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The powder mixtures of calcium oxide (CaO) and silica gel (SiO2) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO3, Ca3Si2O7, Ca2SiO4 compounds and CaO/Ca2SiO4 two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV–vis diffuse reflectance spectroscopy (DRS), N2 adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO·SiO2 and 3CaO·SiO2 calcined at 700 °C, and 3CaO·SiO2 calcined at 900 °C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca2SiO4 complex mixture. The effect of different amount of catalyst used for transesterification (0.2–2 wt%) was analyzed using the most active catalyst i.e. 3CaO·SiO2 calcined at 700 °C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO3, Ca3Si2O7 and Ca2SiO4, phases did not possess catalytic activity.

The continuous biodiesel production from soybean oil was carried out under the subcritical condition of methanol with MnCO3/Na-silicate as a heterogeneous catalyst. The transesterification rate was first investigated in a set of experiments performed in a batch autoclave at 448 K using methanol-to-oil molar ratio of 18:1 and various catalyst loadings (5, 10 and 20 wt% based on the oil mass). The results from these experiments, as well as the experimental data and the appropriate kinetic model recently reported in the literature were used for designing a packed bed tubular reactor (PBTR), a main unit of the pilot plant with the capacity of 100 L of biodiesel per day. The pilot plant was constructed and tested under various operating conditions. The first 11 h of the pilot-plant operation was realized in the tubular reactor packed with inert glass beads (i.e. without the catalyst) in order to analyze the effect of the non-catalyzed subcritical biodiesel (fatty acid methyl esters, FAME) production. Then, glass beads were replaced with a mix of MnCO3/Na-silicate catalyst particles and glass beads, and the catalytic biodiesel production was continuously run under the subcritical methanol condition for 85 h. Two mass balance tests during the continuous pilot plant operation were performed. © 2018 Elsevier Ltd

In the present work, calcium diglyceroxide (CaDG) was synthesized by mechanochemical treatment of CaO dispersed in glycerol, and characterized by X-ray diffraction (XRD), thermal analysis (TGA/DTA), infrared spectroscopy (FTIR), and Hammett indicator method for base strength determination. The obtained CaDG was tested as a catalyst in the methanolysis of sunflower oil under different working conditions: catalyst amount, agitation speed, temperature and methanol to oil molar ratio. The main advantage of CaDG used as a catalyst in methanolysis is related to the initial rate of methanolysis. According to many previously reported data in literature the mass transfer resistance controls the overall rate of methanolysis, but it is not observed with CaDG used as catalyst. Recently developed kinetic model that describes the complex methanolysis process was successfully applied for this system and model parameters were determined, supporting the explanation of the physical effect of the CaDG catalyst on the reduction of mass transfer resistance and increasing the rate of methanolysis. The absence of mass transfer rate at the beginning of process is a consequence of the nature of the CaDG, which is adsorbed at the droplet interfaces between methanol and oil leading to the formation of fine dispersion of these two immiscible liquids.

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 °C for the methanolysis of sunflower oil. However, at 165 °C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 °C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of “free” CaO also showed methanolysis activity at 60 °C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.

The kinetics of heterogeneous methanolysis of sunflower oil and used vegetable oil were studied at different temperatures, ranging from 60 to 96 °C using CaO·ZnO as catalyst (2 wt% on the basis of oil) and methanol to oil molar ratio of 10:1. Heterogeneous CaO·ZnO catalyst was synthesized by mechanochemical treatment of CaO and ZnO powder mixture with the addition of water necessary for the formation of corresponding mixed hydroxides, and their calcination at 700 °C in air. It was shown that kinetics of overall process could be described as pseudo-first order reaction. For the sunflower oil methanolysis at 60 and 70 °C, the rate of process at the beginning of biodiesel synthesis was limited by triglycerides mass transfer to the catalyst surface, and after that it is governed by the rate of chemical reaction at catalyst surface. At higher temperatures the influence of mass transfer resistance is almost negligible implying that the rate of chemical reaction determines the overall kinetic of biodiesel synthesis. In the case of used vegetable oil, the influence of mass transfer resistance was not observed either at higher or lower temperature. The kinetic model that describes the whole process well was proposed, and it comprises both the triglycerides mass transfer and chemical reaction controlled regime. The overall volumetric mass transfer coefficient was defined, assuming that it depends on the conversion of triglycerides.

In this study, the synthesis of biodiesel or fatty acid methyl esters (FAME) from sunflower oil and methanol using CaO·ZnO catalyst was investigated. Catalyst was synthesized by ball milling of Ca(OH)2 and ZnO powder mixture with the addition of water (BMH), as well as solely by ball milling of mentioned powders (BM) and subsequent calcination at 700 °C in air atmosphere. For comparison, the CaO·ZnO mixed oxide was also prepared using usual coprecipitation procedure (CP) followed by calcination at 700 °C of the formed calcium zinc hydroxide hydrate. The BMH, BM and CP catalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), particle size distribution measurement and scanning electron microscopy (SEM and SEM-EDS). In addition, specific surface area (BET), solubility in methanol at 60 °C and alkalinity (Hammett indicator method) were also determined. The activity of BMH, BM and CP catalysts for biodiesel synthesis were tested at 60 °C and 1 bar, using molar ratio of sunflower oil to methanol of 1:10 and with 2 wt% of catalyst based on oil weight.

