2O System Research Articles

Phase equilibrium measurements for the I 2–H 2O and I 2–HI–H 2O systems of the sulfur–iodine cycle using a continuous-flow apparatus

Liquid–liquid equilibrium (LLE) phase behavior was investigated for the binary iodine–water (I 2–H 2O) and the ternary iodine–hydroiodic acid–water (I 2–HI–H 2O) at the elevated temperatures and pressures of interest for the reactive distillation column of the Sulfur–Iodine Cycle. A continuous-flow apparatus, with wetted parts fabricated from tantalum-tungsten alloys, was designed and constructed for the highly corrosive conditions of this work. A central feature of the apparatus is the equilibrium view cell, which allows for the observation and discernment of vapor-liquid, liquid-liquid, and liquid–liquid–vapor equilibria for HIx systems. For the I 2–H 2O system, LLE was observed at temperatures and pressures to 300 °C and 104 bar. Based on our observations, we estimate that the upper critical solution temperature for this system occurs at 310–315 °C. For the I 2–HI–H 2O ternary, VLE, LLE, and LLVE were all observed at 160 and 200 °C, and three compositions on the water-rich side of the LLE phase envelope were determined.

Prediction of vapor–liquid equilibrium and PVTx properties of geological fluid system with SAFT-LJ EOS including multi-polar contribution. Part I: Application to H 2O–CO 2 system

Molecular based equations of state (EOS) are attractive because they can take into account the energetic contribution of the main types of molecular interactions. This study models vapor–liquid equilibrium (VLE) and PVTx properties of the H 2O–CO 2 binary system using a Lennard-Jones (LJ) referenced SAFT (Statistical Associating Fluid Theory) EOS. The improved SAFT-LJ EOS is defined in terms of the residual molar Helmholtz energy, which is a sum of four terms representing the contributions from LJ segment–segment interactions, chain-forming among the LJ segments, short-range associations and long-range multi-polar interactions. CO 2 is modeled as a linear chain molecule with a constant quadrupole moment, and H 2O is modeled as a spherical molecule with four association sites and a dipole moment. The multi-polar contribution to Helmholtz energy, including the dipole–dipole, dipole–quadrupole, and quadrupole–quadrupole contribution for H 2O–CO 2 system, is calculated using the theory of Gubbins and Twu (1978). Six parameters for pure H 2O and four parameters for pure CO 2 are needed in our model. The Van der Waals one-fluid mixing rule is used to calculate the Lennard-Jones energy parameter and volume parameter for the mixture. Two or three binary parameters are needed for CO 2–H 2O mixtures, which are evaluated from phase equilibrium data of the binary system. Comparison with the experimental data shows that our model represents the PVT properties of CO 2 better than other SAFT EOS without a quadrupole contribution. For the CO 2–H 2O system, our model agrees well with the vapor–liquid equilibrium data from 323–623 K. The average relative deviation for CO 2 solubility (expressed in mole fraction) in water is within 6%. Our model can also predict the PVTx properties of CO 2–H 2O mixtures up to 1073 K and 3000 bar. The good performance of this model indicates that: (1) taking account of the multi-polar contribution explicitly improves the agreement of calculated properties with experimental data at high temperatures and high pressures, (2) the molecular-based EOS with just a few parameters fit to data in the sub-critical region can predict the thermodynamic properties of fluids over a wide range of P– T conditions.

Two glass transitions in N, N-diethyl- N-methyl- N-(2-methoxyethyl) ammonium tetrafluoroborate–H 2O mixed solutions

For a room temperature ionic liquid, N,N-diethyl- N-methyl- N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][BF 4]–H 2O system, we have observed two glass transitions in the region of 16.5–30.0 mol% H 2O. The nano-phase separations in [DEME][BF 4] enhanced by a small amount of H 2O may be the cause for this.

Composition and morphology of complicated copper oxalate powder

In Cu(II)-C 2O 4 2--NH 3-NH 4 +-H 2O system, complicated copper oxalate powders were synthesized by coordination-precipitation process with ammonium oxalate as precipitating agent. The composition and morphology of the powders were characterized by chemical analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and thermogravimetric and differential thermal analysis (TGA-DTA). The effects of temperature, copper ion concentration and pH value were investigated. The experimental results show that pure copper oxalate hydrate is prepared below a critical pH value of 6.0, whereas the powder turns to be a complicated copper salt combined with NH 3 over the pH value. Probable chemical formula, CuC 2O 4· x(NH 3) · yH 2O can be assumed, where x and y relate to experimental conditions. Technological parameters, such as temperature, initial copper concentration and solution pH value, have significant effects on particle size, morphology and dispersion of the powders. Powders with various morphologies, pie shape, spindle shape and rod shape, can be synthesized under certain technological conditions.

