2013 23rd Annual

Practical Membrane / Filtration &

Separations Technologies Short Course

Sponsored by: Food Protein R&D Center at Texas A&M University

Daniel Christodoss, Ph.D., P.E.Principal Municipal Engineer

Urs i&e

(817) 894-1357

Tangential Flow Filtration to Enable High Solids Concentration, Improved Process Throughput,

Capacity, and Cost

What is filtration? Types of Filtration?

Filtration Classification

Introduction to TFF and Applications

Configurations & Operational Concerns

Quality Control and Filtrate Monitoring

Increasing Filtration Rate and FiltrationTheory

Advantages of TFF

TFF Design Principles and Example

Outline

Filtration is the use of a medium toseparate solids from liquid.

The solids can be from the size ofparticles down to cells or cellular tissuedown to individual molecules.

Depending on the filtration mediumchosen as the filter material, selectivecut-off of particle sizes are achieved inthe filtration process.

Filtration

Filtration is usually utilized toconcentrate the material for mineralextraction or purification.

Filtration can provide selectivity basedon size, but not on charge.

Selectivity

Filtration is usually broken down into two primary techniques:

– deadend

– cross-flow filtration

Types of filtration

Deadend filtration is when the feedmaterial is forced through themembrane. The flow is only in thedirection perpendicular to themembrane. All the suspended solids inthe feed end up on the membrane in afilter cake

Deadend Filtration

(Through flow)

In cross-flow filtration the feed materialis allowed to flow parallel to themembrane, while the pressure gradientis across the membrane. The primaryadvantage of cross-flow filtration is thatit allows the solids to be kept insuspension and minimizes the build upof a filter cake to plug or foul themembrane

Cross-Flow Filtration

(Tangential Flow Filtration TFF)

Classification of filtration falls into

several categorizes depending on

the size of the substance being

excluded by the membrane

Filtration Classification

MF, UF and RF

Microfiltrationgenerally refers to the filtration of suspension particle such as cells and cellular fragments

Ultrafiltration is the filtration of macromolecules

Reverse Osmosis is the filtration of molecules such as salts and sugars

MF, UF and RF

1 micron is 1×10−6 of a meter

TFF ApplicationsMicrofiltration and ultrafiltration processes incorporating tangential

flow or cross flow filtration is utilized in a wide range of

biopharmaceutical applications. Examples of a few typical

applications are listed below:

1. Water Desalination and Brackish Water Treatment +

Concentration and desalting of protein, peptide, and

oligonucleotide solutions

2. Purification and recovery of antibodies or recombinant proteins

3. Vaccine and conjugate concentration and diafiltration.

4. Fractionation of protein mixtures

5. Blood plasma fractionation and purification

6. Cell broth clarification, concentration

7. Cell culture perfusion such as in monoclonal antibody (Mab)

production

8. Clarification of Fermentation broths

9. Concentration and washing of bacterial cells

10. Water and buffer purification (endotoxin removal)

In cross-flow filtration (TFF) themembrane does the primary workcompared to the combination of cake andmembrane in deadend cake filtration.The cross-flow allows the membrane tobe swept free of solids allowing for alower resistance to fluid flow through themembrane

Cross-Flow or Tangential Flow

Spiral wound

Hollow fiber

Membrane Configurations

Quality Control

Inline real time photometers are an extremely effective way of monitoring filtration performance to achieve the most efficient and cost effective means of clarifying product as it passes from filtration step to filtration step. Sensors can determine the point at which acceptable purity is achieved or detect filter upset or breakthrough.

Quality Control

Inline photometric control guarantees the clarification of final product. Any deviation can be instantly detected, allowing process changes to be initiated immediately. The photometric system becomes an unsurpassed tool for quality assurance and quality control; thereby, reducing lab analysis, visual inspection and increasing filter system automation.

Quality Control

sensor

sensor

Theory of Filtration

In filtration, solid particles are separated from solid-liquid mixtures by forcing the fluid through a filter medium or filter cloth that retains the particles.

The Filtration rate can be improved either by using a vacuum or pressure.

Filter aides such as Diatomaceous Earth which are highly porous also improve the filtration rate.

Filtration theory is used to estimate the rate of filtration.

Ultrafiltration and Microfiltration Theory

Microfiltration0.1 to 10 µm filter sizesUsed to separate cells

UltrafiltrationMW range 2000 to 500,000 (2 to 500 kilo Daltons (kD))Used to concentrate or sieve proteins based on sizeA thin membrane with small pores supported by a thicker membrane with larger poresLow MW solutes pass through the filter and high MW solutes are retainedPressure driven processCan result in concentration polarization and gel formation at membrane surface

The rate of filtration is usually measured as the rate at which liquid filtrate is collected. Filtration rate depends upon:

1. Area of the filter cloth or membrane2. Viscosity of the fluid3. The pressure difference across the

filter4. The resistance to filtration offered by

the cloth or membrane and deposited filter cake.

