195 results found
Ravipati S, Galindo A, Jackson G, et al., 2019, An investigation of free-energy-averaged (coarse-grained) potentials for fluid adsorption on heterogeneous solid surfaces., Phys Chem Chem Phys
Coarse-grained, two-body fluid-solid potentials provide a simple way to describe the interaction between a fluid molecule and a solid in adsorption theories, and also a means to reduce the computational expense in molecular simulations, compared to those employing full atomistic detail. Here we investigate the applicability of a recently proposed mapping procedure to obtain free-energy-averaged (FEA) fluid-solid interactions for fluids on various heterogeneous surfaces. Methane and graphite are chosen as the fluid and the solid, respectively, and the surface graphene layer is modified to create chemical and geometrical heterogeneities; for the latter surfaces, the FEA mapping is appropriately modified to account for vacancies. Adsorption isotherms and fluid density profiles are obtained by performing grand canonical Monte Carlo (GCMC) simulations for explicit-solid and FEA-potential representations, and are compared to gain insights about the applicability and limitations of the FEA potentials. For solids with homogeneous and chemically heterogeneous surfaces, adsorption isotherms and density profiles obtained using FEA potentials are in good agreement with those obtained using an explicit-solid representation. For surfaces containing vacancies, isotherms and density profiles obtained using the unmodified FEA potential differ significantly from their explicit-surface analogues. When using the FEA potential obtained with the modified mapping procedure some deviations are still seen at very high pressure, however, at low to moderate pressures, agreement is, once again, good.
Borhani T, Garcia-Munoz S, Luciani C, et al., 2019, A hybrid QSPR model for the prediction of the free energy of solvation of organic solute/solvent pairs, Physical Chemistry Chemical Physics, Pages: 13706-13720, ISSN: 1463-9076
Due to the importance of the Gibbs free energy of solvation in understanding many physicochemical phenomena, including lipophilicity, phase equilibria and liquid-phase reaction equilibrium and kinetics, there is a need for predictive models that can be applied across large sets of solvents and solutes. In this paper, we propose two quantitative structure property relationships (QSPRs) to predict the Gibbs free energy of solvation, developed using partial least squares (PLS) and multivariate linear regression (MLR) methods for 295 solutes in 210 solvents with total number of data points of 1777. Unlike other QSPR models, the proposed models are not restricted to a specific solvent or solute. Furthermore, while most QSPR models include either experimental or quantum mechanical descriptors, the proposed models combine both, using experimental descriptors to represent the solvent and quantum mechanical descriptors to represent the solute. Up to twelve experimental descriptors and nine quantum mechanical descriptors are considered in the proposed models. Extensive internal and external validation is undertaken to assess model accuracy s in predicting the Gibbs free energy of solvation for a large number of solute/solvent pairs. The best MLR model, which includes three solute descriptors and two solvent properties, yields a coefficient of determination (R2) of 0.88 and a root mean squared error (RMSE) of 0.59 kcal/mol for the training set. The best PLS model includes six latent variables, and has a R2 value of 0.91 and a RMSE of 0.52 kcal/mol. The proposed models are compared to selected results based on continuum solvation quantum chemistry calculations. They enable the fast prediction of the Gibbs free energy of solvation of a wide range of solutes in different solvents.
Galindo A, Rahman S, Lobanova O, et al., 2018, SAFT‑γ force field for the simulation of molecular fluids. 5. Hetero Group coarse-grained models of linear alkanes and the importance of intramolecular interactions, Journal of Physical Chemistry B, Vol: 122, Pages: 9161-9177, ISSN: 1520-5207
The SAFT-γ Mie group-contribution equation of state [Papaioannou J. Chem. Phys. 2014, 140, 054107] is used to develop a transferable coarse-grained (CG) force-field suitable for the molecular simulation of linear alkanes. A heterogroup model is fashioned at the resolution of three carbon atoms per bead in which different Mie (generalized Lennard-Jones) interactions are used to characterize the terminal (CH3–CH2–CH2−) and middle (−CH2–CH2–CH2−) beads. The force field is developed by combining the SAFT-γ CG top-down approach [Avendaño J. Phys. Chem. B 2011, 115, 11154], using experimental phase-equilibrium data for n-alkanes ranging from n-nonane to n-pentadecane to parametrize the intermolecular (nonbonded) bead–bead interactions, with a bottom-up approach relying on simulations based on the higher resolution TraPPE united-atom (UA) model [Martin; , Siepmann J. Phys. Chem. B 1998, 102, 2569] to establish the intramolecular (bonded) interactions. The transferability of the SAFT-γ CG model is assessed from a detailed examination of the properties of linear alkanes ranging from n-hexane (n-C6H14) to n-octadecane (n-C18H38), including an additional evaluation of the reliability of the description for longer chains such as n-hexacontane (n-C60H122) and a prototypical linear polyethylene of moderate molecular weight (n-C900H1802). A variety of structural, thermodynamic, and transport properties are examined, including the pair distribution functions, vapor–liquid equilibria, interfacial tension, viscosity, and diffusivity. Particular focus is placed on the impact of incorporating intramolecular interactions on the accuracy, transferability, and representability of the CG model. The novel SAFT-γ CG force field is shown to provide a reliable description of the thermophysical properties of the n-alkanes, in most cases at a level comparable to the that obtained with higher resolution models.
