Simulated moving bed xylenes separation process, and optimized operating conditions for units treating paraxylene-rich feeds

Patent metadata

Field	Value
Publication number	US-10214467-B2
Application number	US-201815982649-A
Country	US
Kind code	B2
Filing date	May 17, 2018
Priority date	May 17, 2017
Publication date	Feb 26, 2019
Grant date	Feb 26, 2019

Abstract

The present invention describes a process for the simulated moving bed separation of xylenes which can be used for the treatment of paraxylene-rich feeds (more than 25% by weight of paraxylene), in which the operating conditions are optimized by means of a specific relationship between the cycle time and the desorbant flow rate.

First claim

What is claimed is:

1. A process for separating xylenes of a feed (F) to be fractionated in a simulated moving bed with a view to optimizing the purity and yield of paraxylene, the weight content of paraxylene in the feed (F) being in the range 25.01% to 60% by weight, the unit implementing said process using a number of beds in the range 4 to 24 and more preferably in the range 8 to 15, and the distribution of the beds in the various zones being given by the following general formula, which is valid irrespective of the total number of beds (N_total), the index z denoting the number of beds in the zone under consideration, and the second index being that of the zone under consideration:
Nz 1=( N _total*5/24)*(1±0.2)

Nz 2=( N _total*9/24)*(1±0.2)

Nz 3=( N _total*7/24)*(1±0.2)

Nz 4=( N _total*3/24)*(1±0.2)

the 4 chromatographic zones being defined as follows:
Zone 1: paraxylene desorption zone, included between the injection of the desorbant (D) and the withdrawal of the extract (E);
Zone 2: zone for the desorption of isomers of paraxylene, included between the withdrawal of the extract (E) and the injection of the feed (F) to be fractionated;
Zone 3: paraxylene adsorption zone, included between the injection of the feed and the withdrawal of the raffinate (R);
Zone 4: zone located between the withdrawal of the raffinate (R) and the injection of the desorbant (D),

the optimized cycle time (interval of time separating two injections of desorbant to the same location in the column) being determined from the cycle time weighted by means of a correcting factor:

μ

σ
2

·

1

ɛ
i

·

L
lit

the parameter

μ

σ
2

being itself determined by a breakthrough experiment, knowing the length of a bed (L lit ) and its interstitial porosity (ε i ), the measurement of σ 2 obtained in the presence of adsorbent having to be at least 10 times higher, preferably 30 times higher than the measurement σ 2 blank obtained during a test carried out in the absence of adsorbent, with glass beads with a diameter approximately equal to that of the particles of adsorbent,
the ratio of the flow rate of desorbant to the flow rate of paraxylene (QD/QPX), and thus the optimized desorbant flow rate, being determined by means of the following 3 tables as a function of the content of paraxylene in the feed:

TABLE 1

Paraxylene PX in the feed: 25% < % PX, feed ≤ 30%

25% < Paraxylene PX in the feed ≤ 30%

t_cycle wtd (1/m)
Q D /Q PX

Adjustment No 1
320 +/− 25
5.30 +/− 0.55

Adjustment No 2
345 +/− 25
4.85 +/− 0.50

Adjustment No 3
370 +/− 25
4.50 +/− 0.45

Adjustment No 4
395 +/− 25
4.20 +/− 0.45

Adjustment No 5
425 +/− 25
4.00 +/− 0.45

Adjustment No 6
465 +/− 25
3.75 +/− 0.40

Adjustment No 7
510 +/− 25
3.60 +/− 0.40

Adjustment No 8
560 +/− 30
3.55 +/− 0.40

TABLE 2

Paraxylene PX in the feed: 30% < % PX, feed ≤ 45%

30% < Paraxylene PX in the feed ≤ 45%

t_cycle wtd (1/m)
Q D /Q PX

Adjustment No 1
325 +/− 25
4.40 +/− 0.45

Adjustment No 2
345 +/− 25
4.00 +/− 0.40

Adjustment No 3
365 +/− 25
3.75 +/− 0.40

Adjustment No 4
385 +/− 25
3.50 +/− 0.40

Adjustment No 5
415 +/− 25
3.30 +/− 0.35

Adjustment No 6
445 +/− 25
3.15 +/− 0.35

Adjustment No 7
485 +/− 25
3.00 +/− 0.35

Adjustment No 8
530 +/− 25
2.90 +/− 0.35

Adjustment No 9
580 +/− 30
2.80 +/− 0.30

Adjustment No 10
640 +/− 30
2.80 +/− 0.30

TABLE 3

Assignees

• Ifp Energies Now

Inventors

• Vonner Alexandre
• Leinekugel Le Cocq Damien
• Laroche Catherine
• Etienne Pascal

Classifications

• C07C7/13 Primary

  by molecular-sieve technique · CPC title

• B01D15/185

  characterised by the components to be separated · CPC title

• B01D15/1828

  characterised by process features · CPC title

• C07C7/005 Primary

  Processes comprising at least two steps in series · CPC title

• C07C15/08

  Xylenes · CPC title