Predicting the thermodynamic properties and dielectric behavior of electrolyte solutions using the SAFT‐VR+DE equation of state

We extend the SAFT‐VR+DE equation of state to describe 19 aqueous electrolyte solutions with both a fully dissociated and a partially dissociated model. The approach is found to predict thermodynamic properties such as the osmotic coefficient, water activity coefficient, and solution density, across different salt concentrations at room temperature and pressure in good agreement with experiment using only one or two fitted parameters. At higher temperatures and pressures, without any additional fitting, the theory is found to be in qualitative agreement with experimental mean ionic activities and osmotic coefficients. The behavior of the dielectric constant as a function of salt concentration is also reported for the first time using a statistical associating fluid theory (SAFT)‐based equation of state. At high salt concentrations, the stronger electrostatic interactions between the ionic species due to the dielectric decrement, is captured through the inclusion of ion association. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3053–3072, 2015     

Effects of pH,salt type,and ionic strength on the second virial coefficients of aqueous bovine serum albumin solutions

The osmotic pressures of aqueous bovine serum albumin (BSA) solutions were measured at different pH (3.6, 4.6, 5.6, and 7.6) in combination with different concentrations (0.01 M, 0.1 M, 1 M, and 3 M) of salts (sodium, pottasium, and lithum) by using a Wescor colloid membrane osmometer. The osmotic second virial coefficients for BSA were determined from the experimental osmotic pressure. Predominant forces between protein molecules were measured at the various pH, ionic strength, and type of salt. These experimental data were utilized to determine the depth of square-well potential, which accounts for specific interactions between protein molecules at various conditions. This article is dedicated to Professor Chul Soo Lee in commemoration of his retirement from Department of Chemical and Biological Engineering of Korea University.     

An electrolyte CPA equation of state for mixed solvent electrolytes

Despite great efforts over the past decades, thermodynamic modeling of electrolytes in mixed solvents is still a challenge today. The existing modeling frameworks based on activity coefficient models are data‐driven and require expert knowledge to be parameterized. It has been suggested that the predictive capabilities could be improved through the development of an electrolyte equation of state. In this work, the Cubic Plus Association (CPA) Equation of State is extended to handle mixtures containing electrolytes by including the electrostatic contributions from the Debye–Hückel and Born terms using a self‐consistent model for the static permittivity. A simple scheme for parameterization of salts with a limited number of parameters is proposed and model parameters for a range of salts are determined from experimental data of activity and osmotic coefficients as well as freezing point depression. Finally, the model is applied to predict VLE, LLE, and SLE in aqueous salt mixtures as well as in mixed solvents. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2933–2950, 2015     

Efficient recovery of high‐purity aniline from aqueous solutions using pervaporation‐fractional condensation system

Selective recovery of valuable minor component with high‐purity form from dilute aqueous solution is an interesting issue in the area of organophilic pervaporation. High‐purity aniline was recovered with a high production rate from dilute aqueous solution by a pervaporation‐fractional condensation (PVFC) coupling system. The effects of downstream pressure and temperature (the first condenser) on the performance of PVFC system were investigated based on experimental measurements and Aspen simulations. Sorption and desorption experiments demonstrated that the sorption selectivity of poly(ether block amide) (PEBA‐2533) membrane to aniline was extremely high, indicating excellent pervaporation performance for aniline/water solutions. The perfect integration of high‐performance PEBA‐2533 membrane with the fractional condensation process yielded high production rate of 1222.5 g/(m² h) as well as high recovery efficiency (86.5%) for recovering high‐purity aniline in the first condenser when feed concentration and temperature were 1 wt % and 80°C, respectively. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4445–4455, 2015     

Ion-based SAFT2 to represent aqueous multiple-salt solutions at ambient and elevated temperatures and pressures

Ion-based SAFT2 is extended to the properties of aqueous multiple-salt solutions at ambient and elevated temperatures and pressures. The short-range interactions between two different cations are allowed to obtain better representations of the solution properties. The adjustable parameter used in the mixing rule for the segment energy is fitted to the experimental osmotic coefficients of two-salt solutions containing one common anion at various temperatures and low pressures. The predictions of the osmotic coefficients, densities, and activity coefficients of multiple-salt solutions including brine/seawater are found to agree with experimental data.     

