Additivity rules for the prediction of the density of aqueous solutions containing mixed-type solutes

Densities of ternary aqueous solutions of mixed-type solutes have been measured at 25°C to high concentration. Two methods, the one isopycnotic (same density) and the other based on ionic strength, have been used to predict the densities of these solutions. The isopycnotic method proved to be the more accurate. The two methods have been applied in reverse to calculate densities of supersaturated binary aqueous solutions of NaCl and KCl. The methods give concordant results for each salt Deviation parameters for the methods are presented, with a discussion of their use.     

Kinematic viscosity prediction for aqueous solutions with various solutes

In numerous research areas knowledge of aqueous solutions viscosity is very important to interpret the experimental data or to use it in simulation studies. When Kumar’s semitheoretical equation for prediction of the dynamic viscosity of a solution of a single electrolyte is modified for prediction of kinematic viscosities, it is found that the resulting expression is valid both for salts and for certain organic solutes. The parameters characterizing individual solutes in aqueous solution at temperatures between 293.1 and 323.1 K also allow prediction of the kinematic viscosities of solutions of multiple solutes in the same temperature and concentration range, with overall errors of <2.5% in 36 of 39 multi-component systems.     

Electrochemical treatment of aqueous solutions containing urea

Investigations on the anodic decomposition of urea using Ti/Pt and Ti/(RuO₂–TiO₂)_40:60 electrodes were carried out. The kinetics of the process were examined in a periodic electrolyser. The effect of anodic current density, initial urea concentration, and sodium chloride concentration on the effectiveness of the basic process (average rate of urea decomposition, current efficiency, and unit power consumption) is discussed. When a Ti/Pt electrode is applied for urea removal from aqueous solution urea is not decomposed directly at the surface of the electrode, but rather in the bulk of the solution by hypochlorite formed during the process. When the Ti/(RuO₂–TiO₂)_40:60 electrode is used for the removal of urea from aqueous solutions, the reaction of urea with chlorine adsorbed at the electrode predominates. In both cases non-toxic products of urea decomposition (N₂, CO₂,) are formed. Comparison of the effectiveness of anodic decomposition of urea for the Ti/Pt and Ti/(RuO₂–TiO₂)_40:60 electrodes in the periodic electrolyser at optimum process parameters has revealed that the former electrode is more favorable.     

Reverse osmosis separation of inorganic solutes in aqueous solutions using porous cellulose acetate membranes

Using a modified form of the Born expression for the free energy of ion-solvent interaction, to both the bulk solution phase and the membrane–solution interface, a parameter is obtained to express the repulsion of the ion at the interface. This parameter, called the free energy parameter for ions, is then related to solute transport parameter obtained from reverse osmosis experiments. Numerical values of this free energy parameter have been obtained for six monovalent and four divalent cations and for 12 monovalent anions. Using the experimental data for the reverse osmosis separation of sodium chloride as reference, the utility of the above parameter for predicting solute separation in reverse osmosis is illustrated for 32 other inorganic salts.     

Density prediction of multicomponent aqueous solutions from binary data

An isopycnotic (equal density) relation has been developed for non-interacting solutes in multicomponent aqueous solutions. The relation can be used to estimate ternary densities from binary data. Predicted and observed values for 26 systems at 25°C are compared, usoing Young's rule, the isopycnotic, and other methods. Young's rule and the isopycnotic methods give relatively better predictions (<0.2% error) even when applied to concentrated solutions.     

Effect of density on the electrical conductance of aqueous sodium chloride solutions

Concentrated sodium chloride solutions are commonly used in electrochemical machining and a knowledge of their conductance is important. A study was made of the conductivity of a range of concentrations from 0.01 M to 5 M to temperatures >500°C and to pressures of 2000bar. The conductances were found to go through maxima at 250–300°C after increasing in magnitude by a factor of >4.     

