Inorganic Salt Hydrates Research Articles

Development of low-cost inorganic salt hydrate as a thermochemical energy storage material

Thermochemical storage is based on a reversible chemical reaction; energy can be stored when an endothermic chemical reaction occurs and then, energy is released when it is reversed in an exothermic reaction. According to literature and based on the energy storage density (esd), MgCl2·6H2O is a promising candidate material for thermochemical energy storage. Bischofite is an inorganic salt obtained as a by-product material from extraction processes of non-metallic minerals, from Salar de Atacama in Chile, containing approximately 95% of MgCl2·6H2O. Thus, the purpose of this study was to characterize the dehydration reaction of bischofite ore, studied as a low-cost thermochemical storage material. Thermogravimetric data for bischofite were obtained using a TGA instrument coupled to a DSC, at four different isotherms 70°C, 80°C, 90°C and 100°C. The results of conversion reaction (α-t) from the thermal dehydration experiments, demonstrated the first phase of dehydration with the loss of two water molecules. The study showed a typical sigmoid curve with a significant acceleration in the conversion at the beginning of the reaction until it reaches a maximum rate, where the curve keeps constant. The same behavior was observed for all the temperatures used. The kinetics of bischofite dehydration model was determined using the isothermal kinetics method. For this, the thermogravimetric data were fitted to the most used kinetic models (D, F, R, A) and then their respective correlation coefficients R were evaluated. The results indicated that the dehydration reaction of bischofite was described by the kinetics of chemical reaction of cylindrical particles R2. The rate of dehydration reaction and esd of bischofite are lower as compared to synthetic MgCl2·6H2O, at temperatures higher than 80°C. However, the cost of materials to store 1MJ of energy is three times lower for bischofite, which is an evident advantage to promote the reuse of this material left as waste by the non-metallic industry.

Development of novel composite PCM for thermal energy storage using CaCl2·6H2O with graphene oxide and SrCl2·6H2O

The inorganic salt hydrate PCM, CaCl2·6H2O, has a promising potential for thermal energy storage. However, this salt hydrate has tremendous issues of supercooling (the supercooling degree was 25.5°C as found in this research) which restricts its utilization in practical applications. The present study aimed to reduce the supercooling degree of CaCl2·6H2O through the innovative use of hydrophilic graphene oxide (GO) nano-sheets and SrCl2·6H2O as nucleating agents. The percentages of these nucleating agents in PCM were 0.005, 0.01, 0.02, 0.05 and 0.08wt% for GO and 0.2, 0.5 and 0.8wt% for SrCl2·6H2O, respectively. Based on the synergistic/additive effects, a novel composite PCM based on CaCl2·6H2O, GO and SrCl2·6H2O was proposed and developed. The test results showed that the composite PCM containing 0.02wt% GO nano-sheets and 0.8wt% SrCl2·6H2O effectively lowered the supercooling degree of CaCl2·6H2O from 25.5°C to as low as 0.2°C (approximately 99.2% supercooling degree of CaCl2·6H2O was reduced). To the best of authors' knowledge, it was the first time that the combination of GO and SrCl2·6H2O was found effective in reducing supercooling degree of CaCl2·6H2O. Moreover, 99.2% supercooling reduction of CaCl2·6H2O is considered the best achievement so far when compared to other studies related to supercooling reduction of CaCl2·6H2O. Finally, the solidification enthalpy of the composite PCMs was found to be as high as 207.90J/g. Therefore, the developed composite PCM is an excellent candidate for thermal energy storage applications in buildings.

