Laboratory of Membrane Processes, Bioseparations and Diffusion in Polymers (MEMLAB), section on membranes and packaging
The MEMLAB is an Academic Facility based in the Department of Civil, Chemical, Environmental and Materials Engineering of the University of Bologna. The Lab contains all the experimental devices required to analyze the properties of membrane materials and to test their separation and purification performances, as well as the CO2 capture capacity of solid materials (membranes and adsorbents).
The laboratory equipment allows to assess completely the capture ability of novel and commercial materials used in the capture processes in both post combustion and precombustion schemes, in a wide range of operative conditions in terms of temperature, pressure and gas mixture composition. Most facilities are designed and setup over the past 20 years by the personnel of the Group, according to International Standards regulating the determination of fluid transport properties like Permeability, Solubility, Diffusivity and Selectivity. The MEMLAB is continuously updated with the most recent techniques and development and in the field.
The equipment available at UNIBO covers a wide range of operative conditions and can be used to characterize many different materials and processes. In particular, the lab can characterize polymeric, nanocomposite, ceramic and metallic membranes, as well as solid adsorbents, by means of a variety of apparatuses which cover a thermal range between room temperature and 600°C, pressures from sub-atmospheric up to 50 bar, and relative humidity from dry to saturated conditions. Besides conventional permeability and selectivity testing devices which adhere to the international standards, the instrumentation is complemented with morphological, chemical and structural characterization of the material though FTIR analysis, dilatometry, densitometry. Well-trained personnel with more than 20 years of experience in the field can assist in the preparation and execution of the measurements, as well as in the interpretation of the data and extrapolation of the results to different operative conditions, with appropriate modeling tools. Indeed, the group has developed its own proprietary software based on Classical Thermodynamics for the description of gas and vapors solubility and permeability in any kind of polymeric media, and it makes use of commercial tools such as Molecular Dynamics (Scienomics MAPS®), and CFD (finite volume method) to assess material properties in ranges not experimentally reachable.
Pure gas permeability, permeance, diffusivity and selectivity measurement for membranes
Manometric Closed-Volume, variable pressure pure gas permeometer at controlled temperature and pressure gradient built according to standard ASTM D1434. Working with every fluid substance which is in the vapor or gaseous state at the conditions of interest, and is not hazardous (CO2, He, N2, CH4, Ar, O2, H2O vapor, hydrocarbon vapors, etc.). Temperature range accessible is between 25 and 75°C, while upstream and downstream pressure may vary from vacuum to 10 bar. The instrument can be used to test polymeric and composite membrane films up to about 500 micrometer, and the membrane should have some mechanical resistance.
Different properties can be evaluated with the instrument: pure gas permeability or permeance, diffusivity (by the time-lag method), and ideal selectivity. For the evaluation of permeability and diffusivity, a preliminary measurement of the membrane thickness is required, which can be performed in loco with different devices (for values higher than 10 micrometers). If the thickness is below 10 micrometers, other techniques should be used (e.g. SEM), available by other groups in the same department (DICAM).
The area of the membrane can be as small as 2 cm2 and as high as 10 cm2 with thecurrent membrane cells. The piping system is made of stainless steel with vacuum tight connections (Swagelok VCR, Parker Vacuseal or equivalent), which work also at high pressure. Different pressure sensor of variable full-scale value and resolution are available. Proprietary data acquisition codes written in the Labview® environment are available for automated testing.
3 different versions of the instrument are available:
For Permeance: 5%. For Selectivity: negligible. For Permeability: 5% + relative error on the membrane thickness. For Diffusivity: 5% +2x (relative error on the membrane thickness).
