A variable temperature infrared spectroscopy study of NaA zeolite dehydration

Variable temperature diffuse reflectance infrared spectroscopy is used to monitor the dehydration of sodium Linde type A zeolite (NaA). Between ambient temperature and 423 K, water desorbs from NaA α-cages. At 423 K, remaining NaA water molecules are primarily confined to β-cages. Variable temperature infrared difference spectra band shape and intensity trends reflect the influence of water-Na⁺ interactions and hydrogen bonding on α-cage water desorption mechanisms. Difference spectrum variations suggest that water loss is accompanied by rearrangement of the remaining NaA water molecules to establish new interactions and minimize potential energies. Water molecules that do not interact with Na⁺ form multiple water-water hydrogen bonds and attain near bulk water configurations. These waters desorb at the lowest temperatures. Most α-cage waters are involved in Na⁺ interactions. These water molecules participate in hydrogen bonding with neighboring water molecules, but opportunities diminish with increased dehydration, resulting in systematic temperature-dependent vibrational spectrum changes.     

Mid-infrared spectroscopic study of crystallization of cubic spinel phase from metakaolin

The structural changes during thermal conversion of metakaolinite into cubic spinel phase that was in literature considered as Al–Si spinel or γ-Al₂O₃ were investigated by mid-infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) using medium ordered kaolin with high content of kaolinite. Spectrum features were studied in the mid-infrared region from 4000 to 400 cm⁻¹ as function of fractional conversion that resulted from DSC experiments. The increasing contends of Al–O bonds in the octahedral position (AlO₆) was observed during thermal transformation. The high ratio of antisymmetric stretching of Si–O–Al and Si–O–Si bands and bands belonging to stretching of Al–O bonds in the (AlO₄) tetrahedra and (AlO₆) octahedra decreases exponentially with fractional conversion. The antisymmetric stretching band of Si–O–Si bond in the (SiO₄) tetrahedra becomes more expressive due to formation of amorphous SiO₂ phase.     

Investigation of mechanochemical synthesis of zeolite NaA made of metakaolin in the mills with shock-shear type of strain

The possibility of obtaining of the NaA zeolite using dry mixture in a mill with a shock-shear type of strain with anhydrous raw ingredients, metakaolin, aluminium oxide, sodium aluminate was examined. The optimal time of mechanical activation was found.     

Structural alterations and thermal behaviour of mechanically activated alunite ore

Alunite, a potassium alum, was activated mechanically in a planetary ball mill, and the effects of mechanical activation on the structure of alunite have been studied by particle size analysis, scanning electron microscopy, X-ray diffraction and the Fourier transform infrared spectroscopy. The results show that the activation procedure led to amorphisation and structural disordering in the alunite structure. Thermal decompositions of both non-activated and activated alunite samples have been studied by thermogravimetry (TG) and differential thermal analysis (DTA). In non-activated alunite, the dehydration reaction starts after 500 °C. On the contrary, the dehydration of mechanically activated alunite was started after 100 °C. It is observed by X-ray diffraction analysis and thermal analysis that dehydration and desulphation temperatures of alunite decreased with mechanical activation, owing to amorphisation and structural disordering in alunite.     

Later stages of Portland cement hydration influenced by different portions of silica fume,metakaolin and ground granulated blast-furnace slag

Journal of Thermal Analysis and Calorimetry - Two Portland cement (PC) replacement levels (35, 45 mass%) and three locally available supplementary cementitious materials (SCMs; metakaolin...     

Fundamental study on the thermal regeneration stages of exhausted activated carbons: kinetics

In this work the thermal regeneration of activated carbons saturated with p-nitrophenol has been analysed. By thermogravimetry, it was possible to elucidate the different events taking place during the thermal treatment, and relate them to the type of adsorption in the interfacial system. It was found that the mass loss during thermal treatment comprises a complex process in which different stages are involved, such as drying, desorption of physisorbed adsorbate, breaking up of surface functional groups, cracking of products from adsorbate–surface-specific interactions, etc. The analysis of the textural and surface chemistry characteristics of the pristine and regenerated adsorbent confirmed the thermal desorption mechanisms. Moreover, a kinetic study based on temperature-programmed desorption and Suzuki models was performed, using thermogravimetry data at different heating rates (5–20 K min^?1). From this analysis, the values of activation energy involved in each degradation step were estimated.     

Adsorption and diffusion of Xenon in a granulated nano-NaY zeolite

Henry??s law constant and crystal diffusivity of xenon in the granulated nano-NaY zeolite were measured by the pulse gas chromatography method. For this purpose the moments of response peaks of xenon were analyzed. The effect of extra column parts of the utilized chromatographic system was also considered by analyzing the moments of the response peak which was obtained by pulse injection of inert gas of helium into the carrier gas of nitrogen. In addition, the measurement of average velocity of the carrier gas regarding the pressure drop in the extra column parts of the system attributed to precise results. By carrying out the experiments at various temperatures in the range of 30?C110?°C the heat of adsorption and activation energy of crystal diffusivity were estimated. In order to find the binder effect on the adsorption of and diffusion into granules, the aforementioned parameters were also measured for the binderless granules of macron sized NaY zeolite. Results revealed that although the adsorption of xenon on the binder of bentonite was negligible, the diffusion resistance created by this binder was significant such that the effective crystal diffusivity in the granules with 25?% binder was determined to be 96 percent lower than the granules with no binder.     

