Product Of Centrifugal Thermal Activation Research Articles

Wasteless Synthesis and Properties of Highly Dispersed MgAl2O4 Based on Product of Thermal Activation of Gibbsite

The study showed that the interaction of the product of centrifugal thermal activation of gibbsite with an aqueous solution of magnesium nitrate at a cationic ratio Mg:Al = 1:2 leads to the formation of mixed double hydroxides both under hydrothermal treatment at 150 °C and at room temperature. The subsequent thermal treatment at 550 °C of the product of mild interaction leads to ~90% alumina-magnesia spinel and ~10% MgO, while the treatment of the hydrothermal interaction product leads to ~100% spinel with the stoichiometric composition MgAl2O4. The obtained spinel samples possess a high specific surface area (above 100 m2/g) and a hierarchical pore structure formed by the micron-level particles of different sizes (1–2 and 10–20 μm) consisting of ~70 nm crystallites with ~3 nm pores; the samples differ mostly in the total volume and quantitative ratio of the pores. The samples have Lewis acid sites of moderate strength on the surface, the amount of which is much lower to how it is when compared with a sample prepared by precipitation in that they also differ by quantity from each other as well (503 μmol/g for stoichiometric spinel and 304 μmol/g for sample with admixture of MgO). As the calcination temperature is raised to 850 °C, the acidity decreases—only weak Lewis acid sites are observed, the amount of which is also higher for stoichiometric spinel (161 and 39 μmol/g, respectively). The method proposed for the synthesis of alumina-magnesia systems provides a high dispersion and a much lower surface acidity for the oxides; in addition, it minimizes or completely excludes wash water, in distinction to the precipitation method.

Synthesis of Barium Aluminate of Disk-Shaped Morphology Using the Product of Centrifugal Thermal Activation of Gibbsite

Synthesis of Barium Aluminate of Disk-Shaped Morphology Using the Product of Centrifugal Thermal Activation of Gibbsite

Synthesis of Highly Dispersed Aluminum Magnesium Oxides from the Product of Centrifugal Thermal Activation of Gibbsite

Synthesis of Highly Dispersed Aluminum Magnesium Oxides from the Product of Centrifugal Thermal Activation of Gibbsite

Effect of particle size on adsorption kinetics of water vapor on porous aluminium oxide material

Influence of the grain size of aluminium oxide material, being a product of centrifugal thermal activation of hydrargillite, on adsorption kinetics of water vapors was studied. The material was characterized by the BET method and X-ray phase analysis (XRD). Influence of gas flow rate on adsorption dynamics was studied on a laboratory installation using McBain-Bakr quartz balance. It was shown that with the fraction size greater than 0.5-1.0 mm, the rate of water vapor adsorption on this adsorbent decreased, which was connected with the influence of internal diffusion resistance. On the base of the first-order kinetic equation for the water adsorption mathematical modeling was carried out. The kinetic parameters of the equation for the various grain size samples (0.25-0.5 mm and 0.5-1.0 mm and 3.7 x 6 mm granule) were determined.

Dynamic capacity of desiccants based on modified alumina at elevated pressures

Alumina desiccants obtained by extrusion molding of plastic pastes based on pseudoboehmite or bayerite-containing hydroxides including those modified by sodium and potassium ions were studied. The hydroxides were synthesized by hydration of the product of centrifugal thermal activation of gibbsite under mild conditions. The physicochemical and structural-mechanical properties of the desiccants (fresh and after nine adsorption–regeneration cycles) were studied. The dynamic capacity was determined at a pressure of 3MPa under conditions designed to model the industrial conditions. The sample obtained from bayeritecontaining hydroxide had a higher dynamic capacity than the sample obtained from pseudoboehmite-containing hydroxide at close texture and strength characteristics of adsorbents. Modification of the samples obtained from pseudoboehmite-containing hydroxide with potassium and sodium ions leads to decreased granule stability and increased volume, average pore size, and dynamic capacity. The potassium-modified sample of the desiccant had dynamic capacity as high as that of the sample obtained from bayerite-containing hydroxide at low load. After the cyclic tests, the phase composition, alkaline impurity contents, specific surface area, and crushing strength of the samples did not change within the error of determination. It was found that the prepared desiccants were highly stable in many adsorption–desorption cycles and the minimum dew point of –80°C could be reached during the drying.

Dynamic Capacity of Desiccants Based on Modified Alumina at High Pressure

Alumina desiccants prepared by extrusion of plastic pastes based on pseudoboehmite- and bayerite-containing hydroxides, including the ones modified with sodium and potassium ions, were studied. The hydroxides were synthesized via dehydration of the product of centrifugal thermal activation of hydrargillite under mild conditions. Physicochemical and structural-mechanical properties of the desiccants were characterized using fresh samples and the samples undergone 9 adsorption-regeneration cycles. The dynamic capacity was determined at 3 MPa under industrial-modeling conditions. A high dynamic capacity was characteristic of the sample prepared from bayerite-containing hydroxide against that of the sample prepared from pseudoboehmite-containing hydroxide, while close textural and strength parameters were determined for both adsorbents. After the sample prepared from pseudoboehmite-containing hydroxide was modified with sodium and potassium ions, the granules became less strong, volume and average size of pores increased, and dynamic capacity rose. At a low water content in the gas to be dried the dynamic capacity of the potassium modified sample was not inferior to that of the sample prepared from bayerite-containing hydroxide. The phase composition, content of alkali impurities, specific surface area and crashing strength did not change, within the measurement error, after cyclic testing of the samples. A high stability of the prepared desiccants and the possibility of achieving the minimal dew point (–80 °C) was established during repeated adsorption-desorption cycles.

Acid-base properties of alumina prepared from a hydrated product of centrifugal thermal activation of hydrargillite (cta-product)

Acid-base properties of aluminas prepared by thermal treatment of a hydrated CTA-product at 600°C were studied. The CTA-oxides, representing γ-Al2O3, were shown to contain terminal and bridged OH-groups. The concentration of the terminal OH-groups in the CTA-oxides was found to exceed their concentration in γ-Al2O3 prepared by dehydration of the “precipitated” pseudoboehmite, whereas the concentration of the bridged OH-groups in the CTA-oxides was lower than that in γ-Al2O3 prepared from pseudoboehmite. The total concentration of the surface Lewis acid sites in CTA-oxides varies within the limits of 2.80-4.14 mmol/m2 and is essentially above that in g-Al2O3 (2.25 mmol/m2). The distinctive feature of the CTA-oxides is that their surface contains strong Lewis acid sites with nCO = 2220 and 2238 cm-1. The total concentration of basic sites in the CTA-oxides is lower than that in g-Al2O3, however, in contrast to g-Al2O3,they contain strong basic sites with nCDCl3 = 2200 cm-1.