Estimation of thermodiffusion coefficients in ternary associating mixtures

Following the non‐equilibrium thermodynamics formulation and taking into account the complexities in the structure of aqueous associating mixtures, expressions are proposed to estimate the thermodiffusion coefficients in ternary associating mixtures, such as water and alcohol mixtures. The model expressions are used to estimate the thermodiffusion coefficients in methanol–ethanol–water, dimethyl sulfoxide (DMSO)–ethanol–water and DMSO–t‐butanol–water mixtures at various concentrations. The perturbed‐chain statistical associating fluid theory (PC‐SAFT) equation of state is used to obtain the mixture properties, such as the derivatives of the chemical potentials needed to evaluate the thermodiffusion coefficient expressions. The results show that at certain concentrations of one component, variation of the concentration of the other two components can cause a sign change in the thermodiffusion coefficients. While the model cannot be evaluated due to the lack of any pertinent experimental data, the model predictions may be used to choose suitable mixture compositions in space experiments to be performed onboard the International Space Station (ISS) in near future. © 2011 Canadian Society for Chemical Engineering     

Evaluation of SAFT and PC-SAFT models for the description of homo- and co-polymer solution phase equilibria

Statistical associating fluid theory (SAFT) and perturbed-chain SAFT (PC-SAFT) are used to model the phase behavior of polymer-solvent mixtures over a wide temperature and pressure range. Homopolymers (polyolefins) as well as co-polymers are examined. Calculations were performed using various recently proposed robust algorithms for polydisperse polymers. Various polymer properties that affect substantially the phase behavior, such as molecular weight, polydispersity, and macromolecular architecture, were considered. For most of the systems examined, PC-SAFT correlation is marginally closer to experimental data than SAFT. Nevertheless, there are a number of mixtures where SAFT is the preferred model.     

Development of a predictive model for polymer/solvent diffusion coefficient calculations

A new calculation procedure for free‐volume parameters is considered in this work by using viscosity prediction methods and the Levenberg‐Marquardt calculation scheme. All parameters used in the Vrentas–Duda free‐volume theory can be estimated from pure component properties. The prediction results are compared with experimental data for some polymer/solvent systems. The diffusion coefficient calculated by Vrentas–Duda theory can be used in the modeling of membrane separation processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study of solubility and swelling ratio in polymer‐CO2 systems using the PC‐SAFT equation of state

We use the PC‐SAFT equation of state to model the solubility of CO₂ in various homopolymers. We also model the swelling ratio of the PP (polypropylene)‐CO₂ mixture using PC‐SAFT and then compare the results with Sanchez‐Lacombe (S‐L) and Simha‐Somcynsky (S‐S) equations. The results show that PC‐SAFT can describe the solubility of CO₂ in polymers very well. We compare two sets of parameters in the PC‐SAFT equation, Gross et al.'s and Chen et al.'s. As for the swelling ratio, PC‐SAFT using Chen et al. parameters is better than S‐L equation, which is commonly used by early researchers in studying the solubility of CO₂ in polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44804.     

Prediction of solvent‐diffusion coefficient in polymer by a modified free‐volume theory

Several versions of free‐volume theory have been proposed to correlate or predict the solvent diffusion coefficient of a polymer/solvent system. The quantity of free volume is usually determined by the Williams–Landel–Ferry (WLF) equation from viscosity data of the pure component in these theories. Free volume has been extensively discussed in different equation‐of‐state models for a polymer. Among these models, the Simha–Somcynsky (SS) hole model is the best one to describe the crystalline polymer, because it describes it very approximately close to the real structure of a crystalline polymer. In this article, we calculated the fractions of the hole free volume for several different polymers at the glass transition temperature and found that they are very close to a constant 0.025 by the SS equation of state. It is quite consistent with the value that is determined from the WLF equation. Therefore, the free volume of a crystalline polymer below the glass transition temperature (T_g) is available from the SS equation. When above the T_g, it is assumed that the volume added in thermal expansion is the only contribution of the hole free volume. Thus, a new predictive free‐volume theory was proposed. The free volume of a polymer in the new predictive equation can be estimated by the SS equation of state and the thermal expansion coefficient of a polymer instead of by the viscosity of a polymer. The new predictive theory is applied to calculate the solvent self‐diffusion coefficient and the solvent mutual‐diffusion coefficient at different temperatures and over most of the concentration range. The results show that the predicted values are in good agreement with the experimental data in most cases. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 428–436, 2000     

High pressure measurements and molecular modeling of the water content of acid gas containing mixtures