Twenty‐one new theoretically based cubic equations of state for athermal hard‐sphere chain pure fluids and mixtures

Eight new hard‐sphere equations of state (EOS's) were obtained from molecular simulation data for the pair correlation function g_HS(σ) vs. packing fraction η and combined with three theoretical schemes to obtain 21 new cubic EOS's for athermal hard‐sphere chains (AHSC's). The eight new hard‐sphere EOS models successfully reproduced isotropic fluid compressibility factor Z_HS and g_HS(σ) vs. η simulation data and predicted metastable liquid Z_HS vs. η and virial coefficients up through B₁₀. Moreover, calculated Z vs. η and reduced second‐virial coefficient vs. chain length m were compared with molecular simulation data for chains up to m = 201 for a set of representative (eight of twenty‐one) chain equations. Z vs. η for three AHSC binary mixtures was also successfully predicted. The results indicate that the new cubic EOS's give a satisfactory representation of simulation data for chain fluids and can be used to develop theoretically based cubic EOS's for “real” fluids including attractive effects. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1677–1690, 2015     

Evaluation of oriented amorphous regions in polymer films during uniaxial deformation; structural characterization of a poly(vinyl alcohol) film during stretching in boric acid aqueous solutions

We have improved the conventional analytical method of the scattering data obtained with in‐situ synchrotron X‐ray scattering experiments, which is applicable to the structural characterization of the film during stretching. Four components of molecular chains in the film are divided from two‐dimensional wide‐angle X‐ray diffraction patterns. These components are the oriented crystals, the unoriented ones, the oriented amorphous chains, and the unoriented ones, respectively. This method allows to evaluate directly the degree of orientation of the amorphous chains and the amount of the oriented amorphous fraction in addition to each evaluation for the crystalline regions. This method is applied to the structural characterization of the poly(vinyl alcohol) (PVA) film during stretching in boric acid aqueous solutions, suggesting that boric acid accelerates orientation of molecular chains in the amorphous regions, and increases the oriented amorphous fraction by producing the cross‐links between the PVA chains and hindering strain‐induced crystallization. At a film break on stretching in the 3 wt% boric acid solution, the oriented amorphous fraction increases up to 70%, which is much higher compared to that in the film stretched in water, 45%. POLYM. ENG. SCI., 55:513–522, 2015. © 2014 Society of Plastics Engineers     

Experimental studies and modeling of CO2 solubility in high temperature aqueous CaCl2, MgCl2, Na2SO4, and KCl solutions

The phase equilibria of CO₂ and aqueous electrolyte solutions are important to various chemical‐, petroleum‐, and environmental‐related technical applications. CO₂ solubility in aqueous CaCl₂, MgCl₂, Na₂SO₄, and KCl solutions at a pressure of 15 MPa, the temperatures from 323 to 423 K, and the ionic strength from 1 to 6 mol kg^?1 were measured. Based on the measured experimental CO₂ solubility, the previous developed fugacity‐activity thermodynamic model for the CO₂‐NaCl‐H₂O system was extended to account for the effects of different salt species on CO₂ solubility in aqueous solutions at temperatures up to 523 K, pressures up to 150 MPa, and salt concentrations up to saturation. Comparisons of different models against literature data reveal a clear improvement of the proposed PSUCO2 model in predicting CO₂ solubility in aqueous salt solutions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2286–2297, 2015     

