Expanded Bed Chromatography

258 Pages·1999·17.793 MB·English

by  Rolf Hjorth (auth.), Bo Mattiasson (eds.)

Expanded Bed Chromatography
Edited by:
BO MATTIAS SON
Department of Biotechnology,
Center for Chemistry and Chemical Engineering,
Lund University,
Lund, Sweden
Reprinted from Bioseparation, Volume 8, No. 1/5 (1999)
Springer-Science+Business Media, B.V.
Library of Congress Cataloging-in-Publication Data
ISBN 978-90-481-5380-0 ISBN 978-94-017-1519-5 (eBook)
DOI 10.1007/978-94-017-1519-5
Printed on acid-free paper
All Rights Reserved
©
1999 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1999
No part of the material protected by this copyright notice
may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying,
recording or by any information storage and retrieval
system, without written permission from the copyright owner.
Contents
Preface v
Expanded bed adsorption: elution in expanded bed mode
R Hjorth 1
Monitoring, modeling, and control strategies for expanded-bed adsorption processes
T. V. Thelen, W.P. Ramirez 11
Factors affecting dispersion in expanded bed chromatography
S. Yamamoto, N. Akazaki, O. Kaltenbrunner, P. Wat1er 33
Physical and biochemical characterization of a simple intermediate between fluidized and
expanded bed contactors
J. Chi-Wei Lan, G.E. Hamilton, A. Lyddiatt 43
On-line monitoring of the purification of GST-(His)6 from an unclarified Escherichia coli
homogenate within an immobilised metal affinity expanded bed
RH. Clemmitt, L.J. Bruce, H.A. Chase 53
The effect of column verticality on separation efficiency in expanded bed adsorption
LJ. Bruce, S. Ghose, H.A. Chase 69
Evaluation of the effect of in-bed sampling on expanded bed adsorption
LJ. Bruce, H.A. Chase 77
EBA columns with a distribution system based on local stirring
E. Zafirakos, A. Lihme 85
Simplified and more robust EBA processes by elution in expanded bed mode
A. Lihme, E. Zafirakos, M. Hansen, M. Olander 93
CelVadsorbent interactions in expanded bed adsorption of proteins
1. Feuser, J. Walter, M.-R Kula, J. Thommes 99
Validation issues related to expanded bed technology
G. Sofer 111
Highly dense beaded sorbents suitable for fluidized bed applications
N. Voute, E. Boschetti 115
Characterization of very dense mineral oxide-gel composites for fluidized-bed adsorption of
biomolecules
N. Voute, D. Bataille, P. Girot, E. Boschetti 121
Expanded bed adsorption on supermacroporous cross-linked cellulose matrix
A. Pai, S. Gondkar, S. Sundaram, A. Lali 131
Characterisation of STREAMLINE™ Phenyl
J. Eirenmark, J. Gustavsson, 1. Lagerlund, L. Sandberg 139
Use of Streamline chelating for capture and purification of poly-His-tagged recombinant pro-
teins
S. Noronha, 1. Kaufman, J. Shiloach 145
A simplified purification procedure of a-lactalbumin from milk using Ca2+ -dependent adsorp
tion in hydrophobic expanded bed chromatography
W. Noppe, P. Haezebrouck, I. Hanssens, M. De Cuyper 153
Expanded bed adsorption as a unique unit operation for the isolation of bacteriocins from
fermentation media
R. Callewaert, L. De Vuyst 159
Pilot scale recovery of monoclonal antibodies by expanded bed ion exchange adsorption
N. Ameskamp, C. Priesner, l. Lehmann, D. Liitkemeyer 169
Capture of human Fab fragments by expanded bed adsorption with a mixed mode adsorbent
M.B. Hansen, A. Lihme, M. Spitali, D. King 189
Purification of Recombinant Human Serum Albumin. Efficient purification using STREAM-
LINE
A Sumi, K. Okuyama, K. Kobayashi, W. Ohtani, T. Ohmura, K. Yokoyama 195
Direct coupling of expanded bed adsorption with a downstream purification step
l.T. Beck, B. Williamson, B. Tipton 201
Production of plasmid DNA for human gene therapy using modified alkaline cell lysis and
expanded bed anion exchange chromatography
D.L. Varley, AG. Hitchcock, AM.E. Weiss, W.A Horler, R. Cowell, L. Peddie, G.S. Sharpe, D.R.
