionation, and part of the p-xylene by crystallization, the m-xylene rich mixture then being isomerized to produce o and p. The effect of various concentrations of steam and hydrogen on the isomerization is illustrated. Where concentrations of ethyl benzene above the equilibrium, e.g. up to 40 per cent, are present, it may be separated from the product and recycled. Thus, when producing o-xylene from a mixture rich in m, the feed may be blended with an o-rich product containing ethyl benzene above the equilibrium, and part of the o-xylene separated from the blend. The remainder is isomerized to give an o-rich mixture which is blended with the initial mixture. The addition of olefins is detrimental to the isomerization.