NETL Studies High Throughput Membrane Screening

NETL Studies High Throughput Membrane Screening

Membranes offer a potential low-maintenance and economical method for gas separations from power plant flue gas streams. Polymer membranes and supported liquid membranes show great promise to solve problems in the area of clean energy production. Carbon dioxide, a greenhouse gas, is a principal by-product of energy production from fossil fuels. Capturing CO2 from power plant flue gas streams is critical to the goal of reducing the nation’s carbon footprint and preserving the environment. Currently, there is no technology that can meet the goals for carbon capture as set forth by the U.S. Department of Energy. These goals are 90% capture of the CO2 with a less than 35% increase in the cost of energy. 

 Dr. David Luebke at work in the lab
Dr. David Luebke at work in the lab.

The National Energy Technology Laboratory (NETL) is pursuing the development of both polymeric and supported ionic liquid membranes for CO2 capture. Development of adequate membrane technology requires equipment capable of rapidly measuring membrane performance. Typical membrane testing equipment operates under either constant pressure or constant volume conditions. Constant pressure instruments pass feed gas over one side of the membrane and a sweep gas over the other side of the membrane. The feed gas is comprised of the gases which are to be separated while the sweep gas is inert and serves the purpose of carrying away the gas that passes through the membrane (i.e. , the separated gas). By carrying away the separated gas, the sweep gas allows for increased efficiency of the separation. Constant volume instruments are set up with a membrane separating a pressurized vessel and an evacuated vessel. The pressurized vessel contains the gases which are being separated. As the gases permeate through the membrane, the pressure in the evacuated vessel will increase. The rate of pressure increase permits a determination of the ability of the membrane to separate the gases. 

At NETL, membrane development is guided by a thorough understanding of the fundamental membrane transport mechanisms as well as a thorough understanding of materials properties. However, even after carefully selecting promising materials, there are still an abundance of potential membrane material choices. To greatly increase the speed of screening materials for gas separation membranes, a high throughput membrane screening system was developed at NETL. This system is unique, and a patent application covering its design has been submitted. This system was developed by assembling in parallel multiple single cell constant pressure test systems. The instrument consists of 16 membrane cells and, therefore, can test up to 16 membranes simultaneously. The feed gas flows to the 16 cells such that the top side of all 16 membranes has a constant flow of gas passing over the top of the membrane. Similarly, the sweep gas is fed such that the bottom side of all 16 membranes has a constant flow of gas passing over the bottom of each membrane. Special selector valves are used to select one of the gas streams flowing away from the membrane for analysis. The selector valves are then rotated through all 16 cells so that each membrane is sampled. This process permits the testing and analysis of 16 membranes in one instrument.

The NETL membrane screening system accelerates membrane testing by a factor of 12
NETL membrane screening system accelerates membrane testing by a factor of 12.

To illustrate the value of this instrument, consider one type of membrane technology – mixed matrix membranes. These are traditional polymer membranes with filler particles embedded in them. If the particles have favorable gas transport properties, the overall performance of the membrane can be improved. For this type of membrane, there are many variables to be considered including polymer type, filler type, filler loading, and filler size. Simply by selecting one polymer and two fillers, while testing 5 loadings and 5 filler sizes, 50 membranes would need to be tested. Using standard testing equipment, 1 membrane takes 3 days to test. Using the high throughput system, 16 membranes take only 4 days to test. As a result, NETL has greatly enhanced its capability to solve important gas separation problems associated with clean energy production.

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