A growing world population is straining our energy supply. This stress is compounded by our reliance on fossil fuels which are finite and contribute to global warming. The mixing of fresh water with sea water (blue energy) is a potential renewable energy source. While the global potential for energy production is significant, the harnessing of this relatively dilute energy source is problematic. 

Membrane processes typically are used to separate gas and liquid mixtures with the input of energy. However, some processes can be operated in a reverse mode to produce energy by mixing fluids instead. Two such processes proposed for energy production from the mixing of fresh and sea water are: Reverse Electro-Dialysis (RED) and Pressure Retarded Osmosis (PRO).

The potential for energy production using RED is discussed. RED utilizes a set of alternating cation and anion exchange membranes to control diffusion along a chemical potential gradient and directly produce electricity. The design and operation of a cell is described and the main sources of inefficiency quantified including the resistances of the ion exchange membranes and the fresh water compartment. Additionally, inefficiencies arise from flow distribution within the cell and the spacers used to create flow channels.

The potential to improve performance through the superposition of concentration and temperature gradients is examined. Additionally, the engineering of a system for energy production from mixing fluids of different salinity is discussed that offers an alternative to photovoltaics for the conversion of sunlight to electricity.

Novel frontiers of membrane technology for power production have recently interested the design and preparation of high-performance Ion Exchange Membranes (IEMs) for Salinity Gradient Power (SGP) production through Reverse Electrodialysis. A part from the standard case of river/sea water, salinity gradients can be found in several other contexts, e.g. when a concentrated brine is available along with seawater (desalination plants, mining industries, saltworks, etc.). In the SGP-RE process, the use of brines determines a number of advantages such as an increase in the driving force and electrical conductivity of both solutions (reducing the stack resistance) and a possible reduction of bio-fouling in brine channels. On the other side, extremely high concentrations can lead to severe IEMs’ performance reduction.

The REAPower project (www.reapower.eu), funded by the European Commission under the 7^th Framework Programme, aims at the improvement and optimisation of the Reverse Electrodialysis technology applied to the case of seawater and brine adopted as dilute and concentrate solutions. Passing through a number of different activities aiming at the 1) development of highly conductive and permselective IEMs, 2) development, testing and optimisation of new stack designs, 3) multi-scale modelling for simulating the fluid flow behaviour within the stack, the process operation and for process optimisation, the project’s final aim will be the design and construction of a pilot scale unit to be operated with brines from the saltworks located in Trapani (Italy).

An insight on the progresses so far achieved will be presented along with an in-depth analysis of perspectives leading to the design and construction of the pilot unit to be installed. Also model predictions will be used to investigate the large potentials for power density enhancement related to the planned development of novel thin membranes, thus highlighting the extreme relevance of project’s outcomes.

In the 21 century, water shortage has become severe due to climate change, rapid industrialization, and population growth (M.N.A. Hawlader et al, 2000). As a consequence, membrane technologies such as reverse osmosis (RO), nanofiltration, ultrafiltration, and forward osmosis have received significant attention as they can contribute to alleviate water stress. Among the available membrane processes, RO is the most widely used because not only is it reliable, established, and proven technology (P.Sukitpaneenit and T.-S Chung, 2012), but RO is also high efficient for water treatment. However, the environmental issues caused by the disposal of concentrated brine and the requirement of high operating pressure hinder further development of RO. Membrane distillation (MD) has been considered as a substitute to current desalination processes due to its advantages. It is less sensitive to fouling and reduces water production costs (i.e., does not need high operating pressure and can utilize renewable energy resources or waste heat). In spite of its benefits, MD is yet to be commercialized as a stand-alone process since it consumes a relatively high-energy for attaining higher temperatures, thereby increasing operating costs (Mohamed Khayet, 2010; Abdullah Alkhudhiri et al., 2011). For these reasons, a hybrid MD process, which combines MD with other technologies, seems to have a high potential to accelerate the commercialization of MD.
This study aims to introduce and characterize the novel concept of a hybrid desalination process, which is the combination of three processes: MD, RO and pressure retarded osmosis (PRO) (referred to as MD-RO-PRO process). The performance of the proposed hybrid process is estimated by using numerical simulations. Based from the initial numerical study, the hybrid MD-RO-PRO process can be considered as a potent process for desalination and hence, its further improvement would be proposed.

