Biodiesel can
easily become the crucial solution for environmental problems. The
high production rate of soybean oil has been the subject of several
research works to transform it into biodiesel. Knowledge of the thermodynamic
properties of soybean oil biodiesel (SOB) such as densities and coefficients
of expansivity and compressibility play an important role in the understanding
of the intermolecular interactions between the different molecules,
which in turn have an impact on fuel quality. The difficulty in measuring
the thermodynamic properties of biodiesel is because they are complex
structures and high-molecular-weight components. The experimental
density (136 points) for SOB, as a pseudopure component, at several
temperatures (298.15–393.15 K) and pressures up to 140 MPa
is reported. An Anton Paar vibrating tube densimeter, calibrated with
an uncertainty of ±0.7 kg m–3, was used to
perform these measurements. To determine the chemical fatty acid methyl
ester composition, SOB was analyzed by CHNS analysis, 1H NMR, 13C NMR, and gas chromatography–mass spectrometry
and, then, the density experimental data were correlated by the Tait
and perturbed chain-statistical associating fluid theory (PC-SAFT)
equations of state (EoS). The experimental data were compared with
correlated data, resulting in absolute average deviation (AAD = 0.01%),
maximum deviation (MD = 0.03%), average deviation (Bias = −9.88
× 10–7%), and standard deviation (σ =
1.18 × 10–4 g cm–3) for the
empirical Tait equation. Concerning PC-SAFT EoS, the density was reasonably
correlated with AAD = 0.063%. On the other hand, isothermal compressibility,
κ
T
, and isobaric thermal expansivity,
α
p
, were derived from the Tait equation.
The same behavior is observed for κ
T
and α
p
, consistent with the expected
one. The isobaric thermal expansivity, α
p
, presents a crossing point at nearly 35 MPa, in agreement
with what had been observed by other authors.
