Membrane technologies have shown tremendous potential for a variety of separations, and new applications are constantly appearing. These new applications require exploration of materials, operational conditions, and membrane synthesis procedures, and demand accurate and timely evaluation of membrane properties and performance. Many different membrane materials may need to be screened to determine the most appropriate membrane for a separation application, and the large variety of potential membranes and the numerous parameters that may be varied generates a laborious and time-intensive testing process using typically available methods.
Two general methods for membrane material evaluation are the variable-pressure method and the variable-volume method. In the variable-pressure method, a gas permeates through a film into a closed, constant-volume chamber that is pre-evacuated, and the pressure rise in the chamber is recorded as a function of time. In the variable-volume method, the chamber into which a gas permeates is allowed to expand against a low constant pressure, and the volume change of the chamber is recorded as a function of time. The methods are widely used for the determination of steady-state permeation rates for pure gases.
It would be advantageous to provide a system whereby the testing of multiple membranes under substantially identical conditions could occur in order to more rapidly evaluate a large number of candidate membranes for a given gas separation application.
A simple and rapid method for the screening of the permeability and selectivity of membranes for gas separation has been developed. The system employs a specially designed cell block that holds up to 16 cartridge-contained planar membranes for parallel analysis via the constant-pressure membrane testing technique. At a given temperature, membranes are exposed to a flow of constant-pressure gas (mixed or pure) on one side of the membrane (feed side), and a flow of constant-pressure inert gas on the other side of the membrane (sweep side). Use of the sweep gas on the back side of the membrane allows higher-pressure testing with a lower pressure drop across the membrane, preventing membrane rupture. During testing, the pressure of the feed and sweep streams is monitored, and samples of the retentate (i.e., the stream of gas leaving the feed side of the membrane) and permeate streams are automatically withdrawn for on-line analysis of flow rate and composition. Importantly, the modular design of the system permits simultaneous evaluation of a near infinite number of membranes by simply adding more 16-bay cell blocks.
The high-throughput membrane testing system permits simultaneous evaluation of multiple membranes under conditions of moderate pressure and temperature for both pure gases and gas mixtures. The modular design and on-line sample analysis provides a cost-effective approach to identify the optimal membrane for a given gas separation application.