We have demonstrated the advantages of polyoxadiazole and polytriazole membranes for fuel cell application and more recently for membrane distillation.  We are able to synthesize polymers with different hydrophobicity/hydrophilicity levels and specific functionalities.  By choosing the right functionality we can tailor processability and solubility. In this form the polymers offer a versatile opportunity to manufacture membranes in broad range of configurations, from dense films (for fuel cell, Gomes and Nunes, J. Membrane Sci. 2008) to flat-sheet and hollow fibers prepared by phase inversion, as well as electrospinning (membrane distillation, Maab et al. J. Membrane Sci. 2012). 

We will now present new results on porous membranes developed for extended applications, for which extreme conditions  like solvent resistance, high temperature, oxidation stability are requested and where polymeric membranes could compete with ceramics. 

Block copolymers (BCPs) are composed of two or more covalently bonded homopolymer chains and they tend to microphase separate due to the thermodynamic incompatibility between the constituent blocks, leading to periodic structures with feature sizes typically in the range of 5-100 nm. When exposed to selective solvents preferential only to the more polar blocks of the BCPs, domains of the polar blocks will be swollen selectively and mesopores form upon solvent removal, while the major, nonpolar blocks in glassy state hold the infrastructure of the BCP material mainly unchanged. We developed mesoporous membranes based on the selective swelling induced pore generation mechanism. Amphiphilic polystyrene-block-poly (2-vinyl pyridine) were coated on water-filled macroporous PVDF supporting membranes, and submerged in a bath of ethanol to generate mesopores in the BCP layer via the selective swelling mechanism, resulting in a composite membrane with the mesoporous BCP as the size-selective layer and the macroporous membrane as the robust supporting layer. The sizes of pores in the BCP layer could be tuned either by changing swelling conditions, e. g. time and temperature, or by using BCPs with different molecular weights. Interestingly, due to the immigration of the polyelectrolyte-natured blocks onto the pore wall, the resulting membranes possess an intrinsically active surface with enhanced hydrophilicity, fouling resistance, and even a stimuli-response function. The membranes were able to discriminate nanoparticles and proteins with similar sizes or molecular weights. Furthermore, by applying a solvent-annealed process to the coated BCP film, membranes with highly ordered, monodispersed pores were obtained after swelling. Such membranes with uniform pores and active surfaces are expecting to exhibit fine-tunable and sharp size-discriminating properties.

Membrane contactor combines the advantages of membrane separation and absorption, and is recognized as a promising alternative to conventional packed columns in CO₂ absorption processes. The most important features of a membrane absorber are: 1) large gas-liquid interfacial area; 2) small footprint and 3) operation flexibility. The separated gas and liquid phases can be adjusted independently without encountering the problems in conventional absorbers (entrainment, flooding or channelling).

Two membrane contactor processes for CO₂ absorption using novel absorbents are reported in this presentation. CO₂ capture from different sources requires different separation conditions. Among them, the conditions in pre-combustion process are most advantageous while challenging: the high operating pressure (~ 20 bars) and high CO₂ concentration (~ 45%) shifted syngas may benefit the process efficiency, while its high temperature (~200^oC) limits most of the commonly used polymeric membranes and CO₂ absorbents. A membrane absorption process using ionic liquids (ILs) is developed to simultaneously purify H2 and capture CO₂ from pre-combustion syngas at the 2nd stage water-gas shift reaction conditions (15-20 bar and around 190-210^oC). Specially tailored ILs is used as absorbents due to their negligible volatility, good thermal stability, high CO₂ sorption capacity and tuneable physical & chemical properties (e.g. viscosity and CO₂ affinity).
The conditions of CO₂ separation from flue gas are also challenging: very large volume of gas with low CO₂ partial pressure. To prevent wetting of micro porous membranes in the membrane contactor, a nanocomposite membrane is developed and carbonic anhydrase (CA) is used as the CO₂ hydration catalyst in aqueous solvent. CA is recently become a research highlight since it is especially beneficial for CO₂ separation from low CO₂ concentration sources.

