The ethanolysis of triglycerides has potential for improving some
characteristics of biodiesel as fuel of compression–ignition engines
and also increasing its sustainable character as far as bioethanol is
used as the alcohol source. Although there is an increasing interest
in this reaction, to date, it has been much less studied than the
methanolysis of triglycerides, particularly as concerns the reaction kinetics.
In this work, a kinetic model has been developed for the NaOHcatalyzed
ethanolysis of sunflower oil. The model describes the effects
of the ethanol-to-oil molar ratio, catalyst concentration and reaction
temperature on the oil conversion and yields of the final (biodiesel)
and intermediate (diglycerides andmonoglycerides) transesterification
products. In order to capture the most important effects of these variables
it is necessary that the model incorporates the equilibrium of interconversion
between the hydroxide and ethoxide ions as well as
saponification reactions. In this way, it is possible to predict the depletion
of the catalyst that can take place at low values of the catalyst concentration
and ethanol-to-oil ratio. This is the result of the consumption
of hydroxide ions by saponification reactionsmainlywith the glycerides
to form soaps. As a result the equilibrium hydroxide/ethoxide is shifted
towards the hydroxide ions, in detriment of the catalytically active
ethoxide species. A sufficiently high excess of ethanol, with ethanolto-
oil molar ratios between 12:1 and 24:1 for low NaOH contents
(below 0.3 wt.%), is necessary to preserve the ethoxide ions by favoring
the ethanolysis and alkoxide formation reactions in detriment of the saponification
processes. The depletion of the catalyst and the formation
of soaps have been verified experimentally in this work. As concerns
the reaction temperature, the ethanolysis is favored by the increase of
this variable but its effects are not as influential as those of the catalyst
concentration and ethanol-to-oil ratio. The ethanolysis is characterized
by a high production of soaps and intermediate transesterification products
which are detrimental for the quality of the produced biodiesel.