{"title":"Thermodiffusion of CO2 mixtures in the extended critical region","authors":"Gabriela Guevara-Carrion, Denis Saric, Jadran Vrabec","doi":"10.1016/j.fluid.2025.114438","DOIUrl":"10.1016/j.fluid.2025.114438","url":null,"abstract":"<div><div>Thermodiffusion, also known as Soret effect, stands for the mass flux driven by a temperature gradient, leading to partial component separation in fluid mixtures. While typically small in magnitude and often neglected, thermodiffusion can become significant under specific conditions, such as in the extended critical region. In this work, the thermodiffusion behavior of diluted supercritical mixtures of carbon dioxide with methane, ethane, or isobutane is investigated with molecular simulation techniques. Thermodiffusion is studied along the <span><math><mrow><mn>9</mn><mspace></mspace><mi>MPa</mi></mrow></math></span> isobar over a temperature range from <span><math><mrow><mi>T</mi><mo>=</mo><mn>290</mn></mrow></math></span> to 345 K, where singular thermodynamic and transport properties are observed. Attention is given to the crossover region near the critical point, where asymptotic power laws no longer apply, but long-range fluctuations still influence fluid behavior. Within this region, characterized by the Widom line, extreme values for the thermodiffusion and Soret coefficients are predicted. The underlying mechanisms responsible for this behavior are explored, and it is shown to be primarily driven by the extrema of the partial molar enthalpy of the solvent in the extended critical region.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114438"},"PeriodicalIF":2.8,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143842525","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Louis Nguyen , Michele Valsecchi , George Jackson , Amparo Galindo , Christopher J. Tighe
{"title":"Modelling the solubility of CO2 in rubbery and glassy amorphous PS and PMMA with the SAFT-γ Mie group-contribution EoS and the NET-GP approach","authors":"Louis Nguyen , Michele Valsecchi , George Jackson , Amparo Galindo , Christopher J. Tighe","doi":"10.1016/j.fluid.2025.114445","DOIUrl":"10.1016/j.fluid.2025.114445","url":null,"abstract":"<div><div>The sorption of fluids in polymers is important for their industrial application in, e.g., separation membranes, corrosion protection liners and permeation barriers. The solubility of carbon dioxide (CO<sub>2</sub>) in polymers is of interest for its transport and storage. In this work, CO<sub>2</sub> solubility in polystyrene (PS) and polymethyl methacrylate (PMMA), above and below the glass transition temperature <span><math><msub><mi>T</mi><mi>g</mi></msub></math></span> of the pure polymers (both ∼105 °C), is modelled by combining the SAFT-γ Mie group-contribution equation of state (EoS), together with the framework of nonequilibrium thermodynamics for glassy polymers (NET-GP). Selected parameters of the EoS are optimised to fit pure polymer density and CO<sub>2</sub> solubility measurements from the literature at pressures up to 20 MPa, and temperatures from 150 to 200 °C (although the default parameters already give good agreement for CO<sub>2</sub> solubility in PS). Good agreement with solubility measurements at lower temperatures, though still above <span><math><msub><mi>T</mi><mi>g</mi></msub></math></span>, is obtained at up to 40 MPa. Below the <span><math><msub><mi>T</mi><mi>g</mi></msub></math></span> of the pure polymers, between 35 °C and 81 °C, application of NET-GP results in only a small increase in the predicted CO<sub>2</sub> solubility at < 2–3 MPa, when the amount of sorbed CO<sub>2</sub> is small, over that determined from the EoS alone. Thus CO<sub>2</sub> appears to readily plasticise both polymers, inducing an equilibrium rubbery state. The methodology presented is a computationally efficient tool for the investigation of fluid sorption in amorphous polymers, which can be readily extended to other fluid+polymer pairs, including ones with novel chemistries.