A novel sulfonated polybenzimidazole (SPBI) membrane has been developed and investigated for pervaporation dehydration of acetic acid, via a two-step sulfonation modification technique—sulfonation with sulfuric acid followed by a thermal treatment at 450 °C. Both steps are found indispensible in order to produce a stable SPBI membrane with enhanced acid resistance and superior separation performance. Effects of the sulfuric acid concentration and thermal treatment duration have been investigated and found to have significant impact on the pervaporation performance of the resultant SPBI membranes. Various characterizations (FTIR, XPS, TGA and XRD) are employed to elucidate the physicochemical changes of membranes as a function of chemical and thermal modifications. In addition, effects of pervaporation temperature and feed composition are studied not only in terms of flux and separation factor, but also of membrane intrinsic permeance and selectivity. The best pervaporation performance of the SPBI membrane has a flux of 207 g/m2h and a separation factor of 5461 for dehydration of a 50/50 wt% acetic acid/water feed solution at 60 °C, which not only outperforms the conventional distillation process, but also surpasses most other polymeric pervaporation membranes reported in literature. It is therefore believed that the novel developed SPBI membrane may have great potential for pervaporation dehydration of acidic organics, as well as other applications that demand acid-proof materials.

Multi wall Carbon Nano Tubes (CNT) are synthesized by physical method and characterized by using UV-Vis spectrophotometer, SEM and were used as Nano composites for polycarbonate membranes. Solution casting and spin coating method was used to prepare CNT composite polymeric membranes of 20 micron. These membranes are subjected to low temperature N2 ion plasma surface modification technique and were characterized by different technique such as SEM- Scanning electron microscope, Fourier transform infrared spectroscopy, AFM- Atomic Force Microscopy, UV-Vis spectrophotometer before and after treatment. These membranes are subjected for a test of bio adoptability and found that plasma treatment modifies the bio-adoptability of membrane and create active site to enhances the bacterial growth. The results of bio-adoptability of membrane are discussed in this paper.

Block copolymer membranes can achieve isoporous morphology with long-range order, suitable for high flux ultrafiltration^1-3. To achieve this morphology the block copolymer is solubilized in a solution mixture that induces self-assembly. This precursor solution already contains a morphological arrangement correspondent to the surface of the membrane⁴. Small Angle X-ray study of diverse compositions of block copolymer solutions provides insight into the morphology and self-assembly of block copolymer micelles. The effect of solvents at different concentrations of block copolymer is clearly shown and related to the final membrane morphology. The use of cryo-SEM microscopy of such solutions is also used to illustrate the self-assembly of the micelles.

References:
[1] Nunes, S. P., Sougrat R., Hooghan B., Anjum D. H., Behzad A. R., Zhao L., Pradeep N., Pinnau I., Vainio U., Peinemann K. V., Macromolecules, 2010, 43, 19, 8079—8085
[2] Nunes, S. P., Behzad A. R., Hooghan B., Sougrat R., Karunakaran M., Pradeep N., Vainio U., Peinemann K.-V., ACS Nano, 2011, 5, 5, 3516--3522
[3] Nunes S. P., Karunakaran M., Pradeep N., Behzad A. R., Hooghan B., Sougrat R., He H., Peinemann K.-V., Langmuir, 2011, 27, 16, 10184—10190
[4] R. M. Dorin, D. S. Marques, H. Sai, U. Vainio, W. A. Phillip, K. V. Peinemann, S. P. Nunes and U. Wiesner, ACS Macro Letters, 2012, 1, 614-617.

