Description:
By grafting short polymer chains to standard membrane filters, "nanohairs" are fabricated that can be made to move back and forth in an oscillating magnetic field. This induces very localized stirring at the membrane surface, which decreases membrane fouling and improves membrane performance and lifetime without any added chemicals or modifications to the waste stream.
At a Glance
- Membrane filters modified with short polymer chains and magnetic nanoparticles.
- Alternating magnetic field is applied to induce mixing at membrane surface and reduce fouling.
- Reduced fouling improves membrane performance (capacity and selectivity) and membrane lifetime.
- Because no added chemicals or temperature/pH modifications are required to stimulate membrane, there is no inadvertent degradation of product.
- Application in purification of wastewater streams as well as non-aqueous solvent systems.
Detailed Description
Polymer membranes are commonly used as filters for the purification of liquids. However, the performance of membrane filters can be limited by deposition of particulate matter on the membrane surface and concentration polarization, leading to membrane fouling. Fouling decreases membrane performance over time by reducing membrane capacity (throughput) and selectivity (ability to separate components of different types). Although membranes that respond to stimulus (e.g. modification of pH or temperature) have shown increased resistance to fouling, they all suffer from the major disadvantage that the characteristics of the bulk feed must be modified – typically an expensive and time-consuming task that may also degrade the desired product. Accordingly, there is still an unmet commercial need for fouling resistant membranes that are adaptable to numerous feeds.
Researchers in the Chemical and Biological Engineering Department at Colorado State University have developed a new type of responsive membrane that utilizes short polymer chains grafted to the surface of the membrane to stir the feed and suppress fouling. An oscillating magnetic field interacts with magnetic nanoparticles bonded to the ends of the polymer chains and induces the mixing at the membrane interface. The extent of stimulation is controllable and can be actuated during filtration without any adjustments of feed properties. Dead-end filtration tests using both DI water and idealized feed solutions have shown a strong magnetic response, exhibiting improved permeability and rejection capability of the membranes.
This magnetically-responsive membrane technology can be used to improve the performance of any membrane filter, including nanofiltration, microfiltration, and ultrafiltration membranes and is suitable for a variety of aqueous (water-based) and non-aqueous feed solutions in either dead-end or transverse configurations. These membranes should be of particular value in the filtration of wastewaters (e.g. naval bilge waters, coal bed methane wastewater) and other aqueous streams, including desalinization and dairy applications. The membranes are also suitable for filtration of non-aqueous solvent systems and recycling of catalysts, dyes and other high-value chemicals
