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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. Kinetika heterogene metanolize suncokretovog ulja je ispitivana na 60 °C korišćenjem CaO·ZnO katalizatora koji je sintetizovan mehanohemijskim putem. Analiziran je uticaj intenziteta mešanja, mase korišćenog katalizatora u sintezi i različitog molskog odnosa metanola i ulja na brzinu metanolize. Brzina procesa metanolize zavisi od dva otpora - otpora prenosu mase triglicerida do površine katalizatora i otpora brzini hemijske reakcije na površini katalizatora. Oba otpora određuju vrednost ukupnog zapreminskog koeficijenta prenosa mase triglicerida, kmt,TG, odnosno efektivne vrednosti konstante brzine hemijske reakcije pseudo-prvog reda, k. Ovi kinetički parametri određuju vrednost prividne konstante brzine procesa metanolize, kapp, koja se menja sa vremenom u zavisnosti od ostvareneog stepena konverzije triglicerida (TG). Predložen je odgovarajući model kojim je moguće definisati brzinu metanolize i određeni su odgovarajući parametri ovog modela.

The kinetics of heterogeneous methanolysis of sunflower oil and used vegetable oil were studied at different temperatures, ranging from 60 to 96 degrees C using CaO center dot ZnO as catalyst (2 wt% on the basis of oil) and methanol to oil molar ratio of 10:1. Heterogeneous CaO center dot 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 degrees 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 degrees 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.

The transesterification of triglycerides (vegetable oil) with methanol using CaO center dot 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 CaO and ZnO 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 degrees 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 degrees 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.

Biodiesel, the most promising alternative to diesel fuel, is renewable, biodegradable, environmentally friendly and can be used in existing engines. Certain disadvantages of conventional processes of biodiesel, i.e. fatty acid methyl esters (FAME) synthesis could be avoided by applying new technologies which are based on using heterogeneous catalyst under moderate and high temperatures and pressures. Heterogeneous catalyst is easily removed from the products of reaction, making purification and neutralization process much simpler. Beside the fact that synthesis becomes less problematic for environment, it can also improve the economics of biodiesel production and lead to cheaper production costs. In this study a new type of heterogeneous catalyst with K2O as active component on alumina/silica support is synthesized. A starting step when producing catalyst (aerogel and xerogel) is a sol-gel synthesis, method that provides a possibility to add different catalyst constituents in only one step. It is followed by drying of the wet gel: drying at elevated temperature and atmospheric pressure to obtain xerogel and supercritical drying with supercritical carbon dioxide to obtain aerogel. Prepared catalysts were used in the methanolysis of sunflower oil at 200˚C and 37 bar with molar ratio methanol:oil 30:1 and 2 wt% of catalyst (based on oil). For the catalysts that showed better activity the possibility to optimize the process of FAME synthesis was investigated. The efficiency of process under different temperatures (80-200°C), reaction times (15min-8h) and molar ratios of methanol to oil (6:1-30:1) was analyzed. With the yield of FAME over 93% after 15 minutes, some catalysts showed very good activity and are promising catalysts for FAME synthesis. . Određeni nedostaci konvencionalnih načina sinteze biodizela, tj. metil estara masnih kiselina (MEMK) mogu se izbeći primenom novih tehnologija koje se baziraju na korišćenju heterogenih katalizatora. U ovom radu novi tip heterogenog katalizatora sa K2O kao aktivnom komponentom na alumosilikatnom nosaču je sintetizovan sol-gel postupkom. Dobijeni katalizatori korišćeni su u reakciji metanolize suncokretovog ulja. Ispitana je efikasnost procesa pri različitim temperaturama (80-200°C), vremenu trajanja reakcije (15min-8h) i molarnom odnosu metanol:ulje (6:1-30:1). Sa prinosom MEMK od preko 93% za 15 minuta, pojedini katalizatori pokazali su se kao veoma aktivni i efikasni katalizatori za proces sinteze MEMK. .

Certain disadvantages of conventional processes of biodiesel, i.e. fatty acid methyl esters (FAME) synthesis could be avoided by applying new technologies which are based on using heterogeneous catalyst. In this study a new type of heterogeneous catalyst with potassium-oxide or zinc-oxide as active component on alumina/silica support was synthesized using sol-gel method which was followed by drying: at elevated temperature and atmospheric pressure (xerogel) or with the supercritical carbon dioxide (aerogel). Prepared catalysts were used in the methanolysis of sunflower oil. The effects of various reaction variables such as reaction time, temperature and methanol to oil molar ratio on the yield of FAME were investigated. The catalysts were characterized with XRD, FTIR and BET surface area analysis. The results indicated that active component is the main reason for the catalytic activity towards the reaction. It has been determined that the temperature of 393 K and methanol:oil molar ratio of 15:1, are optimal conditions for fatty acid methyl esters synthesis with potassium-oxide as active component of the heterogeneous catalyst. At these conditions, after 15 min the yield of fatty acid methyl esters was above 92%.

