Temperature Extrapolation of Henry’s Law Constants and the Isosteric Heat of Adsorption

Computational screening of adsorbent materials often
uses the Henry’s
law constant (KH) (at a particular temperature)
as a first discriminator metric due to its relative ease of calculation.
The isosteric heat of adsorption in the limit of zero pressure (qst∞) is often calculated along with the Henry’s law constant,
and both properties are informative metrics of adsorbent material
performance at low-pressure conditions. In this article, we introduce
a method for extrapolating KH as a function
of temperature, using series-expansion coefficients that are easily
computed at the same time as KH itself;
the extrapolation function also yields qst∞. The extrapolation
is highly accurate over a wide range of temperatures when the basis
temperature is sufficiently high, for a wide range of adsorbent materials
and adsorbate gases. Various results suggest that the extrapolation
is accurate when the extrapolation range in inverse-temperature space
is limited to |β – β0 | < 0.5 mol/kJ. Application of the extrapolation
to a large set of materials is shown to be successful provided that KH is not extremely large and/or the extrapolation
coefficients converge satisfactorily. The extrapolation is also able
to predict qst∞ for a system that shows an unusually
large temperature dependence. The work provides a robust method for
predicting KH and qst∞ over a
wide range of industrially relevant temperatures with minimal effort
beyond that necessary to compute those properties at a single temperature,
which facilitates the addition of practical operating (or processing)
conditions to computational screening exercises.