Lin, Rui‐Biao | Search NASA

DOE OSTI2022

How Reproducible are Surface Areas Calculated from the BET Equation?

Abstract Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro‐ and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already‐measured raw adsorption isotherms were provided to sixty‐one labs, who were asked to calculate the corresponding BET areas. This round‐robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well‐known Rouquerol criteria and makes an unambiguous BET area assignment possible.

36 MATERIALS SCIENCE↗

DOE OSTI2021

A Molecular Compound for Highly Selective Purification of Ethylene

Purification of C 2 H 4 from an C 2 H 4 /C 2 H 6 mixture is one of the most challenging separation processes, which is achieved mainly through energy-intensive, cryogenic distillation in industry. Sustainable, non-distillation methods are highly desired as alternatives. We discovered that the fluorinated bis(pyrazolyl)borate ligand supported copper(I) complex {[(CF 3 ) 2 Bp]Cu} 3 has features very desirable in an olefin–paraffin separation material. It binds ethylene exclusively over ethane generating [(CF 3 ) 2 Bp]Cu(C 2 H 4 ). This molecular compound exhibits extremely high and record ideal adsorbed solution theory (IAST) C 2 H 4 /C 2 H 6 gas separation selectivity, affording high purity (>99.5 %) ethylene that can be readily desorbed from separation columns. In-situ PXRD provides a “live” picture of the reversible conversion between [(CF 3 ) 2 Bp]Cu(C 2 H 4 ) and the ethylene-free sorbent in the solid-state, driven by the presence or removal of C 2 H 4 . As a result, molecular structures of trinuclear {[(CF 3 ) 2 Bp]Cu} 3 and mononuclear [(CF 3 ) 2 Bp]Cu(C 2 H 4 ) are also presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