This Small Business Innovation Research (SBIR) Phase II project aims to further the development of nanomaterials-based, high permeability, energy-efficient membranes for desalination of water. Membrane-based reverse osmosis (RO) is the dominant desalination technology in many parts of the world, although it provides just a small fraction of potable water demand. This is in large part due to the energy intensiveness of the technology. It is widely acknowledged that improvements in membrane permeability can bring about significant reductions in the energy requirements for seawater RO of between 30-50%. The RO membranes developed under Phase I demonstrated significant improvements in permeability over state-of-the-art membranes, while maintaining a high salt rejection. Phase II aims to scale the process developed in Phase I to produce spiral wound cartridges of an industry standard form factor. The membranes then will be tested to determine their future performance in a large-scale municipal desalination plant.
The broader impact/commercial impact of this project is that the technology is expected to bring RO desalination closer to cost-parity with existing methods of water production. Also, the superior membrane performance achieved in Phase I demonstrates the promise of nanomaterials in RO membrane development. Scaling this process up to the pilot scale will help demonstrate the commercial viability of the technology. In addition, this project is expected to enhance the understanding of the science behind water and ion transport through membranes on the nanometer-scale, an area of current academic interest.
This project was aimed at developing a next-generation reverse osmosis membrane for seawater desalination. The membrane developed used carbon nanotubes (seamless cylinders of graphite rolled into tubes of nanometer dimensions) as pores to efficiently shuttle water through a membrane, while preventing the passage of salt. Such membranes have been shown to possess extremely high water permeability, orders of magnitude greater than current state-of-the-art desalination membranes. With such high permeability, carbon nanotubes membranes could enable much lower energy water purification than conventional membranes (reduced pressure operation, while maintaining water throughput). Energy has been one of the pain points for membrane desalination for decades, and although innovations such as energy recovery devices have been implemented, virtually no innovation in membrane design has occurred over this time to address this issue. As a result, desalination has not been as widely deployed a solution for water scarcity as it could be. The membrane technology developed by NanOasis is anticipated to change that. Over the course of this project, several important milestones were achieved that are key enablers to the commercialization of the carbon nanotube membrane technology. The first important milestone was a method for disentangling and dispersing carbon nanotubes into solution ("functionalization"). We discovered a method for functionalizing carbon nanotubes that prevents the breakage of bonds along their sidewalls, which is key to maintaining the water transport enhancement through their channels. The other key milestone for this project was developing a method of producing an oriented array of carbon nanotubes by entirely wet chemistry means. For this membrane technology to be economical and manufacturable, a method of orienting the nanotubes was needed that required only chemical modifications and would be compatible with roll-to-roll coating. We developed such a process that relies on evaporative alignment forces at a thin-film interface (a "self-assembly" process) to direct the nanotubes normal to the film interface. This was a tremendously challenging problem that previously had only been solved through the use of large external fields (electrical or magnetic). Having achieved these two key milestones over the course of the project, the NanOasis membrane technology is well positioned to impact the desalination industry.
