Process and device for simulated-countercurrent chromatographic separation for the production of metaxylene with high yield

Process for separation of metaxylene by simulated countercurrent chromatography (CCS) starting from a feedstock F that essentially comprises metaxylene and its C8 aromatic isomers, using a zeolitic adsorbent solid based on Y zeolite crystals and a non-zeolitic phase, in which the Y zeolite crystals have a mean diameter of a number that is less than or equal to 1.7 μm, preferably less than or equal to 1.5 μm, and preferably also less than or equal to 1.2 μm, a process that uses at least one adsorber that is divided into 4 chromatographic zones that are defined in the following manner:

• Zone 1:
• Zone for desorption of metaxylene, encompassed between the injection of the desorbent D and the sampling of the extract E,
• Zone 2:
• Zone for desorption of isomers of metaxylene, encompassed between the sampling of the extract E and the injection of the feedstock that is to be fractionated F,
• Zone 3:
• Zone for adsorption of metaxylene, encompassed between the injection of the feedstock and the draw-off of the raffinate R,
• Zone 4:
• Zone located between the draw-off of raffinate R and the injection of the desorbent D,
• with the number of beds of each adsorber being between 6 and 18 beds, and preferably between 8 and 15 beds, with the beds all being identical, and the height of each bed being between 0.7 m and 1.40 m, said process being characterized in that it has a cumulative level (Hcu) of adsorbent solid on the different adsorber(s) of between 6 m and 21 m, and in that the mean surface velocity over each adsorber (Vsl) is between 0.9 cm/s and 1.8 cm/s, with said surface velocity being defined as the volumetric flow rate of mean recycling at the temperature of the process that is divided by the area of the cross-section of the adsorber and the cumulative height (Hcu) of adsorbent solid being distributed in the following manner:
• The cumulative level of adsorbent solid in zone 1, on average over a cycle, is 17%±5% of (Hcu),
• The cumulative level of adsorbent solid in zone 2, on average over a cycle, is 41.5%±5% of (Hcu),
• The cumulative level of adsorbent solid in zone 3, on average over a cycle, is 25%±5% of (Hcu),
• The cumulative level of adsorbent solid in zone 4, on average over a cycle, is 16.5%±5% of (Hcu).