Technical membranesprocessing, maTerials, modificaTion, applicaTions

F r a u n h o F E r I n s t I t u t E F o r I n t E r F a c I a l E n G I n E E r I n G a n d B I o t E c h n o l o G y I G B

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fraunhofer igb – parTner for innovaTive membrane developmenT

Technical membranes are the tool of choice for the separation

of complex mixtures. Depending on the various application

areas, special requirements concerning structure, separation

properties and stability must be fulfilled. At Fraunhofer IGB

we develop innovative membranes for various applications in

your business area.

r&d services offer

We offer various forms of cooperation, which can be individu-

ally adapted to suit your needs including long-term strategic

partnerships. Individual solutions are elaborated in direct con-

tact with our customers. We are ready to deal with projects

ranging from short-term literature studies via feasibility studies

through to product development and optimization. Our ser-

vices include analytical characterization of membranes, design

of membrane modules as well as small batch production.

Energy

Membranes for gas separation (oxygen, hydrogen)

Membranes for fuel cells

Membranes for carbon capture and storage

Membranes for biogas

Membranes for pressure-retarded osmosis

Battery separators

Environment

Membranes for greenhouse gas separation (CO2, N2O)

Membranes for wastewater treatment

Membrane sensors

chemistry

Membranes for gas separation (oxygen, hydrogen)

Membrane reactors

Pervaporation membranes

Concentration of bioethanol, -butanol

Filtration of aggressive media

Pharmacy

Membranes for downstream processing

Medicine

Membranes for medical devices (e.g. dialysis)

Membranes for tissue engineering

Membranes for cell reactors

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1 Wet-spinning of hollow

fiber membranes.

2 Ceramic capillary

membrane.

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membrane processing

Wet-spinning of hollow fiber membranes

Hollow fiber membranes offer the advantage of a large specific

separation area. Spinnerets are available to manufacture fibers

with outer diameters in the range of 0.5 to 4 mm and wall

thicknesses from 50 to 500 µm. Our main focus lies in the pro-

cessing of inorganic or metallic slurries and spinning of bio-

degradable or biocompatible polymers. Asymmetric structures

can be obtained by controlling the phase inversion process.

Casting of flat membranes

Flat membranes with thicknesses between 20 and 200 µm

can be manufactured. Both temperature and atmosphere can

be controlled during casting. Precipitation baths with temper-

atures between 4-90 °C are available. The main focus at Fraun-

hofer IGB lies in the processing of mixed-matrix systems. Both

dense and asymmetric porous membranes can be obtained by

solvent evaporation and phase inversion processes respectively.

Melt-spinning of capillary membranes

Hollow fibers (< 0.5 mm), capillaries (0.5 – 3 mm) and tubes

(up to 10 mm) can be processed with our piston spinning equip-

ment. The parameters of extrusion can be varied from RT up to

320 °C and from 1 to 300 bar. Material amounts ranging from

10 to 500 g can be processed to membranes. Due to low mate-

rial consumption expensive materials like biopolymers, noble

metal-doped materials or valuable ceramics can be used.

Electro-spinning of sub-micron fibers

We use electrospinning methods to develop very thin fibers

(50 nm – 10 µm). Electrospun nonwovens can be used as very

open support structures, as porous matrices for the cultivation

of cells or as a filter layer with a good retention for very small

particles. Beside polymeric fibers like PLA pure ceramic fibers

can also be obtained by adding suitable precursors and sintering.

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1 Wet-spinning of hollow

fiber membranes.

2 Casting of flat mem-

branes.

3 Electro-spinning of sub-

micron fibers.

membrane maTerials

Porous inorganic capillary membranes

We have established a wet-spinning process for the production

of asymmetric ceramic capillary membranes. Capillaries with

outer diameters in the range of 0.5 to 4 mm and wall thicknes-

ses from 50 to 500 µm are available. In a first step microfiltration

membranes are obtained which can be further modified by a

coating with selective layers. Beside oxide ceramics also other

ceramics (e.g. SiC) and even metals (e.g. stainless steel) can be

processed. Production capacities range from just a few meters

on laboratory scale to pilot plant application.

dense perovskite capillary membranes

Dense capillary membranes made of different perovskite

compositions can be produced at the Fraunhofer IGB by

means of a phase inversion process. The geometry of the ca-

pillaries can be influenced both by different spinnerets as

well as spinning parameters. High oxygen permeation can be

achieved by these mixed ionic and electronic conducting

materials. Due to the lattice transport of oxygen in the dense

material the selectivity of O2 to N2 is infinite. Therefore dense

perovskite capillaries are of interest as membranes for syngas

production (gas partial oxidation), as a provider for pure

O2 or for the oxyfuel process.

