Micro Open Parallel Plate Separator (OPPS): Performance and Applications

Blanca H. Lapizco-EncinasDepartment of Chemical and Materials

Engineering University of Cincinnati

OutlineIntroduction.Objectives.Comparison of separators with rectangular and circular cross sections.Modeling OPPS and equation for reduced plate height. Concentration of trace species by displacementPrediction of equilibrium isotherms for protein-salt systems.Conclusions.

Liquid ChromatographyLiquid Chromatography (LC) is one of the most important techniques used for separating a chemical mixture into its components.

Traditionally, LC was used for analytical applications. LC is now being used in preparative modes.

Preparative Liquid chromatography is used for scaling up separations of fragile substances.

Preparative modes of chromatography are becoming essential for pharmaceutical, biological and environmental applications.

Liquid ChromatographyBench scale system

A powerful separation technique….

solvent

sample column

pump

detector

waste

data acquisition

Micro OPPS: Integration of Column and Detector

Interconnecting metal line

Channel

Silicon

Signal in/out

Outlet reservoir

Outlet nipple

Inlet reservoir

Top glass wafer

Channel

Signal in/out

Outlet nipple

ElectrodeBottom glass wafer

Channel

Bonding pad

Bonding wire

External bonding pad

Signal in/out

Outlet nippleOutlet through

Inlet through

Inlet nipple

H.T. Henderson, N. deGouvea-Pinto, Liquid Chromatograph on a Chip. US Patent 6,258,263B1, July 10, 2001.

Advantages of OPPS

Detectorcell

Bottom of themicrochannel

Electrode

Top view

WallChannel.

[111]

cross-section

[111][111]

Results Obtained with the Proof-of-Concept OPPS

Cur

rent

(mA

)

1.5

1.4

1.3

1.2

1.1

300 305 310 315 320 325 330 335 340 345 350

Cl- Br- SO4- -

Time (s)

Which Geometry is Better for Micro Separators?

lengthdi

amet

er

OPPS OTS

lengthde

pth

width

Objectives The goal of this research was to develop a mathematical

model to describe the OPPS, and through simulations achieve the following specific objectives:

To define the optimal geometry as a function of the separation characteristics. To develop an equation for the reduced plate height of a OPPS. To investigate the device capabilities for concentrating trace species by displacement. To study the potential of the OPPS for predicting isotherm data for protein-salt systems.

HETPThe first goal was to identify the parameters that influence the performance of the OPPS.The performance of the OPPS was evaluated by using the height equivalent to a theoretical plate.

Plate 1

Plate 2

Plate 3

Plate 4

Plate 5

1 m.

HETP = 20 cm

Plate 1Plate 2Plate 3Plate 4Plate 5Plate 6Plate 7Plate 8Plate 9Plate 10

HETP = 10 cm

Numerical Model for OPPSA 3-dimensional model was developed

2

2

2

2

2

2

2222

2222

22

22

3zC

yC

xCD

dzbxdzbx

dbdbv

yC

tC

avg

Vavg

b

dy

z

x

Mathematical ModelVelocity profile (Spangler, 1998):

Initial condition

zxKdbdb

vv vavgy ,6 2222

2222

2222

21

dzbxdzbxKv

0 C(X,Y,Z)=0 10 , 10 , 10

Mathematical ModelBoundary conditions

Condition 1: At X=1tq

xCD

bx

*

Condition 3: At Y=1 01

C

Condition 2: At Z=1 D

Condition 4: At X=0, 00

X

C

Condition 5: At Z=0,

Condition 6: At Y=0, C(X,0,)= Cfeed feed 0C(X,0,Z)= 0 feed

01

C 00

C

Numerical ProcedureFinite differences method.Peaceman-Rachford scheme- Alternating Dimension Implicit (ADI).

11

11

33313122

2

2

22

,,0,,223

1,,

2

mj

mjyn

mkjyn

mkjzz

yyn

mkjxx

ZXdb

ZXSCCRRCR 131

nn tt

132

nt

333131 ,,0,,223

2,,

2 ymkjymkjz

zx

xnmkjy

y SCCRRCR 1n 3

1n 3

11

11

222

2

22

mj

mj

ZXdb

ZX13

1nt

1nt

11

11

33313122

22

22

,,0,,221

,,2

mj

mjy

mkjymkjyy

xxn

mkjzz

ZXdb

ZXSCCRRCR 2n 3

2n 313

2nt

Simulation ParametersThe following dimensionless parameters were used to characterize the performance of the OPPS.