Monolayer hydration governs nonideality in osmotic pressure of protein solutions

Strong nonideality observed in the osmotic pressure of concentrated globular proteins in aqueous media of moderate salt concentrations has long been associated with protein–protein interaction. As a consequence, virial expansions, based on the McMillan–Mayer theory, have been used to extract the physical phenomena observed. Our recent articles showed that a free-solvent model assuming hydration and salt binding are dominate factors for nonlinearity, successfully modeled BSA (67 kDa) and IgG (155 kDa) protein aqueous solutions at moderate salt concentrations. Similar findings for lysozyme (HEL, 14 kDa) and ovalbumin (45 kDa) are reported here. More significantly, the independently calculated hydration values regressed from the osmotic pressure data were compared with the solvent accessible surface areas of each protein investigated. The results showed that the hydration values determined from the free-solvent model are remarkably a monolayer equivalent of water.     

An experimental investigation on the influence of phenol on the solubility of CO2 in aqueous solutions of NaOH

Experimental results are presented for the solubility of CO₂ in an aqueous solution of phenol and NaOH (molalties in water: phenol: 0.5; NaOH: 1.0) at (314, 354, and 395) K and pressures up to 10 MPa. The experimental work extends recent investigations on the influence of phenol as well as of (phenol + NaCl) on the solubility of CO₂ in water. In contrast to those previous investigations, the strong electrolyte reacts with carbon dioxide and also with phenol. The experimental results are compared with predictions from a thermodynamic model. That model combines a model for the “chemical” solubility of CO₂ in aqueous solutions of NaOH with a model for the “physical” solubility of CO₂ in aqueous solutions of phenol. An extension is introduced to account for the chemical reaction between the weak acid phenol and the strong base sodium hydroxide. The prediction results nicely agree with the new experimental data. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2832–2840, 2015     

Equation of state for the systems containing aqueous salt: Prediction of high pressure vapor-liquid equilibrium

An equation of state (EOS), which is based upon contributions to the Helmholtz energy, is presented for systems containing aqueous electrolyte solutions at high pressure. The Peng-Robinson equation of state is used to provide the Helmholtz energy of a reference system. The electrolyte terms consist three terms containing a modified Debye-Hückel term for long-range electrostatic interactions, the Born energy contribution for electrostatic works and a Margules term for short-range electrostatic interactions between ions and solvents. The binary and ternary interaction parameters of the equation of state are obtained by experimental osmotic coefficient data. Systems that were studied here are (water+ NaCl+SC-CO₂), (water+NH₄Cl+SC-CO₂), (water+Na₂SO₄+SC-CO₂) and (water+methanol+NaCl+SC-CO₂). It is found that the proposed equation of state is able to accurately represent the experimental data over a wide range of pressure, temperature and salt concentration.     

Numerical study of BSA ultrafiltration in the limiting flux regime — Effect of variable physical properties

Ultrafiltration of BSA solutions in a parallel cell was studied by numerical methods taking into account concentration dependent properties. The Navier-Stokes equations, in the stream function-vorticity formulation, and the mass transport equation were solved simultaneously. The numerical code was validated by comparison with data from benchmark analytical solutions. The flow and concentration fields in the limiting flux regime were studied in detail and compared with the fields for constant properties. Numerical results were also compared with experimental data of the permeate velocity in the limiting flux regime published in the literature. This comparison shows that the concentration dependence of the viscosity, diffusivity and osmotic pressure are all necessary to explain experimental results published in the literature.     

An economically viable removal of methylene blue by adsorption on activated carbon prepared from rice husk

