Equilibria In Complex Systems Research Articles

Effects of different alkyl chain lengths on excess properties of CO2-1-Butyl-1-methyl-pyrrolidinebis(trifluoromethanesulfonyl)imide, CO2-1-hexyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, CO2-1-octyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide systems

The study investigates the solubility of carbon dioxide (CO2) in three ionic liquids [BMP][Tf2N] (1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide), [HMP][Tf2N] (1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide) and [OMP][Tf2N] (1-octyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide). The research is conducted over a temperature range of 303.15 to 363.15 K. The phase equilibria of the binary systems are predicted using the Peng-Robinson (PR) equation of state, the Wilson (WS) mixing rule and the UNIFAC activity coefficient model. The interaction parameter kij is regressed from the vapor-liquid equilibrium (VLE) experimental data. The study also calculates the excess Gibbs free energy (GE), excess enthalpy (HE), and excess entropy (SE) for these systems. The research results indicate that the length of the alkyl chain in the cation has a significant effect on the excess properties of the CO2-ionic liquid systems. As the alkyl chain length increases, the excess Gibbs free energy and excess enthalpy decrease, while the excess entropy increases. The CO2-[OMP][Tf2N] system exhibits stronger interactions between CO2 and the ionic liquid, indicating a higher capacity for CO2 absorption. The study results are helpful for optimization of CO2 capture processes and the broader comprehension of fluid phase equilibria in complex systems.

Applications of Multicomponent Databases to the Improvement of Steel Processing and Design

The steel industry is challenged to develop new and efficient alloys, from the application, energy and environmental points of view. Alternative materials, too, challenge steel in individual applications. The industry has successfully met these challenges in the last 150 years, at least. In the last decades, one of the tools that contributed to this success has been computational thermodynamics, an integral part of the expanding ICME toolbox. In this work, the important change in paradigm brought by computational thermodynamics to solving problems involving equilibrium in complex systems, as those present in the steel industry, is reviewed. Then, examples of applications to problems ranging from steelmaking to processing and alloy design are presented, highlighting the importance of multicomponent databases. The extension from equilibrium to kinetics is included in some examples. It is concluded that computational thermodynamics in the steel industry is mature and, while some limitations may persist in areas of kinetic modeling, these techniques will mature in the near future.

Techno-economic Assessment of Thermal Co-pretreatment and Co-digestion of Food Wastes and Sewage Sludge for Heat, Power and Biochar Production

This study deals with techno-economic assessments of three system scenarios combining various conversion technologies including co-digestion, hydro-methanation, syngas production and integration, thermodynamic and electrochemical aspects of a solid oxide fuel cell (SOFC) system, as well as solving the problem of chemical equilibrium in complex systems. Aspen Plus and SuperPro software packages are used as simulation and optimization tools. The optimized results are compared with other studies and reveals that thermal co-treatment integrated with a two-stage bio-thermal process involving anaerobic digestion and hydrogasification can produce good quality biofuels for a SOFC system. The economics of the final selected thermal co-treatment hybrid process for processing 30000 tons per annum of dry solids is feasible at an electricity selling cost of 0.3 $/kWh, providing project benefits such as an IRR of 29.7%, a benefit to cost ratio of 1.38 and a net present value of 123 million $. This innovative scheme not only reduces CO2 but also improves the economic return and reduces the waste discharge.

Existence of Equilibria and Complexity of Computation in Optimizing Complex Systems

This paper characterizes the generic properties of interior equilibria in complex systems. The field of complexity has been growing and is concerned with the complexity of computation of complex systems. Complex systems are characterized as systems with a large number of adaptive interdependent parts. These systems demonstrate several properties including: emergence, where the whole does not act as the sum of the parts, and sensitivity to initial conditions. As the number of economic factors increases, the recursion of input-output and modeling error propagates. These two particular symptoms of complex systems make them difficult to model. Solutions to optimization problems of this sort may have different properties depending on the functional assumptions. The generic properties of solutions to these problems can help us have some expectations over the complexity of computation. One example of a complex system is the Game Theoretic Interaction between economic agents. The paper also attempts to shed light on the complexity of computation of such systems.

Heating and flooding: A unified approach for rapid generation of free energy surfaces

We propose a general framework for the efficient sampling of conformational equilibria in complex systems and the generation of associated free energy hypersurfaces in terms of a set of collective variables. The method is a strategic synthesis of the adiabatic free energy dynamics approach, previously introduced by us and others, and existing schemes using Gaussian-based adaptive bias potentials to disfavor previously visited regions. In addition, we suggest sampling the thermodynamic force instead of the probability density to reconstruct the free energy hypersurface. All these elements are combined into a robust extended phase-space formalism that can be easily incorporated into existing molecular dynamics packages. The unified scheme is shown to outperform both metadynamics and adiabatic free energy dynamics in generating two-dimensional free energy surfaces for several example cases including the alanine dipeptide in the gas and aqueous phases and the met-enkephalin oligopeptide. In addition, the method can efficiently generate higher dimensional free energy landscapes, which we demonstrate by calculating a four-dimensional surface in the Ramachandran angles of the gas-phase alanine tripeptide.