(Solid + liquid) equilibria in the quinary system [formula omitted] at 288 K

The solubilities and densities of the solid–liquid equilibrium in the quinary system Na +, Mg 2+, K + SO 4 2 − , B 4O 7 2−–H 2O at 288 K were studied experimentally using the method of isothermal solution saturation. On the basis of the experimental data, the dry salt phase diagram, water content diagram and Mg 2+ content diagram of the quinary system were constructed. In the equilibrium phase diagram of the quinary Na +,Mg 2+, K + SO 4 2 − , B 4O 7 2−−H 2O system at 288 K, there are seven invariant points, fourteen univariant curves, and eight fields of crystallization (saturated with MgB 4O 7⋅9H 2O) corresponding to Na 2B 4O 7⋅10H 2O, K 2B 4O 7⋅4H 2O, K 2SO 4, Na 2SO 4⋅10H 2O, MgSO 4⋅7H 2O, K 2SO 4⋅MgSO 4⋅6H 2O, Na 2SO 4⋅MgSO 4⋅4H 2O, and Na 2SO 4⋅3K 2SO 4. The experimental results show that sulfates have larger solubilities than borates in the quinary Na +, Mg 2+, K + SO 4 2 − , B 4O 7 2−–H 2O system at 288 K.

Modeling aqueous perchlorate chemistries with applications to Mars

NASA’s Phoenix lander identified perchlorate and carbonate salts on Mars. Perchlorates are rare on Earth, and carbonates have largely been ignored on Mars following the discovery by NASA’s Mars Exploration Rovers of acidic precipitated minerals such as jarosite. In light of the Phoenix results, we updated the aqueous thermodynamic model FREZCHEM to include perchlorate chemistry. FREZCHEM models the Na–K–Mg–Ca–Fe(II)–Fe(III)–Al–H–Cl–Br–SO 4–NO 3–OH–HCO 3–CO 3–CO 2–O 2–CH 4–Si–H 2O system, with 95 solid phases. We added six perchlorate salts: NaClO 4·H 2O, NaClO 4·2H 2O, KClO 4, Mg(ClO 4) 2·6H 2O, Mg(ClO 4) 2·8H 2O, and Ca(ClO 4) 2·6H 2O. Modeled eutectic temperatures for Na, Mg, and Ca perchlorates ranged from 199 K (−74 °C) to 239 K (−34 °C) in agreement with experimental data. We applied FREZCHEM to the average solution chemistry measured by the Wet Chemistry Laboratory (WCL) experiment at the Phoenix site when soil was added to water. FREZCHEM was used to estimate SO 4 2 - and alkalinity concentrations that were missing from the WCL data. The amount of SO 4 2 - is low compared to estimates from elemental abundance made by other studies on Mars. In the charge-balanced solution, the dominant cations were Mg 2+ and Na + and the dominant anions were ClO 4 - , SO 4 2 - , and alkalinity. The abundance of calcite measured at the Phoenix site has been used to infer that the soil may have been subject to liquid water in the past, albeit not necessarily locally; so we used FREZCHEM to evaporate (at 280.65 K) and freeze (from 280.65 to 213.15 K) the WCL-measured solution to provide insight into salts that may have been in the soil. Salts that precipitated under both evaporation and freezing were calcite, hydromagnesite, gypsum, KClO 4, and Mg(ClO 4) 2·8H 2O. Epsomite (MgSO 4·7H 2O) and NaClO 4·H 2O were favored by evaporation at temperatures >0 °C, while meridianite (MgSO 4·11H 2O), MgCl 2·12H 2O, and NaClO 4·2H 2O were favored at subzero temperatures. Incongruent melting of such highly hydrated salts could be responsible for vug formation elsewhere on Mars. All K + precipitated as insoluble KClO 4 during both evaporation and freezing simulations, accounting for 15.8% of the total perchlorates. During evaporation, 35.8% of perchlorates precipitated with Na + and 48.4% with Mg 2+. During freezing, 58.4% precipitated with Na + and 24.8% with Mg 2+. Given its low eutectic temperature, the existence of Mg(ClO 4) 2 in either case allows for the possibility of liquid brines on Mars today. FREZCHEM also showed that Ca(ClO 4) 2 would likely not have precipitated at the Phoenix landing site due to the strong competing sinks for Ca as calcite and gypsum. Overall, these results help constrain the salt mineralogy of the soil. Differences between evaporites and cryogenites suggest ways to discriminate between evaporation and freezing during salt formation. Future efforts, such as sample return or in situ X-ray diffraction, may make such a determination possible.

