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SUSTAINABLE SOLUTIONS

Hydrogen and its

thermodynamic modeling

Accurate modeling of the
thermodynamic properties of H
2
and its mixtures with other gases
(e.g., natural gas) is essential for
the efficient design of the processes
involved in the hydrogen value chain

Laura Annamaria Pellegrini,
Full Professor of Chemical Plants
Giorgia De Guido, Assistant Professor
Politecnico di Milano

he Group on Advanced Separation Pro-
cesses & GAS Processing (GASP) carried The Process Thermodynamics laboratory (PT lab) of Politecnico di Milano aims at collecting
out a comparative analysis on different experimental data of fluid phase equilibria also for strongly non-ideal systems, for which
data are not available in the literature
Equations of State to provide some gui-
delines in the selection of the most relia-
T ble thermodynamic model for the correct If the potential for a boom in
characterization of pure hydrogen and its mixtures with the global hydrogen economy is
natural gas.
The interest in hydrogen (H ) as a clean, environmentally- “realized, there will be an
2
friendly fuel and energy carrier of the future has grown increase in the need
in many countries and initiated comprehensive research, for accurate hydrogen
development and demonstration activities with the main
objective of scaling up technologies and bringing down thermodynamic property
costs to allow hydrogen to become widely used. standards
Hydrogen is the lightest element in the universe. At
standard temperature and pressure conditions, it is a H can be considered an ideal gas over a wide range
2
colorless, odourless and non-toxic diatomic gas. It is of (not too low) temperatures and (not too high, up
characterized by a high energy density, which makes it to 10 MPa) pressures. However, at some point, its
2
valuable as an energy carrier: indeed, 1 kg of hydrogen thermodynamic behavior deviates from the ideal one
contains ca. 2.5 times more energy than the same mass and it will act like a real gas. Such a behavior can be
of natural gas. One of its drawbacks is its low density, described by means of suitable thermodynamic models,
which makes it necessary to either compress or liquefy it such as cubic Equations of State (EoSs).
for any practical application. Another interesting information about hydrogen, not all
The phase diagram of hydrogen is shown in Figure 1 people may be aware of, is that it is a quantum gas that
(left), where the triple point (dot at 13.952 K and 7.7 kPa) exists in two possible isomeric forms, namely ortho- and
1
1
and the critical point (triangle at 33.19 K and 1.315 MPa) para-hydrogen (respectively denoted by o-H and p-H 2
1
2
are marked. in the following). The difference between the two forms
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