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.