Ravipati S, Aymard B, Kalliadasis S, et al., 2018, On the equilibrium contact angle of sessile liquid drops from molecular dynamics, Journal of Chemical Physics, Vol: 148, ISSN: 0021-9606
We present a new methodology to estimate the contact angles of sessile drops from molec-ular simulations, by using the Gaussian convolution method of Willard and Chandler (J.Phys. Chem. B, Vol. 114, 1954-1958, 2010) to calculate the coarse-grained density fromatomic coordinates. The iso-density contour with average coarse-grained density valueequal to half of the bulk liquid density is identified as the average liquid-vapor (LV) inter-face. Angles between the unit normal vectors to the average LV interface and unit normalvector to the solid surface, as a function of the distance normal to the solid surface, arecalculated. The cosines of these angles are extrapolated to the three-phase contact line toestimate the sessile drop contact angle. The proposed methodology, which is relativelyeasy to implement, is systematically applied to three systems: (i) a Lennard-Jones (LJ)drop on a featureless LJ9-3surface; (ii) an SPC/E water drop on a featureless LJ9-3sur-face; and (iii) an SPC/E water drop on a graphite surface. The sessile drop contact anglesestimated with our methodology for the first two systems, are shown to be in good agree-ment with the angles predicted from Young’s equation. The interfacial tensions requiredfor this equation are computed by employing the test-area perturbation method for the cor-responding planar interfaces. Our findings suggest that the widely adopted spherical-capapproximation should be used with caution, as it could take a long time for a sessile dropto relax to a spherical shape, of the order of100ns, especially for water molecules initiatedin a lattice configuration on a solid surface. But even though a water drop can take a longtime to reach the spherical shape, we find that the contact angle is well established muchfaster and the drop evolves towards the spherical shape following a constant-contact-anglerelaxation dynamics. Making use of this observation, our methodology allows a good es-timation of the sessile drop
Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.
Grant E, Pan Y, Richardson J, et al., 2018, Multi-Objective Computer-Aided Solvent Design for Selectivity and Rate in Reactions, Computer Aided Chemical Engineering, Pages: 2437-2442
© 2018 Elsevier B.V. A hybrid empirical computer-aided methodology to design the solvent for a reaction, incorporating both selectivity and rate, is presented. A small initial set of diverse solvents is used, for which experimental, in situ kinetic data are obtained. A surrogate model is utilized to correlate the reaction kinetics with solvent properties and a computer-aided molecular design (CAMD) multi-objective optimization problem is then formulated to identify solvents with improved performance compared with the initial solvent set. This methodology is applied to an SNAr reaction of 2,4-difluoroacetophenone with pyrrolidine, which demonstrates an interesting effect of solvent on both the selectivity of the ortho-:para-substitution ratio and the overall rate of the reaction. A set of Pareto optimal solutions is identified, highlighting the trade-off between reaction rate and selectivity.