We recently fabricated ≈2× 2mm² large area free standing 55 nm thick [001] single crystalline Silicon membranes using a polymer based mask for KOH etching for the first time and achieved low roughness, defect free crystals for ion channeling applications.

However, as the membranes are ultra-thin and having very large areas, they do get bend. We quantified the bend angle, it typically varies by 0.05° for a 25 µm lateral distance nevertheless, they are sufficiently flat to perform ion channeling experiments using a focused MeV proton beam from a nuclear microprobe at the CIBA accelerator laboratory.

After fabrication and characterization of those membranes, we explored axial and planar ion channeling phenomena in the early stage of its motion. Such studies confirm many simulations previously done in the past 25 years and provide experimental evidence to the existence of the super focusing effect, which can then be used in Sub-atomic/nuclear Microscope.

This new fabrication process opens a route to a better understanding of ion channeling phenomena under highly non-equilibrium conditions.

We are looking for other applications (welcome for collaboration) using these ultra thin crystalline membranes.

Clean water, clean energy, global warming and affordable healthcare are four major concerns globally resulting from clean water shortages, high fluctuations of oil prices, climate changes and high costs of healthcare. Clean water and public health are also highly related, while energy is essential for prosperity. 

Among many potential solutions, advances in membrane technology are one of the most direct, effective and feasible approaches to solve these sophisticated issues. Membrane technology is a fully integrated science and engineering which consists of materials science and engineering, chemistry and chemical engineering, separation and purification phenomena, environmental science and sustainability, statistical mechanics-based molecular simulation, process and product design. 

In this presentation, we will introduce our efforts on FO and PRO to solve some of these issues and enhance earth sustainability. Our recent technology breakthroughs on membrane developments for FO and PRO membranes will be highlighted. 

Acknowledgement

This research was funded by the Singapore National Research Foundation under its Competitive Research Program for the project entitled, “Advanced FO Membranes and Membrane Systems for Wastewater Treatment, Water Reuse and Seawater Desalination” (grant number: R-279-000-336-281) and was also supported by the Singapore National Research Foundation under its Environmental & Water Technologies Strategic Research Programme and administered by the Environment & Water Industry Programme Office (EWI) of the PUB. The author would like to thank Prof. D. R. Paul, Drs. K. Y. Wang, N. Widjojo, P. Sukitpaneenit, S. Zhang, Q. C. Ge, M. M. Ling, S. P. Sun, Ms. X. Li, Ms. R. C. Ong, Miss Y. Cui, Ms. H. H. P. Duong, Miss P. Z. Zhong, Miss X. Z. Fu, Mr. G. Han, Mr. P. Wang and Mr. F. J. Fu for their supports and suggestions. Thanks are also due to BASF, Eastman Chemicals and Mitsui Chemicals for their unique materials and final supports.

References:

1. T. S. Chung, X. Li, R. C. Ong. Q. C. Ge, H. L. Wang, G. Han, Emerging forward osmosis (FO) technologies and challenges ahead for clean water and clean energy applications, Current Opinion in Chemical Engineering 1, 246–257 (2012).
2. T. S. Chung,S. Zhang, K. Y. Wang, J. C. Su, M. M. Ling, Forward osmosis processes: yesterday, today and tomorrow, Desalination  287, 78–81 (2012).

