Formation Of Crystal Hydrates Research Articles

НВЧ методи та засоби вимірювання вологості природного газу

It is established that the most informative and meaningful indicator of humidity in gas hygrometry is the value of dew point temperature — the value of gas temperature at which water vapor contained in isobarically cooled gas becomes saturated above the flat surface of water. Regulatory documents often indicate the dew point temperature of moisture, as this figure is informative. When operating main gas pipelines, it is very important to know the true value of such an indicator of natural gas quality as humidity. When gas dehumidifiers are ineffective, moisture condenses on the inner surface of the main gas pipeline and gas equipment. The latter becomes a source of serious problems: capacity is reduced, there are conditions for the formation of crystal hydrates. Issues related to the existing main methods of measuring the humidity of the gas, their classification, according to which the measurement methods are divided into evaporative-psychrometric, sorption, condensation, physical, chemical and physico-chemical. The state of the issue of gas humidity measurement methods is analyzed, the main shortcomings of the methods are identified and the main issues of the dew point methods are analyzed. The condensation method for measuring gas humidity is the most suitable for use in the gas industry. The review of gas humidity measuring instruments by dew point temperature is performed, the physical bases of measurement processes and their shortcomings are analyzed. Currently known methods of measuring gas humidity do not allow to achieve the required accuracy and speed of humidity measurement, provided that it is the most important parameter for determining gas quality, due to the complexity of measurement due to additional components in the gas and aggressive environment. It also makes it difficult to measure two or more humidity indicators at the same time. Taking into account all the above shortcomings, it is necessary to further improve and refine the method of measuring and determining the dew point temperature of natural gas.

Optimizing the Quality of Food Powder Products: The Challenges of Moisture-Mediated Phase Transformations.

Water is ubiquitous in the environment and is present to varying degrees even within dry powder products and most ingredients. Water migration between the environment and a solid, or between different components of a product, may lead to detrimental physical and chemical changes. In efforts to optimize the quality of dry products, as well as the efficiency of production practices, it is crucial to understand the cause-effect relationships of water interactions with different solids. Therefore, this review addresses the basis of moisture migration in dry products, and the modes of water vapor interactions with crystalline and amorphous solids (e.g., adsorption, capillary condensation, deliquescence, crystal hydrate formation, absorption into amorphous solids) and related moisture-induced phase and state changes, and provides examples of how these moisture-induced changes affect the quality of the dry products.

Understanding the structure and dynamics of cationic surfactants from studies of pure solid phases.

A homologous series of n-alkyl trimethylammonium bromide surfactants, H(CH2)nN+(CH3)3 Br-, from C10TAB to C18TAB have been studied systematically in the bulk over a wide range of temperatures. Common features in the structures are identified, with packing dominated by the co-ordination of the cationic head groups with bromide anions and interdigitation of the hydrocarbon chains. This arrangement provides an explanation for the thin adsorbed bilayers that have been observed at various hydrophilic surfaces from aqueous solutions in previous studies. The molecular volumes and arrangement are comparable with structures of a number of different self-assembled amphiphiles. For these surfactants with bromide counter-ions, formation of crystal hydrates was not observed. The alkyl chains are highly mobile and at high temperatures a plastic phase is found for all materials with a transition enthalpy that is similar to the melting enthalpy of many long alkyl chains. Other unexpected phase transitions depend more markedly on the hydrocarbon chain length and evidently depend on delicate balances of the various contributions to the free energy.

Influence of Nanographene Oxide on Calcium Aluminate Cement Hydration

Abstract: For this work calcium aluminate cement (CAC) was prepared with Al2O3 content ≥ 70 mass-% and a nanographene oxide solution (GOS) additive. SEM, XRD, calorimetry, and electrical conductivity (EC) measurements were carried out. Studies have shown that the addition of GOS has an effect on the hydration of CAC compared to the cement paste only with water. It was determined that nanographene oxide affected the formation of crystal hydrates: in a cement stone with a nanographene oxide additive, the intensities of CAH10 hydrates were shown to be higher. It was determined that nanographene oxide affects CAC at a temperature of 20 °C as follows: the heat flow maximum in a cement paste with the nanographene oxide suspension is fixed after 18.5 h, i.e., 2.5 h earlier than cement paste mixed with water. Electrical conductivity examination showed that the addition of GOS in the CAC suspension accelerated ion release.

