Characterization Of Thin Film Composite Membrane Research Articles

Characterization Assessment on Nanofiltration Membrane using Steric-Hindrance Pore (SHP) and Teorell-Meyer-Sievers (TMS) Models

Interfacial polymerization (IP) is a simple process for modifying thin-film composite (TFC) polymers that can be used as separation membranes in water treatment. This work describes the IP process for the preparation of polyester TFC membranes using organic monomers, in particular triethanolamine (TEOA) and trimesoyl chloride (TMC). This work includes an evaluation of monomer concentration and polymerization reaction time as variables to determine the membrane properties and its performance as acid humic removal. The characterization of TFC membranes was investigated using field emission scanning electron microscopy (FESEM), steric hindrance pore (SHP) and Teorell-Meyer-Sievers model (TMS). This IP technique resulted in the membrane (NF-PES8-35) having the lowest contact angle (θ=34.0±0.35) and lower hydrophobicity (θ=62.6 ± 0.33) compared to the unmodified membrane. The rejection of NaCl by NF-PES8-35 membrane showed the highest 0.001 M NaCl (62.42%), while NF-PES4-15 membrane showed the lowest (2.4%). The highest removal of humic acid (97.8%) was achieved when separation was performed with the NF-PES6-35 membrane and the high performance polyester TFC membranes were exhibited in the water purification filtration system.

Experimental and modeling study of CO2 separation by modified Pebax 1657 TFC membranes

Ionic liquid modified Pebax 1657 thin-film composite (TFC) membranes were synthesized on different porous supports for improved separation of CO2 from CH4 and N2. XRD, SEM, FTIR, TGA, DFT, and BJH tests were utilized for the characterization of TFC membranes and supports. The incorporation of 1,3-Di-n-butyl-2-methylimidazolium chloride ionic liquid into the Pebax 1657 solution led to better compatibility between selective layer and support. The results of gas permeation tests showed an enhanced CO2/CH4 and CO2/N2 selectivity for most of the ionic liquid modified TFC membranes. To derive a predictive model for the permeability of gases in TFC membranes, correction factors (β) for fractional free volumes of TFC membranes were linearly correlated against correction factors (α) for porosity and tortuosity of the substrate in the dusty gas model using CO2 experimental permeance data at 20, 60, 100 and 140 °C. The resulting modified model showed remarkable effectiveness in the prediction of permeability of CH4 and N2 in the TFC membrane at investigated temperatures. The comparison of model predictive performance with previous models showed the supremacy of the new model in terms of average absolute relative errors (AARE) and the standard deviation of relative errors (σ).

Preparation and Characterization of Thin-Film Composite Membrane with Nanowire-Modified Support for Forward Osmosis Process

Internal concentration polarization (ICP) in forward osmosis (FO) process is a characteristic problem for asymmetric thin-film composite (TFC) FO membrane which leads to lower water flux. To mitigate the ICP effect, modification of the substrates’ properties has been one of the most effective methods. A new polyethersulfone-based ultrafiltration membrane with increased surface porosity and high water flux was recently produced by incorporating Zn2GeO4 nanowires. The composite membrane was used as a substrate for the fabrication of TFC FO membrane, by coating a thin layer of polyamide on top of the substrate. The substrate and the nanowires were characterized by a range of techniques such as SEM, XRD, and contact angle goniometry. The water permeability and molecular weight cut-offs (MWCO) of the substrate; and the FO performance of the TFC membrane were also determined. The Zn2GeO4-modified membrane showed ~45% increase in water permeability and NaCl salt rejection of 80% under RO mode. In FO mode, the ratio of water flux to reverse solute flux was also improved. However, lower FO flux was obtained which could be due to ICP. The result shows that Zn2GO4 nanowire may be used as a modifier to the substrate to improve the quality of the polyamide layer on the substrate to improve the flux and selectivity, but not as effective in reducing ICP. This work demonstrates that the incorporation of nanomaterials to the membrane substrate may be an alternative approach to improve the formation of polyamide skin layer to achieve better FO performance.

Ion transport in the polyamide layer of RO membranes: Composite membranes and free-standing films

The permeability of the composite ESPA1 membrane to ferro- and ferricyanide ions without and with an excess of supporting buffer was analyzed by three different methods: filtration followed by phenomenological analysis, and electrochemical impedance spectroscopy and chronoamperometry using free polyamide films isolated from the membrane. Appropriate relations were developed that relate the observed permeability to actual permeability of the trace redox ions and correct for concentration polarization of the trace ion in presence of a more concentrated (dominant) electrolyte. Within the uncertainties associated with polarization correction, coupling of ionic fluxes, and ion association in solution and within the membrane, consistent values of permeabilities, of about 0.03–0.05 μm/s, were obtained by all methods. The results validate that (a) the contribution of convection to salt permeation through the active layer of thin-film composite membranes is small; (b) the procedures used to isolate the active polyamide layer from commercial membranes has a minimal impact on the transport properties of the polyamide films; the isolated free films may then adequately represent the properties of the original active layer in characterization studies. This information may have important implications for studying transport, modeling and characterization of thin-film composite membranes.