New Way to Separate and Purify Molecules Devised

Experts from the University of Minnesota (UM) announce in the July 31st issue of the respected journal Science that they managed to develop a new method to create high-performance membranes out of crystal sieves called zeolites. They argue that the innovation could lead to significant advancements in the understanding of chemical reactions – the basis of our industry – and could also trigger improvements in the energy efficiency of chemical separations of up to 50 times over. Especially prone to the influence of the new find is the process of distillation.

This process is one of the most widely used around the world, and has applications in obtaining a large number of end-products. But, while it's very simple to design and implement, it takes a lot of resources to operate, which essentially translates into higher costs for whatever is produced employing it. For decades, one of the greatest problems in the industry has been removing structural defects in zeolite membranes. These defects severely limit their performances.

In the new method, developed in the lab of UM chemical engineer Michael Tsapatsis, rapid heating treatments are applied to the zeolite, which remove its imperfections with great efficiency. “Using membranes rather than energy-intensive processes such as distillation and crystallization could have a major impact on industry,” Rosemarie Wesson, the National Science Foundation (NSF) program officer, says of the innovation.

Existing methods of producing zeolites rely on growing a film of crystals with small, organic ions added to them, so that they essentially direct the crystal structure and size of the pores. However, “This method for creating zeolite films often leaves cracks at the boundaries between grains of zeolite crystals,” Tsapatsis says. “While it may be possible to correct some of these defects, the repair process is difficult and expensive,” Wesson adds.

In the newly developed Rapid Thermal Processing (RTP) treatment, zeolite films are heated to about 700 degrees Celsius within one minute, and kept at a constant temperature for about two more. During this time, the RTP refines the granular structure of the films, acting like an annealing method. “We observed a dramatic improvement in the separation performance of the RTP-treated membranes,” Tsapatsis concludes.