Realizado em Vitória/ES, de 17 a 19 de Setembro de 2014.
ISBN: 978-85-85905-08-8
TÍTULO: TEMPERATURE DEPENDENCE OF VOLUMETRIC AND ULTRASONIC PROPERTIES IN NATURAL VEGETABLE OILS
AUTORES: Iglesias, M. (UNIVERSIDADE FEDERAL DA BAHIA) ; Ferreira, G. (UNIVERSIDADE FEDERAL DA BAHIA) ; Andrade, R. (UNIVERSIDADE FEDERAL DA BAHIA) ; Arnabat, A. (UNIVERSIDAD DEL PAÍS VASCO) ; Gonzalez, C. (UNIVERSIDAD DEL PAÍS VASCO)
RESUMO: This paper contains the results of a new experimental study of the effect of
temperature on density and ultrasonic velocity for a number of vegetable oils of
triacylglycerol backbone. From the mentioned properties, different derived
magnitudes were calculated due to its importance in the study of the thermodynamic
trend and theoretical calculations. Because of current processes design are
strongly computer oriented, consideration was also given to how accurate different
theoretical prediction methods work. The tested models were selected attending to
their ease of use, accuracy and range of application, a good response at the
studied conditions being observed, despite of geometrical simplifications and the
use of estimated critical magnitudes by molecular group contribution approach.
PALAVRAS CHAVES: Vegetable oil; Thermodynamic properties; Theoretical model
INTRODUÇÃO: In food industry, thermodynamic properties are the most important parameters
required in the design of technological processes and equipments. Knowledge of
these magnitudes is of practical interest to the industrial manufacture of fats
and oils since thermal and mechanical procedures applied are close related on
their temperature and pressure dependence. Despite of their importance, no
systematic experimental measurement property projects have been developed for
materials close related to food technology (more complex molecules, natural
products, etc), a relative scarce of data being encountered in what is referred
to oils and fats. The triacylglycerol molecule is often considered the unique
chemical structure or at least the “theoretical oil” to develop estimative
studies on thermophysical characteristics. This trend is close related to the
most usual orientations adopted: pure empirical computations based on a data
base and algorithms for correlation, corresponding states principle and
molecular group contribution approachs. This consideration is necessary to fill
of physical meaning the fitting parameters, quantify pseudocritical magnitudes
and make feasible the molecular group division, respectively.
In this work, we present the temperature dependence of density and ultrasonic
velocity of a collection of oils with a triacylgliceric molecule as backbone.
From the experimental data, temperature dependent polynomials were fitted, the
corresponding parameters being gathered. Different derived properties were
computed from density and ultrasonic velocity data, due to their importance in
the study of the thermodynamic trend and theoretical calculations. The selected
theoretical models gathered a good response at the studied conditions.
MATERIAL E MÉTODOS: In this work, the densities and ultrasonic velocities of the triacylglycerol
vegetable oils (olive (Olea Europaea), sunflower (Helianthus Annuus), soybean
(Glycine Max), corn (Zea Mays), grape seed (Vitis Vinifera seed), sesame
(Sesamum Indicum), flax seed (Linum Usitatissimum), sweet almond (Prunus
Dulcis), wheat germ (Triticum Aestivum germ), apricot kernel (Prunus Armeniaca)
and safflower (Carthamus Tinctorius)) were studied at the range of temperature
278.15 - 333.15 K and atmospheric pressure. The Gas Chromatography and Mass
Spectrometry techniques were used to confirm that all triacylglycerols studied
were greater than 98% pure in commercial samples and to obtain the compositions
of each oil in terms of fatty acids. From the fatty acid composition, the
average molar mass of each oil was computed.
The densities and ultrasonic velocities of pure componentes and their mixtures
were measured with an Anton Paar DSA-48 vibrational tube densimeter and sound
analyzer, with a resolution of 10-5 gcm-3 and 1 ms-1.
For compact and smooth representation, the density and ultrasonic velocity of
the vegetable oils were correlated as a function of temperature, and the fitting
parameters were obtained by the unweighted least squared method applying a
fitting Marquardt algorithm (Figures 1 and 2). Equations of state and the
Collision Factor Theory (1) were applied, adequated results being obtained at
the studied range of temperature, despite of geometrical simplifications and the
use of estimated critical magnitudes by group contribution methods, due to the
thermolabile character of these substances.
RESULTADOS E DISCUSSÃO: In this work, the densities and ultrasonic velocities of the triacylglycerol
vegetable oils (olive (Olea Europaea), sunflower (Helianthus Annuus), soybean
(Glycine Max), corn (Zea Mays), grape seed (Vitis Vinifera seed), sesame
(Sesamum Indicum), flax seed (Linum Usitatissimum), sweet almond (Prunus
Dulcis), wheat germ (Triticum Aestivum germ), apricot kernel (Prunus Armeniaca)
and safflower (Carthamus Tinctorius)) were studied at the range of temperature
278.15 - 333.15 K and atmospheric pressure, a set of derived magnitudes being
computed. These data were correlated by polynomia expressions which fitted the
data well. Not surprisingly, the systems exhibited a strong expansive tendence
for rising temperatures with an aweaking effect of the intermolecular
interaction, and then increasing the intermolecular free length.
A frequently applied derived magnitude for industrial mixtures is the
temperature dependence of volume which is expressed as isobaric expansibility or
thermal expansion coefficient (α). It could be observed as isobaric
expansibility decreases with temperature at each oil, the lower dependence being
showed for soybean. In this case a slight maxima is showed at 285.15 K, which
could be explained by the unsaturated character of the fatty acids and the high
density of this oil. The selected theoretical models (1) gathered a good
response at the studied conditions with deviations better than 2% for densities
and 10% for ultrasonic velocity at these conditions.
Figure 1
Curves of constant density of the studied vegetable
oils at the range of temperatures 278.15 – 333.15 K.
Figure 2
Curves of constant ultrasonic velocity of the
studied vegetable oils at the range of temperatures
278.15 – 333.15 K.
CONCLUSÕES: As a continuation of a wider project (2, 3), derived properties were computed from
measured data, due to their importance in the study of the thermodynamic trend of
the mixtures and theoretical calculations. Because of the expense of the
measurement of such data and current processes design are strongly computer
oriented, consideration was given to how accurate different theoretical methods
work by comparison with the experimental data. Equations of state and Collision
Factor Theory were applied for the estimation of the properties, which showed a
qualitative capability for the oils analysed.
AGRADECIMENTOS:
REFERÊNCIAS BIBLIOGRÁFICA: (1) Iglesias, M., Orge, B., Domínguez, M., Tojo, J. (1998). Mixing properties of the binary mixtures of acetone, methanol, ethanol, and 2-butanone at 298.15 K. Physics and Chemistry of Liquids (37) 9-29.
(2) Gonzalez, C., Resa, J.M., Lanz, J., Iglesias, M. (2006). Intermolecular interactions in soybean oil + different organic solvents by ultrasonic velocity measurements. Journal of Food Engineering (77) 152–161.
(3) Gonzalez, C., Resa, J.M., Concha, R.G., Goenaga, J.M. (2007). Enthalpies of mixing and heat capacities of mixtures containing acetates and ketones with corn oil at 25ºC. Journal of Food Engineering (79) 1104-1109.