An Examination of Water Vapor Sorption by Multicomponent Crystalline and Amorphous Solids and Its Effects on Their Solid-State Properties

This commentary critically evaluated the unique effects of water vapor sorption by multicomponent solid forms of active pharmaceutical ingredients (APIs), and its effects on their physical and chemical properties. Such multicomponent forms include the following: (1) crystalline salts and cocrystals, and (2) amorphous salts, coamorphous mixtures, and amorphous solid dispersions (ASDs). These solid forms are commonly used to increase the solubility, dissolution, and bioavailability of poorly soluble APIs. To achieve this increase, selected counterions or coformers exhibit much greater polarity, and have a tendency to enhance water vapor sorption, leading to possible instabilities. Such instabilities include salt disproportionation, cocrystal dissociation, and phase separation and crystallization from amorphous forms. Regarding crystalline multicomponent systems, significant instabilities arise on account of deliquescence or crystal hydrate formation. Such behavior often follows water-induced salt disproportionation or cocrystal dissociation. Regarding amorphous salts, coamorphous mixtures, and ASDs, we see the importance of absorbed water as a disrupter of API-coformer interactions and as a plasticizer in bringing about subsequent phase separation and crystallization. In preparing multicomponent solid forms, it is important to measure the water vapor sorption isotherm of the counterion or coformer to better understand the mode by which water is sorbed, and to anticipate and correct possible instabilities.

Study of the composition and properties of products formed in interaction of Na2CO3 with proton-containing reagents

Composition and properties were studied of products formed in treatment of solid Na2CO3 with aqueous solutions containing acetic and citric acids with mass fractions of 0.40–0.60 and 0.33–0.49, respectively, at a Na2CO3/HxAn molar ratio of 2–6, where HxAn = CH3COOH and H3(C6H5O7). It was found that the content of water in the systems under study and the strength of an acid affect the yield of the double salt of carbonic acid, Na2CO3·NaHCO3·2H2O and the composition of derivative proton-containing compounds. It is noted that sodium sesquicarbonate can be formed both by the crystallization mechanism and via a transformation of the primary structure of sodium carbonate. In the resulting powder-like products, water introduced with the acid solution is predominantly consumed for formation of crystal hydrates of carbonate-containing and derivative proton-containing compounds. The hygroscopic point of the resulting salt formulations was determined to be at a level of 70–75%. It was noted that sesquicarbonate-containing salt formulation formed in “dry” neutralization of sodium carbonate by acid solutions can be regarded as a builder for obtaining synthetic household detergents.

Study of formation conditions of sodium sesquicarbonate in H3PO4–Na2CO3–H2O system

Physicochemical transformations were studied in the interaction of powdered Na2CO3 with an orthophosphoric acid–solution at Na2CO3/H3PO4 = 4.0–10.5 and H2O/Na2CO3 = 2.0–5.0 molar ratios providing synthesis of a powder-like product with a moisture content not exceeding 10 wt %, which is of interest as a builder of synthetic detergents. The chemical and phase composition of synthesis products was analyzed and it was shown that the main crystalline phases are Na2CO3∙NaHCO3∙2H2O, Na2CO3∙H2O, NaHCO3, Na3PO4∙nH2O (n = 8–12), and Na2HPO4∙mH2O (m = 2–12). It was found that the Na2CO3/H3PO4 and H2O/Na2CO3 molar ratios affect the yield of sodium sesquicarbonate Na2CO3∙NaHCO2∙2H2O whose formation is due to the interaction of Na2CO3∙H2O, NaHCO3, and H2O. It is noted that water introduced into the Na2CO3–H3PO4–H2O system with the orthophosphoric acid solution is mostly expended for the formation of crystal hydrates of carbonate- and phosphate-containing compounds, and just his circumstance provides that powder-like products with prescribed moisture content are formed.

Glass transition and crystallization of low-temperature amorphous condensates of the water-propane mixture