Physicochemistry of the binary interacting mixtures of cetylpyridinium chloride (CPC) and sodium dodecylsulfate (SDS) with special reference to the catanionic ion-pair (coacervate) behavior

The interaction between the cationic surfactant cetylpyridinuim chloride (CPC) and the anionic surfactant sodium dodecylsulfate (SDS) has been studied both at the air/water interface and in the bulk along with the formation of ‘catanionic coacervate’ or ion-pair amphiphile (IPA) by the coulombic interaction between the binary oppositely charged surfactants. The ternary phase behavior of the CPC/SDS/H 2O system has been investigated. Results have been analyzed in the light of Gibbs adsorption isotherm and the regular solution theory of Rubingh at five different CPC:SDS mole ratios. Of the studied combinations, the equimolar composition has evidenced maximum interaction with a large synergistic effect. The isolated coacervate has been characterized by FTIR, NMR, XRD, and DSC measurements. The Langmuir monolayer formation and its π– A isotherm has been studied for the coacervate film under compression–expansion conditions. The interfacially disposed film has formed morphology differences under compressions. Polarizing microscopic measurements of the transferred monolayer on glass surface have evidenced diffusion limited fractal structures with concentric circular growths whereas the epifluorescence images showed poly and monodisperse domains at the air/water interface.

Influence of gypsum additive on the gyrolite formation process

The influence of gypsum additive on the gyrolite formation process and a sequence of intermediary compounds formation in the CaO–SiO 2·nH 2O–H 2O system was examined and explained. The synthesis has been carried out in unstirred suspensions. The molar ratios of primary mixtures were CaO/SiO 2 = 0.66. The amount of sulphate ions to be added to a raw mixture was 1–10%. The duration of isothermal curing at 200 °C was 4, 8, 16 and 72 h. It was determined that the quantity of sulphur which penetrates into the crystalline structure of gyrolite depends not only on the synthesis conditions but also on the composition of initial mixture. A larger amount of sulphate ions stimulate the formation not only of gyrolite, but also of CaSO 4. Gypsum additive has no influence on the re-crystallization temperature of C–S–H(I), Z-phase and gyrolite into wollastonite. The composition of initial mixtures is recommended to calculate according to molar ratios. In other cases, upon increasing the amount of sulphate ions, the basicity of the mixture decreases and gyrolite forms more difficult.

Optimal configuration design for double-flow thermal-diffusion columns with external recycle

Optimal configuration dimensions for double-flow thermal-diffusion columns, established via an impermeable or a permeable-barrier, with external recycle both ends, are investigated theoretically for the H 2O–HDO–D 2O system. The analytical solutions are obtained using an eigenfunction expansion in terms of a power series. The predicted degree of separation is represented graphically with channel thickness ratio, recycle ratio, and aspect ratio as parameters. Compared to classical Clusius-Dickel thermal-diffusion columns of the same working dimensions, significant improvements can be realized and the improvements from permeable-barrier devices are higher than those which impermeable-barrier devices.

Chilled ammonia process for CO 2 capture

The chilled ammonia process absorbs the CO 2 at low temperature (2–10 °C). The heat of absorption of carbon dioxide by ammonia is significantly lower than for amines. In addition, degradation problems can be avoided and a high carbon dioxide capacity is achieved. Hence, this process shows good perspectives for decreasing the heat requirement. However, a scientific understanding of the processes is required. The thermodynamic properties of the NH 3–CO 2–H 2O system were described using the extended UNIQUAC electrolyte model developed by Thomsen and Rasmussen in a temperature range from 0 to 110 °C and pressure up to 100 bars. The results show that solid phases consisting of ammonium carbonate and bicarbonate are formed in the absorber. The heat requirements in the absorber and in the desorber have been studied. The enthalpy calculations show that a heat requirement for the desorber lower than 2 GJ/ton CO 2 can be reached.

Complexation in the Cu(II)–LiCl–H 2O system at temperatures to 423 K by UV-Visible spectroscopy

Thermodynamic data for the solubility and formation of copper(I)and copper(II) species are required to model innovative designs of the electrolysis cells used in the thermochemical copper-chloride hydrogen production process. Cumulative formation constants of Cu 2+(aq) complexes with Cl −(aq) were determined by Principal Component Analysis of UV-spectra, obtained over a very wide range of solution compositions and temperature, coupled with an appropriate model for activity coefficients of the solution species. Shortcomings in the existing database and future work to extend these studies to higher temperatures and much higher copper concentrations are discussed.

