V. Yu. Prokof’ev

Mechanochemical synthesis of granulated LTA zeolite from metakaolin

LTA zeolite can be prepared from dry mixes in a vibratory mill with an impact-shear loading conditions. For the synthesis of LTA zeolite, it is necessary to use the anhydrous ingredients (Al2Si2O7–metakaolin, γ-Al2O3). The process of synthesis is controlled by X-ray diffraction, IR-spectroscopy, and atomic-force microscopy. The presence of structural water in the initial ingredients (Al2Si2(OH)4–kaolin or Al(OH)3) leads to the formation of feldshpatoids (nepheline, sodalite). It was established that the process of mechanical activation requires the synthesis of sodium aluminate of cubic and/or tetragonal crystal systems with a lattice parameters close to those for LTA zeolite. These sodium aluminate acts as a steric template for an “assembly” of the zeolite. The presence of sodium aluminate with some other crystal structure results in the formation of sodalite. There is an optimal time of mechanochemical activation, which is determined by the synthesis of sodium aluminate with cubic or tetragonal crystal structure. A model of the mechanochemical synthesis of LTA zeolite was proposed.

Natural Mechanisms of Mechanochemical Interactions in Oxide Powders

The effect of hydroxyl and other functional groups on mechanochemical interactions in oxide powders is shown. The general rules of non-covalent mechanochemical synthesis are established. Phenomenological models are discussed and the kinetic equations of mechanochemical synthesis are presented.

Aluminum-calcium based three-component systems with addition of zinc and magnesium compounds for absorption of the hydrochloric acid vapor

To prepare granulated sorbents for absorption of the hydrochloric acid vapor, the formulations ZnO-CaO-Al(OH)3, Zn4CO3(OH)6-CaO-Al(OH)3, and MgO-CaO-Al(OH)3 with a 1: 1: 1 molar ratio of the oxides were studied. Mechanical processing of the mixtures leads to amorphization of compounds of the bivalent metals and to an increase in the size of gibbsite crystallites, accompanied by deformation of its crystal lattice. The composition of the chemisorbent has no effect on the number of basic surface centers, but determines the mechanical strength of grains and their absorbing capacity. The most promising formulation for preparing the chemisorbent is the Zn4(CO3(OH)6-CaO-Al(OH)3 system possessing the highest absorbing capacity for HCl vapor and retains its mechanical strength in tests.

Mechanical coactivation of hydrargillite and calcium compounds

The mechanochemical processes in equimolar mixtures of hydrargillite with CaO, Ca(OH)2, and CaCO3 were studied during activation in a vibratory mill. The chemical reactions involved were identified.

Use of Ultrasonic Processing at Early Stages of LTA Zeolite Synthesis from Metakaolin

The influence of ultrasonic processing (22 kHz) of a suspension of metakaolin, aluminum oxide, and sodium hydroxide with molar ratio Al2O3 · 2SiO2: NaOH : Al2O3 = 6 : 12 : 2, followed by heat-treatment and hydrothermal crystallization on LTA zeolite synthesis, is investigated. It is found that by increasing the S : L ratio at the ultrasonic processing stage it is possible to increase the yield of the desired product. The optimal conditions of ultrasonic processing are determined (amplitude 8 μm, time about 10 min). It is shown that under the optimal conditions the degree of crystallinity of LTA zeolite equals 98%. The mechanisms of LTA zeolite synthesis by means of ultrasonic processing and mechano-chemical activation are compared.

Synthesis of aluminum titanate using stabilizing additives

The advantages of joint preliminary grinding of the initial-material components, as compared to separate grinding, and its effect on the regularities of phase formation in the aluminum oxide — titanium oxide system are considered. Joint activation makes it possible to shorten the time expended on thermal synthesis of TiO2 · Al2O3. The effect of stabilizing additives of magnesium and silicon oxides and talc on the kinetics of thermal synthesis of aluminum titanate is studied. It is proposed that talc in an amount of 7% be used as a stabilizing additive to prevent incongruent melting of TiO2 · Al2O3 accompanied by formation of the initial components.

Studying Solid-Phase Processes in Metakaoline–Sodium Hydroxide Mixtures by Means of Isoconversion Analysis

Processes of the thermal treatment of 6Al2Si4O7: 12NaOH mixtures for the synthesis of zeolites are studied. The mixtures are subjected to ultrasonic treatment and mechanochemical activation, after which the suspensions are evaporated, granulated, and dried. The study is performed using X-ray diffraction, synchronous thermal analysis, and electron microscopy. It is established that calcination below ~500°C leads to the dehydration of the LTA zeolite and sodium hydroaluminates formed earlier, and Al2Si4O7 reacts with LTA and NaOH in the range of 500–800°C to form Na6Al4Si4O17 and Na8Al4Si4O18. Using the Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose methods, the apparent activation energies (E) are calculated for this range. The two methods yield close results. It is found that E grows from 30–80 to 240–300 kJ/mol as conversion increases. It is shown that preliminary ultrasonic treatment and mechanochemical activation reduce apparent energy of activation E due to changes in the morphology of particles.

Co-Grinding of Three-Component Compositions of Al, Ca, Zn, Mg Compounds

The grinding of the compositions ZnO/CaO/Al(OH)3, Zn4CO3(OH)6 /CaO/Al(OH)3, and MgO/CaO/Al(OH)3 in a vibrating mill is studied by means of x-ray diffraction, IR spectroscopy, and scanning electron microscopy. It is found that a new phase Ca(Zn2(OH)6) in the form of prismoidal crystals forms in mixtures containing ZnO. The grinding process is accompanied by surface hydration of the particles, which is the reason for the equalization of the main properties of the compositions. It is shown that the amount of gibbsite in a composition affects the character of the change in the parameters of the crystal structure of gibbsite.

Study of the nonisothermal decomposition kinetics of the Zn4CO3(OH)6/Al(OH)3 system

Friedman and Flynn-Wall-Ozava methods were used to study the nonisothermal decomposition kinetics of the Zn4CO3(OH)6/Al(OH)3 system. It was shown that thermolysis processes occur in the kinetic mode and, after a degree of decomposition exceeding 0.9 is reached, pass under diffusion control. It was found that, upon co-grinding of the components, the apparent activation energy increases as compared with the values for the starting mixture.

Investigation of catalyst Ni/K2O-Al2O3 for vapor conversion of methane

An effect of raw material (aluminum oxide and hydroxide), of amount, and of technique of KOH feed (solid or solution) on a composition of potassium aluminates formed at calcination. Reactivity of the obtaining catalysts at the vapor conversion of methane was studied.