Reference customers and -projects
Here are some references that Mecadi customers have published to get an impression of the diversity of our work in the field of permeation measurements.
Table of Contents:
Tecnoplast is a manufacturer of PTFE corrugated hoses. Due to the almost universal chemical resistance of PTFE, the hoses are suitable for the fluid transfer of aggressive and corrosive media such as strong acids. For Tecnoplast, Mecadi has tested the acid permeation using concentrated nitric acid (65%) in long-term tests over 125 days. At the customer’s request, the corrugated hoses themselves were investigated, despite the challenge of sealing them for the permeation measurement. As a result, however, statements on the pass-through time with complex geometry were possible without extrapolation, and possible influences on the production of the permeation could be taken into account. A passage of nitric acid at room temperature occurs only after weeks or months. The permeation amounts are in the range of μg per day and running meter hose and must be collected for the permeation analysis. The permeation measuring device had to be protected from light since otherwise algae growth would have reduced the recovery rate in the permeate space. To investigate whether the quasi-stationary permeation is reached, the course of the permeation was examined over time.https://www.tecnoplast.de/downloads/Permeationsuntersuchung.pdf (language German)
Protection of buildings against penetrating gases is one of the specialties of the company PAGeotechnical from England. Plastika Kritis S.A (Crete, Greece) is a manufacturer of PE geomembranes.
A reduction of the gas intake in the basement, in buildings on industrial brownfield-sites or in tunnels can be done by the means of passive protective devices in the form of barrier films. For this purpose, for example, polyethylene sheets or films are used. In the United Kingdom, there are building regulations that provide adequate precautions to avoid risks to health and safety caused by soil contamination that is to be covered by buildings and associated soil. These impurities may be of human or natural origin. Among other things, methane, carbon dioxide, radon or hydrogen sulfide can occur as gases, which then gathers inside cellar spaces. Because of this, the films used should have a low permeation for gases and should be installed without leaks. Sensible limit values for permeation barriers or necessary material thicknesses can be determined by calculation. The necessary data are, depending on the application, explosion limits, odor threshold values, temperatures at which the permeation takes place (temperature distribution over time due to temperature dependence of the permeation), areas, volume, air exchange rates and others.
Gas Separation Membranes
Gas Separation Membranes (Polymeric and Inorganic) is a book published in 2015 which provides an overview of membrane-based separation processes for the separation of gases. After a historical overview and the discussion of the advantages of membrane processes, the fundamental principles of gas permeation through porous and non-porous membranes are explained. Transport models for diffusion in rubbery and crystalline polymers and others are reviewed. Membranes of different materials and structures (e.g. mixed matrix membrane, carbon based membrane, asymmetric membrane, liquid membrane, metal-organic framework membrane) and different manufacturing techniques (e.g. phase inversion, multilayer formation, hollow fiber spinning, precipitation by solvent evaporation) as well as the processing to membrane modules and applications are presented. Various membrane characterization methods including advanced methods such as positron annihilation are summarized. The characterization of membranes, test methods for mass transport (permeation, permeability, selectivity), morphology, behavior with temperature change and mechanics are also presented.The book also refers to the technology report that Mecadi has published on the topic of separating carbon dioxide with membranes (http://technologiereport.mecadi.de/) based on scientific papers by Dr. Andreas Konrad. The basic transport equations and measurement methods for the membrane characterization as for the separation with membranes became the technological base of Mecadi GmbH.
Kuraray is a Japanese chemical company, EVAL Europe N.V. is a subsidiary company located in Belgium. Among the specialty polymers that the company produces there are barrier materials with low permeation. For EVAL Europe, Mecadi has tested ethylene vinyl alcohol copolymers (trade name: EVAL™) for their permeability to hydrogen at various temperatures and pressures. These materials are, among other things, known to be good barrier layers against gases (oxygen barrier in food packages or under-floor heating pipes) or as a barrier against solvents (fuels in tanks). For hydrogen as well, EVOH offers a very good gas barrier compared to other thermoplastics, which opens up potential applications for fuel cell applications or energy storage with hydrogen.
The Mecadi measurement values for hydrogen permeation at pressures up to 100 bar and comparative measurements for various thermoplastics are published in the brochure “Eval for hydrogen fuel cell systems” by Kuraray.