Recently, cross-linked polymer networks derived from photodynamic radical-mediated thiol-ene “click” reactions have generated significant interest for diverse applications. Thiol-ene cross-linked polymer networks are formed via a free-radical step-growth process facilitated by a rapid, highly efficient chain-transfer reaction between multifunctional enes and thiols. Thus, the reaction progresses very rapidly and reaches the gel-point at relatively high functional group conversions forming uniform networks. The main advantage of thiol-ene networks is the presence of flexible sulfide bonds, which can lead to flexible membrane hence suitable for applications that require low glass transition temperature and modulus. In order to improve strength, our research focuses on hybrid organic/inorganic membranes – where attributes of thiol/ene functionalized organic and inorganic materials are synergistically combined to improve properties. The talk will focus on synthesis, structure-property relationship of novel membranes prepared using polymerisable ionic liquid and thiol-ene chemistry for energy generation applications.

It is of great significance for membrane distillation to increase permeation flux. A novel membrane distillation process coupled with an asymmetric electrostatic field was designed for a high-flux separation. Providing an asymmetric electrostatic field across a membrane with increasing field intensity in the direction of permeation, water molecules will receive a coupling effect of concentration gradient and electric potential gradient, and thus have a higher permeation flux than that in a conventional process under a single driving force of concentration gradient. Meanwhile transport of salt ions or macromolecules will not be affected by the electric field since they cannot evaporate and permeate through the membrane. To analyze the contribution of electrostatic field on permeation performance, membrane distillation for desalination with a polytetrafluoroethylene microfiltration membrane was investigated. The results showed that water permeation flux could be about twice as high as that of a conventional process without electrostatic field.

A novel food wrapper wherein protease was immobilized on polycaprolactam was studied. Optimum immobilization conditions (namely pH of 8; temperature of 4°C; glutaraldehyde concentration of 0.5%; incubation time of 25 h; and protease concentration of  600μL) for highest activity and stability was standardized.Fourier transform infrared spectrum showed a peak at 1576 cm^-1 which confirmed the presence of -CH=N- , which proved that the protease was immobilized on the polycaprolactam surface. The antibacterial activity and antibiofilm activity of this film was tested against Staphylococcus aureus,Escherichia coli, Bacillus subtilis, Salmonella typhimurium, Aspergillus niger, Fusarium proliferatum and Candida albicans. The modification lowered the colony forming units, biomass, protein and carbohydrate contents in the bacterial and fungal biofilm. The modified film was used to wrap ham steaks and stored at 4 and 20°C for a month. The results showed a 2 to 3 times reduction of Staphylococcus aureus as well as Escherichia coli when compared to samples wrapped with polycaprolactam film, indicating the superiority of this modification.

Materials with anti-fouling properties have received considerable interests for applications in marine, water purification, transport and storage, and biomaterials. Due to the exposure of medical devices to physiologic fluids and tissues, biofouling of surfaces is commonly accompanied by the adsorption of proteins, cells, microorganisms and their metabolic products. The strategies developed for reducing biofouling properties consist of grafting antifouling polymers or self-assembled monolayers onto surfaces. Among all the polymers been explored for this purpose, including polyacrylates, oligosaccharides, and phospholipids, polyethylene glycol (PEG) was the mostly studied molecule for antifouling applications. This study proposed a new route to graft PEG onto the polydopamine coated surface in the combination of azide-alkyne cycloaddition. The substrate surface was firstly alkynated by immobilizing propargylamine onto the dopamine treated surface via its primary amine group. The synthesized mPEG-azide was then clicked onto the alkynated surface with the help of copper-(I) catalysis. This method may provide a new surface modification route for applications in biomedical devices.

Mammalian cell lines have been successfully used for the production of many different therapeutically important biomolecules. Growing demand of many such therapeutic biomolecules necessitate the need of optimizing bioprocess conditions by modification of culture conditions viz  optimization of media components or bioreactor design. Design modifications in bioreactors (for mammalian cell lines) have come a long way from conventional roller bottles, via hollow fiber reactor to disposable bioreactor.