Thatcher, l.A.l. Hanak 209
Development and scale up of a capture step (expanded bed chromatography) for a fusion
protein expressed intracellularly in Escherichia coli
M. Brobjer 219
On-line monitoring of glucose and/or lactate in a fermentation process using an expanded
micro-bed flow injection analyser
M.P. Nandakumar, AM. Lali, B. Mattiasson 229
Binding assays in heterogeneous media using a flow injection system with an expanded micro
bed adsorption column
B. Mattiasson, M.P. Nandakumar 237
Use of a micro-expanded bed containing immobilised lysozyme for cell disruption in flow
injection analysis
M.P. Nandakumar, A Tocaj, B. Mattiasson 247
Flow injection analysis of intracellular ,a-galactosidase in Escherichia coli cultivations, using an
on-line system including cell disruption, debris separation and immunochemical quantification
A Tocaj, M.P. Nandakumar, O. Holst, B. Mattiasson 255
Key word Index 269
Author Index 271
Bioseparation 8: Y, 1999. v
© 1999 Kluwer Academic Publishers.
Preface
Integration is a leading theme in modern process held from which this volume emerges. We have chosen
biotechnology. This is done with an aim to reduce the to collect a broad selection of papers illustrating differ
number of processing steps, to simplify the handling, ent aspects of the technology, all the way from design
to shorten the time a sensitive target molecule has to of new materials, mathematical simulations of column
be in contact with harsh conditions and also to reduce performances, use of the new adsorbents in process
total processing costs. ing conditions both from the research laboratories and
The main emphasis has so far been on integration from the industrial environment. There may some
of bioconversions and the initial steps of downstream times be a lack of some details in a few of the papers
processing, mainly with regard to harvesting small that traditionally would have been expected from an
molecules. academic paper, but in my mind these papers contain
The concept of capturing of biomolecules implies in their present shape significant valuable information
an early enrichment in an isolation step that per se that makes the volume interesting and useful for the
does not necessarily increase the purity to high lev separation science community.
els. It is rather a matter of reducing the processing The symposium covered many aspects of expanded
volumes and, to some extent, also to remove some bed technology. A large proportion of the contributors
contaminants. The use of expanded bed chromatog have submitted material to the volume and one addi
raphy is such a development. This involves the use of tional paper is added after the meeting and that makes
adsorption material which is heterogeneous with re the proceedings a good coverage of the situation in
gard to both particle size and density such that it forms expanded bed chromatography during 1998.
a stable expanded bed when used in upstream chro The scientific committee behind the meeting is
matographic processing under conditions that would gratefully acknowledged for their contribution. The
normally have given a ftuidised bed. committee had the following members:
The format of expanded bed has many applica Dr. Stuart Builder (Chairman), Genetech, USA;
tions in biotechnology. The main area developed so Dr. Howard Chase, University of Cambridge, UK;
far is the capturing approach. However, this volume Dr. Rolf Hjort, Amersham Pharmacia Biotech,
also illustrates use of the expanded bed technology in Sweden;
other areas of biotechnology, such as bioanalysis and Prof. Maria-Regina Kula, University of Diissel
biocatalysis. It seems safe to predict that these areas dorf, Germany;
also hold interesting potential for future development. Prof. Mathias Uhlen, Royal Institute of Technol
One can thus expect that the technology may become ogy, Sweden;
a versatile tool in different areas of modern bioprocess Dr. Joachim Walter, Dr. Karl Thomae Gmbh,
technology. Germany.
The new material that are being developed for use This proceeding is among the first in a line of
in expanded bed chromatography will help to broaden special issues that are planned within the journal of
the area of applications even more. BIOSEPARATION.
The area of expanded bed chromatography is novel Lund in May 1999
and during June 1998 an international meeting was Bo Mattiasson
Bioseparation 8: 1-9, 1999. 1
© 1999 Kluwer Academic Publishers.
Expanded bed adsorption: elution in expanded bed mode
Rolf Hjorth
Amersham Pharmacia Biotech, SE-751 84 Uppsala, Sweden Tel: [phone]; Fax: [phone]; e-mail:
rolf. [email protected]
Received 19 September 1998; accepted 25 November 1998
Key words: elution, expanded bed adsorption, ion exchange, protein recovery
Abstract
Elution in expanded bed mode has been investigated in the expanded bed adsorption process. Elution was per
formed at different sample loads and at different liquid velocities using bovine serum albumin as a model. The
effect on mixing in the liquid phase and on the volume of the eluted peak were determined. Mixing in the liquid
phase was almost unaffected when elution was performed at 100 cmlh, regardless of sample load. However, mixing
increased significantly when elution was carried out at high liquid velocities (300 cmlh) at high sample loads.
