COLLEGE STATION, July 31, 2009 – More environmentally friendly and cost-efficient methods for producing everything from petrochemicals to pharmaceuticals could be on the way thanks to a significant advancement in the way certain molecular filters are manufactured, says a Texas A&M University researcher who has helped develop the new method.
Working with colleagues from the University of Minnesota, Hae-Kwon Jeong, assistant professor in Texas A&M’s Artie McFerrin Department of Chemical Engineering, has developed what the team believes to be a commercially viable membrane that achieves separation of molecules with a precision and efficiency never before realized.
Their findings, which are published in the July edition of “Science,” detail the team’s success in enhancing the performance of a particular type of molecular sieve. As their name implies, molecular sieves are basically very small filters that help to separate molecules needed for important processes from other unnecessary and even sometimes detrimental molecules.
Molecular sieves are used in a variety of applications, ranging from petroleum refining where they help transform crude oil into gasoline to the pharmaceuticals industry in which they play an important role in the manufacturing of drugs.
Jeong’s research involved enhancing the application of molecular sieves by making molecular sieve membranes from zeolites.
Zeolites are inorganic aluminosilicate structures containing numerous uniform pores, each less than a nanometer in diameter. When fabricated as thin films such as membranes, molecules pass through these minute pores as they are separated. Zeolites’ resistance to high temperatures and chemical solvents makes them ideal filters for industrial and scientific uses, but their inherent structure has posed a challenge to scientists looking to utilize them to their fullest potential, Jeong says.
Because zeolite membranes are made up of many small crystals rather than existing as one solid structure, some unwanted molecules are able to slip through the space between these crystals, Jeong explains. Think of the way leaves comes together to form a shrub. Although the shrub itself is one structure, there is space between the many leaves that make up the shrub. These spaces in zeolite membranes are known as “grain boundaries,” and when it comes to filtering molecules, these extra spaces pose performance problems, Jeong says.
“Researchers have been working throughout the last two decades on the development of these membranes, and they have recognized the importance of controlling the grain boundary, but they didn’t know how to remove them,” Jeong says. “They accepted them as something with which they had to live.”
Jeong’s work is poised to change that notion.
Using a technique called “lamp-based rapid thermal processing (RTP),” Jeong and his fellow researchers were able to essentially eliminate grain boundaries, or at least minimize them to the degree that they no longer compromised molecular separation. In their model system, the researchers successfully separated paraxylene molecules from metaxylene molecules using their technique. The size difference between these two similar molecules is very small, making separation a challenge, Jeong says.
“We have demonstrated the capabilities of this approach as a novel means for rapid microstructure development, dramatic reduction of grain boundary defects, and significant improvements in membrane separation performance – all features that should establish the viability and relevance of zeolite membranes for separations and high-value niche applications,” Jeong says.
Prior to Jeong’s work, success in minimizing the effects of grain boundaries has been mixed. Some improved membranes have been developed, but they have been expensive to produce and not easily scalable, Jeong says. Other methods for achieving separation of molecules, such as the utilization of distillation towers, are extremely energy intensive, he adds.
Key to Jeong’s work is the use of a membrane – or sieve – that can be readily and affordably manufactured at different sizes – an aspect that potentially makes it a commercially viable product. In addition to being more cost efficient than other separation methods, Jeong says the enhanced zeolite membrane should achieve separation in a much more energy-conscious manner because of its refined selectivity.
“What we have done is take a commercially scalable membrane and applied an additional step to essentially eliminate the grain boundary structure,” Jeong explains. “In essence, a polycrystalline membrane has been transformed in a single crystal membrane, which has no grain boundary. No selectivity is lost. This is a significant breakthrough in zeolite membranes.”
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Contact: Hae-Kwon Jeong at (979) 862-7137 or via email: jeong@chemail.tamu.edu or Ryan A. Garcia at (979) 845-9237 or via email: ryan.garcia99@tamu.edu.