Interest in gas hydrates stems from the existence of vast reserves of hydrocarbons on the earth in the form of gas hydrates, prospects for using them as a fuel source, and the possibility of storage and transporta� tion of gas in the gas hydrate state. The known meth� ods of production of gas hydrates are based on rela� tively small deviations from the equilibrium condi� tions of gas dissolution. They require the use of high pressures in laboratory or manufacturing equipment. For example, the pressure corresponding to the for� mation conditions of methane hydrate at temperatures near 0°С amounts to tens of bars. In addition, forma� tion of the crystal hydrate requires dispersion of water, which is afforded by longterm and vigorous stirring of the water-gas mixture. In this work, we have proposed another approach implying that hydrates are formed under conditions far from thermodynamic equilibrium. The approach is based on lowtemperature molecularbeam deposi� tion in a vacuum onto a surface cooled by liquid nitro� gen. During this process, amorphous (glassy) layers of the water-gas mixture are initially formed, which are stabilized by high viscosity. Heating of the amorphous layers is accompanied by avalanchetype nucleation and growth of gas hydrate crystallization sites. This method requires neither high pressures nor stirring of the water-gas system. Its advantage is that it is univer� sal and can be used for producing various gas hydrates. This work deals with studying the glass transition and crystallization of amorphous condensates of the binary water-propane system obtained by lowtem� perature condensation to determine the conditions of crystal hydrate formation. Amorphous solid (glassy) layers of lowmolecular� weight substances can be obtained by molecularbeam deposition onto a cooled surface. At low temperatures, the amorphous state of these substances is stabilized by the high viscosity. Molecularbeam deposition onto a copper substrate cooled by liquid nitrogen affords amorphous layers of water and simple molecular com� pounds (1), as well as of aqueous solutions of organic liquids (2). Cooling rates under these conditions are as high as 10 5 -10 7 K/s. On heating, the condensates undergo glass transition (softening) and subsequent spontaneous crystallization. In the course of the latter, a decisive role for phase transformation is played by homogeneous nucleation. The crystallization of amorphous water-gas condensates can result in the formation of gas hydrates (3-5). Hydrate formation is facilitated by the low chemical affinity of the hydrate� forming substance, as well as by the size and shape of its molecules corresponding to the geometry of cavi� ties in the arising clathrate framework. Among such substances, there are light hydrocarbons of the meth� ane series. Experiments with lowtemperature con� densates of the water-methane mixture showed the possibility of producing massive samples of crystal hydrates with high gas content capable of sustained burning (5).

Hydration of ions and formation of crystal hydrates

Effects of electrostatic and entropic factors on the dependence between the type of hydration of ions and their ability to form crystal hydrates from water solutions are discussed. It is shown that in the case of the single-charged ions because of the insignificant electrostatic interaction the crystal hydrates are formed mainly by the salts containing ions with different type of hydration. In the case of poly-charged ions the increase in the electrostatic interaction leads to formation of crystal hydrates mainly by the salts containing ions with the positive type of hydration. It was established also that the formation of salt crystal hydrates is influenced not only by the electrostatic and entropic factors, but also by the spatial arrangement and the electronic density distribution of ions.

Temperature swing adsorption of NOx over Keggin type heteropolyacids

Temperature swing NOx adsorption–desorption cycles with gas mixtures consisting of 1000 ppm NOx, 5% O2, 3% H2O and N2 were carried out on heteropolyacid adsorbents in the temperature range 80–170 °C. Keggin type heteropolyacids having tungsten, molybdenum or their combination in octahedral coordination in combination with P, Si, Ge or B atoms in tetrahedral coordination were investigated. The heteropolyacids were used as pure compounds or supported on zeolite Y or the metal–organic framework Cu3(BTC)2 (BTC represents 1,3,5-benzenetricarboxylic acid). The property of reversible adsorption of equimolar mixtures of NO and NO2 was observed with Keggin type heteropolyacids based on W and combinations of W and Mo. Regeneration of the saturated adsorbent was achieved by cooling in a water vapor containing gas stream. The investigated heteropolyacids showed different water adsorption behavior. The capability of NOx adsorption was found to be related with crystal hydrate formation. Crystal water was much stronger retained in W-based compared to Mo-based Keggin compounds. Co-adsorption of NO and NO2 molecules occurred only on Keggin compounds containing crystal water. The formation of H2NO2+ compound out of NO, NO2 and H2O in the interstitial spaces between Keggin units is proposed. The H-form and Co, Cu, Fe, Ni and Mn salts of Wells–Dawson type heteropolyacids were found to be readily dehydrated upon heating and did not show reversible NOx adsorption. Supported W-based Keggin heteropolyacid showed lower NOx adsorption capacity compared to the unsupported heteropolyacid.

Influence of polymeric excipients on crystal hydrate formation kinetics in aqueous slurries

Crystalline anhydrous active pharmaceutical ingredients (APIs) can potentially transform to the hydrate form during manufacturing processes involving water. The ability to understand and manipulate these transformations is important to maintain control of the solid state form of the API. The influence of various polymeric excipients on the anhydrate to hydrate transformation of caffeine, carbamazepine, and sulfaguanidine was investigated in this study. The transformation of the APIs in aqueous slurries was monitored using in‐line Raman measurements and the resultant kinetic profiles provided insight into the inhibitory ability of the polymers investigated. The results showed that cross‐linked poly(acrylic acid) inhibited the caffeine transformation and hydroxypropyl methylcellulose inhibited the carbamazepine transformation. None of the polymers tested were able to inhibit the sulfaguanidine transformation although some polymers were able to reduce the rate of the transformation with poly(vinylpyrrolidone) showing the greatest effect. It was found that the inhibitory polymers were able to either reduce crystal growth rates and/or increase the induction time preceding the nucleation event. © 2008 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:5198–5211, 2008

