Patent ID: 6838588

Claim:
A process for co-producing paraxylene and metaxylene from a hydrocarbon feed comprising them, the process comprising a first step for separating the feed in a simulated moving bed in at least a first chromatographic column ( 6 ) containing a plurality of beds of at least one adsorbent interconnected into a loop, said column comprising a feed injection ( 1 ), a take-off for a first raffinate ( 4 ), a take-off for a second raffinate ( 5 ) comprising a desorbent, and a mixture containing metaxylene and orthoxylene that is substantially free of ethylbenzene and paraxylene, an injection point for desorbent ( 2 ) and a take-off for an extract delivering very high purity paraxylene, the process comprising periodic simultaneous shifting of the feed and desorbent injection positions and for the extract take-off position by one bed in the direction of flow of a principal stream moving in said first column ( 6 ), the process being characterized in that the second raffinate is distilled to eliminate the desorbent, a mixture ( 12 ) containing metaxylene and orthoxylene is recovered, a second step for separating at least a portion of the mixture of orthoxylene and metaxylene is carried out in at least one second chromatographic column ( 17 ) containing at least one adsorbent and comprising at least one point for injection of the mixture ( 12 ), an injection point for a desorbent ( 16 ), a take-off for an extract ( 18 ) containing desorbent and enriched in the component that is the most adsorbed on the adsorbent, and a takeoff for a raffinate ( 19 ) containing desorbent and enriched in the compound that is the least adsorbed on the adsorbent, the process being further characterized in that the extract containing metaxylene or the raffinate containing metaxylene is distilled to eliminate desorbent and recover metaxylene with a purity of more than 99%.