先锋褐煤的热处理和水热处理改质

通过先锋褐煤热处理和水热处理,结合处理煤结构与性质表征,研究了热处理和水热处理对先锋褐煤结构、抽提和溶胀性能的影响,探讨了热处理过程水的作用。结果表明,低于热解温度下的热处理以非共价键解缔合及部分弱共价键热解为主,水与煤的水热反应能够抑制水热处理过程中煤的热解和小分子化合物释放。高温热处理以热解和脱氧为主,水热反应可以稳定煤热解活性基团,避免其二次裂解和交联,在一定程度上提高处理煤的混合溶剂抽提率,改善其溶胀性能。     

Effect of alkaline modification of products of thermal vacuum and hydrothermal treatment of NH4Na-Y zeolite according to the IR spectral data

The effect of alkaline modification on the structure of the products of heat treatment of NH₄Na-Y zeolite (53% NH ₄ ⁺ , Si/Al - 2.37) in a vacuum at 573 K and in water vapors at 873 K was investigated with the IR spectrum of vibrations of the zeolite framework in the 400–1200 cm^–1 region. It was shown that the high-frequency shift of the bands in the spectra of the products obtained, the stretching vibration of v_as(TO₄) tetrahedrons in particular (T=Si, Al) at 1023 cm^–1 by 6 and 19 cm^–1, is determined by a decrease in the excess negative charge of the framework due to weakening and hydrolytic splitting of Al-O bonds of the deammoniated units with the formation of bridging Si-O(H)...Al and terminal Si-OHHO-Al hydroxyl groups. Treatment of these samples with an aqueous solution of KOH (pH 13.4) at 293 and 353 K restores the normal framework Si-O-Al bonds at the sites of formation of bridging and terminal hydroxyl groups. In the second case, restoration is hindered by substitution of H⁺ by K⁺ with some silanol groups.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. I. V. Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, 199164 St. Petersburg. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1733–1739, August, 1992.     

A process for production of granulated soluble glass in ore-thermal furnaces

A process for production of soluble sodium glass in electric-arc ore-thermal furnaces with three graphite electrodes was suggested and tested on the industrial scale. Fusion of sand with sodium carbonate, followed by rapid cooling of the fusion cake with cold water, yields finely grained sodium metasilicate with a developed network of microcracks as a result of a thermal impact in the course of aqueous granulation of the fusion cake.     

FTIR-ATR study of the surface of a tubular zeolite NaA membrane ultrasonically reacted with water and acetic acid.

For the dehydration process of biomass alcohol using a zeolite NaA (LTA) membrane supported by an alumina porous support tube, it is very important to understand damage of the surface crystal, which may be caused by acetic acid. Therefore, the surface structure and the chemical composition of the LTA membrane that reacted with water or acetic acid (pH 3-4) were investigated by the Fourier Transform Infrared Attenuated Total Reflectance method (FTIR-ATR), with a diamond prism as the waveguide, scanning electron microscope and an energy-dispersive X-ray analysis. For leaching experiments using water and acetic acid, ultrasonication was applied to promote the leaching rate and to surely prepare damaged membranes as a model experiment. The Si-O asymmetric stretching vibration spectra of the original LTA membranes showed a bimodal peak. LTA membranes after water leaching also showed the same peak. However, for the LTA membrane reacted with acetic acid of pH 3, damage of the surface LTA crystal and the loss of sodium by dissolution were clearly observed. Also, its Si-O spectral shape was broad, which suggests amorphous-like substances secondarily formed on the membrane surface. Sodium acetate was not detected for all LTA membranes reacted with acetic acid. To evaluate surface-damaged and sodium-loss membranes, FTIR-ATR can sensitively detect a Si-O spectral change corresponding to the surface structure and the chemical composition of the LTA membrane.     

IR study of the peculiarities of alkaline realumination of the highly dealuminated product of hydrothermal treatment of zeolite Y

The effect of alkaline modification on the structure of highly dealuminated zeolite Y, prepared by steaming (at 973 K) the ammoniation product of NH₄-Y zeolite (53% NH₄ ⁺, Si/Al=2.37) pretreated at 873 K in a humid atmosphere, was studied by means of IR spectra of the zeolite lattice vibrations. Treatment of the sample with 0.25 N KOH at 293 K causes the dissolution of the non-framework aluminum hydroxide species with formation of basic aluminate, and the cleavage of linear siloxane bridges at the dealuminated sites. At 353 K the cleavage involves the non-linear disiloxane bonds, while the interaction of potassium aluminate with the terminal Si-O(H,K) bonds thus formed brings about the regeneration of normal Al-O-Si bridges; however, parallel amorphization of the zeolite structure takes place due to pronounced depolymerization of the high-siliceous framework.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 797–799, April, 1993.The author is grateful to V.Lutz (ZIPhCh, Germany) who kindly submitted samples1,2, and4, and to N. N. Feoktistova (IChS of the RAS), for the samples of silicaalumogel.     

