Advances in Polymer-based Nanostructured Membranes for Water Treatment

Membranes are widely used in industrial separation processes, particularly for gas separation and desalination processes. To develop membrane materials with improved permeability, selectivity can achieve more energy-efficient membrane separations and reduce costs. Since composite membranes offer improved performance, the aim of this research is to develop polymer-based composite membranes with improved performance for gas separation and water desalination applications. First, in order to obtain a composite membranes with high chlorine tolerance, a carbonaceous poly(furfuryl alcohol) (PFA) composite membrane was synthesized at a low temperature carbonation by formation and post-treatment of a thin PFA layer on porous polymer substrates. The carbonaceous PFA membrane exhibits high selectivity and excellent chemical stability in seawater desalination. The low-temperature carbonization method developed in this study is promising for developing a wide range of other carbonaceous polymer composite membranes for water desalination. Next, in order to apply PFA to other applications, understanding the effects of polymerization conditions on the properties of the PFA composite membrane is required. The PFA membrane was fully characterized in terms of microstructure and separation properties. Suitable synthesis conditions for the preparation of PFA composite membranes with smooth surfaces and uniform structure were (1) FA/ H2SO4 molar ratios: 74-300, (2) polymerization temperatures: 80-100°C and (3) solvents: ethanol and acetone. The preparation conditions were also optimized. The PFA composite membrane prepared with a FA/ H2SO4 molar ratio of 250, a polymerization temperature of 80°C and with ethanol as the solvent exhibited the highest H2/N2 ideal selectivity (αH2/N2=24.9), and a H2 permeability of 206 Barrers. This work led to a better understanding of the effect of the preparation procedures on the membrane performance. In order to investigate the effects of the incorporation of molecular sieve nanoparticles on the membrane structure and membrane performance, silicalite-poly(furfuryl alcohol) (PFA) mixed matrix composite membranes were successfully synthesized based on the best synthesis condition obtained previously. The silicalite-PFA mixed matrix composite membrane with 20% w/w silicalite loading had a high ideal selectivity (αo2/N2= 3.5 and αco2/N2= 5.4) and a good permeability (Po2= 821.2, Pco2= 1263.7, PN2= 233.3 Barrers) at room temperature. This membrane can be a good candidate for oxygen enrichment applications. Finally, in order to investigate the effects of the incorporation of silicalite nanocrystals on the desalination property of polyamide membranes, silicalite nanocrystals were also incorporated into polyamide matrix to synthesize silicalite-polyamide mixed matrix membranes. With an increase in the loading of silicalite nanocrystals, the water flux of silicalite-polyamide mixed matrix composite membranes increased whereas the salt selectivity significantly decreased. The silicalite-polyamide mixed matrix composite membrane prepared from TMC-hexane with 0.5% (w/v) silicalite had water flux of 2.7×10-6 m3/m2·s and NaCl rejection of 50% at a feed pressure of 34.5 bar which 2000 ppm salt solution was used as the feed. The silicalite-polyamide mixed matrix composite membrane is promising for developing high water flux composite membranes for water desalination. In this research, composite membranes with improved permeability, selectivity and chemical resistance were successfully synthesized for desalination and gas separation. For desalination, carbonaceous PFA composite membranes with high chlorine tolerance and silicalite-PA mixed matrix composite membranes with high salt rejection and water flux were successfully obtained. For gas separation, an optimized composite membranes PFA synthesis condition was found and silicalite-PFA mixed matrix composite membranes with high O2/N2 separation were successfully synthesized.

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

Both brackish water desalination and seawater desalination processes are well established and in common use around the globe to create new water supply sources. The farther the location of the source water from the ocean or seashore, the lower the salinity (TDS) of the water and the lower the osmotic pressure that needs to be overcome when desalinated water is produced. This is one of the major reasons that brackish desalination is often considered less costly than seawater desalination. A number of project considerations, however, indicate that seawater desalination can be beneficial and more cost-effective than brackish water desalination. To make a fair comparison, we need to properly compare all major aspects of both types of projects to define the best and most appropriate desalination technology. While brackish water has less feed water TDS, it is more challenging to dispose of the produced concentrate. Also, although brackish water desalination needs less energy to overcome osmotic pressure, it usually requires more energy to draw the water from the well than it takes to pump seawater from the open ocean intake. Another factor is that the temperature of the brackish well water may be lower than the temperature of ocean water, giving seawater desalination an advantage in energy demand. In comparing brackish to seawater desalination, these major aspects should be evaluated: (1) Locations of seawater and brackish water plants, relative to the major consumers of the desalinated water, (2) Transportation (pumping and disposal) costs of the feed water and produced water, (3) Potential colocation of a seawater plant with a large industrial user (e.g., power plant) of the seawater for cooling or other purposes, (4) Produced quality of brackish water and seawater desalination in terms of major minerals and emerging contaminants, (5) Sustainability of the water source: capacity and depth of the brackish water wells, as well as the type of soil. (6) Technical and economic aspects of produced concentrate disposal, (7) Permitting process costs for brackish and seawater desalination, and (8) The economics of both brackish and seawater desalination treatment processes: capital costs, operational and maintenance (O&M) costs, lifetime water cost, and total water cost (TWC). This paper discusses the major evaluation criteria and considerations involved in properly comparing the economic and technical aspects of brackish and seawater desalination to determine the more favorable desalination technology for a given desalination project.

