Metanoliza suncokretovog ulja katalizovana negašenim krečom
Quicklime-catalyzed methanolysis of sunflower oil
Committee membersVeljković, Vlada
Banković-Ilić, Ivana B.
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The synthesis of fatty acid methyl esters (FAME) from sunflower oil by the quicklime-catalyzed methanolysis reaction was investigated. The catalyst was obtained by calcination of quicklime which was characterized as a mesoporous material with higher basicity and specific area than uncalcinated quicklime. In order to investigate the influence of the methanol-to-oil molar ratio and the catalyst amount on the reaction rate and the FAME yield, sunflower oil methanolysis catalyzed by quicklime was performed in a batch reactor under moderate reaction conditions (reaction temperature 60°C and atmospheric pressure), at different molar ratios of methanol to oil (6:1 – 18:1) and catalyst amounts (1- 10 % based on the oil weight). The variations of the FAME concentration during the reaction were sigmoidal. The FAME formation rate in the initial period of the reaction was slow due to the mass transfer limitation in the three-phase system (methanol-oil-quicklime), followed by the period of the fast...er FAME formation rate which became slower as the reaction approached the completion. The overall reaction rate depended on the catalyst amount and increased with increasing the catalyst amount due to the increase of the number of catalyst particles and, consequently, the number of active sites on the catalyst surface. Further, the influence of the methanol-to-oil molar ratio on the FAME yield depended on the catalyst amount. At lower catalyst amounts, the FAME yield was slightly higher at higher initial amounts of methanol because the excess of methanol shifted the reaction equilibrium towards the FAME formation. However, the equilibrium was achieved at almost the same time for all methanolto- oil molar ratios. On the other hand, at higher catalyst amounts the molar ratio of methanol to oil had no effect on the reaction rate and the FAME yield. The continuous process for the FAME synthesis was developed and the experiments were conducted in two types of reactors. In order to estimate the significance of the influence of the reaction conditions and their interactions on the FAME yield, the methanolysis reaction was performed in a single-stage fixed-bed reactor at 40 and 60 °C, under atmospheric pressure, at different molar ratios of methanol to oil (6:1–18:1) and specific mass flow rates of the reaction mixture (0,188–0,376 kgreaction mixture/(h·kgcat)) corresponding to the residence time of 1-2 h. The reaction conditions were optimized to maximize the FAME yield. According to the statistical analysis, the reaction temperature had the most significant influence on the FAME yield, followed by the residence time and the methanol-to-oil molar ratio. The experimental data on the FAME yield were fitted to the second-order polynomial equation using the regression model. The results showed a very good agreement between the experimental and predicted values of the FAME yield. The graphical presentation of the regression model indicated the possible influence of the reaction conditions and their interactions on the FAME yield and it was suitable for defining the optimal reaction conditions to maximize the FAME yield. Based on the response surfaces it was concluded that the FAME yield increased with the increase of the reaction temperature, residence time and methanol-to-oil molar ratio. At lower reaction temperature, the influence of methanol-tooil molar ratio on the FAME yield was more significant and depended on the residence time. The influence of the particle size of quicklime on the FAME yield and leaching of the catalyst into the reaction mixture were also investigated. The particle size of the catalyst had no effect on the FAME yield but leaching of the catalyst was noticed. The content of Ca2+ in the methyl ester phase was higher than the EN 14214 standard limit so the FAME synthesized by the continuous quicklime-catalyzed methanolysis required the Ca2+ removal or lowering its level to the standard acceptable value. The kinetics of the quicklime-catalyzed sunflower oil methanolysis under continuous conditions was monitored in a multi-stage reactor. The FAME yield increased with the decrease of the specific mass flow rate. However, the required height of the catalyst layer in the reactor at which the complete TAG conversion is achieved decreased with the decrease of the specific mass flow rate. The increase of the methanol-to-oil molar ratio enhanced the FAME yield and reduced the required height of the catalyst layer in the reactor, too. The model that included a changing mechanism and the autocatalytic behavior of the reaction was applied for kinetic modeling of quicklime-catalyzed methanolysis. This model successfully described the kinetics during the whole course of the reaction without complicated computations. Also, for the first time the model included the influence of the FAME concentration on the methanolysis reaction rate in kinetic modeling of oil methanolysis. The apparent rate constants of the methanolysis reaction under batch and continuous conditions were determined. For the reaction performed under batch conditions, the apparent rate constant depended on the catalyst concentration and the initial methanol-to-oil ratio, while under continuous conditions it depended on the specific mass flow rate of the reaction mixture and the initial methanol-to-oil molar ratio. Afterwards, the reaction rate constants were determined from the established parameter dependency. The results of the simulation of quicklime-catalyzed methanolysis were in a very good agreement with experimental data. The simple application of the developed model will ensure its use in the reactor design and the process simulation and control.