Zhao B, Lindeboom T, Benner S, et al., 2017, Predicting the Fluid-Phase Behavior of Aqueous Solutions of ELP (VPGVG) Sequences Using SAFT-VR., Langmuir, Vol: 33, Pages: 11733-11745, ISSN: 0743-7463
The statistical associating fluid theory for potentials of variable range (SAFT-VR) is used to predict the fluid phase behavior of elastin-like polypeptide (ELP) sequences in aqueous solution with special focus on the loci of lower critical solution temperatures (LCSTs). A SAFT-VR model for these solutions is developed following a coarse-graining approach combining information from atomistic simulations and from previous SAFT models for previously reported relevant systems. Constant-pressure temperature-composition phase diagrams are determined for solutions of (VPGVG)n sequences + water with n = 1 to 300. The SAFT-VR equation of state lends itself to the straightforward calculation of phase boundaries so that complete fluid-phase equilibria can be calculated efficiently. A broad range of thermodynamic conditions of temperature and pressure are considered, and regions of vapor-liquid and liquid-liquid coexistence, including LCSTs, are found. The calculated phase boundaries at low concentrations match those measured experimentally. The temperature-composition phase diagrams of the aqueous ELP solutions at low pressure (0.1 MPa) are similar to those of types V and VI phase behavior in the classification of Scott and van Konynenburg. An analysis of the high-pressure phase behavior confirms, however, that a closed-loop liquid-liquid immiscibility region, separate from the gas-liquid envelope, is present for aqueous solutions of (VPGVG)30; such a phase diagram is typical of type VI phase behavior. ELPs with shorter lengths exhibit both liquid-liquid and gas-liquid regions, both of which become less extensive as the chain length of the ELP is decreased. The strength of the hydrogen-bonding interaction is also found to affect the phase diagram of the (VPGVG)30 system in that the liquid-liquid and gas-liquid regions expand as the hydrogen-bonding strength is decreased and shrink as it is increased. The LCSTs of the mixtures are seen to decrease as the ELP chain length is in
Hutacharoen P, Dufal S, Papaioannou V, et al., 2017, Predicting the solvation of organic compounds in aqueous environments: from alkanes and alcohols to pharmaceuticals, Industrial and Engineering Chemistry Research, Vol: 56, Pages: 10856-0876, ISSN: 0888-5885
The development of accurate models to predict the solvation, solubility, and partitioning of nonpolar and amphiphilic compounds in aqueous environments remains an important challenge. We develop state-of-the-art group-interaction models that deliver an accurate description of the thermodynamic properties of alkanes and alcohols in aqueous solution. The group-contribution formulation of the statistical associating fluid theory based on potentials with a variable Mie form (SAFT-γ Mie) is shown to provide accurate predictions of the phase equilibria, including liquid–liquid equilibria, solubility, free energies of solvation, and other infinite-dilution properties. The transferability of the model is further exemplified with predictions of octanol–water partitioning and solubility for a range of organic and pharmaceutically relevant compounds. Our SAFT-γ Mie platform is reliable for the prediction of challenging properties such as mutual solubilities of water and organic compounds which can span over 10 orders of magnitude, while remaining generic in its applicability to a wide range of compounds and thermodynamic conditions. Our work sheds light on contradictory findings related to alkane–water solubility data and the suitability of models that do not account explicitly for polarity.
Diamanti A, Adjiman CS, Piccione PM, et al., 2016, Development of Predictive Models of the Kinetics of a Hydrogen Abstraction Reaction Combining Quantum-Mechanical Calculations and Experimental Data, Industrial & Engineering Chemistry Research, Vol: 56, Pages: 815-831, ISSN: 0888-5885
The importance of developing accurate modeling tools for the prediction of reaction kinetics is well recognized. In this work, a thorough investigation of the suitability of quantum mechanical (QM) calculations to predict the effect of temperature on the rate constant of the reaction between ethane and the hydroxyl radical is presented. Further, hybrid models that combine a limited number of QM calculations and experimental data are developed in order to increase their reliability. The activation energy barrier of the reaction is computed using various computational methods, such as B3LYP, M05-2X, M06-2X, MP2 and PMP2, CBS-QB3, and W1BD, with a selection of basis sets. A broad range of values is obtained, including negative barriers for all of the calculations with B3LYP. The rate constants are also obtained for each method, using conventional transition state theory, and are compared with available experimental values at 298 K. The best agreement is achieved with the M05-2X functional with cc-pV5Z basis set. Rate constants calculated at this level of theory are also found to be in good agreement with experimental values at different temperatures, resulting in a mean absolute error of the logarithm (MAEln) of the calculated values of 0.213 over a temperature range of 200–1250 K and 0.108 over a temperature range of 300–499 K. Tunnelling and vibrational anharmonicities are identified as important sources of discrepancies at low and high temperatures, respectively. Hybrid models are proposed and found to provide good correlated rate-constant values and to be competitive with conventional kinetic models, i.e., the Arrhenius and the three-parameter Arrhenius models. The combination of QM-calculated and experimental data sources proves particularly beneficial when fitting to scarce experimental data. The parameters of the model built on the hybrid strategy have a significantly reduced uncertainty (reflected in the much narrower 95% confidence intervals) compa
Eriksen DK, Lazarou G, Galindo A, et al., 2016, Development of intermolecular potential models for electrolyte solutions using an electrolyte SAFT-VR Mie equation of state, Molecular Physics, Vol: 114, Pages: 2724-2749, ISSN: 1362-3028
