Liquid purification or separation – With means to add treating material – Chromatography
Reexamination Certificate
2000-01-18
2002-04-23
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
With means to add treating material
Chromatography
C210S659000
Reexamination Certificate
active
06375839
ABSTRACT:
SUMMARY OF THE INVENTION
The invention relates to a process and a device for separating at least one component of a mixture by contact between liquid and solid phases in variable-length chromatographic zones.
It applies to chiral separations and in particular to the separation of stereoisomers that are used especially in the field of pharmaceutics.
There are different chromatographic processes that can be used for the production of chemical components on a large scale.
The publication by R. M. NICOUD and M. BAILLY (Choice and Optimization of Operating Mode in Industrial Chromatography, Proceeding of the 9th International Symposium on Preparative and Industrial Chromatography, PREP 92, April 1992, Nancy, pp. 205-220) illustrates this technological background.
These processes can be classified according to several criteria: the process can be either discontinuous or continuous, the composition of the eluent can be isocratic, or a composition gradient can be carried out.
One of these possibilities is the true standard moving-bed 4-zone countercurrent process where in a moving-bed system, with a view to producing a continuous countercurrent effect, solids circulate continuously in a closed loop past the fixed feedstock and eluant introduction points alternately with draw-off points for a raffinate and an extract.
Since this process is perfectly well known and described, only the characteristics that are required to understand the nature of this invention are summarized below. For the operating mode in a True Moving Bed, countercurrent contact between the liquid and solid phases is made in the column, which can be divided into four different zones.
Zone I: Everything that is located between the eluant injection lines and the extract draw-off lines
Zone II: Everything that is located between the extract draw-off lines and the feedstock injection lines
Zone III: Everything that is located between the feedstock injection lines and the raffinate draw-off lines
Zone IV: Everything that is located between the raffinate draw-off lines and the eluant injection lines.
Because of the inlet/outlet flow rates, the liquid flow rate varies according to the zone, whereby Q
I
, Q
II
, Q
III
, and Q
IV
are the respective flow rates in zones I, II, III, and IV.
In 1961, the UOP Company patented a process that makes it possible to simulate the movement of the solid by an elegant connection between the columns that are interconnected in a closed loop (U.S. Pat. No. 2,985,589 and U.S. Pat. Nos. 3,291,726, 3,268,605). This process, called a Simulated Moving Bed (LMS), then makes it possible to produce the True Moving Bed in practice in a simple way. Said process is characterized in that the feedstock and eluant introduction points are periodically advanced downstream (in the direction of circulation of the main fluid), while the draw-off points for a raffinate and an extract are advanced simultaneously by one column or column section.
All of the inlet and outlet lines are therefore moved simultaneously with each period &Dgr;T and cycle time, at the end of which time they find that their initial position is equal to Nc x &Dgr;T, whereby Nc is the total number of columns.
The prior art is also illustrated by the patent application of the applicant, FR-A-2 754 730, and by U.S. Pat. No. 4,498,991.
This process has been extensively described particularly by CHARTON and NICOUD (Complete Design of a Simulated Moving Bed, Journal of Chromatography 1995, 702, 97-102).
Only the minimum information that is necessary for good comprehension of this invention will be recapped below.
The inlet/outlet positions are moved simultaneously at fixed intervals. It is advised that the position of the line be marked by line (n), which indicates that at a given moment, a given inlet/outlet line is connected to the inlet of column n. For example, in a 12-column system, feedstock (9) means that the feedstock line is connected to the inlet of column 9, whereas raffinate (11) means that the raffinate line is connected to the inlet of column 11.
By using this definition, a system can be represented by: El(3)/Ext(6)/Peedstock(9)/Raff(11). For this configuration, the numbers of columns in zones 1, II, III, and IV are respectively: 3/3/2/4. The configuration of the system is then completely defined by:
Inlet/Outlet No. of Columns
At time 0: El(3)/Ext(6)/Feedstock(9)/Raff(11) 3/3/2/4
After a given time (the PERIOD), all of the inlet/outlet positions are moved simultaneously by one column, and the system is described as follows:
At time &Dgr;T: El(4)/Ext(7)/Feedstock(10)/Raff(12) 3/3/2/4
After a new period, all of the positions will again be moved simultaneously by one column, and the system will then be described as follows:
At time 2×&Dgr;T: El(5)/Ext(8)/Feedstock(11)/Raff(1) 3/3/2/4
At time 2×&Dgr;T, the position of the raffinate has been moved from position 12 to position 1. Notice that position 1 can be written as position 13 modulo 12. ([13]
12
).
This presentation can be generalized to simulated moving beds that comprise a number of columns Nc. For a simulated moving bed that consists of Nc columns, it is obvious that no position can exceed Nc. For the sake of simplicity, we will simply increase all of the positions by one unit with each movement, and we will define all of the modulo Nc positions (for example, [8]
Nc
=3 if Nc=5).
If, at a given moment, the configuration of the simulated moving bed is El(e)/Ext(x)/Feedstock(f)/Raff(r), simple reasoning makes it possible to find the number of columns that are contained in each zone:
Zone 1: Nb1=[x-e]
Nc
; Zone 2: Nb2=[f-x]
Nc
Zone 3: Nb3=[r-f]
Nc
; Zone 4: Nb4=[e-r]
Nc
It is possible to verify simply that: Nb1+Nb2+Nb3+Nb4=Nc and the system is completely defined by Table 1.
TABLE 1
No. of Columns
Inlet/Outlet
in Each Zone
At time 0:
E1(e)/Ext(x)/Feed(f)/Raff(r)
Nb1/Nb2/Nb3/Nb4
At time &Dgr;T:
E1([e + 1]
Nc
)/Ext([x + 1]
Nc
)/
Nb1/Nb2/Nb3/Nb4
Feed([f + 1]
Nc
)/Raff([r + 1]
Nc
)
At time n × &Dgr;T:
E1([e + n]
Nc
)/Ext([x + n]
Nc
)/
Nb1/Nb2/Nb3/Nb4
Feed ([f + n]
Nc
)/Raff([r + n]
Nc
)
The injection points and draw-off points are shifted by one column after a period &Dgr;T and by Nc columns after Nc periods. The number of columns in each zone remains unchanged. The injection points and draw-off points therefore regain their initial positions after cycle time Nc×&Dgr;T.
The main characteristics of the simulated moving bed systems (providing a practical implementation of the true moving bed) are defined by:
1. Zones that are defined by the positions of the inlet/outlet lines,
2. A set number of columns per zone, constant over time,
3. Zones of fixed length that are constant over time,
4. Synchronized movement of all of the inlet/outlet lines.
Characteristics 2, 3, and 4 are due to the fact that the simulated moving bed simulates the behavior of the true moving bed.
According to Patent FR. 2 721 528, it is possible to correct the composition disturbances of the extract and the raffinate that are caused by the dead volume of the recycling pump that is located between the last and first beds of the adsorption column by increasing by a suitable value the period of connection of a fluid injection flow or draw-off in the system each time that this flow passes from one position that is immediately in front to a position that is immediately behind the dead volume, and then by reducing said connection period when this flow moves from the position that is immediately behind the dead volume to the next position. Once per cycle, however, all of the inlets and outlets are shifted simultaneously. This technique makes it possible to compensate for the technological imperfections in a simple way in order to make it operate in a way that is close to that of an ideal simulated moving bed.
In th
Adam Phillippe
Bailly Michel
Ludemann-Hombourger Olivier
Nicoud Roger Marc
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Therkorn Ernest G.
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