Voltammetric behaviour of platinum in aqueous solutions containing sodium hypophosphite

The anodic and cathodic behaviour of polycrystalline Pt in sodium hypophosphite solutions has been investigated by cyclic voltammetry. In acid solutions the voltammograms show that, owing to the presence of the reducing agent, electrooxidation of species related to H₃PO₃ occurs in the potential range 0.6 to 1.4 V with respect to NHE. In alkaline solutins the presence of NaH₂PO₂ partially inhibits the HER and displaces the formation of the oxygen monolayer on platinum to higher potentials. The voltammetric peaks are attributed to the electrooxidation of the products resulting from the chemical decomposition of NaH₂PO₂ in contact with the Pt surface.     

On the choice of methods for the prediction of the water-activity and activity coefficient for multicomponent aqueous solutions

Some of the various methods of predicting thermodynamic properties of multi-component aqueous solutions have been critically examined and interrelated. Recommendations are made for the best choice of method according to data available, accuracy required and type of solute.     

Reverse osmosis separations of some organic and inorganic solutes in aqueous solutions using aromatic polyamide membranes

The reverse osmosis separations of some ethers, ketones, aldehydes, monocarboxylic acids, and inorganic salts in single-solute (55–454 ppm) aqueous solution systems using aromatic polyamide membranes have been studied at 250 psig. It was found that reverse osmosis separation was essentially a function of steric parameter for ethers, and of both polar and steric parameters for ketones, aldehydes, and alcohols. Solute separations for monocarboxylic acids passed through a minimum at a pK_a value of ～4.8. The values for the free-energy parameter for Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and F^?, Cl^?, Br^?, I^?, and IO₃^? ions have been calculated for the polyamide membranes used. The above values for cations are negative and those for anions are positive, suggesting that the polyamide membrane surface behaves as if it is positively charged. Further, the data show that the polyamide membrane material is only about 40% as polar as that of the cellulose acetate membrane material studied earlier.     

An equation for multi-solute adsorption from dilute aqueous solutions involving energetic heterogeneity of the solid and differences in molecular sizes of the solutes

This work presents a simple model for multi-solute adsorption from dilute aqueous solutions on solids. The proposed model leads to a simple relationship defining dependence between adsorbed amounts and concentrations of two arbitrary solutes. This relationship is derived by assuming ideality of both phases, energetic heterogeneity of the solid and different molecular sizes of solutes.The experimental data for bi-solute adsorption from dilute aqueous solutions on activated carbon, available from literature, are used to examine the proposed equation. These studies show that the new equation gives good representation of the bi-solute adsorption data.     

Enthalpy-entropy relationships in the fluid kinetics of aqueous electrolyte solutions containing positively hydrated ions

By using new criteria for testing the validity of enthalpy-entropy relations it is shown that previously reported non-linear relationships between the activation parameters for the fluidity of aqueous electrolytes containing positively hydrated ions are essentially valid. It is impossible to establish valid enthalpy-entropy relations directly from ΔH3_φvs ΔS3_φ, and equally impossible to do so merely by transformation from log φ₁, and log φ₂. Validity can only be established by determining the true functional dependence in log φ₁, and log φ₂vs molality (m) and demonstrating its consistent appearance through log φ₁vs log φ₂ and ΔH3_φvs ΔS3_φ and ΔS3_φvs m.     

Treatment of aqueous solutions containing nickel using crandallite‐type compounds