Investigating the mechanism of clofibric acid removal in Fe 0/H 2O systems

Since the introduction of iron wall technology, the inherent relationship between contaminant removal and iron corrosion has been mostly attributed to electron transfer from the metal body (direct reduction). This thermodynamically founded premise has failed to explain several experimental facts. Recently, a new concept considering adsorption and co-precipitation as fundamental contaminant removal mechanisms was introduced. This consistent concept has faced very skeptic views and necessarily needs experimental validation. The present work was the first independent attempt to validate the new concept using clofibric acid (CLO) as model compound. For this purpose, a powdered Fe 0 material (Fe 0) was used in CLO removal experiments under various experimental conditions. Additional experiments were performed with plated Fe 0 (mFe 0: Fe 0/Pd 0, Fe 0/Ni 0) to support the discussion of removal mechanism. Main investigated experimental variables included: abundance of O 2, abundance of iron corrosion products (ICPs) and shaking operations. Results corroborated the concept that quantitative contaminant removal in Fe 0/H 2O systems occurs within the oxide-film in the vicinity of Fe 0. Additionally, mixing type and shaking intensity significantly influenced the extent of CLO removal. More importantly, HPLC/MS revealed that the identity of reaction products depends on the extent of iron corrosion or the abundance of ICPs. The investigation of the CLO/Fe 0/H 2O system disproved the popular view that direct reduction mediates contaminant removal in the presence of Fe 0.

Eutectic freeze crystallization from the ternary Na 2CO 3–NaHCO 3–H 2O system : A novel scraped wall crystallizer for the recovery of soda from an industrial aqueous stream

Eutectic freeze crystallization was tested in a scaled up version of a scraped cooled wall crystallizer on an industrial aqueous sodium carbonate–sodium bicarbonate waste stream containing traces of molybdenum. A heat transfer rate of 5 kW m −2 was maintained in the crystallizer. Sodium carbonate decahydrate with molybdenum content below 1 ppm and pure ice were produced by continuous crystallization at −3.8 °C by operating within the metastable zone width of bicarbonate. At −4.0 °C bicarbonate started to co-crystallize. The bimodal size distribution of the mixture resulted in poor filtration and purity of the salt product.

Hydrothermal synthesis of Mn–Zn ferrites from spent alkaline Zn–Mn batteries

Nanocrystalline Mn–Zn ferrites (Mn 0.6Zn 0.4Fe 2O 4) with particle size of 12 nm were synthesized hydrothermally using spent alkaline Zn–Mn batteries, and accompanied by a study of the influencing factors. The nanocrystals were examined by powder X-ray diffraction (XRD) for crystalline phase identification, and scanning electron microscopy (SEM) for grain morphology. The relationship between concentration of Fe(II), Mn(II), and Zn(II) and pH value was obtained through thermodynamic analysis of the Fe(II)–Mn(II)–Zn(II)–NaOH–H 2O system. The results showed that all ions were precipitated completely at a pH value of 10–11. The optimal preparation conditions are: co-precipitation pH of 10.5, temperature of 200 °C and time of 9 h.

Synthesis, characterization and thermochemistry of a Pb-jarosite

The enthalpy of formation from the elements of a well-characterized synthetic Pb-jarosite sample corresponding to the chemical formula (H 3O) 0.74Pb 0.13Fe 2.92(SO 4) 2(OH) 5.76(H 2O) 0.24 was measured by high temperature oxide melt solution calorimetry. This value ( Δ H ∘ f = −3695.9 ± 9.7 kJ/mol) is the first direct measurement of the heat of formation for a lead-containing jarosite. Comparison to the thermochemical properties of hydronium jarosite and plumbojarosite end-members strongly suggests the existence of a negative enthalpy of mixing possibly related to the nonrandom distribution of Pb 2+ ions within the jarosite structure. Based on these considerations, the following thermodynamic data are proposed as the recommended values for the enthalpy of formation from the elements of the ideal stoichiometric plumbojarosite Pb 0.5Fe 3(SO 4) 2(OH) 6: Δ G ∘ f = −3118.1 ± 4.6 kJ/mol, Δ H ∘ f = −3603.6 ± 4.6 kJ/mol and S° = 376.6 ± 4.5 J/(mol K). These data should prove helpful for the calculation of phase diagrams of the Pb–Fe–SO 4–H 2O system and for estimating the solubility product of pure plumbojarosite. For illustration, the evolution of the estimated solubility product of ideal plumbojarosite as a function of temperature in the range 5–45 °C was computed (Log( K sp) ranging from −24.3 to −26.2). An Eh–pH diagram is also presented.

