Simulated moving bed chromatography is a continuous separation process that achieves higher productivity and purity compared to single column batch chromatography while reducing solvent consumption and labor. It involves connecting multiple columns in a loop with ports between columns to continuously feed and withdraw extract and raffinate streams while periodically switching the ports to simulate the movement of the stationary and mobile phases. This allows separation of components as they move in opposite directions through the stationary phase. Simulated moving bed chromatography has applications in purifying proteins, antibodies, chiral compounds, and pharmaceutical ingredients.

1. SIMULATED MOVING BED
CHROMATOGRAPHY
1
Extract
FeedRaffinate
Eluent
Direction of the flow
and column switching
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2. AN OVERVIEW.
2
The Simulated Moving Bed (SMB) technology has been applied to both small and large molecules.
Compared to single column batch chromatography, SMB separations achieve higher productivity and purity while
at the same time reducing solvent consumption and labor not to mention deriving a reproducible and reliable
process.
The challenge created by the increase in biological treatment in medicine (monoclonal antibody or vaccines) has
made the manufacturers look for new directions other than batch mode chromatography.
Very small differences in the composition of these large biomolecules as well as very low levels of impurity can
have serious heath detriment for the patient with an already compromised immune system. Thus the need for high
quality processing methods that include non leaching and non contaminating process media.
The downstream purification processes is also under pressure to keep up with the higher titer achieved during the
upstream production.
Although the interest in bio-separation processes has been rising it has yet to reach the widespread use it has in
other area of continuous and automated separations.
Other applications have had considerable use such as separation of proteins, sugars, ionic molecules, optical
isomers and even some monoclonal antibodies.
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3. AN OVERVIEW.
3
A number of API (Active Pharmaceutical Ingredients) are now manufactured using SMB technology. It is
also the case for the separation and purification of optically active chiral compounds.
There are well established methods for reliable operations and scale-ups that have resulted from analytical
experiments.
In the last few years, rapid developments have been made in the areas of design, improved process
schemes, optimization and robust control.
The purpose of this overview is to provide the fundamentals of the SMB science and technology and some
practical issues concerning the operation of SMB units.
The “triangle theory”, a design tool that is used both in the academia and industry for the design of SMB
processes is also mentioned very briefly.
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4. AN OVERVIEW.
4
Traditional batch chromatography had an important role in the purification however the large amounts of
solvent, as well as buffers makes the process prohibitive as the volume of load increases.
Furthermore when it consists of large scale production the cost of labor is no longer competitive with an
automated continuous process such as SMB.
In light of such given a number of equipment manufactures have indeed designed purification systems based
on SMB chromatography.
A series of high-pressure and preferably high performance columns are used in series making a circulating
loop.
There are two sets of ports between each column:
Inlet ports for “feed” and “solvent” streams and outlet ports for “extract” and “raffinate” streams.
The feed and solvent are supplied continuously while at the same time extract and raffinate are
also drawn continuously from the ports.
The inlet and outlet ports are switched in a coordinated rhythm and with known intervals in the same
direction as the flow of the liquid.
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5. BASIC OPERATION.
5
Extract
FeedRaffinate
Eluent
Direction of the
flow and column
switching
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6. BASIC OPERATION.
6
ExtractFeed
Raffinate Eluent
Direction of the
flow and column
switching
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7. BASIC OPERATION.
7
Extract
Feed Raffinate
Eluent
Direction of the
flow and column
switching
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8. BASIC OPERATION.
8
Extract Feed
RaffinateEluent
Direction of the
flow and column
switching
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9. BASIC OPERATION.
9
Extract
FeedRaffinate
Eluent
Direction of the
flow and column
switching
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10. BASIC OPERATION.
10
ExtractFeed
Raffinate Eluent
Direction of the
flow and column
switching
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11. BASIC OPERATION.
11
Extract
Feed Raffinate
Eluent
Direction of the
flow and column
switching
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12. BASIC OPERATION.
12
Extract Feed
RaffinateEluent
Direction of the
flow and column
switching
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13. 13
SIMULATED MOVING BED CHROMATOGRAPHY HAS ALSO BEEN PICTURED AS A FAST
MOVING, COMPONENT (RABBIT) AND A SLOW MOVING COMPONENT, (TURTLE) ON
A CONVEYOR BELT.
CONSIDERING THE BELT SPEED AS
THE SPEED OF THE RABBIT AS
THE SPEED OF THE TURTLE AS
BOTH IN THE OPPOSITE DIRECTION,
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14. 14
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THE TURTLE WOULD THEN BE CARRIED BY THE BELT AT A SPEED OF
WHEREAS THE RABBIT WOULD OUTRUN THE BELT AT A SPEED OF

