Dejan Skala

Alumina/silica supported K2CO3 as a catalyst for biodiesel synthesis from sunflower oil.

The new type of catalyst for fatty acid methyl esters (FAME or biodiesel) synthesis with K(2)CO(3) as active component on alumina/silica support was synthesized using sol-gel method. Corresponding catalyst (xerogel) was prepared by 12h drying the wet gel in air at 300 degrees C, 600 degrees C or 1000 degrees C at atmospheric pressure. The catalysts activity in the methanolysis of sunflower oil was compared to the activity of the pure K(2)CO(3). The effects of various reaction variables on the yield of FAME were investigated. It was found that the temperature of 120 degrees C and methanol to oil molar ratio of 15:1, are optimal conditions for FAME synthesis with synthesized catalyst. Repeated use of same amount of catalyst indicated that effect of potassium leaching obviously existed leading to decrease of catalyst activity.

Biodiesel synthesis at high pressure and temperature: analysis of energy consumption on industrial scale.

Analysis of several different schemes for industrial FAME production at higher pressure and temperature (catalytic or non-catalytic synthesis) was realized with the aim to find the best route to reduce the energy consumption (EC) and to improve the life cycle energy efficiency. Obtained results indicated that the EC (MJ/kg FAME) mainly depends on degree of conversion of triglycerides being almost 25% smaller if degree of conversion increase from 97 mass% to complete conversion. Further significant decrease of EC might be obtained at subcritical conditions but only after substantial decrease of methanol to oil molar ratio (from 42 to 15) which requires use of appropriate catalyst. On account of that, the kinetics of heterogeneous catalyzed methanolysis of triglycerides was analyzed using data published in literature (CaO) as well as own experimental data (K(2)CO(3)/Al-O-Si) with a goal to obtain reliable kinetic rate constant which might be used for process simulation. This study shows that if heterogeneous process of biodiesel synthesis is realized at subcritical conditions then further decrease of EC is possible.

Kinetics and modelling of oil shale pyrolysis

Abstract The pyrolysis kinetics of oil shales from Yugoslavia, Northern Korea and the USSR, were investigated under non-isothermal conditions using thermogravimetric analysis (TGA) and differential scanning calorimetry (d.s.c.). Additional kinetic investigations were performed on samples obtained by chemically and thermally treating each oil shale. The results obtained were incorporated into the multi-step kinetic model (MSM) which was adjusted according to the specific properties of particular oil shale samples, and tested by comparison of the experimental and simulated TGA, DTG and d.s.c. curves. The modelling procedure developed for Aleksinac oil shale was found to be useful in modelling the pyrolysis of other oil shales of the same kerogen type.

Thermogravimetrically and differential scanning calorimetrically derived kinetics of oil shale pyrolysis

Abstract Thermogravimetry (TG) and differential scanning calorimetry (d.s.c.) were used to investigate the kinetics of non-isothermal pyrolysis of Aleksinac oil shale from Yugoslavia. The samples used included oil shale, demineralized oil shale and bitumen extracted from the original, as well as from the thermally treated oil shale. Kinetic parameters were determined by assuming a single first-order kinetic model, using the integral method for TG analysis, and ASTM procedure E-698 for d.s.c. analysis. The influence of cracking catalyst addition was examined with respect to the overall kinetics and to conversion in particular temperature regions. Higher values of kinetic parameters were obtained by d.s.c. analysis, and the reasons for the differences between those and the TG results are discussed.

Modeling the kinetics of calcium hydroxide catalyzed methanolysis of sunflower oil.

The kinetics of Ca(OH)(2)-catalyzed methanolysis of sunflower oil was studied at a moderate temperature (60 degrees C), a methanol-to-oil molar ratio (6:1) and different catalyst amounts (from 1% to 10% based on oil weight). The methanolysis process was shown to involve the initial triglyceride (TG) mass transfer controlled region, followed by the chemical reaction controlled region in the latter period. The TG mass transfer limitation was caused by the low available active specific catalyst surface due to the high adsorbed methanol concentration. Both the TG mass transfer and chemical reaction rates increased with increasing the catalyst amount.

