Process for the simulated moving bed separation of xylenes, and optimized operating conditions

Patent metadata

Field	Value
Publication number	US-10150717-B2
Application number	US-201815918222-A
Country	US
Kind code	B2
Filing date	Mar 12, 2018
Priority date	Mar 13, 2017
Publication date	Dec 11, 2018
Grant date	Dec 11, 2018

Abstract

The present invention describes a process for the simulated moving bed separation of xylenes, in which the operating conditions are optimized by means of a specific relationship between the cycle time and the flow rate of the desorbant.

First claim

The invention claimed is:

1. A process for the simulated moving bed separation of xylenes with the aim of optimizing the purity and paraxylene yield, the content of paraxylene in the feed being in the range 20% to 25% by weight, said unit using a number of beds in the range 4 to 24, and the distribution of the beds in the various zones being given by the general formula which is applicable irrespective of the total number of beds, N_total:
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 four chromatographic zones being defined in the following manner:
zone 1: paraxylene desorption zone, included between the injection of desorbant D and the withdrawal of the extract E;
zone 2: desorption zone for paraxylene isomers, included between the withdrawal of the extract E and the injection of the feed to be fractionated F;
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, defined as the interval of time separating two injections of desorbant at the same location in the column, being determined from the weighted cycle time using the following correction factor:

weighted
⁢

⁢
cycle
⁢

⁢
time

=

cycle
⁢

⁢
time
*

[

μ

σ
2

·

1

ɛ
i

·

L
bed

]

the parameter

μ

σ
2

in turn being determined by means of a breakthrough experiment carried out on the one hand with the solid adsorbant, and on the other hand with a set of inert beads with the same diameter as that of the solid adsorbant, in a manner such as to verify that the measurement of σ 2 obtained in the presence of adsorbant is at least 10 times higher than the measurement σ 2 blank obtained during this same test carried out on the inert beads,
knowing the length of a bed (L bed ) and its interstitital porosity (ε i ),
the ratio of the flow rate of desorbant to the flow rate of paraxylene, and thus the optimal desorbant ratio, is determined using the following table:

t_cycle, weighted

(l/m)
Q D /Q PX

Setting No. 1
320 +/− 20
6.7 +/− 0.3

Setting No. 2
340 +/− 20
6.1 +/− 0.3

Setting No. 3
360 +/− 20
5.7 +/− 0.3

Setting No. 4
380 +/− 20
5.3 +/− 0.3

Setting No. 5
405 +/− 20
5.1 +/− 0.3

Setting No. 6
425 +/− 20
4.85 +/− 0.3 

Setting No. 7
452 +/− 20
4.6 +/− 0.3

Setting No. 8
485 +/− 20
 4.5 +/− 0.3.

2. The simulated moving bed xylenes separation process as claimed in claim 1 , in which the operating temperature is in the range 100° C. to 250° C., and the pressure is in the range between the bubble pressure of the mixture of xylenes constituting the feed and 3 MPa.

3. The simulated moving bed xylenes separation process as claimed in claim 1 , in which the water content in the feed is in the range 70 to 140 ppm.

4. The simulated moving bed xylenes separation process as claimed in claim 1 , in which the desorbant is paradiethylbenzene.

5. The simulated moving bed xylenes separation process as claimed in claim 1 , in which the recycle ratio is in the range 2.0 to 8, the recycle ratio being defined as the ratio between the mean flow rate flowing in the various beds of the adsorber and the flow rate for injection of feed into said adsorber.

Assignees

• Ifp Energies Now

Inventors

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

Classifications

• B01D15/1864

  using two or more columns · CPC title

• B01D15/1807

  using counter-currents, e.g. fluidised beds · CPC title

• C07C7/13 Primary

  by molecular-sieve technique · CPC title

• C07C7/005

  Processes comprising at least two steps in series · CPC title

• B01D15/1835

  Flushing · CPC title