Application of an agricultural waste material, rice husk, has been investigated for preparation of activated carbon. The rice husk‐activated carbon (RHAC) was successfully utilised for the removal of a cationic dye, methylene blue (MB) from aqueous solutions. The activated carbon was prepared in presence of ZnCl₂ as an activating agent under inert nitrogen atmosphere. RHAC was characterised for surface area, pore structural parameters, and point zero charge (pH_ZPC). The activated carbon was further characterised by Fourier transformation infrared (FT‐IR) spectrometer, X‐ray diffractometer (XRD), and scanning electron microscope (SEM). The effect of different parameters such as contact time and initial concentration, adsorbent dose, and temperature on removal of the dye from aqueous solutions was investigated. The experimental data fitted well in both the Freundlich and Langmuir isotherm models. The maximum adsorption capacity for MB was found to be 9.73 mg g⁻¹ at 303 K. During the study of effect of adsorbent dose, almost a 100% removal was achieved at a higher dose of RHAC. Most of the experiments were carried out at an initial concentration of MB of 60 mg/L and at 303 K. Different thermodynamic parameters, viz., changes in free energy (G°), enthalpy (H°), and entropy (S°) have also been determined to explain feasibility of the process of removal. The sorption of MB on RHAC was found to be feasible, spontaneous, and endothermic in nature.     

Protein adsorption on functionalized multiwalled carbon nanotubes with amino‐cyclodextrin

A novel amino‐cyclodextrin was synthesized, and it was covalently attached to multiwalled carbon nanotubes (MWNTs). The functionalized MWNTs (f‐MWNTs) have very good aqueous dispersibility. Bovine serum albumin (BSA) was adsorbed onto f‐MWNTs through noncovalent interactions, including the hydrophobic interaction of the residues of BSA with the wall of MWNT and the guest–host interaction of the residues with the cyclodextrin (CD) moieties of f‐MWNTs. The ultraviolet–visible (UV–vis) absorption of the f‐MWNT‐BSA hybrid was measured with UV–vis spectrometer, and the absorbance can be described well with the Beer–Lambert law. The X‐ray diffraction patterns have indicated that the crystalline form of BSA has been changed after the adsorption of BSA on f‐MWNTs. The circular dichroism spectra have shown that a high percentage of α‐helical content can be retained for BSA adsorbed on f‐MWNTs. The results also indicate that the change of secondary structure of BSA is mainly due to the hydrophobic interaction of the residues of BSA with the wall of f‐MWNT, whereas the secondary structure is much less affected by the interaction of the CD moieties with BSA. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Simultaneous SAXS and WAXS investigations of changes in native cellulose fiber microstructure on swelling in aqueous sodium hydroxide

Simultaneous small‐ and wide‐angle X‐ray scattering was used to follow changes in the microstructure of native cellulose (cellulose I) fibers during conversion to sodium cellulose I (Na‐cellulose I) by aqueous sodium hydroxide. Wide‐angle X‐ray scattering was used to monitor the extent of conversion, while small‐angle X‐ray scattering was used to explore what occurs at the higher structural levels of the elementary fibrils, microfibrils, and interfibrillar voids. Native cellulose fibers, swollen in either water or aqueous sodium hydroxide, exhibited an increase in the void volume fraction and a decrease in the void cross‐section size, as the swelling agent separated elementary fibrils, opening up the structure, and creating many small voids. After conversion of swollen native cellulose to sodium cellulose I, the void volume fraction and average void cross‐section dimensions both increased. During conversion from dry cellulose I fibers to swollen Na‐cellulose I fibers, the void cross‐section dimensions went through a minimum, suggesting that the void structure may go via an intermediate similar to the water swollen structure of cellulose I. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1209–1218, 2002     

Osmotic compressibility of partially deuterated polymer solutions

Elastic neutron scattering by partially deuterated polymer solutions has played an essential role in elucidating the large scale conformations in good solvents. The long wavelength limit of the structure factor yields the osmotic compressibility of the deuterated monomers (assuming that the data have been analysed in terms of the large deuteron coherent scattering). In this paper, we present a rather general theory of this deuterated monomer osmotic compressibility as a function of percentage deuteration for general interactions among monomers. This method yields known results for neutral excluded volume systems and some new predictions for polyelectrolytes.     