We present a theoretical framework and parameterisation of intermolecular potentials for aqueous electrolyte solutions using the statistical associating fluid theory based on the Mie interaction potential (SAFT-VR Mie), coupled with the primitive, non-restricted mean-spherical approximation (MSA) for electrolytes. In common with other SAFT approaches, water is modelled as a spherical molecule with four off-centre association sites to represent the hydrogen-bonding interactions; the repulsive and dispersive interactions between the molecular cores are represented with a potential of the Mie (generalised Lennard-Jones) form. The ionic species are modelled as fully dissociated, and each ion is treated as spherical: Coulombic ion–ion interactions are included at the centre of a Mie core; the ion–water interactions are also modelled with a Mie potential without an explicit treatment of ion–dipole interaction. A Born contribution to the Helmholtz free energy of the system is included to account for the process of charging the ions in the aqueous dielectric medium. The parameterisation of the ion potential models is simplified by representing the ion–ion dispersive interaction energies with a modified version of the London theory for the unlike attractions. By combining the Shannon estimates of the size of the ionic species with the Born cavity size reported by Rashin and Honig, the parameterisation of the model is reduced to the determination of a single ion–solvent attractive interaction parameter. The resulting SAFT-VRE Mie parameter sets allow one to accurately reproduce the densities, vapour pressures, and osmotic coefficients for a broad variety of aqueous electrolyte solutions; the activity coefficients of the ions, which are not used in the parameterisation of the models, are also found to be in good agreement with the experimental data. The models are shown to be reliable beyond the molality range considered during parameter estimatio
Brand CV, Graham E, Rodriguez J, et al., 2016, On the use of molecular-based thermodynamic models to assess theperformance of solvents for CO₂capture processes:monoethanolamine solutions, Faraday Discussions, Vol: 192, Pages: 337-390, ISSN: 1364-5498
Predictive models play an important role in the design of post-combustion processes for the capture of carbon dioxide (CO2) emitted from power plants. A rate-based absorber model is presented to investigate the reactive capture of CO2 using aqueous monoethanolamine (MEA) as a solvent, integrating a predictive molecular-based equation of state: SAFT-VR SW (Statistical Associating Fluid Theory-Variable Range, Square Well). A distinctive physical approach is adopted to model the chemical equilibria inherent in the process. This eliminates the need to consider reaction products explicitly and greatly reduces the amount of experimental data required to model the absorber compared to the more commonly employed chemical approaches. The predictive capabilities of the absorber model are analyzed for profiles from 10 pilot plant runs by considering two scenarios: (i) no pilot-plant data are used in the model development; (ii) only a limited set of pilot-plant data are used. Within the first scenario, the mass fraction of CO2 in the clean gas is underestimated in all but one of the cases, indicating that a best-case performance of the solvent can be obtained with this predictive approach. Within the second scenario a single parameter is estimated based on data from a single pilot plant run to correct for the dramatic changes in the diffusivity of CO2 in the reactive solvent. This parameter is found to be transferable for a broad range of operating conditions. A sensitivity analysis is then conducted, and the liquid viscosity and diffusivity are found to be key properties for the prediction of the composition profiles. The temperature and composition profiles are sensitive to thermodynamic properties that correspond to major sources of heat generation or dissipation. The proposed modelling framework can be used as an early assessment of solvents to aid in narrowing the search space, and can help in determining target solvents for experiments and more detailed modelling.
Struebing H, Obermeier S, Siougkrou E, et al., 2016, A QM-CAMD approach to solvent design for optimal reaction rates, Chemical Engineering Science, Vol: 159, Pages: 69-83, ISSN: 1873-4405
The choice of solvent in which to carry out liquid-phase organic reactions often has a largeimpact on reaction rates and selectivity and is thus a key decision in process design. A systematicmethodology for solvent design that does not require any experimental data on the effect ofsolvents on reaction kinetics is presented. It combines quantum mechanical computations forthe reaction rate constant in various solvents with a computer-aided molecular design (CAMD)formulation. A surrogate model is used to derive an integrated design formulation that combineskinetics and other considerations such as phase equilibria, as predicted by group contributionmethods. The derivation of the mixed-integer nonlinear formulation is presented step-by-step.In the application of the methodology to a classic SN2 reaction, the Menschutkin reaction,the reaction rate is used as the key performance objective. The results highlight the tradeoffsbetween different chemical and physical properties such as reaction rate constant, solventdensity and solid reactant solubility and lead to the identification of several promising solventsto enhance reaction performance.
Papadopoulos AI, Badr S, Chremos A, et al., 2016, Computer-aided molecular design and selection of CO2 capture solvents based on thermodynamics, reactivity and sustainability, Molecular Systems Design & Engineering, Vol: 1, Pages: 313-334, ISSN: 2058-9689
The identification of improved carbon dioxide (CO2) capture solvents remains a challenge due to the vast number of potentially-suitable molecules. We propose an optimization-based computer-aided molecular design (CAMD) method to identify and select, from hundreds of thousands of possibilities, a few solvents of optimum performance for CO2 chemisorption processes, as measured by a comprehensive set of criteria. The first stage of the approach involves a fast screening stage where solvent structures are evaluated based on the simultaneous consideration of important pure component properties reflecting thermodynamic, kinetic, and sustainability behaviour. The impact of model uncertainty is considered through a systematic method that employs multiple models for the prediction of performance indices. In the second stage, high-performance solvents are further selected and evaluated using a more detailed thermodynamic model, i.e. the group-contribution statistical associating fluid theory for square well potentials (SAFT-γ SW), to predict accurately the highly non-ideal chemical and phase equilibrium of the solvent–water–CO2 mixtures. The proposed CAMD method is applied to the design of novel molecular structures and to the screening of a data set of commercially available amines. New molecular structures and commercially-available compounds that have received little attention as CO2 capture solvents are successfully identified and assessed using the proposed approach. We recommend that these solvents should be given priority in experimental studies to identify new compounds.