Crystallization of inorganic salt hydrates in polymeric foam for thermal energy storage application

Inorganic salt hydrates as phase change material (PCM) offers high energy storage density, low heat of combustion and relatively high thermal conductivity than organic PCMs at a reasonable cost. Moreover, these are nonflammable and also available in the large temperature range for the thermal energy storage (TES) application. However, phase segregation, supercooling and incongruent melting are the main disadvantages which confine them for TES application. In this present study, open cell polyurethane foam (PU foam) as a heterogeneous surface was introduced to mitigate the problem of phase segregation during its repeated thermal cycles. Composite (PU-PCM) having a combination of porous polyurethane foam sheet and saturated inorganic salt solution, by soaking different saturated salt solutions within pores, was prepared. Solution crystallization process was carried out to develop inorganic salt hydrate crystals within the pores from their aqueous solutions. For thermal insulation application, a model experimental setup was constructed and performance of PU-PCM composite sheet compared with the performance of dry PU foam. Various melting and freezing cycles of salt hydrates inside the porous structure were analyzed and the results are discussed.

Preparation and properties of phase change ceramisite loaded with inorganic salt hydrate

Preparation and properties of phase change ceramisite loaded with inorganic salt hydrate

Polyvinyl Alcohol-salt Hydrate Mixtures as Passive Thermal Energy Storage Systems

Inorganic salt hydrates are promising candidates as latent heat storage materials entailing, for example, a high thermal energy storage density and cheap price [1,2] in spite that they have many handicaps. For almost all applications, Phase change materials (PCMs) have to be encapsulated, that is, they have to be hermetically sealed within barrier containments, preferably within small microcapsules. Encapsulation improves heat transfer, cycling stability, and material compatibility with the environment. However, no attempt has been completely successful to microencapsulate salt hydrates so far due to the high surface polarities of these substances, edge alignment effects, their tendency to alter their water content [3]. This work is aimed to encapsulate some commonly used salt hydrates; sodium sulphate decahydrate (Na2SO4.10H2O) and calcium chloride hexahydrate (CaCl2.6H2O) in a hydrophilic polymer; polyvinyl alcohol (PVA) stably for passive thermal energy storage systems. So that an economically beneficial application mean will be validated.

Influence of microwave radiation on temperature characteristics of dehydration

In crystal hydrates of inorganic salts, water is in a particular, bound state. The crystal lattice of each crystal hydrate is individual, and by default it should be similar to the structure of the water ice Ih, which is not observed in practice. It is assumed that the water of crystallization with the crystal hydrate is frozen water in other forms of ice that correspond to specific phases of ice, and salt simulates the application of high pressure. Due to the study of weight loss, the assumption is confirmed. Using microwave radiation also allows to reduce the adsorbent recovery temperature, which is very important for lower energy expenditure. So, many crystal hydrates are melted in the water of crystallization, which makes it necessary to evaporate water from it, and can also fill in the recovery installation. Microwave radiation is weakly absorbed directly by ice because of the symmetry in it, and weak intermolecular vibration, in depth, and, therefore, it starts from the surface. The appearance of the salt in the water of crystallization can also be presented in the form of ice, and this significantly improves the absorptivity and allows the water of crystallization to volatilize, which provides recovery. Thus, using a microwave oven as an alternative method of recovery is highly relevant.

Assessment of T-History Method Variants to Obtain Enthalpy–Temperature Curves for Phase Change Materials With Significant Subcooling

To assess the potential of thermal energy storage systems using phase change materials (PCMs), numerical simulations rely on an enthalpy–temperature curve (or equivalent specific heat curve) to model the PCM thermal storage behavior. The so-called “T-history method” can be used to obtain an enthalpy–temperature curve (H versus T) through conventional laboratory equipment and a simple experimental procedure. Different data processing variants of the T-history method have been proposed yet no systematic comparison between these versions exists in the literature nor is there a consensus as to which should be used to obtain reliable enthalpy–temperature curves. In this paper, an inorganic salt hydrate is tested in both heating and cooling. Four different data processing variants of the T-history method are used to characterize the PCM and produce enthalpy–temperature curves for this original experimental data set. Differences in the results produced by the different methods are discussed, the issues encountered are indicated, and possible approaches to overcome these problems are provided. A specific variant is recommended when using the T-history method to determine enthalpy–temperature curves. For PCMs that exhibit subcooling, an alternative interpretation using an absolute temperature interval is described so that the subcooling phase is taken into account in the enthalpy–temperature curve.

