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Abstract: There is intense ongoing worldwide research to develop improved solvents and processes for CO2 capture from flue gas. The number of publications was almost 1000 in 2011, and may be expected to exceed 10,000 by 2020 if exponential extrapolation of the number of past publications is applicable. Applied thermodynamics is a valuable tool to make sense of this vast body of research, and we present three examples of its contribution to CO2-capture process technology. Aqueous-ammonia processes have been proposed as energy-efficient alternatives to traditional alkanolamine process, and early proponents claimed that a significant advantage of the technology is that the CO2 enthalpy of solution is exceptionally low, about −27kJ/mol. A rigorous thermodynamic model with correct speciation estimated that the CO2 heat of solution is closer to about −65kJ/mol, a number that was later confirmed by calorimetric measurements. The thermodynamic model enabled realistic analysis of the chilled-ammonia process, and these results have been supported by subsequent studies by other researchers. Further work on this subject established the rigorous and complete form of the Gibbs–Helmholtz equation, and demonstrated its value in evaluating the consistency between vapor–liquid equilibrium and calorimetric data. Theoretical and experimental studies have been used to find the best solvent for CO2 capture. Some researchers have assumed that the goal is seek solvents with high CO2 capacity and a low enthalpy of solution. This notion was tested by inventing solvents with various properties, the only restriction being that the properties must be thermodynamically consistent. The results have provided insight into the interplay between CO2 absorption and the heat of regeneration (through the Gibbs–Helmholtz equation), and reveal subtle characteristics that may guide the development of future solvents. A promising step-out technology for CO2 capture is “CO2-binding liquids with polarity-swing-assisted regeneration.” Reliable analysis and design of this complex technology requires a thermodynamic model that describes the chemical absorption (i.e., speciation) as well as vapor–liquid–liquid equilibrium. The initial thermodynamic model has enabled useful projections of process performance. The model limitations and the need for future improvements are also discussed. [Copyright &y& Elsevier]

Abstract: The CO2-capture literature is difficult to follow because the number of papers and patents has exploded, and the claims of the authors are difficult to substantiate. From a beginning in the early 90s with just a handful of papers each year, the number of yearly papers has grown exponentially, reaching almost 1,000 publications in 2011. If this exponential rate of increase continues – and there is reason to believe that it will do so – the number of yearly publications will exceed 10,000 before 2020! The number of patents shows a similarly explosive growth. We believe that scientists and engineers who follow this important technology will be aided if they had some structure to guide them, and this paper represents our attempt to initiate the development of such guidelines. [Copyright &y& Elsevier]

Abstract: There is strong world-wide interest in developing new and improved processes for post-combustion capture of CO2, usually using chemical absorption. Developers of new processes make positive claims for their proposals in terms of low energy consumption, but these are usually difficult to validate. This paper demonstrates that rigorous application of thermodynamic analysis and process simulation provides a powerful way to quantitatively evaluate the energy requirements of CO2-capture processes by applying this methodology to the analysis of the chilled-ammonia process. [Copyright &y& Elsevier]