Polymer membranes

We develop polymer membranes in flat and hollow fiber

geometry. Established processes include: phase inversion for

cellulose derivates, polysulfone, polyethersulfone and biopoly-

mers; solvent evaporation for Nafion®, sulfonated polyether-

etherketone and polybenzimidazole as well as processes for

their respective mixtures with hydrophilic agents, conductivity

enhancers, inorganic fillers and reinforcements. We have ex-

pertise in the replacement of toxic solvents (e.g. NMP, metha-

nol) by non-toxic solvents.

Mixed-matrix membranes

Mixed-matrix membranes (MMM) are organic-inorganic

hybrid materials. The inorganic phase can improve the memb-

rane properties such as stability, permeability and selectivity.

The inorganic particles are commercially available or formed

at Fraunhofer IGB via precipitation or sol-gel chemistry. Due to

further modification of the inorganic phase by means of sila-

nes bearing functional groups, tailor-made membranes can be

prepared for various kinds of application (e.g. fuel cells).

supported ionic liquid membranes

Compared to common organic solvents, ionic liquids have

almost no vapor pressure and a high thermal stability up to

450 °C. In combination with (especially ceramic) membranes

as support structure liquid membranes are possible which

are safe from drying out. Different geometries and membrane

materials as well as the huge number of ionic liquids have

the potential for a broad range of applications. One goal is

the development of supported ionic liquid membranes (SILM)

to be applied in waste gas treatment of power plants.

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4 I 5

4 Mixed-matrix mem-

branes.

5 Supported ionic liquid

membranes.

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membrane modificaTion

Plasma modification

Plasma glow discharge is a versatile tool especially suitable

for the chemical surface modification of polymeric membranes.

Using this technique, etching, (regioselective) functionalization

or deposition of a thin film in the nanometer range is possible

with only a very tiny consumption of precursor chemicals. In

this way the pore size of asymmetric membranes can be influ-

enced in a defined manner by etching or plasma polymeriza-

tion to adjust the filtration characteristics or to create a closed

pinhole-free thin film with an adjustable crosslink density to

create a solvent-stable permselective layer for the separation

of organic vapors or solvents.

Sol-gel modification

At Fraunhofer IGB we have longstanding expertise in the han-

dling of nanoparticle dispersions. We stabilize and functionalize

such particles and, equipped with all the necessary infrastruc-

ture, characterize them by laser scattering or zetapotential

measurements, for example. We use such dispersions to adjust

the molecular weight cut-off of ceramic membranes coming

from micro- to nanofiltration membranes. Or we disperse the

particles in polymer solutions leading directly to mixed-matrix

membranes with tailored properties.

catalytically active membrane surfaces

We modify the surface of our membranes with noble metal

precursors. After reductive sintering, membrane surfaces with

a high catalytic activity are obtained. These systems can be

used as membrane reactors e.g. for hydrogenation or dehy-

drogenation. In addition, we modify our membranes with

supported catalysts, e.g. for fuel cell applications.

Metal-coated membranes

After impregnation of the ceramic capillary membranes with

noble metal seeds, the membranes can be coated inside or out-

side with a dense metallic layer like palladium by an electroless

plating process. Such layers can be further modified by less

noble metals like silver, copper or nickel. After tempering alloys

can be obtained which are suitable e.g. for hydrogen separation.

Molecular imprinted membranes

For the specific separation of individual components out of

a substance mixture we develop new composite membranes

consisting of molecular imprinted nanoparticles (so-called Nano-

MIPs) with typical particle sizes of between 100 and 300 nm

acting as effective selectors. For their synthesis, molecular

templates are embedded in the polymer matrix during mini-

emulsion polymerization. After elution of the templates nano-

particles with highly selective binding sites can be used as a

key solution in diverse separation problems arising in the fields

of chemical and biological technology.