Thermodynamic simulation of biomass gas steam reforming for a solid oxide fuel cell (SOFC) system

This paper presents a methodology to simulate a small-scale fuel cell system for power generation using biomass gas as fuel. The methodology encompasses the thermodynamic and electrochemical aspects of a solid oxide fuel cell (SOFC), as well as solves the problem of chemical equilibrium in complex systems. In this case the complex system is the internal reforming of biomass gas to produce hydrogen. The fuel cell input variables are: operational voltage, cell power output, composition of the biomass gas reforming, thermodynamic efficiency, electrochemical efficiency, practical efficiency, the First and Second law efficiencies for the whole system. The chemical compositions, molar flows and temperatures are presented to each point of the system as well as the exergetic efficiency. For a molar water/carbon ratio of 2, the thermodynamic simulation of the biomass gas reforming indicates the maximum hydrogen production at a temperature of 1070 K, which can vary as a function of the biomass gas composition. The comparison with the efficiency of simple gas turbine cycle and regenerative gas turbine cycle shows the superiority of SOFC for the considered electrical power range.

Phase equilibria determination in complex slag systems

Despite the wealth of information available on phase equilibria of oxide systems, there remain many gaps and inconsistencies in the knowledge base. From an industry perspective, there is an ongoing need to adequately describe the phase chemistry of slag systems in order to optimise process performance and improve productivity. Since this chemical behaviour cannot be predicted from first principles it follows, there is also an ongoing need for accurate experimental data. The advancements made in recent years in the capabilities of sophisticated analytical and measurement equipment have made it possible to develop new experimental techniques for the direct determination of phase equilibria in low order and complex multicomponent slag systems. In addition, the development of powerful computer modelling tools makes it possible to provide more comprehensive descriptions of the phase chemistry, to present the information in a range of perspectives, and to critically analyse the various types of related thermodynamic and structural information available. This review provides an overview of the types of information that can be used to determine phase equilibria in slag systems, analyses the influence of uncertainty and the relative importance of these types of data, and describes the advantages and limitations of the various experimental techniques that can be employed to obtain this information. Examples of recent studies are provided that demonstrate how an integrated approach to the determination of phase equilibria in complex systems, involving the use of targeted experimental studies and systematic thermodynamic model development, can lead to a better utilisation of the current research capabilities and resources, and more accurate descriptions of these systems.

A new algorithm for the automation of phase diagram calculation

We propose a new algorithm for minimizing the Gibbs energy functional and constructing phase diagrams through utilizing geometric properties of the energy surfaces together with effective sampling techniques to improve on the starting points for the minimization. The new method possesses advantages over existing methods in terms of computational complexity and can be used to automate the calculation of phase equilibria in complex systems. Numerical results for binary and ternary systems are presented. Generalizations to higher dimensions are discussed.

Phase equilibria in complex systems of palm oil deodorizer condensates and supercritical carbon dioxide: experiments and correlation

Experimental phase equilibrium data were determined for supercritical carbon dioxide and complex mixtures of palm oil deodorizer condensates containing fatty acids and tocopherols. A static analytical apparatus was used, and samples from liquid and vapor phases were analyzed by gas chromatography (GC). The distribution coefficients of individual components or pseudocomponents could thus be determined. The data obtained were correlated with the Peng–Robinson and Redlich–Kwong–Aspen equations of state using van der Waals type and Wong–Sandler mixing rules. The predictive PSRK model was also used. Furthermore, literature data of the CO 2–oleic acid system was treated with these equations. The Redlich–Kwong–Aspen model performed best in the (pseudo-)binary systems, while the g E-model mixing rules were not successful. None of the models was able to correlate the pseudoternary system CO 2–fatty acids–tocopherols in a satisfactory manner.

A comprehensive comparison of mixing rules for calculation of phase equilibria in complex systems

Abstract Five different mixing rules for the SRK-EOS have been investigated for phase equilibrium calculations in chemically complex systems at high pressures. The mixing rutts are those of van der Waals with two binary parameters, the Huron-Vidal rule with three binary NRTL-parameters, the MHV2-model with UNIFAC-group parameters, the Schwarzentruber - Galivel-Solastiouk - Renon rule with three binary parameters, and the density dependent local composition rule with three binary parameters. The mixing rules are investigated both with and without temperature-dependent parameters. For each mixing rule the parameters are estimated using binary data for systems containing H2O, CO2, N2, H2S, CH3OH and n-alkanes up to n-decane. With the estimated parameters, multicomponent data have been predicted and compared with experimental results. Furthermore the influence of the thermodynamic consistency of the binary data has been investigated. There is found a large discrepancy in the predicted results for multicomponent phase equilibria between the different mixing rules, although almost the same results are obtained for the correlation of the binary data. For the investigated systems, the Huron-Vidal model gives the best overall predictions. If temperature dependent parameters are used, it is necessary to be very careful when extrapolation of temperature is performed.

The computation of chemical equilibrium in complex systems containing non-ideal solutions

A general algorithm for the computation of chemical equilibria in complex systems containing non-ideal solutions has been developed. The method is a G-minimization based on repeated linear and nonlinear programming steps. A computer program (THERIAK) based on this algorithm has been written and was used to solve a great variety of problems, ranging from a simple blast furnace calculation to liquid-liquid unmixing in a four component silicate melt. The computing times are in the magnitude of 1 2 to 2 seconds for each calculation. The method can also be used to test the consequences of thermodynamic models and data in systems of interest to many fields, including chemistry, geochemistry and metallurgy.