NIST Issues References on Molecular Filtration

Zeolite Y, here magnified with dark field scanning transmission electron microscopy, is used to increase the yields in petroleum refinery catalytic cracking units. Scale of the image is approximately 7 micrometers across. Photo courtesy of NIST.

The National Institute of Standards and Technology (NIST, www.nist.gov) has issued three new reference materials to support researchers studying the properties of commercially important zeolites. Zeolites, which were first described in the 18th century, have seen increasing use in industry for applications such as catalysts in oil refineries, molecular sieves for chemical separations, and as absorbents.

Zeolites belong to class of materials called alumino-silicates whose crystal structures form highly porous, nanoscale "cages" that can filter and trap small molecules. Naturally occurring zeolites are mined and widely used as absorbents, while tailored synthetic zeolites have a wide variety of more specialized applications. Because they can be designed with pores that pass only molecules of a certain size and shape, zeolites have excited considerable interest as molecular sieves for chemical separations, according to NIST.

NIST says it is often extremely difficult to make precision measurements of key chemical characteristics for zeolites because they are ferociously hygroscopic. Humidity must be precisely controlled, and specified, to make meaningful measurements of the elemental content, for example. NIST says this has made it difficult to compare experimental results between different labs.

To provide a common basis for research on three widely used industrial zeolites, NIST has issued reference materials for Zeolite Y (RM 8850), Zeolite A (RM 8851) and Ammonium ZSM-5 Zeolite (RM 8852). While these materials do not come with the certified property values and uncertainty estimates furnished with NIST Standard Reference Materials (SRMs), these RMs do provide a common source of zeolite materials for measurement comparisons. Reference and information values are provided for major and trace element content, key atomic ratios, enthalpy of formation, unit cell parameters, and particle size distributions.
For technical details, visit https://srmors.nist.gov/tables/view_table.cfm?table=106-7.htm.