Water content of three carbon dioxide containing natural gas mixtures in equilibrium with an aqueous phase was measured using a dynamic saturation method. Measurements were performed up to high temperatures (477.6 K = 400°F) and pressures (103.4 MPa = 15,000 psia). The perturbed chain form of the statistical associating fluid theory was applied to predict water content of pure carbon dioxide (CO₂), hydrogen sulfide (H₂S), nitrous oxide (N₂O), nitrogen (N₂), and argon (Ar) systems. The theory application was also extended to model water content of acid gas mixtures containing methane (CH₄). To model accurately the liquid‐liquid equilibrium at subcritical conditions, cross association between CO₂, H₂S, and water was included. The agreement between the model predictions and experimental data measured in this work was found to be good up to high temperatures and pressures. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3038–3052, 2015     

A method of estimating the standard gibbs free energy of formation

Standard Gibbs free energy of formation (ΔG_f⁰), an important property needed in design calculations has been estimated using molar refraction, R_M. The linear relationships derived between ΔG_f⁰ and R_M tested with the data on 8 series of hydrocarbons at 228 compounds yielded average deviations comparable to the methods cited in recent literature. The method can be used as an alternative to the existing ones, because of its simplicity combined with reasonable accuracy.     

Application of the functional renormalization group method to classical free energy models

A simple functional renormalization group method is presented to correct the behavior of classical free energy models near the critical point. This approach is applied to the Soave–Redlich–Kwong equation of state to illustrate its ability to better reproduce the phase behavior of simple fluids and to understand the influence of its parameters on the shape of the vapor‐liquid phase diagram. The method is then extended to account for the correlations induced by intramolecular bonds. It is then applied to a first‐order thermodynamic perturbation theory for chain fluids to examine fluids composed of linearly bonded Lennard‐Jones atoms. Unlike previous approaches for applying renormalization group corrections to chain fluids, this is able to accurately reproduce the critical point without predicting an overly flat liquid‐vapor coexistence region. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2985–2992, 2015     

Diffusion of Model Contaminants in High‐Density Polyethylene

Four liquid solvents – 1,1,1‐trichloroethane, toluene, chlorobenzene and octane – are used as model contaminants in sorption experiments in polyethylene in order to study their diffusion behavior between 40 and 70 °C and assess the plausibility of utilizing recycled plastics as safe functional barriers in food packaging applications. A hybrid model that combines molecular and free volume theory elements is used to interpret the collected experimental data. This helps in evaluating microstructural characteristics pertaining to the penetrant‐polymer systems tested, correlating these characteristics with the molecular properties of the solvent, and has an eventual role in predicting sorption and diffusivity in similar untested systems.

     

Hybrid model for the diffusion of simple and complex penetrants in polymers

A hybrid model, which combines the characteristic features of the Pace–Datyner molecular model with those of the Kulkarni–Stern free‐volume model, was developed to assess the effect of temperature, penetrant concentration, and polymer crystallinity on penetrant diffusivity. The predictive capabilities of the proposed model were tested by a direct comparison with experimental data. The diffusivity of ethylene and propylene vapors in semicrystalline polyethylene and isotactic polypropylene was experimentally measured using a magnetic suspension microbalance. Sorption kinetic measurements were carried out at temperatures up to 80°C and pressures up to 80 atm. The diffusivity was found to increase with temperature and penetrant concentration. Apparently, there was a very good agreement between the theoretical values predicted by the new hybrid diffusion model and the experimentally determined diffusivities. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

二种估算苯酚在改性活性炭上脱附活化能模型

应用程序升温吸附(TPD)技术分别测定了苯酚在空白活性炭以及负载Fe3+,Ag+的活性炭上TPD曲线,并采用理想TPD模型和改进的TPD模型估算苯酚在这些吸附材料上的脱附活化能,讨论了吸附材料表面负载Fe3+,Ag+对苯酚脱附活化能的影响。结果表明:采用改进的TPD模型估算得到的脱附活化能要低于理想TPD模型估算得到的活化能4.9%—5.9%,这是由于理想TPD模型忽略了脱附过程中可能出现的吸附质被再吸附现象。苯酚从负载硬酸Fe3+活性炭表面上脱附活化能大于其从原始活性炭表面脱附的活化能,而它从负载属于软酸的Ag+的活性炭表面上脱附所需的活化能小于其从空白活性炭表面脱附的活化能。     

A model for the evaporation of biomass pyrolysis oil droplets

This paper presents a numerical model for the evaporation and pyrolysis of a single droplet of pyrolysis oil derived from biomass. Continuous thermodynamics theory for multi-component droplet evaporation is used, with the fuel being represented by four fractions: organic acids, aldehydes/ketones, water, and pyrolytic lignin, each of which is described by a separate distribution function. Pyrolysis of the lignin fraction is included, and detailed properties for all fractions are presented. The model is compared with the results of suspended droplet experiments, and is shown to give good predictions of the times of the major events in the lifetime of a droplet.     