Research of the Activity of Catalysts on the Base of H3PW12O40 in Partial Oxidative Conversion of C3–C4 alkanes

Catalysts from heteropoly acid H3PW12O40 and its Cs, Na, Ba, Pb, Ca, Cd, Cr, Mn, V, La salts supported on clinoptilolite, alumosilicate are highly active in oxidative conversion of propane–butane (OCPB) mixture and formation of C2–C4 olefins, oxygen-containing compounds at temperatures T = 100–800 °C. Optimum yields of ethylene and propylene are achieved on heteropoly acid its Cs and Cr salts. The processes of oxidative dehydrogenation (ODPB) and cracking are concurrent in formation of olefins. High activity is caused by dispersity of supported catalysts (XRD, IRS) both formation of crystal hydrates and an amorphous phase of heteropoly acid in a condition of interaction with the carrier.

Influence of moisture on the crystal forms of niclosamide obtained from acetone and ethyl acetate.

The purpose of this study was to elucidate the formation of crystal hydrates of niclosamide and to delineate the effect of relative humidity on the crystal forms obtained from acetone and ethyl acetate. Recrystallization of niclosamide was performed in the presence and absence of moisture. Two hydrates and their corresponding anhydrates were isolated. The hydrates obtained by the process of recrystallization from acetone (Form I) and that obtained from ethyl acetate (Form II) were classified based on differences in their dehydration profile, crystal structure, shape, and morphology. Crystals obtained in the absence of moisture were unstable, and when exposed to the laboratory atmosphere transformed to their corresponding hydrates. Differential scanning calorimetry thermograms indicate that Form I changes to an anhydrate at temperatures below 100 degrees C, while Form II dehydrates in a stepwise manner above 140 degrees C. This finding was further confirmed by thermogravimetric analysis. Dehydration of Form II was accompanied by a loss of structural integrity, demonstrating that water molecules play an important role in maintaining its crystal structure. Form I, Form II, and the anhydrate of Form II showed no significant moisture sorption over the entire range of relative humidity. Although the anhydrate of Form I did not show any moisture uptake at low humidity, it converted to the monohydrate at elevated relative humidity (>95%). All forms could be interconverted depending on the solvent and humidity conditions.

Study of bound water in quercetin

Study of bound water in medicinal preparations has both great practical value and independent theoretical and experimental significance [1]. Various substances, including the quercetin standard, are frequently obtained in the high-purity form by the method of recrystallization from 70% aqueous ethanol. As is known, this procedure may lead to the formation of crystal hydrates whose stability depends on the temperature and water content in the ambient medium [2]. Because quercetin standard is used for the certification of drugs and raw plant materials [3, 4], it is necessary to know precisely the content of water in the standard preparation. Taking into account that quercetin is dried at a temperature of 105~ prior to the analysis, after which it may be exposed to various temperature and humidity conditions, k was of interest to study the amount and state of water in quercetin depending on the hydrothermal parameters of the surrounding.

Influence of solvent composition on the solubilities and solid-state properties of the sodium salts of some drugs

The solubilities of the sodium salts of some sulfonamides, barbiturates and hydantoins have been determined in mixtures of propylene glycol and water. In many cases, the solubilities of the salts in the mixed solvents were lower than those in water, however, several compounds exhibited enhanced solubilities in the mixed solvents. This unexpected increase in solubility was not related to the lipophilicity of the acidic forms of the drugs and occurred in at least one member of each group of compounds. Analysis of the solid phase which had been equilibrated with each solvent indicated the formation of crystal hydrates for most of the solutes, and in at least one instance, mixed solvates. These compounds could be categorized on the basis of their desolvation temperatures. Those compounds with low temperatures of desolvation had increased solubilities in propylene glycol-water mixtures while compounds with high desolvation temperatures had decreased solubilities in the mixed solvents. These data indicate that crystal hydrate formation plays a significant role in determining if a cosolvent can be used to enhance the solubilities of certain sodium salts.

Investigation of the interaction of molybdate and tungstate ions with water

1. The WO42su−1 ion forms stronger bonds with water in solution than the MoO42su−1 ion. 2. In the crystal hydrates Na2MO4 · 2H2O (M=Mo, W), the opposite picture is observed; this is evidently explained by structural changes, accompanying the formation of crystal hydrates.