Polymer Membranes

Research People Equipment Publications

 

Department profile

 

 

Research activity of the department is focused on the innovative membrane separation techniques and membrane applications in energetics. New polymers, designed for the membrane preparation, are synthesized, new membranes are fabricated and their physicochemical properties are investigated. The methods implemented in the department include determination of permeabilities and diffusivities (in dry or swollen state), kinetics and extent of sorption in membranes, gas pycnometry and membrane ion conductivity.

Recently we are participating in the development of new generation of lithium bateries for automotive industry. Our goal is to prepare non-flamabel gel electrolytes based on polymerizable ionic liquids.

Activities include also education of young generation interested in the topic, international cooperation inside of European membrane community i.e. European Membrane Society and European Membrane House, participation in Czech Membrane Platform.

 

Membranes and Membrane Technology

The membrane is a thin semipermeable barrier to mass transport, i.e, some molecules or particles permeate easily through the membrane while others permeate very little or not at all. Membranes are thus often used for the separation of mixtures. Macromolecules and small molecules can be “fitered” from their water solutions and mixtures of liquids or gases can be separated. The key advantages of membrane technologies (compared to the traditional separation processes such as like distillation and absorptions) are less energy demand, minimal environmental impact as no additional reagents are needed, reliability and sometimes higher separation efficiency. The most developed membrane applications include water desalination, wastewater treatment, pure water preparation, ethanol dehydration, gas separations and blood purification by haemodialysis. Membrane processes are important  21st century technologies.

 

 

Gas separation and purification
Gas separation units are nowadays applied in hydrogen separation from ammonia-plant purge-gas streams, nitrogen or oxygen production from air, air dehumidification, syngas ratio adjustments, etc. Besides the well-established applications there are a number of emerging membrane gas separations. These are, for example, natural gas hydrocarbon dewpointing, olefin/paraffin separation and separation of hydrocarbon isomers.
 
In our department we develop new polymeric and (nano)composite materials specially designed for membrane gas separations. Large attention is focused on synthesis of new types of polyimides belonging to the group of “high-performance” polymers. Polyimides exhibit not only excellent separation properties but also very high mechanical, chemical and thermal stability. New polymers are characterized with various techniques including  chromatography, spectral and calorimetric analysis and various microscopic techniques. Gas transport properties are measured in specially designed apparatus with constant volume cell (permeation is calculated from the pressure increase of gas which permeated through the membrane per time unit).
   

A novel method for gas separation and sorption was invented in the department. Gases can be separated from their mixtures using polymer foams with closed cells. Each cell serves as a gas container which is filled through its walls – separation membranes. Foam, as a manifold membrane system, utilizes transient states of permeation thus take advantage of different diffusion rate of each gas. Large scale manufactured polystyrene and polypropylene foams were chosen to demonstrate the phenomenon. The method was designed especially for hydrogen and helium purification. It takes the advantage of fast diffusion of both the gases

 

   
Dynamic “absorption” of hydrogen (green) from gas mixture into a polymer foam bead    “desorption” of hydrogen from the  bead

 

 Membranes for fuel cells and electrolysis  
Wind turbines and solar photovoltaic power plants are nowadays very important sources of electricity. The output of these plants depends however on weather and daytime: either they do not supply the necessary current or they supply it in excess and endanger thus the transmission grid. It is envisaged to use the excess electrical energy for the production of hydrogen by water electrolysis. When needed, the stored hydrogen will be used as a fuel in a fuel cell, in which electric current is again produced.
In the present electrolyzers, the electrolyte is a concentrated solution of potassium hydroxide (a highly corrosive and dangerous material) and an asbestos diaphragm separates produced hydrogen and oxygen. (The uses of asbestos are banned in the EU and the USA, but their application in electrolyzers is temporarily excluded from the ban). At the Institute of Macromolecular Chemistry we develop within the framework of European and Czech projects conductive polymer membranes that will allow to replace asbestos diaphragms and to decrease or fully eliminate the use of potassium hydroxide.
     