Artificial neural network for the second virial coefficient of organic and inorganic compounds: An ANN for B of organic and inorganic compounds

An artificial neural network (ANN) to estimate the second virial coefficient, valid for organic and inorganic compounds, is presented. First, we statistically analyzed 6,531 experimental points, belonging to 234 fluids, collected from literature. The data were investigated with a factor analysis approach to identify the most significant parameters that influence the second virial coefficient. The factor analysis, combined with physical considerations, allowed to find four (T_r, T_c, P_c, ω) or five (μ_r) parameters as input variables for the ANN, according to the specific chemical family. The architecture of the proposed multi-layers perceptron (MLP) neural network consists of one input layer with five input variables (T_r, T_c, P_c, ω, μ_r), one output layer with one neuron (B) and two-hidden-layers with 19 neurons each. We trained, validated and tested several configurations of the neural network to obtain this network topology that minimizes the deviations between experimental and calculated points. Results show that the ANN is able to calculate the second virial coefficient with greater accuracy (RMSE?=?29.38?cm³/mol) than that of correlations available in literature. To identify the outliers and applicability domain of the proposed MLP neural network, an outlier diagnosis based on the Leverage approach was performed. This analysis shows that the model is statistically valid.     

Stress‐induced densification of glassy polymers in the subyield region

Constitutive equations are derived for the viscoelastic response of amorphous glassy polymers in the region of subyield deformations. The model treats an amorphous polymer as a composite material consisting of an ensemble of flow units, immobile holes, and clusters of interstitial free volume moving through a network of long chains to and from voids. Changes in macropressure lead to an increase in the equilibrium concentration of interstitial free volume that, in turn, induces diffusion of free‐volume elements from holes. The mass flow results in dissolution of voids that is observed as time‐dependent densification of a glassy polymer. It is demonstrated that the model correctly predicts stress relaxation and a decrease in the specific volume observed in uniaxial tensile and compressive tests on polycarbonate at room temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1705–1718, 1999     

从反应活化能垒角度探讨多晶硅还原机理

三氯氢硅还原反应是改良西门子法生产多晶硅的主要过程,本文对三氯氢硅还原反应进行分子模拟,采用密度泛函理论方法(DFT)研究了三氯氢硅还原成多晶硅的能量变化,对其分子结构进行优化,通过LST/QST方法计算多晶硅还原过程中可能出现的过渡态及能量的变化,得到过渡态TSa、TSb、TSc。结果表明,三氯氢硅还原反应通道Path a所得过渡态的活化能垒较低,过程进行较顺利。     

Polymer-cosolvent systems: 7. The application of free volume theory to the classical cosolvent systems formed from polystyrene in acetone and n-alkanes

The Prigogine-Patterson theory of polymer solutions has been applied to the cosolvent systems formed from mixtures of acetone (1) with n-alkanes (2). The necessary reduction parameters were calculated taking due account of acetone/alkane interactions as characterized by the Flory X₁₂ parameter. The effect of relatively increased free volume differences in the solvent mixtures is counteracted by a marked decrease in the enthalpy term which brings about an overall decrease in the polymer/solvent interaction parameter (χ). It is suggested that cosolvency is predominantly enthalpic in origin and a possible mechanism is postulated.     

Calculation of the redox potential of the protein azurin and some mutants

Azurin from Pseudomonas aeruginosa is a small 128-residue, copper-containing protein. Its redox potential can be modified by mutating the protein. Free-energy calculations based on classical molecular-dynamics simulations of the protein and from mutants in aqueous solution at different pH values were used to compute relative redox potentials. The precision of the free-energy calculations with the lambda coupling-parameter approach is evaluated as function of the number and sequence of lambda values, the sampling time and initial conditions. It is found that the precision is critically dependent on the relaxation of hydrogen-bonding networks when changing the atomic-charge distribution due to a change of redox state or pH value. The errors in the free energies range from 1 to 10 k(B)T, depending on the type of process. Only qualitative estimates of the change in redox potential by protein mutation can be obtained.