Our research group envisaged the possible application of biopolymeric membrane, as a suitable alternative for culturing anchorage dependent cell lines due to their biocompatibility, non-toxicity and comparatively higher availability compared to synthetic polymers, with a broader vision of their application in disposable membrane bioreactor. In order to answer some such issues of scientific interests, we have studied the growth and proliferation of mammalian cell line on membranes (of abundantly available natural biopolymer) prepared using phase inversion technique. Membranes were characterized for different physiochemical properties such as water holding capacity, swelling percentage, porosity, thickness, intra and intermolecular bonding by FTIR spectroscopy and thermal stability by DSC. The study will pave the way for further research on possible application of biopolymers as an alternative carrier material for different anchorage dependent cell lines.

Keywords: Biopolymeric, cell lines, membrane, bioreactor

The spatial distribution of anions like Cl^- and HCO3^- in cells and tissue is not even and misregulation in their transmembrane transport is a hallmark of the common life-shortening genetic disease cystic fibrosis. In recent years, a large set of genetic diseases has been associated with malfunctioning ion channels and has been brought together under the term channelopathies. Synthetic low molecular weight transport molecules can exert powerful effects on biological systems by mimicking the action of natural ion channels. At present, the few synthetic transporters that have been evaluated for chloride ion transport in epithelial cells have yielded promising results. An immediate goal is to provide lead compounds for channel replacement therapies.

Experience in anion binding of oxacalix[2]arene[2]pyrimidine-based (thio)ureido¹ and selenacalix[3]triazine^2,3receptors let to the design of a completely new class of anion receptors, aryl pyrrole derivatives,⁴ with a particular focus on chloride/bicarbonate selectivity and compatibility with cell membrane lipids. The compounds were analyzed for their anion binding properties and compared to known anion receptors/transporters. In addition, these synthetic anion transporters can be employed in technologies such as membrane-based sensors, separation processes and organocatalysis.

References

1) Van Rossom, W.; Caers, J.; Robeyns, K.; Van Meervelt, L.; Maes, W.; Dehaen, W. J. Org. Chem. 2012,77, 2791–2797.

2) Thomas, J.; Van Rossom, W.; Van Hecke, K.; Van Meervelt, L.; Maes, W.; Dehaen, W. Chem. Commun.2012, 48, 43–45.

3) Van Rossom, W.; Thomas, J.; Terentyeva, T. G.; Maes, W.; Dehaen W. Eur. J. Org. Chem. 2013, Accepted.

4) Van Rossom, W.; Terentyeva, T. G.; Ariga, K.; Hill, J. P. Submitted.

Solid polymer electrolytes have become increasingly attractive because of their technological application in the development of solid state electrochemical devices such as fuel cells, sensors and electrochemical devices. The polymer electrolyte properties such as thermal, mechanical, morphological and electrical properties can be improved at ambient temperature. One of the main objectives in polymer research is the development of polymeric system with high ionic conductivity at ambient temperature with good mechanical and thermal stability properties. Among the various type of polymer poly vinyl alcohol and poly N-vinyl pyrrolidone is a biodegradable and water soluble polymer. PVP is an amorphous polymer possessing high Tg and PVA materials having a high dielectric strength and good storage capacity. The pure polymer electrolyte PVA and PVP has the ionic conductivity found to in the order of 10^-10 and 10^-11 S/cm respectively.

Ascorbic acid is a naturally occurring organic compound  with antioxidant  properties. It was originally called L-hexuronic acid. When it is dissolved in water gives acetic solution. The structure of Ascorbic acids contains four OH group. It is interesting to see the effect of conductivity in Bio-degradable PVA & PVP. PVA and PVP are doped with Ascorbic acids different concentration (0.1 molecular weight percentage to 0.4 molecular weight percentage). It has been observed from impedance analysis as we increase the concentration of ascorbic acids the ionic conductivity is found increase from 10^-10 and 10^-11 to 10^-07 for both PVA & PVP respectively. XRD and FTIR spectrum confirm the complex formation. Dielectric and Modulus studies also have been done.