Middle-range Interaction Research Articles

A modified LIQUAC model for prediction of the vapor pressure of single liquid desiccant at high concentration and regeneration temperature

A comparative study is conducted to find that there are significant prediction deviations of single liquid desiccants vapor pressure at high concentration and regeneration temperature (high temperature) based on existing typical models. Some factors affecting water activity are not taken into account in these models, and they become more significant at high temperature and high concentration. This paper proposes a modified LIQUAC model to improve the prediction accuracy of single liquid desiccants vapor pressure at high temperature and high concentration. In the modified thermodynamic model, the middle-range interaction is derived by enhancing temperature and concentration dependence. By analyzing the prediction results of three typical liquid desiccants, it is found that the theoretical framework of the novel model is better than that of two typical models (using same data base for parameterization) at high temperature and high concentration. The interaction parameters in the modified model have precise physical meanings and make the model can be extended to other electrolyte solutions.

Solubility measurement and thermodynamics modelling for potassium dihydrogen phosphate in a water-ethanol system from 293.2 to 323.2 K

The phase equilibrium and thermodynamic properties of potassium dihydrogen phosphate (KDP) in the binary water-ethanol system are of critical significance for the salting-out crystallization of KDP production using ethanol as anti-solvent. The solubility of KDP in water-ethanol solvent was determined by the static equilibrium method under constant pressure at temperatures ranging from 293.2 to 323.2 K, with the molar fraction of water varying between 0.3885 and 1.0. The solubility of KDP significantly decreased with the addition of ethanol and increased with rising temperature. A new group of parameters (middle-range interaction) of the mixed-solvent electrolyte model (MSE model) of KDP in the water-ethanol system were obtained by regressing all experimental solubility data. The MSE model with the newly acquired parameters was successfully used to simulate the KDP precipitation process in KH2PO4/C2H5OH/H2O systems and could predict the distribution of ion speciation and activity coefficients. This paper provides fundamental thermodynamic properties and a prediction model for the anti-solvent crystallization process for KDP production.

Solubility Determination and Thermodynamic Modeling for the System NaCl–NH4Cl–Diethanolamine–H2O

In this work, the solubility behavior of salts NaCl and NH4Cl was investigated in aqueous diethanolamine (DEA) solution by varying both temperature and the solvent composition. DEA has been prevalently used in the postcombustion process to capture CO2, but a limited amount of references can be found pertaining to any solid–liquid system containing DEA. It was experimentally determined that the solubility of NaCl decreases, whereas the solubility of NH4Cl increases with the addition of DEA (x′DEA = 0–0.2). The solubility of both salts increases if temperature is raised from 283 to 353 K. The common-ion effect was examined for the quaternary system when both salts are present in the solution. By the regression of solubility data with the Mixed Solvent Electrolyte model, we proved that readjusting the middle-range interaction parameters between Cl–-DEA and DEAH+-Cl– would lower the relative deviation (within 5%) for each proposed ternary system. A comprehensive chemical model was further constructed based on...

Modeling of glycine solubility in aqueous HCl–MgCl2 system and its application in phase transition of glycine by changing media and supersaturation

The solubility of glycine in HCl and HCl–MgCl2 solutions was measured from 283.15 to 343.15K and found to increase with temperature and increase linearly with the concentration of HCl. The MSE model integrated in the OLI platform was modified by regressing the experimental and literature solubility data through the adjustment of the middle-range interaction parameters. After parameterization, the model can accurately calculate the solubility with the average absolute deviation lower than 3.5% and thus be able to predict supersaturation of glycine. Crystallization of different polymorphs of glycine in water, HCl, NaOH, MgCl2, and HCl–MgCl2 aqueous solutions was performed. The effects of medium, temperature, supersaturation, and time on the crystallization were investigated. It was found that only in the HCl solution the formation of single α-glycine phase was achieved under all the investigated temperature and holding time. α-glycine or its mixture with γ-glycine or C4H18N2O4·HCl was produced in systems other than HCl solution depending on the conditions.

Solubility Measurement and Chemical Modeling of MgSO4·7H2O in the Ti(SO4)2–H2SO4–H2O System

The solubility of MgSO4·7H2O in the H2SO4–H2O and Ti(SO4)2–H2SO4–H2O systems was investigated from (278.2 to 308.2) K with initial H2SO4 concentrations of (0 to 5.5) mol·kg–1 by dynamic method. It was found that the solubility of MgSO4·7H2O in the H2SO4–H2O system gradually decreased and then slightly increased with the concentration of H2SO4. Each solubility curve has its own minimum which is temperature dependent. For the MgSO4–Ti(SO4)2–H2SO4–H2O system, the solubility of MgSO4·7H2O decreased sharply with increasing concentrations of H2SO4 and Ti(SO4)2 throughout the entire range investigated. A new chemical model was developed by regression of the experimental data for MgSO4·7H2O solubility to obtain new middle range interaction parameters for the mixed-solvent electrolyte (MSE) model. The model, with the newly obtained parameters, was applied to predict the speciation, water activity, and ionic activity coefficients in the MgSO4–H2SO4–H2O and MgSO4–Ti(SO4)2–H2SO4–H2O systems.