Mixed gas permeability, permeance, selectivity measurement for membranes
Mixed Gas permeometer with cell at controlled temperature and humidity. Working with any fluid substance in the vapor or gaseous phase at the experimental conditions (CO2, He, N2, CH4, Ar, O2, H2O vapor, hydrocarbon vapors, etc.); can also work with hazardous gases (CO, H2) thanks to a dedicated fume hood and gas sensors. Temperature is controlled via a high-power oven (Carbolite), where the cell is located, and can range from 70 to above 250 °C. Upstream and downstream pressure can vary from atmospheric up to 10 bar. Gas flows for both feed and sweep streams are regulated via a digital interface connected to a PC. Three different gases can be fed to the cell at the same time, while a fourth is used as a sweep. Humidity on both upstream and downstream is regulated via liquid flow controllers, which inject a specific amount of water in the gas stream. The composition of each stream can be measured online via a microGC. The system can be employed to test self-standing and composite polymeric membranes with a total thickness of 200 micrometers. Permeability, permeance and mixed gas selectivity can be obtained from a single test at a specific temperature and humidity. In case permeability is tested, the thickness of the film must be previously assessed. This can be done in loco if the value is higher than 10 microns or employing a different technique (e.g. SEM), available from the research groups in the same department (DICAM). The cell requires a membrane with a diameter of 47 mm, but smaller films (up to 10 mm in diameter) may be tested by applying a masking tape (operation conducted in the laboratory). Pipes and connections are in stainless steel (Swagelok).
Measurable permeances can vary from 1 to 10000 GPU (minimum measurable permeance can depend on the gas analyzed). The feasibility of the tests must be evaluated previously, for each specific case.
For Permeance: 10 %, Selectivity: depends on the low permeating gas, Permeability: 10 % + relative error on the thickness measurement.
Sorption and diffusion apparatus for membranes and sorbents (pure and mixed gases)
Closed-Volume, Variable pressure sorption device (“pressure-decay” technique) at controlled temperature and equilibrium pressure. It measures the uptake of every substance both vapors and gases at the conditions of interest, if not hazardous (CO2, He, N2, CH4, H2O vapor, hydrocarbon vapors, etc.). Temperature range accessible is between 25 and 75°C, while equilibrium pressure may vary from sub-atmospheric to 10 bar. The instrument can be used to test the transient and equilibrium gas uptake of solid materials of any shape and geometry: polymeric and composite membrane films of any thickness, powders, microporous materials, pellets, zeolites, MOFs, graphene, graphene oxide, fibers, electrospun networks, ceramics, monoliths, metals, etc. The tests do not require the materials to present any mechanical resistance, and are not destructive.
Different properties can be evaluated with the instrument: gas or vapor solubility or adsorption capacity, sorption kinetics, diffusivity (for specimens of controlled shape and size, es. films). For the evaluation of diffusivity, a preliminary measurement of the membrane thickness is required, which can be performed in loco with different devices (for values higher than 10 micrometers). If the thickness is below 10 micrometers, other techniques should be used (e.g. SEM), available by other groups in the same department (DICAM). Proprietary data acquisition codes written in the Labview® environment are available for automated testing. The piping system is made of stainless steel with vacuum tight connections (Swagelok VCR or Parker Vacuseal or equivalent), which work also at high pressure.
3 different versions of the instrument are available:
Currently the system is calibrated to work with binary CO2-CH4 mixtures and it is coupled to a micro Gas Chromatograph for analysis of gas mixtures. The samples should have sufficient CO2 sorption capacity to be detected; the determination of diffusivity is not feasible in this configuration. These tests allow the direct measurement of sorption-selectivity of membranes and sorbent materials in real conditions.
For Solubility: 5%. For Sorption-Selectivity: negligible. For Diffusivity: 5% +2x (relative error on the membrane thickness).
Membrane preparation in the form of flat sheets and coatings
Polymeric and composite membranes of different nature are prepared by using several different techniques in the form of flat sheets or coatings with homogeneous thicknesses ranging from of 100 nm to 0.2 mm by means of knife and Meyer bars, as well as spin or dip coating. Samples having a calibrated gas permeance can also be prepared.
Other key test instrumentation
Besides MEMLAB, the DICAM department encompasses a group of applied chemists and material scientists, who possess SEM instrumentation, DSC and TGA machines as well as DMTA or tensile tests and other instruments for assessment of the mechanical properties, that allow for a thorough characterization of many types of solid, dense and porous materials.