The combined extraction of sage (Salvia officinalis L.): ultrasound followed by supercritical CO2 extraction.

A wide spectrum of phytochemicals could be isolated from sage (Salvia officinalis L.) using different extraction or distillation technique: the supercritical fluid extraction (SFE), the volatiles compounds (monoterpenes and sesquiterpenes) isolation using hydrodistillation or higher molecular compounds with Soxhlet extraction or ultrasound-assisted extraction. The combination of ultrasound-assisted extraction followed by re-extraction of obtained extract with supercritical CO(2) was performed in this study. The goal of performed investigation was to concentrate diterpenes present in sage extract which are generally considered to be responsible for antioxidant activity of extracted compounds. The fractionation using the supercritical CO(2), and different combination of the ultrasound-assisted solvent extractions (water-ethanol mixture or only water) followed by supercritical CO(2) re-extraction of obtained extract or treated plant material were analyzed and compared. Based on the results of these investigations it could be proposed the best extraction procedure: the ultrasound pretreatment of plant material with distilled water and re-extraction of plant material (residue) using supercritical CO(2). That procedure gives two valuable products: the ultrasound extract which is rich in sugars and possess the immunomodulatory activity and supercritical extract which is rich in diterpenes and sesquiterpenes.

A Comparison Between the Oil, Hexane Extract and Supercritical Carbon Dioxide Extract of Juniperus communis L.

Abstract Volatile compounds from the berries of common juniper (Juniperus communis L.) were isolated by hydrodistillation, hexane extraction and supercritical CO2 extraction. The hydrodistillation yield was 2.17%, the hexane extraction yield 5.31 % and supercritical CO2 extraction yield 0.96%. Their compositions were compared using GC/M S as the method of analysis. Analyses reveal that samples differ quantitatively and qualitatively. The concentrations of monoterpene hydrocarbons (α-pinene, sabinene, myrcene) were higher in the hydrodistilled oil, while some less volatile compounds were present in extracts, especially in the hexane extract.

Alumina/silica aerogel with zinc chloride alkylation catalyst: Influence of supercritical drying conditions and aerogel structure on alkylation catalytic activity

Abstract Alumina/silica aerogel with zinc chloride alkylation catalyst, was obtained using one step sol–gel synthesis and subsequent drying with the supercritical carbon dioxide. The high density supercritical carbon dioxide drying conditions resulted in zinc chloride removal from the catalyst surface, surface area and pore volume increase and catalytic activity decrease. The low density supercritical carbon dioxide drying conditions, pore size distribution centred around 6 nm pore radius and high degree of mixed Al–O–Si bonds in the alumina/silica aerogel network, were found to increase the catalytic activity of the obtained aerogel catalysts.

Kinetics of heterogeneous methanolysis of sunflower oil with CaO∙ZnO catalyst: Influence of different hydrodynamic conditions

The kinetics of heterogeneous methanolysis of sunflower oil was studied at 60°C using mechanochemically synthesized CaO∙ZnO as catalyst. Influence of agitation speed, catalyst amount and methanol to oil molar ratio on the rate of reaction was analyzed. The rate of the process depends on the two resistances - mass transfer of triglycerides to the catalyst surface and chemical reaction on the catalyst surface, which are defined as the values of the overall triglyceride volumetric mass transfer coefficient, kmt,TG, and the effective pseudo first-order reaction rate constant, k, respectively. These kinetic parameters actually determine the value of the apparent reaction rate constant, kapp, whose change with time is defined with the change of triglyceride (TG) conversion. The kinetic model was proposed and the model parameters determined. [Projekat Ministarstva nauke Republike Srbije, br. 45001]

Effects of aeration on extracellular dextransucrase production by Leuconostoc mesenteroides

Abstract The effect of oxygen transfer rate on extracellular dextransucrase production by Leuconostoc mesenteroides in batch fermentation without pH control was studied. The optimum aerobic conditions for both growth and dextransucrase formation were found to be at an oxygen transfer rate of about 1.0 mmol l −1 h −1 .