Iranian Journal of Chemical Engineering (IJChE)

Abstract Polymer chains- tethered membranes exhibited a technic to improve membrane surface, and can be commonly used to change the inherent surface physico-chemical properties of materials. So, the grafting of poly(methyl methacrylate) (PMMA) chains onto poly(vinylidene fluoride) (PVDF) substrate was carried out via surface initiated atom transfer radical polymerization (SI-ATRP) at room temperature. Surface coverage and grafting density were controlled by adjusting the  concentration of the initiator. The attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA) results indicated that the PMMA brush was successfully synthesized on the substrates. The study examined the alterations in the physical characteristics of a the PVDF membrane modified with polymer brushes using the scanning electron microscopy. The results showed that PMMA brushes were attached not only to the outer surface of the membrane but also to the surfaces of its pores. Results from the atomic force microscopy and water contact angle measurements confirmed the homogeneous grafting of PMMA chains onto the substrate.

Abstract The polysulfone mixed matrix membranes (MMM) with different concentrations of graphene oxide (0, 0.25, 0.5 wt % of the polymer) are fabricated by a phase separation method. The cross-sectional structures and their upper surface were assessed by the (SEM) surface roughness of the membranes assessed by (AFM). The mechanical and thermal stability of the fabricated membranes were evaluated as well. The separation of Carbon dioxide, nitrogen and methane from natural gas was considered. Also, by increasing the concentration of graphene oxide in the polymer matrix, the thickness of the spongy structure increases and the holes of the finger-like membranes are also destroyed. From the cross-sectional images of the outer surface of the MMM, it was concluded that an active selector layer was created on the lower surface of the membrane. The membrane tensile strength and the length of the membrane at fracture point increased slightly with an increase in the concentration of graphene oxide. Transition Glass temperature of the membrane increased by the addition of graphene oxide to the structure. From TGA analysis, in the presence of graphene oxide, the thermal stability improved. From the gas permeation test, by the addition of 0.25 % of graphene oxide to the polymer, CO₂ permeability was increased from 61.22 GPU to 76.04 GPU, while the addition of 0.5 wt % resulted in a lower permeability (69.55 GPU). The Nitrogen gas permeation flux of membranes decreased from 10.93 GPU to 3.91 GPU by the addition of 0.50 wt % of graphene oxide. The Methane gas permeation flux is reduced from 11.31 GPU to 6.95 GPU and 4.92 GPU by the addition of 0.25 % and 0.50 % of graphene oxide respectively. In conclusion, an increase in the concentration of graphene oxide increased the carbon dioxide selectivity.

Abstract In this paper, the performance of nanofiltration membrane process in removing Pb(II) from aqueous solution was modeled by the pore flow-concentration polarization model. The model was fabricated based on the simultaneous resolving of Extended Nernst–Planck equation(ENP), film theory, and osmotic pressure model. The effects of various operational parameters such as the applied pressure, feed concentration, and cross-velocity on lead Pb(II) ion rejection and solvent flux were investigated. The applied pressure, feed concentration, and cross-velocity varied between 10-50 bar, 5-15 ppm, and 0.2-1.2 m/s, respectively. It was found that lead rejection increased initially and reached the maximum value; then, it decreased with a further increase in pressure, while solvent flux increased linearly within the whole pressure range. This phenomenon is attributed mainly to the developed concentration polarization layer. This effect was significantly decreased with increasing cross-velocity to 1.2 m/s. Ultimately, the proposed model successfully predicted the filtration process in terms of real and observed rejections as well as solvent flux

Abstract Nowadays, forward osmosis (FO) with many advantages in water treatment, are so attractive for researchers and investigators that the studies are going to optimize and increase its efficiency. However one of the most controversial operating malfunctions of FO process is fouling that limits the FO global application. In the following research, vertically aligned carbon nanotube (VACNT) on alumina membrane is introduced with high water permeability and less biofouling potential in forward osmosis for seawater osmotically dilution systems. VACNT membranes were prepared via pyrolysis of polymer into the pores of alumina. The effect of the temperature of pyrolysis process on CNT’s structure are assessed which indicated crystallinity of the CNTs increase in higher pyrolysis temperature of 800 °C. A small scale setup is designed for FO analysis and measurements of biofouling, flux and the effect of osmotic pressure were measured. Furthermore, all analysis were compared with commercial TFC membrane and results demonstrated that VACNT membrane has 40% less biofouling potential and 2 times better flux results.

Abstract > Secondary growth technique was successfully applied for the synthesis of nanostructure sodalite membranes with vacuum seeding on tubular α-Al2O3 supports. In the seeding process, a thin, uniform and continuous seeding layer was closely attached to the support external surface by the pressure difference between the two sides of the support wall. The final nanostructure sodalite top-layers were synthesized on the seeded support into a stainless steel autoclave with a Teflon holder. The effect of seeding time on the microstructure of the synthesized sodalite top-layers was investigated at four different levels 60, 120, 180 and 240 s. The synthesized membranes were characterized by XRD, SEM and mercury porosimetry. The obtained results showed that sodalite zeolite was synthesized on the membranes top-layers with uniform surfaces. But, the top-layers thickness increases by increasing the seeding time and tends to reach a plateau. Further increasing the seeding time causes dense top-layers to form. Also, the performance of the manufactured sodalite membranes was evaluated by permeations of single gases (H2 and N2) under different pressure differences at a temperature of 283K. It is found that the membrane permeance shows a maximum value at seeding time 180 s with a constant permselectivity (H2/N2) of about 2.5. The permeation results were confirmed by SEM micrographs which showed a thick and low-dense top-layer in the membranes manufactured with the seeding time of 180 s.

Abstract Dialysis is a membrane based separation process in which the concentration gradient across the membrane is the driving force resulting in a flow of material from one side of the membrane to the other. In this study membranes (Accurel, Celgard, GVHP, PM30 and PTHK) with different pore sizes were employed to characterise the transport of lithium ion in various (0.01, 0.1, 0.5, 1 and 2.5 w/v percent) initial feed concentrations via the dialysis process. This may be considered as a basis for wastewater treatment containing metal ions. The results show that low initial feed concentration causes less passage of ions through the membrane due to low driving force i.e. concentration gradient across the membrane. The investigation of the effect of membrane pore size on ion transport revealed that large pore size membranes provide less penetration of the metal ions through the membrane. These reproducible results, which are not expected, have been explained by the transport mechanism. Two types of mechanisms (extensive versus intensive) have been suggested for metal ion transport through different membranes. If the mechanism of ion transport is intensive, more ions pass through the membrane. Extensive mechanism results in lower ion transport through the membrane.