Gopinath S, Jackson G, Galindo A, et al., 2016, Outer approximation algorithm with physical domain reduction for computer-aided molecular and separation process design, AICHE Journal, Vol: 62, Pages: 3484-3504, ISSN: 0001-1541
Integrated approaches to the design of separation systems based on computer-aided molecular and process design (CAMPD) can yield an optimal solvent structure and process conditions. The underlying design problem, however, is a challenging mixed integer nonlinear problem, prone to convergence failure as a result of the strong and nonlinear interactions between solvent and process. To facilitate the solution of this problem, a modified outer-approximation (OA) algorithm is proposed. Tests that remove infeasible regions from both the process and molecular domains are embedded within the OA framework. Four tests are developed to remove subdomains where constraints on phase behavior that are implicit in process models or explicit process (design) constraints are violated. The algorithm is applied to three case studies relating to the separation of methane and carbon dioxide at high pressure. The process model is highly nonlinear, and includes mass and energy balances as well as phase equilibrium relations and physical property models based on a group-contribution version of the statistical associating fluid theory (SAFT-γ Mie) and on the GC+ group contribution method for some pure component properties. A fully automated implementation of the proposed approach is found to converge successfully to a local solution in 30 problem instances. The results highlight the extent to which optimal solvent and process conditions are interrelated and dependent on process specifications and constraints. The robustness of the CAMPD algorithm makes it possible to adopt higher-fidelity nonlinear models in molecular and process design.
Gopinath S, Galindo A, Jackson G, et al., 2016, A feasibility-based algorithm for Computer Aided Molecular and Process Design of solvent-based separation systems, 26th European Symposium on Computer Aided Process Engineering (ESCAPE 26), Publisher: Elsevier, Pages: 73-78, ISSN: 1570-7946
Computer-aided molecular and product design (CAMPD) can in principle be used to find simultaneouslythe optimal conditions in separation processes and the structure of the optimal solvents.In many cases, however, the solution of CAMPD problems is challenging. In this paper, we proposea solution approach for the CAMPD of solvent-based separation systems in which implicitconstraints on phase behaviour in process models are used to test the feasibility of the processand solvent domains. The tests not only eliminate infeasible molecules from the search space butalso infeasible combinations of solvent molecules and process conditions. The tests also providebounds for the optimization of the process model (primal problem) for each solvent, facilitatingnumerical solution. This is demonstrated on a prototypical natural gas purification process.
Galindo A, Adjiman, Jackson G, et al., 2015, Application of the SAFT-γ Mie group contribution equation of state to fluids of relevance to the oil and gas industry, Fluid Phase Equilibria, Vol: 416, Pages: 104-119, ISSN: 0378-3812
The application of the SAFT-γ Mie group contribution approach [Papaioannou et al., J. Chem. Phys., 140 (2014) 054107] to the study of a range of systems of relevance to the oil and gas industry is presented. In particular we consider carbon dioxide, water, methanol, aromatics, alkanes and their mixtures. Following a brief overview of the SAFT-γ Mie equation of state, a systematic methodology for the development of like and unlike group parameters relevant to the systems of interest is presented. The determination of group-group interactions entails a sequence of steps including: the selection of representative components and mixtures (in this instance carbon dioxide, water, methanol, aromatics and alkanes); the definition of an appropriate set of groups to describe them; the collection of target experimental data used to estimate the group-group interactions; the determination of the group-group interaction parameters; and the assessment of the adequacy of the parameters and theoretical approach. The predictive capability of the SAFT-γ Mie group contribution approach is illustrated for a selection of mixtures, including representative examples of the simultaneous description of vapour-liquid and liquid-liquid equilibria, the densities of the coexisting phases, second derivative thermodynamic properties, and excess properties of mixing. Good quantitative agreement between the predictions and experimental data is achieved, even in the case of challenging mixtures comprising carbon dioxide and water, n-alkanes and water, and methanol and methane.