The removal of nickel from aqueous solutions streams has been investigated using an artificial amorphous crandallite‐type compound, CaAl₃(OH)₆(HPO₄)(PO₄) (Ca‐crandallite), synthesized in our laboratory. Equilibrium ion‐exchange isotherms in an aqueous medium of Ca²⁺/Ni²⁺ at different pH values at 293 K have been determined. The experimental equilibrium data were satisfactorily correlated using a Langmuir‐type empirical equation. At low pH values, the hydrogen ion competes with the heavy metal cation and the percentage removal of metal declines. It was found that the operating capacity of Ca‐crandallite with respect to the metal ion increased with the pH of the solution, in accordance with a second‐degree polynomial equation. However, the pH should not be allowed to rise to levels at which chemical precipitation as nickel hydroxide would occur, with 7.00 the highest value tested. Taking into account the variation of operating capacity with pH, the system exhibited a unique separation factor, namely all the experimental points can be described by a unique isotherm in a dimensionless form. The Ca‐crandallite showed a high capacity, 2.176 meq g^?1, for the exchange of Ni(II) from nickel nitrate solutions and the rate of exchange of metal increases with increasing solution temperature due to the enhancement of effective intraparticle diffusivity. Copyright © 2005 Society of Chemical Industry     

Surfactant precipitation in aqueous solutions containing mixtures of anionic and nonionic surfactants

The salinity tolerance (precipitation phase boundary) is measured for a mixed anionic/nonionic surfactant system above the CMC. For any total surfactant concentration, the salinity tolerance is shown to increase as the percentage of nonionic surfactant in the system is increased. A model is developed which can predict the phase boundaries for the mixed surfactant system from the pure anionic surfactant phase boundary and information about mixed micelle formation. In the model, precipitation is viewed as a solubility product relationship between the anionic surfactant monomer and the total unassociated counterion. The reason that salinity tolerance (or counterion concentration necessary to cause precipitation) increases with addition of nonionic surfactant is that mixed micelle formation reduces the anionic surfactant monomer concentration. For the experimental studies, sodium dodecyl sulfate is the anionic surfactant, a polyethoxylated nonylphenol is the nonionic surfactant, and sodium chloride is the added salt.     

Mixing rules for high density polyethylene-polypropylene blends

High-density polyethylene (HDPE) and polypropylene (PP) blends of varying composition have been evaluated in an effort to establish a mixing rule for melt flow index (MFI). In addition, a previously established relationship between MFI and $\overline{M_w}$ for linear polymers was also evaluated for these blends. It was found that a parabolic relationship existed between the composition (by weight fraction) and MFI and that the MFI and $\overline{M_w}$ relationship held for this set of polymeric materials. Additionally, all properties and relationships were evaluated over five extrusion cycles, which showed minimal to no deviations over the five cycles.     

液液萃取技术在低浓度乙醇水溶液样品检测前处理中的应用

采用液液萃取技术浓缩水中的低浓度乙醇后,用气相色谱法进行测定。首先优化以甲基叔丁基醚(MTBE)为萃取剂的萃取条件:初始乙醇溶液的质量分数win=1.032%、水相与有机相的体积比5∶1,萃取温度291.2 K,搅拌速度为200 r/min.在此基础上,分别加入固体无机盐和离子液体强化液液萃取过程,结果表明固体无机盐K2CO3的盐效应最为明显;随着盐浓度的增加,萃取后有机相中乙醇的质量分数wo也随之增大,从而实现对乙醇水溶液的显著浓缩作用。盐效应的分离机理进一步通过红外光谱分析和量子化学计算,从分子结构和分子间相互作用力方面进行解释,因而实验、理论分析和计算结果保持一致。该样品检测前处理方法具有重现性好、准确度高、快速、简便的特点,且无工业放大效应,为分析水中低浓度有机物提供参考价值。本文中将化工分离过程强化技术应用于样品检测前处理中,体现了化学工程与分析化学的跨学科结合。     

Modeling and prediction of pH and water activity in aqueous amino acid solutions

Water activity and pH of amino acids (alanine, glicine, arginine and proline) in aqueous and buffer solutions were measured at various concentrations and 25°C. The partial dissociation phenomenon was considered and the UNTFAC model, combined with solvation equations, was used for the water activity and pH predictions. The validity of the model was tested for the aminoacids in water and two buffer solutions. Mean deviations of 0.64% for the water activity and 2.5% for the pH were obtained.