Thermodynamic Study of Selected Cyclohexanediamines─Sorbents of Carbon Dioxide

Abstract

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 CO 2 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.