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"597 ","pages":"Article 114445"},"PeriodicalIF":2.8,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143904449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"ANN-based estimation of pure-component parameters of PC-SAFT equation of state using quantum chemical data","authors":"Hiroaki Matsukawa, Yusuke Miyagi, Katsuto Otake","doi":"10.1016/j.fluid.2025.114444","DOIUrl":"10.1016/j.fluid.2025.114444","url":null,"abstract":"<div><div>The perturbed chain-statistical associating fluid theory equation of state (PC-SAFT EoS) is a physical property estimation tool that can be used to calculate a wide range of substance types, temperatures, and pressures. To perform calculations using the PC-SAFT EoS, substance-specific pure-component parameters are required, which are generally determined from liquid density and saturated vapor pressure. Few studies have reported on these parameters, and methods that can obtain pure-component parameters without relying on measured physical properties remain elusive. In this study, an artificial neural network (ANN) is introduced to predict the pure-component parameters of the PC-SAFT EoS. The molecular information estimated from a Gaussian software was used as the input. In addition, we optimized the structure of the ANN by varying the transfer function, number of neurons, and number of hidden layers. The optimized ANN comprises a hard sigmoid transfer function composed of two hidden layers, with 20 and 10 neurons in the first and second layer, respectively. This model can determine the pure-component parameters of the PC-SAFT EoS for a wide range of substance types. Furthermore, SHapley Additive exPlanations analysis on the optimized ANN demonstrates that the contributions of the polarizability and dipole moment are large. However, the feature values related to the shape of the substance are lacking. These results contribute to expanding the range of applications for property estimation using EoS.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114444"},"PeriodicalIF":2.8,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143842524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Using Physical Property Models and Artificial Intelligence to Design Chemical Products","authors":"Kevin G. Joback","doi":"10.1016/j.fluid.2025.114441","DOIUrl":"10.1016/j.fluid.2025.114441","url":null,"abstract":"<div><div>Designing chemical products is the process of combining pieces, e.g., molecular fragments or ingredients, into an assembly, e.g., chemical structures or mixture formulations, whose properties satisfy a set of design constraints. We explain how computational techniques, specifically artificial intelligence techniques, can greatly assist this design process. We demonstrate how proper representation of knowledge is essential for enabling the computer to manipulate substructures, how combinatorial algorithms are used to generate structures and enumerate isomers, how rule-based systems help select the estimation techniques needed to test each generated candidate chemical, and how machine learning can be used to improve the models used to find promising candidates.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114441"},"PeriodicalIF":2.8,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143870265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Artificial neural network-based estimation of interaction parameters between carbon dioxide and organic solvents using the Peng–Robinson equation of state with the van der Waals one-fluid mixing rule and quantum chemical data","authors":"Hiroaki Matsukawa, Emiri Kobayashi, Katsuto Otake","doi":"10.1016/j.fluid.2025.114443","DOIUrl":"10.1016/j.fluid.2025.114443","url":null,"abstract":"<div><div>The Peng–Robinson (PR)-van der Waals (vdW) model, which combines the PR equation of state with the vdW one-fluid mixing rule, is often used to estimate the physical properties of CO<sub>2</sub>/organic solvent mixtures. Calculating these properties using the PR-vdW model requires interaction parameters <em>k<sub>ij</sub></em>; however, reports on these parameters are limited. This article introduces an artificial neural network (ANN) to predict <em>k<sub>ij</sub></em> between CO<sub>2</sub> and organic solvents, using pure-component parameters and molecular information as inputs. The molecular information is obtained through the general-purpose quantum chemical calculation software Gaussian. In addition, the ANN is optimized by varying the transfer function, number of neurons, and number of hidden layers. The optimized ANN employs a tanh function as the transfer function for the hidden layers, with two hidden layers containing 40 and 10 neurons. This model effectively predicts <em>k<sub>ij</sub></em> for a wide range of substances and temperature conditions. Furthermore, SHapley Additive exPlanations analysis of the optimized ANN reveals a significant contribution from the quadrupole moment, likely due to quadrupole interactions between CO<sub>2</sub> and the organic solvents. These results support the estimation of the physical properties of CO<sub>2</sub>/organic solvent mixtures.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114443"},"PeriodicalIF":2.8,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143834443","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Florian Fleckenstein, Stefan Becker, Hans Hasse, Simon Stephan
