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

摘要

This invention describes a process for separation of xylenes for the purpose of the production of high-purity metaxylene, a simulated countercurrent process using at least one adsorber with a limited cumulative total level (Hcu) of adsorbent at a surface velocity (Vsl) that is less than 2 cm/s.

主权项

1. A process for separation of metaxylene by simulated countercurrent chromatography (CCS) starting from a feedstock F that comprises metaxylene and its C8 aromatic isomers, said process comprising contacting said metaxylene and C8 aromatic isomers with 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 in which process at least one adsorber is divided into 4 chromatographic zones that are defined in the following manner:
Zone 1: a zone desorbing metaxylene, encompassed between injection of a desorbent D and sampling of an extract E, Zone 2: a zone desorbing isomers of metaxylene, encompassed between the sampling of the extract E and injection of a feedstock F that is to be fractionated, Zone 3: a zone desorbing metaxylene, encompassed between injection of the feedstock and draw-off of a raffinate R, Zone 4: a 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 with the beds all being identical, and the height of each bed being between 0.7 m and 1.40 m, wherein in said process the adsorber(s) have a cumulative level (Hcu) of adsorbent solid of between 6 m and 21 m, a mean surface velocity over each adsorber (Vsl) 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).