Al Ghafri SZS, Forte E, Galindo A, et al., 2015, Experimental and Modeling Study of the Phase Behavior of (Heptane plus Carbon Dioxide plus Water) Mixtures, Journal of Chemical and Engineering Data, Vol: 60, Pages: 3670-3681, ISSN: 1520-5134
We report experimental measurements ofthree-phase equilibria in the system (heptane + carbon dioxide+ water) obtained with a quasi-static analytical apparatus withcompositional analysis by means of gas chromatography. Theapparatus was calibrated by an absolute area method and thewhole measurement system was validated by means ofcomparison with the published literature data of the system(heptane + carbon dioxide). The compositions of the threephases coexisting in equilibrium were measured along fiveisotherms at temperatures from (323.15 to 413.15) K withpressures ranging from approximately 2 MPa to the uppercritical end point pressure at which the two nonaqueousphases became critical. The experimental results have been compared with the predictions of the statistical associating fluidtheory for potentials of variable range. The unlike binary interaction parameters used here are consistent with a previous study fora ternary mixture of a different n-alkane, while the alkane−water binary interaction parameter is found to be transferable and thealkane−carbon dioxide binary interaction parameter is predicted using a modified Hudson-McCoubrey combining rule.Generally, good agreement between experiment and theory was found
Jover J, Galindo A, Jackson G, et al., 2015, Fluid-fluid coexistence in an athermal colloid-polymer mixture: thermodynamic perturbation theory and continuum molecular-dynamics simulation, MOLECULAR PHYSICS, Vol: 113, Pages: 2608-2628, ISSN: 0026-8976
Chremos A, Forte E, Papaioannou V, et al., 2015, Modelling the phase and chemical equilibria of aqueous solutions of alkanolamines and carbon dioxide using the SAFT-γ SW group contribution approach, Fluid Phase Equilibria, Vol: 407, Pages: 280-297, ISSN: 0378-3812
The speciation reactions that take place in mixtures of water, carbon dioxide (CO2), and alka-nolamines make the modelling of the chemical and uid-phase equilibria of these systems chal-lenging. We demonstrate for the rst time that the statistical associating uid theory (SAFT),formulated within a group-contribution (GC) framework based on transferable intermolecularsquare-well (SW) potentials (SAFT- SW) can be used to model successfully such complexreacting systems. The chemical reactions in these mixtures are described via a physical associ-ation model. The concept of second-order groups is introduced in the SAFT- SW approach inorder to deal with the multifunctional nature of the alkanolamines. In developing the models,several compounds including ethylamine, propylamine, ethanol, propanol, 2-aminoethanol and3-amino-1-propanol are considered. We present calculations and predictions of the uid-phasebehaviour of these compounds and a number of their aqueous mixtures with and without CO2.The group-contribution nature of the models can be used to predict the absorption of carbondioxide in aqueous solutions of 5-amino-1-pentanol and 6-amino-1-hexanol. The proposed pre-dictive approach offers a robust platform for the identi cation of new solvents and mixturesthat are viable candidates for CO2 absorption, thereby guiding experimental studies.
Sadeqzadeh M, Papaioannou V, Dufal S, et al., 2015, The development of unlike induced association-site models to study the phase behaviour of aqueous mixtures comprising acetone, alkanes and alkyl carboxylic acids with the SAFT-γ Mie group contribution methodology, Fluid Phase Equilibria, Vol: 407, Pages: 39-57, ISSN: 0378-3812
Providing accurate predictions of the thermodynamic properties of highly polar and hydrogen bonding compounds and their mixtures is challenging from a theoretical perspective. The combination of an equation of state (EoS) based on the statistical associating fluid theory (SAFT) with a group contribution (GC) methodology offers both accuracy and predictive capability for the thermodynamic properties of mixtures. In our current work, the SAFT-γ Mie equation of state is used to capture the underlying complexity of systems in which specific interactions (e.g. hydrogen bonding, dipolar interactions, chemical association) play an important role, by incorporating highly versatile association-site schemes to model mixtures in which unlike induced association interactions occur; this is done by assigning to the functional groups a number of association sites that are inactive in the pure fluid, but become active in certain mixtures. We refer to this type of association mechanism as "unlike induced" association and to the sites involved in this interaction as "unlike induced" association sites. The concept of unlike induced association sites is applied here to develop reliable SAFT-γ Mie group contribution models to describe the properties of acetone, alkyl carboxylic acids, and their mixtures with water and n-alkanes. The parameter table of available SAFT-γ Mie models is expanded to incorporate the corresponding group interaction parameters for acetone, which is treated as a molecular group, the carboxyl group COOH, and their unlike interaction group parameters with water, and the methyl CH<inf>3</inf>, methanediyl CH<inf>2</inf>, and methanetriyl CH alkyl groups. In particular, one unlike induced site is used with the acetone model to mediate hydrogen bonding of the acetone oxygen in mixtures containing hydrogen bond donors, and two pairs of unlike induced sites are included on the COOH group to mediate hydrogen
