This Small Business Innovation Research Phase I project is developing novel high flux, compaction-resistant and durable polymer mesocomposite membranes for sustainable drinking water purification and water reuse. The new membranes exhibit 1) superior resistance to internal damage and pore compaction, 2) increased permeability with retention of separation selectivity, and 3) resistance to chemical degradation and mechanical wear with little or no shedding of particles under pressure. The key to our innovation is the use of mesoporous silica particle (MPS) as polymer reinforcing additives and surface polarity modifiers. The MPS additives, which are prepared through surfactant-templated supramolecular assembly processes, have precisely tailored pore sizes in the mesometric range 2 to 50 nm and beyond. Because the MSP pores are larger than the van der Waals diameter of the polymer chains, the polymer can partially penetrate the particle mesopores and bind to membrane pores. The resulting reinforcement, together with the accompanying densification of the membrane, affords the aforementioned advances in water processing performance. To illustrate the technological potential of the innovation, a 5 wt % MSP - polysulfone membrane exhibits a two-fold increase in permeability, a concomitant improvement in rejection selectivity, and a ten-fold decrease in membrane compaction at 40 psi
The broader impact/commercial potential of this project is its potential to ease the world's growing needs for clean, potable water. The problems caused by a lack of clean water are legion and include 1.8 million annual deaths from diarrheal diseases, most of which are preventable with access to safe water. A number of techniques are used for transforming non-potable water into potable water. Of these, membrane filtration is widely used in industrial applications due to its ability to efficiently remove virtually all particles larger than 0.2 um. However, for addressing the broader need for clean water, there remains a need for new materials-based strategies for membranes which achieve extended longevity and high flux separations without sacrificing selectivity. This proposed SBIR project will demonstrate that the challenges can be overcome through the invention of a new class of mesoporous membrane composites reinforced with silicate mesophases. Products based on this technology will be sold into the global water purification market, with key customers being some of the world's leading companies in this field.
The overall objective of this SBIR Project was to improve the properties of ultrafiltration (UF) membranes through the use of micelle-templated mesoporous metal oxides particles, particularly mesoporous silica particles (also referred to by our trade name Mezzopore™) as mixed matrix membrane additives. Although particles of various compositions and structure types have been investigated as additives in composite compositions for water purification, none possess the unique combination of textural properties provided by micelle templated mesoporous silica particles. In addition, our Phase I project also studied the effectiveness of representative mesophases of alumina, zirconia, and aluminosilicates for improving UF membrane performance. This Phase I SBIR project successfully demonstrated the technical viability of our new approach to the improvement of polymeric UF and RO membranes for water purification based on the use of proprietary mesoporous metal oxide compositions as membrane additives. We have shown that our additive technology favorably impacts the permeability, rejection properties, mechanical strength, and fouling resistance of the three most important polymer systems in present use for the ultrafiltration of water, namely, polysulfone, polyether sulfone, and polyvinylidene difluoride. Also, our preliminary Phase I results for cellulose acetate membranes show that our particle additive technology promises to improve the properties of reverse osmosis membranes for desalination applications. The improvement in the flux and rejection properties for both types of membrane systems depends on the interplay between the polymer matrix and the mesopore size, particle size, and surface polarity of the metal oxide particles. The associated mechanical properties and stability to cleaning agents also depends on these textural properties of the additives. Although the majority of our Phase I studies have focused on the use of mesoporous silica for demonstrating our technology concept, we also have found that complementary mesoporous oxide compositions, such as mesoporous alumina, zirconia, and titania provide superior advantages under certain applications conditions. For instance, whereas silica mesophase additives are well suited to applications below pH=10, alumina and zirconia mesophases are more stable to higher pH environments. This finding broadens the range of applications of our additive technology. Most importantly, the presence of mesoporous titania particles in the composite membrane matrix improves flux as well as stability to sequential fouling and chemical cleaning cycles.