German Agricultural Society
The DLG (short for ) is an association of German food and agriculture. In the DLG test center “Technik und Betriebsmittel” at Groß-Umstadt near Frankfurt (main), agricultural and communal engineering as well as agricultural equipment are subjected to practical tests and evaluated for their suitability. In cooperation with DLG, Mecadi has tested films for gas storage on their gas permeability (methane permeation). In the safety regulations for biogas plants of the agricultural liability insurance association, a limit for the permeability to methane is laid down in particular for plastic films of <1000 cm³ / (m² x dx bar) (section 2.4.1). The pressure described by this measuring unit refers to the partial pressure difference of methane and not to the overpressure represent in the bioreactor. A partial pressure difference, which is the driving force for the permeation (through a defect-free film) of 500 mbar (corresponds to 500 hPa) is therefore present with a methane content of 50% (biogas typical: 50-75% methane content). Deviating from this, the absolute pressure difference is the driving force for leakages (defects, interfaces at sealing points). However, biogas plants are normally operated with low absolute pressure differences (a few mbar of overpressure to ambient pressure). The contribution of the permeation for the total loss of methane of a biogas plant can be estimated to be approximately 50% calculated from the limit values for the permeation of the film and the permissible leakage rates (section 1.2.2. Safety rules) (assumption: operation at 2 mbar overpressure, films and leaks on the limit).
The proportion of the permeation becomes even more relevant when it is considered that the permeation is strongly temperature-dependent. That means that a film which has been tested for permeation under laboratory conditions (23 ° C.) has a higher permeation rate in application. The permeation rate doubles when the temperature increases by 10 Kelvin. In case of a mesophilic fermentation, the permeation rates to be expected for the film in contact with the fermenter are about twice as high as at room temperature. In thermophilic processes or in summer climatic conditions and exposure to sunlight, where temperatures up to 70 ° C can be achieved, the permeation is approximately 16 times higher than at room temperature.
The Federal Office for Energy in Switzerland has examined the methane emissions of EPDM gas storage systems and their economic and ecological consequences by Axpo Genesys AG. For this purpose, new EPDM membranes as well as up to 3.5 years aged samples from 10 different biogas plants from different locations in Switzerland were tested for methane permeability under application-conducive conditions (42 ° C) in the Mecadi GmbH laboratory. The results of the measurements did not show a statistically significant increase in permeability for the application period, although there are indications that there is a correlation of the permeation rate of methane through the EPDM film and the exposure of the films to organic acids in the fermenter.
For the application-oriented study, EPDM membranes were measured with respect to their permeability without elongation and 40% elongated. The 40% elongation corresponds to a 2/3-filled hemisphere in plant operation. For this purpose, a permeation measuring cell was modified by Mecadi in such a way that samples could be installed under tensile loading and the permeation measuring device could be tightly closed after application of a uniaxial strain. For the foil thickness and the methane permeability, a linear reciprocal relationship was found, which means for practical purposes, that the percent decrease of the
(At 40% elongation, approx. 22% thickness reduction) corresponds approximately to the percentage increase of the gas permeation.
Model calculations with the permeation data show that the economic effect caused by permeation losses is small and permeation only contributes a small extent (< 10%) to the methane emission of the plants. The effect of the permeation gets more relevant to plant operation because parallel to the methane permeation, a release of odor-intensive gases such as ammonia and hydrogen sulfide also takes place by permeation through the membranes of the plants which are intrinsically “dense”. The ratios of methane to ammonia and hydrogen sulfide permeability are material-dependent and require a separate consideration from material to material.
Technical University of Chemnitz
The Technical University of Chemnitz has investigated the production and characterization of composite membranes from zeolite particles bounded laterally by a polymer matrix. For this purpose, membranes were prepared from zeolites and polymers, “mixed matrix” membranes and tested for their permeability for water vapor and for the gases oxygen and nitrogen with a permeation cell designed by Mecadi GmbH, with a special design for the absorption of membrane samples with porous supports. Compared to water vapor permeability, very low permeabilities of nitrogen and oxygen were found for the membranes. The permeability to water vapor indicates accessible pores and transport through the pore system of the zeolites. The permeability which cannot be measured with the applied methods for the other gases, on the other hand, also indicates a low defect density of the membranes produced. Membrane selectivities (water to nitrogen) of over 1600 were found.
Rommelag® (www.rommelag.com) is a manufacturer of blow-fill-seal systems. In a study, the multilayer Blow-Fill-Seal containers for pharmaceutical packaging were tested for their properties. The aim of the study was to find a simple, fast and sensitive method for the development of OTR (oxygen transmission rate). Full, filled high-barrier containers should be measured and reliable results should be available within 10-20 days. The investigated, water-filled containers have volumes of 10 to 20 ml and contain as barrier an EVOH layer. For the determination of the oxygen permeation, Rommelag compared four methods: displacement with subsequent iodometry (USP), redox indicator with UV-VIS spectroscopy, rapid test with hydrogen (carried out by Mecadi GmbH), oxygen concentration in the gas space above the liquid with laser absorption spectroscopy ,
The oxygen barrier of EVOH is moisture-dependent. The humidity conditioning of the barrier layer, which takes about 10 days, can be measured as a time-determinant in the comparative analysis with hydrogen for the oxygen permeation or gas barrier ranking as a rapid test method, while stationary permeation can be measured after approx. 2 h. The method allows to measure seal seam effects.
The method of determining the oxygen content in the gas chamber by laser spectroscopy was determined as the best method for the application. The method is fast and non-destructive, but assumes that the packaging material is permeable to the wavelength of the laser light used.