Chow YTF, Eriksen DK, Galindo A, et al., 2015, Interfacial tensions of systems comprising water, carbon dioxide and diluent gases at high pressures: Experimental measurements and modelling with SAFT-VR Mie and square-gradient theory, Fluid Phase Equilibria, Vol: 407, Pages: 159-176, ISSN: 0378-3812
Experimental interfacial tensions of the systems (H<inf>2</inf>O+CO<inf>2</inf>), (H<inf>2</inf>O+N<inf>2</inf>), (H<inf>2</inf>O+Ar), (H<inf>2</inf>O+CO<inf>2</inf> +N<inf>2</inf>) and (H<inf>2</inf>O+CO<inf>2</inf> +Ar) are compared with calculations based on the statistical associating fluid theory for variable range potentials of the Mie form (SAFT-VR Mie) in combination with the square-gradient theory (SGT). Comparisons are made at temperatures from (298 to 473)K and at pressures up to 60MPa. Experimental data for the systems (H<inf>2</inf>O+CO<inf>2</inf>), (H<inf>2</inf>O+N<inf>2</inf>) and (H<inf>2</inf>O+CO<inf>2</inf> +N<inf>2</inf>) are taken from the literature. For the (H<inf>2</inf>O+Ar) and (H<inf>2</inf>O+CO<inf>2</inf> +Ar) systems, we report new experimental interfacial-tension data at temperatures of (298.15-473.15)K and pressures from (2 to 50)MPa, measured by the pendant-drop method. The expanded uncertainties at 95% confidence are 0.05K for temperature, 70kPa for pressure, 0.016× γ for interfacial tension in the binary (Ar+H<inf>2</inf>O) system and 0.018× γ for interfacial tension in the ternary (CO<inf>2</inf> +Ar+H<inf>2</inf>O) system.The parameters in the SAFT-VR Mie equation of state are estimated entirely from phase-equilibrium data for the pure components and binary mixtures. For pure water, the SGT influence parameter is determined from vapour-liquid surface-tension data, as is common practice. Since the other components are supercritical over most or the entire temperature range under consideration, their pure-component influence parameters are regressed by comparison with the binary interfacial-tension data. A geometric-mean combining rule
Cristino AF, Morgado P, Galindo A, et al., 2015, High-temperature vapour-liquid equilibrium for ethanol-1-propanol mixtures and modeling with SAFT-VR, FLUID PHASE EQUILIBRIA, Vol: 398, Pages: 5-9, ISSN: 0378-3812
Dufal S, Lafitte T, Galindo A, et al., 2015, Developing intermolecular-potential models for use with the SAFT-VRMie equation of state, AIChE Journal, Vol: 61, Pages: 2891-2912, ISSN: 0001-1541
A major advance in the statistical associating fluid theory (SAFT) for potentials of variable range (SAFT-VR) has recently been made with the incorporation of the Mie (generalized Lennard–Jones [LJ]) interaction between the segments comprising the molecules in the fluid (Lafitte et al. J. Chem. Phys. 2013;139:154504). The Mie potential offers greater versatility in allowing one to describe the softness/hardness of the repulsive interactions and the range of the attractions, which govern fine details of the fluid-phase equilibria and thermodynamic derivative properties of the system. In our current work, the SAFT-VR Mie equation of state is employed to develop models for a number of prototypical fluids, including some of direct relevance to the oil and gas industry: methane, carbon dioxide and other light gases, alkanes, alkyl benzenes, and perfluorinated compounds. A complication with the use of more-generic force fields such as the Mie potential is the additional number of parameters that have to be considered to specify the interactions between the model molecules, leading to a degree of degeneracy in the parameter space. A formal methodology to isolate intermolecular-potential models and assess the adequacy of the description of the thermodynamic properties in terms of the complex parameter space is developed. Fluid-phase equilibrium properties (the vapor pressure and saturated-liquid density) are chosen as the target properties in the refinement of the force fields; the predictive capability for other properties such as the enthalpy of vaporization, single-phase density, speed of sound, isobaric heat capacity, and Joule–Thomson coefficient, is appraised. It is found that an overall improvement of the representations of the thermophysical properties of the fluids is obtained using the more-generic Mie form of interaction; in all but the simplest of fluids, one finds that the LJ interaction is not the most appropriate.
