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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]

The kinetics of the absorption of CO2 into two nonaqueous CO2-binding organic liquid (CO2BOL) solvents were measured at T=35, 45, and 55 °C with a wetted-wall column. Selected CO2 loadings were run with a so-called 'first-generation' CO2BOL, comprising an independent base and alcohol, and a 'second-generation' CO2BOL, in which the base and alcohol were conjoined. Liquid-film mass-transfer coefficient ( k′g) values for both solvents were measured to be comparable to values for monoethanolamine and piperazine aqueous solvents under a comparable driving force, in spite of far higher solution viscosities. An inverse temperature dependence of the k′g value was also observed, which suggests that the physical solubility of CO2 in organic liquids may be making CO2 mass transfer faster than expected. Aspen Plus software was used to model the kinetic data and compare the CO2 absorption behavior of nonaqueous solvents with that of aqueous solvent platforms. This work continues our development of the CO2BOL solvents. Previous work established the thermodynamic properties related to CO2 capture. The present paper quantitatively studies the kinetics of CO2 capture and develops a rate-based model. [ABSTRACT FROM AUTHOR]

We have improved the estimation of the solubility of hydrogen and carbon monoxide in a range of linear alcohols and alkanes (between C 4 and C 32 ) by using the method of molecular dynamics (MD) together with experimental data and traditional thermodynamics analysis. The goal of the study was to use a fundamental molecular-based method, after validation, to fill gaps in data in current literature, especially for systems considered challenging for traditional measurement and estimation methods. The simulation system used semi-permeable membranes to mimic actual experimental studies of gas solubility. Our combined analysis of both data and simulation results demonstrated that for higher carbon numbers (C N ) both CO and H 2 individually have similar Henry’s constant values in the two solvents, with H 2 values being roughly 50% higher in both solvents. The data and simulation results were also used to estimate limiting values of the mass-based Henry’s constant for H 2 and CO in the higher alcohols (large C N ). [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]

Highlights: [•] We study the performance of CO2-capture solvents using solution thermodynamics. [•] New solvents are created for which the only rule is thermodynamic consistency. [•] The conventional wisdom is that solvents with high capacity and low heat are best. [•] Our study shows that solvents with medium heat and mid-range capacity are optimum. [•] Our study clarifies and sharpens the rational search for new CO2-capture solvents. [Copyright &y& Elsevier]

The Gibbs–Helmholtz (G-H) equation connects vapor–liquidequilibrium (VLE) and calorimetric data. If experimental measurementsfor the heat of solution are not available, they may be estimatedthrough the G-H equation. Further, if both VLE and heat-of-solutiondata are available, their mutual thermodynamic consistency can beevaluated through the G-H equation, to develop the most accurate andreliable model. This kind of analysis is particularly useful for chemical-absorptionsystems, such as the capture of CO2using aqueous solutionsof amines, where regeneration energies are significant. In this work,the G-H equation is derived to unambiguously relate the commonly usedform to the rigorous and general form, including for systems wherephase equilibrium is accompanied by chemical reactions in any phase.The effect of approximations and the range of applicability of thecommon G-H equation are first applied to data generated for a simpleVLE system by an equation of state, with different reliability foundfor the vapor and liquid phases. Next, consistency is evaluated formany VLE and calorimetric data for CO2absorption in aqueousMEA (monoethanolamine). It is shown that some VLE and/or calorimetricdata sets are likely to be in error and that the experimental VLEand CO2heat of solution at the highest temperatures arecurrently uncertain. [ABSTRACT FROM AUTHOR]

Abstract: There is strong world-wide interest in developing new and improved processes for post-combustion capture of CO2, often 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 estimate the energy requirements of CO2-capture processes by applying the methodology to the analysis and evaluation of the chilled-ammonia process. [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]

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]

Abstract: Examples are used to illuminate ways in which applied thermodynamics is being successfully deployed in chemical technology and the challenges that need to be overcome. Nitric-acid plant modeling was very difficult two decades ago because of the complexity of the thermodynamic properties and the need to describe kinetic and mass-transfer limitations in the process equipment. This complex process and other similar processes are routinely modeled today thanks largely to advances in applied thermodynamics. In fact, applied thermodynamics is an established cornerstone of chemical engineering. Excel is an effective tool for custom applications and teaching since most scientists and engineers use it regularly. We demonstrate that the Excel add-in for Aspen Properties facilitates the creation of useful custom applications (e.g., analysis and understanding of flammability limits and analysis of pressure variation in batch reactors) – usually within a few hours – enabling big improvements in education and wide deployment of chemical technology. Modern software enables modeling of complex processes – and highlights the challenging areas. This point is elucidated through a promising process for hydrogen production via thermochemical water splitting: the sulfur iodine cycle. The sulfuric acid decomposition section of this process can be simulated accurately, but other sections (acid generation and hydrogen iodide decomposition) illustrate the difficulty of modeling phase behavior, particularly liquid-phase immiscibility, in complex electrolyte systems. The difficulties arise from model inadequacies as well as a lack of fundamental data. However, these difficulties will likely be overcome soon mainly through new data, but also through advance in molecular-thermodynamic models. Property estimation and data regression have progressed as independent silos for the development of applied thermodynamic models. We discuss the seminal contribution of a recent proposal that combines a segment-based NRTL model with a few (3–4) solubility measurements for a target solute to develop a predictive method for the solubility of this solute in most solvents and solvent mixtures of interest. This proposal creates an effective and efficient work process for solvent selection in the pharmaceutical and specialty chemical industries. The paper concludes by summarizing challenges that remain for the future use of applied thermodynamics in chemical technology. [Copyright &y& Elsevier]

Process modelling is invariably the basis for the quantitative design and evaluation of chemical processes in general and CO 2 -capture processes in particular. Several points need to be resolved in order to establish the validity and accuracy of the model. How good are the underlying data and models? Where are they weak and where are they strong? Which data are most important to develop reliable models? How accurate should the data be? How large should the design margins be? An effective way to resolve these important points is through uncertainty analysis. Understanding the validity and accuracy of a model through uncertainty analysis can be valuable for determining appropriate plant design margins. This work proposes a practical approach to first ensure that the model properly meets asymptotic limits (e.g., predicts equilibrium behavior for high kinetics or long contact times), and then to devise practical perturbation schemes for calculated properties in order to provide quantitative engineering insight into process uncertainties. Error propagation in process modelling is difficult because simply varying model parameters usually does not give meaningful answers from an engineering perspective, and therefore we have devised a practical scheme to perturb designated calculated properties. The results show that our approach to uncertainty analysis enables the design engineer to gain an intuitive understanding of how the uncertainty of the process models used for solvent-based CO 2 capture affects the process performance, and is complementary to the mathematically complex methods. As an example, specific results obtained in this work are that the most important properties for operations (in particular, solvent flow rate and heat rate) are phase equilibrium and chemical kinetics, followed by packing interfacial area, This paper completes a study that was first presented at the 12th International Conference on Greenhouse Gas Control Technologies (GHGT-12), Austin, TX, October 5–9, 2014. [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]