Tatjana Novaković

The Influence of Acid Treatment on the Nanostructure and Textural Properties of Bentonite Clays

The nanostructure and textural properties of acid-activated bentonite clays from the Bogovina coalmine were investigated. The acid activation was performed with HCl in the concentration range 1.5-7.5 M. The atomic force microscopy followed by image analysis was used in order to establish the influence of the acid treatment on the size of bentonite particles. Nitrogen adsorption-desorption isotherms at -196 °C were used to estimate the specific surface area, pore volume and pore size distribution. The acid treatment reduces the size of bentonite particles and increases the specific surface area and pore volume of the investigated bentonites. These effects are improved by increasing the acid concentration up to 4.5 M HCl. Further increase in acid concentration does not result in development of new porous structure.

Properties of activated alumina obtained by flash calcination of gibbsite

Abstract On exposing gibbsite, with granulation below 10 μm to flash calcination of 0.5 s in the regime of pneumatic transport and at temperatures above 883 K, a microcrystalline material with a high degree of amorphization was obtained, as established from data of XRD analysis. It was shown that at 883 K the mechanism of gibbsite dehydration changes with a decrease of the activation energy from 141 to 53 kJ/mol. The obtained activated alumina is characterized by a specific surface area of over 200 m 2 /g and a pore structure with micro- and mesopores developed in the inside of grains of the starting material.

RESPONSE SURFACE OPTIMIZATION FOR ACTIVATION OF BENTONITE USING MICROWAVE IRRADIATION

Microwave irradiation as a means for heating bentonites during acid activation has been investigated in the past but it has never been optimized for industrial applications. The purpose of this study was to apply a factorial 23 experimental design to a Serbian bentonite in order to determine the influence of microwave heating on the acid-activation process. The effect of acid activation under microwave irradiation on the textural and structural properties of bentonite was studied as a model reaction. A mathematical, second-order response surface model (RSM) was developed with a central composite design that incorporated the relationships among various process parameters (time, acid concentration, and microwave heating power) and the selected process response of specific surface area of the bentonite. The ranges of values for the process parameters chosen were: time, 5–21 min; acid concentration, 2–7 M; and microwave heating power, 63–172 W. The effect of individual variables and their interaction effects on the textural and structural properties of the bentonite were determined. Statistical analysis showed that the duration of microwave irradiation was less significant than the other two factors. The model showed that increasing the time and acid concentration improved the textural properties of bentonites, resulting in increased specific surface area. This model is useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g−1 was achieved with an acid concentration of 5.2 M, activation time of 7.4 min, and microwave power of 117 W.

Preparation of ZrO2 and Al2O3 Thin-Films on Stainless Steel by Spray Pyrolysis

We have investigated the deposition of ZrO2 and Al2O3 films on a stainless steel (SS) substrate by spray pyrolysis method. The ZrO2 films were deposited from aqueous solution of zirconium dinitrate oxide. For Al2O3 films, a boehmite sol was used. The specific surface areas of samples were determined by the BET-method and sample surfaces were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The spray pyrolysis method permits the preparation of ZrO2 and Al2O3 thin films on SS with good adhesion. This method enables preparation of oxide layers with relatively high specific surface area, suitable for applications as catalysts supports.

Study of the effect of Mg(II) addition and the annealing conditions on the structure of mesoporous aluminum oxide using Plackett–Burman design

A statistical design was used to investigate the effect of various pro- cessing conditions on the structure of sol-gel derived Mg(II) doped alumina. Six process variables were selected based on the Plackett-Burman design: concentration of magnesium nitrate, time and temperature of alcohol evapor- ation, temperature and time of annealing and heating rate were changed at two levels. For every set of conditions, samples with different specific surface area and degree of crystallinity were obtained. Analysis of the results showed that the annealing temperature, heating rate and concentration of magnesium nitrate were the main factors affecting the average crystallite size of the predominant alumina phase. In the case of the specific surface area, two of selected six variables had pronounced effects; however, the temperature of annealing was more effective than others. The present results showed that the proposed model that uses crystallite size as a response variable is preferable to other research.

β-Carotene removal from soybean oil with smectite clay using central composite design

In this study removal of β-carotene from soybean oil by adsorption on acid activated smectite clay from Serbia was investigated and a factorial 23 experimental design was applied. The effects of relevant factors, such as temperature, solid-to-liquid ratio and time, on removal of β-carotene were investigated. In order to check these factors and their effect on the removal of β-carotene, we have established a model of this technique following a methodological strategy using experiments design. The mathematical model is established using a central composite design. The model describes the changes of the measured responses of β-carotene removal efficiency according to the temperature, solid-to-liquid ratio and time. The graphical representation of this model in the space of the variables enabled us to define the optimum conditions of these parameters. The optimum conditions to obtain the maximum removal of β-carotene from soybean oil were a temperature of 80°C, a solid-to-liquid ratio of 1: 25 and a time of 1255 s. Under these optimal conditions, the experimental values agreed with the predicted values, using analysis of variance, indicating a high goodness of fit of the model used and the success of response surface methodology for optimizing adsorption β-carotene of acid activated smectite clay from soybean oil.

THE STABILITY OF POROUS ALUMINA CATALYST SUPPORT AGAINST SINTERING

The high surface area alumina with well developed open porosity of nano-scale pore diameter, which is used as a catalyst, catalyst support or a membrane top-layer, has in recent years been obtained by a sol-gel process, using aluminium alcoxide as a precursor1–6.

Polymer-Based Monolithic Porous Composite

Porous monolithic glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA) copolymer [PGME] and three composite samples with alumina (PGME/alumina) were synthesized by radical copolymerization in a cast and functionalized by reaction of diethylene triamine (deta) with epoxy groups in GMA. All the samples were characterized using FTIR-ATR spectroscopy, SEM, AFM, solid state NMR, thermogravimetry and mercury porosimetry. Additionally, amino functionalized PGME/alumina with the highest alumina content (PGME/alumina50-deta) was loaded with chromium [Cr(VI)] ions. Kinetics of Cr(VI) sorption was investigated in batch static experiments, at 298 K and pH = 2, for various initial concentrations (C i = 0.5, 1.5 and 2.5 mM) and analyzed using three kinetic models. Cr(VI) sorption by PGME/alumina50-deta obeys the PSO kinetic model, while IPD model suggests some degree of intraparticle pore diffusion control.