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1 Oleophobic modified

membrane.

2 Catalytically active

membrane surfaces.

3 Molecular imprinted

membranes.

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membrane applicaTions

Gas separation

Gas mixtures can be separated by different types of mem-

branes. In comparison to the cryogenic methods of gas sepa-

ration, membranes offer higher gas selectivities and are much

more energy-efficient. For hydrogen separation we have de-

veloped Pd-coated alumina capillary membranes. If the oper-

ating temperature is high, dense perovskite capillaries can be

implemented in the process e.g. for oxygen separation from

air, CO2 capture and storage or catalytic reactions such as

syngas production. A new research field of our group is the

development of membrane-supported ionic liquids for CO

and CO2 separation e.g. from biogas.

Forward osmosis

In forward osmosis (FO) two liquids of different osmotic

pressure are contacted via a semi-permeable membrane.

Water transfers towards the chamber with high osmotic

pressure while solutes are retained. Most current membranes,

developed and optimized for pressure-driven processes, do

not perform in FO due to excessive concentration polarization.

Major applications are the recovery of drinking water from

contaminated water sources, the production of energy from

salt concentration differences (e.g. river to seawater) by pres-

sure-retarded osmosis (PRO) or the reduction of fouling in

the concentration of landfill leachate.

1 Perovskite membrane. 1 Perovskite membrane.

J(O2) [mL/(min·cm2)]

Wall thickness 120 µm 180 µm 250 µm

Temperature [°C]

0750 800 850 900 950

1

2

3

4

6

5

Gas separation: oxygen permeation through

dense perovskite capillaries.

Forward osmosis: Model for the energy output of

a membrane for pressure retarded osmosis.

10,007,000

3,000

-1,000

-5,000

-9,000

-13,00

Module energyoutput [W/m2]

Thickness of selective layer [μm]

Thickness of support layer [μm]

PEM fuel cells

Polymer electrolyte membranes (PEM) consist of ionomer

materials where acidic or basic functionalities account for the

ion flow through the material. Our specialty is the introduction

of an additional inorganic phase into the polymer to enhance

chemical, mechanical and thermal stability and to increase the

barrier function for other substances e.g. fuel, oxidant and

intermediates. We are especially interested in the application

as direct alcohol fuel cell and high-temperature PEM-FC.

Membrane electrode assembly

The membrane electrode assembly (MEA) is the heart of the

fuel cell and combines the membrane and the catalyst in a

complex way. Requirements range from an appropriate poros-

ity for the supply and removal of reactants to low electrical

resistance. Of special importance is the interface between cat-

alyst layer and membrane, in our case a sPEEK-based mixed-

matrix membrane. To optimize compatibility of these two lay-

ers we have developed a screenprint technique with an

aqueous sPEEK-based binder system.

Membrane reactors

Our membranes can be used to shift thermodynamic equi-

libria as in the case of water splitting or to decrease kinetic

hindrance as in the case of greenhouse gas nitreous oxide

splitting. Reactants can be dosed by the membranes e.g. for

selective hydrogenation, or micropollutants can be degraded

effectively.

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1 Perovskite membrane.

1

PEM fuel cells: control of ethanol cross-over by a modi-

fied mixed-matrix membrane for direct ethanol fuel cell.

nmodifier / msilica[mmol g-1]

Pethanol [∙10-8 cm s-1]70

60

50

40

30

20

10

0 0,0 0,2 0,4 0,6 0,8 1,0

T[°C]2540

Mixed-Matrix

sPEEKREF

1 Perovskite membrane.

Pervaporation

Our mixed-matrix membrane approach accounts for an easy

shift of solubility properties by varying functional modifiers.

In this way the membrane properties can be tuned from hydro-

philic to hydrophobic. A broad area of application can be cov-

ered ranging from dehydration of alcohols to the concentra-

tion of alcohols from diluted aqueous solutions (bio-ethanol,

bio-butanol).

downstream processing

Increased standards of product quality and a renaissance of

natural materials for industrial applications require new and

efficient production and processing methods. Fraunhofer IGB

develops solutions for optimized downstream processes: iso-

lation, separation and purification of (biotechnical) products

by membranes. One approach is the development of affinity

membranes by molecular imprinting. Strategies are under de-

velopment to imprint epitopes of larger proteins for their se-

lective separation.