�

Theory of Filtration

1. increase the filtration area (A)

2. reduce the filtration pressure drop (membrane cleaning) ∆P decreases α, which causes filtration rate to increase.

3. reduce the cake mass

4. reduce the liquid viscosity (by dilution)

5. reduce specific cake resistance (α)1. Increase porosity

2. Reduce particle size

Increasing filtration rate

UF Cross-Flow Filtration (TFF)

The term cross-flow or TF refers to

the fact that the flow direction of the

retentate is perpendicular to the flow

direction of permeate. The

pressure gradient for the flow is still

across the membrane, while the

retentate is allowed to flow through

the system

Cross-Flow or Tangential Flow

Cross-flow also allows the concentration of the retentate

without the contamination with filter aids. Therefore TFF

can be used to collect either the permeate or the retentate

Advantages of Cross-flow Filtration

Process Goal Cross-

flow

Filtration

Deadend Filtration

Ability to handle

wide variation in particle size

Excellent Generally poor

Ability to handle wide

variations in solids

concentration

Excellent Poor or unacceptable

Continuous

concentration with

recycle

Excellent Poor or unacceptable

Waste minimization Superior Can minimize waste if handling low

solids feed where cartridge disposal

is infrequent

High product purity or

yield

Excellent Performance is generally acceptable

except in situations involving high solids

or adsorptive fouling

Cross-flow Filtration Systems

Many products start out in very low concentrations in the original broth

This requires very high concentration or removal of most of the water from the system

Concentration Factors

Solids effects

TFF System Design

Define the purpose of the TFF process

– The biomolecule of interest in your sample is called a product. Separation can occur by choosing a membrane that retains the product while passing any low molecular weight contaminants.

– Alternatively, a membrane can be chosen that passes the product while retaining higher molecular weight components in the sample.

– It is important to know the concentration factor or the level of salt reduction required in order to choose the most appropriate membrane and system for the process.

TFF System Design

Choose the membrane molecular weight

cutoff

– The molecular weight cutoff (MWCO) of a

membrane is defined by its ability to retain a given

percent of a molecule in solution (typically 90%

retention). To retain a product, select a membrane

with a MWCO that is 3 to 6 times lower than the

molecular weight of the target protein. For

fractionation, select a membrane MWCO that is

lower than the molecular weight of the molecule to

be retained but higher than the molecular weight of

the molecule you are trying to pass.

TFF System Design

Determine the required membrane area for the application

– Choosing an appropriate TFF system depends on

the total sample volume, required process time, and

desired final sample volume.

– Use the following equation to calculate the

membrane area required for processing a sample in

a specified time:

Example 1: What TFF system should I use to concentrate

10 liters to 200 mL in 2.5 hours? Assume the average

filtrate flux rate of 50 liters/m2/hour (L/m2/h, LMH).

Transmembrane Pressure (TMP)

driving force for liquid transport through the ultrafiltration membrane, calculated as the average pressure applied to the membrane minus any filtrate pressure.

In most cases, pressure at filtrate port equals zero.

PRESSURE DROP

DP = (30 - 20) = 10 PSIInlet Pressure minusRetentate Pressure

BASIC TFF APPLICATIONS

Clarification - Product Passes ThroughMembrane, Large Particles Retained

Concentration - Product Retained, SolventPasses Through Membrane

Diafiltration or Buffer Exchange - Product Retained, Solvent Passes Through Membrane with unwanted salts (50%) and New Solvent Added to Product to ultrafilter remaining 50%

FILTER RATINGS

Microfiltration

– Rated by pore size

0.1 - 0.65 Micron

Ultrafiltration

– Rated by size of molecule retained

1,000 - 1,000,000 NMWL

Reverse Osmosis

– Rated by retention of marker ions

NaCl

MEMBRANE CHEMISTY

Microfiltration

– PVDF (Durapore™)

– Polyethersulfone

Ultrafiltration

– Polyethersulfone (Biomax™)

– Regenerated Cellulose (Ultracell™)

Reverse Osmosis

– Thin Film Composite (TFC)

– Polyamide on Polysulfone

UF Membranes

– Conventional with subsurface voids

– New void-free

– composite structure

– (Ultracell™)

Successful Scaleup of a TFF Process

Understanding of the process objectives

purity, yield, times, volumes, concentrations, etc.

Select Correct Membrane

Select Correct Device

Collect Adequate Data to Select Proper Operating

Conditions

Flux vs. Crossflow

Flux vs. TMP

Flux vs. Concentration

Collect Data for Multiple Runs to Prove Robustness