Kinetics of the biphasic liquid–liquid transesterification of vegetable oils into biodiesel
Tóm tắt
Alkaline transesterifications (methanolysis, ethanolysis) of vegetable oils (soybean, sunflower) were conducted under conditions selected by an experimental design, producing biodiesels (fatty methyl esters 97.5 wt%; fatty ethyl esters 96.7 wt%) with high quality characteristics identified by reduced sodium content (0.11 mg kg−1), low levels of glycerol concentration (0.01 wt%), acidity (0.31 mg NaOH g−1) and viscosity (4.81 mm2 s−1). Evidence indicated that in a first stage, the triglyceride slowly dispersed in the alcohol phase, and then promoted the rapid production of esters: the biodiesel yield increased from 52.0 to 97.5% in methanolysis and from 44. 0 to 96.7% in ethanolysis. A mathematical model was formulated, including biphasic effects between the liquid phases, with respect to partition equilibrium, mass transfer and chemical reaction. The kinetics of the biphasic transesterification processes were characterized quantitatively through the order of magnitude of the mass transfer coefficient of the triglycerides (K
TG
= 5.82 × 10−4 s−1, at 303 K − 5.86 × 10−2 s−1, at 353 K), and of the specific reaction rate (k = 3.48 × 10−3 s−1, at 303 K − 5.78 × 10−3 s−1 at 353 K). Resistances related to these effects indicated that they compete during the evolution of the processes.
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