The eluted peak volume increased with liquid velocity and increased sample load. It was approx. 80% higher in
expanded bed mode than in packed bed from an adsorbent completely saturated with protein eluted at 300 cmlh.
Introduction Hjorth et al., 1995; Karau et al., 1997; ThOmmes et
al., 1995); however, very little attention has been paid
to the elution process of expanded beds. It has been
Expanded bed adsorption is an efficient technique
recommended that expanded beds be eluted in packed
for recovery of protein from unclarified feedstocks.
bed mode (Amersham Pharmacia Biotech). Neverthe
It is based on stable ftuidisation of an adsorbent in
less, the few reports describing elution in expanded
a purposely designed column. Due to the ftuidisa
bed mode (Hjorth et al., 1995; ThOmmes et al., 1996)
tion process the space between the adsorbent particles
clearly demonstrate that it might be a useful alterna
is increased, allowing feed material containing cells
tive. Hjorth et al. (1995) have shown that elution in
and/or cell debris to be pumped through the column
expanded bed mode could be performed without ad
without blocking it. This makes expanded bed adsorp
verse effects and that the volume of the eluted peak
tion an attractive technique for recovery of proteins
increased only 40% compared with elution under sim
from particle-containing feedstocks. Several examples
ilar conditions in packed bed mode. ThOmmes et al.
where biomolecules have been recovered from mam
(1996) described the use of elution in expanded bed
malian cell suspensions (Zapata et al., 1996), yeast cell
mode for recovery of IgG from a protein A containing
suspensions (Nod a et al., 1996) and E. coli (Barnfield
adsorbent. This mode of operation was reported to re
Frej et al., 1994; Johansson et al., 1996) in pilot and
sult in an increase of the eluted peak volume due to the
industrial scale using expanded bed adsorption have
increased bed voidage in an expanded bed compared to
been published. Recently, Thatcher et al. (1997) re
a packed bed.
ported the recovery of plasmid DNA from an E. coli
Selecting elution in expanded bed mode will cer
homogenate by expanded bed adsorption in pilot scale.
tainly affect both equipment design and the process
Expanded bed adsorption has been reviewed in terms
itself and therefore it is important to gain more infor
of both its basic principles (Chase, 1994, Thommes,
mation about this mode of operation. It is under certain
1997) and its industrial applications (Hjorth, 1997).
conditions (Amersham Pharmacia Biotech) necessary
Several reports have been published during the
to carry out elution in expanded bed mode in order
last few years describing the adsorption process of
to avoid excessive back pressure. Furthermore, since
expanded bed adsorption (Chang and Chase, 1996b;
2
elution in expanded bed mode minimises contact be viscosities of the elution buffers are given in Table I.
tween the adsorbent particles it will help prevent bead Elution liquid velocities were nominally 100,200 and
aggregation and hence make the subsequent cleaning 300 cm h -1; the actual values are given in the results
in place procedure more efficient. Finally, elution in and discussion section. The distance between the bed
expanded bed mode could facilitate a simpler design surface and the upper adapter during elution in ex
of the expanded bed column through the use of a fixed panded bed mode was in the range of 1-6 cm, unless
upper adapter instead of a movable adapter (Thbmmes otherwise stated. For comparison, experiments were
et aI., 1996). run in which elution was performed in packed bed
In this paper we report data on elution in expanded mode, at liquid velocities of 100 and 300 cm h-1.
bed mode and its effect on the hydrodynamic prop In order to ensure proper function of the adsorbent it
erties of the expanded bed as well as the functional was cleaned in place (CIP) every third or fourth cycle
performance of the expanded bed. by washing with I M NaOH during 30 min contact
time. Some experiments were repeated to check that
the adsorbent behaved in a similar manner between
Materials and methods experiments, (data not shown).
Bed expansion was evaluated by the Richardson
Expanded bed adsorption experiments were carried Zaki equation u=UtEn (Richardson and Zaki, 1954),
out using a STREAMLINE™ 25 column (inner diam where U is the liquid superficial velocity, Ut the par
eter, 2.5 cm) filled with 76 ml STREAMLINE DEAE ticle terminal velocity, E the bed voidage and n the
(Amersham Pharmacia Biotech AB, Sweden), which Richardson-Zaki coefficient. The value of E was cal
corresponds to 15.5 cm sedimented bed height. The culated from H/Ho=(l-Eo)/(l-E) where Ho is the
base matrix in STREAMLINE adsorbents is a highly sedimented bed height, H the expanded bed height
cross-linked 6% beaded agarose containing crystalline and Eo the voidage in the sedimented bed. In this study
quartz to increase the density of the beads. The av a value of 0.4 was used for Eo as determined in earlier
erage density is 1.2 g ml-1. The particle size range published work (Draeger and Chase, 1991; Thbmmes
from 100 to 300 {.Lm with an average size of 200 {.Lm. etaI.,1996).
