New Variant of the Universal Constants in the Perturbed Chain-Statistical Associating Fluid Theory Equation of State

The Perturbed Chain-Statistical Associating Fluid Theory Equation of State (PC-SAFT EOS) has been successfully applied to model phase behavior of various types of systems, while it is also well-known that the PC-SAFT EOS has difficulties in describing some second-order derivative properties. In this work, the temperature and volume dependencies of the PC-SAFT EOS have been analyzed based on the total reduced residual Helmholtz free energy from the well-established reference equations. The ranges of parameters and temperature, in which the original PC-SAFT EOS give zero or more than three volume roots, have been analyzed. Then, a practical procedure has been proposed to refit the universal constants of the PC-SAFT EOS with the purpose of fixing the numerical pitfalls in the real application ranges and reusing the original parameters. It is shown that the new universal constants have practically resolved the mostly criticized numerical pitfall, that is, the presence of more than three volume roots at real application conditions. Finally, the possibility of using the original PC-SAFT EOS parameters with the new universal constants has been investigated for the phase equilibria of the systems containing hydrocarbons, chemicals, water, or polymers

Modeling Water Containing Systems with the Simplified PC-SAFT and CPA Equations of State

Numerous studies have been presented for modeling of water containing systems with the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EOS), and more than 20 water parameter sets have been published with emphasis on different applications. In this work, eight of these sets and new estimated parameters with different association schemes are systematically compared on describing properties of pure water, the liquid–liquid equilibria (LLE) of water with hydrocarbons, and the vapor–liquid (VLE) and/or vapor–liquid–liquid equilibria (VLLE) of water with 1-alcohols. An interactive procedure is further proposed for including the LLE of water with hydrocarbons into the pure fluid parameter estimation. The results show that it is possible for PC-SAFT to give an accurate description of the LLE of water and hydrocarbons while retaining satisfactory accuracy for both vapor pressure and saturated liquid density of water. For the aforementioned aqueous systems, the PC-SAFT correlations using the newly developed parameters are compared with the corresponding correlations of the cubic plus association EOS. The two models show comparable results for phase equilibria, and both of them fail to describe second-order derivative properties of water, i.e., residual isochoric heat capacity and speed of sound. The ability of the models to predict the monomer (free site) fractions of saturated pure water is investigated and discussed from various aspects. The results suggest that more experimental or theoretical studies are needed

Optimal Design of Aqueous Two-Phase Systems for Biomolecule Partitioning

Aqueous two-phase systems (ATPS) have exhibited superior performance in many biotechnological applications. To promote the implementation of these powerful platforms by industry in the downstream processing, an optimal design method is developed to tailor high-performance ATPS for partitioning biomolecules in this work. In this design method, two machine learning (ML) models that combine the artificial neural network (ANN) algorithm and group contribution (GC) method are respectively employed to predict the phase equilibrium composition of polymer-electrolyte ATPS and the partition of biomolecules in these aqueous systems. By integrating these two ANN-GC models into the computer-aided design technique, the optimal ATPS is identified by solving an optimization-based mixed-integer non-linear programming (MINLP) problem. As a proof of concept, results of partitioning cefazolin and β-amylase are presented. In the case of cefazolin, the partitioning performance of our tailored ATPS (PPG600 + KNaSO4 + H2O) is nearly 7 times greater than that of the reported ATPS (PEG6000 + Na3C6H5O7 + H2O). Meanwhile, the ATPS of PPG600 + KNaSO4 + H2O gives a cefazolin recovery of 95.0 wt % and an agent input of 0.154 kg/kg aqueous solution, and for the ATPS of PEG6000 + Na3C6H5O7 + H2O, these values are 90.6 and 0.233, respectively. For the second case, the partition coefficient of β-amylase in our proposed ATPS (PPG400 + KNaHPO4 + H2O) is about 13.5 times higher than that of the reported ATPS (PEG10000 + KH2PO4 + H2O). In addition, the ATPS of PPG600 + KNaSO4 + H2O gives an β-amylase recovery of 97.3 wt % at a cost of 0.387 kg agent input/kg aqueous solution, and for the ATPS of PEG6000 + Na3C6H5O7 + H2O, they are 66.3 and 0.252, respectively