Crystal structures of hydrates of simple inorganic salts. I. Water-rich magnesium halide hydrates MgCl2·8H2O, MgCl2·12H2O, MgBr2·6H2O, MgBr2·9H2O, MgI2·8H2O and MgI2·9H2O

The previously reported structures of the hydrates of simple inorganic salts that crystallize at room temperature are generally well determined. This is not true for water-rich hydrates, which crystallize at temperatures below 273 K. In this series, investigations of the crystal structures of water-rich hydrates crystallized from aqueous solutions at low temperatures are presented. Reported herein are the structures of a set of magnesium salts. Crystals of MgCl2·8H2O (magnesium dichloride octahydrate), MgCl2·12H2O (magnesium dichloride dodecahydrate), MgBr2·6H2O (magnesium dibromide hexahydrate), MgBr2·9H2O (magnesium dibromide nonahydrate), MgI2·8H2O (magnesium diiodide octahydrate) and MgI2·9H2O (magnesium diiodide nonahydrate) were grown from their aqueous solutions at temperatures below 298 K according to the solid-liquid phase diagrams. All structures are built up from Mg(H2O)6 octahedra. Dimensions and angles in the hexaaqua cation complexes are very similar and variation is not systematic. The anions are incorporated into a specific network of O-H...X hydrogen bonds.

Review of Cellulose Non-Derivatizing Solvent Interactions with Emphasis on Activity in Inorganic Molten Salt Hydrates

During cellulose dissolution in non-derivatizing solvents, the inter- and intramolecular hydrogen bonds of the polymer are deconstructed. This occurs either by hydrogen bond formation between one or more components of the solvent systems and the hydroxyl groups of the cellulose or by coordination bond formation between the metal ion present in the medium and the hydroxyl group of cellulose molecules. None of the polymer molecules are actually chemically modified during dissolution. In the first part of this review, we examine the literature pertaining to the different interaction mechanisms between cellulose and non-derivatizing solvent systems with emphasis on the inorganic molten salt hydrates. In the second part of this effort, we further review inorganic molten salt hydrates from the point of view of the changes they impart to the physical properties of the cellulose and the various chemical reactions that can be performed in it.

Investigation and Development on Phase Transition Temperature Control and Adjustment of Inorganic Salt Hydrates

Whereas inorganic salt hydrates are typical inorganic phase change materials suitable for the temperature range of 0-150°C, their investigation and applications on thermal energy storage have received more and more during the recent years. A review on investigation progress and applications of their phase transition temperature control and adjustment was made in this paper, which is of important reference and practical value for understanding and predominating the investigation and engineering applications on their phase transition temperature control and adjustment.

Triboluminescence of crystals and suspensions of inorganic salts of lanthanides

It is found that the triboluminescence spectra of crystalline hydrates of inorganic salts of Ln3+ (Ce3+, Pr3+, Gd3+, Eu3+, Tb3+, and Dy3+) during mechanical trituration and ultrasonic treatment (22 kHz) of crystal suspensions in perfluorodecalin (in the sonotriboluminescence) exhibit gaseous and solid-state components. The first component contains emission lines of N2 in an electric discharge. The spectrum of the second component coincides with the photoluminescence spectrum of the crystals, including ions that cannot be excited due to the absorption of emission from N2: Ce3+, Pr3+, and Gd3+. Among the different salts of Ln3+, the highest intensity of luminescence is observed in sulfates; the highest yields of tribo- and sonotriboluminescence are characteristic of the Ce3+ salts. The triboluminescence of Ln3+ nitrates is not registered. Possible mechanisms of excitation of the Ln3+ ions are discussed. The main source of the solid-state component of the triboluminescence of Ln3+ salts is assumed to be the electroluminescence typical of crystalline phosphors. It is shown that, along with lines of N2, the spectrum of the triboluminescence observed in the atmosphere of He, Ar, and O2 contains lines of these gases.