Polyvinylidene fluoride (PVDF)/g-C3N4/Chitosan thin film membranes were prepared by immersing of PVDF/g-C3N4 membrane in solution containing various concentrations of chitosan for removal of Direct Blue 14 dye (an anionic dye) from aqueous solutions. The resulting membranes were characterized by XRD, FESEM, TEM and AFM. Also, pure water flux, salt rejection, water content and antifouling properties of prepared membranes were investigated. The resulting demonstrate that pure water flux was decreased (from 70.98 to 14.7%) by increasing of chitosan concentration (2–4%), while water content (42.5–94.78%), salt rejection (from 62.66 to 88.98%) and antifouling properties were increased. It is found that chitosan has major impact on the membrane structural properties due to transform of the PVDF membrane into hydrophilic ones. It is reported that maximum 93% rejection of Direct Blue 14 was obtained by PCC3 (PVDF/g-C3N4-chitosan 4% w/v) membrane. Compared to the PVDF/g-C3N4 membrane, the experimental results showed that PVDF/g-C3N4/Chitosan membranes demonstrated high potential mainly due to greater hydrophilicity and further minimizing membrane fouling.

Influence of Polyethersulfone substrate properties on the performance of thin film composite forward osmosis membrane: Effect of additive concentration, polymer concentration and casting thickness

The membrane process for industrial application is characterized by a large market profile, such as brackish and sea water desalination, the production of ultrapure water, or hemodialysis and a large number of small market segments in the food, chemical and pharmaceutical industries, analytical laboratories and especially in the treatment and purification of industrial waste water streams (Lonsdale, 1982; Mears, 1976). It is seemed to be difficult to make a reasonably accurate forecast about the future developments of the market for membranes (Strathmann, 2004). However, due to the fact that the environmental problem of Global Warming is increasing drastically resulting in that the demand of industrial water and fresh water with the required quality are steadily decreasing worldwide(Wang, & Hsieh, 2009). There should be a need for energy efficient and affordable processes for the production of high quality water from sea and brackish water sources as well as from waste or polluted surface waters. Since membrane processes have proven to be among the most energy efficient and economic means for this purpose it is quite likely that for the foreseeable future the membrane water purification industry will continue to grow (Hwang, & Kammermeyer, 1975). The growth will also depend on further developments of membranes with improved selectivity and higher fluxes as well as better chemical, thermal and mechanical stability. Long-term experience with their application in large plants will also contribute to increase the useful life of the membranes thus making the processes more reliable and economical (Huang, 1991). The separation of a metal ion from a multi-ionic mixture by selective transport through membrane processes was of importance from both fundamental and practical viewpoints owing to the serious lack of earth resource. For the selective permeation, the desired metal ion in a mixture has to be preferentially absorbed into the membrane phase and then be transported across the membrane phase. Subsequently, such membranes were used for desalination purposes (Helfferich, 1962). An appropriate driving force was essential for an uphill transport resulting in building up of the concentration of the permeating ion across the concentration gradient ( Nobel, 1987). The driving force could be due to difference in pH of the solutions, concentration difference of the permeating species or an electrical potential. The pH difference was generally responsible for the transport in liquid membrane systems,