The transesterification of triglycerides (vegetable oil) with methanol using CaO·ZnO mixed oxides catalyst were conducted to produce FAME (Fatty Acid Methyl Esters, i.e. biodiesel). Catalyst was synthesized by ball milling of CaO and ZnO powder mixture (using molar ratio of Ca and Zn of 1:2 and 1:4) with the addition of water, as well as solely by ball milling (molar ratio of 1:2) of mentioned powders and subsequent. After ball milling prepared mixtures were calcinatied at 700 oC in air atmosphere. The samples of formed catalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The particle size distribution as well as the base strength using Hammett indicator was determined, too. CaO.ZnO catalysts were used in the methanolysis of sunflower oil, at 60 oC and 1 bar, using molar ratio of sunflower oil to methanol of 1:10 and with 2 wt% of catalyst based on oil weight. All catalysts exhibited good activity in the methanolysis of sunflower oil, with the yield of FAME above 90% after 4 hours of reaction.

Supercritical CO2 extraction was studied using dried leaves of Mentha, originated from the northern part of Libya. Leaves were milled and sieved to obtain different average particles (dp = 0.25-0.80 mm). They were treated with supercritical CO2 at 313 K and 10 MPa in order to isolate essential oil. The new approach of supercritical extraction modelling on the basis of proposed "pseudo kinetic model" (PKM) was investigated and compared to most applied in literature Sovova's model. The main focus of these investigation was to determine the influence of particle size on extractions yield and to determine optimal methodology for determination parameters of PKM. Achieved results showed good agreement between both models and experimental results and good prospects for further usage of PKM.

The transesterification of triglycerides (vegetable oil) with methanol using CaO·ZnO mixed oxides catalyst were conducted to produce FAME (Fatty Acid Methyl Esters, i.e. biodiesel). Catalyst was synthesized by ball milling of CaO and ZnO powder mixture (using molar ratio of Ca and Zn of 1:2 and 1:4) with the addition of water, as well as solely by ball milling (molar ratio of 1:2) of mentioned powders and subsequent. After ball milling prepared mixtures were calcinatied at 700 °C in air atmosphere. The samples of formed catalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The particle size distribution as well as the base strength using Hammett indicator was determined, too. CaO.ZnO catalysts were used in the methanolysis of sunflower oil, at 60 °C and 1 bar, using molar ratio of sunflower oil to methanol of 1:10 and with 2 wt% of catalyst based on oil weight. All catalysts exhibited good activity in the methanolysis of sunflower oil, with the yield of FAME above 90 % after 4 hours of reaction.

The kinetics of Ca(OH)2-catalyzed methanolysis of sunflower oil was studied at a moderate temperature (60 °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 methanolysis of sunflower oil was studied in the presence of CaO previously calcined at various temperatures and the optimal temperature for CaO calcination was determined. The sigmoidal process kinetics was explained by the initial triglyceride (TG) mass transfer controlled region, followed by the chemical reaction controlled region in the latter reaction period. The TG mass transfer limitation was due to the small available active specific catalyst surface, which was mainly covered by adsorbed molecules of methanol. In the later phase, the adsorbed methanol concentration decreased, causing the increase of both the available active specific catalyst surface and the TG mass transfer rate, and the chemical reaction rate become smaller than the TG mass transfer rate.

The sunflower oil methanolysis was studied in a stirred reactor at different agitation speeds. The measurements of drop size, drop size distribution and the conversion degree demonstrate the effects of the agitation speed in both non-reaction (methanol/sunflower oil) and reaction (methanol/KOH/sunflower oil) systems. Drop size distributions were found to become narrower and shift to smaller sizes with increasing agitation speed as well as with the progress of the methanolysis reaction at a constant agitation speed. During the methanolysis reaction, the Sauter-mean drop diameter stays constant in the initial slow reaction region, rapidly decreases during the fast reaction period and finally reaches the equilibrium level. Due to the fact that the interfacial area increases, one can conclude that the rate of reaction occurring at the interface will also be enhanced progressively. The "autocatalytic" behavior of the methanolysis reaction is explained by this "self-enhancement" of the interfacial area, due to intensive drop breakage process.

In this paper, the demulsification has been achieved with the use of freeze/thaw (F/T) method and microwave radiation (MWR). The object of investigation were emulsion samples prepared by mixing the metal-working-oil, FESOL 09, produced by FAM, Krusevac, Serbia, and deionized water. F/T method has been successfully applied for the removal of oil from emulsions in our previous work. In this work, MWR has been additionally used for separation and enhanced heating of emulsion samples. The efficiency of oil removal has been improved with the assistance of MWR, up to 90%.