Application of Wada’s Group Contribution Method to the Prediction of the Speed of Sound of Biodiesel

Abstract

Biofuels are an important alternative to environmental sustainability, and biodiesel has a detached contribution to this scenario. The increasing use of biodiesel requires the knowledge of several thermophysical properties of this biofuel. This work addresses the measurements of the speed of sound and density at atmospheric pressure of five fatty acid methyl esters (methyl caprylate, methyl caprate, methyl palmitate, methyl stearate, and methyl linoleate). These data are used to test Wada's group contribution method recently proposed by us and its ability to predict the speed of sound of biodiesel fuels and to expand the application of this model to the prediction of the speed of sound of biodiesel fuels. The overall average relative deviations (OARD) obtained were 0.12% for the methyl esters and 0.29% for biodiesels. An extension of this model to high pressures is also proposed and tested with success, presenting an OARD of 1.0% for six biodiesel fuels.

Measurement and prediction of speeds of sound of fatty acid ethyl esters and ethylic biodiesels

“…Moreover, since the FAMEs present a higher value for density than the corresponding FAEEs with the same number of carbon atoms in acid moiety, as already shown in Pratas et al [9] the magnitude of the densities for ethylic biodiesels is expected to be lower than that of the corresponding methylic biodiesels. Regarding the speed of sound, as previously observed for methylic biodiesels [13], a difference in the speed of sound of only ca. 1.0% is observed between the four types of biodiesels studied.…”

“…In a previous work, we showed that this model could provide a good prediction of the speed of sound of methyl esters and the corresponding methylic biodiesels [13]. This model simply relates speed of sound (u in m s À1 ) with density (q in kg m À3 ), molecular mass (M w in g mol À1 ) and molecular compressibility (j m ) according to the following equation:…”

“…As described in our previous works [13,28], to carry out the predictions of speed of sound using the Wada's model, the ester molecule must be split into five main groups: ACH 3 A and ACH 2 A to account the linear and saturated alkyl chain, ACH@CHA to describe the contribution of the unsaturation of the alkyl chain and ACH 3 COOA and ACH 2 COOA to take into account the ester contribution from methyl and ethyl esters, respectively. Then the corresponding Wada's constants reported in Daridon et al [28], are used to estimate the speed of sound for each ethyl ester in the range of temperatures investigated.…”

“…While some works focused on establishing novel approaches to improve the production and purification [5][6][7] others have oriented their line of research to the study of thermophysical properties of fatty esters and biodiesels [8][9][10][11][12][13][14][15][16] to enhance the quality of biodiesels, i.e., their properties in accordance with the Norm CEN EN 14214 [17] in Europe and the Norm ASTM D6751 in United States of America [18].…”

“…Unfortunately there are but a few data available in the literature for fatty acid methyl esters (FAMEs) [13,21,12,[23][24][25][26][27] being the experimental speeds of sound of fatty acid ethyl esters (FAEEs) even more scant [28], although some studies were already done for the shorter methyl and ethyl esters [29]. There at, this work aims at providing new experimental data of speed of sound for nine saturated and unsaturated FAEE and four ethylic biodiesels, measured at atmospheric pressure and temperatures from 293.15 to 343.15 K, and then using them to evaluate the predictive ability of Wada's group contribution method [28].…”