Yafei Guo

Interference of Lithium in Measuring Magnesium by Complexometry: Discussions of the Mechanism

There is usually a large concentration of magnesium in the brine of salt lakes and as a consequence it is difficult to measure Mg2

Arsenic species analysis in freshwater using liquid chromatography combined to hydride generation atomic fluorescence spectrometry

A novel pretreatment system and method for arsenic species continuous analysis of arsenite, arsenate, monomethylarsenate (MMA) and dimethylarsonate (DMA) in freshwater using liquid chromatography combined to hydride generation atomic fluorescence spectrometry (LC-HG-AFS) was designed. Arsenic species of As(III), As(V), MMA and DMA in freshwater samples can be well separated, and the analytical time using the developed method is shortened twice compared to the conventional analytical procedure. Besides, the signal of As(V) can be increased by about 50% and the sensitivity to As(V) has been enhanced. The common coexisting ions in freshwater samples have no interferences with arsenic speciation analysis. A sensitive, low cost and interference-free procedure was developed and successfully applied to arsenic speciation in freshwater with the recoveries of four arsenic species within 89.2–106.2%. LC-HG-AFS has good prospects for speciation analysis of trace and ultra trace elements allowing for hydride generation.

Thermal Characteristics of Room Temperature Inorganic Phase Change System Containing Calcium Chloride

A novel inorganic calcium-based phase change material(PCM-Ca) consisted of 47.1%(mass fraction) water, 47.7% calcium chloride, 2% potassium nitrate, 2% potassium bromide and 1.2% strontium chloride with a solid-liquid phase change temperature of 21.4 °C was investigated systematically. Among the components of PCM-Ca, calcium chloride and water act as the latent heat storage materials, and potassium nitrate, potassium bromide and strontium chloride work as the modifier, thickener and nucleating agent, respectively. Thermochemical properties including melting point, latent heat, density and thermal conductivity of the PCM-Ca were measured experimentally. The experimental results indicate that the melting latent heat, thermal conductivity at the melting point and density at room temperature for the PCM-Ca are 203.3 kJ/kg, 1.3637 W·m–1·K–1 and 1.55×103 kg/m3, respectively. Moreover, a thirty-run-cycling test showed that the PCM-Ca has a good thermal characteristic with no phase segregation or supercooling, and the maximum deviations of latent heat and phase change temperature are only 0.2% and 1.6%, respectively.

Thermodynamic Study of Solid–Liquid Equilibrium in NaCl–NaBr–H2O System at 288.15 K

The solubility data, composition of the solid solution and refractive indices of the NaCl–NaBr–H2O system at 288.15 K were studied with the isothermal equilibrium dissolution method. The solubility diagram and refractive index diagram of this system were plotted at 288.15 K. The solubility diagram consists of two crystallization zones for solid solution Na(Cl,Br) · 2H2O and Na(Cl,Br), one invariant points cosaturated with two solid solution and two univariant solubility isothermal curves. On the basis of Pitzer and Harvie-Weare (HW) chemical models, the composition equations and solubility equilibrium constant equations of the solid solutions at 288.15 K were acquired using the solubility data, the composition of solid solutions, and binary Pitzer parameters. The solubilities calculated using the new method combining the equations are in good agreement with the experimental data.

Phase and Physicochemical Properties Diagrams of Quaternary System Li 2 B 4 O 7 + Na 2 B 4 O 7 + Mg 2 B 6 O 11 + H 2 O

The phase and physicochemical properties diagrams of the quaternary system (Li2B4O7 + Na2B4O7 + Mg2B6O11) at 288.15 K and 0.1 MPa were constructed using the solubilities, densities, and refractive indices measured. In the phase diagrams of the system there are one invariant point, three univariant isothermic dissolution curves, and three crystallization regions corresponding to Li2B4O7 · 3H2O, Na2B4O7 · 10H2O, and Mg2B6O11 · 15H2O, respectively. The solution density, refractive index of the quaternary system changes regularly with the increasing of Li2B4O7 concentration. The calculated values of density and refractive index using empirical equations of the quaternary system are in good agreement with the experimental values.

Solubilities, Densities, and Refractive Indices in the Quaternary System (Li 2 B 4 O 7 + Na 2 B 4 O 7 + Mg 2 B 6 O 11 + H 2 O) at 298.15 K

Solubilities, densities, and refractive indices in the quaternary system (Li2B4O7 + Na2B4O7 + Mg2B6O11 + H2O) at T = 298.15 K and p = 0.1 MPa were investigated experimentally with the method of isothermal dissolution equilibrium. According to the experimental data, the phase diagrams and the diagrams of densities and refractive indices versus lithium tetraborate composition in the solution were plotted, respectively. In the phase diagrams of the quaternary system at 298.15 K, there are one invariant point, three univariant isotherm dissolution curves, and three crystallization regions corresponding to Li2B4O7 · 3H2O, Na2B4O7 · 10H2O and Mg2B6O11 · 15H2O, respectively. The size of crystallization areas of salt is in the order Mg2B6O11 · 15H2O > Na2B4O7 · 10H2O > Li2B4O7 · 3H2O, which demonstrates Mg2B6O11 · 15H2O can be more easily separated from solution in this quaternary system. The solution density and refractive index of the quaternary system at 298.15 K change regularly with the increasing of Li2B4O7 concentration. The calculated values of density and refractive index using empirical equations of the quaternary system are in good agreement with the experimental values.

