Process and apparatus for simulated counter-current chromatographic separation for high-productivity production of paraxylene

A process for separation of paraxylene by simulated counter-current (SCC) chromatography from a charge F essentially comprising paraxylene and its aromatic C8 isomers, utilising a zeolitic adsorbent solid based on zeolite crystals X and a non-zeolitic phase, in which the zeolite crystals X have an average diameter by number of between 0.1 and 1.5 microns and preferably between 0.1 and 1.2 microns, said process using at least one adsorber divided into 4 chromatographic zones defined in the following fashion:

• Zone 1:
• zone for desorption of the paraxylene, between injection of the desorbent D and withdrawal of the extract E.
• Zone 2:
• zone for desorption of the isomers of the paraxylene, between the withdrawal of the extract E and injection of the charge F to be fractionated.
• Zone 3:
• zone for adsorption of the paraxylene, between injection of the charge and withdrawal of the raffinate R.
• Zone 4:
• zone between withdrawal of the raffinate R and injection of the desorbent D,
• the number of adsorption beds being between 6 and 18 and preferably between 8 and 15 beds, the beds all being identical, and the height of each bed being between 0.7 m and 1.4 m, said process being characterised in that it has a cumulated height of adsorbent solid in relation to the different adsorber or adsorbers (Hcu) of between 6 m and 21 m and that the mean superficial velocity over each adsorber (Vsl) is between 1 cm/s and 2 cm/s, said superficial velocity being defined as the mean recycling flow rate by volume at the temperature of the process divided by the area of the section of the adsorber, and the cumulated height (Hcu) of adsorbent solid being distributed in the following fashion:
• the cumulated height of adsorbent solid in zone 1 on average over a cycle is 21%±5% of (Hcu),
• the cumulated height of adsorbent solid in zone 2 on average over a cycle is 37.5%±5% of (Hcu),
• the cumulated height of adsorbent solid in zone 3 on average over a cycle is 29%±5% of (Hcu),
• the cumulated height of adsorbent solid in zone 4 on average over a cycle is 12.5%±5% of (Hcu).