LD

bvavgX

2

LD

dvavgZ

2

D

LvPe

avg

eqdHh

2

bd

X

Z

ba

Existing Models for OPPS and OTS

Giddings et al. developed two models for predicting the reduced plate height of OTS and OPPS.

v r48

11166 2 avgCOTS D

RRh

105

5184352 22avg

eqOPPS

vDb

dRR

h

SimulationsSimulations for the OPPS and OTS were performed using the parameters shown below.The solute was assumed to be KBr ion exchanging on a PEI activated surface.

Feed volume = 4% of the column volume

3 cm

Vavg 0.2 cm/s

C

q*

iii Caq *ai=0.00792 cm

Cfeed= 1000 mol/cm3

10 – 100 m

10-1000 m

Simulations for OTSThe first simulations were performed by using a program for the OTS in order to compare the simulation results with an existing OTS model (Giddings et al., 1983).

0

2

4

6

8

10

12

14

0 20 40 60 80 100OTS radius rC (m)

h OTS

OTS simulator Giddings et al.

v r48

11166 2 avgC

OTS DRRh

Simulations for OPPSSimulations for the OPPS were performed, and the simulation results were compared with Giddings model for OPPS

0

2

4

6

8

10

12

14

0.0 0.5 1.0 1.5 2.0 2.5

X x 102

h OPP

S

OPPS simulatorGiddings et al.

=1

105

5184352 22avg

eqOPPS

v

Db

d

RRh

Simulations for OPPSSimulations for the OPPS were performed changing the depth to width ratio ()

0

2

4

6

8

10

12

14

0.0 0.5 1.0 1.5 2.0 2.5

X x 102

h OPP

S

2

bd

X

Z

Why is the Depth to Width Ratio Important?

Concentration gradients develop along the microchannel width and depth (10 m wide channel)

At one tenth of the channel length

150.6

150.8

151.0

151.2

151.4

151.6

151.8

152.0

152.2

152.4

0.2

0.4

0.6

0.8

1.0

0.20.4

0.60.8

(Con

cent

ratio

n/C

feed

)x10

3

X (w

idth

pos

ition)

Z (depth position)

=1

=100

center of

the channel

48.5

48.6

48.7

48.8

48.9

49.0

0.2

0.4

0.6

0.8

1.0

0.20.4

0.60.8

(Con

cent

ratio

n/C

feed

)x10

3

X (w

idth

pos

ition

)

Z (depth position)

=1

=100

At the END of the channel length

Why is the Depth to Width Ratio Important?

Concentration gradients develop along the microchannel width and depth (50 m wide channel)

At one tenth of the channel length At the END of the channel length

Our OPPS ModelAfter performing a wide range of simulations, an empirical equation for reduced plate height was developed

92.035.0

27.0

37.381.4

XOPPS PePe

h

105

5184352 22avg

eqOPPS

vDb

dRRh

0

2

4

6

8

10

12

14

0.0 0.5 1.0 1.5 2.0 2.5

Our model

X x 102

hO

PPS

Conclusions: HETP EquationIt was proven that reduced plate height models for OPPS can not be developed by analogy with OTS since concentration gradients along the depth influence the chromatographic characteristics.

A reduced plate height equation must include the following parameters: OPPS geometry, flow and adsorption characteristics.

By using the predictions of the OPPS simulator, an empirical equation has been developed for predicting plate height in OPPS.

Lapizco-Encinas, B.H., and Pinto, N.G., Performance Characteristics of Novel Open Parallel Plate Separator, Separation Science and Technology, Vol. 37, No. 12, 2745-2762, 2002.

Concentration of Trace Species by Displacement

Why concentrate trace species?In drug development it is necessary to concentrate samples of pharmaceuticals in order to continue with the experiments.

What is Displacement Chromatography?

Feed

Displacer

sampledevelopment

Product train

Displacement ChromatographyThe ability to separate and concentrate a sample makes displacement chromatography particularly attractive for the enrichment of trace species.Displacement chromatography has been used extensively in analytical applications.Displacement chromatography has an enormous potential for preparative applications since high product-throughput can be obtained by displacement.

Chen, T.W., N.G. Pinto and L. Van Brocklin, Rapid Method for DeterminingMulticomponent Langmuir Parameters for Displacement Chromatography, of Chromatogr., 484, 167 (1989).