The isobaric heat capacities and thermodynamic properties of ionic liquid 1-ethylpyridinium bis(trifluoromethylsulfonyl)imide

Ionic liquid 1-ethylpyridinium bis(trifluoromethylsulfonyl)imide ([C2py][NTf2]) was synthesized and characterized by 1H NMR spectroscopy, 13C NMR spectroscopy and thermal gravity analysis. The molar heat capacities of [C2py][NTf2] were measured using a heat-flow calorimeter with “3D Calvet” calorimetric sensor from (293 to 312)xa0K. The experiment value of molar heat capacity 502.15xa0Jxa0K−1xa0mol−1 at 298.15xa0K was obtained. Moreover, the estimation values of molar heat capacity were calculated by using 4 methods at 298.15xa0K, and the result showed the Paulechka et al.’s method was more appropriate for predicting the molar heat capacity of IL [C2py][NTf2], and the error was less than 2%. In addition, the freezing point T* was calculated by freezing point depression, which was approximately equal to experimental value 305.08xa0K. The molar enthalpy of fusion ΔfHmxa0=xa026.77xa0kJxa0mol−1, molar melting entropy ΔdeSmxa0=xa090.60xa0Jxa0mol−1xa0K−1 and the freezing constant Kf were also calculated.

Synthesis and thermal energy storage properties of a calcium-based room temperature phase change material for energy storage

In order to obtain a low-cost, high latent heat and thermostable phase change material with a phase change temperature between 18 and 25xa0°C as a room temperature phase change material, a novel solid–liquid calcium-based composite named as PCM-Ca of 44.6% CaCl2, 6.9% Ca(NO3)2, 1.2% SrCl2 and 47.3% H2O with a phase change temperature of 21.8xa0°C and latent heat of 155.5xa0Jxa0g−1 was developed. The determination of thermal performances of PCM-Ca indicated that the thermal conductivities in liquid and solid state are of 0.6429 and 0.8256xa0Wxa0m−1xa0K−1, and the thermal conductivity in the phase change point is 1.2401xa0Wxa0m−1xa0K−1; the specific heat capacities at the temperature range of 5.5–26.5xa0°C and 31.5–38.5xa0°C were fitted as yu2009=u20090.0001x4xa0−xa00.0042x3u2009+u20090.0707x2xa0−xa00.4151xu2009+u20093.9526 (ru2009=u20090.9999) and yu2009=u2009−0.0001x4u2009+u20090.0208x3xa0−xa01.1155x2u2009+u200926.477xu2009+u2009231.57 (ru2009=u20090.9984), respectively. The stability analysis demonstrated that PCM-Ca is stable at the temperatures less than 130xa0°C, and no phase separation and the obvious supercooling phenomenon were presented after thirty times cycle use. This material PCM-Ca has a potential for energy storage application.

Recovery of Boron from Underground Brine by Continuous Centrifugal Extraction with 2-Ethyl-1,3-hexanediol (EHD) and Its Mechanism

In order to economical and environmental-friendly recycle of boron from underground brine, the extraction of boron was carried out in this work by the continuous centrifugal technique using 2-ethyl-1,3-hexanediol (EHD)u2009+u2009sulfonated kerosene (SK) extraction system, and the extraction mechanism was also investigated by the combination of FT-IR with slope method. The results showed that boron can be effectively extracted from underground water with the concentration of boron 5.43u2009g·L−1 by five-stage centrifugal extraction using 30% EHDu2009+u200970% SK at pHu2009=u20092.0–3.0, R(O/A)u2009=u20091u2009:u20092, and the extraction rate reached 98.46%. Boron in the organic phase can be well five-stage back-extracted by 1.0u2009mol·L−1·NaOH at R(O/A)u2009=u20091u2009:u20091 with a back-extraction rate of 97.00%. About 88.32% boron in the aqueous phase obtained by back-extraction can be recycled in H3BO3 form by evaporation crystallization after acidified to pHu2009<u20092.5. The extraction mechanism indicated that the extraction is completed mainly based on the esterification reaction between alcoholic hydroxyl in EHD and -OH in B(OH)3 at the stoichiometric ratio 1u2009:u20091 to generate a stable six-membered ring structure of boric acid ester.

Thermal energy storage using calcium chloride hexahydrate

The solid-liquid phase change material named as PCM-Ca with 49.1% in mass water, 49.7% calcium chloride, and 1.2% strontium chloride was discovered and outlined in this paper. Differential scanning calorimetry, simultaneous thermal analyzer, thermal conductivity analyzer, temperature recorder, and digital vibrating-tube densimeter were used to characterize the thermal properties of PCM-Ca. The results indicated that PCM-Ca has the phase change temperature at 28.7 °C, the latent heats in the process of fusing and crystallizing are 193.4 and 193.0 kJ/kg, the thermal conductivity is 1.2801 W/mK at the melting point, and the density is 1.48 ⋅103 kg/m3 at room temperature. Thirty times repeated thermal cycling tests show excellent thermal stability in terms of latent heat and nucleation temperature, and the maximum deviations of the latent heat and the phase change temperature of PCM-Ca are 0.2% and 2.7%, respectively.