Ramrattan NS, Avendano C, Mueller EA, et al., 2015, A corresponding-states framework for the description of the Mie family of intermolecular potentials, MOLECULAR PHYSICS, Vol: 113, Pages: 932-947, ISSN: 0026-8976
Dufal S, Lafitte T, Haslam AJ, et al., 2015, The A in SAFT: developing the contribution of association to the Helmholtz free energy within a Wertheim TPT1 treatment of generic Mie fluids, Molecular Physics, Vol: 113, Pages: 948-984, ISSN: 1362-3028
An accurate representation of molecular association is a vital ingredient of advanced equations of state (EOSs), providing a description of thermodynamic properties of complex fluids where hydrogen bonding plays an important role. The combination of the first-order thermodynamic perturbation theory (TPT1) of Wertheim for associating systems with an accurate description of the structural and thermodynamic properties of the monomer fluid forms the basis of the statistical associating fluid theory (SAFT) family of EOSs. The contribution of association to the free energy in SAFT and related EOSs is very sensitive to the nature of intermolecular potential used to describe the monomers and, crucially, to the accuracy of the representation of the thermodynamic and structural properties. Here we develop an accurate description of the association contribution for use within the recently developed SAFT-VR Mie framework for chain molecules formed from segments interacting through a Mie potential [T. Lafitte, A. Apostolakou, C. Avendaño, A, Galindo, C. S. Adjiman, E. A. Müller, and G. Jackson, J. Chem. Phys. 139, 154504 (2013)]. As the Mie interaction represents a soft-core potential model, a method similar to that adopted for the Lennard-Jones potential [E. A. Müller and K. E. Gubbins, Ind. Eng. Chem. Res. 34, 3662 (1995)] is employed to describe the association contribution to the Helmholtz free energy. The radial distribution function (RDF) of the Mie fluid (which is required for the evaluation of the integral at the heart of the association term) is determined for a broad range of thermodynamic conditions (temperatures and densities) using the reference hyper-netted chain (RHNC) integral-equation theory. The numerical data for the association kernel of Mie fluids with different association geometries are then correlated for a range of thermodynamic states to obtain a general expression for the association contribution which can be applied for varying values
Papadokonstantakis S, Badr S, Hungerbühler K, et al., 2015, Toward Sustainable Solvent-Based Postcombustion CO<inf>2</inf> Capture: From Molecules to Conceptual Flowsheet Design, Computer Aided Chemical Engineering, Vol: 36, Pages: 279-310, ISSN: 1570-7946
Solvent-based postcombustion carbon dioxide (CO<inf>2</inf>) capture requires minimum retrofitting of current CO<inf>2</inf>-emitting power plants but is challenging because of the high energy penalty in solvent regeneration and the environmental impacts of solvent degradation. Research efforts are predominantly based on lab and pilot-scale experiments to select solvents and process systems which improve the overall performance of this technology. Notwithstanding the value of the experimental efforts, this study proposes an efficient computational approach for screening a vast number of commercial and novel solvents and process configurations. Computer-aided molecular design, advanced group contribution methods, process synthesis, and multicriteria sustainability assessment are combined to provide new insights in solvent-based CO<inf>2</inf> capture. This study provides details of the data requirements, highlights several high-performance solvents and process configurations, and quantifies the benefits from economic, life cycle, and hazard assessment perspective. Thus, it also provides information for the experimental approaches, focusing on a narrower, near-optimum design space.
Jover JF, Mueller EA, Haslam AJ, et al., 2015, Aspects of Asphaltene Aggregation Obtained from Coarse-Grained Molecular Modeling, ENERGY & FUELS, Vol: 29, Pages: 556-566, ISSN: 0887-0624
Gopinath S, Galindo A, Jackson G, et al., 2015, Computer aided molecular and process design using complex process and thermodynamic models: A screening based approach, Pages: 107-109
Copyright © American Institute of Chemical Engineers. All rights reserved. The design of optimal processing materials (molecules) and optimal process variables for a given process is referred to as Computer Aided Molecular and Process Design (CAMPD). Processing materials used to achieve process goals include mass separating agents (such as solvents for absorption, extraction, leaching and adsorbents), catalysts, heat transfer fluids and reaction medium solvents. Choosing processing molecules influences the optimal process variables and vice versa. Molecular and process decision variables are linked, interacting with each other in a complex manner. Hence, neither of these decisions can be made in isolation.
Burger J, Papaioannou V, Gopinath S, et al., 2015, A hierarchical method to integrated solvent and process design of physical CO<inf>2</inf> absorption using the SAFT-γ Mie approach, AIChE Journal, Vol: 61, Pages: 3249-3269, ISSN: 0001-1541
Molecular-level decisions are increasingly recognized as an integral part of process design. Finding the optimal process performance requires the integrated optimization of process and solvent chemical structure, leading to a challenging mixed-integer nonlinear programming (MINLP) problem. The formulation of such problems when using a group contribution version of the statistical associating fluid theory, SAFT-γ Mie, to predict the physical properties of the relevant mixtures reliably over process conditions is presented. To solve the challenging MINLP, a novel hierarchical methodology for integrated process and solvent design (hierarchical optimization) is presented. Reduced models of the process units are developed and used to generate a set of initial guesses for the MINLP solution. The methodology is applied to the design of a physical absorption process to separate carbon dioxide from methane, using a broad selection of ethers as the molecular design space. The solvents with best process performance are found to be poly(oxymethylene)dimethylethers.
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