Fluid-Filled Gate Provides Precise Separation

April 21, 2015
Tunable mechanism can handle multiphase streams and resists clogging

Taking a cue from nature, researchers at Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston and Cambridge, Mass., have developed a flow-gating mechanism — similar to micropores in living plants — that responds selectively to a range of materials without clogging or fouling.

Filtration Researcher

Figure 1. Joanna Aizenberg and her team have developed a fluid-gating system that separates materials with high selectivity and no clogging or fouling. Source: Wyss Institute at Harvard University.

The mechanism uses a fluid in micropores to modulate their opening and closing, enabling them to serve as reversible, reconfigurable gates that can separate a variety of liquids and gases. The system can selectively separate one material from complex liquid/gas combinations as well as three-phase air/water/oil mixtures. More details on the system appear in a recent issue of Nature.

The researchers say key advantages of the approach are the broad tuning that’s possible — simply by adjusting the pressure, which can be varied over a wide range — to optimize specific separations, fast and repeatable control over multiphase flows, freedom from membrane fouling, and energy savings from potentially lower operating pressures than conventional membranes, as well avoiding their energy losses due to clogging and fouling.

“… The basic mechanism of the liquid gate is unique in that it allows us to do all of these things in one single, relatively simple system. At present, several complex systems can achieve certain types of specific separations, but these require such specific and often complicated designs that they can only be used for single dedicated applications. In addition, existing technologies generally lack the capacity to be tuned such that liquids flow at lower critical pressures than gases. The … new concept overcomes many of these conflicting requirements and can serve as a general platform for membrane design,” says Joanna Aizenerg, a professor at the university who led the reasearch.

The development promises benefits to water treatment. “… The membranes can be tuned to enable high flow rates with less pressure and are inherently antifouling, which can potentially make water treatment less expensive and reduce energy consumption. In addition, since the system can be made from a variety of common materials, the cost of using it on a large scale can be substantially lower than existing technologies, and it can potentially be optimized to handle a variety of types of wastewater,” notes Aizenberg.

The tunability, antifouling properties, and dynamic switchable control over multiphase flows also benefits microscale reactor operation by enabling selectively timed modulation and harvesting of liquid and gas components, thus optimizing both the efficiency of product recovery and the reaction progress itself, she adds.

The team reports the next step is to increase the throughput of the system for large-scale applications and commercialization. “…We are exploring a variety of membrane materials and chemistries that can increase pressure stability (enabling higher flow rates) and be tailored to reduce the pressure required for a given flow rate. This is an ongoing effort — since the system is tunable, we can continuously optimize throughput and efficiency for each new application,” says Aizenberg.

For example, the team is looking at inorganic membrane materials that are mechanically stronger than those used in their study to develop systems with high pressure stability.

“… Focusing on the materials enables us to take advantage of the many technologies already available for designing materials with different pore sizes, pore shapes, and surface properties — not only for 2D but also for 3D systems, which we believe will greatly extend our gating concept for real-world applications,” she adds.

Aizenberg says key challenges include how to get very stable, large-scale membrane materials, reduce the gating liquid loss during the real-world application, and make the liquid gating system smart — beyond the inherent responsive properties.

If all goes well, the team plans to select one specific application to test their approach on a larger laboratory scale. “We could use our larger system for the wastewater treatment to remove the harmful gases and the waste from water. This would follow several optimizations at the smaller scale.”

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