Jen, S.C.D. and N.G. Pinto, Use of Sodium Salt of Poly(vinylsufonic acid)as a Low Molecular Weight Displacer for Protein Separations by Ion-Exchange Displacement Chromatography, J. of Chromatogr., 519, 87 (1990).

Jen, S.C.D. and N.G. Pinto, Theory of Optimization of Ideal Displacement Chromatography of Binary Mixtures, J. Chromatogr., 590, 3 (1992).

Jen, S.C.D. and N.G. Pinto, Influence of Displacer Properties on the Displacement Chromatography of Proteins:A Theoretical Study, Reactive Polymers, 19, 145 (1993).

Why Combine Displacement Chromatography with the OPPS?Preparation on conventional bench-scale systems is impractical in cases where the sample amount is limited or expensive. Preparative separations of trace species are often performed using microbore columns: detection sensitivity solvent

consumption.

column capacity pressure-drop.

ObjectivesTo investigate the capability of the OPPS for concentrating trace species.

To make a comparison with OTS, and quantify the performance of the microdevices by using the throughput and pressure drop

To perform a parametric study with the objective of maximizing throughput.

Equations

Throughput was calculated as follows:

jj

nc

j

ii

jj

nc

j

iiii

CK

Ca

CK

CKVmq

11

11*

DFT

S

TTmTH

The Langmuir isotherm model was used for simulating the non-linear behavior:

Comparing OPPS and OTS, Different Pe

0

2

4

6

8

10

12

14

16

18

2.4 2.6 2.8 3.0 3.2 3.4

Time/T0

C/C

F1

tracedisplacer

OTS, Pe = 1.5 x 10 4

0

2

4

6

8

10

12

14

16

18

1.5 1.7 1.9 2.1 2.3 2.5

Time/T0

C/C

F1

trace displacer

OPPS, Pe = 7.5 x 10 4

= 1

0

2

4

6

8

10

12

14

16

18

2.4 2.6 2.8 3.0 3.2 3.4

Time/T 0

C/C

F1

tracedisplacer

OTC, Pe = 7.5 x 10 4

2

4

6

8

10

12

14

16

18

1.5 1.7 1.9 2.1 2.3 2.5

Time/T0

C/C

F1

trace displacer

OPPS, Pe = 1.5 x 10 4

= 1

Comparing OPPS and OTS, Different

Pe x 10

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8 9

- 4

THO

PPS

/ TH

OTS

OPPS, a= 1

OPPS, a= 4

OPPS, a= 9

OPPS, a= 25

Purity = 99%

Channel width or diameter = 50 m

Comparing OPPS and OTS, Different

Channel width or diameter = 20 m

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7 8 9

Pe x 10- 4

THO

PPS

/ TH

OTS

OPPS, a= 1OPPS, a= 4OPPS, a= 9OPPS, a= 25

Purity = 99%b = r C= 10 m

Comparing OPPS and OTS, Different SameP

0

2

4

6

8

10

12

14

16

18

20

0 1 2 3 4 5 6 7 8 9 10 11 12 13

P x 102 (psia)

THO

PPS

/ TH O

TC

OPPS, a= 1OPPS, a= 4OPPS, a= 9OPPS, a= 25

Purity = 99%

Channel width or diameter = 50 m

Conclusions: Concentration of Trace Species

Simulations demonstrated that the rectangular geometry of the OPPS offers advantages over the circular geometry of the OTS for concentrating trace species.

It was proven that the OPPS has an enormous potential for concentrating trace species.

Product throughput increases with high depth-to-width ratios.

Lapizco-Encinas, B.H., and Pinto, N.G., A Comparison of Preparative Characteristics of OPPS and Microbore Columns for Concentration of Trace Species by Displacement Chromatography, in press, Journal of Chromatography A, 2002.

Conclusions: Concentration of Trace Species

Massively parallel OPPS offers significant advantages for high throughput. Silicon wafers can be stacked to create a larger microchannel.

5 stacked wafers make each channel five times larger.

• A single 5 cm wafer can have 1000 microchannels.

• By stacking up wafers we increase the cross-section area which increases the production tremendously.

chan

nel

chan

nel

1 mm

Adsorption IsothermsAdsorption Isotherm expresses the equilibrium between the amount of solute in the mobile phase and the solute adsorbed in the stationary phase.The shape of the adsorption isotherm can determine the chromatographic behavior of the solute.