A kinetics study of crystallization from discotic mesophases

The polymorphism of hexa- n -octanoate of rufigallol (RHO) was used to investigate the crystallization kinetics when starting from two different discotic mesophases, namely, a hightemperature enantiotropic mesophase and a low-temperature monotropic mesophase. In all cases, an Avrami exponent of n 3 was obtained, suggesting two-dimensional sporadic nucleation and growth. Although the same overall mechanism was predicted to operate for all crystallization temperatures investigated, the Avrami constant b has a temperaturedependence which is different for different starting columnar phases, indicating a strong influence on the rates of nucleation and of growth of the different molecular arrangements of the starting mesophases. Differential scanning calorimetry was used for the studies, supplemented by direct observations through optical polarizing microscopy.     

Experimental and modeling study on production of activated carbon from pistachio shells in rotary reactor

In this study, activated carbons were prepared by physical activation from pistachio shell with steam in a rotary reactor. Experiments were performed based on the central composite design (CCD) in DX8 software. A quadratic model for prediction of iodine number and a quadratic model for burn-off were developed using CCD in the activation process. The optimum iodine number and burn-off for physical activation were, respectively, 1,478.17 mg/g and 22.09 wt%, which showed good agreement with the experimental values. The optimum values were achieved at the activation temperature of 816.5 °C, dwell time of 40 min, and gas flow rate of 47.4 l/min.     

Effects of organic additives on crystallization process and the adsorption performances of zeolite A

The crystallization of zeolite A was monitored by measuring the adsorption capacities of synthetic products. The influences of organic additives on the crystallization process and adsorption performances of zeolite were investigated. SDS (sodium dodecyl sulphonate), TWEEN (Tween-80), and PEG (poly(ethylene glycol)) shorten the induction period by reducing the interfacial energy while SCMC (sodium carboxymethylcellulose) can prolong the induction period by increasing the interfacial energy. TEA (triethanolamine) can also suppress the nucleation through reducing the effective supply of aluminum. All the organic additives but SCMC diminish the rate of crystal growth. CTAB (cetyltrimethylammonium bromide) causes the destruction of crystal structure and reduce the concentration of OH^? ions. As a result, the rate of crystal growth is significantly reduced. Meanwhile, PAM (poly(acrylamide)), SDS, TWEEN, HMTA (hexamethylenetetramine), and PEG increase the viscosities of synthesis systems, thus, diminish the growth rate. PAM restrains the transformation of zeolite A crystal into hydroxysodalite one, therefore, tremendously improves the stability of crystals of zeolite A. In addition, PAM can promote the rates of n-hexane adsorption on zeolite 5A because of the impact of PAM on the crystal-size distributions of zeolite 5A.     

纯相ZSM-11分子筛在双模板剂水热体系中的合成及表征研究(英）

在水热体系中利用双模板剂合成了纯相ZSM 11分子筛,并考察了合成条件的影响。同时利用多种表征手段对产品的物理化学性质进行了表征。     

Rapid crystallization and morphological adjustment of zeolite ZSM-5 in nonionic emulsions

Zeolite ZSM-5 was synthesized for the first time in a nonionic emulsion composed of polyoxyethylated alkylphenol, butanol, cyclohexane and tetraethylammonium hydroxide (TEAOH)-containing zeolite synthesis mixture. The crystallization kinetics in the emulsion was investigated and the ZSM-5 product was characterized in detail by XRD, SEM, FT-IR, TG, N₂ adsorption and CHN analysis techniques. Compared with the conventionally hydrothermal synthesis with the same structure directing agent TEAOH, the emulsion system allows rapid crystallization of ZSM-5. The ZSM-5 product exhibits unusual agglomerated structure and possesses larger specific surface area. The FT-IR, TG results plus CHN analysis show the encapsulation of a trace of emulsion components in the emulsion ZSM-5. Control experiments show the emulsion system exerts the crystallization induction and morphological adjustment effects mainly during the aging period. The effects are tentatively attributed to the confined space domains, surfactant-water interaction as well as surfactant-growing crystals interaction existing in the emulsion.     

铝离子在beta沸石晶化过程中对多形体A富集的影响

以四乙基氢氧化铵为有机结构导向剂,采用超浓水热方法,从氟离子体系合成出手性多形体A(简称A形体)富集的全硅beta沸石。在同样的初始混合物中引入铝源后,所合成的beta沸石中A形体含量明显降低,产物为普通的硅铝beta沸石。用粉末X射线衍射、元素分析、热重-差热分析、氮气吸附、扫描电子显微镜和固体魔角自旋核磁共振等表征手段对全硅beta沸石和硅铝beta沸石进行了详细的表征,并研究了其晶化过程。结果表明,铝源的引入可以加速beta沸石的晶化,得到的硅铝beta沸石晶体粒径明显减小。在硅铝beta沸石的晶化过程中生成了五配位铝物种,五配位铝物种可能是导致产物中A形体含量降低的原因。