Fuel cells Fuel cell is an electrochemical device that directly converts chemical energy into electrical power. On the catalyst, a fuel, most often hydrogen, is split into protons ans electrons. The electrons flow the the external circuit and produce electrical power. The protons permeate through the membrane. At the other side of the membrane electrons, protons and oxygen coming from outside combine to form water. Fuel cells can operate permanently until the supply of hydrogen and oxygen is stopped. At the Institute of Macromolecular Chemistry, polymer ion-exchange membranes for fuel cells are being prepared and studied. In the past, we developed heterogeneous ion-exchange membranes, which are now manufactured in the MEGA Company for the desalination of water solutions. The application of these membranes for fuel cells and for water electrolysis is being studied. Our research also deals with the preparation of homogeneous ion-exchange membranes based both on aromatic and aliphatic polymers. The current research is also focused on the preparation of membranes whose active component is a phosphonic acid group, e.i.the membranes with enhanced stability.
     
Heterogeneous ion-exchange membrane  
Research and development of new materials for ion-exchange membranes improves the properties of heterogeneous membranes and thus extends their utilization in all industrial applications.  The membranes based on new materials are characterized by different methods such as is ion-exchange capacity determination, chemical stability tests, water sorption measurements and mechanical properties determinations. This research is carried out in cooperation with Czech industry. The heterogeneous ion-exchange membranes are manufactured by MEGA company (www.mega.cz) under the trade name RALEX and are used on a large scale in electrodialysis, electrophoresis,  electrodeionization and membrane electrolysis.
   

Molecular characterization of polymers &
Analysis of low-molecular-weight compounds

 
High-quality research of polymers is possible only with good knowledge of their molecular characteristics. Even if the monomer from which the polymer is prepared and which reflects in its name consisted of identical molecules these molecules can connect in a multitude ways given by conditions and reaction mechanism. Properties of the resulting polymer strongly dependent on how monomer units are connected in its molecules especially on the number of interconnected units, i.e. on polymer molecular weight. Not only samples of the same polymer, e.g. polystyrene, with different molecular weight exist but molecules of different molecular weight can be found in the same sample. Probability to find a molecule of the certain molecular weight, i.e. molecular-weight distribution, is characteristic for given sample.

The department has a strong group for determination of molecular-weight distribution of polymers by various separation methods (size exclusion chromatography, field flow fractionation, mass spectrometry) not only for the department but for the whole Institute. Besides service measurements the group deals also with the methodological development, including application of the method to problems of polymer branching or compositional heterogeneity of copolymers.

            Analysis of low-molecular-weight compounds is important for polymer chemistry as well and not only for identification of monomers and verification of their purity. Besides main polymers polymer materials contain also low-molecular-weight additives such as stabilizers or plasticizers, which strongly modify their properties. Pyrolysis, i.e. controlled heat degradation of a polymer, followed by analysis of  products by gas chromatography with mass detection is an intersection of polymer characterization with low-molecular-weight analysis.

 

 Cooperation

The Department of polymer membranes cooperates with industrial establishments in the field of research and development of the new membranes with required properties and realization of new membrane preparation technologies.

     Mega, a.s.
     www.mega.cz
  Company is providing first-class technology and complex services in fields of water treatment, material surface finishing and ecology. It is the producer of the heterogeneous ion-exchange membranes RALEX for electrodialysis, electrophoresis, electrodeionization and membrane electrolysis.
   
  Astris, s.r.o.
  www.astris.cz
  Astris Energi is headquartered in Mississauga, Ontario, Canada, providing intelligent electronic test loads, fuel cell and batteries test equipment and compatible testing software. The Company has a subsidiary in the Czech Republic, Astris s.r.o., that conducts its manufacturing and research of alkaline fuel cells.

 

 

 

 

BIOpolymer POstdoctoral Laboratory and educational center - BIOPOL

Otto Wichterle Centre of Polymer Materials and Technologies - CPMTOW

Centre of Biomedicinal Polymers - CBMP

Centre of Polymer Sensors - CPS

Polymers for Power Engineering - Energolab


 

Institute of Macromolecular Chemistry AS CR, v.v.i.
Heyrovského nám. 2
CZ-162 06 Praha 6
Czech Republic
phone:+420 296 809 111
fax:+420 296 809 410

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