High-dose versus conventional-dose irradiation in cisplatin-based definitive concurrent chemoradiotherapy for esophageal cancer: a systematic review and pooled analysis

<div><p>We investigate whether high-dose (HD, ≥60 Gy) radiotherapy in definitive concurrent chemoradiotherapy (CCRT) based on cisplatin could yield benefits compared to conventional-dose (CD) CCRT. PubMed, Embase and Google Scholar were searched and data were pooled and analyzed for response rate, survival, failure patterns and toxicity. Results showed advantages in response rate, 5-year overall survival rate, local regional recurrence and distant failure rate compared to the CD arm with no difference in Grade ≥3 acute and late esophagitis, other toxicities were rare with moderate tolerance, subgroup analysis of squamous cell carcinoma also showed advantages for HD arm. We concluded that ≥60 Gy CCRT improved clinical outcomes compared to the CD arm, especially for esophageal squamous cell carcinoma. Our findings may provide a basis for future trials.</p></div

Investigation of the Alcohols and Water Hydrogen Bonding Structure via Monomer Fraction Studies

The hydrogen bonding structure of alcohols and water is studied in this work using two association equations of state (cubic-plus-association (CPA); perturbed-chain statistical associating fluid theory (PC-SAFT)) and a theory connecting the relative static permittivity (RSP) with hydrogen bonding (RSP theory). The results from the two models are compared to experimental and molecular simulation data for free-site, monomer, and k-times bonded fractions, as well as for tetrahedrally bonded fractions for water. The agreement is satisfactory for alcohols but less so for water, especially when the most recent structural data for water are considered. This indicates that the four-site or roughly tetrahedral assumption incorporated for water in both approaches may be erroneous. It has been attempted to fit the RSP theory parameters to recently obtained data; such data show a rather small number of tetrahedral water molecules. These data are obtained from studies related to the water two-state theory. The results provide some insight into whether water can be assumed to be a homogeneous liquid or a two-state liquid, at least in the context of the theories (CPA, PC-SAFT, and RSP theory). The results are also discussed in the context of other theories and recent developments

The Connection between the Debye and Güntelberg Charging Processes and the Importance of Relative Permittivity: The Ionic Cloud Charging Process

The Debye and Güntelberg Charging Processes are essential tools for deriving electrolyte solutions’ activity coefficient models. The Debye–Hückel, Born, and Mean Spherical Approximation are among some famous theories derived via charging processes. How they relate to each other, or if both charging processes are equivalent, or even if both are consistent, has been a matter of discussion in the literature for many years. In this work, we evaluate the results from both charging processes using the Debye–Hückel and the Born equations, using different dependencies of the relative permittivity concerning salt concentration, temperature, and partial charging variable. Our results show that both charging processes are connected through a charging process here called the Ionic Cloud Charging Process. We show how these three charging processes relate to each other, verifying the magnitude of the derivatives of relative permittivity on the final models and their origin from the Ionic Cloud Charging Process

Investigation of the Limits of the Linearized Poisson–Boltzmann Equation

This work presents a comparison between a numerical solution of the Poisson–Boltzmann equation and the analytical solution of its linearized version through the Debye–Hückel equations considering both size-dissimilar and common ion diameters approaches. In order to verify the limits in which the linearized Poisson–Boltzmann equation is capable to satisfactorily reproduce the nonlinear version of Poisson–Boltzmann, we calculate mean ionic activity coefficients for different types of electrolytes as various temperatures. The divergence between the linearized and full Poisson–Boltzmann equations is higher for lower molalities, and both solutions tend to converge toward higher molalities. For electrolytes of lower valencies (1:1, 1:2, 2:1, and 1:3) and higher distances of closest approach, the full version of the Debye–Hückel equation is capable of representing the activity coefficients with a low divergence from the nonlinear Poisson–Boltzmann. The size-dissimilar full version of Debye–Hückel represents a clear improvement over the extended version that uses only common ion diameters when compared to the numerical solution of the Poisson–Boltzmann equation. We have derived a salt-specific index (Θ) to gradually classify electrolytes in order of increasing influence of nonlinear ion–ion interactions, which differentiate the Debye–Hückel equations from the nonlinear Poisson–Boltzmann equation