Temperature-Dependent Distortions of the Host Structure of Propylene Oxide Clathrate Hydrate

A detailed study of the water host of a structure II clathrate hydrate with propylene oxide as the guest has been performed on high-resolution, constant-wavelength neutron powder diffraction data. The structure is cubic in space group Fd3m, with lattice parameters falling in the range (1.7086−1.7282) nm in the temperature range (5−250) K. Static disorder of water molecules and dynamic disorder of deuterium atoms produces a hydrogen-bond geometry in the host water structure, which is significantly different from that of 2H2O ice Ih, but displays similarities to high-pressure ices and to crystalline hydrates of inorganic salts. The structural description of the water host can be divided into three regimes of temperature, where the bond distances and angles display greater or lesser similarity to those of 2H2O ice Ih. These temperature-dependent variations in structure are related to size, shape, and dynamics of the guest molecules, as well as the dynamics of the host itself. As in other hydrates experienci...

Evaluation of molten inorganic salt hydrates as reaction medium for the esterification of cellulose

Molten inorganic salt hydrates are highly efficient solvents forcellulose. The carboxymethylation of the polymer dissolved in this new group ofcellulose solvents was investigated. The homogeneous carboxymethylation ofcellulose in molten LiClO4•3H2O using sodiummonochloroacetate in the presence of NaOH is possible. The formation of CMC wasconfirmed by FT- Raman spectroscopy. Structure analysis by means of HPLC afterchain degradation showed the formation of CMC with a DS of 2 after a shortreaction time of 4 h. The derivatives exhibit a statisticaldistribution of substituents along the polymer chain if prepared in moltenLiClO4•3H2O as solvent. A substituent distributioninthe order C-6 > C-2 ≈ C-3 for anhydroglucose units (AGU) was concludedfrom 1H-NMR measurements. The synthesis of CMC in the swellingmediumLiCl•xH2O (2 ≤ x ≤ 5) yields polymers with astatistical distribution of functional groups along the chain. The watercontentof the salt melts has a dramatic influence on the DSCMC.

Penicillin Acylase-Catalyzed Solid-State Ampicillin Synthesis

The ability of immobilized penicillin acylase from E. coli to retain a remarkable catalytic activity in solid-state systems has been demonstrated. Stabilization of immobilized penicillin acylase by inorganic salt hydrates allowed us to exploit nearly the whole catalytic activity of the enzyme at a very low water content. Using this technique, enzymatic synthesis of ampicillin in solid-state systems was performed with high yields (up to 70% starting from equimolar mixture of reagents) and rates comparable to the corresponding values in homogeneous solutions and heterogeneous systems, “aqueous solution-precipitate”. Peculiarities of the enzymatic solid-state acyl transfer process, such as absence of the clear-cut maximum on the ampicillin accumulation curves and dependence of the synthetic efficiency on the enzyme loading, have been observed. The space-time yield of solid-state enzymatic ampicillin synthesis was shown to be up to ten times higher compared to the homogeneous solutions and heterogeneous “aqueous solution-precipitate” systems.

Proton mobility in hydrates of inorganic acids and acid salts

Published data on the mechanisms of hydrogen ion transport in solids and aqueous solutions are described systematically, including defect formation, rotational mobility of proton-containing groups, proton hopping along a hydrogen bond, proton translational mobility, and proton conduction. Resorting to the authors" theoretical results and published data, the main criteria for the selection of systems possessing high proton mobility are formulated.

Thermal Analysis and Kinetics of Solid-State Reactions Its Application to Education in Chemistry

In an attempt to show the importance of preparing extensively teaching materials for comprehensive education in thermal analysis at an undergraduate level, the significance of the teaching materials concerning the thermal analysis and kinetics of the solid-state reactions is discussed by reviewing our teaching activities at Hiroshima University. Application of the thermoanalytical techniques to thermal decomposition of basic copper(II) salts is appropriate for an introductory experiment to thermal analysis. Microscopic observations of the textural change during the thermal dehydration of inorganic salt hydrates are suitable for introducing the kinetics of solid-state reactions. A computer practice of drawing the experimental master plot enables students to understand the kinetic theory.

