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Workshop Chairs:
Millicent Firestone
(ANL/Materials Science Division)
Tom Irving
(Illinois Institute of Technology)
Jin Wang
(Advanced Photon Source)
Randall Winans
(ANL/Chemistry Division)

Next Generation Membrane Materials & Structures for Energy-Efficient Gas Separations

W. J. Koros

The Georgia Institute of Technology

Atlanta , Georgia 30327-0100

Introduction

Membrane-based gas separations became a commercial reality roughly thirty years ago, and solution-processable polymers that can be made into asymmetric forms still dominate the large scale market for this technology [1, 2]. Over the past three decades, a diverse array of gas and vapor processing applications for membranes have been identified (Table 1). Moreover, for large scale separations, many membrane types (Table 2) have been investigated to advance the state-of-the-art even beyond current solution-processable polymers [2-9]. These more advanced materials have not significantly assisted in the displacement of entrenched older technologies, thereby suggesting the need for a more comprehensive strategy to encourage their introduction.

Membranes that are intrinsically more selective and robust than the current generation should have positive impacts on large energy-intensive applications in Table 1; however, this alone is not a sufficient driving force. Indeed, some new membrane materials are known to offer higher selectivity and resistance to aggressive operating conditions; however, defects and high module production costs currently prevent their widespread adoption. The current inability of membranes to broadly displace conventional technology is, therefore, not just a “materials” problem: it is also a “materials-processing” problem. Integration of scientifically sound methods for processing advanced materials into economical large scale modules is the most pressing challenge currently facing the gas separation membrane field.

A Realistic Path Forward to Next Generation Membranes

During the past three decades, a revolutionary path involving attempts to jump directly from the current technology to a much higher performance goal have understandably been popular with funding agencies. One example of such a revolutionary approach is given by fixed-site “facilitated transport” materials with the potential to significantly improve membrane selectivity without inhibiting permeation rates of the desired component. Molecular sieve and selective surface flow membranes are additional types of “revolutionary” approaches [4-9] with potential performance well beyond those of simple solution-processable polymers. Despite their attractive potential capabilities, manufacturing cost and durability difficulties have limited the actual application of all three of these revolutionary types of materials to small scale specialty cases.

An alternate evolutionary path to the next generation of membranes for large scale applications is proposed here. This approach links cost increases with performance increases that are required for success in specific applications, thereby building credibility with users. H ybrid materials, comprising domains of two or more intrinsically different materials types, (e.g., organic and inorganic domains) provide a broad platform for evolutionary advancements. Indeed, such materials offer a spectrum of properties that potentially include the best transport and manufacturing characteristics of each of the components [10-12] and encompass both organic and inorganic types of materials. Therefore, the generalized “hybrid material” platform deserves much more attention than it has received as a possible method to deal with the challenge of economical membrane manufacturing.

Conclusions

A combination of technical and economic advantages makes hybrid materials the highest potential new area to expand the range of application of membrane-based gas separations. Although attractive, forming practical large-scale membrane modules based on such hybrid materials involves an array of fundamental science questions and technical challenges that must be addressed properly. Interfaces between domains, morphologies at multiple structural levels and the relationship of these factors to processing approaches must be understood better. The equipment and expertise of individuals associated with sophisticated institutions like the advanced photon source are ideally suited for such an undertaking. Indeed, control of the complex nanoscale interfaces between the two major phases in a hybrid material represents the key hurdle to be overcome in transitioning from a lab-scale to a production scale. Better ways to probe adhesion and the resulting influence on the transport properties of the interphase region between the two phases would help advance this field enormously. Many of the key questions involved in this technology push the state of the art in terms of theory and characterization techniques in the materials science and engineering fields. As such, involvement of a broader array of “non-membrane” colleagues would be beneficial.

References

  1. Lonsdale, J. K., The Growth of Membrane Technology, J. Membr. Sci., 10, 81-181 (1982)
  2. Koros , W. J, and R. Mahajan, Pushing the Limits on Possibilities for Large Scale Gas Separations; Which Strategies?, J. Membr. Sci., 175, 181-196 (2000).
  3. Buxbaum, R. E., Hydrogen Transport Through Non-Porous Metal Membranes of Palladium-coated Niobium, Tantalum and Vanadium, J. Membrane. Sci., 85, 29 (1993).
  4. Nishiyama, N, L. Gora, V. Teplyakov, F. Kapteijn, and J. A. Moulin, Evaluation of Reproducible High Flux Silicalite-1 Membrane: Gas Permeation and Separation Characterization, Sepn. and Purif. Techn., 22, 295-307 (2001).
  5. Akin, F. T. and Y. S. Lin, Oxidative Coupling of Methane in Dense Ceramic Membrane Reactor with High Yields , AIChE Journal 48(10), 2298-2306 (2002).
  6. Kita, H., H. Maeda, K. Tanaka, and K. Okamoto, Carbon Molecular Sieve Membrane Prepared from Phenolic Resin, Polymeric Materials Science and Engineering, 77, 323 (1997).
  7. Nair, S. and M. Tsapatsis, “S ynthesis and Properties of Zeolitic Membranes”, pp. 867-919 , Handbook of Zeolite Science and Technology , S. M. Auerbach, K. A. Carrado, P. K. Dutta, eds., Marcel Dekker, New York, NY, Publisher: Marcel Dekker, Inc., New York, N. Y (2003).
  8. Sircar, S., M. B. Rao, and C. M. Thaeron, Selective Surface Flow Membrane for Gas Separation, Sepn. Sci. and Techn., 34, 2081-2093 (1999).
  9. Brinker, C. J. and G. W. Scherer, Sol-Gel Science: The Physics & Chemistry of Sol-Gel Processing, , Academic Press, London, UK,1990.
  10. Mahajan, R and W. J. Koros , Factors Controlling Successful Formation of Mixed-Matrix Gas Separation Materials , Industrial & Engineering Chemistry Research, 39(8), 2692-2696 (2000).
  11. Pechar, T. W., M. Tsapatsis, E. Marand and R. Davis, Preparation and Characterization of a Glassy Fluorinated Polyimide Zeolite-Mixed-Matrix Membranes, Desalination, 146, 3-9 (2002).
  12. Merkel, T. C., Freeman, B. D., Spontak, R. J., He, Z., Pinnau, I. , Meakin, P. and A. J. Hill, Sorption, Transport, and Structural Evidence for Enhanced Free Volume in Poly(4-methyl-2-pentyne)/Fumed Silica Nanocomposite Membranes, Chemistry of Materials, 15(1), 109-123 (2003).

 

Table 1: L arge gas & vapor membrane-based separation applications