Nanomembrane Interactive Forward Osmosis (FO) Polymers for Desalination and Remediation

Supported by DOE and NSF SBIR grants for nanomembrane manufacturing and Quality Assurance, Covalent LLC is developing manufacturing methods and materials for a new class of ultra low energy, single atomic layer nanomembranes for Desalination and water purification operating at the lowest possible energy (Topic 15A). The completed membranes are expected to reduce desalination energy requirements by 66% over current best practice and drop capital and operating costs approximately 50%, placing desalination costs within the range of current water purification costs. The membranes would replace current high-energy/low-yield technologies including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, ultraviolet and other energy-intensive methods for desalination, water purification and wastewater remediation. Desalination’s energy sources are gravity (27” water head pressure) plus an energy addition to part of the system to provide unprecedented specificity in high value separations (Topic 15A). Energy savings, higher yields of usable water, and lower costs reflect the membrane’s virtually non-existent tortuosity and extreme thinness. The completed desalination membrane has 3 layers plus a water binding polymer 1. On top, the Protective layer provides a diffusion barrier to prevent fouling. 2.The anomembrane provides selectivity to separate impurities from water. 3. On the bottom, the porous Substrate supports the nanomembrane. 4. In the substrate pores and under the substrate is a hydrophilic polymer that provides the energy to remove water across the nanomembrane when the osmotic pressure of the feed solution exceeds the head pressure limits of the nanomembrane. This proposal addresses the removal of water from higher concentrations of salt than can be supported by pressure on the atomically precise nanomembrane (#2) An atomically-precise single atomic layer nanomembrane is inherently delicate and cannot be subjected to the extreme pressures found in Reverse Osmosis Membranes (0.5nm thick vs 12,000nm). This is feature and a curse. Thin membranes mean low energy requirements and high surface area with high flux. Thin membranes also have a low limit to the pressure one can use to drive osmotic processes. To address desalination we propose to use a Forward osmosis draw solution that consists of an environmentally sensitive polymer that will take up water and carry it to a location away from the membrane where energy can be added to change the polymer conformation and allow it to release its bound water. The hydrophilic polymer will then be recycled back to the nanomembrane to repeat the cycle. We propose to: (1) Demonstrate feasibility of our approach to create a conformationally-adaptable polymer that can be used as an FO draw material in a closed loop system while interacting with specifically designed nanomembrane pores; (2) Evaluate methods for adding energy to the system to change the polymer conformation, releasing water; (3) Develop analytical methods to prove that this method of FO is commercially viable in terms of energy reduction; (4) Show FO polymer integrity during sufficient water adsorption/release cycles to be economically viable. While nanomembranes are the completed membrane’s atomically-precise element, the FO system has a set unusual requirements the FO draw material including: (1) Binding to the substrate pore or nanomembrane surface when in the “dehydrated” state; (2) Not binding to the substrate pore or the nanomembrane underside when in the “hydrated” state; (3) Being small enough or having components small enough to fit into the substrate pores (under the nanomembrane); (4) Having appropriate physical characteristics to support transfer away from the nanomembrane (similar to a polymer in a fluidized bed reactor); (5) Having a commercially viable lifetime; (6) Being cost effective to manufacture for the market (e.g. sea water desalination).During Phase 1, Covalent will show that: (1) Evaluate the use of existing stimuli-responsive materials as draw materials in experimental simulation of a “water only” environment as is anticipated to be seen on the output side of the nanomembrane; (2) Determine if “functional group” specific energy absorption can cause a response in a stimuli responsive material; (3) Develop analytical methods for evaluation of the degree of in-situ water release; (4) Proof that the above (1 and 2) areas are feasible leads to the development of a scalable process for low energy FO, and thus low cost, high TDS desalination/remediation.