NIRT: Precise Building Blocks for Hierarchical Nanomanufacturing of Membranes with Molecular Resolution

This research was received in response to the Active Nanostructures and Nanosystems initiative, NSF 06-595, category NIRT. Its focus is on one of the most promising developments in the field of separations: molecular sieve or zeolite membrane technology. It has become evident that zeolite membrane technology for large scale processes depends on reliable manufacturing that can generate large membrane areas while achieving essential film characteristics: film continuity with low defect density, appropriate pore orientation, and small membrane thickness well under the micrometer range. This NIRT team undertakes the challenge to make the leap forward towards developing such a process.

In the last decade, a set of mechanistic principles for the nucleation and growth of certain molecular sieve materials has been identified. These principles motivated the research experimental efforts, which attempt to control size and shape of zeolite nanoparticles to an unprecedented level and use these nanoparticles as precisely engineered building blocks for molecular sieve thin films made by hierarchical nanomanufacturing. It was hypothesized that synthesis in a confined environment will enable manipulation and control of undesirable aggregation steps and will ultimately yield the desirable perfection in zeolite particle shape and the needed monodispersity in size. The precisely shaped nanoparticles will be used subsequently as building blocks to form closed packed, crystallographically aligned, monolayers using reactive attachment. Following secondary growth, the developed continuous films will be tested for permeation properties, and their microstructure and performance will be compared with the current state-of-the-art. Significant molecular sieve membrane capital and operating cost benefits are the expected outcome of the proposed work. These improvements represent a major leap forward for wider use of energy efficient molecular sieve membrane separation technology. In addition to enabling the thinnest, and consequently most productive, zeolite membranes ever made, the research hierarchical film processing technology may impact other technologies, like microelectronics and sensors. One of these potential uses, i.e., low-k dielectrics for microprocessors, will also be evaluated.

Separations currently represent 15% of global energy consumption. With the global commodity production expected to increase six-fold by 2040, a business as usual scenario is not sustainable. An order of magnitude increase in efficiency of separation and purification processes is a necessary step towards sustainable global prosperity. One of the most promising developments in the field of separations using membranes is that of molecular sieve or zeolite membrane technology. By enabling separations with molecular resolution to replace thermally driven processes, it can meet this efficiency goal and is emerging as an area of nanotechnology and energy research. Zeolites and other molecular sieves are crystalline inorganic frameworks with pores capable of recognizing molecules by shape and size. This ability, along with their thermochemical stability and catalytic activity, has led to their use in a broad variety of applications as catalysts, adsorbents, and ion exchangers. The desire of incorporating these materials in thin film devices with molecular resolution can be traced back in the 1940's. However, it has been only about a decade since the first commercial zeolite membranes targeting small scale distributed applications (i.e., membrane modules of about ten square meters) became available. Since then, commercialization progress has been stagnant, hampered by problems in scale-up from laboratory to commercial scale. The proposed comprehensive and systematic investigations will lead to the development of a scalable and economic fabrication technique resulting in the thinnest zeolite membranes ever made transforming the vision of energy efficient molecular sieve membranes to a commercial reality.