The ion exchange capacity for STREAMLINE DEAE Mixing in the liquid phase was evaluated by de
is O.I 7±0.04 mmol Cl- per ml adsorbent. The termination of axial dispersion. The axial dispersion
STREAMLINE column is purpose designed for use coefficient, D A, was calculated using D A= u H /2N E
in expanded bed adsorption. It is equipped with a liq (Barnfield Frej et aI., 1997), where U is the liquid su
uid distribution inlet consisting of a perforated plate, perficial velocity, H bed height and E the bed voidage.
which generates the pressure drop necessary to obtain N is the number of theoretical plates calculated as
an even plug flow in the column as there is no pres N = t2/(J2, where t is the residence time and (J2 the
sure drop over the expanded bed. The set-up of the variance. The parameters t and (J were determined
by residence time distribution (RTD) analysis for ex
equipment was as described in Barnfield Frej et al.
(1994) except that conductivity was monitored using a panded bed mode using the positive-step signal from
experiments where 0.2, 0.5 and 1 M NaCl were ap
conductivity monitor (Amersham Pharmacia Biotech
AB, Sweden). All buffer chemicals were of analyti plied as described in Barnfield Frej et ai. (1997). Axial
dispersion was also determined from the conductivity
cal grade. Adsorption was performed in expanded bed
trace of NaCI during elution of BSA in expanded bed
mode using bovine serum albumin (BSA), (Intergen,
Toronto, Canada) at a concentration of 2 mg ml-1 mode.
The Bodenstein number, Bo, was used as a dimen
in 50 mm Tris buffer, pH 8, at 300 cm h-1 liquid
sionless number for describing the axial mixing in a
velocity. The amounts of BSA loaded were 30, 300
and 2100 mg. When 2100 mg of BSA were loaded fluidised bed system (Sofer and Hagel, 1997). It was
calculated as Bo=uH/EDA, where U is the liquid su
a slight breakthrough of protein could be observed,
indicating that the dynamic binding capacity of the perficial velocity, H the expanded bed height, E the
adsorbent was fully utilised. Elution was carried out bed voidage and D A the axial dispersion coefficient.
The peak volume of the eluted peak was measured
using 50 mM Tris buffer containing 0.5 M NaCl. In
at 10% of the maximum peak height.
certain experiments where the hydrodynamics of the
elution process were studied, Tris buffer containing
0.2 or 1 M NaCl was also used. The densities and
3
Table 1. The effect of salt concentration and liquid velocity on expanded bed height, degree of expansion and hed porosity
Buffer Density Viscosity Liquid Expanded bed Degree of Bed porosity E
(kg m-3) (Pa s) velocity height expansion (-) (-)
(cm/h) (cm)
50 mM Tris 999.7 1.0l5e-03 0 15.5 0.40
50 mM Tris 999.7 1.015e-03 107 25.6 1.64 0.63
20S 33.5 2.15 0.72
309 42.1 2.70 0.7S
50 mM Tris+0.2 M NaCl 1006.4 1.021e-03 107 25.7 1.65 0.64
20S 35.2 2.26 0.74
309 46.7 2.99 O.SO
50 mM Tris+0.5 M NaCI 101S.7 1.04Se-03 104 25.9 1.67 0.64
200 35.1 2.26 0.73
299 4S.0 3.10 O.SI
50 mM Tris+ 1.0 M NaCl I03S.6 1.094e-03 104 26.7 1.72 0.65
20S 37.5 2.42 0.75
302 52.S 3.23 O.SI
Results and discussion 55
50
The elution of ion exchange adsorbents is commonly
performed either by increasing the salt concentration 45
or by changing the pH of the elution buffer. In the case
40
E
of changing pH, the change in physical parameters,
~
like density and viscosity, which will affect the perfor :J: 35
mance of the expanded bed, are very minor. However,
30
the addition of salt to the elution buffer will signifi
cantly change these parameters. To study the effects 25
of different elution buffers on bed expansion and axial
20
dispersion three elution buffers, containing 0.2, 0.5 50 100 150 200 250 300 350
and 1 M NaCI were evaluated. Elution experiments U (em/h)
were carried out using three different loads of BSA in Figure 1. The influence of liquid velocity and salt concentration on
order to study the effects on mixing in the liquid phase expanded bed height. NaCI concentrations: (e) 0 M; (0) 0.2 M; (T)