Water treatment is, collectively, the industrial-scale processes that make water more acceptable for an end-use, which may be drinking, industry, or medicine. Due to the increasingly severe water shortage problem and growing concerns on the water quality, water treatment, which is closely relative to daily life, has always been placed under the spotlight of scientific research so far. Conventionally, water has been treated primarily using physical-chemical treatment such as sand filtration and disinfection. Not only these conventional methods required large area of operations that would require high operational cost, but may also be incapable to treat several persistence pollutants. Membrane separation is a technology which selectively separates (fractionates) materials via pores and/or minute gaps in the molecular arrangement of a continuous structure. Membrane separation has many advantages such as no chemical addition, small operation area, relatively high filtration efficiency, low cost and et al. Not only that, the stringent standard required for water supply and effluent discharge also promotes the innovative development of separation membranes and membrane separation process. Based on the type of material, membranes can be classified into polymeric membranes and inorganic membranes. Despite the fact that some polymeric membranes have already been commercialized and emerged as a favourable filter media for water treatment, there are still several limitations such as relatively low flowrate, low antifouling property and low mechanical properties. Therefore, many additives have been added into polymeric membranes to synthesize polymer-based composite membranes to tackle these problems and to further enhance the efficiency of water treatment. In this thesis, three different types of materials have been chosen as additives to incorporate into microfiltration or ultrafiltration polymeric membranes, aiming to enhance the water treatment performance. The first type of materials is germanate nanowires with different lengths. We for the first time found that the lengths of nanowires play a key role in determining the morphology change and subsequent water treatment performance; thus by controlling the length, we successfully obtains nanowire-enhanced polymeric membranes with fast permeation at the maintenance of rejection. In the second part, we developed a simple, economic and practical method to coat cheap chitosan onto the top of polymeric membranes. Though such membranes show a slight decrease of flux, the rejection, antifouling property and antibacterial property were greatly improved. Theoretical calculation shows that the weakened bonding between foulant and membrane surface resulting from chitosan-grafting is responsible for the improved antifouling property. The third type of material is alumina particles. The main purpose of this part is to study how inorganic particle size and loading affect the morphology change, performance and mechanical property of polymeric membranes with hollow shape. Results show that such inorganic particle/polymeric membranes have higher tensile and compressive properties compared to the pristine polymeric membranes and both particle size and particle loading matters in determining the improvement of mechanical properties. Despite the improvement in mechanical properties, the rejection of such membranes was greatly sacrificed due to the detachment of particles from polymer during the formation of membranes, especially when high-loading micron-sized alumina was used. Therefore, CNTs were further added into high loading micron-sized alumina/polymeric membranes to hinder such detaching effect. Results show that the incorporation of CNTs not only further enhance the permeation and mechanical properties but also the rejection and antifouling property. All in all, in this thesis, we choose three different types of materials and incorporate them into polymeric membranes to enhance the water treatment performance (flux, rejection, antifouling and mechanical properties), offering some useful and practical designing knowledge or methods to the synthesis of high-performance polymer-based membranes for water treatment processes.

The fabrication of new membranes with improved performance for water desalination and other treatment is still an important strategy to overcome worldwide water scarcity and quality problems. In this study, cellulose acetate propionate/halloysite nanotube (HNT) composite membranes were prepared using the phase‐inversion process, applying different concentrations of HNTs ranging from 0 to 0.11 wt%. The composite membranes' physicochemical properties were examined using thermogravimetric analysis, field emission scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and contact angle measurements. A dead‐end filtration system was applied when examining the membranes' performance. The results showed clear improvements in the membrane hydrophilicity, permeability, salt rejection, antifouling, and stability properties with the addition of HNTs. The contact angle decreased from 69° to 38°, while the water uptake increased from 18% to 33%. Moreover, the permeation flux increased from 8 to 23 L m−2 h−1 at 1 bar, corresponding to an improvement of about 188%. The membrane containing 0.08 wt% of HNTs showed the optimal results, exhibiting salt rejection of 85% for sodium chloride and 95% for magnesium sulfate, corresponding to improvements of 109% and 154%, respectively, in addition to an improved flux recovery of 80% determined after 120 minutes.

Fabrication and water desalination performance of piperazine–polyamide nanocomposite nanofiltration membranes embedded with raw and oxidized MWCNTs

Polarization phenomena in integrated reverse osmosis and membrane distillation for seawater desalination and waste water treatment

Sea water desalination becomes more and more important as the consumption of fresh water. Forward osmosis (FO) is a novel technology for sea water or brackish water desalination, where a most important device, semi-permeable membrane, are required low resistance, high selection and inexpensive. In this study, based on molecular dynamic simulations, we explored the performance of porous graphene as the semi-permeable membrane for sea water desalination. Fluorine (F) and nitrogen (N) are adopted to optimize the property of graphene pore. We found that although pure pore have highest water flux (indicating lower resistance), N modified pore has the best selection due to the high electronegativity of N atoms. The about 60 L/cm2/h water flux and 100% solute rejection ratio confirm the graphene with N modified pores is good candidate as a semi-permeable membrane for sea water desalination.

Water pollution comprises all of those compounds that change the quality of groundwater and surface water, therefore reducing the suitability of natural water for human use and other vital processes. These compounds result from human activities, especially those that are industrial, agricultural and domestic.The polyamide thin film composite reverse osmosis membranes become important in desalination of sea water and brackish water or waste water. However the polyamide reverse osmosis membranes tend to fouling due to their hydrophobic and rough surfaces. In this study flux and rejection of waste water from aluminum production industry were obtained during filtration process by using modified commercial composite membranes. Amount of fouling was evaluated with unmodified and modified membranes. Rejection of iron particles and PH of feed and permeate solutions were determined after filtration process. Results shows that modified membranes were performed higher metal ion rejection and antifouling performance than unmodified membranes.

Recent transitions in ultrapure water (UPW) technology: Rising role of reverse osmosis (RO)

Production of ultra pure water by desalination of seawater using a hydroxy sodalite membrane

The role of desalination in bridging the water gap in Jordan