++ Isotherm data

C

q* == Design of

separation process Product AByproduct B

Prediction of IsothermsIsotherm data are essential for scaling-up chromatographic processes.

The need for accurate equilibrium isotherm data is critical in preparative chromatography.

Traditionally, isotherms are obtained by batch methods, which are time consuming as they require significant amount of chemicals.

Dynamic methods based on chromatography can be used for the prediction of isotherm data with the advantages of higher accuracy and speed.

Why Use the OPPS for Isotherm Prediction

Low sample consumption, an advantage of microsystems, is very significant when dealing with expensive substances such as: proteins, pharmaceuticals, antibodies, etc.

Microsystems allow fast response.

Isotherm data obtained from the OPPS have the potential to be used for scaling up chromatographic operations.

Objectives for Isotherm Prediction

To predict equilibrium data for protein-salt systems by using the H-Root Method (HRM) and the numerical model of the OPPS.

To check the validity of the assumptions made in HRM.

To explore the capabilities of the OPPS as a tool for isotherm prediction.

H-Root MethodHRM was derived from the H-Transformation Theory (HTT) of chromatography (Helfferich and Klein, 1970).

HTT was developed to predict the chromatographic response.

HRM mainly consists of performing a back-calculation of HTT

0

2

4

6

8

10

12

14

16

18

1.5 1.7 1.9 2.1 2.3 2.5

Time/T0

C/C

F1

Operating conditionsLangmuir parameters

HTT

HRM

HRM HRM is restricted to compounds obeying the Langmuir isotherm model.

HRM consists of two main parts: linear elution experiments used to calculate the linear isotherm coefficient ai, and nonlinear frontal experiments to calculate the competitive interference parameter Kmi.

jj

nc

j

ii

jj

nc

j

iiii

CKm

Ca

CKm

CKmVmq

11

11*

HRM CalculationsLinear elution experiments: obtain retention time

Nonlinear frontal experiments: obtain breakthrough time

Time

Con

cent

ratio

n

TR3

TR2

TR1

Time

Con

cent

ratio

n TB3 TB2 TB1

0

0,

T

TTk iRi

linear capacity factor

0

0,

T

TTK iBi

frontal capacity factor

HRM Equations Linear elution experiments: calculation of ai

Nonlinear frontal experiments: calculation of Kmi

iii Caq *

bTTa iR

i

1

0

,

n

i

n

i

ii

KkCFKm

1

011

nj 11

n

i

j

i

j

j

ii

k

k

K

KCFKm

1

1

1

01

1

Simulations

Simulations were carried out for 3 protein-salt systems:1. Conalbumin-NaCl CON-NaCl. -Lactoglobulin-NaCl LAC-NaCl3. Myglobin-NaCl MYG-NaCl

%100%

realpredictedrealdeviation

Linear Elution ExperimentsResults Prediction of ai

iii Caq *

X,NaCl

0%

1%

2%

3%

4%

5%

6%

7%

8%

0 2 4 6 8 10 12 14 16

x 10 4

devi

atio

n p

redi

ctio

n of

ai

CONLACMYGNaCl

Pe NaCl = 1500

Nonlinear Frontal Experiments Results Prediction of Kmi

iii Caq *

-200%

-150%

-100%

-50%

0%

50%

100%

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

X,NaCl x 104

devi

atio

n p

redi

ctio

n of

Km

i

CONLACMYGNaCl

PeNaCl = 150

Conclusions: Isotherm Prediction by Using HRM and OPPS

It was found that operating and geometrical conditions have an effect on the accuracy of the isotherm predictions.

It was found that the HRM has an enormous potential for isotherm prediction under appropriate operating and geometrical conditions.

The application of the HRM is simple and it produces satisfactory results.

Lapizco-Encinas, B.H., and Pinto, N.G., Characterization of Equilibrium Adsorption Behavior of Protein-Salt Systems Using Micro Separators and H-Root Method, to be submitted, Journal Separation Science, 2002.

Concluding RemarksBy using the predictions of the OPPS simulator, an empirical equation has been developed for predicting plate height in OPPS. It was proven that geometry of the separator has an influence on the chromatographic performance.

It was found that that the OPPS has an enormous potential for concentrating trace species since it offers higher throughputs than the traditional circular columns.

Isotherm data were predicted successfully by employing the OPPS and the H-Root Method (HRM). The OPPS offers the advantage of saving time and chemicals. The application of the HRM is simple and it produces satisfactory results.

Questions and Comments