This work presents a review of the published studies approaching
the thermodynamics of the ethanol conversion to 1,3-butadiene (BD),
completed with our own calculation results. A spontaneity analysis,
for the global reaction transforming ethanol into BD, has evidenced
that a frequently used principle, considering negative variations
of the standard Gibbs free energy, as a criterion for practically
relevant equilibrium reactant conversions, appears as relatively conservative.
The calculation of spontaneity domains, for the global reaction of
BD synthesis from ethanol, showed that equilibrium ethanol conversions
up to 80% can be obtained, even at positive values of standard Gibbs
free energy variation. The characteristics of the ethanol conversion
to BD, at chemical equilibrium, were calculated using reaction schemes
describing the accepted process mechanisms and chemical species observed
experimentally. The necessary properties of the chemical species were
extracted mainly from the database of Aspen Plus simulator, whose
computing facilities were also used for most of equilibrium calculations
presented. The results confirm the previously published information,
indicating that the process BD yield, at equilibrium, decreases to
practically uninteresting values, when the calculation schemes include
the secondary products observed experimentally. This proves that the
practical catalytic processes of ethanol conversion to BD are kinetically
controlled. An evaluation of the two process alternatives for producing
butadiene, i.e., directly from ethanol and ethanol–acetaldehyde
mixture, showed that the latter process is slightly favored thermodynamically,
in comparison with the first (one-step) alternative.