Technical membranes processing, Materials, modification, applications

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1 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 Technical membranes processing, Materials, modification, applications

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3 2 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 individually adapted to suit your needs including long-term strategic partnerships. Individual solutions are elaborated in direct contact 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 services 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 (CO 2, N 2 O) 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 1 Wet-spinning of hollow fiber membranes. 2 Ceramic capillary membrane. Medicine Membranes for medical devices (e.g. dialysis) Membranes for tissue engineering Membranes for cell reactors 2 I 3

4 1 2 3 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 processing of inorganic or metallic slurries and spinning of biodegradable or biocompatible polymers. Asymmetric structures can be obtained by controlling the phase inversion process. 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 equipment. 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 material consumption expensive materials like biopolymers, noble metal-doped materials or valuable ceramics can be used. 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 temperatures between 4-90 C are available. The main focus at Fraunhofer 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. 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. 1 Wet-spinning of hollow fiber membranes. 2 Casting of flat membranes. 3 Electro-spinning of submicron fibers.

5 4 5 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 thicknesses 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. Polymer membranes We develop polymer membranes in flat and hollow fiber geometry. Established processes include: phase inversion for cellulose derivates, polysulfone, polyethersulfone and biopolymers; solvent evaporation for Nafion, sulfonated polyetheretherketone and polybenzimidazole as well as processes for their respective mixtures with hydrophilic agents, conductivity enhancers, inorganic fillers and reinforcements. We have expertise in the replacement of toxic solvents (e.g. NMP, methanol) by non-toxic solvents. 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 capillaries 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 O 2 to N 2 is infinite. Therefore dense perovskite capillaries are of interest as membranes for syngas production (gas partial oxidation), as a provider for pure O 2 or for the oxyfuel process. 4 Mixed-matrix membranes. 5 Supported ionic liquid membranes. Mixed-matrix membranes Mixed-matrix membranes (MMM) are organic-inorganic hybrid materials. The inorganic phase can improve the membrane 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 silanes 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. 4 I 5

6 1 2 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 influenced in a defined manner by etching or plasma polymerization 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 handling of nanoparticle dispersions. We stabilize and functionalize such particles and, equipped with all the necessary infrastructure, 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. Metal-coated membranes After impregnation of the ceramic capillary membranes with noble metal seeds, the membranes can be coated inside or outside 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 miniemulsion polymerization. After elution of the templates nanoparticles 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. 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 dehydrogenation. In addition, we modify our membranes with supported catalysts, e.g. for fuel cell applications. 1 Oleophobic modified membrane. 2 Catalytically active membrane surfaces. 3 Molecular imprinted membranes.

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8 Membrane applications Gas separation Gas mixtures can be separated by different types of membranes. In comparison to the cryogenic methods of gas separation, membranes offer higher gas selectivities and are much more energy-efficient. For hydrogen separation we have developed Pd-coated alumina capillary membranes. If the operating temperature is high, dense perovskite capillaries can be implemented in the process e.g. for oxygen separation from air, CO 2 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 CO 2 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 pressure-retarded osmosis (PRO) or the reduction of fouling in the concentration of landfill leachate. Gas separation: Oxygen permeation through dense perovskite capillaries. Forward osmosis: Model for the energy output of a membrane for pressure retarded osmosis. J(O2) [ml/(min cm 2 )] Module energy output [W/m 2 ] Thickness of Temperature [ C] support layer [μm] 1 Perovskite membrane. 1 Perovskite membrane. Wall thickness 120 µm 180 µm 250 µm Thickness of selective layer [μm] 10,00 7,000 3,000-1,000-5,000-9,000-13,00

9 1 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 porosity for the supply and removal of reactants to low electrical resistance. Of special importance is the interface between catalyst layer and membrane, in our case a speek-based mixedmatrix membrane. To optimize compatibility of these two layers we have developed a screenprint technique with an aqueous speek-based binder system. PEM fuel cells: Control of ethanol cross-over by a modified mixed-matrix membrane for direct ethanol fuel cell. P ethanol [ 10-8 cm s -1 ] Membrane reactors Our membranes can be used to shift thermodynamic equilibria 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 ,0 0,2 0,4 0,6 0,8 1,0 n modifier / m silica [mmol g -1 ] T speek Mixed- [ C] REF Matrix 1 Perovskite 25 membrane Perovskite membrane. 8 I 9

10 1 2 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 hydrophilic to hydrophobic. A broad area of application can be covered ranging from dehydration of alcohols to the concentration 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: isolation, separation and purification of (biotechnical) products by membranes. One approach is the development of affinity membranes by molecular imprinting. Strategies are under development to imprint epitopes of larger proteins for their selective separation. Wastewater treatment The rotating disk filter is a dynamic membrane filter developed at Fraunhofer IGB where the particle layer on the membranes is controlled by means of the centrifugal force field created. This opens the possibility for a low energy wastewater treatment. Another approach is the modification of surface 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 optimized 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 electrolytes 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 signal 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. 1 Rotating disk filter. 2 Medical membrane.

11 Services Membrane development Ceramic, polymer, mixed-matrix, composite membranes Hollow fiber, capillary and tubular membranes Flat sheet membranes Membrane modification (plasma, sol-gel) Contact Dr. Thomas Schiestel Inorganic Interfaces and Membranes Tel 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 Dr. Christian Oehr Head of Interfacial Engineering and Material Sciences Department Tel christian.oehr@igb.fraunhofer.de 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) 10 I 11

12 Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB (Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB) Nobelstrasse Stuttgart Germany Tel Fax Director Prof. Dr. Thomas Hirth Tel 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 economic efficiency and sustainability. Our strengths are to offer complete solutions from laboratory 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 engineering, nanotechnology and industrial biotechnology or wastewater purification. The Fraunhofer IGB is one of 57 research institutes of the Fraunhofer-Gesellschaft, Europe s leading organization for application-oriented research.