0.5 M; (Il) 1 M.
and on the volume of the eluted peak in relation to the
concentration of the sample being eluted. Elution of
BSA from the adsorbent was performed using 0.5 M
NaCl only, as that concentration of NaCl was found bed porosity increased from 0.63 in buffer at 100 cm
to desorb BSA quantitatively from STREAMLINE h-1 liquid velocity to 0.81 in 1 M NaCI at 300 cm
DEAE (data not shown). For certain experiments, the h -I. That means that the change in bed porosity under
yield ofBSA in the eluted fraction was determined and a broad range of operational conditions is relatively
it exceeded 95% in all cases tested. small.
One important criterion for the stability of an ex
Bed expansion panded bed is the relationship between the liquid
velocity in the bed and the corresponding void in the
The results from determining the effect of salt con bed. This relationship is described by the Richardson
centration and liquid velocity on expanded bed height Zaki equation. The stability of the expanded bed is
(Fig. I) , degree of expansion and bed porosity are characterised by the value of the exponent n and for
shown in Table 1. These results are in accordance a stable bed it is 4.65 + 19.5dpl D where dp is the par
what could be expected from such measurements. The ticle diameter and D the diameter of the column, if the
4
1,0 5x1G"
•
0,9 (a)
0,8 4x10,6
.2:-
'> 0,7
ti
':c0:> 0,6 i( j) 3x1G" • 0
"0 0,5
Q) «
.r2o 0,4 0 2x10~ ..
Qi ..
0:: 0,3 0
0,2 1x10-6
• ..
0,1
0,0
10 11 50 100 150 200 250 300 350
Time (min) u (em/h)
Figure 3. Axial dispersion for buffer containing different concentra
1,0 tions of N aCI at different liquid velocities. The axial dispersion co
0,9 (b) efficient, D A, was calculated from the RTD measurements obtained
0,8 from the conductivity trace of the salt front. NaCI concentrations:
.2:- (e) 0.2 M; (0) = 0.5 M; (~) I M .
'> 0,7
U
::> 0,6
'c0
0(QJ ) 0,5 of the bed when using different salt concentrations in
.2
ro 0,4
the eluent; and for determining the mixing during elu
Qi
0:: 0,3
tion of BSA. The formula used for calculation of the
0,2
axial dispersion coefficient was suggested by Leven
~ •
0,1 •
spiel (1972) but its use for accurately describing the
0,0
0 10 11 12 dispersive mass transport in chromatographic beds has
Time (min) been questioned (Sofer and Hagel, 1997). It should be
Figure 2. Fitting of experimental data from RTD measurements of pointed out that the dispersion coefficients presented
the conductivity trace of the salt front during elution in expanded
might contain contributions from effects, which results
bed mode. The variance was calculated between the relative con
from the actual experimental conditions. Such contri
ductivities 0.158 and 0,842 (indicated by arrows). (A) Sample load,
300 mg; elution at 300 cm h-I liquid velocity; (8) sample load, butions might originate from changes in bed expansion
2100 mg; elution at 300 cm h-I liquid velocity. (e) Experimental and/or mixing effects due to changed viscosity in the
values; (-) Gaussian fit.
tracer pulse. However, this approach has shown to be
valuable for monitoring hydrodynamic properties dur
particles Reynolds number is less than 0.2 (Richardson ing scale-up of packed bed chromatography, where the
and Zaki, 1954). Under the experimental conditions running conditions are quite similar between different
used in this study an optimal value of n should be 4.8. experiments (Sofer and Hagel, 1997). The importance
In this investigation the values of n varied between 4.5 of using a correct model for measuring the axial dis
and 5.7 and there was no significant difference if the persion has been described by Swaine and Daugulis
measurements were taken in Tris buffer alone or in (1988). Fig. 2 shows the fitting of experimental data
the presence of a salt-containing buffer. The observed for the relative conductivity in the salt front in compar
values of n are in accordance with values reported ear ison with a Gaussian distribution. The results obtained
lier for STREAMLINE adsorbents (Chang and Chase, show a good correlation to the expected theoretical
1996b; Karau et aI., 1997). These results show that values. It was estimated that cr2could be calculated
the bed behaved as a stable expanded bed both in with an accuracy of ±5% of the theoretical value.