Wastewater treatment

The rotating disk filter is a dynamic membrane filter devel-

oped at Fraunhofer IGB where the particle layer on the mem-

branes is controlled by means of the centrifugal force field

created. This opens the possibility for a low energy wastewa-

ter treatment. Another approach is the modification of sur-

face chemistry and roughness of ultrafiltration membranes to

reduce especially biofouling on the membrane surface. We

have also tested the applicability of NanoMIPs in wastewater

treatment for the separation of pharmaceutical substances

and other micropollutants.

Biomedical applications

We modify your medical membrane device (e.g. for dialysis)

to optimize the contact to body fluids, to separate toxins or to

reduce fouling. The surface of our membranes can be opti-

mized to enhance sticking and growth of cells or to diminish

the adherence of unwanted microbes. To form membranes

from biodegradable polymers is part of our expertise.

sensors

Electrochemical gas sensors can improve the efficiency of

combustion processes significantly. Today common sensor elec-

trolytes are made of organic solvents, which have the great

disadvantage that they evaporate at temperatures higher than

60 °C. Therefore they can only be used in cooled down waste

gas streams. Non-volatile electrolytes, which are safe from

drying out like ionic liquids with a high thermal stability (up to

450 °C), are a promising replacement. Consequently a reduced

reaction time between feed / oxygen controller and sensor sig-

nal is achieved. Our supported ionic liquid membranes (SILM)

for gas separation can be used in gas sensors at temperatures

up to 300 °C, where standard organic solvents would fail.

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1 Rotating disk filter.

2 Medical membrane.

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services

Membrane development

Ceramic, polymer, mixed-matrix, composite membranes

Hollow fiber, capillary and tubular membranes

Flat sheet membranes

Membrane modification (plasma, sol-gel)

Module development

Full ceramic modules

Polymer modules

application studies / lab scale test equipment

Gas separation (RT up to 1000°C)

Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF)

Reverse osmosis (RO), forward osmosis (FO),

pressure-retarded osmosis (PRO)

Pervaporation

Vapor transfer

Membrane characterization

Microscopy (SEM, FESEM, AFM)

Flux, permeability and selectivity

MWCO determination

Pore size and pore size distribution (BET)

Conductivity (ion, electron)

Mechanical properties

Thermal properties (TGA, dilatometry)

Surface analysis (ESCA, XPS, wetting)

Membrane swelling

Membrane degradation

Post mortem analysis (membranes and modules)

contact

Dr. Thomas Schiestel

Inorganic Interfaces and Membranes

Tel. +49 711 970- 4164

thomas.schiestel@igb.fraunhofer.de

Dr. Christian Oehr

Head of Interfacial Engineering and

Material Sciences Department

Tel. +49 711 970-4137

christian.oehr@igb.fraunhofer.de

Fraunhofer Institute for

Interfacial Engineering

and Biotechnology IGB

(Fraunhofer-Institut für

Grenzflächen- und

Bioverfahrenstechnik IGB)

Nobelstrasse 12

70569 Stuttgart

Germany

Tel. +49 711 970-4401

Fax +49 711 970-4200

info@igb.fraunhofer.de

Director

Prof. Dr. Thomas Hirth

Tel. +49 711 970-4400

thomas.hirth@igb.fraunhofer.de

www.igb.fraunhofer.de

Fraunhofer IGB brief profile

The Fraunhofer IGB develops and optimizes processes and products in the fields of medicine,

pharmacy, chemistry, the environment and energy. We combine the highest scientific quality

with professional know-how in our competence fields Interfacial Engineering and Material

Sciences, Molecular Biotechnology, Physical Process Technology, Environmental Biotechnology

and Bioprocess Engineering, as well as Cell and Tissue Engineering – always with a view to eco-

nomic efficiency and sustainability. Our strengths are to offer complete solutions from labora-

tory scale to pilot plant. Customers benefit from the constructive cooperation of the various

disciplines at our institute, which is opening up novel approaches in fields such as medical en-

gineering, nanotechnology and industrial biotechnology or wastewater purification. The Fraun-

hofer IGB is one of 57 research institutes of the Fraunhofer-Gesellschaft, Europe’s leading

organization for application-oriented research.

www.igb.fraunhofer.de