Karlsruhe Institute of Technology
Membrane module for separation with membranes
Ms Dr. Anette Franz has worked at the Faculty of Chemical Engineering and Process Engineering of the Karlsruhe Institute of Technology for the Production of Hydrogen with Microalgae. For this work, Mecadi GmbH has designed and manufactured a customer-specific membrane module for the testing of flat membranes for gas permeability.
For experiments on the separation of hydrogen and carbon dioxide, a laboratory apparatus with a membrane module was constructed, in which arbitrary flat membranes can be tested. To determine permeances, selectivities and separation results, the volume flows and compositions of the individual streams as well as the retentate and permeate pressure are measured. Both CO2- and H2-permeable polymer membranes, with varying temperature, retentate pressure and feed composition, were tested. Furthermore, it was possible in the permeation module of the Mecadi to investigate the influence of the flow conditions in the feed channel by changing the volumetric flow and the flow cross-section, as well as the use of flow-reversing materials.
The overall conclusion of the study is that for the economic implementation of hydrogen production by algae, considerable improvements at the biological and process engineering level are necessary. In particular, the photon conversion efficiency of hydrogen by algae so far achieved at laboratory experiments is 1.6 percent far below the theoretical maximum of direct biophotolysis of 11-16%.
The publication is only available as a paper version in German language: ISBN 978-3-8439-1964-7
Hydrogen production with microalgae, process studies on the dynamics of growth, product generation and product gas treatment, Anette Franz, Verlag Dr. Hat, Munich, Germany
University of Saarland
Investigations on the effect of moisture on permeation
Water can act as a plasticizer in polymers with respect to material properties, e.g. permeation and glass transition temperature. For applications where moisture-saturated gases are present and polymers with significant water uptake are used, it is not sufficient to use permeation rates measured under dry conditions to calculate permeation rates. Mecadi has developed permeation cells for the present study.
In the work, due to methane permeation by polyamide and polyethylene mono- and multilayer films were measured by the direct coupling of a gas chromatograph with a permeation measurement cell. Methane permeabilities for single layer films were measured (in each case unit [in cm 3 (STP). mm.d-1 .bar-1 .m-2]: 335 for polyethylene (PE) at 40 ° C., 0.64 for polyamide ( PA) 6 / 6.6 with dry gas and 8.7 for PA 6 / 6.6 with
steam saturated test gas.
By replacing PE with polyamide as a fermenter cover under the operating conditions of 40 ° C (water vapor saturated), methane emissions by permeation can be reduced by a factor of 40.For further information about the article please follow:
TITK – Perfect results from a special permeation measurement
The Thüringische Institut für Textil- und Kunststoff-Forschung e.V. TITK (Thuringian Institute for Textile and Plastics Research) goes back to the Institut für Textiltechnologie der Chemiefasern (ITC), founded in 1954, and has since then developed into an internationally recognized Material Research Institute for Fibre and Polymer Materials. As a link between university, basic research and industrial development, the TITK is also affiliated institute of the TU Ilmenau.
Materials research is the basis of every product development at the TITK. The area of expertise includes polymer materials, with a focus on change and processing of polymers that are chemically produced or derived from nature. The scientific staff of the TITK develops new materials, modifies their properties and functionalizes polymer materials adapted to the specific requirements in different applications.
Task & challenge
Our cooperation with the TITK is mainly affected by the project support over several years. A task therefrom was to measure the permeation of coated films. Challenging was in these non-standard measurements the high sensitivity of the samples, since the barrier nanosheets were not applied within the films, but on its surface. We were dealing here with very low permeation rates here. In addition to the screening of large numbers of samples in pretests, a high measurement accuracy was necessary due to a thin coating of the support film. We had to measure prototypes and sample pretreatment / masking was necessary. Parts of the task package was the determination of water permeation in accordance with ASTM E96, DIN 53122-1 and ISO 15106-1 as well as the measurement of the gas permeability of the sample material for oxygen by the carrier gas method according to ASTM D-3985 and DIN 53380-3.
Dr. Blankenburg from TITK e.V. at the coating plant for the production of flexible polymer solar cells
Thanks to the many years of know-how by Mecadi in the field of permeation special measurements, we have made a project-specific selection of measurement methods. We have done the sample preparation by ourselves. For the actual determination of the permeation rate, we have modified the Mecadi measuring cells for the measurement of sensitive samples. The masking of the samples was also done by ourselves as well as the masking of the seal face with flat gaskets made of soft polymers.
The difficult permeation measurements were carried out with success. Cooperation between TITK and Mecadi in the field of special measurements for films was very efficient and successful.
The TITK brought in this context in its competencies in "Functional thin films", including material development and application in the form of R2R-Coating followed by surface and film characterization, which facilitated the work of the Mecadi team significantly. Joint projects are also planned in the future, in which further permeation measurements about the research field "transparent barrier films for polymer electronics" will be performed.