Predicting the Solubility of Solid Phenanthrene: A Combined Molecular Simulation and Group Contribution Approach

A simple correction to the infinite dilution activity coefficient computed via molecular simulation for a nonelectrolyte solid solute in solution is proposed. The methodology adopts the concept that the activity coefficient may be fundamentally interpreted as a product of a residual and combinatorial term. The residual contribution is assumed to be insensitive to concentration, and the combinatorial term is modeled using the athermal Flory–Huggins theory. The proposed method uses only properties for the solute computed at infinite dilution to estimate solution‐phase properties at finite concentrations. Properties of the pure solid solute are estimated using the group contribution method of Gani and coworkers, allowing for efficient blind solubility predictions to be made. The method is applied to predict the solubility of solid phenanthrene in 17 different solvents. For all cases, the combinatorial correction lowers the predicted solubility relative to the infinite dilution approximation, and in general, improves agreement with experiment. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2647–2661, 2013     

Nonequilibrium equation of state for Lennard‐Jones fluids and the calculation of strain‐rate dependent shear viscosity

Nonequilibrium molecular dynamics simulation data for a 12‐6 Lennard‐Jones fluid are obtained over a wide range of temperatures, densities and strain‐rates. The data, which cover 660 different state points, are used to deduce the nonequilibrium contributions to the energy and pressure of the fluid under steady‐state conditions. These contributions are analysed and used in conjunction with an equilibrium equation of state to obtain an accurate nonequilibrium steady‐state equation of state for the 12‐6 Lennard‐Jones fluid. Comparison with simulation data indicates that the nonequilibrium contributions can be obtained with a similar accuracy to the equilibrium contributions. Relationships for the shear viscosity as functions of density and pressure are obtained, which adequately reproduce the shear viscosity simulation data. The isochoric shear viscosity as a function of pressure is shown to be independent of strain‐rate at sufficiently high strain‐rates. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

A modified perturbed chain-statistical associating fluid theory equation of state for water which includes an association dependent hard sphere diameter

The concept of an association dependent hard sphere diameter is introduced as a means to obtain an accurate perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state model for water. The new approach is demonstrated to be a step change in accuracy for the representation of pure water properties as compared with standard PC-SAFT applications. Extension of the approach to mixtures is discussed.     

Bilayer-mediated assembly of cationic nanoparticles adsorbed to lipid bilayers: Insights from molecular simulations

Understanding interactions between functionalized gold nanoparticles (NPs) and lipid bilayers is essential for biomedical applications. Experiments have shown that NPs that are stable in solution can assemble into clusters when adsorbed to a lipid bilayer, suggesting that bilayer-mediated interactions facilitate assembly. In this work, we use coarse-grained molecular dynamics simulations to study bilayer-mediated interactions between NPs adsorbed to single- and multicomponent lipid bilayers. We perform unbiased simulations and umbrella sampling calculations using an implicit solvent force field to determine the thermodynamic contributions to assembly. We show that bilayer-mediated interactions drive the assembly of NPs into linear aggregates on liquid-disordered bilayers, which we attribute to a reduction in bilayer curvature. Similar bilayer-mediated interactions induce the alignment of NP clusters with phase boundaries in phase-separated bilayers. Together, these simulation results provide new physical insight into the balance of forces that dictate the assembly of charged NPs at multicomponent lipid bilayer interfaces.     

Adsorption of glucose into zeolite beta from aqueous solution

Hydrophobic zeolites, including Ti‐ and Sn‐beta, have been found to adsorb and isomerize glucose into fructose. An experimental question has been the significance of the entropic contribution to the free energy of transfer of glucose from solution to zeolite. We here perform Gibbs ensemble Monte Carlo calculations to quantify the enthalpy, entropy, and free energy of transfer of glucose from the aqueous phase to the zeolite phase. We find that the entropic contribution is large and positive, nearly compensating for an unfavorable enthalpy of transfer in all‐silica zeolite beta. A significant component of the positive entropy of transfer from the aqueous phase to zeolite is the unstructuring of first coordination shell waters around glucose as it leaves the solution. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3523–3529, 2013     

Dynamic modeling and validation of a biomass hydrothermal pretreatment process—a demonstration scale study

Hydrothermal pretreatment of lignocellulosic biomass is a cost effective technology for second generation biorefineries. The process occurs in large horizontal and pressurized thermal reactors where the biomatrix is opened under the action of steam pressure and temperature to expose cellulose for the enzymatic hydrolysis process. Several by‐products are also formed, which disturb and act as inhibitors downstream. The objective of this study is to formulate and validate a large scale hydrothermal pretreatment dynamic model based on mass and energy balances, together with a complex conversion mechanism and kinetics. The study includes a comprehensive sensitivity and uncertainty analysis, with parameter estimation from real‐data in the 178–185°C range. To highlight the application utility of the model, a state estimator for biomass composition is developed. The predictions capture well the dynamic trends of the process, outlining the value of the model for simulation, control design, and optimization for full‐scale applications. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4235–4250, 2015     