Prediction of Gas Injection Effect on Asphaltene Precipitation Onset Using the Cubic and Cubic-Plus-Association Equations of State

Gas injection is a proven enhanced oil recovery technique. The gas injection changes the reservoir oil composition, temperature, and pressure conditions, which may result in asphaltene precipitation. In this work, we have used a modeling approach from the literature in order to predict asphaltene precipitation onset condition during gas injection. The modeling approach is used with the Soave–Redlich–Kwong, Soave–Redlich–Kwong-Plus-Huron–Vidal mixing rule and cubic-plus-association (CPA) equations of state (EoS). Six different reservoir fluids are studied with respect to asphaltene onset precipitation during nitrogen, hydrocarbon gas mixture, and carbon dioxide injection. It is also shown how to extend the modeling approach when the reservoir fluid is split into multiple pseudocomponents. It is observed that the modeling approach using any of the three models can predict the gas injection effect on asphaltene onset conditions. The CPA EoS is more reliable than the other two models, which are sensitive to asphaltene molecular weight and sometimes predict highly nonlinear behavior outside the experimental temperature range used for fitting the model parameters

Modeling of Gas Solubility Using the Electrolyte Cubic Plus Association Equation of State

The prediction of the solubilities of carbon dioxide and methane in aqueous solutions of inorganic salts is important for geological carbon storage, enhanced oil recovery, gas hydrate formation, and seawater desalination. Few electrolyte equations of state can be used for accurate gas solubility calculations over wide ranges of temperature, pressure, and salt molality. This work presents a thermodynamic modeling study on the solubilities of carbon dioxide and methane in aqueous solutions of several inorganic salts with the electrolyte cubic plus association equation of state. The binary interaction parameters between ions and gas are obtained by fitting the experimental data of gas solubility in single-salt solutions. It is shown that the equation of state can satisfactorily correlate the gas solubility over a wide range of conditions, with deviation less than the reported experimental uncertainties (7%) for most systems. The equation of state is then used to predict the gas solubility in multi-salt solutions, and a satisfactory performance is achieved. The salting-out effects resulting from ion size, charge density, and salt concentration are also extensively discussed

Hydrogen bonded configurations in liquid water and their correlations with local tetrahedral structures

Hydrogen-bonded structures in liquid water lies at the root of its many anomalous properties. The ability of water to form hydrogen bonds is perceived to be the reason for the formation of locally favored tetrahedral structures (LFTS) in liquid water. These tetrahedral environments also lay the foundation for the two-state theories of water. In molecular dynamics simulations, hydrogen bonds are often assigned between molecules if they satisfy certain geometric or energetic criteria, or a combination of both. Potential of Mean Force landscapes may be used to identify the geometric criteria for identifying hydrogen bonds, and distinguishing ‘ice-like’ hydrogen bonds. In this work, we report the statistical information of hydrogen-bonded structures in liquid water from molecular simulations of the iAMOEBA water model. The fraction of different hydrogen-bonded structures is also compared with the fraction of LFTS molecules to gain insights into the hydrogen-bonded configuration of LFTS molecules. The structure of different hydrogen-bonded configurations, using various structural descriptors is also reported. We find that tetrahedral environments in liquid water (as modeled by the iAMOEBA force-field) are largely, but not exclusively constituted by the molecules that donate and accept two hydrogens each when ‘ice-like’ hydrogen bonds are considered.</p