{"title":"Vapor–liquid interfacial properties of the system acetone + CO2: Experiments, molecular simulation, density gradient theory, and density functional theory","authors":"Florian Fleckenstein, Stefan Becker, Hans Hasse, Simon Stephan","doi":"10.1016/j.fluid.2025.114436","DOIUrl":"10.1016/j.fluid.2025.114436","url":null,"abstract":"<div><div>Vapor–liquid interfacial properties of the system acetone + CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> were studied using pendant drop experiments as well as multiple theoretical approaches, namely molecular dynamics (MD) simulations, density gradient theory (DGT), and density functional theory (DFT). The surface tension as well as relative adsorption of CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> were obtained from the experiments for temperatures between 303.15 K and 373.15 K. The experimental results were compared to predictions from the three theoretical approaches, which also provide insights into the structure of the interface and data on the interfacial enrichment of CO<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> and the interfacial thickness, which is not feasible by the experiments alone. The results from all three theoretical approaches are found to be in good mutual agreement as well as in agreement with the experimental results. Additionally, MD, DGT, and DFT were used to study the nanoscopic structure at the interface.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114436"},"PeriodicalIF":2.8,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143834441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Maurício Prado de Omena Souza , Débora Costa do Nascimento , Diego Tavares Volpatto , Gustavo Gondran Ribeiro , Antonio Marinho Barbosa Neto , Mariana Conceição da Costa
{"title":"Modeling flash points of biofuels using neural networks","authors":"Maurício Prado de Omena Souza , Débora Costa do Nascimento , Diego Tavares Volpatto , Gustavo Gondran Ribeiro , Antonio Marinho Barbosa Neto , Mariana Conceição da Costa","doi":"10.1016/j.fluid.2025.114439","DOIUrl":"10.1016/j.fluid.2025.114439","url":null,"abstract":"<div><div>The search for renewable energy resources is driven by environmental hazards caused by petroleum derivatives, price fluctuations, and the unsustainability of fossil fuels. In Brazil, biodiesel and bioethanol are established renewable fuels, while butanol shows promise as an alternative fuel, requiring research into their safety and efficiency. The Flash Point (FP) is crucial for flammability assessment and safety in combustion processes, but its experimental measurement is resource-intensive. This study evaluates the capability of artificial neural networks (ANNs) to predict FP for some biofuels and their blends, using a dataset of 490 points. Notably, 24 of these points were newly acquired, while the remaining 466 were sourced from literature. A robust ANN model was trained using a 5-fold cross-validation with an 80/20 data split, incorporating average molar mass, vapor pressure natural logarithmic, and experimental method as input features. The final model, featuring three hidden layers determined through a parametric analysis, achieved a Root Mean Square Error (RMSE) of 4.22 K and a Mean Absolute Error (MAE) of 3.09 K for 98 unknown points. The model achieved satisfactory accuracy, with MAE ranging from 1.51 K to 3.63 K, and performed comparably to traditional UNIFAC thermodynamic models. These results highlight the potential of ANNs for FP prediction across diverse datasets.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114439"},"PeriodicalIF":2.8,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143806862","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mohammad Hossein Hadipanah, Seyed Hossein Mazloumi