Computational screening of porous carbons,zeolites, and metal organic frameworks for desulfurization and decarburization of biogas,natural gas,and flue gas

Eighteen kinds of porous materials from carbons, zeolites, and metal organic frameworks (MOFs) have been extensively investigated for desulfurization and decarburization of the biogas, natural gas, and flue gas by using a molecular modeling approach. By considering not only the selectivity but also capacity, Na‐5A, zeolite‐like MOF (zMOF), and Na‐13X, MIL‐47 are screened as the most promising candidates for removal of sulfide in the CH₄? CO₂? H₂S and N₂? CO₂? SO₂ systems, respectively. However, for simultaneous removal of sulfide and CO₂, the best candidates are zMOF for the natural gas and biogas (i.e., CH₄? CO₂? H₂S system) and MOF‐74‐Zn for the flue gas (i.e., N₂? CO₂? SO₂ system). Moreover, the regeneration ability of the recommended adsorbents is further assessed by studying the effect of temperature on adsorption. It is found that compared to the zMOF and MIL‐47 MOFs, the Na‐5A and Na‐13X zeolites are not easily regenerated due to the difficulty in desorption of sulfide at high temperature, which results from the stronger adsorbent–adsorbate interactions in zeolites. The effect of sulfide concentration on the adsorption properties of the recommended adsorbents is also explored. We observe that the zMOF and MIL‐47 are also superior to the Na‐5A and Na‐13X for desulfurization of gas mixtures containing high sulfide concentration. This is because MOFs with larger pore volume lead to a greater sulfide uptake. The effects of porosity, framework density, pore volume, and accessible surface area on the separation performance are analyzed. The optimum porosity is about 0.5–0.6, to meet the requirements of both high selectivity and uptake. It is expected this work provides a useful guidance for the practical applications of desulfurization and decarburization. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2928–2942, 2013     

Material design using molecular modeling for hydrogen storage

Using grand canonical Monte‐Carlo simulations, the adsorption capacities and isosteric heats of hydrogen on activated carbons, graphite nanofibers, and bundles of carbon nanotubes are estimated for identical thermodynamic states. These computations allow a systematic, meaningful, and unbiased comparison of the adsorption properties of hydrogen in such porous materials. The comparison shows that the hydrogen storage capacity can be optimized, but only to a limited extent, in adjusting the material pore sizes and functionalizing a part of the adsorption sites. Therefore, at room temperature and up to 70.0 MPa, for the three models of carbonaceous adsorbents, the hydrogen maximal excess adsorption is of the order of 2% of the adsorbent mass. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

On facilitated computation of mesoscopic behavior of reaction‐diffusion systems

Various cellular and subcellular biological systems occur in the conditions where both reactions and diffusion take place. Since the concentration of species varies spatially, application of reaction‐diffusion master equation has served as an effective method to handle these complicated systems; yet solving these equation incurs a large CPU time penalty. Counter to the traditional technique of generating many sample paths, this article introduces a method which combines Grima's effective rate equation approach (Grima, J Chem Phys. 2010;133:3) with a linear operator formalism for diffusion to capture averaged species behaviors. The formulation also shows correct results at various choices of compartment sizes, which have been found to be an important factor that can affect accuracy of the final predictions (Erban, Chapman, Phys Biol. 2009;6:4). It is shown that the method presented allows the computation of the mesoscopic average of reaction‐diffusion systems at considerably accelerated rates (exceeding a thousand fold) over those based on sample path averages. © 2017 American Institute of Chemical Engineers AIChE J, 63: 5258–5266, 2017     

Simulations of crystal aggregation and growth: Towards correct crystal area

Simulating crystal growth and aggregation can provide insight into factors that control the final product properties. Classical models involve formation of a volume-equivalent single crystal upon aggregation. This approach does not preserve particle area, resulting in an inadequate model of supersaturation depletion. Alternatively, crystal area can be computed accurately by a Monte Carlo method where each primary particle of an aggregate is described in its full geometric complexity. However, the drawback of this method is its computational cost. Thus, a third method is introduced as a compromise, describing particles by their volume and area and preserving both upon aggregation. The so-obtained two-dimensional model requires growth rate expressions in volume and area. We provide a method for parametrizing these expressions so that total volume and area closely match the values obtained with the method based on full geometric information. The parameters depend on primary particle geometry and the amount of growth. © 2019 American Institute of Chemical Engineers AIChE J, 65: e16525, 2019     

Solvation pressure in spherical mesopores: Macroscopic theory and molecular simulations

Fluids adsorbing in nanoporous solids cause high solvation pressures that deform the solids and affect properties of the fluids themselves. We calculate solvation pressure of nitrogen adsorbed at 77.4 K in spherical silica mesopores using two methods: the macroscopic Derjaguin–Broekhoff–de Boer theory and molecular simulations. We show that both approaches give consistent results, and the observed pressures increase in smaller pores reaching the order of a hundred megapascals. The results are also typical for the solvation pressure in mesoporous materials, yet noticeably differ from the results for the cylindrical pore geometry. Furthermore, we show that the dependence of the solvation pressure at saturation on the reciprocal pore size is linear, and we use this relation for the calculation of the solid–liquid surface energy. The results can be employed for the prediction of the solvation pressure and the adsorption-induced deformation in the material with the spherical pore geometry.     