15. 15
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WHEN CONSIDERING THE INTERCONNECTED COLUMNS OF A SIMULATED
MOVING BED AND SIMPLIFYING IT TO A SINGLE COLUMN WE WOULD GET A
SYSTEM TO WHICH “FEED” AND “SOLVENT” ARE INJECTED CONTINUOUSLY
AND FROM WHICH “EXTRACT” AND “RAFFINATE” ARE WITHDRAWN
CONTINUOUSLY AS WELL.
Feed
SOLVENT
Simulated
Movement of the
Bed resulting from
column switching RaffinateExtract

16. The Simulated Movement of the Bed through switching of the columns, creates the
effect that the “Feed”, “Raffinate”, “Eluent”, and “Extract” are moving in the same
direction as the flow of the fluid while the movement of the bed is in the opposite
direction with a very controlled speed.
This apparent speed of the bed is given by the length of the column divided by the
switching intervals.
The goal is to add length to “column/s” and therefore increase the resolution of
the separation while at the same time evolving it to a continuous mode.
It is clear that the final “resolution” is an increment of the sum total of the
“resolution” of each column in the system.
The process is well established for a binary mixture and an isocratic solvent.
Attempts are made to move beyond and there should be no surprise to see it
happen.
16
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17. The first step is an analytical one in order to choose the right media
with the right resolution as well as the appropriate solvent/buffer.
The analytical performances to look for are:
• High resolution,
• High selectivity,
• Low retention time.
During that process one should keep in mind that the intent of the
separation is to isolate and purify a product and avoid any added
contamination. It is therefore important to check for:
• Low column bleeding,
• High column stability
• Low column back pressure 17
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18. The preferred column would have high resolution, low retention
time, no bleeding , high stability and therefore long life.
t1<t2< 15 min using a 4.6 mm ID column at a linear flow rate of
360 cm/hr and a length of 250 mm.
18
Absorbance
t1 t2 Retention time
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19. The column loadability is another parameter to be considered.
That is the maximum load the column can support before reaching its saturation
point under kinetic conditions.
Any two products in this example can be considered to assess the media for its
suitability for the operation of a binary mixture.
19
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Nitrobenzene
Thiourea
BenzylAlcohol
Aniline
MethylSalicylate
Toluene
10 8 min32 4 5 6 7
mAU
0
50
25
75
100
200
125
150
175
• The higher the load the faster the overall
operation.
• The higher the capacity of the columns the
fewer needed for a system.
• The more stable the media the more usage
in the process.
• The less bleeding from the stationary phase
the higher the purity of the end product.
• The lower the back pressure of the media
the faster the run.

20. 20
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The “Triangle Theory” is a complex tool used to determine the starting
conditions of the SMB.
Nowadays the manufacturers of SMB
systems as well as independent software
company have addressed the issue.
Far less trial and error steps are needed
to reach the optimal conditions for the
separation.
a
b
HB HA
Impure Extract
Impure Raffinate
m2
m3
Pure Extract
Impure Raffinate
Impure Extract
Pure Raffinate

21. The isolation of biotechnological products however has special criteria to be met
in order to have widespread use with Simulated Moving Bed technology.
As early as 1997, Gottschlich and Kasche have reported the biospecific purification
of monoclonal antibodies by SMB.
Although they report a ≥ 90 % yield and a removal of more than 99 % of the
contaminating proteins and most importantly a single step process to reach those
results, it leaves room to achieve that golden number of 100 % uncompromised
should the end product be used as a therapeutic in humans with poor heath.
Thus far the majority of the stationary phases used were unstable reversed phase
silica based compound with minimal capacity compared to stable hard gel and
porous polymeric.
Affinity media has also been scarcely used and so have all other chromatographic
regimen that are to pave the way for the SMB in becoming a universal process in
the isolation and purification of biopharmaceuticals including vaccines.
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