Proton mobility in the solid inorganic hydrates of acids and acid salts

The method for the calculation of the proton-transfer frequency (nt) and its activation energies (Et) was suggested. Results of the calculations were presented. The experimental data on the activation energy of proton-containing group rotation and protonconductivity values for some hydrates of inorganic acids and acid salts were compared with the calculated ones.

Accommodation of the actual solid-state process in the kinetic model function

The degree of coordination between the kinetic information from the thermonalytical measurements and the kinetic theory of the solid-state reactions was investigated through the microscopic study of the thermal dehydration of several inorganic salt hydrates. An accommodation function was applied to the conventional kinetic model functionsf(α), in an attempt to reduce the disagreement between the actual process and the idealized one assumed in formulatingf(α). The significance of the non-integral kinetic exponent in the kinetic model function was discussed with its physico-chemical meanings.

Prevention of supercooling and stabilization of inorganic salt hydrates as latent heat storage materials

Abstract Various inorganic salt hydrates have been studied as a latent heat storage medium. A super-absorbent polymer (SAP) made from an acrylic acid copolymer is proposed as an effective thickener to prevent undesirable phase separation of the high hydrate inorganic salts (Na2SO4· 10H2O, Na2HPO4·12H2O, Na2CO3·10H2O). Most of these materials can be stabilize by the addition of 3 to 5 wt% SAP as a thickener. For the low hydrate inorganic salts (CH3COONa· 3H2O, Na2S2O3·5H2O), carboxymethyl cellulose (CMC) is found to be an effective thickener. Similarly, the phase separation of the low hydrate salts can be prevented by the addition of 2 to 4 wt% thickener. To overcome the supercooling of the thickened phase change materials, various potential nucleators have been evaluated. For the thickened Glauber's salt, borax reduces supercooling of the salt from 15 to 3–4°C. Three different powders of carbon (1.5–6.7 μm), copper (1.5–2.5 μm) and titanum oxide (2–200 μm) are found to reduce the supercooling of thickened Na2HPO4·12H2O. Also, the supercooling of thickened CH3COONa·3H2O is reduced from 20 to 2–3°C by adding 2 wt% potassium sulfate. New compositions for preventing supercooling and phase separation of PCMs are developed in the temperature range 30–60°C: Glauber's salt/SAP/borax (94/3/3 wt%, Tm = 35°C), Na2CO3·10H2/SAP/Sr(OH)2 (93/3/4 wt%, Tm = 32°C), Na2HPO4·12H2O (92.8/3.5/3.7 wt%, Tm = 35°C), Na2S2O3·5H2O/CMC/ SrSO4 (92/3/5 wt%, Tm = 48°C), CH3COONa·3H2O/CMC/K2SO4 (95/3/2 wt%, Tm = 58°C).

The behaviour of acetamide under ‘Galisol’ heat storage conditions

Acetamide, as a phase-change material for energy storage, is preferable to other organic materials because of its noncorrosive behaviour and the high storage capacity (264 MJ/m3). In the paper a possibility is offered for a considerable decrease of the supercooling tendency and for the prevention of the disturbing sublimation effects, by modifying the dynamic working function principle ‘Galisol’. For this purpose we have used a heat-transfer liquid with a partial solubility for acetamide. The study reviews solubility data, investigations of the thermal behaviour by the DTA method with large samples, cloud point investigations, equilibrium surface tensions and heat-storage investigations of combinations of acetamide and heat-transfer liquids. A phase diagram of the acetamide-trichloroethylene system is presented. The heat-storage behaviour of acetamide in its combination with trichloroethylene and a surface active material is very promising and offers a high heat-transfer power comparable to that of inorganic salt hydrates under ‘Galisol’ conditions. Nevertheless, the fact that water-free acetamide, which is very expensive, has to be used must be taken into consideration.