Transferable intermolecular potentials for carboxylic acids and their phase behavior

Transferable step potentials are characterized for 39 carboxylic acids. The reference potential is treated with discontinuous molecular dynamics, including detailed molecular structure. Thermodynamic perturbation theory is used to interpret the simulation results and to provide an efficient basis for molecular modeling and characterization of the attractive forces. Four steps are used for representation of the attractive forces with only the first and last steps varied independently. The two middle steps are interpolated such that each site type is characterized by three parameters: the diameter, σ, the depth of the inner well, ε₁, and the depth of the outer well, ε₄. The depths of the attractive wells are optimized to fit experimental vapor pressure and liquid density data. Generally, the vapor pressure is correlated to an overall 43% average absolute deviation (% AAD) and the liquid density to 5% AAD. The deviations tend to be largest for the higher molecular weight acids. These deviations are larger than the errors previously encountered in characterizing organic compounds, but carboxylic acids present exceptional challenges owing to their peculiar dimerization behavior. Simultaneous correlation of vapor pressure, vapor compressibility factor, and phase equilibria of water + carboxylic acids place several constraints on the nature of the potential model, with the parameters of the present model representing a reasonable tradeoff. In other words, our model represents minimal deviations for vapor pressure, vapor compressibility factor, and phase equilibria of all acids simultaneously while varying the parameters σ, ε₁, ε₄, ε^CC(dimerizing site bonding energy), ε^AD(acceptor‐donor bonding energy), and K^HB(hydrogen bonding volume) for the acid O? and OH site types. The present model is characterized by one acceptor and one dimerizing site on the carbonyl oxygen and one acceptor and one donor site on the hydroxyl oxygen. The acceptor and donor are capable of interacting with water while the dimerizing site is not. With this model, the saturated vapor compressibility factor of acids with seven or fewer carbons is near 0.5 while higher carbon ratios lead to a compressibility factor approaching 1.0. To compensate for the high vapor pressure deviations of the transferable potential model, a correction is introduced to customize the molecule‐molecule self interaction energy. This adaptation results in deviations of 3.1% for vapor pressure of the pure acid database. To validate the behavior of the model for carboxylic acids in mixtures, 33 binary solutions were considered. Acids in this database ranged from formic to hexadecanoic. The average absolute deviation in bubble pressure for aqueous acid systems is 4.4%, 10.5% for acid + acid systems, and 4.7% for acid + n‐alkane systems without a customized interaction correction. When applying the correction, deviations were 2.4% for aqueous systems, 2% for acid systems, and 2.8% for acid + n‐alkane systems. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Osmotic coefficients of polyelectrolyte solutions, measurements and correlation

Osmotic coefficient data for aqueous sodium polyanetholesulfonic acid, sodium polyacrylate and polydiallyl dimethylammonium chloride solutions were determined at 298 K by employing the isopiestic method. The measured osmotic coefficients increase with increasing concentration in the experimental concentration range (0.1-1.5 m). A molecular thermodynamic model developed previously for polyelectrolyte solutions has been used to fit the experimental data. The concentration dependence of the osmotic coefficients can be described satisfactorily.     

用PT立方型状态方程关联电解质水溶液的渗透系数

本文将Debye-Huckel静电作用项增加至Patel-Teja立方型状态方程中,建立了适用于电解质体系的新模型.该模型仍然保持了密度立方型的优点.仅用一个可调参数将该模型用于单盐水溶液的渗透系数关联,取得了与实验数据一致的结果.     

利用变阱宽方阱链流体状态方程计算1：1电解质溶液热力学性质

将变阱宽方阱链流体状态方程拓展到1：1强电解质水溶液热力学性质的计算中,通过关联溶液的平均离子活度系数和溶剂的渗透系数得到了22种离子的链节直径和方阱能量参数,40余种电解质溶液的平均离子活度系数和溶剂渗透系数的总平均相对偏差分别为6.03%和5.83%。计算结果表明,建立的电解质型状态方程可以满意预测电解质溶液的密度和宽广温度下溶液的蒸气压,总体平均相对偏差分别为0.22%和4.69%。进一步说明模型参数的可靠性。