Abstract
This paper reports the results of an international interlaboratory study led by the National Institute of Standards and Technology (NIST) on the measurement of high-pressure surface excess carbon dioxide adsorption isotherms on NIST Reference Material RM 8852 (ammonium ZSM-5 zeolite), at 293.15 K (20 °C) from 1 kPa up to 4.5 MPa. Eleven laboratories participated in this exercise and, for the first time, high-pressure adsorption reference data are reported using a reference material. An empirical reference equation {n_{ex}}=frac{d}{{{{(1+exp [left( { - {text{ln}}(P)+a} right)/b~])}^{c~~}}}}~, [nex-surface excess uptake (mmol/g), P-equilibrium pressure (MPa), a = −6.22, b = 1.97, c = 4.73, and d = 3.87] along with the 95% uncertainty interval (Uk = 2 = 0.075 mmol/g) were determined for the reference isotherm using a Bayesian, Markov Chain Monte Carlo method. Together, this zeolitic reference material and the associated adsorption data provide a means for laboratories to test and validate high-pressure adsorption equipment and measurements. Recommendations are provided for measuring reliable high-pressure adsorption isotherms using this material, including activation procedures, data processing methods to determine surface excess uptake, and the appropriate equation of state to be used.
Highlights
Adsorbent materials have many applications, including those related to gas storage, gas separation and purification, catalytic reforming, and environmental remediation (Dabrowski 2001; Yang 2003)
Challenges still exist for obtaining reliable high-pressure adsorption isotherms, as demonstrated in a series of interlaboratory studies (ILSs) on molecular hydrogen (Broom and Hirscher 2016; Hurst et al 2016; Moretto et al 2013; Zlotea et al 2009), carbon dioxide (Gensterblum et al 2009, 2010; Goodman et al 2004, 2007; Gasparik et al 2014) and small hydrocarbons (Gasparik et al 2014)
The workshop recommended that an interlaboratory study of high-pressure adsorption isotherm measurements on an existing National Institute of Standards and Technology (NIST) reference material be undertaken (Thommes and van Zee 2015)
Summary
Adsorbent materials have many applications, including those related to gas storage, gas separation and purification, catalytic reforming, and environmental remediation (Dabrowski 2001; Yang 2003). Challenges still exist for obtaining reliable high-pressure adsorption isotherms, as demonstrated in a series of interlaboratory studies (ILSs) on molecular hydrogen (Broom and Hirscher 2016; Hurst et al 2016; Moretto et al 2013; Zlotea et al 2009), carbon dioxide (Gensterblum et al 2009, 2010; Goodman et al 2004, 2007; Gasparik et al 2014) and small hydrocarbons (Gasparik et al 2014) These challenges are associated, in part, with the lack of standardized protocols, reference materials, and reference data (Espinal et al 2013; Broom and Webb 2017). An aspect that distinguishes this ILS from previous studies is that differences among submitted data were investigated and, as a collaborative effort, participants were given the opportunity to remeasure or reprocess submitted isotherms before the reference isotherm was derived
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