The synthesis of fatty acid methyl esters (FAME), i.e. biodiesel, in the methanolysis of triglycerides (TG) in the presence of solid catalyst was studied. Heterogeneous catalyst was synthesized by mechanochemical treatment of CaO and ZnO powder mixture with the addition of water required for the formation of corresponding mixed hydroxides, CaZn2(OH)6·2H2O, followed by calcination at 700 °C in air to obtain CaO∙ZnO composite powder. After detailed characterization CaO∙ZnO catalyst was used in methanolysis of refined sunflower as well as used vegetable oil (UVO) in the batch conditions. Influence of temperature, agitation speed, catalyst amount and methanol to oil molar ratio on the rate of reaction was analyzed in order to determine parameters that completely define the rate of methanolysis and indicate the basic resistances on which it depends. It was revealed that 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 reciprocal value of , the overall triglyceride volumetric mass transfer coefficient and , the effective pseudo-first order reaction rate constant. These kinetic parameters actually determine the value of the apparent reaction rate constant, , which changes with the progression of the methanolysis process, i.e. with the change of triglyceride conversion. The rate of the process is thus described with the simple kinetic model of irreversible pseudo-first order reaction with the variable apparent rate constant, which takes into account both the triglycerides mass transfer and chemical reaction between TG and methanol. The overall volumetric mass transfer coefficient, , was found to depend on interfacial area between the oil and methanol, and can be presented as the function of TG conversion. This assumption is based on the observed effect that when critical conversion of TG is achieved, after formation of small amounts of MG, DG and FAME, the mass transfer rate starts to be higher than the rate of chemical reaction on the catalyst surface. Then the chemical reaction starts to control the overall process rate... U ovoj disertaciji ispitivana je sinteza metil estara masnih kiselina (MEMK), odnosno biodizela u reakciji metanolize triglicerida (TG) u prisustvu čvrstog katalizatora. Sinteza katalizatora izvršena je mehanohemijskim putem polazeći od CaO i ZnO prahova uz dodatak vode, kako bi se dobio prekursor CaZn2(OH)6·2H2O, koji se ţarenjem na 700 °C prevodi u smešu oksida CaO∙ZnO. Nakon detaljne karakterizacije, CaO∙ZnO katalizator korišćen je u reakciji metanolize rafinisanog suncokretovog i korišćenog biljnog ulja (KBU) koja je izvedena u šarţnim uslovima. U cilju odreĎivanja parametara koji u potpunosti definišu brzinu metanolize i ukazuju na osnovne otpore od kojih ona zavisi, analiziran je uticaj temperature, molarnog odnosa metanol:ulje, mase katalizatora i intenziteta mešanja na brzinu procesa. UtvrĎeno je da brzina procesa zavisi od otpora prenosu mase TG do površine katalizatora i otpora hemijskoj reakciji na površini katalizatora, koji su definisani kao recipročna vrednost ukupnog zapreminskog koeficijenta prenosa mase, , i konstante brzine reakcije pseudo prvog reda, . Ovi kinetički parametri odreĎuju vrednost prividne konstante brzine koja se menja sa napredovanjem procesa metanolize, odnosno sa promenom stepena konverzije TG. Brzina procesa je na taj način opisana kinetičkim modelom nepovratne reakcije prvog reda sa promenljivom prividnom konstantom brzine koja uzima u obzir i prenos mase TG i brzinu hemijske reakcije izmeĎu TG i metanola. UtvrĎeno je da ukupan zapreminski koeficijent prenosa mase, , zavisi od specifične meĎufazne površine, kao i da se moţe predstaviti kao funkcija stepena konverzije TG. Ova pretpostavka se bazira na uočenom efektu da se dostizanjem odreĎene kritične konverzije TG nakon stvaranja prvih količina monoglicerida (MG), diglicerida (DG) i MEMK, brzina prenosa mase znatnije uvećava i postaje veća od brzine hemijske reakcije na površini katalizatora. Tada reakcija na površini katalizatora počinje da kontroliše brzinu ukupnog procesa...