{"title":"Development of equation of state for a double square-well fluid","authors":"Mohammad Hossein Hadipanah, Seyed Hossein Mazloumi","doi":"10.1016/j.fluid.2025.114437","DOIUrl":"10.1016/j.fluid.2025.114437","url":null,"abstract":"<div><div>A double square-well potential function is proposed to describe the interaction between unbounded particles. This model is constructed based on the Lennard-Jones potential function and has three adjustable parameters. Based on the two-layers local composition model, a coordination number model for this double square-well fluid is developed and then by using the generalized van der Waals partition function a new expression for the attractive part of equation of state is derived. Two new equations of state are presented by sum of the attractive term and repulsive expressions of Carnahan-Starling and van der Waals. These models have three adjustable parameters, which are obtained by simultaneously fitting vapor pressures and liquid densities of pure substances. The capability of these two models in correlation of the vapour pressure and liquid density and in prediction of the vapour molar volume and heat of vaporization of pure compounds is investigated. Good results obtained especially with the new EOS in which Carnahan-Starling repulsive term has been used. The results of this EOS are excellent even for large molecules such as long- chain alkanes from C<sub>10</sub> to C<sub>20</sub>.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114437"},"PeriodicalIF":2.8,"publicationDate":"2025-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143800237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Speed-of-sound measurements in liquid n-heptane and 2,2,4-trimethylpentane (isooctane)","authors":"T. Dietl, A. El Hawary, K. Meier","doi":"10.1016/j.fluid.2025.114432","DOIUrl":"10.1016/j.fluid.2025.114432","url":null,"abstract":"<div><div>This paper reports comprehensive and accurate measurements of the speed of sound in liquid <em>n</em>-heptane and 2,2,4-trimethylpentane (isooctane). The measurements were carried out by a double-path-length pulse-echo technique and cover the temperature range between 200 K and 420 K with pressures up to 100 MPa. The expanded uncertainties (coverage factor <span><math><mrow><mi>k</mi><mo>=</mo><mn>2</mn></mrow></math></span>) amount to 2.1 mK in temperature, 0.005% in pressure, 0.02% in speed of sound in <span><math><mi>n</mi></math></span>-heptane, and 0.015% in speed of sound in isooctane, with the exception of a few state points at low pressures, where it increases up to 0.03% for <span><math><mi>n</mi></math></span>-heptane and up to 0.035% for isooctane. Our data are more accurate than previously published data for both fluids. The measurements for isooctane extend the range in which the speed of sound had been measured before from 293 K down to 200 K and from 373 K up to 420 K. We also provide accurate correlations for the speed of sound as a function of temperature and pressure in the range of our measurements. Our data can contribute to developing new, more accurate equations of state for both fluids.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114432"},"PeriodicalIF":2.8,"publicationDate":"2025-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143747738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Crystallization risk of aromatic compounds in LNG production Part III: The solubility of o-xylene in methane down to cryogenic temperatures","authors":"Salem Hoceini, Marco Campestrini, Paolo Stringari","doi":"10.1016/j.fluid.2025.114434","DOIUrl":"10.1016/j.fluid.2025.114434","url":null,"abstract":"<div><div>Following a series of works dealing with the experimental determination of the solubility limits of the BTEX components in methane rich-mixtures down to cryogenic temperatures, this work presents new measurements for the solubility of solid o-xylene in solvent methane. The measurements have been obtained using a static-analytic method that allows sampling of the fluid phase at equilibrium with the solid one at temperatures from 242 K down to 123 K and at nominal pressures of 3 and 6 MPa. Despite the importance of BTEX in assessing the risk of crystallization during the liquefaction of natural gas, the solubility of o-xylene in methane rich mixtures was not known in the literature before this work. As a consequence, these original data will give new insights into the solid-fluid equilibrium behaviour of the o-xylene + methane mixture down to LNG temperatures and then provide crucial information for the proper tailoring of the purification units upstream of the liquefaction unit. Measured solid-liquid and solid-vapor equilibria have been compared to the modelling results obtained by coupling a cubic equation of state and a model for the solid phase, and good agreement has been observed.</div></div>","PeriodicalId":12170,"journal":{"name":"Fluid Phase Equilibria","volume":"596 ","pages":"Article 114434"},"PeriodicalIF":2.8,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143806861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}