Thermodynamic analyses and optimization of a transcritical N 2O refrigeration cycle

Thermodynamic analyses as well as optimization studies based on maximum cooling COP of a transcritical N 2O cycle and both energetic and exergetic comparisons with CO 2 cycle are presented in this article. Effects of superheating, internal heat exchanger and expansion turbine are studied as well. An expression for optimum discharge pressure has been developed. Variation trends of optimal parameters for the N 2O system are similar to that of a CO 2 system. The N 2O cycle exhibits higher cooling COP, lower compressor pressure ratio and lower discharge pressure and temperature, and higher second law efficiency when compared to CO 2 based systems; however, it is inferior in term of volumetric cooling capacity at the optimum condition. Effect of superheating in evaporator is negligible and effect of introducing an internal heat exchanger is moderate whereas effect of employing a work recovery turbine is significant on COP improvement and discharge pressure reduction at the optimal condition for both working fluids.

Modeling of a three-compartment membrane electrodialysis in H 2SO 4–(NH 4) 2SO 4–NH 3·H 2O system

In this paper, a mathematic model of a three-compartment membrane electrodialysis in H 2SO 4–(NH 4) 2SO 4–NH 3·H 2O system has been developed to calculate the exit concentration of ammonium sulfate in the desalting cell. The model is established on the basis of electromigration and concentration diffusion, and it includes several parameters such as electrolyte solution diffusion coefficient, diffusion boundary layer thickness, current density as well as ionic transference number in the solution and in the membrane. These parameters can be deduced from a reliable procedure based on some experimental data. The model can predict the ammonium sulfate exit concentration according to actual operating conditions. In the context of this model, we discuss the current density effect on the exit concentration. The results showed that calculation data were in accordance with experimental data in large current density range, but deviated from them in a small current density range. The good agreement between experimental data and model data confirms the reliability of the model predictions.

Determination of the supersaturation in the LiIO 3–HIO 3–H 2O system using a refractive index value at near saturation concentration

The exact determination of supersaturation is essential for the studies of crystal growth processes in solutions. Due to peculiarities in the solubility of LiIO 3, the refractive index of the solution is chosen as a measure of the supersaturation instead of undercooling. The experimental setup is based on a refractometer and a special setup to create supersaturation in the cuvette by means of successive evaporation of small amounts of solvent. The refractive index is measured at different solution concentrations and pH and the data are correlated as dependences of concentration and pH on the refractive index. The accuracy of the method and the adequacy of the model are discussed.

Preparation and properties of porous glass using fly ash as a raw material

The porous glasses were prepared by a conventional phase separation method using coal fly ash as a raw material, and the properties of these porous glasses were investigated. The composition of coal fly ash is basically composed of SiO 2–Al 2O 3–Fe 2O 3–CaO system and the SiO 2–B 2O 3–Al 2O 3–CaO–Na 2O system of glass was chosen as base glass composition. The pore diameter increases proportional to cube root of heating time ( t 1/3), however, the early stage of phase separation is not clear. It is estimated that the rate determining step may be the diffusion process of structural units involving oxygen ions and the phase separation may take place by the nucleation and growth mechanism, and the relatively larger pores of above 1 μm can be obtained easily. The chemical composition of porous glasses is SiO 2–B 2O 3–Al 2O 3(–CaO–Na 2O). A relatively large amount of fly ash (>40%) can be used successfully for the preparation of porous glass.

Thermodynamic modeling of the vapor–liquid equilibrium of the CO 2/H 2O mixture

In order to evaluate the feasibility of CO 2 sequestration in geological formations detailed knowledge of the mutual solubilities of the CO 2/H 2O system is required. In this work we employ three models, which all involve the well-known Peng–Robinson equation of state, to study the CO 2/H 2O phase equilibrium, with emphasis on the solubility of CO 2 in the aqueous phase and the solubility of H 2O in the CO 2-rich phase. The considered models include the Peng–Robinson equation of state coupled with the conventional van der Waals one fluid mixing rules or the universal mixing rules, and the cubic-plus-association equation of state that uses the Peng–Robinson equation of state in order to account for the usual attractive and repulsive forces and an extra association term to account for the strong hydrogen bonding interactions. The required model parameters are calibrated using experimental data up to 1500 bar for pressure, and up to 673 K for temperature. To improve the accuracy of the proposed models we consider two temperature ranges. Temperatures lower than 373 K are of interest to the geological CO 2 sequestration, while higher temperatures are of interest to fluid-inclusion studies. Good agreement is obtained between the experimental and the correlated solubilities.