Characterization Of Nanofiltration Membranes Research Articles

Preparation and Characterization of Nanofiltration Membrane for Recycling Alcoholic Organic Solvent

Preparation and Characterization of Nanofiltration Membrane for Recycling Alcoholic Organic Solvent

Preparation and Characterization of Nanofiltration Membranes Synthesized by Hyperbranched Polyester and Terephthaloyl Chloride (TPC)

Thin-film composite (TFC) nanofiltration (NF) membranes were developed by terephthaloyl chloride (TPC) crosslinked the hydroxyl ended groups of hyperbranched polyester (HPE) on polyacrylonitrile (PAN) support. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that a thin layer of crosslinked HPE molecules were deposited on PAN porous membrane surface successfully. The preparation conditions were also optimized. The separation performance of PAN-HPE-TPC NF membranes are mainly related with the concentration of monomer in the aqueous phase rather than that in the organic phase. Water permeability and salts rejections of the membranes were measured. The flux and rejection of these NF membranes for Na2SO4 (1 g/L) reached 11.43 L/m2h and 96.5% under 0.6 MPa, respectively. At the same time, the nanofiltration properties were compared with other membranes prepared with hyperbranched polymers. All NF membranes prepared with hyperbranched polymers showed relative high permeate flux.

A method for characterizing membranes during nanofiltration at extreme pH

This work presents a method for molecular weight cut off (MWCO) characterization of nanofiltration membranes, in a broad range of acidic and alkaline environments. Polyethylene glycols (PEG) have been identified as suitable marker molecules with sufficient chemical stability under the harsh conditions of interest. PEG molecular weight distributions have been analyzed using gel permeation chromatography (GPC). To allow quantitative GPC analysis, a protocol is presented to overcome the problem of an overlapping salt peak in the GPC elugram. The method is applied to a well-known commercial nanofiltration membrane (NF-270, DOW FILMTEC™) in the pH range 2–12. This membrane has similar MWCO (∼270 g mol −1) and permeance (∼10 L m −2 h −1 bar −1) in acid environment and at neutral conditions. At pH = 12 a reversible increase was observed for the MWCO (∼380 g mol −1) and the permeance (∼12 L m −2 h −1 bar −1). This demonstrates the added value of our method to observe the change of MWCO as a function of pH during nanofiltration at the relevant conditions.

Preparation and characterization of nanofiltration membranes by coating polyethersulfone hollow fibers with sulfonated poly(ether ether ketone) (SPEEK)

A new type of nanofiltration membrane is reported based on coating a sulfonated poly(ether ether ketone) (SPEEK) layer on top of a polyethersulfone support. The membranes were characterized by dextran mixtures, salt solutions as well as negatively charged dyes. The SPEEK coated nanofiltration membranes showed molecular weight cutoff for dextran in the range of ultrafiltration, however, rather high rejection for sodium sulfate; retention for salts in the order of R N a 2 S O 4 > R NaCl > R MgC l 2 ; in addition, the membranes showed a 97–100% retention to the organic dyes. The rejection rates were improved by an increase in the coating thickness and the polymer concentration in the coating solution at the penalty of permeability decrease. Furthermore, it was found that pore penetration of SPEEK into the support membrane effectively constrained the swelling rate of SPEEK and increased the retention. The Donnan–Steric Pore Model was used to describe the transport properties of the membrane. Modeling identified a very tortuous passage within the active separation layer.

Physico‐Chemical Characterization of Nanofiltration Membranes

This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly.

Characterization of nanofiltration membranes by their morphology, charge and filtration performance parameters

Characterization of nanofiltration membranes by their morphology, charge and filtration performance parameters

Characterisation of nanofiltration membranes: Structural analysis by the DSP model and microscopical techiques

The Donnan steric pore model in the simplified and integrated version, proposed by Bandini et al., has been used to obtain the pore size and membrane thickness along with the charge concentration for a PCI nanofiltration membrane (AFC-80). This has been done by fitting the experimental results on retention versus flux for NaCl aqueous solutions. Pore size and equivalent membrane thickness (thickness to porosity ratio) have been confirmed also by fitting for a cyclohexanone solution. Charge has been seen to follow a Freundlich isotherm. The structural parameters fitted by the model showed a good agreement with those obtained from AFM including pore radius, thickness and porosity. Water permeability has also been correctly predicted.

AFM and STM Characterization of TiO2—Ultrafiltration Membranes

Atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) were used to investigate the surface of TiO2 ultrafiltration membranes with pore sizes of 10 nm. It is widely accepted that conventional AFM with Si3N4 or Si tips is not able to resolve pores in supported ceramic membranes with a diameter of <40 nm. In this study it should be tested whether it is possible to lower this border for further characterization of nanofiltration membranes. Here we present different ways of imaging and discuss alternative sample preparation techniques.© 1997 John Wiley & Sons, Ltd.

AFM and STM Characterization of TiO2?Ultrafiltration Membranes

Atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) were used to investigate the surface of TiO2 ultrafiltration membranes with pore sizes of 10 nm. It is widely accepted that conventional AFM with Si3N4 or Si tips is not able to resolve pores in supported ceramic membranes with a diameter of <40 nm. In this study it should be tested whether it is possible to lower this border for further characterization of nanofiltration membranes. Here we present different ways of imaging and discuss alternative sample preparation techniques.© 1997 John Wiley & Sons, Ltd.