Binary and ternary mixtures of liquid crystals with CO2

Liquid crystals, elongated molecules with a structured liquid phase, may be used as new solvents for CO₂ capture. However, no molecule has been found yet with optimal properties. Therefore, mixtures of two liquid crystals and CO₂ are investigated. Also, the phase behavior of some binary subsystems of the investigated ternary systems is studied for comparison. In the mixtures investigated, 4,4′‐pentyloxycyanobiphenyl + 4,4′‐heptyloxycyanobiphenyl + CO₂ and 4,4′‐propylcyclohexylbenzonitrile + 4,4′‐heptylcyclohexylbenzonitrile + CO₂, the nematic phases form a nematic homogeneous solution and the solid phases form an eutectic system, leading to a material with improved properties for CO₂ capture. Moreover, the ternary mixture of 4,4′‐propylcyclohexylbenzonitrile + 4,4′‐heptylcyclohexylbenzonitrile + CO₂ showed an increased solubility of CO₂ compared with the binary subsystems. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2977–2984, 2015     

Properties of supercritical N2, O2, CO2, and NH3 mixtures from the virial equation of state

We report virial coefficients up to sixth order in density for N₂ , O₂ , NH₃ , and CO₂ , covering temperatures from 50 to 1,000 K. The reported values include coefficients and their first three temperature derivatives, for the pure species as well as all of those needed to evaluate full composition dependence of mixtures formed from any or all of these compounds. The values are obtained by calculation of appropriate cluster integrals using Mayer sampling Monte Carlo, with intermolecular interactions described by the Transferable Potential for Phase Equilibria (TraPPE) force field. All coefficients are fit as a function of temperature, yielding a thermodynamic model with analytic dependence on temperature, density, and composition. The coefficients and properties computed from them are compared to experimental data where available.     

Revisiting electrolyte thermodynamic models: Insights from molecular simulations

Pitzer and electrolyte nonrandom two‐liquid (eNRTL) models are the two most widely used electrolyte thermodynamic models. For aqueous sodium chloride (NaCl) solution, both models correlate the experimental mean ionic activity coefficient (γ_±) data satisfactorily up to salt saturation concentration, that is, ionic strength around 6 m. However, beyond 6 m, the model extrapolations deviate significantly and diverge from each other. We examine this divergence by calculating the mean ionic activity coefficient over a wide range of concentration based on molecular simulations and Kirkwood–Buff theory. The asymptotic behavior of the activity coefficient predicted by the eNRTL model is consistent with the molecular simulation results and supersaturation experimental data. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3728–3734, 2018     

Design of semiconductor ternary quantum dots with optimal optoelectronic function

The function of nanometer‐size quantum dots (QDs) of ternary compound semiconductors, such as In_xGa_1?xAs and ZnSe_1?xTe_x, used in the fabrication of optoelectronic and photovoltaic devices can be optimized by precise tuning of their electronic band gap through control of the QD composition (x) and diameter. Results on compositional distributions in ternary QDs and how they affect the QDs' electronic band gap are reported. A hierarchical modeling approach is followed that combines first‐principles density functional theory calculations and classical Monte Carlo simulations with a continuum model of species transport in spherical nanocrystals. In certain cases, the model predicts the formation of core/shell‐like structures with shell regions rich in the surface segregating species. A systematic parametric analysis generates a database of transport properties, which can be used to design post‐growth thermal annealing processes that enable the development of thermodynamically stable QDs with optimal electronic properties grown through simple one‐step colloidal synthesis techniques. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3223–3236, 2013     

Modeling of aggregation kernel using Monte Carlo simulations of spray fluidized bed agglomeration

The present work attempts to consider the microscopic mechanisms of spray fluidized bed agglomeration while modeling the macroscopic kinetics of the process. A microscale approach, constant volume Monte‐Carlo simulation, is used to analyze the effects of micro‐processes on the aggregation behavior and identify the influencing parameters. The identified variables, namely the number of wet particles, the total number of particles, and the number of droplets are modeled and combined in the form of an aggregation kernel. The proposed kernel is then used in a one‐dimensional population balance equation for predicting the particle number density distribution. The only fitting parameters remaining in the population balance system are the collision frequency per particle and a success fraction accounting for the dissipation of kinetic energy. Predictions of the population balance model are compared with the results of Monte‐Carlo simulations for a variation of significant operating parameters and found to be in good agreement. © 2014 American Institute of Chemical Engineers AIChE J, 60: 855–868, 2014