Modeling Phase Equilibria for the Glycine–NH4Cl–Methanol–Water System and Its Application for the Industrial Monochloroacetic Acid Process

As a continuation of our previous study, this work focuses on the determination and modeling of phase equilibria for the mixed-solvent electrolyte system containing glycine, ammonium chloride (NH4Cl), methanol, and water. This electrolyte is used in the monochloroacetic acid (MCA) process for glycine production. The solubilities for the NH4Cl–methanol–water and glycine–NH4Cl–methanol–water systems were determined from 283.15 to 323.15 K. The MSE model embedded in the OLI platform was modified by regressing experimental data through adjustment of the UNIQUAC and the middle-range interaction parameters. With the new model parameters, solubilities in the quaternary system were predicted with excellent agreement. The average absolute deviations between the prediction and the experimental solubility are 3.46 and 0.54% for glycine and NH4Cl, respectively. OLI Stream Analyzer 9.1 was used with this new MSE model to investigate the effect of the methanol composition and temperature on the yield of glycine crystallization in the MCA process. It was found that a methanol mole fraction of 0.65–0.70 at ambient temperatures was optimal for enhancing the theoretical yield of glycine to 96.5% while minimizing the methanol consumption.

Molecular dynamics study of the bulk temperature effect on primary radiation damage in uranium dioxide

The effect of bulk temperature on the primary damage induced by a displacement cascade was investigated in uranium dioxide using classical molecular dynamics simulations. In this study, the Morelon potentials were used to model the middle-range interactions between the atoms that constitute the host matrix during the radiation events. Cascades were initiated by accelerating a uranium primary knock-on atom at 10keV inside a perfect UO2 lattice at a temperature between 700K and 1800K, a range which comprises in-pile temperatures of oxide fuels in light water reactors in standard operating conditions. Cascade overlap sequences were also simulated at 700K and 1400K in order to study the radiation damage accumulation in the oxide fuel. This study reveals the maximum damage level which the material can accommodate for decreases with the temperature. Furthermore the direct formation of vacancy clusters under irradiation is considerably slowed down above 1000K, notably during cascade overlap sequences.

Structures and thermodynamics of particle systems with long- and middle-range interactions

Structures and thermodynamics of particle systems with long- and middle-range interactions

Thermodynamic modeling and experimental measurement of calcium sulfate in complex aqueous solutions

A newly developed database for the Mixed Solvent Electrolyte (MSE) model of the OLI Systems software was employed to model the solid and aqueous phase equilibria of calcium sulfate hydrates in electrolyte solutions containing NiSO 4, H 2SO 4, MgSO 4, Fe 2(SO 4) 3, LiCl and HCl from 25 to 90 °C. The MSE model is a variant of an excess Gibbs free energy model for Mixed Solvent Electrolyte systems which takes into account long-range electrostatic interactions from a Pitzer–Debye–Hückel equation, middle-range interactions from a second virial coefficient-type equation and short-range interactions from the UNIQUAC model. The effect of cations with similar anions on the solubility was investigated and it was found that the solubility depends mainly on the anion type while the cation has a minor effect. The effect of acid addition and the acid type was also studied. The addition of both HCl and H 2SO 4 increases the solubility; however H 2SO 4 has a less pronounced effect due to the common ion effect. Furthermore, the effect of phase transitions between different calcium sulfate hydrates was studied. The transformation of CaSO 4 dihydrate to anhydrite results in a significant decrease in the solubility, which complicates the chemistry of the system. Since it is not practical to measure solubility data under all conditions of interest, the model developed and the experimental results obtained serves the purpose of assessing the calcium sulfate scaling potential for a wide variety of complex aqueous industrial streams.

Consideration of long and middle range interaction on the calculation of activities for binary polymer solutions

We established a thermodynamic framework of group contribution method based on modified double lattice (MDL) model. The proposed model included the long-range interaction contribution caused by the Coulomb electrostatic forces, the middle-range interaction contribution from the indirect effects of the charge interactions and the short-range interaction from modified double lattice model. The group contribution method explained the combinatorial energy contribution responsible for the revised Flory-Huggins entropy of mixing, the van der Waals energy contribution from dispersion, the polar force, and the specific energy contribution from hydrogen bonding. We showed the solvent activities of various polymer solution systems in comparison with theoretical predictions based on experimental data. The proposed model gave a very good agreement with the experimental data.

Vapor–liquid equilibria of perfluorinated SPE/fuel system using group-contribution method

The LIQUAC model is extended to describe water activities of polymer electrolyte at the operating condition of polymer electrolyte fuel cell (PEFC). The proposed model includes the long-range interaction contribution caused by the Coulomb electrostatic forces, the middle-range interaction contribution from the indirect effects of the charge interactions and the short-range interaction contribution represented by the chain length dependence of a polymer. Theoretical predictions and experimental results are in good agreement.