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The family of Gibbs-Helmholtz equations connect phase and chemical equilibrium with enthalpy and volume. This family of equations is one of the most useful--yet unappreciated and poorly understood--mathematical relations in chemical thermodynamics. This paper rigorously derives several variants of the Gibbs-Helmholtz equation that are applicable to chemical process technology, and evaluates their use for educational and industrial purposes. The focus of the contribution is the manner in which fundamental chemical thermodynamics contributes to the industrial practice of process technology. Some rigorous thermodynamic equations are more useful than others in particular applications of chemical process technology. The paper also studies the early historical development of the Gibbs-Helmholtz equation. [ABSTRACT FROM AUTHOR]

Itis widely recognized by experts that the computer-based designof chemical processes depends strongly on the correlated thermodynamicand transport properties, and the effect of property uncertaintiesshould be incorporated into the design. The most significant sourceof property uncertainties on process design is from the correlationsof phase equilibrium. Many approaches have been proposed, but uncertaintyanalysis is not a routine component of today’s industrial practice,mainly because education and awareness is lacking, and the proposedmethods are difficult to apply. The purpose of this paper is to reporta new approach to uncertainty analysis that is intuitively appealingand easy to apply in process simulation. The proposed approach focuseson activity coefficients and is based upon the simplification that,for the purpose of perturbation, the liquid mixture can be treatedas a set of pseudobinaries described by the Margules equation. Theresulting perturbation in the activity coefficient of component igoes to zero when its mole fraction approaches unity,and also is relatively small when its estimated activity coefficientis close to unity (i.e., near-ideal systems are likely to be modeledmore accurately than highly nonideal systems). In practice, the proposeduncertainty analysis is performed by varying a single parameter foreach component in the mixture. The utility of the proposed uncertaintymethod is demonstrated by application to two problems: (1) a propylene–propanesuperfractionator for which small changes in correlated relative volatilitieshave a large effect on the design of the distillation column, and(2) a dehexanizer column that separates a mixture containing manyclose-boiling components. It is demonstrated that the proposed analysisprovides quantitative insight into the effect of property uncertaintiesand helps to quantify the safety factors that need to be imposed uponthe design. While the proposed method is applied to activity-coefficientmodels, the same idea is applicable to other models such as equationsof state. [ABSTRACT FROM AUTHOR]

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]

Experimental data have served two critical roles in chemical process technology: (1) by providing the definitive quantitative basis to evaluate competing processes, to optimize designs, and ultimately to guarantee plant performance; and (2) by guiding the form and structure of applied-thermodynamics correlations. This paper first presents two representative applications to highlight the role of thermodynamic and transport properties in chemical process technology: ammonia recovery from syngas using water as solvent, and design of a caustic-guard system to eliminate small residual concentrations of SO2 from a gas stream. These applications illustrate the first role of experimental data. The paper next studies the second role by examining the historical contribution of experimental data-over two centuries— in guiding the development of key concepts and correlations, such as Henry's law (1802), group-contribution methods (Kopp, 1842), Raoult's law (1878), second-virial-coefficient correlation (Berthelot, 1907), surface-tension correlation (Macleod, 1923), the use of one property to estimate another (Othmer, 1940), cubic equations of state (Redlich and Kwong, 1949), electrolyte systems (van Krevelen, 1949), acentric factor (Pitzer, 1955), and highly accurate equations of state (Span and Wagner, 2003). The analysis reveals that careful, accurate, and wide-ranging experimental data have identified the patterns of the underlying phenomena. [ABSTRACT FROM AUTHOR]

Thermodynamic properties have always played essential roles in the engineering of chemical products and in the processes that manufacture them. Further, contemporary and future chemical technologies depend more than ever on property model formulation and application. This work explores how properties are utilized in process and product engineering, including opportunities and constraints of current property models, the current status of data availability and needs, and the interplay of data and models. Several case studies are given to illustrate underlying concepts, strategies for development, and methods of application to some industrial systems. [ABSTRACT FROM AUTHOR]