buffer and in the presence of NaCI in concentrations The effects of viscosity and density of the liquid on
appropriate for elution of proteins from ion exchange axial dispersion at different liquid velocities is shown
in Fig. 3. As can be seen, the axial mixing increases
adsorbents.
with increased liquid velocity, a behaviour which has
been reported earlier (Dasari et aI., 1993; Goto et
Axial dispersion
aI., 1995). It is also clear that increased viscosity and
The use of the axial dispersion coefficient was two density of the liquid result in a decreased mixing in
fold: as a measure of the mixing in the liquid phase the liquid phase, e.g., compare the lower axial disper-
5
16x10-6 Table 2. Bodenstein numbers for different sam-
ple loadings determined for two ranges of liquid
14x10-6
velocities
12x1Q-6
10x10-6 Sample load (mg) Liquid velocity Bo (-)
"' (cmh-I)
N.s- 8x10-6
0< 6x10-e 0 104 161
4x1il-' 0 299 167
2x10-6
30 109 175
30 305 204
50 100 150 200 250 300 350
II (rom/h) 300 110 103
Figure 4. Axial dispersion in the zone of eluted protein during elu
300 303 61
tion in expanded bed mode at different liquid velocities and loads
of BSA. The axial dispersion coefficient. D A, was calculated from
RTD measurements of the conductivity trace of the salt front. Elu 2100 114 124
tion was performed in 50 mM Tris buffer containing 0.5 M NaCI. 2100 305 31
Sample loads: (e) = 0 mg; (0) 30 mg; (T) 300 mg; (v) 2100 mg.
sion for 1 M NaCl with that for 0.2 M NaCl. This is sample loads (30 mg protein) there is no significant
contrary to the observations described by Chang and change between the axial dispersion coefficient ob
Chase (1996b) studying mixing in expanded beds in tained with protein present and that obtained without,
the presence of high concentrations of glycerol, where i.e., eluent alone, at the liquid velocities tested. That
they found increased mixing with increased viscos behaviour is expected as the average protein concen
ity of the liquid. The most possible explanation for tration in the eluted peak is low (0.3-0.5 mg ml-I)
these different observations, are differences in how the and the corresponding increase in viscosity and den
experiments were performed. In this work, the RTD sity will not cause any disturbance in the liquid zone.
data were calculated from the salt front when buffer However, at increased sample loadings, and hence in
containing salt was introduced into a bed expanded in creased protein concentration in the eluted peak, there
buffer only. Chang and Chase (1996b) on the other is a significant increase in axial dispersion. This in
hand used acetone as tracer in the solution used for creased mixing is directly dependent on the liquid
expansion of the bed. In this work axial dispersion velocity. At a low liquid velocity (l00 cm h -I) there
was thus measured when changing from one solution is no difference in axial dispersion for different BSA
to another, in the case of Chang and Chase (1996b), concentrations in the eluted peak compared to axial
axial dispersion was measured in a bed already ex dispersion for the eluent alone, even if the average
panded in a solution with high viscosity and density. BSA concentration in the eluted peak is 14 mg ml-I .
Values for the axial dispersion coefficient in the range On the other hand, at higher liquid velocities (300 em
of 1-5x lO-6 m2 s-I have also been reported by oth h-I) there is a 7-fold increased in the axial dispersion
ers using similar conditions (Batt et aI., 1995; Chang coefficient.
and Chase, 1996b; Karau et aI., 1997; Lindgren et The Bodenstein number, Bo, was calculated in
aI., 1993). From these data it can be concluded that order to compare mixing in the liquid phase in the ex
an increase in viscosity and density of the desorption panded bed with data obtained by Karau et aI. (1997).
eluent will not introduce any additional mixing in the The results are shown in Table 2. These Bodenstein
expanded bed when elution is performed in expanded numbers obtained in this study are higher than those
mode. obtained by Karau et al. (1997) where Bo numbers of
More interesting is how axial dispersion is affected 80-100 were reported for STREAMLINE DEAE run
by the presence of protein in the salt front, as in a at liquid velocities ranging from 180 to 540 cm h -I us
real situation when a protein is eluted from adsor ing a bed with a sedimented bed height of 14 cm. One
bent. The results from such experiments are shown explanation for this difference might be that a column
in Fig 4. From these data it is clear that both sample of different design (e.g., liquid distribution inlet) was
load and liquid velocity affect axial dispersion. At low used in the study by Karau et al. (1997). They also