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Synthesis of biodiesel from various plant oils is realized by the transesterification of triglycerides with methanol or by a reaction usually defined as methanolysis. The usage of low-quality oils, such as waste cooking oil (WCO), is followed by undesirable side reactions as a result of the increased content of free fatty acids (FFA), and water. The presence of FFA in WCO usually requires a pretreatment stage before subjecting it to methanolysis. In the present work, heterogeneously catalyzed methanolysis of WCO with and without pretreatment was investigated. Removal of FFA from WCO was conducted by using only quicklime or with the addition of a small amount of methanol (FFA to methanol = 1:3 molar ratio). The obtained results showed that pretreatment of WCO with quicklime at 30 °C after 1 h reduces the FFA content by 72 %, while the adsorption capacity was determined to be 910 mg g-1. The adsorptive pretreatment, as a simple operation, using low-cost quicklime under mild conditions, had a positive effect on the transesterification rate with CaO∙ZnO as a catalyst, enabling the achievement of over 96 % of biodiesel yield in only 15 min, compared to 1 h without the pretreatment. Furthermore, pretreated WCO allows an increase in repeated catalyst use and overall savings in the necessary amount of catalyst. The present study showed that quicklime is an economic, environmental-friendly, and sustainable material for FFA removal from WCO.

The kinetic model, which was originally developed for sunflower oil methanolysis catalyzed by CaO.ZnO, was examined for several other calcium-based catalysts like neat CaO, quicklime and Ca(OH)2. This model including triacylglycerols mass transfer- and chemically-controlled regimes demonstrated a good agreement with the experimental data in terms of a high coefficient of determination (0.971±0.022) and acceptable mean relative percentage deviation (±15.9%). Hence, this model is recommended for modeling the kinetics of sunflower oil methanolysis over calcium-based catalysts under widely ranging reaction conditions. [Projekat Ministarstva nauke Republike Srbije, br. III 45001]

Today, homogeneous base-catalyzed methanolysis is most frequently used method for industrial biodiesel production. High requirements for the quality of feedstocks and the problems related to a huge amount of wastewaters have led to the development of novel biodiesel production technologies. Among them, the most important is heterogeneous base-catalyzed methanolysis, which has been intensively investigated in the last decade in order to develop new catalytic systems, to optimize the reaction conditions and to recycle catalysts. These studies are a base for developing continuous biodiesel production on industrial scale in near future. The present work summarizes up-to-date studies on biodiesel production by heterogeneous base-catalyzed methanolysis. The main goals were to point out the application of different base compounds as catalysts, the methods of catalyst preparation, impregnation on carriers and recycling as well as the possibilities to improve existing base-catalyzed biodiesel production processes and to develop novel ones.

The kinetic model originally developed for quicklime-catalyzed methanolysis of sunflower oil was tested for another three calcium-based catalysts, namely, neat CaO, Ca(OH)2, and CaO·ZnO. This model includes the changing reaction mechanism and the triacylglycerol (TAG) mass transfer. The applicability and generalization capability of this model for heterogeneous methanolysis reaction catalyzed by calcium-based catalysts was evaluated. As indicated by the high coefficient of determination and the relatively small mean relative percentage deviation, the model was a reliable predictor of the time variation of TAG conversion degree in the sunflower oil methanolysis over all four calcium-based catalysts within the ranges of the reaction conditions applied. This model is recommended in general for describing the kinetics of sunflower oil methanolysis over calcium-based catalysts. [ABSTRACT FROM AUTHOR]

The continuous sunflower oil methanolysis catalyzed by quicklime in a packed-bed tubular reactor of 60 cm height was studied at 60 °C using methanol-to-oil molar ratios from 6:1 to 18:1 and weight hourly space velocities from 0.188 to 0.376 (kg/kg cat h). The main goal was to establish the effect of the process variables on the fatty acid methyl esters (FAME) synthesis. A full factorial design was used to evaluate the significance of the three process factors (methanol-to-oil molar ratio, flow rate of the reactants and bed height) statistically. Moreover, the recently reported kinetic model of methanolysis was used to describe variations of FAME and triacylglycerols (TAG) concentrations along the reactor length. The kinetic model predicted the axial concentration profiles of TAG and FAME in the reactor with acceptable accuracy. A high FAME content (98.5%) could be achieved at the two thirds of the bed of quicklime bits without loss of catalytic activity within 30 h of continuous operation. [ABSTRACT FROM AUTHOR]

The goal of this study was to prepare a CaO•ZnO catalyst containing a small amount of K2CO3 and analyze its activity for biodiesel synthesis. The catalyst was prepared using the following procedure: CaO and ZnO (mole ratio of 1:2), water and K2CO3 (in various amounts) were mechanochemically treated and after milling heated at 700 °C in air atmosphere for obtaining mixed CaO•ZnO/xK2CO3 oxides (x = 0, 1, 2 and 4 mol of K2CO3 per 10 mol of CaO). All the samples were characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), scanning electron microscopy/ energy-dispersive spectroscopy (SEM/EDS), particle size laser diffraction (PSLD) distribution, solubility measurement of Ca, Zn and K ions in methanol as well as by determination of their alkalinity (Hammett indicator method). Prepared CaO•ZnO/xK2CO3 composite powders were tested as catalysts for methanolysis of sunflower oil at 70 °C using mole ratio of sunflower oil to methanol of 1:10 and with 2 mass% of catalyst based on oil weight. The presence of K2CO3 in prepared samples was found to increase the activity of catalyst, and that such effect is caused by homogeneous--heterogeneous catalysis of biodiesel synthesis. [ABSTRACT FROM AUTHOR]

The kinetics of heterogeneous methanolysis of sunflower oil was studied at 60 °C using mechanochemically synthesized CaO⋅ZnO as catalyst. The 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, the time dependence of which is defined by the change of triglyceride (TG) conversion. A kinetic model is proposed and the model parameters are determined. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mechanochemical synthesis of CaO·ZnO catalyst and its testing in methanolysis of virgin sunflower and used vegetable oil. [•] Determination of heterogeneous methanolysis kinetics and kinetic parameters evaluation. [•] Definition of the overall volumetric mass transfer coefficient as a function of triglycerides conversion. [•] Proposal of the kinetic model to describe the heterogeneous methanolysis kinetics. [ABSTRACT FROM AUTHOR]

Abstract: 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 1bar, using molar ratio of sunflower oil to methanol of 1:10 and with 2wt% of catalyst based on oil weight. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The kinetics of the sunflower oil methanolysis process was studied at lower temperatures (10–30°C). The sigmoidal kinetics of the process was explained by the mass transfer controlled region in the initial heterogenous regime, followed by the chemical reaction controlled region in the pseudo-homogenous regime. A simple kinetic model, which did not require complex computation of the kinetic constants, was used for simulation of the TG conversion and the FAME formation in the latter regime: the fast irreversible second-order reaction was followed by the slow reversible second-order reaction close to the completion of the methanolysis reaction. The mass transfer was related to the drop size of the dispersed (methanol) phase, which reduced rapidly with the progress of the methanolysis reaction. This was attributed to the formation of the emulsifying agents stabilizing the emulsion of methanol drops into the oil. [Copyright &y& Elsevier]