Thermodynamic Study of Selected CyclohexanediaminesSorbents of Carbon Dioxide

Atmospheric processes, especially those related to the
greenhouse
effect and gradual climate change, are crucial topics of the 21st
century. The most abundant pollutant produced by a full spectrum of
human activities is carbon dioxide. Carbon capture and storage/utilization
(CCS/CCU) processes can serve as a means not only to reduce the carbon
dioxide emissions but also to lower its atmospheric concentration
to preindustrial times in the future, not to mention the possibility
of direct application of captured carbon dioxide for other processes.
Among CCS techniques, direct air capture of carbon dioxide (DAC) is
a promising technology, but sorbents with sufficient absorption efficiency
and feasible consecutive release are still to be searched for. The
traditionally used amines and amino alcohols are not very effective,
so alternatives are being sought. Recently, cyclohexane-based diamines
have been shown to be promising substitutes; moreover, the captured
carbon dioxide forms solid reaction products with the sorbents (carbamic
acids) that can be easily separated from the process. The easy recovery
of the liquid sorbents, together with the release of CO2 for further use, represents a significant advantage over currently
used technologies. Four cyclohexane-based diamines, including the
most promising one of the previously tested compounds, isophorone
diamine, were chosen for thorough thermodynamic characterization to
facilitate the introduction of these compounds for industrial use.
A phase behavior study was performed to determine the temperature
range of their applicability. Combustion enthalpies were measured
with a bomb calorimeter, and heat capacities were measured using a
Tian-Calvet calorimeter. Vapor pressures were studied by means of
a static method, and temperature-dependent enthalpies of vaporization
were derived.